Not cheap at about $1,000 for just 140mg
Life
extension may come as a surprise, but it is interesting because it is well
studied and, in mice at least, easy to measure.
Most research into mTOR relates to cancer, but this is a very complex
condition. With various feedback loops it means that sometimes the actual
effect is the opposite of what was predicted.
For example, a substance that can help prevent cancer can actually
become harmful later and promote its growth.
Direct
inhibition of mTOR with Everolimus and similar drugs (variants/analogs of
Rapamycin, all called Rapalogs) has not been as successful as hoped in cancer
research. Trials of direct inhibition of
mTOR will shortly start in one rare single gene type of autism (TSC). The drugs are so expensive that many
providers do not want to pay for them.
As you will
see mTOR is just one process in a cloud of interrelated processes. Almost everything has a role/effect:- growth
factors, cytokines, amino acids, mitochondria, dendritic spines, PPAR gamma,
hormones, oxidative stress, autophagy ….
While it
would be nice to think that a single protein complex like mTORC1 or mTORC2 is
the root of all evil in autism, I rather doubt it can be so simple.
The
knowledge that one factor controlling mTORC1 and mTORC2 is oxidative stress,
does raise the possibility that, yet again, the root problem could be oxidative
stress.
Nonetheless,
we will see in today’s post that too much mTOR activity is clearly not good and
that it is associated with lots of bad things:-
·
Epilepsy
·
Autistic
behaviours
·
Food
allergies
·
Mitochondrial
dysfunction
·
Cognitive
impairment
as well as
aging, cancer ….
Indirect reduction in mTOR activity
Rather than
the very expensive first and second generation mTOR inhibiting drugs developed
for cancer, I think the safe way forward
for autism (and aging) may be indirect reduction in mTOR activity, and there is
already a wide choice of methods.
Ketogenic Diet, (or just reduction in carbohydrate intake)
This diet has been used for a hundred years to control
epilepsy, which it now seems can be triggered by elevated mTOR. Research has shown that the ketogenic diet
reduces mTOR.
Low glycemic index diet
This is a low carbohydrate, no
sugar diet, typical of someone with diabetes.
It avoids rapid change in blood sugar. This will lower mTOR and has recently been
shown in a mouse model to improve autistic behaviors.
Growth factors
The blood levels of growth
factors such as insulin and IGF-1 reflect the fed status of the organism. When
food is plentiful, levels of these growth factors are sustained and promote
anabolic cell processes such as translation, lipid biosynthesis, and nutrient
storage via mTORC1. So, dietary
restriction, which lowers IGF-1, will reduce mTOR; but it will also reduce
growth.
Note that one autism therapy
under trial does just the opposite, it is to increase IGF-1 levels via
injections of IGF-1.
Increase amino
acids, particularly leucine
Reduce oxidative
stress
We know
how to do that
NMDA agonists
NMDA
receptor activation decreases mTOR signaling activity.
This
might be achieved using D-Cycloserine, Aminocyclopropanecarboxylic acid, cis-2,3-Piperidinedicarboxylic
acid, Aspartic acid, Glutamic acid, Quinolinate, Homocysteic acid, D-Serine, L-Serine, D-Alanine, L-Alanine, ACPL
Note that D-Cycloserine is
used in autism and D-Serine is used in schizophrenia
Increase PTEN, for example with a
Statin drug
Reduce RAS signaling, for example with a
Statin drug
I am
not the first person to realize this.
Here is a very highly cited paper:-
Since the
body is controlled via feedback loops, there might exist a clever way to
“trick” the body into lowing mTOR. For
example PPAR gamma, which we have come across in earlier posts, is controlled
via mTOR. If you stimulate PPAR gamma
externally this might well have an effect back stream on mTOR activity, via
these feedback loops. Just like if you
supplement Melatonin, you will likely affect the behaviour back stream of the pineal
gland.
mTOR and Aging
A surprising
number of emerging autism therapies are actually also put forward by the life
extension people. In case you did not
know, there is a small industry of pills and potions dedicated to making you
live longer. Some serious institutions like
MIT and Harvard are involved, as in the paper below.
We earlier
saw that PAK-1 is probably there to make sure you do eventually die, reducing
mTOR signaling can probably extend your lifetime and, more importantly, your
healthy lifetime.
Ketogenic Diet
We did see a case report a while back from Martha
Herbert, from Harvard, who has a good result with the ketogenic diet.
The Science
of mTOR
In the following section there are numerous scientific
papers explaining mTOR, so you can choose just how deep you want to go into the
details.
You may notice on the complex diagram below various
substances that we have already encountered in this blog as relevant to autism.
·
PTEN ( increased by Statins) reduced
in some autism
·
Growth factors (disturbed in autism
and therapeutic to some)
·
Ras / Rasopathy (increased by statins,
linked to some autism and MR/ID )
·
Wnt (affects morphology of those dendritic
spines, malformed in autism)
·
Lipid metabolism/synthesis (disturbed
in autism)
·
TSC1
(tuberous sclerosis autism variant)
·
PPAR alpha and gamma affecting inflammation
·
Mitochondrial metabolism, dysfunctional in
autism
·
Autophagy was explained in recent post and,
if impaired, will degrade cellular health and function, particularly in
mitochondria
·
Note Stress/Hypoxia, we have mentioned
Hypoxia before. REDD1 inhibits
mTOR. REDD1 was
first identified as a gene induced by hypoxia and DNA damage, other
environmental stresses such as energy stress, glucocorticoid treatment and
reactive oxygen species have also been reported to induce REDD1 transcription
Pathway Description: The
mechanistic target of Rapamycin (mTOR) is an atypical serine/threonine kinase
that is present in two distinct complexes.
