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Toll-like receptors in Chronic Lymphocytic Leukaemia
How stress can have an impact on
epigenetics of sperm
introduction
Stress is something that everyone in the world has experienced at one point of their
human life. Stress is something that can come from anything and in some cases
extremely unavoidable. Stress is something that can affect people in any field or
work it can also have an effect on humans’ body parts as well as animals. The word
stress means “pressure or tension exerted on a material object’ by definition. In this
literature review I will be talking about the effects of stress on epigenetics, as there
are reports talking about epigenetics and its link to sperm. In particular the studies
show that micro- RNAs can be passed on via sperm and these can then imprint the
foetus with stress factors.
What is Epigenetics?
What is epigenetics, well epigenetics is the study of biological mechanism that switch
genes and on and off. To get an idea of what epigenetics you need know the basic
fundamentals of the DNA and how it is comprised, and the bases involved.
Cells are extremely fundamental parts of every human being and living thing. All the
cells contain deoxyribonucleic acid, also known as DNA which contain instructions to
direct their activities. DNA is made from more than 3 billion different nucleotide
bases. There are four main types of bases that come together to create DNA. These
are adenine, cytosine, guanine and thymine. They are more commonly known as A,
C, G and T. there is an extra bases for RNA which is uracil (U) and this takes the
place of thymine (T). It is very important the way the sequences of the bases are
made from as the sequences determine the way we are made. It is very interesting
that our DNA sequences are most similar to that of a chimpanzee but is different due
to the way that sequences that makes us human. Within the 3 billion bases, there
are about 20,000 genes. Genes are specific sequences of bases that provide
instructions on how to make important proteins – complex molecules that trigger
various biological actions to carry out life functions. (What is Epigenetics? (2019
)
What I hope to find
I hope to find in this literature review is a link between sperm and stress and also the
effects it can have being long-lasting or just temporary. I also hope to find what
different experiment procedures that they had to go through in order to get the link
that stress can be imprinted into the foetus of an unborn child.
Article that support: How stress can have an impact on epigenetics of sperm
According to an article by Katherine J. Wu who is a Digital Editor at PBS NOVA and
Story Collider producer. She holds a Ph.D. in Microbiology and Immunobiology from
Harvard University. She states in her article about “Dads Pass on More Than
Genetics in Their Sperm” that your body will remember and possibly pass the
consequences onto your kids. In the past several years there have been mounting
evidence that has shown that sperm can take note of a father’s lifestyle decisions
and transfer this baggage to offspring. There have been two complementary studies
by scientist that tell us how this has been done in detail.
(katherine.
J wu (2018)
As the sperm travels through the male reproductive system, they carry genetic cargo
that alters the sperm before ejaculation. These modifications of the sperm not only
communicate the father current state of mind and well-being, but they could also
have a drastic impact on the viability of the future offspring. On average roughly
there are 76,000 children born as the result of assisted reproductive techniques,
which mostly involve a type of invitro fertilisation (IVF). For an invitro fertilisation to
take place you need to get an egg from a female and sperm out of the human body,
the transfer then results in a fertilised egg which is embryo. The embryo is then
placed inside the female’s uterus. There are different types of invitro fertilisation
(IVF) that exist, in some cases male infertility can occur which can cause the sperm
to struggle to swim. In these cases, sperm is then surgically extracted from the
testes or the epididymis which is a long-convoluted duct that cradles each testis.
(katherine. J wu (2018)
After the sperm is produced in the testis, they go through a long and harrowing
journey through the epididymis, which in a human male is roughly 6 meters long
https://www.smithsonianmag.com/author/katherine-j-wu/
)
when stretched in a line on to storage. The sperm wander in the epididymis for two
weeks before end of the path where they are fully motile. When the sperm is fully
mature it can be dumped on the egg that is waiting to be fertilised. Sperm that taken
from the testis and epididymis must be injected directly into the egg with a very fine
needle. Whatever the source of the sperm these techniques have been proven to
have birthed healthy children in four decades of successful procedures. Scientist
know that genes are not the whole package. Over the course of a single human life
time, the way our genomes where originally written have stayed the same, however
when and why genetic instructions are followed can majorly change without altering
itself. This is called epigenetics this explains why genetically looking individuals know
as twins can still act in different ways and factors like stress and dieting are capable
of cranking up our genes. (katherine. J wu (2018)
One of the most powerful tools in epigenetics is a molecule called small RNAs. Small
RNAs are capable of concealing genetic information from cellular information from
cellular machinery that carry out their instructions, as a result of this they can ghost
genes out of existence. (katherine. J wu (2018)
In most of the article it mostly relays the idea that sperm is able to carry information
that most people would not think that sperm can carry such as stress, it also goes on
to say in the first part of the article it is mainly the male sexual reproductive system
that imprints the foetus with
In another study two scientist Upasna Sharma and Colin conine both working under
Oliver rando, who is a professor of biochemistry at the university of Massachusetts
Medical school, where some of the researches to report the findings in 2016. In their
work they noted that in mice with immature testicular sperm contains DNA which is
identical to that of a mature sperm can relay different information. They found that
small RNAs can undergo small post testes information and gain information from the
testes of the father’s physical health or lack of health after they are born. (katherine.
J wu (2018)
To solve the mystery, they decided to track the composition of small RNAs within the
mouse sperm, when they fled the testes all the way through the epididymis. Her
)
colleagues then isolated the sperm of several different aged mice, including the ones
that were currently developing testes and those entering the early part of epididymis
and the late stages epididymis. Sharma was surprised to find that many small RNAs
seemed to be discarded or destroyed when they entered the epidermis. then the
Newley vacated sperm reacquired epigenetic information that reflected the father
state of mind and being. (katherine. J wu (2018)
The fact that they did two studies on the subject shows that the first one had to be a
success I order to continue to the next study, also they used a range of variables in
the experiments that did using a variety of mice at different age groups with different
maturities shows that the results that the sperm carries out the information of stress
markers during the early stages of development of an offspring and furthermore
epigenetics also helps in the passing of genetic information such as a poor diet
requirements and most importantly in this situation stress.
There was only one possible source for the small RNA reacquisition: the cells of the
epididymis. Which meant that cells outside of the sperm were transmitting
information into future generations. The epidermis is the least studied organ in the
body,” says Rando, who was senior author on both papers. “And it turns out this tube
that no one ever thinks about plays a central role in reproduction.” To confirm that
the epididymis was the culprit, Sharma’s team added a chemical marker to a set of
small RNAs in the epididymis and tracked their migration. As they suspected, tiny
shipments of RNAs popped off of cells in the epididymis and fused with the sperm.
Each stealthy swimmer then bore these epigenetic elements all the way to its final
union with the egg. It seemed that sperm at different points along the reproductive
tract had the same genetics, but not the same epigenetics. Was this difference big
enough to matter? Colin Conine, who led the second of the two new studies, next
tested if using immature sperm would have noticeable effects on the offspring of
mice. He and his colleagues extracted sperm from the testes, early epididymis and
late epididymis and injected them into eggs. All three types of sperm were able to
fertilize eggs. However, when Conine transferred the resulting embryos into mouse
surrogates, none derived from early epididymal sperm—the intermediate stage
devoid of most small RNAs—implanted in the uterus. The least and most mature
https://www.cell.com/developmental-cell/fulltext/S1534-5807(18)30541-0
sperm of the bunch were winners—but somehow, those in the middle were burning
out, even though all their genes were intact. (katherine. J wu (2018)
I can say after reviewing the article with two studies in how stress can affect the
epigenetics of the sperm and pass on characteristics such as dieting and stress. I
can positively say that there is a connection between the two as there are arrange of
studies done by professionals that tell us this furthermore, I can say that there are
trends in the research with all of the research in this topic about the small RNAs
having an big influences on stress and that in particular the father can pass on
information via the male reproductive system that in turn will go to the offspring
causing the offspring to get these bits of information of traumatic experience in
bedded into them.
The reason why I choose the topic stress is ,because it is what everyone
experiences in day to day life, but the reason why I chose epigenetics and stress on
comes sperm is because there are lots of studies going on in the recent years that
test this theory and a lot of the articles conclude there is a correlation between stress
and the epigenetics of the sperm which could lead to the stress being imprinted in
the foetus. Another reason why this is important is because the world we live in now
is more stressed than ever meaning that up coming generations could be passing on
this trait to the next offspring.
Bibliography
What is Epigenetics? (2019). A Super Brief and Basic Explanation of Epigenetics for Total
Beginners. [online] Available at: https://www.whatisepigenetics.com/what-is-epigenetics/
[Accessed 2 Mar. 2019].
katherine. J wu (2018). Dads Pass on More Than Genetics in Their Sperm. [online]
Smithsonian. Available at: https://www.smithsonianmag.com/science-nature/dads-
pass-more-genetics-their-sperm-180969760/ [Accessed 2 Mar. 2019].
Understandingsingle amino acid repeats in proteins
“Single amino acid and trinucleotide repeats: function, evolution and human disorders”
Abstract
Amino acid repeats (AARs) are common features of protein sequences; they are
segments of proteins made up of simple patterns of amino acids, often strings of a
single amino acid. They have quite frequently been recognised to be common
features of eukaryotic proteins, they have several functions and are involved in a
number of human diseases; one of which is the inability to form amino acid repeats
due to formation of precipitates/aggregates. Despite of their versatility the amino acid
repeats are classified into categories depicted on their characteristics, so much that
it would seem appropriate to have a database where all these can be stored in and
later used for analysis All these diverse facets of amino acid repeats are explored in
this review.
Introduction
An amino acid is a simple organic compound containing both a carboxyl (—COOH)
and an amino (—NH2) group that combine to form proteins. Large proportion of cells,
muscles and tissue in the human body are primarily made up of amino acids, the
structure and function of these proteins are depended on where the amino acids are
localised and how they are inter-connected to each other, being a total of twenty
amino acids found within proteins expresses an immense range of chemical
versatility.
PhD student Luo and scientist Nijveen both wrote an article about understanding and
identifying amino acid repeats (AARs); they suggested a majority of AARs are found
in protein sequences since they have a specific role in protein function in eukaryotes
in addition to this; Spanish researchers Subirana and Palau have written a
hypothesis on the structural features of single amino acid repeats in proteins and
had suggested while amino acids are able to form repeats some amino acids cannot,
this may be due to the fact that those amino acids can form aggregates because of
the formation of incipient lamellar crystals. Subirana and Palau mention in their
abstract that single amino acid repeats found in different kind of proteins can be
pathogenic, similarly Luo and Nijveen also mention the potential risks leading to
disease due to abnormal functions caused by variations in sequence length,
according to Luo and Nijveen; the variations to the length of the sequences and point
mutation in repeat regions occur due to simple repeat patterns generated by DNA
slippage, in addition; four Indian chemists; Katti, Sami-subbu, Ranjekar and Gupta
studied the aspect of amino acid repeat patterns in protein sequences; their diversity
and structural-functional implications and they point out that simple sequence
repeats originate from replication errors and unequal crossing-over which are caused
by the formation of slipped strands or hairpins; they further explain that these fall into
the category under unusual DNA secondary structures, they continue to explain that
these repeats which are located in the coding region may be translated into single
amino acid repeats which can then dictate protein structure and function.
Subirana and Palau explain that in many cases the repeats give rise to aggregates
which build abnormal actions in the cell, they continue by claiming that these actions
are pathogenic but then later go on stating that this has been proved wrong because
even in the absence of aggregates; toxic behaviour was still detected. According to
Luo and Nijveen; inter-domain aggregation can be prevented by ‘gate-keeper’
residues which stabilise the leucine-rich repeat and WD repeat; they originate from
internal gene duplication and are functional domain repeats that contain complex
patterns, Katti et al refers to these patterns as periodic and mentions that there is
one advantage of these patterns and that is that they compare and contrast similar
functional groups which then create zip-like interactions with target molecules, they
continue on by explaining that this provides a different perspective on predicting
structural models and the design of new proteins.
Luo and Nijveens’ article on Understanding and identifying amino acid repeats looks
into the classification aspect of the AAR and the different categories they are
allocated to depending on the characters of the repeat units, they also look into and
quite briefly define the three major approaches for detecting amino acid repeats
which are; the self-comparison strategy, the pattern recognition strategy and the
complexity measurement strategy. The article starts off with brief background
information about single amino acid repeats and ends with what they developed and
what they hope their product will do to aid in the identification of different types of
protein sequences. In Subirana and Palau’s’ article on Structural features of single
amino acid repeats in proteins they mention in the first part of the article that they will
throughout the paper clarify fibrillary aggregation of single amino acid repeats are
related to the process of polymer crystallisation in lamellar crystal and they will also
analyse why some single amino acid repeats are commonly found in nature. They
start off their article briefly explaining what they will be mentioning throughout the
paper and go on describing the role of amino acid repeats in proteins, they end their
article mentioning both processes for protein folding; protein aggregation and homo-
polymer crystallisation and that they should be considered as equal. Katti et al article
on Amino acid repeat patterns in protein sequences: their diversity and structural-
functional implications is all about creating a database that carries an infinite amount
of information on proteins containing single amino acid repeats of various types and
end their article reflecting what their study provides in the sense of protein
sequences.
Luo and Nijveen looked into classification of AAR patterns at sequence level; the
writers introduce three approaches to classifying AARs into different categories
depending upon; the characteristics. Sequence similarity, distance and the
complexity of the sequence pattern of the repeat units, they then later mention that
the approaches used to classify AARs being based on the protein sequence are
insufficient to reveal the biological significance of AARs because proteins play their
functional roles by folding into particular secondary and tertiary structures, which are
difficult to construe through amino acid patterns at sequence level. The writers gave
an overall description of each approach; the first approach to classifying AARs was
according to the similarity among the repeat units. AARs were classified into two
main groups; perfect repeats and imperfect repeats or otherwise termed as divergent
repeats. Perfect repeats had identical repeat units whereas imperfect/divergent
repeats had the opposite; they were extremely variable but still recognisable. The
second approach was based on the distance between each unit; they were classified
as either tandem repeats (TRs) or non-tandem repeats (NTRs), units in TRs were
continuously spread out whereas units in NTRs were scattered. The third approach
was based on the complexity of the sequence pattern where the AARs can be
classified as simple repeats which refer to continuous runs of amino acid residues or
complex repeats which have sophisticated patterns of repeat units with variable
lengths ranging from ten to a hundred residues.
There are a few human disorders with regards to AARs; Luo and Nijveen mention
amino acid repeats can sometimes cause mis-folding of prion proteins which are
highly populated in the nervous system but also occurs in other tissues throughout
the body, furthermore can modify the repeat length which may result in abnormal
function, they further explain this by introducing a typical case known as the
expansion of polyQ; this phenomenon results in many neurological disorders such as
mental retardation, Huntington Disease and muscular dystrophy; this disease is
involved in muscle weakness and loss of muscle tissue which deteriorates over time.
Subirana and Palau explain that because expressed trinucleotide repeats (TNRs) at
DNA level generate single amino acid repeats in silent regions of the genome, an
abnormality in the DNA structure may cause inability of expansion of the trinucleotide
repeats thus will be unable to produce single amino acid repeats in nature, they go
on by explaining that this phenomenon will not only cause problems to the RNA
structure level and effect the availability of tRNA but also may prevent transcription
of DNA sequences to occur in the cell, according to Subirana and Palau; these
expansions can quickly become associated with diseases when the TNRs expansion
reaches a certain threshold due to alternative DNA structures.
Subirana and Palau constructed a table (Table 1) in their article and interpret the
data; their interpretation of the table was about how many single amino acid repeats
will tend to crystallise as incipient lamellar structures and will therefore cause
insoluble aggregates which will in turn lose the cells’ effectiveness. They carry on by
explaining that the resistance to aggregation present is due to the amphipathic
nature of the amino acid side chains; this means they have both polar and non-polar
portions in its structure.
Katti et al end their article by outlining their expectations from both their database
and their overall study; they hope their database will reveal the extent of repeat
patterns and to aid in further analysis of internal repeats from their origin and
knowing beforehand of any implications on protein structure and function that follow,
they expect their study to be further extended using amino acid similarity mediums in
addition to identity matches. Subirana and Palau end their article by giving an
overview characterising single amino acid repeats and contrasting between polymer
crystallisation and protein aggregation; they do this by stating the likelihood of long
repeats of single amino acid being avoided in proteins so they can either aggregate
the writers used hydrophobic amino acids as an example here, or it will have strong
electrostatic interactions such like charged amino acids do which will then precipitate
proteins with an opposite charge, and also mentioning how the length of the repeats
will depend on the properties of each amino acid side chain. They end with pointing
out that polymer crystallisation can be well predicted by simulation methods that
have been developed for folding protein. They further explain that both protein
aggregation and homo-polymer crystallisation should be considered as the same
concept and should result in a cross-fertilisation of both fields. Luo and Nijveen
conclude their article by introducing the database they produced and clarify that the
data base will act as a powerful analysis tool for biologically interesting properties of
any questions there may be. They also mention their future work where they will be
making large-scale orthologous comparisons on protein repeats over a broad
taxonomy range especially eukaryotes.
Conclusion
All three articles in their own ability have very well defined what amino acid repeats
are, their role and what their implications may be. I was given the title “single amino
acid repeats and trinucleotide repeats; function, evolution and human disorders”, but
I decided to look into detail of only amino acid repeats that too specifically in proteins
because what better location can amino acid repeats be present and also because I
knew I would find a lot of articles which can relate to my topic. Each chosen article
had their own central point even though they were about the same topic, one article
was mainly about the basic information on amino acid repeats, another article was
mainly about the information that is required to produce a database about amino acid
repeats and protein sequences, and the third article was mainly about aggregation
formed by amino acids and how they affect the structural features of AARs.
Bibliography
Faux, N. (2012) ‘Single Amino Acid and Trinucleotide Repeats’, Advances in
Experimental Medicine and Biology. Springer, pp. 26–40.
Katti, M., Sami-Subbu, Ranjekar, P. and Gupta, V. (2000) ‘Amino acid repeat
patterns in protein sequences: Their diversity and structural-functional
implications’, Protein Science, 9(6), pp. 1203–1209.
Luo and Nijveen (2013) ‘Understanding and identifying amino acid
repeats’, Briefings in Bioinformatics, 15(4), pp. 582–591.
Subirana, J. and Palau, J. (1999) ‘Structural features of single amino acid repeats in
proteins’, FEBS Letters, 448(1), pp. 1–3.
Dietary patterns, body image perception and obesity
in female adolescents
Introduction
The rise in child and adolescent obesity is a global concern. Current figures
reveal an increase in overweight and obese children in developed countries of
approximately 7% since 1980, with the United Kingdom being the 9th most
prevalent (PHE, 2016a). In England alone 28% of children are overweight and
obese (NHS Digital, 2016) with a higher proportion in adolescents (PHE,
2016c). Obesity is associated with numerous health complications in adults
such as: cancer, type 2 diabetes (T2D) and cardiovascular disease (CVD) (Pi-
Sunyer, 2009) as well as increasing the risk of death (Solomon, and Manson,
1997). However, T2D, hypertension and sleep apnoea among others are
becoming prevalent in adolescents due to the increasing trend of obesity
(Ebbeling, Pawlak and Ludwig, 2002). Furthermore, if a child is obese they
have a higher probability of becoming an obese adult (Serdula, Ivery and
Coates et al., 1993) particularly if they are still obese in adolescence, (Guo
and Chumlea, 1999) thus promoting the opportunity to develop additional
comorbidities.
