Aspartic acid is a metabolite of the sweetener Aspartame; not a surprise when you taste it
Today’s post is about the amino acid aspartic acid, which our reader Tyler has been supplementing. The short version of this post would answer the question should we all follow Tyler and supplement L-Aspartic acid? I guess the answer is that it is well worth a trial.
There is a great deal of complex science showing that aspartic acid is dysfunctional in autism, but we cannot prove that supplemental aspartic acid corrects these dysfunctions. Supplemental aspartic acid will have other effects and it may be these that are beneficial in Tyler’s case and possibly yours.
Correcting the core dysfunctions relating to Aspartic acid would be very helpful, if it were possible. You could write an entire book just about the contents of today’s post, so for most people understanding all of it will take quite some time.
You can read Tyler’s many comments on this subject by entering the following into google.
You can read Tyler’s many comments on this subject by entering the following into google.
aspartate "site:epiphanyasd.blogspot.com"
This gives you a list of those posts, where he left comments on aspartate.
Then press the “crtl” key and the “f” key and this will find the mentions of “aspartate” in that post and its comments
Here are some comments.
Malate-Aspartate Shuttle
I wonder if the reason supplemental aspartic acid may help some people comes from something called the Malate-Aspartate Shuttle. Now this does get complicated, but is links together many things we already know:-
· Disturbed calcium channel signaling and excess physical calcium in autistic brains
· Abnormal myelination
· Oxidative stress
· Mitochondrial abnormalities
· Microglial activation
· Disturbed BDNF, VEGF, CRH etc.
There is also a very interesting potential protective genetic variation (SLC25A12) that appears to protect some siblings from developing autism.
It appears that the excessive level of (cytosolic) Ca2+ increases the expression of AGC1 (the mitochondrial aspartate/ glutamate carrier number 1) via CREB (cAMP response element-binding protein).
CREB is a cellular transcription factor that regulates numerous genes including c-fos, BDNF, tyrosine hydroxylase, numerous neuropeptides (somatostatin, enkephalin, VGF, corticotropin-releasing hormone CRH, etc.), and genes involved in the circadian clock (PER1, PER2).
For instance, multiple stimuli induce the phosphorylation of the cyclic AMP-responsive element-binding protein (CREB) at Ser-133, which recruits the CREB-binding protein (CBP) to gene promoters. CBP catalyses the acetylation of histones, leading to changes in chromatin structure that facilitate the recruitment of RNA polymerase II and the activation of gene-transcription programs that promote synapse development12,15.
In addition to stimulating CREB-dependent gene transcription, neuronal activity-dependent calcium influx into neurons triggers the dephosphorylation of the transcription factor myocyte enhancer factor 2 (MEF2) by calcineurin, disrupting the association of MEF2 with histone deacetylases and leading to the recruitment of CBP and the stimulation of gene transcription26.
Neuronal activity that functions through CREB, MEF2 and multiple other activity-regulated transcription factors — including SRF, Fos27 and NPAS428 — induces the transcription of the genes encoding proteins that function directly at synapses, including Bdnf, Arc and Ube3A12,15.
For example, activity-regulated MEF2 by activating Arc suppresses the number of excitatory synapses26,29, whereas CREB and NPAS4, by activating Bdnf transcription, control the number of inhibitory synapses that form on excitatory neurons28,30.
CREB is down regulated in Alzheimer’s.
CREB proteins are activated by phosphorylation from various kinases, including PKA.
A number of existing drugs can raise or lower PKA levels in the body.
You would want to raise PKA in Alzheimer’s and some autism.
If AGC1 is over-activated this could be corrected using a PKA inhibitor, but this is easier said than done. PKA does very many different things.
PDE4 inhibitors used to treat asthma and COPD (Ibudilast and Daxas) raise PKA.
PDE4 inhibitors also reduce microglial activation. See the reference to gliosis below.
As our reader Nat knows, Ca2+ ions are the source of numerous problems in autism. The route problem seems to be too much calcium released from the stores within each cell (endoplasmic reticulum) and/or faulty voltage gated calcium channels allowing Ca2+ to enter from outside the cell.