The first, mTOR complex 1 (mTORC1), is composed of
mTOR, Raptor, GβL, and DEPTOR and is inhibited by Rapamycin. It is a master
growth regulator that senses and integrates diverse nutritional and
environmental cues, including growth factors, energy levels, cellular stress,
and amino acids. It couples these signals to the promotion of cellular growth
by phosphorylating substrates that potentiate anabolic processes such as mRNA
translation and lipid synthesis, or limit catabolic processes such as
autophagy. The small GTPase Rheb, in its GTP-bound state, is a necessary and
potent stimulator of mTORC1 kinase activity, which is negatively regulated by
its GAP, the tuberous sclerosis heterodimer TSC1/2. Most upstream inputs are
funneled through Akt and TSC1/2 to regulate the nucleotide-loading state of
Rheb. In contrast, amino acids signal to mTORC1 independently of the PI3K/Akt
axis to promote the translocation of mTORC1 to the lysosomal surface where it
can become activated upon contact with Rheb. This process is mediated by the
coordinated actions of multiple complexes, notably the v-ATPase, Ragulator, the
Rag GTPases, and GATOR1/2.
The second complex, mTOR complex 2 (mTORC2), is
composed of mTOR, Rictor, GβL, Sin1, PRR5/Protor-1, and DEPTOR. mTORC2 promotes
cellular survival by activating Akt, regulates cytoskeletal dynamics by
activating PKCα, and controls ion transport and growth via SGK1
phosphorylation.
Aberrant mTOR signaling is involved in many disease
states including cancer, cardiovascular disease, and diabetes.
Growth factors regulate mTORC1
Energy and stress regulate mTORC1
mTOR regulates metabolism in
mammals
mTOR in fasting and starvation
mTOR, over-feeding, and insulin
sensitivity
One of the most efficient forms of energy storage are triglycerides,
because they provide a high energetic yield per unit of mass. mTORC1 mediates
lipid accumulation in fat cells
mTORC1 may impact on PPAR-γ activity by increasing its translation118 and by
activating the transcription factor SREBP-1c . Active SREBP-1c enhances PPAR-γ
activity and
transactivates a set of genes directly involved in lipid synthesis. At
present, the molecular links between mTORC1, SREBP-1c and PPAR-γ activity
remain to be clarified.
Thus, mTORC1 coordinates food
intake with energy storage at multiple levels, from central control of food
seeking to energy storage and expenditure in peripheral tissues. This
multi-level regulation explains the profound consequences that dysregulated
mTOR signaling exerts on human metabolism.
Aging
Due to its role at the interface of growth
and starvation, mTOR is a prime target in the genetic control of ageing, and
evidence from genetic studies supports the view that mTOR may be a master
determinant of lifespan and ageing in yeast, C. elegans,
flies and mice.
The only ‘natural’ method available to
counter ageing is dietary restriction (DR), where the caloric intake is decreased
anywhere from 10% to 50%. DR appears to act mainly through the inhibition of
mTORC1, and genetic inactivation of mTORC1 pathway components provides no
additional benefit over DR. In mice, DR causes lifespan extension and changes
in gene expression profile similar to those resulting from loss of S6K1 further
supporting the view that DR acts through inhibition of mTORC1
Finally, it remains to be seen whether limiting mTOR activity in adult
humans would really enable a longer lifespan, or it would only bring an
increase in the quality of life and the way we age, without necessarily
affecting how long we live.
mTOR in food allergy
Highlights
mTOR pathway is implicated in gut–brain axis
of food allergy-induced ASD-like behavior.
Food
allergy is associated with enhanced mTOR signaling in the brain and gut.
mTORC1 inhibitor Rapamycin improved the
behavioral deficits of allergic mice.
Rapamycin
reduced mTORC1 activity in the brain and gut of allergic mice.
Rapamycin
inhibited food allergy and increased the number of Treg cells in the ileum.
5. Conclusions
In conclusion, the current studies provide strong and first evidence
that the enhanced mTOR signaling pathway in the brain as well as in the intestines plays a pivotal role in the
behavioral and immunological changes in CMA mice. mTOR might be the linking pin
involved in gut-immune-brain axis in ASD and
the intestinal tract could be a potential target in the treatment of patients
with ASD and comorbid intestinal symptoms. It is a compelling hypothesis that an enhanced mTOR
activity throughout the body may account for both the behavioral as well as the
gastrointestinal dysfunctions in patients with ASD. Whether inhibition
of mTOR is able to treat both allergic and behavioral deficits of
ASD patients remains to be further investigated. Importantly, increased
gastrointestinal deficits and in particular
behavioral abnormalities are commonly reported in other neurodevelopmental
diseases such as attention deficit hyperactivity disorder
(ADHD), multiple sclerosis , schizophrenia, Parkinson's disease , however the
role of mTOR needs to be investigated. Our findings
on the gut-immune-brain connection in a murine model of CMA indicate that targeting mTOR signaling pathway might be
applicable to various neurological disorders. Future studies focusing on the
mTOR signaling pathway should shed more light on the effective treatment of ASD
and other neurodevelopmental disorders.