Whilst several factors contribute to this epidemic, the underlying principle of
obesity is understood through the concept of energy balance. This denotes a
person’s body weight is unchanged as energy intake (food and drink
consumption) and energy expenditure (basal metabolic rate, thermogenesis
and physical activity) are equal (Spiegelman and Flier, 2001). However, if an
imbalance occurs whereby energy intake is more than energy expended, the
additional energy is stored and a positive energy balance is inevitable (Hill,
Wyatt and Peters, 2012), thus the individual gains weight. This literature
review will discuss the relationship between dietary patterns of female
adolescents and body image perceptions in contributing to obesity.
Dietary Habits in Adolescence
Adolescence marks the stage between childhood and adulthood whereby
major physiological and psychological changes occur such as: physical and
sexual development, body composition and enhanced cognitive and social
development. Optimal nutrient requirements, including energy, are essential
to facilitate this growth. Nevertheless, the environment makes this difficult as
less nutritious foods that are more satisfying are made easily accessible
(Neumark-Sztainer et al., 1999) at low economic costs (Drewnowski and
Darmon, 2005). Extensive literature suggests that adolescents consume
energy dense foods (Phillips et al., 2004) and soft drinks (Johnson and Frary,
2001) that ironically contain “empty calories” (Reedy and Krebs-Smith, 2010).
These foods lack beneficial nutrients such as vitamins and minerals and are
processed with high amounts of sugar, fat and/or salt which increases energy
consumption through calories. A preference for these foods is at the expense
of nutrient rich foods such as: wholegrains and vegetables (Nelson et al.,
2007), with only 8% of adolescents consuming the recommended amount of
fruits and vegetables per day (Public Health England, 2016b). A 10-year
longitudinal study involving adolescent females showed that those who
followed a diet predominately rich in vegetables, fruits and grains resulted in a
lower waist circumference than those whose diet included less nutritious
desserts, confectionary and other snack-type foods (Ritchie et al., 2007). This
study therefore demonstrates the importance of consuming fruits and
vegetables in preventing obesity.
In addition to the common food choices of adolescents, eating patterns are
also associated with the prevalence of obesity. Snacking in adolescence has
become a central part of the diet with an approximate 20% increase from
around 1970 (Sebastian, Goldman and Enns, 2010). The preferred snacks
are typically processed foods and confectionary (Anderson, Macintyre and
West, 1994), thus low in nutrient quality as previously discussed. Conversely,
many studies show that an increase in snack consumption does not lead to an
increase in BMI (Field et al., 2004), yet among other studies there has been a
positive association between obesity and drinks high in sugar (Malik, Schulze
and Hu, 2006). A study by Keast, Nicklas and O’Neil (2010) shows that
increased snack consumption has an inverse relationship with obesity due to
lower BMI and waist circumference values among female subjects. A possible
explanation is that the 24-hour dietary recall method that was used, is
associated with underreporting energy values (Johansson et al., 2001). This is
supported by Poppitt et al’s (1998) finding where regardless of weight status,
females underreported energy intake from snacks. Additionally, adolescents
who are more likely to snack, skip meals more frequently (Savige et al.,
2007), particularly missing breakfast (Brooks et al., 2015). This eating
behaviour is more prevalent in females and they are twice as likely to skip
breakfast than males (Brooks et al., 2015). Studies have shown a relationship
between those who consume breakfast with having a lower BMI than those
who do not (Gleason and Dodd, 2009). Thus although snacking may have a
positive outcome, it should not be used to replace meals as this may increase
the risk of obesity.
Body Image Perceptions
Body image perception is critical in adolescence as individuals become more
aware of their evolving physical characteristics (Christie and Viner, 2005).
Adolescents may exert feelings of body dissatisfaction whereby they are
unhappy with their body size or they may distort their own body image with an
unrealistic estimation of their perceived body size (Pesa, Syre and Jones,
2000). Both of these aspects reflect a negative body image perception that is
most common in females (Skemp-Arlt, 2006). This dissatisfaction has been an
on-going trend due to the impact that the media has on adolescent’s desire to
become thinner (Groesz, Levine and Murnen, 2001). With technology
becoming increasingly available, a study by Tiggemann and Slater (2013) has
shown a significant difference between adolescent females who spend more
time on the Internet and use Facebook with the desire to be thinner than
those who did not. Additionally negative body image in females’ increases
with age as 26% of 11 years olds and 50% of 15 year olds believe they are
“too fat” (Brooks et al., 2015). Unrealistic ‘thin’ imagery is contrary to the
actual body changes that occur during adolescence. Throughout puberty
females acquire more body fat than boys (Siervogel et al., 2003), which is
predominately stored in the hip region forming a ‘curved’ figure typical of a
fully developed woman (Ross et al., 2014), but this is not typically preferred.
Siegela et al (1999) showed that body dissatisfaction was highest in females
who began puberty early, suggesting that physical changes in body
composition are not desirable. Furthermore, Neumark-Sztainer et al (2002)
showed that overweight females were more dissatisfied with their bodies than
those of ‘normal’ weight. Nevertheless, whilst body weight estimation was
fairly accurate, still 30% of ‘normal’ weight females thought they were
overweight.
Body Image Perceptions and Dietary Patterns
Body image perceptions (distortion and dissatisfaction) are associated with
eating patterns in adolescents (Skemp-Arlt, 2006). Numerous studies have
shown a relationship between negative body image and unhealthy eating
patterns, which may lead to eating disorders (Stice and Shaw, 2002) and
obesity. Adult’s eating patterns are generally formed based on those in
adolescence, thus positive eating patterns should begin in adolescence (Ross
et al., 2014).
As previously discussed, particularly evident in female adolescents is the
desire to have a thin body (Groesz, Levine and Murnen, 2001). Consequently,
many females feel insecure about their weight status and will attempt to
manage their weight themselves, with one quarter of 15 year olds currently
trying to lose weight (Brooks et al., 2015). Dieting is a common method of
attempted weight loss in adolescence; nevertheless a study by Vander Wal
and Thelen (2000) revealed that dieting is significantly higher in girls than
boys and more significant if the girls were obese. In agreement with Neumark-
Sztainer et al’s (2002) theory, the obese girls were least happy with their body
weight explaining their desire to diet. There were similar findings in an
additional study with a large number of subjects (1370 adolescents). Girls with
an increased body weight and lower body satisfaction were more likely to
restrict eating and/or overeat (Mäkinen et al., 2012). Whilst the primary goal of
dieting is to lose weight, it is evident that overeating will have the opposite
effect- weight gain (Haines and Neumark-Sztainer, 2006). Studies have
shown that females who have attempted to lose weight are also inclined to
‘binge’ eat (Neumark-Sztainer et al., 1998). Binge eating is again associated
with body dissatisfaction, as those who resort to this increased food
consumption may do so as a result of not gaining their ideal body weight.
A study has shown a correlation between girls who ate breakfast regularly and
snacked more frequently with having a lower body weight that those who did
not (Bibiloni et al., 2013), supporting Gleason and Dodd’s (2009) findings.
However, energy consumption differed among the cohort as overweight girls
consumed less energy from food overall, because they were more likely to
snack often and skip full meals. It is important to mention that the overweight
girls were unhappy with their body size, thus being the reason for their dietary
choices (choosing snacks rather than meals) and therefore little energy
intake. Whilst this study did not specifically assess patterns of weight
management, this energy restriction may have been due to the adolescents’
attempting to lose weight (Skemp-Arlt, 2006). An additional study confirms
that adolescents are more likely to attempt to lose weight when they are
unhappy with their physical body appearance (Nowaka, 1998), which in turn
has an impact on their food choices. Females who were attempting to lose
weight at the time of the study consumed less fat-type foods such as: ice
cream, cakes and chocolate, thus portraying healthy weight loss attempts.
Nevertheless, this is still associated with an attempt to restrict calories due to
less frequent meals being consumed and no significant increase in healthier
foods like fruits and vegetables. Another study reported similar findings
among overweight females. Those with a higher BMI and most dissatisfied
with their body weight generally consumed less chocolate, biscuits and other
fat containing foods, but with an additional increase in fruits and vegetables
than those of an average weight (Bibiloni et al., 2013). This study is evidence
that low body satisfaction in overweight females has a more positive effect on
eating habits than average weight females attempting to lose weight. An
additional longitudinal study assessed adolescent’s eating habits in relation to
body dissatisfaction over 5 years (Neumark-Sztainer et al., 2006). This study
showed that regardless of weight status, adolescents with low body
satisfaction engage in behaviours shown to be unhealthy, including dieting
and binge eating. On the contrary, they also sought the highest amount of
healthy ways to control weight status. Far from a contradiction, these results
are more demonstrative of the fluctuations in adolescent’s dietary behaviours
over time. The need to tackle body dissatisfaction still stands, which in turn
will avoid the likelihood of adolescents taking drastic measures to control their
weight. Nevertheless a final study by Sonneville et al (2012) has
demonstrated the importance of high body satisfaction with better eating
habits over time. The study involved a cohort of obese female adolescents
whose eating habits and body image satisfaction were assessed and followed
up after 11 years. Findings show that individuals who were most happy with
their body size at the start of the study had lost more weight than those least
satisfied, demonstrating that increased body satisfaction is preventative
against obesity.
Conclusion
In conclusion, adolescent obesity and several other associated health
complications have become increasingly prevalent. Although obesity is
complex with many factors contributing to it, this literature review has primarily
focussed on the relationship between adolescent’s eating patterns in relation
to body image perception. In adolescence these elements are a major
concern, as the greatest changes in both aspects are present at this time
period and are likely to continue into adulthood. Unhealthy dietary patterns
have shown to be associated with negative body image perceptions in
numerous studies- predominantly in females. Negative feelings are not only
evident in overweight females but also those of a ‘normal’ weight due to
distorted image perception. Modern day pressure from the internet and on
social media to be thinner is a major factor in forming a negative body image,
with unhealthy dietary patterns as an additional consequence. In addition,
these unhealthy eating patterns such as meal skipping, binge eating and low
consumption of fruits and vegetables have been associated with obesity.
Healthy eating habits were only associated with low body dissatisfaction for
attempted weight loss. Finally, females with higher body satisfaction had
better eating habits and were less likely to become obese. Collectively this
shows the importance of body satisfaction in relation to dietary choices that in
turn are likely to lead to obesity.
More work needs to be done to encourage healthy body image on social
media and the internet by reflecting more realistic body types/shapes in order
to increase body satisfaction in adolescents, thus reducing the prevalence of
obesity.
Word Count: 2107
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Literature Review
“THE RELATIONSHIP BETWEEN STRESS, MENTAL HEALTH, WELLBEING AND FOOD
INTAKE/HABITS.”
PAGE 1
Table of contents:
•
Introduction
•
Search Results
•
Gaps in the Literature
•
Conclusion
•
References
PAGE 2
Introduction
Stress refers to a state of emotional strain, in which the perceived or real
demands of a situation or stimulus the body’s perceived or real capacity to
manage it (Dweck, Jenkins & Nolan,2014).Stress can be physical, psychological
or social in nature ( Shalev & Belsky, 2016).Stress is both beneficial for survival
in allowing the body to flee quickly from a dangerous situation, and potentially
deadly, leading to chronic disease (van Strien Roelofs & Weerth, 2013).Evidence
suggests that nearly 500.00
0
individuals within the UK suffer from chronic work –
related stress, depression or anxiety, or about 1,510 people for every 100,00
0
workers (Health and Safety Executive,HSE,2016).Stress also accounts for more
than one third of all work – related injuries or illnesses within the UK
(HSE,2016).The impacts of stress on health are multitudinous, and have
substantial and immeasurable effects on society at large (Katterman et
al.,2014).Stress produces long-term physiological changes that affect mental
wellbeing (Stagl et al.,2015).Most notably, stress leads to the production of
cortisol, which suppresses the immune system and contributes to insomnia,
depression and low affect (van Strien et al.,2013).The purpose of this paper is to
review literature pertaining to the relationship between stress, mental wellbeing
and food intake/habits. An attempt was made to include the most important
literature based on this results of this review and the large number pf papers that
have been published on this topic. A search of the PubMed database was
performed using the following keywords: stress, mental health; wellbeing and food
intake/habits. A combination of data sources was included and studies that were
published within peer reviewed academic journals. Literature most relevant to the
study topic will be hand selected from the search results and critically reviewed in
a chronological format.
Search Results
A search of the above terms revealed a total of seven studies within the PubMed
database that contained all items. No studies contained all three items within the
titles and abstract of studies. Additional searches were performed seeking to link
all three terms in titles and abstracts of studies, yielding no additional items. Of
the seven studies located in the search, just four directly pertained to the
research question being addressed and were hand- selected from the list of
seven. The results of the search are presented in Table 1 below:
PAGE 3
Table 1. Search results
Table 2 shows the four included in this review that directly pertained to the
relationship between stress, mental wellbeing and food intake, and also
contained primary data. The sample populations, intervention /design,
comparators and outcomes are included. Benton & Donohoe (1999) conducted a
review, seeking to evaluate the causes of emotional eating, which they found
was related to endorphin release. Epel et al. (2001) performed an experimental
design with 59 pre- menopausal women, comparing changes in eating behaviors
with the presence of cortisol. Wallis & Hetherington (2004) also used an
experimental design to assess the causes of food intake habits with 38 female
university students, seeking to determine the role of ego- threat on emotional
eating. Finally, Polivy & Herman (2005) performed the most extensive review to
date on this topic, evaluating literature published from 1994 to 2004 that
identified factors underpinning emotional eating. Results of these studies and
their relevance to previous research are discussed in the following paragraphs.
Search Query Items found
1 Search -Stress and
Mental wellbeing & food
intake
7
2 Search-
Stress/Title/Abstract
and mental wellbeing
(Title/Abstract) and
Food intake
(Title/Abstract) Schema
all.
0
3 Search-
Stress/Title/Abstract
and mental wellbeing
(Title/Abstract) and
Food intake
(Title/Abstract)
0
PAGE 4
Table 2. Studies included in review
Study Population Intervention/Design Comparator Outcome
Benton &
Donohoe
(1999)
N/A Review N/A Emotional
eating is likely
caused by
endorphin
release
Epel et al.
(2001)
59 health pre-
menopausal
women
between 30
and 45
Repeated measures
experimental design
Baseline scores Women with
high reactivity
to cortisol
consumed
large amounts
of calories
when exposed
to stress and
consumed
sweeter foods
Wallis &
Hetherington
(
2004)
38 female
university
students from
the UK
Mixed factorial and
experimental design
Neutral
(control)
Ego treat
resulted in 23
percent more
eating, while
emotional
eating was
associated with
more intake
only after ego
threat in
comparison to
controls.
Polivy &
Herman (2004)
Unidentified
number of
studies
conducted over
previous 10
years (1994-
2004)
Literature Review N/A Strong support
for physical
stress on
emotional
eating,
particularly with
fatty and
sugary foods.
Many
correlates were
identified.
PAGE 5
Two of the studies included in this review adopted experimental designs and two
adopted literature reviews. Irrespective of the design, studies assessing the
relationship between stress, mental wellbeing and food intake were conducted
with a high degree of rigour and the use of controls and bias risk reduction
techniques serves as an advantage of those studies included in this review.
However, eating behaviours were commonly measured through self-report and
did not actually include dietary monitoring (Polivy & Herman,2005). Though these
studies do offer insight into hypothetical eating behaviours, long-term intervention
studies are needed to track actual food consumption to determine the impacts of
stress and related biomarkers (e.g. cortisol) on food consumption behaviours.
Research showed that individuals consumed more food when exposed to
different types of stress (Epel et al., 2001).This finding supports previous studies
related to the effects of stress on copying styles (Bennet, Greene & Schwartz-
Barcott,2013;Raspopow et al.,2013).Individuals who perceive a threat as greater
than their individual capacity to manage it, will engage in coping that reduces the
severity of the stressor (Raspopow et al., 2013).For example, one study showed
that women consumed more food when they experienced threats to their ego
(Wallis & Hetherington,2004).Another study showed that women with higher
reactivity to cortisol were more likely to engage in emotional eating (Epel et a.,
2001).These findings are fairly consistent with biopsychosocial and psychological
manifestation of stress symptoms. Results show that stress, either physical
based on the production of cortisol in a cognitively demanding task, or
psychological or emotional based on the threat to the ego, increase the desire or
likelihood to seek stimulation and comfort trough food. The reasons for this
behaviour are not fully understood and are likely multidimensional in nature.
One possibility for this finding is that some of foods stimulate the production of
neurochemicals like serotonin and dopamine, which offer immediate chemical
relief from the effects of stress (Bennett et al.,2013).Another possible explanation
is that some individuals have developed conditioned responses to associate food
with comfort, and their parasympathetic nervous system initiate a relaxation
response when near food (Bongers et al.,2015).This effect is also potentially
evolutionary in nature (Bongers et al.,2015)
Benton and Donohoe (1999) offered a seminal review in which they
speculated about the effect of nutrients on affect. Like many authors, these
concluded that many foods stimulate the release of endorphins, which drives
emotional eating in the event of environmental stress ( Zenk et al., 2013;
Jaaskelainen et al.,2014) These authors also speculated that nutrients deficiency
drives emotional eating based on cravings for distinct nutrients that body is
lacking. Therefore, diets that promote restrained eating can be detrimental to
wellbeing and eventually to health because of their promotion of on – again or
off-again eating habits (Zenk et al., 2013). These fluctuations increase the
likelihood of temporary nutrient deficiencies and carvings for certain foods,
PAGE 6
particularly fats and sugars (Benton & Donhoe 1999). Therefore, consistency and
stability in the diet appears to be critical for general wellbeing.
Epel et al., (2001) studied the role of cortisol in stimulating emotion based eating,
performing an experimental design that exposed women to cognitive and
emotional stress and assessed attitudes towards eating. These authors found
that women were more likely to engage in emotional eating when they
demonstrated a high reactivity to cortisol, suggesting that this chemical has a
distinct effect on mood and wellbeing. In particular, women craved sweet foods
when exposed to stress and having high cortisol reactivity. This finding offers
support for the effect of glucose in elevating mood based on its rapid metabolism
and dissemination into the bloodstream. This emotionally based consumption of
sweet foods is a potential contributor to diabetes and these findings help illustrate
the psychological drivers of this disease (Jȁȁskelainen et al., 2014)
Wallis and Hetherington (2004) performed a novel experiment to assess the
effects of stress on food intake. These authors conceived an experiment
involving the Stroop task, which assesses performance under cognitively
demanding conditions. Participants in this study were allocated to one of four
experimental conditions based on the presence of ego – threat and/or cognitive
demand. Results showed that emotional eating was significantly increased after
cognitively demanding tasks, but only if they were threatening to the ego. This
condition created an emotional response that may have initiated an emotion
based copying style. Previous research has shown that emotion based copying
occurs when perceived demands of a situation exceed one’s perceived
resources (Jaaskelainen et al.,2014). In those participants who experienced
threats to their egos, emotional alleviation was seen as the only viable solution.