The malate-aspartate shuttle “functions to move reducing equivalents into the mitochondrial matrix in the form of malate, whereas the major mitochondrial output through this complex is aspartate”. Specifically, AGC1 moves cytoplasmic glutamate into mitochondria, while moving mitochondrially synthesized aspartate out. Without AGC1, brain mitochondrial glutamate import and aspartate export are crippled. Studies with AGC1 knockout mice showed a dramatic drop in brain aspartate levels, with a concomitant reduction in NAA (N-acetylaspartate) synthesis.
AGC1 activation increases mitochondrial metabolism and oxidative stress
Reduction in N-acetylaspartate (NAA) synthesis causes hypomyelination.
N-acetylaspartate (NAA) is synthesized from acetyl CoA and aspartate. NAA is very important in the brain; too little NAA causes reduced myelination (hypomyelination) which is a feature of autism. Studies show that NAA is reduced in the brains of young people with autism, but interestingly not in older people with autism.
In autism we expect to see activated AGC1 and reduced NAA
It does look like NAA is something you do not want to be deficient in, but you also do not want too much. NAA is synthesized from acetyl CoA and aspartate and without going into details you might just say, why not just add some extra aspartate, which you can buy as an OTC powder.
There is a very more complex explanation, which comes back to aberrant calcium signaling being the demon of most autism. That would suggest:-
“Pharmacological treatments able to modulate extracellular Ca2+ entry, intracellular Ca2+ release from the endoplasmic reticulum or putative upstream immune mechanisms affecting either or both the pathways are, at least in principle, already available”
Overexpression of mitochondrial aspartate/glutamate carrier AGC1/ aralar1 (annoyingly, some research use the term Aralar1 while others use AGC1) encoded by encoded by the SLC25A12, caused by excess calcium Ca2+ either from intracellular release from stores in the endoplasmic reticulum or extracellular Ca2+. Recall the post about Gargus’ theory that a key nexus in autism is the IPR3 receptor, in the Endoplasmic Reticulum within each cell. He believes this is core defect in much autism.
Canavan disease is a rare condition caused by far too much NAA, a genetic error prevents the normal breakdown of NAA and this disrupts myelination leading to death in childhood.
Also part of the malate-aspartate shuttle we have GLutamate ASpartate Transporter (GLAST) or Excitatory Amino Acid Transporter 1 (EAAT1). We know that both glutamate transporters EAAT1 and EAAT2 are over-expressed in the cerebellum of post-mortem tissue from autism patients. Because EAAT expression is controlled in part by the extracellular concentration of glutamate, it is possible that the EAAT overexpression is due to the increased glutamate concentration seen in plasma and spectroscopic studies.
Glutamate & Glutamine
Since I have mentioned glutamate, note that numerous studies show high levels of glutamate but low levels of its precursor glutamine in autism. Gliosis is one possible explanation. This connects with those activated microglia which are another recurring feature of autism:-
“An increase in gliosis, which is characterized by enhanced activation of astrocytes and microglia, has been observed in the brains of individuals with autism. Interestingly, Ortinski et al. have reported that activated astrocytes downregulate the expression of glutamine synthetase, whereby glutamate is converted into glutamine, which in turn results in reduced glutamine coupled with elevated glutamate. In addition, glutaminase, another enzyme related to glutamate/glutamine metabolism via its conversion of glutamine into glutamate, has been shown to be upregulated in activated microglia. Thus, it is tempting to assume that the process of gliosis generation may be related to the etiology of autism, as mediated by activated astrocytes and/or activated microglia, which may disturb the regulation of certain types of enzymes and thereby alter the metabolism of glutamate/glutamine. Taken together with previous findings, our results demonstrating glutamate/glutamine abnormalities in the plasma of individuals with autism may be indicative of a gliosis process in the autistic brain.”
Amino Acids and the BBB
Amino acids are present inside the brain but some do not cross easily across the BBB. If they do not cross the BBB then taking a supplement is not going to help much.