mTOR and Autism
Hyperconnectivity of neuronal circuits due to increased
synaptic protein synthesis is thought to cause autism spectrum disorders
(ASDs). The mammalian target of Rapamycin (mTOR) is strongly
implicated in ASDs by means of upstream signaling; however, downstream
regulatory mechanisms are ill-defined. Here we show that knockout of the
eukaryotic translation initiation factor 4E-binding protein 2 (4E-BP2)—an eIF4E
repressor downstream of mTOR—or eIF4E overexpression leads to increased
translation of neuroligins, which are postsynaptic proteins that are causally
linked to ASDs. Mice that have the gene encoding 4E-BP2 (Eif4ebp2)
knocked out exhibit an increased ratio of excitatory to inhibitory synaptic
inputs and autistic-like behaviours (that is, social interaction deficits, altered
communication and repetitive/stereotyped behaviours). Pharmacological inhibition of eIF4E activity or
normalization of neuroligin 1, but not neuroligin 2, protein levels restores
the normal excitation/inhibition ratio and rectifies the social behaviour
deficits. Thus,
translational control by eIF4E regulates the synthesis of neuroligins,
maintaining the excitation-to-inhibition balance, and its dysregulation
engenders ASD-like phenotypes.
Reversing autism by targeting downstream mTOR signaling
Autism spectrum disorders (ASDs) are a group of
clinically and genetically heterogeneous neurodevelopmental disorders
characterized by impaired social interactions, repetitive behaviors and
restricted interests. The genetic defects in ASDs may interfere with synaptic
protein synthesis. Synaptic dysfunction caused by aberrant protein synthesis is
a key pathogenic mechanism for ASDs Understanding the details about aberrant
synaptic protein synthesis is important to formulate potential treatment for
ASDs. The mammalian target of the Rapamycin (mTOR) pathway plays central roles
in synaptic protein. Recently, Gkogkas and colleagues published exciting data
on the role of downstream mTOR pathway in autism
Previous studies have indicated that
upstream mTOR signaling is linked to ASDs. Mutations in tuberous sclerosis
complex (TSC) 1/TSC2, neurofibromatosis 1 (NF1),
and Phosphatase and tensin homolog (PTEN) lead to syndromic ASD with
tuberous sclerosis, neurofibromatosis, or macrocephaly, respectively.
TSC1/TSC2, NF1, and PTEN act as negative regulators of mTOR complex 1 (mTORC1),
which is activated by phosphoinositide-3 kinase (PI3K) pathway. Activation of
cap-dependent translation is a principal downstream mechanism of mTORC1. The
eIF4E recognizes the 5′ mRNA cap, recruits eIF4G and the small ribosomal
subunit. The eIF4E-binding proteins (4E-BPs) bind to eIF4E and inhibit
translation initiation. Phosphorylation of 4E-BPs by mTORC1 promotes eIF4E
release and initiates cap-dependent translation. A hyperactivated mTORC1–eIF4E
pathway is linked to impaired synaptic plasticity in fragile X syndrome, an
autistic disorder caused by lack of fragile X mental retardation protein (FMRP)
due to mutation of the FMR1 gene, suggesting that downstream mTOR signaling
might be causally linked to ASDs. Notably, one pioneering study has identified
a mutation in the EIF4E promoter in autism families, implying that deregulation
of downstream mTOR signaling (eIF4E) could be a novel mechanism for ASDs.As an eIF4E repressor downstream of mTOR,
4E-BP2 has important roles in synaptic plasticity, learning and memory. Writing
in their Nature article, Gkogkas and colleagues reported that deletion of the
gene encoding 4E-BP2 (Eif4ebp2) leads to autistic-like behaviors in mice. Pharmacological inhibition of
eIF4E rectifies social behavior deficits in Eif4ebp2 knockout mice.
Their study in mouse models has provided direct evidence for the causal link
between dysregulated eIF4E and the development of ASDs.Are these ASD-like phenotypes of the
Eif4ebp2 knockout mice caused by altered translation of a subset mRNAs due to
the release of eIF4E? To test this, Gkogkas et al. measured translation initiation
rates and protein levels of candidate genes known to be associated with ASDs in
hippocampi from Eif4ebp2 knockout and eIF4E-overexpressing mice. They found
that the translation of neuroligin (NLGN) mRNAs is enhanced in both lines of
transgenic mice. Removal of 4E-BP2 or overexpression of eIF4E increases protein
amounts of NLGNs in the hippocampus, whereas mRNA levels are not affected, thus
excluding transcriptional effect. In contrast, the authors did not observe any
changes in the translation of mRNAs coding for other synaptic scaffolding
proteins. Interestingly, treatment of Eif4ebp2 knockout mice with selective
eIF4E inhibitor reduces NLGN protein levels to wild-type levels. These data thus indicate that
relief of translational suppression by loss of 4E-BP2 or by the overexpression
of eIF4E selectively enhances the NLGN synthesis. However, it cannot be
ruled out that other proteins (synaptic or non-synaptic) may be affected and
contribute to animal autistic phenotypes.Aberrant information processing due to
altered ratio of synaptic excitation to inhibition (E/I) may contribute to
ASDs. The increased or decreased E/I ratio has been observed in ASD animal
models In relation to these E/I shifts,
Gkogkas et al then examined the synaptic transmission in hippocampal slices of
Eif4ebp2 knockout mice. They found that 4E-BP2 de-repression results in an
increased E/I ratio, which can be explained by the increase of vesicular
glutamate transporter and spine density in hippocampal pyramidal neurons. As expected, application of
eIF4E inhibitor restores the E/I balanceFinally, in view of the facts that genetic
manipulation of NLGNs results in ASD-like phenotypes with altered E/I balance
in mouse models and NLGN mRNA
translation is enhanced concomitant with increased E/I ratio in Eif4ebp2
knockout mice, Gkogkas et al. tested the effect of NLGN knockdown on synaptic
plasticity and behaviour in these mice . NLGN1 is predominantly postsynaptic at
excitatory synapses and promotes excitatory synaptic transmission. The authors found that NLGN1
knockdown reverses changes at excitatory synapses and partially rescues the
social interaction deficits in Eif4ebp2 knockout mice. These findings
thus established a strong link between eIF4E-dependent translational control of
NLGNs, E/I balance and the development of ASD-like animal behaviors (Figure 1).