Findings from this study also reflect the heightened impact of stress on emotional
eating in individuals which low restraint and low problem based copying (i.e.
eating), and particularly relates to women based on the all-female sample.
However, the generalisability of the findings is limited based on this exclusivity to
one population demographic.
The impact of stress on eating and wellbeing has been made fairly clear, though
the direction of this relationship has remained the subject of debate. One study in
this review investigated this effect (Polivy & Herman,2005). Though these
authors adopted a literature review design, a large number of studies included in
their design found support for physical environmental stressors on emotional
eating. This effect was particularly strong for fatty and sugar foods. Cravings for
fatty foods may be related to the production of neurochemicals in the stomach.
Additional factors that were identified as correlates of stress-based eating habits,
mood and focus of attention (Polivy & Herrman,2005). These findings reflect the
complex and multidimensional nature of stress effects on mental wellbeing and
food intake. However, each of these effects support copying research and the
theory of problem versus ‘emotion based copying (Jȁȁskelainen et al., 2014).
Evidence from Polivy and Herman’s (2005) review suggest that this emotion
PAGE 7
based copying behaviour is underpinned by a biological desire or need for
glucose and fat-induced serotonin release. This biological contribution to eating
behaviours is important for dieticians and nutritionists, as well as helping
individuals to reduce shame or guilt associated with this copying behaviour.
Research included in the current review showed that shame and guilt are
common drivers, as well as effects, of emotional eating (Polivy & Herman,2005).
However, these findings also illustrate that care needs to be taken to promote a
more problem based copying style and to promote eating habits that provide
sustainable energy throughout the diet and less fluctuation of glucose and fat –
induced neurochemical production to prevent obesity, diabetes and other diet-
related diseases. This relationship between mental health and eating behaviours
is clearly bi directional and efforts are needed at both ends to promote healthy
eating and mood regulation (Polivy & Herman ,2005)
Gaps in the Literature
Results from this study offer support for the impact of nutrients on mood and the
relationship between stress mental wellbeing and food intake. However, some
gaps in the literature exist that warrant further consideration. Perhaps most
importantly, intervention research is needed based on the knowledge that stress
adversely impacts mental health and wellbeing and stimulates unhealthy eating
habits. The promotion of small, consistent meals that a prevent severe reductions
in nutrients is recommended as a counter to diet – induced depression. Reducing
stigmas associated with emotional eating are also important to modifying food
intake habits, as they produce more stress and cortisol, leading to increased
tendency for emotional eating. Interventions are needed that target these
outcomes to promote long- term behavioural change.
Conclusion
The purpose of this review was to identify trends in the literature pertaining to the
relationship between stress, mental wellbeing and food intake. A total of four
studies were located through a search of the PubMed database. Two of these
studies were experimental in nature and the other two were reviews. All four
found support for the impact of environmental stress on emotional eating, though
each offered novel proposed mechanisms driving this effect. It was clear from
this study that stress produces a biological, psychological and sociological
response that facilitates increased food consumption, particularly in women,
individuals with high cortisol reactivity, those with mood disorders and those with
genetic susceptibility to nutrient deficiencies or fluctuations in blood glucose
levels. This response may also be behavioural in nature based on a conditioned
PAGE 8
association between food consumption and positive mood, relaxation and affect.
Future research is needed that explores interventions designed to promote mood
stability, and it prevents reductions in individual’s nutrients be promoted to avoid
cravings. Behavioural modification may also be needed to eliminated paired
associations, while targeting correlates to high stress and emotion based copying
(e.g., low self-esteem, depression) would be appropriate for many. For more
details, refer to the References section.
PAGE 9
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PAGE 10
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ego- threat and cognitive demand on food intake in restrained and emotional
eaters. Appetite,43(1), pp.39-46.
Zenk, S.N., Schulz, A.J., Izumi, B.T., Mentz, G., Israel, B. A. and Lockett, M.,
(2013). Neighbourhood food environment role in modifying psychosocial stress-
diet relationships. Appetite,65, pp.170 – 177.
According to a 2015 United Nations report on world population ageing1, the number of people aged 60 and older worldwide is projected to more than double in the next 35 years, reaching
almost 2.1 billion people. Most of this growth will come from developing
regions of the world, although the oldest old, who are more than 80 years
of age, are the fastest growing segment of the population in developed
regions. Despite these improvements in life expectancy, Alzheimer’s
disease (AD) and related neurodegenerative conditions have arguably
become the most dreaded maladies of older people. The observation
that almost all aged brains show characteristic changes that are linked
to neurodegeneration raises the question of whether these hallmarks
represent lesser aspects of brain ageing that do not considerably affect
function or whether they are the harbingers of neurodegenerative
diseases (Fig. 1). Immune cells and secreted communication factors,
which are responsible for tissue homeostasis in general, probably play
important parts in brain ageing and neurodegeneration. However, com-
prehending or controlling the immune response in ageing has been a
challenge. In the ageing organism, the brain seems to be susceptible to
both cell-intrinsic and local signals, as well as to cues from the systemic
environment. Animal models suggest that cues that are present in the
circulatory system can either accelerate or slow aspects of brain ageing
and cognitive function. This Review will synthesize present knowledge
on brain ageing and neurodegeneration and discuss the prospect of
stalling or even reversing these processes through circulatory factors.
Overlap between ageing and neurodegeneration
Population-based autopsy studies of the brains of aged people who
had not been diagnosed with a neurological disease consistently report
the presence of amyloid plaques, neurofibrillary tangles, Lewy bodies,
inclusions of TAR DNA-binding protein 43 (TDP-43), synaptic dys-
trophy, the loss of neurons and the loss of brain volume in most of the
brains2. These features vary greatly between individuals, with particular
lesions dominating a particular brain or restricted to specific regions. It
is unknown what causes such lesions and whether they are the precur-
sors to neurodegeneration and disease or simply the products of brain
ageing. As well as classic protein deposits, other subcellular structures
that consist of cross-linked proteins, carbohydrates or lipids accumulate
in ageing brains, either in the extracellular space (for example, cor-
pora amylacea) or inside glial cells or neuronal cells (for example, stress
granules, lipofuscin, Marinesco bodies and Hirano bodies). Although
most of these structures are characterized poorly and their importance
in neurodegeneration is unclear, it is probable that they take a toll on
normal brain function3.
The presence of age-related protein abnormalities and inclusion bod-
ies in the ageing brain points to defects in proteostasis, an idea that is
supported by mounting evidence from experiments. According to one
such hypothesis, in normal ageing, macromolecules become oxidized
and can no longer be degraded by lysosomes4. This leads to the fur-
ther production of lysosomal enzymes that are also unable to digest
the cellular material. A well-known deposit that results from lysosomal
inefficiency is lipofuscin, which is an accepted marker of ageing for
postmitotic cells4. Similarly, the increase in damaged proteins and dying
cells that accompanies ageing can overwhelm phagocytic processes and
lead to an accumulation of material in lysosomes. Indeed, myelin debris
have been demonstrated to accumulate in ageing microglia, in which
it forms insoluble, lipofuscin-like lysosomal inclusions5. With ageing,
and even more so with neurodegeneration, the brain shows increased
levels of many lysosomal proteins and enzymes, and neurons and
other cell types show abnormal endosomes, lysosomes and autophago-
somes6–8. Whether these abnormalities contribute to or are the result of
ageing must still be elucidated. However, the genetic manipulation of
autophagy-related pathways in transgenic mice that overexpress amy-
loid precursor protein (also known as amyloid-β A4 protein) or the
protein tau results in prominent changes in the accumulation of these
proteins or the progression of disease9–11. Furthermore, stress granules,
which consist of RNA and protein and can form in response to cellular
stress, might have an important role in amyotrophic lateral sclerosis
and frontotemporal dementia12. Stress granules are also associated with
aggregates of tau in the brains of people with AD and in the brains of
mice that overexpress mutated tau protein, and the overexpression of
stress-granule protein TIA1 seems to stimulate a tauopathy13. These
studies underline the importance of protein homeostasis in brain func-
tion and suggest that ageing and neurodegeneration could result partly
from a loss of proteostasis. Although cause and effect must again be
established, it is probable that the stabilization of protein homeostasis
would benefit the ageing brain.
Our limited knowledge about the relevance of protein abnormalities
in the brain is demonstrated by a striking discrepancy between the clini-
cal manifestations of dementia and its associated physical characteris-
tics in the brain, particularly in the oldest old. For example, in a study
1Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Palo Alto, California 94304, USA. 2Center for Tissue Regeneration, Repair and Restoration, VA Palo Alto
Health Care System, Palo Alto, California 94304, USA.
Although systemic diseases take the biggest toll on human health and well-being, increasingly, a failing brain is the
arbiter of a death preceded by a gradual loss of the essence of being. Ageing, which is fundamental to neurodegeneration
and dementia, affects every organ in the body and seems to be encoded partly in a blood-based signature. Indeed, fac-
tors in the circulation have been shown to modulate ageing and to rejuvenate numerous organs, including the brain. The
discovery of such factors, the identification of their origins and a deeper understanding of their functions is ushering in
a new era in ageing and dementia research.
Ageing, neurodegeneration
and brain rejuvenation
Tony Wyss-Coray1,2
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of a large series of brains from cognitively unimpaired aged people,
almost all had abnormal accumulation of tau, roughly half had depos-
its of amyloid-β or TDP43 and one-fifth had deposits of α-synuclein2,
although the regional distribution of these lesions should be consid-
ered when assessing their relevance to neurodegeneration. The brains
of people who were aged 90 and older were found to weigh 11% less
than those of individuals in their fifties2, which indicates that more than
150 g of brain tissue had vanished in the older brains. This disappear-
ance could be due to the loss of neurons or glial cells, myelin, fluid or
other factors, and it will be important to determine whether it is related
to neurodegeneration or is simply a part of normal brain ageing. Simi-
larly, in a population-based sample of nonagenerians and centenarians
without dementia, almost half fulfilled the neuropathological criteria of
AD or had a mix of numerous pathologies14. Yet of the nonagenerians
and centenarians who had been clinically diagnosed with dementia,
12% were free of pathological features, 23% could be considered to have
AD and 45% had mixed dementia14. These observations are supported
by studies of cerebrospinal fluid biomarkers for amyloid-β and tau, as
well as positron-emission tomography imaging tracers in people, which
show that around 30% of cognitively unimpaired elderly individuals
are positive for these otherwise highly predictive markers of disease.
Such individuals could be at a preclinical stage of AD, a stage of the
disease that seems to be gaining clinical acceptance15. Around one quar-
ter of cognitively healthy elderly people or people with mild cognitive
impairment have pathological levels of tau in their brains in the absence
of amyloid-β, a condition called suspected non-AD pathophysiology
(SNAP)16,17. Most such individuals do not express the apolipoprotein ε4
(APOE4) isoform, which is consistent with the observation that APOE4
promotes the accumulation of amyloid-β and that the APOE locus is
linked to longevity.
In summary, clinical diagnoses often do not correlate with relevant
pathological features in the brain, and there are few people above the age
of 80 whose brains lack these features. The processes that characterize
neurodegenerative diseases and, in particular, AD take place in most old
brains; however, some people might have compensatory mechanisms
that enable them to cope with these processes and to maintain normal
cognition.
Causes of brain ageing and neurodegeneration
Given that neurodegenerative diseases in the elderly are common and
that disease-free brains, especially in the oldest old, are rare, it is possible
that normal brain ageing forms a continuum with neurodegeneration
and disease, and that stochastic factors, framed by a person’s genetics
and environment, determine the type of neurodegenerative disease that
will dominate their brain eventually (Fig. 2). It is therefore tempting
to view neurodegenerative diseases as expressions of accelerated age-
ing. However, this simplification is unhelpful because it does not accu-
rately capture the underlying mechanisms that tie neurodegeneration
to ageing, and all age-related diseases could essentially be described
as forms of accelerated ageing. Instead, our understanding of how age
contributes to disease is more likely to be advanced by dissecting how
environmental factors and genes intersect in a particular disease with
distinct hallmarks of ageing and by identifying the importance of these
processes in the disease (Fig. 2). For example, lesions associated with
a disease rather than ageing are often more region specific and cogni-
tive changes with age seem to be distinct from those observed in AD18.
Twin studies show that the heritability of the human lifespan is
20–30% and that the genetic contribution increases with age19–21. The
lower heritability at younger ages is probably caused by a greater num-
ber of accidental deaths at such ages22. Environmental factors therefore
account for at least 70% of variation in lifespan and an increasing num-
ber of studies show that lifestyle, diet, exposure to toxins, including
drugs of abuse, can have profound effects on healthspan, longevity and
the development of neurodegenerative diseases, although the molecular
pathways that underpin effects are mostly unknown. (The epidemiology
of longevity is reviewed comprehensively elsewhere23.) Further insights
into the links between ageing and neurodegeneration are being gener-
ated from genetic studies that explore not only longevity and exceptional
lifespan but also the genetics of disease-free ageing24,25 and the integra-
tion of genetics with other omics approaches26.
Exceptional longevity is linked consistently to the TOMM40–APOE–
APOC1 locus, and other strong links are observed at genes such as
FOXO3 and IL6 (refs 21, 23 and 27). In a large meta analysis of cente-
narian cohorts, many of the single nucleotide polymorphisms (SNPs)
linked to longevity with the greatest significance were linked negatively
to AD and coronary heart disease28. Interestingly, healthy ageing — that
is, ageing without developing a disease — does not seem to be linked to
longevity genes; instead, it might be associated with the absence of risk
factors for AD and cardiovascular disease24. In the same study, analysis
of the genes of people aged 80 years or older who had not been affected
by chronic diseases revealed links to SNPs that are involved in cognitive
performance, which offers the possibility that brain health and cogni-
tion might be surrogates for or even determinants of healthy ageing.
Another approach to deciphering the mechanistic contribution of
ageing to neurodegeneration examines the pace of ageing in a cell- and
pathway-specific fashion that focuses on gene expression, DNA meth-
ylation and other epigenetic DNA modifications (Fig. 2) that change
dramatically with age. For example, a comparison of age-related changes
in gene expression in the brains of people with AD and those without the
disease revealed that AD is characterized by signatures of accelerated
ageing in a neuronal-stress gene expression module, which includes
genes that are involved in protein folding and metabolism, and in an
inflammation module, which is defined by genes involved in cytokines
and microglia29. A strong positive correlation between ageing in vari-
ous regions of the brain and methylation was observed in several hun-
dred human brains30, a finding consistent with the epigenetic clock — a
generalized DNA methylation pattern that seems to characterize most
tissues31. Analysis of this pattern in Parkinson’s disease showed that
DNA methylation in blood cells is consistent with accelerated ageing32.
A correlation of the pathology of AD with DNA methylation across the
genome in almost 1,000 autopsied brains in two independent studies
identified methylation sites close to the genes ANK1, CDH23, RHBDF2
and RPL13 that were linked to the disease33–35. Remarkably, all of these
genes except for CDH23 have biological links to the AD-associated gene
PTK2B. A combination of transcriptome and epigenome analyses in
Young Aged
Abnormal
lysosomes
Abnormal
protein assemblies
Old
Normal ageing
Rejuvenation
Regeneration
Restoration
Cognitive
impairment
Neurodegeneration
and dementia
Figure 1 | Ageing, neurodegeneration and brain rejuvenation. As the
brain ages, abnormal protein assemblies and inclusion bodies take hold and
abnormal lysosomes are observed more frequently. It is unclear whether
these defects promote ageing and neurodegeneration or whether they are
innocent bystanders. Aged brains become highly prone to neurodegenerative
diseases in which the same lesions amass as those that are found in old brains
in smaller numbers. The relationship between such lesions and cognitive
impairment is often blurred and normal aging and neurodegeneration and
dementia can overlap. The concept of rejuvenation posits that old brains are
malleable and that aspects of the ageing process can be reversed to a younger
stage. If this can be achieved, it might also be possible to slow or reverse
neurodegeneration and cognitive impairment.
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brains affected by AD and in a mouse model of AD-related neurodegen-
eration enabled the discovery of a downregulation of genes and regu-
latory regions involved in synaptic plasticity as well as a concomitant
increase in the expression of genes involved in immune response and
regulatory regions36 — most notably SPI1, which encodes PU.1, a tran-
scription factor with importance for the development of the myeloid
lineage, including microglia37.
Genetic and epigenetic studies can therefore help to uncover the
molecular pathways that link ageing with neurodegeneration. More
refined omics studies, conducted with single cells isolated from defined
brain regions, will probably deepen our insights and enable us to iden-
tify new targets to delay aspects of ageing in a disease-specific fashion.
The circulatory proteome of organismal ageing
Through plastic surgery, people can look years younger than their wrin-
kled hands, and although stretching the skin might not change its intrin-
sic age, it poses the question of whether all of a person’s organs age at a
similar pace. Ageing has been categorized into nine separate processes
or hallmarks38, seven of which consist of molecular, mostly cell-intrinsic,
changes such as telomere shortening, mitochondrial dysfunction or
DNA damage. The other ‘integrative’ hallmarks include stem-cell age-
ing and dysfunction of intercellular communication38. The molecular
or pharmacological manipulation of several of these processes has been
shown to affect lifespan in mammals.
From an organismal perspective, intercellular communication is of
particular interest as it could provide insights into the ageing process as
well as help to identify biomarkers of ageing. Cellular communication
occurs at numerous levels, from cells to tissues, across an organism and
is accomplished by a myriad of molecules, including secreted proteins,
lipids and metabolites, which must be tightly controlled. This network
of communication factors changes as an organism develops, ages or
is affected by disease. It is possible that age-related changes in cellu-
lar communication are simply adaptations to ageing. However, such
changes might also contribute to ageing, either locally or distantly, and
as a consequence, a particular organ or cell type might modulate or even
control ageing at the organismal level (Fig. 3).