This point is quite relevant because one study showed that arginine deprivation plays a key role in Alzheimer’s, but the mass media pointed out that taking arginine supplements is not going to help. Had they read this blog they would have known that if you want to increase arginine in the brain, you want to take citrulline. So citrulline for Alzheimer’s? well worth investigating.
The amino acid transporters that control the level in the brain are themselves disturbed in autism. So it may be that the level of many amino acids in autistic brains is disturbed, regardless of diet and what the blood/urine levels indicate.
Amino acid gradients between brain and plasma
Amino acid concentrations in plasma and brain. The plasma and CSF concentrations were grouped and the CSF-to-plasma ratio expressed as percent of the plasma. CSF concentrations are assumed to approximate brain ECF (54,102). With the exception of glutamine, the concentrations of all AAs in the ECF are much lower than the concentrations of AAs in plasma.
The concentrations of all naturally occurring AAs in the cerebral spinal fluid (CSF) (presumably similar to the extracellular fluid (ECF) of the brain), with the exception of glutamine, are ∼10% or less than the plasma concentrations (Fig. 4) (54). This situation cannot be explained by the consumption of AAs by brain because the arteriovenous differences across brain of most AAs are imperceptible (55–57), as are the arteriovenous differences of ammonia (NH4+), a byproduct of AA catabolism (58). These observations indicate that AAs leave the brain against a concentration gradient. From this it may be concluded that active (e.g., Na+-dependent) systems on the abluminal membrane have an important role in maintaining both homeostasis of brain AA content as well as the lower concentration in the extracellular fluid. Based on similar observations Bradbury wrote “there is a strong indirect argument in favor of the hypothesis that most AA must be moved against a concentration gradient from interstitial fluid to blood” (34).
The present view of the BBB is that cerebral endothelial cells participate actively in regulating the composition of brain extracellular fluid and the AA content of the brain. The luminal and abluminal membranes work in a complementary fashion with the Na+-dependent transport of AAs occurring at the abluminal membrane, and with facilitative transport at the luminal membrane, or, in the case of LNAAs, at both membranes (97).
Although the BBB determines the availability and therefore the brain content of essential AAs, astrocytes and neurons participate in maintaining the extracellular concentrations. Astrocytes and neurons have Na+-dependent transport systems capable of transporting NAAs and acidic AAs (98–100). These systems are actively involved in regulating AA concentrations in ECF and are especially important in the maintenance of low concentrations of neurotransmitter AAs such as glutamate, aspartate, and glycine. On the other hand, it now seems clear that the BBB also participates in the active regulation of brain ECF composition, and the abluminal membrane is especially important in this role.
Characteristics of L-citrulline transport through blood-brain barrier in the brain capillary endothelial cellline (TR-BBB cells)
Background
L-Citrulline is a neutral amino acid and a major precursor of L-arginine in the nitric oxide (NO) cycle. Recently it has been reported that L-citrulline prevents neuronal cell death and protects cerebrovascular injury, therefore, L-citrulline may have a neuroprotective effect to improve cerebrovascular dysfunction. Therefore, we aimed to clarify the brain transport mechanism of L-citrulline through blood-brain barrier (BBB) using the conditionally immortalized rat brain capillary endothelial cell line (TR-BBB cells), as an in vitro model of the BBB.
Conclusions
Our results suggest that transport of L-citrulline is mainly mediated by LAT1 in TR-BBB cells. Delivery strategy for LAT1-mediated transport and supply of L-citrulline to the brain may serve as therapeutic approaches to improve its neuroprotective effect in patients with cerebrovascular disease.
Our results demonstrated that L-citrulline transport might be mainly mediated by LAT1 in TR-BBB cells. Understanding the transport characteristics of L-citrulline to the brain through BBB might contribute to the transport strategy for L-citrulline as a potential therapeutic agent for cerebrovascular diseases such as brain ischemia.