In
summary, Gkogkas et al. have provided a model for mTORC1/eIF4E-dependent
autism-like phenotypes due to dysregulated translational control (Gkogkas et al.,
2013). This novel regulatory mechanism will prompt investigation of
downstream mTOR signaling in ASDs, as well as expand our knowledge of how mTOR
functions in human learning and cognition. It may narrow down therapeutic targets
for autism since targeting downstream mTOR signaling reverses autism.
Pharmacological manipulation of downstream effectors of mTOR (eIF4E, 4E-BP2,
and NLGNs) may eventually provide therapeutic benefits for patients with ASDs.
3.3. Autism
As with epilepsy, the link between aberrant mTOR
activation and autism is strongest in tuberous sclerosis complex; between 20
and 60% of tuberous sclerosis patients are diagnosed with autism [219, 237], which may account for 1–4% of all autism
cases [238]. In addition to tuberous sclerosis, however,
there is growing evidence that dysregulated mTOR activity may contribute to a
wider variety of autism spectrum disorders. As with epilepsy, mutations in PTEN
that lead to aberrant activation of mTOR are associated with autism [239]. In addition, mutations in the downstream mTOR
target eukaryotic translation initiation factor 4E (eIF4E) have also been
associated with autism [240]. There is also evidence for a strong
association between macrocephaly (large head size) early in life and autism
spectrum disorders, as well as genetic diseases linked to autism and mTOR
hyperactivation, including tuberous sclerosis complex, neurofibromatosis type
I, Lhermitte-Duclos syndrome, and Fragile X syndrome [241]. Taken together these data suggest that disinhibited mTOR may cause, or
at least contribute to, many cases of autism spectrum disorder. Clinical trials
are ongoing to assess whether Everolimus can reduce autistic symptoms in
tuberous sclerosis patients.
Given the breadth of pathological conditions
where mTOR has already been implicated, it seems likely that additional
therapeutic uses for mTOR inhibitors will be discovered in the near future.
While potential negative effects of mTOR inhibition need to be addressed, they
appear generally manageable and, as new mTOR inhibitors continue to be
developed, it may be possible to maximize the beneficial effects of targeted
mTOR inhibition while reducing adverse effects.
This paper is very
comprehensive and this graphic has everything you could ever need to know. You can use it to figure out your own
therapy.
mTOR and seizures
Epilepsy, a common neurological disorder and cause of significant
morbidity and mortality, places an enormous burden on the individual and
society. Presently, most drugs for epilepsy primarily suppress seizures as
symptomatic therapies but do not possess actual antiepileptogenic or
disease-modifying properties. The mTOR (mammalian target of Rapamycin)
signaling pathway is involved in major multiple cellular functions, including
protein synthesis, cell growth and proliferation and synaptic plasticity, which
may influence neuronal excitability and be responsible for epileptogenesis.
Intriguing findings of the frequent hyperactivation of mTOR signaling in
epilepsy make it a potential mechanism in the pathogenesis as well as an
attractive target for the therapeutic intervention, and have driven the
significant ongoing efforts to pharmacologically target this pathway. This
review explores the relevance of the mTOR pathway to epileptogenesis and its
potential as a therapeutic target in epilepsy treatment by presenting the
current results on mTOR inhibitors, in particular, Rapamycin, in animal models
of diverse types of epilepsy. Limited clinical studies in human epilepsy, some
paradoxical experimental data and outstanding questions have also been
discussed.
The ketogenic diet (KD) is an effective treatment for epilepsy, but its
mechanisms of action are poorly understood. We investigated the hypothesis that
KD inhibits mammalian target of Rapamycin (mTOR) pathway signaling. The
expression of pS6 and pAkt, markers of mTOR pathway activation, was reduced in
hippocampus and liver of rats fed KD. In the kainate model of epilepsy, KD blocked
the hippocampal pS6 elevation that occurs after status epilepticus. As mTOR
signaling has been implicated in epileptogenesis, these results suggest that
the KD may have anticonvulsant or antiepileptogenic actions via mTOR pathway
inhibition.
Highlights
•
Tsc1 deletion in neurons causes epilepsy and
autism-like behaviors in mice.
•
Epileptiform activity spreads to the
brainstem.
•
mTOR becomes hyperactivated in 5-HT neurons
following seizure onset.
•
mTOR hyperactivity in 5-HT neurons causes
autism behaviors.
•
Autism-like behaviors can be reversed
following treatment with Rapamycin.