Technologies for studying the proteome, the lipidome and the
metabolome can be used to characterize age-related changes, and an
increasing number of studies are describing changes in the blood that
occur with normal brain ageing or with neurodegeneration, under the
hypothesis that such changes mirror, in part, changes in the brain. As
there are few studies of blood-based lipids or metabolites that regulate
brain function, I will focus instead on studies that quantify secreted
signalling proteins involved in intercellular communication — a subset
of the proteome that has been dubbed the communicome39. The most
comprehensive study of the cellular communicome of ageing quanti-
fied around 1,100 proteins using aptamer-based assays of the blood
of about 800 people40. The protein most strongly correlated with age-
ing, chordin-like protein 1, is an antagonist of bone morphogenetic
protein 4 and might therefore be involved in neural stem-cell fate and
angiogenesis. Other proteins with links to ageing include pleiotrophin,
which is a neurotrophic and mitogenic factor, the metalloproteinase
inhibitor TIMP1 and the cysteine-proteinase inhibitor cystatin-C, all of
which were also associated strongly with ageing in human cerebrospinal
fluid41. Of the 281 proteins detected in cerebrospinal fluid, 81 were cor-
related significantly with age in 90 cognitively unimpaired people aged
between 21 and 85 (ref. 41), which indicates that the brain is exposed
to very different environments depending on the expression of these
communication factors. Using antibody-based multiplex assays, several
studies have measured tens to hundreds of known communication fac-
tors in the blood plasma of people with various stages of AD, reporting
protein signatures that characterize the prodromal stages of the disease42
or the progression from early to late-stage AD39,43,44. Other studies have
described protein signatures that correlate with APOE genotypes45 or
with cerebrospinal-fluid levels of amyloid-β and tau in people with
AD46,47. The aptamer platform, which is more encompassing and pre-
cise than alternative methods, was also used to measure 1,001 proteins
in almost 700 people with no cognitive impairment, mild cognitive
impairment or AD: 14% of proteins showed a significant association
with AD and 13 proteins could be used to classify AD with 70% accu-
racy48. By combining plasma proteomic data from healthy individuals,
AD and frontotemporal dementia with existing brain gene-expression
data and data from genome-wide association studies (GWAS), the most
prominent changes in AD were found to relate to TGF–BMP–GDF sig-
nalling, the activation of complement and apoptosis, and GDF-3 was
linked to neurogenesis and AD49. Although common factors, including
APOE, complement, CCL5, clusterin and ICAM1, have been identified
in these studies, it will be crucial to replicate them independently and to
establish the in vivo biological importance of newly discovered proteins.
If validated, such proteins or their combinations could become use-
ful markers for brain ageing or neurodegeneration, as well as potential
therapeutic targets.
To address this challenge, several communication factors were
measured in the plasma of both young and aged mice, as well as in
mice exposed to the blood of young or aged mice through heterochro-
nic parabiosis, using an antibody-based multiplex assay50. (Parabiosis
is established by surgically joining two mice at their flanks, leading
to the formation of a vascular anastomosis and a shared circulatory
system.) One of the factors that correlated most strongly with ageing
and the effects of parabiosis on hippocampal neurogenesis was eotaxin
(also known as CCL11), a small chemokine with a role in allergies
and certain types of parasitic infections. Indeed, systemic administra-
tion of recombinant CCL11 to young mice was sufficient to reduce
neurogenesis and to impair cognition (Table 1). In line with these
potentially detrimental effects on the brain and cognition, the level
of CCL11 increases in the choroid plexus during ageing51 and in fat
deposits with obesity, and it decreases after exercise in people who are
obese52,53. Similarly, β-2-microglobulin (B2M), a component of major
histocompatibility complex class I (MHC I) molecules, was found to
be a pro-ageing factor that can impair cognition and neurogenesis in
young mice and is necessary to maintain these functions in old mice54
(Table 1). Together with studies that link MHC I molecules with syn-
aptic plasticity and brain repair55, these findings further implicate the
MHC I locus in brain ageing and neurodegeneration. Importantly,
these studies also indicate that proteins in the blood circulation
Figure 2 | Cell-specific and pathway-specific acceleration of
ageing. Ageing can be dissected into individual processes, including a
loss of protein homeostasis that leads to the development of aggregates and
inclusion bodies, DNA damage, lysosomal dysfunction, epigenetic changes
and immune dysregulation. The genetic predisposition of an individual,
together with his or her exposure to the environment, determine the incidence
and prevalence of the lesions that result from such processes, probably in a
cell-specific manner. Various diseases might develop in accordance with the
spatiotemporal distribution of the lesions.
Genes
Environment
Disease A
Disease B
Disease C
Loss of protein
homeostasis
DNA damage
Lysosomal
dysfunction
Epigenetic
changes
Immune
dysregulation
Time
Young brain
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involved in intercellular communication are both correlated with and
able to modulate brain ageing, and they demonstrate the feasibility
of using plasma proteomics to discover factors of relevance to brain
ageing and cognitive function.
Abnormal intercellular communication and inflammation
Interestingly, the immune factors CCL11 and B2M, as well as the
chemokines CCL2, CCL12 and CCL19 and haptoglobin, which are
linked to negative effects on neurogenesis during parabiosis50, might
be part of a low-grade inflammation that is linked to ageing, known
as inflammageing56. Inflammatory factors in the ageing brain could
originate from microglia and astrocytes as they become senescent and
adopt a senescence-associated secretory phenotype57. Some ageing
astrocytes express increased levels of cytokines, intermediate filament
proteins and intracellular protein aggregates, which is consistent with
the phenotype58. As discussed previously, this senescent phenotype
could result from epigenetic changes that activate immune-response
genes targeted by, for example, the transcription factor PU.1 (ref. 36).
Alternatively, microglia that change their gene-expression repertoire
dramatically with age in a brain-region-specific manner59 might become
reactive and inflamed as a result of impaired phagocytosis and protein
dyshomeostasis. (A detailed discussion of microglia in brain ageing is
presented elsewhere60.)
A role for inflammatory factors in autosomal dominant forms of
neurodegeneration was suggested by the observation that numer-
ous SNPs in the chemokine cluster that contains the gene CCL11
were linked to a 10-year difference in the age of onset of clinical
AD symptoms in 72 people carrying a highly penetrant presenilin 1
mutation61. Indeed, inflammation has long been associated with neu-
rodegeneration62,63, and the use of non-steroidal anti-inflammatory
drugs for several years before the onset of clinical symptoms is asso-
ciated with a reduced risk of AD64–66. However, the same drugs do
not seem to benefit people with Parkinson’s disease67. It is unclear
exactly how inflammation contributes to AD but it might involve
both local and systemic mechanisms. In support of a detrimental
role for systemic inflammation in the early stages of AD, the number
of systemic inflammatory events (such as urinary tract infections)
correlate positively with the progression and severity of AD68,69.
Genome-wide transcriptome studies of numerous brain regions in
more than 1,600 brains provide further evidence of a role for immune
mechanisms in ageing and AD; they also show that the expression of
genes involved in inflammation increases considerably with normal
ageing and precedes the development of AD29. Another bioinfor-
matics-based study used signalling pathway and network analysis to
conclude that the gene TYROBP (also known as DAP12), restricted
mainly to microglia in the brain, is deregulated in AD70. DAP12 is
an adaptor for several receptor molecules, including complement
receptor 3, an important phagocytic receptor expressed by micro-
glia, and TREM2 (ref. 71). The most direct evidence that altered
immune function has a role in AD emerged from genetic studies
that showed that rare polymorphisms in the myeloid-lineage gene
TREM2 increase the risk of developing AD several fold72,73. GWAS
also identified further polymorphisms in genes involved in immune
responses that modify the risk of developing AD74–76. In the brain,
most of these genes, including TREM2, are expressed predominantly
or exclusively by microglia. Dysfunction of microglia would probably
impair the capacity of these cells to uptake and degrade amyloid-β
and could therefore directly promote or even initiate AD. Antibodies
that bind amyloid-β to facilitate its clearance by microglia are being
tested in the clinic at present77.
Together, the genetic, transcriptomic and proteomic evidence sug-
gests that changes in inflammation and intercellular communication
represent chief aspects of normal brain ageing and neurodegeneration.
However, it is unclear whether inflammatory pathways simply drive
ageing and disease or whether aspects of the inflammatory response
fulfil reparative and regenerative functions.
Brain rejuvenation and the manipulation of ageing
The concept of organismal and systemic ageing has been tested radi-
cally using heterochronic parabiosis78, which enables the exchange of
blood, including its cells and factors, between young and old organisms.
This surgically and conceptually simple model can therefore be used to
investigate whether a youthful intercellular communicome can inhibit
or reverse age-related abnormalities in an old mouse or whether an aged,
and possibly dysfunctional, communicome can promote ageing in a
young mouse. According to studies from nine independent laboratories,
stem-cell activity is increased and other indices of ageing are delayed or
reversed in several tissues of aged mice that share a circulatory system
with young mice. These studies included: initial observations of effects
on muscle and the liver78; reports of effects on the brain by four separate
laboratories50,79–81 (Table 1); and observations of rejuvenating effects in
the pancreas82, the heart83, bone84 and muscle85 (for detailed reviews, see
refs 86 and 87). By contrast, the ageing thymus does not seem to benefit
from parabiosis; however, the injection of young epithelial cells enabled
thymic regrowth88. Perhaps most remarkable, with respect to the brain,
is that the repeated intravenous administration of plasma, the soluble
fraction of blood, from young mice (performed systematically for the
first time in 2011, to study ageing factors50), was sufficient to improve
cognitive function in old mice in several behavioural tests80 (Fig. 3).
These functional changes were accompanied by molecular, subcellular,
cellular and electrophysiological correlates, which suggests that factors
in young blood have the capacity both to regulate brain function and
to improve it to levels found in younger mice (Table 1). Parabiosis of
amyloid-precursor protein transgenic mice with young mice, or the
Figure 3 | Brain rejuvenation through circulatory factors from a young
mouse. Protein factors and other molecules that circulate in the blood
of a young mouse exert rejuvenating effects on the brain of an old mouse
after intravenous delivery. Such factors might affect the brain through
various mechanisms, including: the active transport of factors into the brain
parenchyma; the passive transport or diffusion of factors into the brain; and
the activation of endothelial cells by factors. Other mechanisms might include
the uptake of factors into the brain in areas that lack the blood–brain barrier,
such as the neurogenic subventricular zone and circumventricular organs (not
shown). As well as exerting effects on the endothelium, factors that enter the
brain parenchyma might act on neurons, microglia or oligodendrocytes (not
shown). The reported rejuvenating effects of young blood or young plasma on
the old brain are listed.
Neuron
Brain rejuvenation
Plasticity genes
Dendritic spine density
Vascular remodelling
Neurogenesis
Olfactory discrimination
Learning and memory
In�ammatory pathways
Protein
factors
OldYoung
Blood
transfer
Microglia
Astrocyte
Brain
endothelial cell
Active transport
into the brain
Passive
transport
into the brain
Activation of
endothelial cells
Blood vessel
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intravenous administration of plasma from young mice, also reversed
the loss of synaptophysin and calbindin (an indicator of cognitive
decline both in people with AD and in transgenic mouse models of
the disease), normalized MAPK–ERK signalling and improved their
working memory89.
A deficiency in growth hormone or insulin–insulin-like growth
factor I signalling has been linked to deficits in memory, and the acti-
vation of growth hormone and insulin-like growth factor I signalling
has been associated with improved brain function after injury or under
conditions in which these proteins are lacking (reviewed in ref. 90). Few
studies have treated healthy aged animals or people with growth factors
and even fewer have demonstrated beneficial effects of such treatment
(Table 1). For example, although insulin-like growth factor I increases
neurogenesis91 and insulin-like growth factor II increases memory92
in young rodents, these factors have not been tested in aged animals.
And in healthy older women or women with mild cognitive impair-
ment, treatment with insulin-like growth factor I for 1 year showed
no effect on bone density, bone strength, mood or memory93. By con-
trast, systemic administration of growth hormone-releasing hormone
(GHRH), which triggers the hypophyseal release of growth hormone
and increases the levels of circulating insulin-like growth factor I,
among other factors, resulted in improved cognition in healthy elderly
people or in people with mild cognitive impairment94. On the basis of
the observation that the hypothalamus might have a role in regulating
organismal ageing, systemic treatment of aged mice with gonadotropin-
releasing hormone I (GnRH I) was found to increase neurogenesis and
to improve cognitive function95.
In a search for factors that decrease with ageing and that might be
responsible for the beneficial effects of heterochronic parabiosis on the
heart, GDF-11 was identified as a potential heart-rejuvenation factor83.
Subsequently, GDF-11 was found to increase neurogenesis, to improve
olfaction and to exert beneficial effects on the brain vasculature81
(Table 1), as well as on aged muscle85. Other studies were unable to
repeat these effects on systemic tissues96, and mass-spectrometry-
based assays for GDF-11 and the related protein myostatin (GDF-8)
observed no decrease in GDF-11 levels in human plasma with ageing
and also found that GDF-11 levels are associated with frailty in people
with cardiovascular disease97. Further studies will need to determine
whether particular forms of GDF-11 (for example, mature, immature or
post-translationally modified GDF-11) can explain these discrepancies
and, most importantly, whether systemic administration of GDF-11
might be beneficial for human brains.
Overall, parabiosis with young mice or the transfer of young plasma
seems to be capable of restoring brain function in old mice to more
youthful levels. GHRH, GnRH I and GDF-11 are putative brain-reju-
venation factors and it is probable that other age-related proteins with
detrimental or beneficial effects on the brain will be discovered. So far,
it is unknown how the plasma from young animals or the factors listed
in Table 1 exert their effects. It is possible that some of these proteins
enter the brain actively or passively through the blood–brain barrier
or at sites that lack a functional barrier, including the circumventricu-
lar organs and, perhaps, the neurogenic niches (Fig. 3). Other proteins
might modulate vascular function by interacting with endothelial cells
and modulating the neurovascular unit81. In the future, studies will have
to determine these modes of action and explore their potential for use
as therapeutic approaches.
Outlook
In humans, the old brain shows the classic hallmarks of ageing and is
particularly susceptible to abnormal protein accumulation and impair-
ments in the phagolysosomal system, which leads to fluid boundaries
between ageing and neurodegenerative diseases. Consequently, many
old people have pathological abnormalities of the brain that do not
necessarily correlate with their cognitive abilities. This has important
implications for the treatment of those with clinical symptoms as well
as for designing clinical trials to target protein abnormalities in a spe-
cific manner. Given the crucial functions that immune responses and
inflammation have in brain ageing and neurodegeneration, it will be
essential to discern beneficial attempts to maintain or repair damage
from maladaptive ones. Clearly, the term neuroinflammation fails to
capture the age- or disease-related changes in this sophisticated inter-
play between the surveillance, identification, targeting and execution
functions of immunity and should probably be avoided. When studying
age-related neurodegenerative diseases in animal models, it is impor-
tant to consider ageing; those that have been genetically engineered to
develop disease during adolescence and before midlife are unlikely to be
influenced sufficiently by ageing and are therefore not very informative
about age-related factors in sporadic neurodegeneration.
The increasing number of studies that show systemic effects on the
brain, including those of young plasma or heterochronic parabiosis, as
well as the effects of the microbiome, should remind neuroscientists that
neurons do not function in isolation; instead, they are part of a sophisti-
cated network that includes glial cells, vascular cells and peripheral cells.
So far, there is no published evidence that young blood or plasma has
beneficial effects on an ageing human body, and the observation that
young plasma can modulate brain ageing in mice presents more ques-
tions and opportunities than answers. Only a handful of proteins, which
might represent factors involved in ageing or rejuvenation, have been
Table 1 | Effects of systemically administered ageing and rejuvenation factors on healthy brains
Factors Organism or model Effect on the brain References
Blood or plasma from old mouse Young adult mouse In the young brain: reduction in neurogenesis; increase in
microglial reactivity; reduction in learning and memory.
50
CCL11 Young adult mouse In the young brain: reduction in neurogenesis; increase in
microglial reactivity; reduction in learning and memory.
50
B2M Young adult mouse In the young brain: reduction in neurogenesis; increase in
microglial reactivity; reduction in learning and memory.
54
Blood or plasma from young mouse Aged mouse Increase in neurogenesis; reduction in microglial reactivity;
improvement in learning and memory; improvement in olfactory
discrimination.
80, 81
IGF1 Young adult rat Increase in neurogenesis. 91
IGF2 Young adult mouse Increase in retention and persistence of working, short-term and
long-term memory.
92
GHRH Healthy older people; people with mild
cognitive impairment
A 20-week treatment improved executive functions in both groups
of people.
94
GnRH Aged mouse Increase in neurogenesis; improvement in memory. 95
GDF-11 Aged mouse Increase in neurogenesis; increase in cerebrovascular integrity. 81
IGF, insulin-like growth factor; GHRH, growth hormone-releasing hormone; GnRH, gonadotropin-releasing hormone; GDF-11, growth and differentiation factor 11.
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shown to mimic the effects of plasma. However, many more proteins or
other types of molecules are likely to exist, some of which might have
direct therapeutic applications. Basic research will address the exciting
questions that surround the origins of these factors, how they signal
to the brain and why they change with age. Ultimately, it is hoped that
by using such knowledge to alter basic processes involved in ageing, it
will become feasible to counter the cellular abnormalities that lead to
neurodegeneration. ■
Received 3 May; accepted 2 September 2016.
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Acknowledgements I would like to thank T. Montine at Stanford University for his
critical reading of the manuscript. This work was supported by the US Department
of Veterans Affairs and the US National Institute on Aging (AG045034).
Author Information Reprints and permissions information is available at
www.nature.com/reprints. The author declares competing financial interests: see
go.nature.com/2ekr43u. Readers are welcome to comment on the online version
of this paper at go.nature.com/2ekr43u. Correspondence should be addressed to
T.W.-C. (twc@stanford.edu).
Reviewer Information Nature thanks F. Gage, M. Mattson and the other anonymous
reviewer(s) for their contribution to the peer review of this work.
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TARGETTING THE Pl3K-AKT SIGNALLING PATHWAY IN POINT OF CARE
MALIGNANT MELANOMA DIAGNOSIS AND SUBSEQUENT TARGETTED
TREATMENTDEVELOPMEN�
ABSTRACT
a a
Advances in the understanding of the, nature, mechanism and regulation of the Pl3K-
AKT signalling pathway in malignant melanoma has allowed for possibilities in the
areas of point of care molecu lar diagnostics and targeted personalized medicine.
This review addresses the mutations and functions of genes and proteins of the
Pl3K-AKT signalling pathway and cross-talk with other siigna lling pathways in
melanoma development. The potential of improving mellanoma diagnoses through
the use of molecular detection assays and the development of more efficient
therapies tihat aim to directly correct molecular dysfuncti:on is rife.
INTRODUCTION
Malignant melanoma is one of the most aggressive cancers of the skin which is
primar ily caused by excessi v e ultraviolet radiation (UVR) exposure (Chaidemenos et
al., 2008). This UVR penetrates the skin and causes irreparable DNA damage to
melanocytes as well as resullting in gene mutations that disrupt vari ous signalling
pathways that typically inhibit or repress cell growth and proliferation, thus leading to
tumour formation (King and Robins, 2006}. There are various cross-talk siignalling
pathways that play major roles in maligna elanoma formation and metastases;
one of the main signalling pathways being the P13K-AKT pathway which is the main
focus of this review. This pathway functions to control and regulate· cell growth and
proliferation in healthy individuals (Vidwans et al., 201
1
). There are numerous
treatments available for melanoma depend ing on the cancers characteristics and
TMN staging (Chaidemenos et a/., 2008). In malignant melanoma diagnosis there is
potential for point of care diagnostic te sting that target siignalling pathways and
specific affected genes for more accurate molecular abnormality detection.
Following such detection there is further potential for the development of molecular
targeted and personalized treatments that worl< to directly repair abnormalities in
specific signal pathways.
1
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Biology and Medicine, 2014.
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Lim, Hui Jun, Philip Crowe, and Jia-Lin Yang.
“Current clinical regulation of
PI3K/PTEN/Akt/mTOR signalling in treatment
of human cancer”, Journal of Cancer
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Bader, C Späth, E Drecoll, G Keller, H Höf ler,
J Slotta-Huspenina, and K-F Becker.