Disturbed amino acid transporters and levels in blood/urine
Since we know that the amino acid transporters that carry amino acids across the blood brain barrier are disturbed in autism what is the relevance of blood/urine tests and standard reference levels? Unless you lest amino acid levels in spinal fluid (i.e. within the central nervous system) do lab tests really help? You certainly need to be aware of their limitations.
So as you can see even the summary is highly complicated.
Very many things associated with aspartate are messed up in autism and Tyler finds his son benefits from L-aspartate supplementation.
We saw in an earlier post that NT girls had three times the level of excreted aspartic acid than NT boys and that people with autism had very low levels of excreted aspartic acid.
If you could fix the underlying problem with elevated Ca2+ as proposed by Gargus, you would solve the AGC1/NAA problem. It may be that by supplementing L-aspartate you do have an effect on the malate-aspartate shuttle, even though there is no solid understanding of exactly how this occurs.
IP3R controls the release of calcium from the ER (Endoplasmic Reticulum inside each cell). In the brain, calcium is used to communicate information within and between neurons, and it activates a host of other cell functions, including ones regulating learning and memory, neuronal excitability and neurotransmitter release – areas known to be dysfunctional in ASD. It also causes the release of Protein Kinase C which then acts to change the function of numerous proteins (via phosphorylation) and trigger a series of signaling cascades.
N-acetylaspartate in autism spectrum disorders: Regional effects and relationship to FMRI activation
Rapid progress in our understanding of macrostructural abnormalities in autism spectrum disorders (ASD) has occurred in recent years. However, the relationship between the integrity of neural tissue and neural function has not been previously investigated. Single-voxel proton magnetic resonance spectroscopy and functional magnetic resonance imaging of an executive functioning task was obtained in 13 high functioning adolescents and adults with ASD and 13 age-matched controls. The ASD group showed significant reductions in N-acetyl aspartate (NAA) in all brain regions combined and a specific reduction in left frontal cortex compared to controls. Regression analyses revealed a significant group interaction effect between frontal and cerebellar NAA. In addition, a significant positive semi-partial correlation between left frontal lobe NAA and frontal lobe functional activation was found in the ASD group. These findings suggest that widespread neuronal dysfunction is present in high functioning individuals with ASD. Hypothesized developmental links between frontal and cerebellar vermis neural abnormalities were supported, in that impaired neuronal functioning in the vermis was associated with impaired neuronal functioning in the frontal lobes in the ASD group. Furthermore, this study provided the first direct evidence of the relationship between abnormal functional activation in prefrontal cortex and neuronal dysfunction in ASD.
This study extended prior work in this area by establishing that neural abnormalities, which have been identified using 1H-MRS predominantly in younger and likely lower functioning autistic individuals), may also be present in a higher functioning broadly inclusive ASD sample. None of the individuals in our sample had IQs in the mentally retarded range and the sample included individuals with diagnoses in the less severe end of the autism spectrum; approximately 43% of the sample was diagnosed as PDD-NOS or Asperger’s disorder.
Recent postmortem studies have identified neuroinflammation as a compelling potential pathological mechanism for reduced levels of NAA in individuals with ASD (Laurence and Fatemi, 2005; Vargas et al., 2005). Vargas and colleagues documented microglial activation in postmortem middle frontal gyrus, anterior cingulate, and cerebellar tissue, and in cerebral spinal fluid (CSF) of children and adults with autism. Laurence and Fatemi found increased glial fibrillary acidic protein in area 9, area 40 and the cerebellum in autism. Ongoing neuroinflammatory processes may produce alterations in brain tissue that would result in reduced NAA (secondary to cell loss or damage), as was observed in the current study.
We found that high functioning individuals with ASD have reduced levels of NAA compared to age-matched controls. The most consistent area of abnormality was observed in the left middle frontal gyrus. In addition, the relationship between level of NAA in the frontal lobes and NAA in the cerebellar vermis differed between groups. These findings of biochemical alterations in ASD may reflect early brain growth dysregulation and ongoing neuroinflammatory processes. Reduced levels of NAA in ASD were also directly related to neurofunctional abnormalities observed in the FMRI study of executive functioning. This study is the first to directly link functional activation to neuronal integrity in ASD, and provides direct evidence that primary neuronal dysfunction, in addition to hypothesized aberrant neural connectivity leads to neurofunctional impairment in high functioning individuals with autism spectrum disorders.