Abstract
Epilepsy and autism
spectrum disorder (ASD) are common comorbidities of one another. Despite the
prevalent correlation between the two disorders, few studies have been able to
elucidate a mechanistic link. We demonstrate that forebrain specific Tsc1 deletion in mice causes epilepsy and autism-like
behaviors, concomitant with disruption of 5-HT neurotransmission. We find that
epileptiform activity propagates to the raphe nuclei, resulting in
seizure-dependent hyperactivation of mTOR in 5-HT neurons. To dissect whether
mTOR hyperactivity in 5-HT neurons alone was sufficient to recapitulate an
autism-like phenotype we utilized Tsc1flox/flox;Slc6a4-cre mice, in which mTOR is restrictively hyperactivated
in 5-HT neurons. Tsc1flox/flox;Slc6a4-cre mice displayed alterations of the 5-HT system and
autism-like behaviors, without causing epilepsy. Rapamycin treatment in these
mice was sufficient to rescue the phenotype. We conclude that the spread of
seizure activity to the brainstem is capable of promoting hyperactivation of
mTOR in the raphe nuclei, which in turn promotes autism-like behaviors. Thus
our study provides a novel mechanism describing how epilepsy can contribute to
the development of autism-like behaviors, suggesting new therapeutic strategies
for autism.
mTOR inhibition via carbohydrate restriction
Amino acids and mTOR
The activity of mammalian target of
Rapamycin (mTOR) complexes regulates essential cellular processes, such as growth,
proliferation or survival. Nutrients such as amino acids are important regulators
of mTOR Complex 1 (mTORC1) activation, thus affecting cell growth, protein
synthesis and autophagy.
Here, we show that amino acids may
also activate mTOR Complex 2 (mTORC2). This activation is mediated by the activity
of class I PI3K and of Akt. Amino acids induced a rapid phosphorylation of Akt
at Thr308 and Ser473. Whereas both phosphorylations were dependent on the presence
of mTOR, only Akt phosphorylation at Ser473 was dependent on the presence of
rictor, a specific component of mTORC2. Kinase assays confirmed mTORC2
activation by amino acids. This signaling was functional, as demonstrated by
the phosphorylation of Akt substrate FOXO3a. Interestingly, using different
starvation conditions, amino acids can selectively activate mTORC1 or mTORC2.
These findings identify a new signaling pathway
used by amino acids underscoring the crucial importance of these nutrients in
cell metabolism and offering new mechanistic insights.
Finally, this report shows the crucial importance
of dietary restriction/starvation conditions for understanding the amino acid signaling.
Several studies show the effects of amino acid intake in obesity [23,27,28],
and of dietary restriction in human cancers [79,80]. Although more
physiological studies are needed to link these effects to mTOR complex
regulation, it is noteworthy that a study in human muscle shows activation of both
mTORC1 and mTORC2 by ingestion of
a leucine-enriched amino acid-carbohydrate mixture
[86]. It has been recently
described that branched-chain amino acid dietary supplementation increased the
average life span in mice and cardiac and skeletal muscle improvement [87]
validating the physiological relevance of amino acid supplementation. In
this context, we now report that cell supplementation with amino acids can
activate both mTOR complexes (Figures 10 and 11). In summary, this manuscript shows for the first time that
amino acids can activate mTORC1 and mTORC2 complexes, thus underscoring the
crucial importance of these nutrients in cell metabolism and offering new
mechanistic insights with potential therapeutic applications in cancer, obesity
and aging.
Recent evidence points to a strong relationship between increased
mitochondrial biogenesis and increased survival in eukaryotes. Branched-chain
amino acids (BCAAs) have been shown to extend chronological life span in yeast.
However, the role of these amino acids in mitochondrial biogenesis and
longevity in mammals is unknown. Here, we show that a BCAA-enriched mixture
(BCAAem) increased the average life span of mice. BCAAem supplementation increased mitochondrial biogenesis
and sirtuin 1 expression in primary cardiac and skeletal myocytes and in
cardiac and skeletal muscle, but not in adipose tissue and liver of middle-aged
mice, and this was accompanied by enhanced physical endurance. Moreover, the reactive oxygen
species (ROS) defense system genes were upregulated, and ROS production was
reduced by BCAAem supplementation. All of the BCAAem-mediated effects
were strongly attenuated in endothelial nitric oxide synthase null mutant mice.
These data reveal an
important antiaging role of BCAAs mediated by mitochondrial biogenesis in
mammals.
Amino acid deficiency causing Autism
A rare, hereditary form of autism has been
found — and it may be treatable with protein supplements.
Genome sequencing of six children with autism
has revealed mutations in a gene that stops several essential amino acids being
depleted. Mice lacking this gene developed neurological problems related to
autism that were reversed by dietary changes, a paper published today in Science
shows1.
Some children with autism have low blood
levels of amino acids that can't be made in the body.
“This might represent the first treatable
form of autism,” says Joseph Gleeson, a child neurologist at the University of
California, San Diego, who led the study. “That is both heartening to families
with autism, and also I think revealing of the underlying mechanisms of
autism.”
He emphasizes, however, that the mutations
are likely to account for only a very small proportion of autism cases. “We
don’t anticipate this is going to have implications for patients in general
with autism,” says Gleeson. And there is as yet no proof that dietary
supplements will help the six children, whose mutations the researchers
identified by sequencing the exome — the part of the genome that codes for
proteins.
In mice, at least,
the chemical imbalance can be treated. The mutant mice had neurological problems typical of
mouse versions of autism, including tremors and epileptic seizures. But those
symptoms disappeared in less than a week after the mice were put on diets
enriched in branched-chain amino acids.
Gleeson’s team has
tried supplementing the diets of the children with this form autism, using
muscle-building supplements that contain branched-chain amino acids. The
researchers found that the supplements restore the children's blood levels of
amino acids to normal. As for their autism symptoms, Gleeson says, the “patients did not get any worse and their parents
say they got better, but it’s anecdotal”.
This paper is very recent and suggests, at least in one mouse model,
that oxygen consumption in the brain is dysfunction and that this was rescued
using the mTOR inhibitor Rapamycin.