“Activation of the PI3K/AKT pathway
correlates with prognosis in stage II colon
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cancer”, British Journal of Cancer, 2014.
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cycle arrest through phosphoinositol-3-
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melanoma invasiveness: advances in
clarif ying E2F1 f unction”, Expert Review of
Anticancer Therapy, 11/2010
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– The role and importance of autophagy in carcinogenesis
Autophagy is a survival mechanism used by ceHs duri.ng times of nutrient stress, for
example, the absence of amino acids,. nitrogen and/or carbon. Lysosomal
degradation of organelles and protein aggregates generates energy for the cell in
order for i t to survive, as wellll as limiting the cellll’s ability to produce toxic substances
such as reactive oxidative species (ROS), for example, hydrogen peroxide. Ros£m
damage DNA, effectin • A replication and protein synthesis. Eventually, this can
lead to carcinogenesis. :A.atophagy has a paradoxical effect, where it can induce
carcinogenesis in normal celllls, but within adv:am:ed cancerous cells. it assiis.ts with
the survival of the tumour. Over recent years a lot of cancer therapies have been
trialled and developed, based O’IT.IM•”‘�””‘iting autophagic regulators (proteins).
However, we still remain unawa ‘ ut the exact mechanisms of regulators such as
b . – /.
In normal cells, autophagy pllays an iimportant role in recycling damaged organelles
and dysfonctional proteins for energy usage in order to maintain the cell’s integrity.
This survival mechanism is not limited to the removal of injurious substances from
the cell, but it also plays a part in promoting cell senesce,nce. T ui der normal
conditions, autophagy is a key component in the prevention of c _[ genesis (Glick
et al, 2010). My research question pertains to the role of the B eclin-1 protein in
carcinogenesis, a protein which induces autophagy. Therefore, this literature review
intends to analyse the current .literature on autophagy in cancer, our current
understanding of autophagy, how the analysed literature relates to my research
•question and how we can progress with the current literature we have. The review
will include, but not be exclus,ive to Beclin-1. Instead it will look at the relationship
between autophagy and carcinogenesis on a wider scope, allowing me to evaluate
more liteLatu . Eventually, coming to a conclusion as to why I have chosen to use
Beclin- In research question, how the field can progress and how promising the �
current state of research is. liafll
There are three type s of autophagy, macro-autophagy, micro-autophagy and
chaperone-mediated a utophagy. Macro-autophagy is essentially the rem ova I of
structures, not necessarily organelles, but also aggregated proteins for example,
which may have lost their functionality. The structures are encased in a double-
membrane vesicle known as an autophagosome. This autophagosome will transport
the contents to a destructive lysosome, where the constituents can be used to
synthesise more protein or used as an energy source (Boya et al, 2013). In micro
autophagy, th e damaged/dysfunctional contents of the cell are directly taken up by
the lysosome via invagination (Glick et al, 2010). Finailly, in chaperone-mediated
autophagy the structures are transported to the lysosome by chaperone proteins,
which are then translocated iinto the lysosome. These chaperone proteins are
granted entry into the lysosome due to the presence of llysosome associated
membrane proteins (LAM Ps ). Deficiency of these proteins means the structures
can not be trans!ocated into the lysosome (Huynh et al, 2007). Perhaps a deficiency
in these proteins contributes to carcinogenesis? Research into the deficiency of
QM
FINAL GRADE
54/0
Literature Review
GRADEMARK REPORT
GENERAL COMMENTS
Instructor
Do ne well:
Yo u have demo nstrated enthusiasm f o r the to pic
and been able to identif y so me key, relevant
primary so urces and reviews. Yo u have
attempted to intro duce a high pro po rtio n o f
discussio n into the review.
Fo r impro vement:
Overall, the review required a systematic
intro ductio n o f key f actual material o n which
discussio n co uld be based.
T here was an episo dic structure that made it
so metimes dif f icult to f o llo w yo ur reaso ning.
Pay attentio n to my co mments in the text
Abstract: 0/5
Review: 24 /4 0
Ref erencing: 3/5
PAGE 1
Comment 1 | Present at ion
Yo u were instructed to begin yo ur literature review with an abstract. T his is missing f ro m the
submissio n.
Having read the paragraph and no ted the lack o f ref erences, yo u may have intended this to
be an abstract. Witho ut a title o r heading, this is in f act the beginning o f yo ur review. See my
co mment belo w.
Comment 2
ins: may
A/E
Af f ect/Ef f ect:
T he verb “af f ect” means “to inf luence o r pro duce an ef f ect o n.” As a no un “ef f ect” is a
result. As a verb “ef f ect” means “to bring into existence.” While in mo st cases, an ef f ect is
the result o f all that has been do ne to af f ect a situatio n, it is po ssible f o r o ne perso n to
ef f ect change.
Strikethrough.
Comment 4
QM
QM
o n
Comment 5
A very vague sentence intro ducing a number o f so f ar unexplo red co ncepts. Otherwise an
adequate intro ducto ry passage marred by the co mplete absence o f ref erences. T his latter
po int suggests that yo u co nsider this to be an abstract. I suggest that yo u read so me article
abstracts caref ully to see ho w they are co nstructed.
Comment 6
T here is insuf f icient inf o rmatio n presented here f o r this co nclusio n to be drawn.
Tick
(T ick)
Strikethrough.
Comment 8
Vague. T here must be a purpo se to this wider review. What questio n are yo u seeking to
address? What are the bo undaries f o r yo ur review?
Comment 9
Go o d to include a statement o f intent, but do es need to be precise and co ncise.
PAGE 2
Citation required
Yo u have no t ref erenced the so urce o f this inf o rmatio n.
Fo r advice o n ref erencing, please go to http://www.westminster.ac.uk/library- and- it/suppo rt-
and- study- skills/guides- and- tuto rials/ref erencing- yo ur- wo rk
Comment 10
Go o d questio n, but why start discussing limitatio ns to kno wledge here when the three
mo dalities have no t been described in any detail?
It is no t suf f icient to state that research is “f lawed” witho ut presenting evidence to suppo rt
this assertio n.
Comment 11
T his is no t required…
Comment 12
f o r
Comment 13
Do no t use demo tic English in academic writing. A reader f o r who m English is a seco nd o r
third language may no t understand the idio m (yeast f issio n o r gro wing trees?)
Comment 14
T here are several co ncepts intro duced into this o ne paragraph. T hese sho uld be presented
http://www.westminster.ac.uk/library-and-it/support-and-study-skills/guides-and-tutorials/referencing-your-work
QM
QM
in separate paragraphs f o r clarity (unless they are being co mpared directly)
Comment 15
Yo u need to present evidence f o r this. Yo u have to reveal the gaps in kno wledge bef o re
making such a statement.
Comment 16
Do no t co ntract wo rds in f o rmal writing.
Go o d to see the enthiusiasm f o r the to pic, but there are to o many “interesting to pics” and
to o f ew details o f what these might be…
Comment 17
Date required
Comment 18
Warning: dysplasia is NOT cancer. Please use Weinberg (2014 ) as a co re ref erence to build
yo ur kno wledge o f cancer bio lo gy.
Comment 19
Go o d idea f o r discussio n, but yo u need to present (brief ly) the evidence…
Comment 20
Marking will be with a lighter to uch f ro m here, but be aware o f the nature o f the co mments
that I have made already
Citation required
Yo u have no t ref erenced the so urce o f this inf o rmatio n.
Fo r advice o n ref erencing, please go to http://www.westminster.ac.uk/library- and- it/suppo rt-
and- study- skills/guides- and- tuto rials/ref erencing- yo ur- wo rk
Comment 21
What is p62 and what do es it do ? Yo u have still to explain the mechanics o f auto phagy
Comment 22
A serio us interpretatio nal erro r here. Yo u will have seen that auto phagy is a pro cess f o und
in yeasts, wo rms, mice and humans. T his suggests tremendo us selectio n pressure f o r
co nservatio n o f genes and f unctio n.
Conceptual understanding
What do es this mean? T here sho uld be a suppo rting explanatio n o r discussio n that
demo nstrates yo ur understanding o f the co ncept.
Comment 23
it is no t a PK…but yo u will be lo o king at the distributio n o f the pro tein.
PAGE 3
Comment 24
http://www.westminster.ac.uk/library-and-it/support-and-study-skills/guides-and-tutorials/referencing-your-work
QM
T here is a great deal mo re in the literature o n the implicatio ns o f BECN1 haplo insuf f iciency
f o r cancer risk…
Comment 25
Co ncept issue: yo u need to think abo ut (1) mo dern scientif ic metho do lo gy and the
f e# alsif icatio n o f hypo theses and (2) ho w o ne can “pro ve” a negative…
Comment 26
Right idea, but described so minimally as to make little sense.
Comment 27
T his sho uld be a review o f the literature that identif ies with justif icatio n a specif ic research
pro blem. T his “internal” co nversatio n is to be had with yo ur superviso r o r peers and sho uld
no t be here.
Makes no sense
T his do es no t make sense.
PAGE 4
Comment 28
Mo stly waf f le…
Comment 29
An explanatio n is required.
PAGE 5
Comment 30
Ref erences must be listed alphabetically by f irst autho r
PAGE 6
RUBRIC: COURSEWORK FEEDBACK SHEET
RELEVANCE
A
B
C
D
E
F
ANALYSIS
A
B
C
D
E
F
PRESENT ED QUA
A
B
C
D
E
F
QUALIT Y REF
A
B
B
Relevance o f co ntent, depth o f discussio n and demo nstratio n o f understanding
First Class Ho no urs. (>7 0%)
Upper Seco nd Class Ho no urs. (60- 69%)
Lo wer Seco nd Class Ho no urs. (50- 59%)
T hird class Ho no urs. (4 0- 4 9%)
Fail. (30- 39%)
Fail. (<30%)
C
Analysis and evaluatio n o f ref erence material
First Class Ho no urs. (>7 0%)
Upper Seco nd Class Ho no urs. (60- 69%)
Lo wer Seco nd Class Ho no urs. (50- 59%)
T hird class Ho no urs. (4 0- 4 9%)
Fail. (30- 39%)
Fail. (<30%)
C
Quality and co herence o f arguments presented
First Class Ho no urs. (>7 0%)
Upper Seco nd Class Ho no urs. (60- 69%)
Lo wer Seco nd Class Ho no urs. (50- 59%)
T hird class Ho no urs. (4 0- 4 9%)
Fail. (30- 39%)
Fail. (<30%)
C
Quality o f ref erence so urces selected and co rrect citatio n o f tho se ref erences
First Class Ho no urs. (>7 0%)
Upper Seco nd Class Ho no urs. (60- 69%)
C
D
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PRESENT AT ION
A
B
C
D
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F
Lo wer Seco nd Class Ho no urs. (50- 59%)
T hird class Ho no urs. (4 0- 4 9%)
Fail. (30- 39%)
Fail. (<30%)
C
Length o f submissio n, written style, o rganisatio n and presentatio n
First Class Ho no urs. (>7 0%)
Upper Seco nd Class Ho no urs. (60- 69%)
Lo wer Seco nd Class Ho no urs. (50- 59%)
T hird class Ho no urs. (4 0- 4 9%)
Fail. (30- 39%)
Fail. (<30%)
- Literature Review
by Elliot Gibson
Literature Review
GRADEMARK REPORT
FINAL GRADE
GENERAL COMMENTS
Instructor
RUBRIC: COURSEWORK FEEDBACK SHEET
1Howard Hughes Medical Institute and the Department of Cell and Molecular Biology, St. Jude Children’s Research Hospital, Memphis, Tennessee 38105, USA. 3Department of Neurology, University
of Massachusetts Medical School, Worcester, Massachusetts 01655, USA. 4Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, California 92093, USA. 5Department of
Cellular and Molecular Medicine, University of California, San Diego, La Jolla, California 92093, USA.
Amyotrophic lateral sclerosis (ALS) is a prototypical neuro-degenerative disease that is characterized by the progressive degeneration of motor neurons in the brain and spinal cord.
The condition was first described by the neurologist Jean-Martin
Charcot, and its name reflects both the degeneration of corticospinal
motor neurons, the descending axons of which in the lateral spinal cord
seem scarred (lateral sclerosis), and the demise of spinal motor neurons,
with secondary denervation and muscle wasting (amyotrophy). Corti-
cospinal neurons make direct or indirect connections with spinal motor
neurons, which innervate skeletal muscles and trigger their contraction
(Fig. 1a). This Review summarizes the clinical and pathological features
of ALS and describes how discoveries in ALS genetics have illuminated
important themes in the molecular pathophysiology of the disease.
ALS is known as Lou Gehrig’s disease in the United States and as
motor neuron disease in the United Kingdom. Although onset of the
disease occurs commonly in mid-adulthood (at a mean age of 55 years),
ALS might begin as early as in the first or second decade of life or could
even emerge in later life. Similar to most neurodegenerative diseases,
it starts focally and spreads: symptoms that start as subtle cramping or
weakness in the limbs or bulbar muscles progress to the paralysis of
almost all skeletal muscles. Some subsets of motor neurons, including
those that innervate the extraocular muscles or sphincters, are spared
until late in the progression of the disease. However, ALS is invariably
fatal. Death occurs typically 3–5 years after diagnosis, although some
forms of the disease demonstrate protracted survival.
ALS is an orphan disease that is diagnosed in 1–2 individuals
per 100,000 each year in most countries; the prevalence of ALS is about
5 cases per 100,000 people, which reflects the rapid lethality of the dis-
ease1. In the United States and United Kingdom, ALS causes more than
1 in 500 deaths in adults, a statistic that suggests that more than 15 mil-
lion people who are alive at present will succumb to the disease.
The clinical manifestations of ALS
Considerable heterogeneity exists in the general rubric of ALS. Clinical
subsets of the disease are distinguished by the involvement of different
sets of motor neurons or different regions of the body. Depending on the
location of the main pathology, those affected might develop weakness
with flaccidity and atrophy of the limbs (known as progressive muscular
atrophy, which mainly affects spinal neurons or lower motor neurons),
prominent hyperreflexia and spasticity with increased limb tone but
little muscle atrophy (known as primary lateral sclerosis, which affects
corticospinal motor neurons with limited involvement of spinal motor
neurons), tongue atrophy with thickness of speech and difficulty swal-
lowing (known as bulbar ALS, which affects brainstem motor neurons
that serve the muscles of tongue movement, chewing, swallowing and
articulation) or slow and highly dysfunctional speech and swallowing
in the absence of tongue atrophy, often accompanied by the accentua-
tion of emotional reflexes (known as pseudobulbar palsy, which affects
cortical frontobulbar motor neurons). Importantly, ALS shares clinical
and pathological features with several other adult-onset degenerative
disorders, including, most frequently, frontotemporal dementia (FTD),
which could constitute a clinical spectrum (Box 1).
Genetic contributions to ALS
About 10% of ALS cases are transmitted in families, almost always as a
dominant trait and frequently with high penetrance. The first genetic
mutations found to cause ALS, reported in 1993, affected the gene SOD1
(ref. 2) and more than 50 further potential ALS genes have been published
since, although validating the causality of specific variants remains a chal-
lenge. By applying rigorous criteria, a list of genes with mutations that
are implicated unequivocally in the pathogenesis of ALS can be gener-
ated (Table 1). These genes can be grouped into several loose categories:
genes that alter proteostasis and protein quality control; genes that perturb
aspects of RNA stability, function and metabolism; and genes that dis-
turb cytoskeletal dynamics in the motor neuron axon and distal terminal.
The mutations involved are mostly missense substitutions, although the
genetic lesion in C9orf72 is an enormous expansion of an intronic hexa-
nucleotide repeat.
Although sporadic ALS should refer strictly to disease that presents
without a family history of ALS, this term is sometimes mistakenly
used to refer to ALS that occurs without a genetic basis. Technological
advances that facilitate broad DNA sequencing in people with sporadic
ALS have revealed that genetic variants in established ALS genes are not
infrequent. For example, it is now evident that 1–3% of sporadic cases
of ALS are caused by missense mutations in SOD1 (ref. 3) and another
5% or more are caused by intronic expansions in C9orf72 (ref. 4).
Pathogenic mutations in other ALS genes, including TARDBP, FUS,
HNRNPA1, SQSTM1, VCP, OPTN and PFN1, have also been identified
Amyotrophic lateral sclerosis (ALS) is a progressive and uniformly fatal neurodegenerative disease. A plethora of genetic
factors have been identified that drive the degeneration of motor neurons in ALS, increase susceptibility to the disease
or influence the rate of its progression. Emerging themes include dysfunction in RNA metabolism and protein homeo-
stasis, with specific defects in nucleocytoplasmic trafficking, the induction of stress at the endoplasmic reticulum and
impaired dynamics of ribonucleoprotein bodies such as RNA granules that assemble through liquid–liquid phase separa-
tion. Extraordinary progress in understanding the biology of ALS provides new reasons for optimism that meaningful
therapies will be identified.
Decoding ALS: from genes
to mechanism
J. Paul Taylor1, Robert H. Brown Jr3 & Don W. Cleveland4,5
1 0 N O V E M B E R 2 0 1 6 | V O L 5 3 9 | N A T U R E | 1 9 7
REVIEW
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in people with sporadic ALS, although they are rare.
Genetic variants that enhance susceptibility to ALS or that modify the
clinical phenotype are of immense interest, even if the variants them-
selves do not cause ALS. For example, large expansions of repeats of the
trinucleotide CAG in the coding sequence of the gene ATXN2 cause
spinocerebellar ataxia type 2, in which motor weakness is sometimes
an early presentation. It is striking therefore that modest expansions to
27–33 CAG repeats in ATXN2 increase the risk of developing ALS5. By
contrast, variants that reduce expression of the axonal guidance gene
EPHA4 improve the overall survival of people with ALS6.
The pathology of ALS
Autopsies of people with ALS reveal the degeneration of motor neu-
rons in the motor cortex of the brain, in the brainstem motor nuclei
and in the anterior horns of the spinal cord. As spinal motor neurons
degenerate, their target muscles become atrophied. Degeneration of
the spinal processes of corticospinal neurons results in scarring in the
lateral tracts of the spinal cord. As ALS progresses further, affected
spinal motor neurons shrink and accumulate rounded or thread-
like deposits of aggregated proteins that are referred to collectively as
inclusions (Fig. 1b). The cytoplasmic inclusions in ALS often become
ubiquitinated; an initial target for ubiquitination is TAR DNA-binding
protein 43 (TDP-43), encoded by the gene TARDBP, which forms the
main component of ubiquitinated inclusions in most cases of ALS7.
Other pathological features are associated with specific genes. For
example, cases of ALS caused by a large expansion of a hexanucleotide
repeat in C9orf72 show intranuclear RNA foci8, as well as neuronal cyto-
plasmic inclusions, predominantly in the cerebellum and hippocampus,
that contain the protein sequestosome-1 (also known as ubiquitin-bind-
ing protein p62 and encoded by the gene SQSTM1) but are distinct from
TDP-43 inclusions that are also present in such individuals (ref. 9). Cases
of ALS caused by mutations in the genes SOD1 or FUS are pathologi-
cally distinct because they exhibit inclusions of abnormal SOD1 or FUS
proteins, respectively, rather than those of TDP-43. In addition to these
findings in motor neurons, there is also abundant evidence of relevant
pathology in non-neural cell types (for example, insidious astrogliosis
and microgliosis). It is probable that both of these forms of non-cell-
autonomous cellular reactivity influence adversely the progression of ALS.
Pathogenic mechanisms of ALS
The molecular era of discovery in ALS began with the identification of
dominant mutations in the gene SOD1, which encodes an abundant,
ubiquitously expressed cytoplasmic enzyme called Cu–Zn superoxide
dismutase2. An important antioxidant, the normal function of SOD1 is
to catalyse the conversion of highly reactive superoxide (most frequently
produced by errors in mitochondria) to hydrogen peroxide or oxygen.
The expression of mutant SOD1 in mice demonstrated that the degen-
eration of motor neurons is driven by one or more acquired toxicities of
the mutant protein10,11 and is independent of dismutase activity12. The
more than 170 ALS-causing mutations that have now been identified
(http://alsod.iop.kcl.ac.uk/) lie in almost every region of the 153-amino-
acid SOD1 polypeptide. Moreover, although many variants retain par-
tial or full dismutase activity, there is no correlation between a reduction
in activity and the age of disease onset or the speed of disease progres-
sion13. These findings led to the consensus that disease arises from one
or more toxic properties of the many SOD1 mutants rather than from
reduced dismutase activity.
A sobering reality, however, is that in the 23 years since the discovery
of mutations in SOD1, no consensus on the main toxicity of mutant
SOD1 has emerged. Instead, a plethora of toxic mechanisms that medi-
ate the degeneration and death of motor neurons have been proposed
(Fig. 2). A prominent finding is that a proportion of each ALS-causing
SOD1 mutant fails to fold properly, which implicates the accumulation
of misfolded SOD1 as a possible contributor to toxicity in ALS. Mis-
folded SOD1 forms ubiquitinated cytoplasmic inclusions that can occur
early in ALS and that escalate as the disease progresses14.
The accrual of ubiquitinated SOD1 aggregates in people with SOD1
mutations is paralleled by the accrual of ubiquitinated TDP-43 aggre-
gates in people with TARDBP mutations (as well as in most people
with sporadic ALS), which highlights a correlation between protein
aggregation and ALS. However, as has been demonstrated for other
neurodegenerative diseases, large aggregates of disease-causing mutant
SOD1 are not sufficient to drive disease because their elimination fails
to affect any aspect of the fatal disease that develops in mice expressing
ALS-linked mutants of SOD1 (ref. 15).
Non-cell-autonomous toxicity
Similar to the genes implicated in other main neurodegenerative diseases,
all genes in which ALS-causing mutations occur are expressed in many
cell types. Indeed, it is now clear that ALS arises, in part, through non-
cell-autonomous mechanisms. This means that the disease is the result of
a combination of damage from mutant SOD1 in both motor neurons and
their glial partners, rather than from damage to neurons alone.
For mutant SOD1, this concept is underscored by studies in mice
Figure 1 | Components of the nervous system that are affected by
ALS. a, ALS mainly affects the descending corticospinal motor neurons
(upper motor neurons) that project from the motor cortex into synapses in
the brainstem and spinal cord, and the bulbar or spinal motor neurons (lower
motor neurons) that project into skeletal muscles. b, Subtypes of ALS show
typical pathological features: SOD1 aggregates (arrows) in spinal motor
neurons in SOD1-related familial ALS (top left); TDP-43 redistribution to
cytoplasmic inclusions (arrows) in spinal motor neurons in sporadic ALS (top
right); RNA foci in the nucleus (arrows) and the cytoplasm (arrowhead) of a
cortical neuron affected by C9 ALS–FTD (bottom left); GA (bottom centre)
and GR (bottom right) dipeptide-repeat pathology in the dentate nucleus of a
brain affected by C9 ALS–FTD (bottom right).
b
a
Descending
corticospinal neuron
Motor cortex
Tongu
e
Arm
Leg
Sacral
Lumbar
Thoraci
c
Cervical
Brainstem
Spinal motor neuron
1 9 8 | N A T U R E | 5 3 9 | 1 0 N O V E M B E R 2 0 1 6
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Springer
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2016
Macmillan
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Limited,
part
of
Springer
Nature.
All
rights
reserved.
revealing that high levels of mutant SOD1 expression in all motor neu-
rons is not sufficient to cause early onset disease16. Conversely, a reduc-
tion in the synthesis of mutant SOD1 in motor neurons does not slow
the rate of progression after the onset of disease, even when applied
before symptoms occur17–19. Therefore, ALS is a disease not just of the
motor neuron but also of the motor system, which is comprised of
motor neurons and intimately associated cells of several types.
The crucial role of glia in ALS
The importance of glial cells in the degeneration and death of motor
neurons emerged from studies in which the synthesis of mutant SOD1
was silenced in microglia, astrocytes or oligodendrocyte precursor cells.
Microglia, which are the innate immune cells of the nervous system,
become activated in all types of ALS (Fig. 2b). The synthesis of mutant
SOD1 by microglia is an important determinant of rapid disease progres-
sion, as determined by selectively silencing the mutant gene SOD1 in
microglia19 or by using cell grafts to replace microglia expressing mutant
SOD1 with normal microglia20. Consistent with these findings, inhibi-
tion of the transcription factor NF-κB suppresses this neuroinflamma-
tory component of microglial toxicity in co-cultured motor neurons21.
A further mechanism of damage that results from mutant SOD1 pro-
duced by microglia is counterintuitive: stimulation of the excessive extra-
cellular production of superoxide22. Misfolded mutant SOD1 can associate
with the small GTPase RAC1, which controls the activation of NADPH
oxidase, a complex that produces superoxide (Fig. 2b). So, instead of its
normal function of removing intracellular superoxide, mutant SOD1
could drive microglia to produce high levels of extracellular superoxide.
Disturbances in microglial function have also emerged as a potential
contributor to ALS that is associated with mutations in C9orf72. Rec-
ognition that mutations in C9orf72 result in the decreased expression
of C9orf72 in people with ALS8 suggests that the loss of C9orf72 func-
tion might contribute to disease. The protein that C9orf72 encodes is a
potential guanine exchange factor for one or more as-yet-unidentified
G proteins. Its inactivation in mice results in abnormal microglia and
age-related neuroinflammation, providing evidence that non-cell-auton-
omous, microglial-mediated inflammation might contribute to ALS23–25.
A crucial contribution of mutant SOD1 to pathogenesis is driven
by oligodendrocytes, which are cells that myelinate the axons of upper
motor neurons and the initial axonal segments of lower motor neurons.
A reduction in the synthesis of mutant SOD1 early in oligodendrocyte
maturation produces a more striking delay in the onset of disease26
than does similar suppression of mutant SOD1 synthesis in motor
neurons16,19. Oligodendrocytes also support motor neuron function by
directly supplying the energy metabolite lactate to the axon through
the action of monocarboxylate transporter 1 (MCT 1) (Fig. 2c). Mutant
SOD1 impairs the expression of MCT 1 by oligodendrocytes in mouse
models of ALS27. A similar reduction in the accumulation of MCT 1 is
found in sporadic ALS27, which is consistent with a non-cell-autono-
mous role for the reduced supply of energy from oligodendrocytes as a
general component of ALS pathogenesis.
Another type of glial cell, the astrocyte, provides motor neurons with
nutrients, ion buffering and recycling of the neurotransmitter gluta-
mate. The selective reduction of mutant SOD1 synthesis by astrocytes
in mice slowed the onset28 or progression18 of disease. This delay was
accompanied by a delay in the activation of microglia, demonstrating a
functional crosstalk between mutant-SOD1-expressing astrocytes and
microglia.
One of the earliest proposed mechanisms to underlie ALS was gluta-
mate excitotoxicity, which is the excessive firing of motor neurons that
is derived from a failure to rapidly remove synaptic glutamate (Fig. 2d).
Astrocytes limit the firing of motor neurons through the swift recov-
ery of glutamate, a function that is mediated by excitatory amino acid
transporter 2 (EAAT2), which transports glutamate into the astrocyte
(Fig. 2d). The loss of EAAT2 has been observed both in SOD1-mutant
rodent models of ALS14,29 and in samples from people with familial
or sporadic ALS30. The resulting failure of astrocytes to quickly clear
synaptic glutamate triggers the repetitive firing of action potentials
and a corresponding increase in calcium influx, as well as endoplasmic
reticulum (ER) and mitochondrial stress as the result of overwhelming
the calcium storage capacities of these organelles.
Astrocytes also protect motor neurons from excitotoxic damage
through the release of an unidentified soluble factor or factors that
induce motor neurons to upregulate the glutamate receptor subunit
GluR-2 (ref. 31). The incorporation of GluR-2 into glutamate recep-
tors in neurons reduces the permeability of these receptors to calcium,
which provides protection from excitotoxicity by decreasing the influx
of calcium. Astrocytes that express mutant SOD1 fail to regulate GluR-2
expression in co-cultured neurons, thereby increasing their vulnerabil-
ity to excitotoxic damage31.
Several teams of researchers have used in vitro co-cultures of motor
neurons and astrocytes (or astrocyte-conditioned medium) to show
that astrocytes expressing ALS-linked mutations produce a toxicity that
diffuses to motor neurons32–36 (Fig. 2d). However, there is no consensus
on the identity of the toxic species. Notably, astrocytes from people with
familial ALS or sporadic ALS (obtained directly from autopsy samples36
or by isolating neuronal precursor cells that can be converted into astro-
cytic precursor cells and then astrocytes35) are toxic to co-cultured nor-
mal motor neurons. This finding35 is especially provocative because it
indicates that neuronal precursor cells in portions of tissue from people
with sporadic ALS have already acquired damage and that this dam-
age is retained following several divisions of these cells in culture and
their subsequent differentiation. Whether toxicity from sporadic ALS-
derived astrocytes is mediated by changes in SOD1 (ref. 35) or not36
remains unsettled.
Most importantly, a non-cell-autonomous contribution of astro-
cytes to ALS-like disease has been demonstrated in rodents expressing
mutant SOD1 in which transplantation to the spinal cord of lineage-
restricted astrocyte precursors without SOD1 mutations delayed pro-
gression of the disease37.
ALS genes induce ER stress or impair protein degradation
ER stress has been implicated broadly in ALS (Fig. 2a). Initial evidence
arose from studies of mutant SOD1 in which misfolded SOD1 binds to
the cytoplasmic surface of the ER integral membrane protein derlin-1
(ref. 38). This binding leads to the inhibition of ER-associated degrada-
tion (ERAD), the pathway for extraction and degradation of misfolded
proteins from the ER. Moreover, relieving ER stress delays the progres-
sion of disease in an animal model of ALS39.
There is now overwhelming evidence to show that disruption of the
Careful observation of people with ALS over the past 30 years has
revealed clinical, pathological and genetic overlap with several
other neurodegenerative disorders. In particular, the loss of motor
neurons may be accompanied by the loss of cortical neurons in the
frontal and temporal cortices of the brain. This correlates clinically
with FTD, a condition of impaired judgment and executive skills,
which often leads to behavioural disturbances. About 20% of people
with ALS meet the clinical criteria for a concomitant diagnosis of
FTD, although as many as 50% of people with ALS experience
cognitive impairment. Less frequently, ALS occurs together with
Paget’s disease of bone (PDB) or inclusion body myopathy (IBM).
Similar to ALS, both FTD and IBM are characterized by inclusions
of TDP-43 and related RNA-binding proteins. The relationship
between ALS, FTD, PDB and IBM has been extended though genetic
evidence, which potentially places them in the continuum of a
broader degenerative disorder.
BOX 1
ALS overlap syndromes
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two main protein clearance pathways, the ubiquitin–proteasome system
and autophagy, can be central components of the disease mechanism
in ALS (Fig. 2a). Several ALS-causing mutations occur in genes with
products that are involved directly in protein degradation, includ-
ing ubiquilin-2 (ref. 40) and sequestosome-1 (ref. 41), both of which
function as adapters that bring polyubiquitinated proteins to the pro-
teasome or the autophagosome for degradation. Mutations have also
been reported in optineurin42, a proposed receptor for autophagy43,
and valosin-containing protein (VCP)44, which has a role in ERAD and
sorting endosomal proteins. Other studies have reported FTD-linked
mutations in CHMP2B45, which encodes a protein that has been impli-
cated in maturation of the autophagosome and endosomal cargo sorting
and degradation. ALS-linked mutations are also found in VAPB46, the
product of which functions in the unfolded protein response in the
delivery of ER-ejected substrates to the proteasome. A preponderance
of biochemical evidence has demonstrated a decrease in the activities of
the proteasome in lumbar spinal cords before symptoms occur in mice
that express mutant SOD1 (ref. 47) or following the sustained expression
of mutant SOD1 in a cultured line of neurons48.
Axonal disorganization and disrupted transport in ALS
Disorganization of the axonal cytoskeleton, and especially of the neuro-
filaments, is a conspicuous feature both of familial ALS and sporadic ALS
(Fig. 2e). As the most asymmetric cells in nature, and with axons that can
reach more than 1 metre in length, motor neurons must rely on axonal
transport to deliver components that are synthesized in the cell bodies to
axons and synapses. ALS-linked mutant SOD1 has been demonstrated
to slow both anterograde49 and retrograde50,51 transport routes months
before neurodegeneration. Indeed, reduction in retrograde transport
through mutations in dynactin52, which is an activator of the retrograde
motor cytoplasmic dynein53, provokes motor neuron disease in humans.
Owing to the peculiar architecture of neurons, it is a challenge for these
cells to alter local gene expression at the synapse in response to neuronal
input or changes in the synaptic environment. To achieve this, neurons
must transport all necessary components for translation (for example,
messenger RNA, ribosomes and translation factors) to distal sites for local
protein synthesis54. The spatial distribution of mRNAs depends on the
proper microtubule-dependent transport of neuronal RNA transport
granules and other factors, and it is regulated by several RNA-binding
proteins that are associated with ALS, including TDP-43, FUS and hetero-
geneous nuclear ribonucleoprotein (hnRNP) A1. ALS-causing mutations
in TDP-43 impair the axonal transport of RNA granules in Drosophila
and in cultured neurons, including motor neurons derived from people
with ALS55.
A prion-like spread in inherited ALS
The prion-like, templated conversion of a natively folded protein into
a misfolded version of itself is now recognized as a prominent feature
of the cell-to-cell spread of protein aggregates in neurodegenerative
diseases. Examples include α-synuclein templating in Parkinson’s dis-
ease, amyloid-β aggregation in Alzheimer’s disease and tau misfolding
in chronic brain injury (reviewed in further detail in ref. 56). Evidence
for similar templated toxicity has emerged for misfolded SOD1 (refs 57
and 58), with wild-type SOD1 exacerbating the toxicity of mutant SOD1
in mice59. Prion-like propagation and development of disease that is ini-
tiated focally has been shown to occur after the injection of lysates con-
taining mutant SOD1 into mice that express mutant SOD1 (ref. 60). This
finding replicates the correlation between focal initiation and spreading
in people with familial ALS or sporadic ALS61.
That said, prion-like propagation of SOD1 (or other ALS-linked pro-
teins) has not been achieved in rodents without the coexistance of a
pre-existing, weakly active mutant ALS gene. It is unresolved whether
this evidence challenges the prion-like spread model of sporadic ALS
or, alternatively, whether it raises the possibility that there must be a
pre-existing sensitivity in individuals who develop sporadic ALS that
facilitates such spreading. Coupled with the recognition that mis-
folded mutant SOD1 can be secreted by motor neurons or astrocytes62,
potentially through the newly discovered pathway in which misfolded
proteins are secreted unconventionally as an adaptation to proteasome
dysfunction63, stochastic focal initiation provides a plausible mechanism
for the age-dependent onset of disease and its subsequent spread. As
most cases of ALS are marked by aggregated TDP-43 rather than SOD1,
an unresolved question is whether TDP-43 also exhibits templated mis-
folding that can spread from cell to cell.
Table 1 | The genetics of ALS
Locus Gene Protein Protein function Mutations Proportion of ALS Date of discovery
Familial Sporadic
21q22.1 SOD1 Cu–Zn superoxide dismutase Superoxide dismutase >150 20% 2% 1993 (ref. 2)
2p13 DCTN1 Dynactin subunit 1 Component of dynein
motor complex
10 1% <1% 2003 (ref. 52)
14q11 ANG Angiogenin Ribonuclease >10 <1% <1% 2006 (ref. 141)
q36 TARDBP TDP-43 RNA-binding protein >40 5% <1% 2008 (refs 67 and 142)
16p11.2 FUS FUS RNA-binding protein >40 5% <1% 2009 (refs 68 and 69)
9p13.3 VCP Transitional endoplasmic
reticulum ATPase
Ubiquitin segregase 5 1–2% <1% 2010 (ref. 44)
10p15-p14 OPTN Optineurin Autophagy adaptor 1 4% <1% 2010 (ref. 42)
9p21-22 C9orf72 C9orf72 Possible guanine nucleotide
exchange factor
Intronic GGGGCC
repeat
25% 10% 2011 (refs 8 and 77)
Xp11.23-Xp13.1 UBQLN2 Ubiquilin 2 Autophagy adaptor 5 <1% <1% 2011 (ref. 40)
5q35 SQSTM1 Sequestosome 1 Autophagy adaptor 10 <1% ? 2011 (refs 41 and 143)
17p13.2 PFN1 Profilin-1 Actin-binding protein 5 <1% <1% 2012 (ref. 144)
12q13.1 HNRNPA1 hnRNP A1 RNA-binding protein 3 <1% <1% 2013 (refs 70 and 71)
5q31.2 MATR3 Matrin 3 RNA-binding protein 4 <1% <1% 2014 (ref. 76)
2q36.1 TUBA4A Tubulin α-4A chain Microtubule subunit 7 <1% <1% 2014 (ref. 145)
22q11.23 CHCHD10 Coiled-coil-helix-coiled-coil-helix
domain-containing protein 10
Mitochondrial protein of
unknown function
2 <1% <1% 2014 (ref. 146)
12q14.1 TBK1 Serine/threonine-protein kinase
TBK1
Regulates autophagy and
inflammation
10 ? ? 2015 (ref. 147)
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The intersection of RNA biology and ALS pathogenesis
In 2006, Virginia Lee and colleagues reported the mislocalization of
RNA-binding protein TDP-43 from its predominantly nuclear location
to ubiquitin-containing cytoplasmic inclusions in affected areas of the
brain and the spinal cord of people with ALS7. TDP-43 mislocalization is
now recognized widely as the hallmark of both sporadic ALS and most
familial forms of ALS. This seminal discovery has implications beyond
ALS because TDP-43 mislocalization to cytoplasmic inclusions is also
the hallmark of FTD that lacks tau-containing inclusions (about half of
all cases of FTD) and inclusion body myopathy (IBM)7,64, which are dis-
eases that show genetic overlap with ALS. Moreover, TDP-43 pathology
is also found as a secondary pathological feature in a subset of people
with Alzheimer’s disease or Parkinson’s disease65,66. The importance of
TDP-43 in pathogenesis was cemented by the identification of ALS-caus-
ing mutations in this protein67. The subsequent identification of ALS-
causing mutations in related proteins that bind RNA, including FUS and
hnRNP A1, focused substantial attention on the role of RNA biology in
ALS pathogenesis68–71 (Fig. 2f).