Tuberous sclerosis (TSC) is associated with autism spectrum disorders and
has been linked to metabolic dysfunction and unrestrained signaling of the
mammalian target of Rapamycin (mTOR). Inhibition of mTOR by Rapamycin can
mitigate some of the phenotypic abnormalities associated with TSC and autism,
but whether this is due to the mTOR-related function
in energy metabolism remains to be elucidated. In young Eker rats, an animal
model of TSC and autism, which harbors a germ line heterozygous Tsc2 mutation, we previously
reported that cerebral oxygen consumption was pronouncedly elevated. Young
(4 weeks) male control Long–Evans and Eker rats were divided into control
and Rapamycin-treated (20 mg/kg once daily for 2 days) animals.
Cerebral regional blood flow (14C-iodoantipyrine) and O2
consumption (cryomicrospectrophotometry) were determined in
isoflurane-anesthetized rats. We found significantly increased basal O2
consumption in the cortex (8.7 ± 1.5 ml O2/min/100 g
Eker vs. 2.7 ± 0.2 control), hippocampus, pons and cerebellum.
Regional cerebral blood flow and cerebral O2 extractions were also
elevated in all brain regions. Rapamycin had no significant effect on O2 consumption in any
brain region of the control rats, but significantly reduced consumption in the
cortex (4.1 ± 0.3) and all other examined regions of the Eker rats.
Phosphorylation of mTOR and S6K1 was similar in
the two groups and equally reduced by Rapamycin. Thus, a Rapamycin-sensitive, mTOR-dependent but
S6K1-independent, signal led to enhanced oxidative metabolism in the Eker
brain. We
found decreased Akt phosphorylation in Eker but not Long–Evans rat brains,
suggesting that this may be related to the increased cerebral O2
consumption in the Eker rat. Our
findings suggest that Rapamycin targeting of Akt to restore normal cerebral
metabolism could have therapeutic potential in tuberous sclerosis and autism.
Mitochondrial
Dysfunction and mTOR
Mitochondria are organelles that
play a central role in processes related to cellular viability, such as energy
production, cell growth, cell death via apoptosis, and metabolism of reactive
oxygen species (ROS). We can observe behavioral abnormalities relevant to
autism spectrum disorders (ASDs) and their recovery mediated by the mTOR
inhibitor Rapamycin in mouse models. In Tsc2+/- mice, the transcription of
multiple genes involved in mTOR signaling is enhanced, suggesting a crucial
role of dysregulated mTOR signaling in the ASD model. This review proposes that
the mTOR inhibitor may be useful for the pharmacological treatment of ASD. This review offers novel
insights into mitochondrial dysfunction and the related impaired glutathione
synthesis and lower detoxification capacity. Firstly, children with ASD
and concomitant mitochondrial dysfunction have been reported to manifest
clinical symptoms similar to those of mitochondrial disorders, and it therefore
shows that the clinical
manifestations of ASD with a concomitant diagnosis of mitochondrial dysfunction
are likely due to these mitochondrial disorders. Secondly, the adenosine triphosphate (ATP)
production/oxygen consumption pathway may be a potential candidate for
preventing mitochondrial dysfunction due to oxidative stress, and disruption of
ATP synthesis alone may be related to impaired glutathione synthesis. Finally, a decrease in total
antioxidant capacity may account for ASD children who show core social and
behavioral impairments without neurological and somatic symptoms.
PTEN-type Autism and mTOR
Germline mutations in PTEN, which encodes a widely
expressed phosphatase, was mapped to 10q23 and identified as the susceptibility
gene for Cowden syndrome, characterized by macrocephaly and high risks of
breast, thyroid, and other cancers. The phenotypic spectrum of PTEN mutations expanded to
include autism with macrocephaly only 10 years ago. Neurological studies of patients with PTEN-associated autism
spectrum disorder (ASD) show increases in cortical white matter and a distinctive
cognitive profile, including delayed language development with poor working
memory and processing speed. Once a germline PTEN mutation is found, and a
diagnosis of phosphatase and tensin homolog (PTEN) hamartoma tumor
syndrome made, the clinical outlook broadens to include higher lifetime risks
for multiple cancers, beginning in childhood with thyroid cancer. First described as a tumor
suppressor, PTEN is a major
negative regulator of the phosphatidylinositol 3-kinase/protein kinase
B/mammalian target of Rapamycin (mTOR) signaling
pathway—controlling
growth, protein synthesis, and proliferation. This canonical function combines
with less well-understood mechanisms to influence synaptic plasticity and
neuronal cytoarchitecture.
Several excellent mouse models of Pten loss or
dysfunction link these neural functions to autism-like behavioral
abnormalities, such as altered sociability, repetitive behaviors, and
phenotypes like anxiety that are often associated with ASD in humans.
These models also show the promise
of mTOR inhibitors as
therapeutic agents capable of reversing phenotypes ranging from overgrowth to
low social behavior. Based on these findings, therapeutic options for patients with PTEN hamartoma tumor syndrome
and ASD are coming into view, even as new discoveries in PTEN biology add complexity
to our understanding of this master regulator
Intellectual
Disability (MR) and mTOR
Protein synthesis regulation via mammalian target of Rapamycin
complex 1 (mTORC1) signaling pathway has key roles in neural development and
function, and its dysregulation is involved in neurodevelopmental disorders
associated with autism and intellectual disability. mTOR regulates assembly of
the translation initiation machinery by interacting with the eukaryotic
initiation factor eIF3 complex and by controlling phosphorylation of key
translational regulators. Collybistin
(CB), a neuron-specific Rho-GEF responsible for X-linked intellectual
disability with epilepsy, also interacts with eIF3, and its binding
partner gephyrin associates with mTOR. Therefore, we hypothesized that CB also binds mTOR and affects
mTORC1 signaling activity in neuronal cells. Here, by using induced
pluripotent stem cell-derived neural progenitor cells from a male patient with
a deletion of entire CB gene and from control individuals, as well as a
heterologous expression system, we describe that CB physically interacts with
mTOR and inhibits mTORC1 signaling pathway and protein synthesis. These
findings suggest that disinhibited mTORC1 signaling may also contribute to the
pathological process in patients with loss-of-function variants in CB.