TDP-43, FUS and hnRNP A1 are members of the hnRNP family of
proteins that regulates RNA metabolism at every stage of the RNA life
cycle. They bind to thousands of RNA targets72–75, which means that
a disturbance in the function of one or more of these proteins has the
potential to affect RNA metabolism on a broad scale. Further links
between the pathogenesis of ALS and RNA biology have emerged from
the identification of ALS-causing mutations in the RNA-binding pro-
tein matrin-3 (ref. 76), an appreciation of the increased risk of develop-
ing ALS in association with certain alleles of the RNA-binding protein
ataxin-2 (ref. 5) and the recognition of RNA-related mechanisms of
disease that are associated with mutations in C9orf72 (refs 8 and 77).
Phase separation gives rise to membraneless organelles
RNA metabolism occurs in complex RNA–protein assemblies that can
coalesce into a variety of membraneless organelles such as nucleoli and
stress granules. Interestingly, these organelles behave as complex liquids
that arise through phase separation, a process in which protein-laden
RNAs separate from the surrounding aqueous nucleoplasm or cytoplasm
in a manner that is akin to the separation of oil from vinegar78. Phase
separation is mediated by low-complexity domains that are present in
RNA-binding proteins such as TDP-43, FUS and hnRNP A1 (refs 79–81)
(Fig. 3a, b). The assembly of membraneless organelles is a strategy of cel-
lular compartmentalization that governs many biological processes. How-
ever, the contribution of phase transition to this process presents a risk
because RNA-binding proteins with low-complexity domains, which are
prone to fibrillization, are placed in close proximity. Indeed, mutations
that cause ALS are found frequently in the low-complexity domains of
TDP-43 (ref. 82), FUS83 and hnRNP A1 (ref. 70). As a consequence, these
mutations alter the dynamics of membraneless organelles and also accel-
erate fibrillization, which results in the formation of amyloid-like fibrils
that are deposited in the cell bodies and the neuropil79–81, 84 (Fig. 3c).
Mutations in the low-complexity domains of at least six different
hnRNPs result in a clinico-pathological spectrum that ranges from ALS
and FTD to IBM (Fig. 3a and Box 1). Notably, some disease-causing muta-
tions in RNA-binding proteins do not affect low-complexity domains. For
example, several ALS-causing mutations in FUS and hnRNP A1 disturb
the nuclear localization sequence of these proteins and result in their
accumulation in the cytoplasm68,69,71. Phase transition by RNA-binding
proteins that contain low-complexity domains is exquisitely dependent
on concentration79, and it is probable that the increased accumulation of
FUS and hnRNP A1 in the cytoplasm as a consequence of mutations that
affect the nuclear localization signals of these proteins is sufficient to drive
excess phase separation, as shown by the hyperassembly of stress granules
in cells derived from people with relevant mutations70,85.
RNA metabolism defects in ALS
Disturbance of the normal phase transitions carried out by RNA-binding
proteins can have deleterious consequences, including altering the mate-
rial properties of RNA granules and impairing their function55. Moreover,
persistent assembly of RNA-binding proteins in the highly concentrated
liquid state may promote the formation of amyloid-like fibrils that have
toxic properties79,80 and may also result in a partial or complete loss of the
normal function of important RNA-binding proteins86. A well known
feature of ALS histopathology is the redistribution of TDP-43 from the
Figure 2 | Mechanisms of disease
implicated in ALS. a, Familial
ALS-associated mutations
frequently affect genes that
are components of the cellular
protein quality control system.
Other mutations, such as those
in SOD1, affect protein folding.
b, Hyperactivation of microglia
produces extracellular superoxide,
which triggers inflammation
and degeneration in motor
neurons. c, A reduction in the
levels of the lactate transporter
MCT 1 diminishes energy
supplied by oligodendrocytes
to motor neurons. d, A failure
of astrocytes to clear synaptic
glutamate via the transporter
EAAT2 triggers repetitive firing of
motor neurons and excitotoxicity.
e, Disruption of the cytoskeleton
and impaired axonal transport
limits the exchange of essential
macromolecules and organelles
between the neuronal cell
body and distal compartments.
f, Disturbances in aspects of
RNA metabolism, including
RNA processing, transport and
utilization, are largely the result of
impaired hnRNP function.
Proteasome
a
Muscle
Diminished energy
supply from
reduction in MCT1
transporter
Hyperactivation
of microglia
Excitotoxicity from reduced
glutamate uptake
Astrocyte
Microglia
Oligodendrocyte
Oligodendrocyte
EAAT2
Glutamate
Spinal motor
neuron
Schwann cell
Toxic
signal
MCT1
Lactate
ER
Disturbances in protein quality control
Descending
corticospinal neuron
2O
–
b c
d
Endosome–lysosome Autophagosome
e
Alternative splicing miRNA biogenesis
Sequestration of
RNA-binding proteins Translation
Pro�lin1
Dynactin
Cytoskeletal defects and
altered axonal transport
Disturbances in RNA metabolismf
Dynein
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nucleus to the cytoplasm7. A similar redistribution is observed for FUS
and hnRNP A1 when disease-causing mutations occur in the genes that
encode these proteins68,69,71. This redistribution of proteins might reflect
a cytoplasmic sink that is produced by the hyperassembly of cytoplasmic
granules or by poorly dynamic RNA granules that fail to disassemble
appropriately, the deposition of amyloid-like fibrils and defects in nucleo–
cytoplasmic trafficking, as well as other potential mechanisms.
The culmination of this redistribution is the depletion of RNA-bind-
ing proteins in the nucleus that has the potential to cause a consider-
able loss of nuclear function. A well known function of TDP-43 in the
nucleus is the regulation of alternative splicing87. Experimental deple-
tion of TDP-43 in rodents was found to alter hundreds of splicing events
in the brain, resulting in the depletion of several RNAs that encode
synaptic proteins73. The loss of nuclear TDP-43 also facilitates the use of
cryptic splice sites88 that, in general, might lower the levels of correctly
spliced protein-encoding mRNAs. Furthermore, TDP-43 autoregulates
its synthesis73, which establishes the possibility of a feed-forward mecha-
nism that amplifies the impact of the partial loss of TDP-43 function.
The loss of FUS or hnRNP A1 from the adult nervous system produces
defects analogous to those associated with the loss of TDP-43, although
different subsets of mRNAs are linked to the depletion of each of these
RNA-binding proteins74,75. An important, unanswered question concerns
the extent to which ALS caused by other genetic perturbations, espe-
cially C9orf72-related ALS, also involves disturbances in RNA biology that
intersect mechanistically with mutations in TDP-43, FUS and hnRNP A1.
The biogenesis of regulatory RNA and its function in ALS
Both TDP-43 and FUS are components of macromolecular complexes
that generate small non-coding RNAs known as microRNAs (miRNAs)
with functions in RNA silencing. The loss of TDP-43 or FUS results in
a reduction in the expression of miRNAs in model systems, including
Drosophila models and induced pluripotent stem (iPS)-derived motor
neurons from people with TDP-43 mutations, which suggests a possible
role for altered RNA silencing in ALS89. Various miRNAs contribute to
the maintenance of neuromuscular junctions, implying that motor neu-
rons might be particularly sensitive to disturbances in the biogenesis of
miRNA90,91. Indeed, global downregulation of miRNAs has been reported
in motor neurons from people with sporadic ALS92, although the role
of reduced levels of miRNAs in the pathogenesis of ALS remains to be
established92. Nonetheless, the expression of regulatory RNAs seems to
be altered robustly and consistently in the serum of people with ALS, and
this could present an opportunity for the development of biomarkers93.
The curious case of C9orf72-related ALS and FTD
Although the identification of ALS-causing mutations that affect SOD1
and RNA-binding proteins highlighted pathophysiological pathways
through which disease might arise, most of the genetic burden of ALS
remained unaccounted for until 2011. Genetic linkage studies94,95 fol-
lowed by several large genome-wide association studies96–99 identified
the location of a gene in the chromosome 9p21 locus in which muta-
tions cause both ALS and FTD. During sequencing of the non-coding
regions of candidate genes in chromosome 9p21, a pathogenic expan-
sion of a hexanucleotide repeat in C9orf72 was identified as the basis for
C9orf72-related ALS and FTD (C9 ALS–FTD)8. In healthy individuals,
the sequence GGGGCC was present as 2–23 repeats but in affected
individuals it was expanded to hundreds or thousands of repeats. In
parallel, an independent study also discovered a pathogenic expansion
of GGGGCC repeats in C9orf72 (ref. 77).
The consequences of repeat expansion in C9orf72
Three non-exclusive mechanisms have been proposed through which
expanded GGGGCC repeats might cause C9 ALS–FTD (Fig. 4). First,
a reduction in the expression levels of C9orf72 in people with C9 ALS–
FTD100 has led to speculation that the loss of C9orf72 protein may
contribute to disease. The function of C9orf72 is poorly understood;
however, the protein is known to contain a conserved DENN domain
and can function as a guanine–nucleotide exchange factor for several
Rab proteins in experimental systems101. In cultured cells and in zebrafish,
the depletion of endogenous C9orf72 can exacerbate the toxicity of
aggregation-prone proteins such as polyglutamine-expanded ataxin-2
(ref. 102). However, the reduction of endogenous C9orf72 mRNA with
antisense oligonucleotides was well tolerated in mice and did not result
in impairments to behaviour or motor functions103. Furthermore, the
conditional knockout of the gene C9orf72 in the brains of mice did not
cause noticeable motor neuron or other neurodegenerative phenotypes,
and there was no evidence of the hallmark pathological features of ALS
or FTD104. Mice in which there was a complete ablation of C9orf72 in all
tissues developed and aged normally without the occurrence of motor
neuron disease; however, they also developed progressive splenomegaly
Figure 3 | ALS mutations impair the assembly, dynamics and function of
membraneless organelles. a, A schematic representation of six hnRNPs
(FUS, TDP-43, hnRNP A1, hnRNP A2/B1, hnRNP DL and TIA-1) harbouring
mutations that produce a spectrum of disease that ranges from ALS or FTD to
myopathy. LCD, low-complexity domain; MSP, multisystem proteinopathy;
NLS, nuclear localization signal; RRM, RNA recognition motif. b, RNA-
binding proteins that contain a low-complexity domain can undergo phase
separation, which is the transition from a single, mixed phase (top) to two
distinct phases (bottom), one of which is a concentrated liquid droplet
(green). c, Phase separation contributes to the assembly, dynamics and liquid
properties of membraneless organelles; however, the high concentration and
close positioning of the low-complexity domains risks the transitioning of such
proteins (for example, TDP-43) to pathological, amyloid-like fibrils. RBP, RNA-
binding protein; RNP, ribonucleoprotein.
RNA
granule
TDP-43
�brils
a
b
Membraneless organelle
c
MSP
FUS
LCD
TDP-43LCD
hnRNP A1
hnRNP A2/B1LCD
LCD
hnRNP DLLCD
TIA-1LCD
ALS–FTD
Myopathy
Mixed proteins
Phase separation
ALS–FTD MSP Myopathy
Individual RNPs
RNA
LCD
RRM
Fibrillization
of RBPs
Phase-separated
mesenger RNPsmessenger RNPs
(RBPs bound
to RNA)
RRM
NLS
Mutation causing:
Two phases
Deposition of
amyloid-like �brils
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and lymphadenopathy23–25,105. These mice were found to have abnormal
macrophages and microglia, as well as age-related neuroinflammation23,105
and signs of autoimmunity25, which raises the possibility of a non-cell-
autonomous inflammatory contribution to C9 ALS–FTD.
Nevertheless, the dominant inheritance pattern of C9 ALS–FTD, the
absence of people with ALS or FTD with null alleles or missense muta-
tions in C9orf72 and the absence of neurodegeneration in C9orf72-knock-
out mice provide arguments against the loss of C9orf72 function as the
sole driver of disease. Indeed, most empirical evidence points to the gain
of toxic functions as the main mechanisms that drive neurodegeneration
in C9 ALS–FTD. For example, the adeno-associated virus-mediated deliv-
ery to the brain of a construct that expresses expanded GGGGCC repeats
elicits neurodegeneration106, although the nature of the toxic species in
C9 ALS–FTD remains unclear.
Gain of toxic function from repeat-containing RNA
The initial description of the mutation in C9orf72 was accompanied by
evidence to show that RNA foci containing the GGGGCC repeat accumu-
late in the brains and spinal cords of people with C9 ALS–FTD8 (Fig. 1b),
and this suggested a second possible disease mechanism, involving toxic
gain of function by repeat-containing RNA (Fig. 4). It was then noted
that the gene C9orf72 can be transcribed bidirectionally and that foci
containing sense (GGGGCC) or antisense (CCCCGG) RNA transcripts
accumulate in affected cells107–109. The accrual of such foci in C9 ALS–FTD
is reminiscent of the pathological RNA foci that are observed in myotonic
dystrophy type 1, myotonic dystrophy type 2 and fragile X-associated
tremor and ataxia syndrome, which are also caused by the expansion of
nucleotide repeats in non-coding regions110. In these diseases, the accu-
mulated repeat-containing RNA sequesters RNA-binding proteins that
are involved in splicing, which leads to defects in splicing that underlie
some aspects of pathogenesis110. Similarly, a number of RNA-binding
proteins bind to expanded GGGGCC or GGCCCC repeats in vitro, and
a rare co-localization with RNA foci has been observed for several of these
proteins in tissue from affected individuals111-115.
Simple model systems have illustrated the functional consequences
of the sequestration of some hexanucleotide repeat-binding proteins,
including transcriptional activator protein Pur-α and Ran GTPase-
activating protein 1 (RanGAP1), but the contribution of these interac-
tions to the development of disease is not yet established114,116. Notably,
repeats of GGGGCC (but not of CCCCGG) can adopt a stable second-
ary structure known as a G-quadruplex, which might contribute to the
persistence of this species of RNA as well as to its ability to reach distal
neurites and associate with RNA-binding proteins in transport granules
and potentially interfere with local translation117–119.
Gain of toxic function from dipeptide repeats
Substantial evidence has also accrued to implicate a third disease mecha-
nism in C9 ALS–FTD; specifically, toxicity from DPR proteins that are
produced by repeat-associated non-AUG (RAN) translation (Fig. 4).
This unconventional type of translation occurs in the absence of an ini-
tiating AUG codon and might rely on secondary structures formed by
repeat-expanded RNA120. In C9 ALS–FTD, RAN translation occurs in
all reading frames and from both sense and antisense transcripts, and it
results in the production of five DPR proteins: glycine-alanine (GA) and
glycine-arginine (GR) from sense GGGGCC transcripts; proline-arginine
(PR) and proline-alanine (PA) from antisense GGCCCC transcripts; and
glycine-proline (GP) from both sense and antisense transcripts107–109. All
of these DPR proteins are produced in people with C9 ALS–FTD and they
account for the neuronal cytoplasmic and intranuclear inclusions that
contain ubiquitin and sequestosome-1 but lack TDP-43 that are found
widely in the brain and spinal cord107,109,113,121,122 (Fig. 1b).
The timing, location and level of expression of each species of DPR
protein in the brains of affected people are yet to be clarified. Several
reports have described the deposition of DPR proteins in the brains of
people with C9 ALS–FTD, and in some instances an inverse relationship
has been described between the regional burden of DPR proteins and the
corresponding severity of neurodegeneration123,124. These studies were
based on the post-mortem examination of brains with end-stage disease
and relied on the detection of large inclusions using immunohistochem-
istry, an approach that probably under-represents the pathological bur-
den of soluble DPR proteins. However, the apparent discrepancy between
the burden of DPR-protein deposition, the levels of which are greatest in
the cerebellum, and the severity of neurodegeneration, which is greatest
in the motor cortex and spinal cord, needs to be resolved to understand
the role of DPR proteins in the development of disease.
Some species of DPR proteins have been shown to be toxic in cultured
cells and animal models of disease, although high levels of expression were
sometimes used to produce short-term toxicity. The arginine-containing
DPR proteins GR and PR seem to be most toxic. For example, when GR or
PR is added to cells in culture, it enters and accumulates in nucleoli, which
leads to defects in RNA processing and subsequent cell death125. Similarly,
the independent expression of each of the five species of DPR proteins
in cultured neurons revealed that GR and PR are very toxic, whereas PA,
GA and GP are well tolerated. Observations in Drosophila engineered
to express each of the five DPR proteins have also shown that GR and
PR are extremely toxic to neuronal tissue, whereas GA is modestly toxic
and GP and PA seems to be non-toxic126–128. A recent discovery is that
the arginine-containing DPR proteins GR and PR bind to proteins that
contain low-complexity domains129,130. Furthermore, GR and PR alter the
phase separation of such proteins, resulting in the perturbed assembly,
dynamics and function of membraneless organelles such as stress gran-
ules and nucleoli129. This finding mirrors the defects in phase transitions
that are observed with disease-causing mutations in the low-complexity
domains of TDP-43, FUS and hnRNP1, suggesting a common pathologi-
cal mechanism.
However, other investigations have reported that toxicity is associated
with the expression of GA in cell culture131–133 and its adeno-associated
virus-mediated delivery to the mouse brain133. It should be noted that
these efforts to model the toxicity of DPR proteins have used short (fewer
than 100) repeats. How the properties of those short DPR proteins com-
pare with the possibly larger products of RAN translation in affected
individuals is also unknown.
A defect in nucleocytoplasmic trafficking
Whereas the nature of the gain of toxic function is still an open question,
Figure 4 | Proposed mechanisms for the development of
C9 ALS–FTD. Expansion of an intronic hexanucleotide repeat (GGGGCC)
in C9orf72 from fewer than 23 copies to hundreds or thousands of copies
causes C9 ALS–FTD. This mutation results in a modest reduction in the
levels of C9orf72 protein (left) that seems insufficient to cause disease but
might contribute to its progression through abnormal microglial responses.
Meanwhile, the expression of sense and antisense RNA transcripts that contain
the expanded repeat probably drive a toxic gain of function (right). The
two main gain-of-function modes that are implicated are: toxicity through
the sequestration of RNA-binding proteins in RNA foci by the expanded
GGGGCC repeat RNA transcript; and the production of DPR proteins through
RAN translation, leading to toxicity through several cellular targets such as
membraneless organelles and nuclear pores.
Decreased levels of
C9orf72 protein
Abnormal microglial
responses
RNA foci
Impaired
nucleocytoplasmic transport
Sequestration of
RNA-binding proteins
DPR proteins through
RAN translation
Exons
C9orf72
21a 1b 3 4 5 6 7 8 9 10 11
ATG TAA
(GGGGCC)n
Loss of function Gain of function
Expanded GGGGCC-repeat
RNA transcript
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converging evidence suggests that impaired nucleocytoplasmic traffick-
ing is one of the downstream consequences of mutations in C9orf72.
A comprehensive, unbiased screen in Drosophila for genetic modi-
fiers of the toxicity that is mediated by expanded GGGGCC repeats
identified 18 genes that are connected to the nuclear pore complex
and nucleocytoplasmic trafficking128. A separate unbiased screen for
genetic modifiers of PR toxicity in yeast also identified numerous genes
that encode components of the nuclear pore complex and effectors of
nucleocytoplasmic trafficking134. A third study focused on the nucleocy-
toplasmic transport factor RanGAP1, which binds to the RNA sequence
GGGGCC. Genes encoding RanGAP1 and other nucleocytoplasmic
transport factors were identified as modifiers of toxicity mediated by
expanded GGGGCC repeats in Drosophila116. Consistent with these
results, morphological abnormalities were found in the nuclear enve-
lope architecture in both cell-based and animal models of disease, as
well as in the brains of people with C9 ALS–FTD. Moreover, defects in
the nucleocytoplasmic transport of RNA and proteins were found in
neurons derived from the iPS cells of people with C9 ALS–FTD116,128,134.
Approaches to therapy for C9 ALS–FTD
The relative contributions of the various proposed modes of toxicity to
the development of C9 ALS–FTD is an important consideration that will
influence strategies for therapeutic intervention. Efforts are underway
to impede RAN translation with small molecules but the success of
such an approach will depend on the role of DPR proteins in disease.
Irrespective of the main basis for the toxic gain of function, the mutant
gene C9orf72 presents an attractive target for therapeutic intervention.
For example, antisense oligonucleotides are able to reverse pathologi-
cal features in neurons derived from iPS cells103,135,136 or in fibroblasts103
from people with C9 ALS–FTD. Indeed, neurons and glial cells derived
from iPS cells might prove to be a useful model system in which to
develop approaches for mitigating toxicity related to mutant C9orf72
even before the basis of toxicity has been elucidated fully.
Therapeutic efforts will be aided further by the development of trans-
genic mouse models that express human C9orf72 that contain about
450 hexanucleotide repeats, which recapitulate aspects of the molecu-
lar pathology24,137–139, neuropsychological deficits24,139 and the motor
phenotype139 of C9 ALS–FTD. It is also particularly promising that
pathological abnormalities can be reversed, and that the development
of neuropsychological deficits can be delayed, by a single-dose infusion
of an antisense oligonucleotide that induces the catalytic degradation
of hexanucleotide-containing RNAs without exacerbating a reduction
in RNAs encoding the C9orf72 protein24.
Looking forward
Clearly, there has been dramatic progress towards defining the genetic
topography and molecular biology of ALS. There is also little doubt
that the pace of discovery will continue or even accelerate in several
areas of research.
First, it is certain that our understanding of the genetic basis of ALS
will continue to evolve. Research programmes are already in place to
collect and sequence thousands of whole genomes from people with
ALS. More genes that are implicated in ALS are likely to be defined,
both through conventional Mendelian genetics and through enhanced
association studies that identify increased burdens of rare genetic vari-
ants, including those found in non-coding DNA. In parallel, enhanced
scoring and recording of quantifiable clinical parameters will permit the
definition of variants that modify the phenotype of ALS. The existence
of extensive ALS genome databases will enable the first comprehensive
studies of epistasis, characterizing the interactions of numerous genes
to perturb the viability of motor neurons.
Second, although the past two decades have witnessed extraordinary
progress in understanding familial ALS, it is probable that insights that
help to elucidate sporadic ALS will be acquired. One view is that all cases
of sporadic ALS will ultimately be shown to reflect several genetic deter-
minants. Alternatively, there is increasing interest in exogenous factors
that might trigger sporadic neurodegeneration, and atypical infections or
the activation of endogenous retroviruses140 are proposed to have such a
role. Although the role of external environmental factors in ALS has been
elusive, there is fresh interest in the influence of the intrinsic environment,
represented by the microbiome, on development of the disease.
Last, and perhaps most importantly, there will be considerable
achievements in the development of therapies for ALS. Although daunt-
ing, the complexity of the molecular pathology of ALS is promising as
a roadmap for defining therapeutic targets. Moreover, for types of ALS
that arise from well-defined genetic defects, advances in gene silenc-
ing and gene editing technologies will permit personalized therapeutic
programmes. When combined with improved methods for the delivery
of therapies to the central nervous system, these approaches will lead to
strategies for attenuating the lethal course of ALS. ■
Received 7 July; accepted 13 September 2016.
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Acknowledgements We apologize for the many studies we were unable to cite
because of space limitations. The authors gratefully acknowledge the artwork and
editorial assistance provided by N. Nedelsky and H.-J. Kim and the provision of
histopathology images by J. Ravits and S. Saberi. J.P.T. receives support from the
Howard Hughes Medical Institute, the US National Institute of Neurological Disorders
and Stroke (NINDS), the American Lebanese Syrian Associated Charities, Target
ALS and the US ALS Association. R.H.B. receives support from NINDS, the ALS
Association, ALS Finding a Cure, ALS ONE, the Angel Fund for ALS Research and
Project ALS. D.W.C. receives salary support from the Ludwig Institute for Cancer
Research and is supported by funding from NINDS (R01 NS27036), the ALS
Association and Target ALS.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. The authors declare competing financial interests: see
go.nature.com/2exlcwy. Readers are welcome to comment on the online version
of this paper at go.nature.com/2exlcwy. Correspondence should be addressed to
J.P.T. (jpaul.taylor@stjude.org), R.H.B. (robert.brown@umassmed.edu) or D.W.C.
(dcleveland@ucsd.edu).
Reviewer Information Nature thanks I. Dikic, J. Rothstein and the other anonymous
reviewer(s) for their contribution to the peer review of this work.
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fJ
fJ
The rolle of complement system In Haematopoletic stem cell transplantation (HSCT)
exploring current therapies and new developments
.
Abstrw:
Being autologous (the paf t’s own stem cells are used) or allogeneic (the stem
cells come from a donor), Hematopoietic stem cell transplantation (HSCT) is the
transplantation of multipotent hematopoietic stem cells, usually derived from bone
marrow, peripheral blood, or umbilical cord blood. It is commonly used to treat
haematollogical, and increas.ingly, non-hae logical disorders (NHS
Commissioning board, 2013). Following the first donor recruitment drive in 1973, the
number of bone marrow and peripheral haematopoietic stem cell donors has
increased all over the wor,ld with more than 18 million donors now regist.ered
(Gluckman, IE, 2015).
fJ
Literature Review:
Hematopoietic stem-cell transplantation is used priw for hematologic and
lymphoid cancers but also for many other disorders. Donors receive granulocyte
colony stimulating factor (G-CSF) to mobilize haemato oietic stem cells (HSCs),
which are collected by leukaQheresis (where abnormal white blood cellls are
separated fro’fl sample of blood) (Cancer Research UK. 2015). In autolog!ous
HSCT there’s a reduced risk of infection during the immune-compromised stag:e of
the tre ent as the recovery of the patient’s immunity is rapid. In allogeneic HSCT,
as the patient is given donor stem cells, this may cause an immunological response.
The donor is likely to be a close relative such as a sibling, with a close match for the
human leucocyte antigen (HLA). However, the risk of leukaemia rellapse and
mortality with autologous HSCT is higher than for allogeneic HSCT.
OOn0,11′
(H matthed sibl ng or unrela ed donor)
( )
Pon m_rrow
a pirated froirn
(b)
1
Hclflt,n,nd & p ……
Figure a: Allogeniic SCT and b: autologous SCT
P;i t
(re pi nt)
Pt nt
Patients are prepared for HSCT by a conditioning regimen involving chemotherapy
al radiation, which can be myeloablative or non-myeloablative.
• M eloaola tive regimens- These re desi nea to kill all resiaual cancer cells in
auto-ous o� allogenic transplantatio .
• No n-m eloablative re imens – These a re immunosu Qressive and rell on the raft
il/ersus-tumour effect to kill tumour cells with donor T cells and is typically used in
high-risk patients.
A complicatio n in this is graft versus host diseas e (GVHD). GVHD happens when
articular ty__Qes of white blood cell (T cells in the donated bone marrow or stem cells
attack our own bod cells. This happens because thlj>nated cells (the graft) see
�our bod cells (the host} as forei n and a ck the . Acute GvHD (aGVHD) occurs
.
ost freguentl after engraftment, leading to an arbitrary period of 100 days post
HSCT which has defined the acute versus chronic manifestation ofthi1s disease. The
characteristic pathologic feature of aGVHD is target tissue (skin, liiver,
gastrointestinal [GI] tract) apoptosis. aGVHD was initially described as a “cytokine
storm” involviing a three�step disease process. These steps involve:
1) transplant conditioning and associated inflammation:
Foll owing conditioning (radiation and/or chemotherapy), the integrity of the G
I
mucosa becomes compromised allowing the release of DAMPS and PAMPS. These
in turn promote the production of pro-:inflammatory cytokines from recipient cells.
These cytokines contribute to host APC (hematopoietic and non-hematopoietic)
activation in the gut and lymphoid tissue. GVHD impacts on the gut micro biota,
reducing iits diversity with a loss of enteric commensal organisms and an outgrowth
of pathogenic microbes that further aggravates the pathological DAMP/PAMP
ca scade.
a
CONDITIONING TISSUE DAMAGE
I
,
RADJATtON
I
I
I
\
( \
\
•
CHEMOTHERAPY
t MHC
Ci>itimuladon
Figure 1: GVHD pathophysiology phase 1- transplant conditloning1 and Inflammation.
a
2) Donor T-cell priming and differentiation:
Donor CD4 T cells contained within the graft are activated by the inflammatory
environment early after conditioning, facilitating their rapid access to the gut and
lymphoid tissue. Once in the gut, MHC class II-expressing recipient non
hematopo1ietic APCs ca n initiate priming to host antigens while recipient
hematopo,ietic APC initiate priming In lymphoid tissue. Recipient hematopoi:etic APCs
appea.r to be the dominant APCs for CD8 T-cell priming. Donor APCs can further
ntribute to this priming process. Activation in the presence of various cytokines
instructs T-oell differentiation along specific lineage pathways (type 2:, type 117, and
type 1 , respectively). The tra.nscription factors GA T A-3, RO Rgt, and T-bet are critica I
for these Th2, Th17, and Th1 differentiation pathways. Tregs are differentiated in the
presence of I L-2 and TGFb (in the absence of IL-6) and abrogate the differentiation
of effector T cells via effects on DCs and effector T cells themselves.
•
lymph
node
–
ll-12
IL�
TGFP
Figure 2: Phase 2- donor T-cell priming and differentiation.
GAlA•3
3) An effector phase of tissue apoptosis mediated by inflammatory
cytokines and cellular (T and NK cell) effectors:
• •
During the effector phase of GVHD, inflammatory cytokines derived from
macrophages and T cells mediate apoptosis in target tissues, particularly within the
gut. Donor Th 1 /T c1 , Th2/T c2, and Th 17 /T c17 cells e I icit GVH D wi1th relatively tissue
specific patterns mediated in part by their respective chemokine profil’es and the
relative sensitivity of the target to effector cytokines generated by each lineage.
Cytolytic T and NK cells mediate antigen-dependent killing of targetti issues via the
perforin/granzyme and TN F member pathways.
SKIN
LUNG
LVER
TNF/LTa
IL-6
Figure 3: GVHD pathophysiology phase 3- the effector phase.
Meticulous supportive care is vital for P-atients with both acute and chronic GVHD
owing to the extended duration of immunosu9-pressive regimens as the man drugs
administered could have synergistic toxic effects. Such care includes early
interventions in cases of suspected infections, extensive infectious prophylaxis, and
prophylaxis against non-infectious side-effects of drugs 1table). These complications
need rapid responses to prevent serious, irreversible damage and are best handled
by a close and efficient colllaboration between the primary doctor and th,e transplant
specialist.
Table 1: Recommendations for supportive care
Other
Viral lnfec:dons
Cyt.:ome:ga1avirus
�sprrato,y viruses
fi!v«, chil s, pain,
erythema
Fewr. (hills,; sepsis
symptoms
Gastroenteritis.
Routln�·mQnltQring
Clinical�. che,t radiCJ!iraph
or CT scan for pos,lble
pneumo.,:ie
Blood cytomeg.aknrirus PCR Ol
lntemltli!I p,,eurr,onla pp6S ant gen l’l!”els
Symptoms of uwer or Cllnle<1I monitoring
low1:r ,,�r,torr-tract
in·fe,etiom
Varictll’a•tost« virus 1/ciielilar skin I sions Clini�I monit,0�114
Funpl and othet Infections
Asperglllo,1$, other
�m …..,.fungal
infections
candida
l’neumocy,tis
Jl\llmona,y lesions, Galaetom�nnan, usavs In
sinusitils. stin nodules high-risk pa�cnts. CT $G;lO if
signs of infectio n
Th,ust,, pvlmonarr
k!sioru
Fe\lef, hypo – ii;
resplratorydl,tress
Clinical eomim:ation,. CT scan if
signs: of infection
Clintcal a ssessment
Otflertoxic effects of Im munosuppres.sive :agents
Cllcineurininhibitors. Tremor Clintcal .asses.s:me11t.. ,drug
t;Qn(entrat1Qfl$
Caldneurlnlnhll>ltors N·eurotaxk effects Assess mental slat.us
Calcineurininhibitor5- Renalimp.airment Creatini.ne· le..-ets. ilnd gk,merular
flltr.atloo r.at,e,
Caldneurlnlnhll>ltor$ Hypertensfon Blood pressure monitoring
�lclneurloinhlbltor$, Trans?1uN1ssoci.t d /Weubloodsm arfor
Cortirnsteroids
Curlirosieroids
Corllrosterolds
Lat.i eraft 111ilur.
81ood disorder$
microonsiopathy
Oislla,(s dise.1st
symptoms
Diabetes
l!leedlnB wrnpto�
aMemi:I
Tllitk, R-mmendalions for SltPPor1 i…e �re
ha.emolysis, sch�tocytes
Assessment of llooe density
Sloodc()<)nt,
AntibiOti(;.$ in hi(h•ililk �tientS (hill,IH!OSt
torticosterolds o.r .aspfenia). lntravenaus.
lmmunoglobu11n If lgG, level Pfe-emptlYe treatment in ,p.atient:s with reactivation
Annual lnftuenzo vaccination (stardns 6 month$ post
Hcr), •a,«ln.ition of eares,\>ers
Aciclovir prophylaxii
Vorloonazole, or pol.(!Conatole proph'(la•ls In hlgh-rl�k
patients l�g. high·d0<1e steroids)
�lucon.nole jaspergillus prophyl•�is prote<:ts �ga inst
c.rndida too)
CotrilillO.Xarole. or pentamadine until 1 rrnonth off
mmunosuppre.u1on
Adjust dose todesired trough levels
Adequate fluiduptate(about 3 l pe,darl
utrition:al gvida nee
Obc,in cgtEutM, �mmtdi�t·� intravt’ftOus
.antibfotic treatmenl. ,,emove line
Obtain tuitvtt$:, imrnediat� inttavenous
broad-sp,,ctrum antibiotics, became of’risk of
oveMhelmlngsepslswithln ho 1s
Antiviral treatment lg.anclclovir. v.alganciclovir.
orfoscarnet)
E’.arlv t,eatment with neuramlnld�se fnhlb!to,s
(lnftuenu), other antislral$
Trcatmnnt dom of anti,irals
Anti fungal trealment
T reatme:nt d05es of’.a nti•PCP drugs
,Stop caldneurln Inhibitors
lntravenoo:s. fluids
Anti hypertensive treatment
(angiorer\sln,.ecn.e,rtln-lt’enzvme l!\hlblto,,,
�-blockil’\8 agents),
Stop ca clneurin lnt.lbl1ors, plasrnapher.uls
Insulin tre:atment
Growth, “1c1or� [&raouloevte eclonv-$\lmul;illns
‘foetor), �roJlO(‘ti”1, ttMrlu!iOns As touched upon earlier, an increasingly frequent treatment for GVHD is
extracorporeal photopheresis. During this, the patient’s white blood cells are gathered
by apheresis, incubated with the DNA-intercalating agent 8- methoxypsoralen,
exposed to ultraviolet light, and returned to the patient. Extra.corporeal photopheresis
is known to indte cellular apoptosis, which has strong anti-inflammatory effects in
several syste s, including prevention of rejection of solid organ gra. fts. Experiments
conducted on animals shows that extraco, rporeal photopheresis reverses acute
GVHD by increasing the number of regulatory T cells in blood {Ferrara,J et al. 2009).
The number of allogeneic haemo12oietic-cell transplantations (HCTsJ continues to
rise, with over 25 000 procedures undertaken annually. The graft-versus-leukaemia
or graft-versus-tumour effect during this Qrocedure effectively eradicates many
haematollo ical malignant diseases.
Over the last 60 y,ears, animal models have played a crucial role in shaping the
understanding of GVHD and GVL responses. This could possibly be the greatest
contribution to the field. Nonetheless, they have also generated major new
paradigms that have instructed clinical practices. As we move forward, it is useful to
consider where the next advances will come from and how we should assess the
potential of a therapeutic intervention defined in a preclinical study to translate into
clinical practice (Markey,K et al. 2014).
While randomized trials provide some way to directly compare transplantation
strategies over a set of pre-defined endpoints, these studies are challenging to
conduct because of time involved and the cost as well as the difficulty of generating
adequate sample sizes wi�hin single-centre or oligo-centre studies. Randomized
studies in HSCT r,equire a llarge amount of planning and large cooperative
infrastructures, which cannot easily keep up with the rapid development of new
HSCT strategies. Many of the changes in HSCT practice are therefore likely to come
from the interpretation of non-randomized studies. l
International collaboration through a number of non-profit organisations has been a
key factor for �he development of haematopoietic stem celll transplantation.
Thanks to the dedication and far-sighted view of a few pioneers, it was realised that
it is essential to work together in order to facilitate the development of
haematopoietic stem cell transplant, help new centres and laboratory facilities to be
established, provide guidel ines, develop accreditation through JACIE and promote
the development of new research protocols. Refer,ences:
Canoer Research UK. (2015). What is leukapheresis?. Available: Ferrara,J, Levine.,J, Reddy,P, Holler.IE, .. (2009). Graft-versus-host disease. Seminar.
373 (3), p1550-1557.
Gluckman, IE. (2012). A brief history of HSCT . In: Gluckman, IE The, EBMT
Handbook 2012 edition. London: . p22-25.
Markey,K, MacDonald,K, IHillll,G. (2014). The biology of graft-versus-host disease:
experimental systems instructing clinical NHS Commissloning Board. (2013). Clinical Commissioning Policy: Haematopoietic
Stem Cell Transplantation (HSCT) (All Ages).Available:
https://www.engiand.nhs.uk/wp-content/uploads/2013/1 O/b04-p-a . Last accessed
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disease”, Nature Reviews Immunology, R M Egeler. “Acute GvHD: pathogenesis and
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questions/what-is-leu ka pheresis. Last accessed 9th January 2015.
practice. http://www. bloodjournal. orgkontent/124/3/354. full.html. 12:4 (3), p354-359.
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