mTORC2 as opposed to mTORC1 as a target in Autism Research
The goal of my DOD-supported research is determine the role of the new
mTOR complex (mTORC2) in Autism Spectrum Disorder (ASD). ASD individuals
exhibit impaired social interactions, seizures and abnormal repetitive
behavior. In addition, 70-80% of autistic individuals suffer from mental
retardation. Autism is a heritable genetically heterogeneous disorder and mutations
in negative regulators of the mammalian target of Rapamycin complex 1 (mTORC1)
signaling pathway, such as PTEN were associated with ASD. Here, we show that in
the hippocampus of Pten fb-KO mice – where Pten is conditionally deleted in the
murine forebrain – the activity of both mTORC1 and mTORC2 is increased. In
addition, Pten fb-KO mice exhibit seizures, learning and memory and social
deficits. Our remarkable preliminary data show that genetic inhibition of
mTORC2 activity in Pten-deficient mice significantly promotes survival. In
addition, Pten-rictor fb- double KO (DKO) mice, in which mTORC2 activity is
restored to normal levels, EEG seizures, learning and memory as well as social
phenotypes, are all rescued. In the second year, we will study the molecular mechanism
underlying this process. These insights hold the promise for new treatment of
ASD.
1. Introduction:
Autism represents a heterogeneous group of disorders,
which are defined as “autism spectrum disorders” (ASDs). ASD individuals
exhibit common features such as impaired social interactions, language and
communication, and abnormal repetitive behavior. In addition, 70-80% of
autistic individuals suffer from mental retardation1-3. The major goal of this
award is to determine the role of mTORC2 in two mouse models of ASD.
Recently, we have shown that mTORC2 plays a crucial role
in long-term memory formation. Briefly, mice lacking mTORC2 showed impaired
long-lasting changes in synaptic strength (L-LTP) as well as impaired long-term
memory (LTM). In addition, we have found that by promoting mTORC2 activity,
with a new agent A-443654, it facilitates L-LTP and enhances long-term memory
formation in WT mice. Interestingly, mTORC2 activity is altered in both ASD
patients and ASD mouse models harboring mutation in Tsc and Pten5,6. Hence,
in this proposal we will test the hypothesis that the neurological dysfunction
in several ASD mouse models is caused by dysregulation of mTORC2 rather than
mTORC1 activity.
4. Key Research Accomplishment
- We developed a way to specifically block mTORC2 activity in
Pten-deficient mice.
- Genetic deletion of mTORC2 prolongs the survival of Pten-deficient
mice.
- Genetic deletion of mTORC2 dramatically attenuates seizures in
Pten-deficient mice.
- Genetic deletion of mTORC2 improves cognitive and social phenotypes
in Pten-deficient mice.
5. Conclusion
It has been proposed that the
increased mTORC1 in Pten-deficient or Tsc-deficient mice causes the cellular
and behavioral phenotypes associated with ASD. Our
new data challenge this view and posit that the neurological dysfunction in
ASD, at least in the Pten-ASD mouse model, is caused by dysregulation of
mTORC2.
Hence, these preliminary data are very important since they identified a new
signaling pathway involved in ASD and seizure disorders that could be targeted
and lead to the development of new treatments for ASD and seizure disorders.
E/I
Imbalance in Schizophrenia and Autism
This paper looks really useful and does refer to mTOR,
but is not open access
Autism Spectrum Disorders (ASD)
and Schizophrenia (SCZ) are cognitive disorders with complex genetic
architectures but overlapping behavioral phenotypes, which suggests common
pathway perturbations. Multiple lines of evidence implicate imbalances in
excitatory and inhibitory activity (E/I imbalance) as a shared
pathophysiological mechanism. Thus, understanding the molecular underpinnings
of E/I imbalance may provide essential insight into the etiology of these
disorders and may uncover novel targets for future drug discovery. Here, we
review key genetic, physiological, neuropathological, functional, and pathway
studies that suggest alterations to excitatory/inhibitory circuits are keys to
ASD and SCZ pathogenesis.
NMDA activation, Sociability and mTOR
Highlights
•
Several syndromic forms of ASD are associated
with disinhibited activity of mTORC1.
•
Rapamycin,
an inhibitor of mTORC1, improved sociability in mouse models of TSC.
•
NMDA receptor-mediated neurotransmission
regulates sociability in mice.
•
NMDA
receptor activation decreases mTOR signaling activity.
•
D-Cycloserine
improved sociability in the Balb/c and BTBR mouse models of ASD.
Abstract
Tuberous Sclerosis Complex is one example of a
syndromic form of autism spectrum disorder associated with disinhibited
activity of mTORC1 in neurons (e.g., cerebellar Purkinje cells). mTORC1 is a
complex protein possessing serine/threonine kinase activity and a key
downstream molecule in a signaling cascade beginning at the cell surface with
the transduction of neurotransmitters (e.g., glutamate and acetylcholine) and
nerve growth factors (e.g., Brain-Derived Neurotrophic Factor). Interestingly, the severity of
the intellectual disability in Tuberous Sclerosis Complex may relate more to
this metabolic disturbance (i.e., overactivity of mTOR signaling) than
the density of cortical tubers. Several recent reports showed that Rapamycin,
an inhibitor of mTORC1, improved sociability and other symptoms in mouse models
of Tuberous Sclerosis Complex and autism spectrum disorder, consistent with
mTORC1 overactivity playing an important pathogenic role. NMDA receptor activation may also
dampen mTORC1 activity by at least two possible mechanisms: regulating
intraneuronal accumulation of arginine and the phosphorylation status of a
specific extracellular signal regulating kinase (i.e., ERK1/2), both of which
are “drivers” of mTORC1 activity. Conceivably, the prosocial effects of targeting the NMDA
receptor with agonists in mouse models of autism spectrum disorders result from
their ability to dampen mTORC1 activity in neurons. Strategies for dampening mTORC1 overactivity by
NMDA receptor activation may be preferred to its direct inhibition in
chronic neurodevelopmental disorders, such as autism spectrum disorders.
Dendritic Spine Dysgenesis in Autism and
mTOR
The activity-dependent structural and functional
plasticity of dendritic spines has led to the long-standing belief that these
neuronal compartments are the subcellular sites of learning and memory. Of
relevance to human health, central neurons in several neuropsychiatric
illnesses, including autism related disorders, have atypical numbers and
morphologies of dendritic spines. These so-called dendritic spine dysgeneses found
in individuals with autism related disorders are consistently replicated in
experimental mouse models. Dendritic spine dysgenesis reflects the underlying
synaptopathology that drives clinically relevant behavioral deficits in
experimental mouse models, providing a platform for testing new therapeutic approaches.
By examining molecular signaling pathways, synaptic deficits, and spine
dysgenesis in experimental mouse models of autism related disorders we find
strong evidence for mTOR to be a critical point of convergence and promising
therapeutic target.
3. Spine dysgenesis in
autism related disorders Spine dysgenesis has been described in autopsy brains
of several ARDs, their genetic causes ranging from hundreds of affected genes
to one, with their pervasiveness relating to both severity and number of
clinical symptoms. By examining common clinical phenotypes correlated to spine
and synaptic abnormalities between the disorders, we can work to recognize
causalities in dysgenesis and identify potential targets for therapeutic
intervention.
4. mTOR: a convergence
point of spine dysgenesis and synaptopathologies in ASD Dysgenesis
of dendritic spines occurs in the majority of individuals afflicted with ARDs,
as well as in most experimental mouse models of these syndromes. It would,
therefore, follow that there must be a converging deregulated molecular pathway
downstream of the affected genes and upstream of dendritic spine formation and maturation.
Identifying this pathway will not only define a causal common denominator in
autism-spectrum disorders, but also open new therapeutic opportunities for
these devastating conditions. The Ras/ERK and PI3K/mTOR pathways, which
regulate protein translation in dendrites near excitatory synapses, have
received the most attention as such candidate convergence points
5. Conclusion Cajal once
postulated, “the future
will prove the great physiological role played by the dendritic spines”
[229]. And indeed, it is now widely accepted that dendritic spines are the site
of neuronal plasticity of excitatory synapses and the focal point for synaptopathophysiologies
of ARDs. Individuals and
mouse models of ARDs all display spine dysgenesis, with mTOR-regulated protein
translation being a critical point of convergence. Deviations from
optimal levels of protein synthesis correlate with the magnitude of dendritic
spine pruning and LTD in ARDs. Alleviation of heightened mTOR activity rescues
both synaptic and behavioral phenotypes in FXS and TS animals. Correcting mTOR signaling levels
also reversed ARD phenotypes in adult fully symptomatic mice, challenging the
traditional view that genetic defects caused irreversible developmental defects
[230]. More excitingly, these observations demonstrate the potential of
pharmacological therapies for neurodevelopmental disorders. The list of ARDs
that have been reversed in adult symptomatic mice continues to grow, and also
includes RTT [231], DS [232,233], and AS [92]. Together, these findings demonstrate
the remarkable plastic nature of the brain and imply that if the causal
denominator of ARDs could be found and therapeutically targeted, we may be able
to allow the ARD brain to rewire itself and relieve clinical symptoms once
believed to be irreversible. The analysis of correlative physiological
and behavioral phenotypes and identification of the common mTOR pathway will
hopefully provide such potential targets.
Clinical Trials
It will be interesting to see the results of the current trials on children with Tuberous Sclerosis Complex, a rare type of autism, that is the most likely to respond to mTOR inhibition.
The purpose of this study is to assess the feasibility and safety of
administering rapalogs sirolimus or everolimus, in participants with Tuberous Sclerosis
Complex (TSC) and self-injury and to measure cognitive and behavioral changes,
including reduction in autistic symptoms,
self-injurious and aggressive behaviors, as well as improvements in cognition
across multiple domains of cognitive function.
Tuberous sclerosis complex (TSC) is a genetic disease that leads to mental
retardation in over 50% of patients, and to learning problems, behavioral
problems, autism and epilepsy in up to 90% of
patients. The underlying deficit of TSC, loss of inhibition of the mammalian
target of Rapamycin (mTOR) protein due to
dysfunction of the tuberin/hamartin protein complex, can be rescued by everolimus. Everolimus has been
registered as treatment for renal cell carcinoma and giant cell astrocytoma
(SEGA). Evidence in human and animal studies suggests that mTOR
inhibitors improve learning and development in patients with TSC.