Atypical trajectory of brain growth in autism spectrum disorders (ASDs) has been recognized as a potential etiology of an atypical course of behavioral development. Numerous neuroimaging studies have focused on childhood to investigate atypical age-related change of brain structure and function, because it is a period of neuron and synapse maturation. Recent studies, however, have shown that the atypical age-related structural change of autistic brain expands beyond childhood and constitutes neural underpinnings for lifelong difficulty to behavioral adaptation. Thus, we examined effects of aging on neurochemical aspects of brain maturation using 3-T proton magnetic resonance spectroscopy (1H-MRS) with single voxel in the medial prefrontal cortex (PFC) in 24 adult men with non-medicated high-functioning ASDs and 25 age-, IQ- and parental-socioeconomic-background-matched men with typical development (TD). Multivariate analyses of covariance demonstrated significantly high N-acetylaspartate (NAA) level in the ASD subjects compared with the TD subjects (F=4.83, P=0.033). The low NAA level showed a significant positive correlation with advanced age in the TD group (r=−0.618, P=0.001), but was not evident among the ASD individuals (r=0.258, P=0.223). Fisher's r-to-z transformation showed a significant difference in the correlations between the ASD and TD groups (Z=−3.23, P=0.001), which indicated that the age–NAA relationship was significantly specific to people with TD. The current 1H-MRS study provided new evidence that atypical age-related change of neurochemical aspects of brain maturation in ASD individuals expands beyond childhood and persists during adulthood.
In conclusion, the present findings demonstrated an absence of typical age-related medial prefrontal NAA decrement in ASD individuals during adulthood. Such an atypical relationship between age and NAA levels might contribute to a significant NAA increase in the ASD subjects compared with the TD adults. Although future studies should examine potential localization of atypical age-related NAA change and longitudinal course of autistic NAA abnormality, the current study has provided a new suggestion with regard to a role of atypical age-related NAA changes in the pathophysiology of ASD.
An interesting way to increase NAA:-
Supplement 'boosts' brain power
An interesting way to increase NAA:-
Supplement 'boosts' brain power
"They were asked to be more active and cut down on unhealthy snacks and fizzy drinks.
At the same time, they were given two capsules a day of the VegEPA supplement, which contains an omega-3 fatty acid called EPA.
Tests done at the end of the three-month study found the children showed an increase in reading age of well over a year, their handwriting became neater and more accurate and they paid more attention in class.
Brain scans which identified a chemical called N-Acetylaspartate (NAA) which is linked to the growth of nerve fibres in the brain also showed dramatic changes, said Professor Puri.
Although the children were encouraged to change their diet, there was no evidence they did this to any great extent, suggesting the improvements in the children were a result of the supplement.
Brain growth
"In three months you might expect to see a small NAA increase.
"But we saw as much growth as you would normally see in three years.
"It was as if these were the brains of children three years older. It means you have more connections and greater density of nerve cells, in the same way a tree grows more branches."
The boys in the study showed the most improvement, he added.
Omega-3 fatty acids are found naturally in oily fish such as mackerel, salmon, herring and tuna or seeds such as flax, pumpkin and hemp.
A systematic review of fish oil supplements in children published by the Food Standards Agency last year found there were too many inconsistencies in current evidence to come to any conclusion.
Professor Puri said he believed that it was EPA specifically which conferred the benefits which was why studies of fish oil supplements which also contain a fatty acid called DHA showed confusing results.
He is now planning to carry out a larger placebo-controlled study.
Professor Robert Grimble, professor of nutrition at the University of Southampton said it was vital that larger studies were done to clarify the issue.
"My view is we can't come to any clear conclusion until a proper trial is done.
"These small bits of weak data just confuse the public. The FSA looked at this very carefully and I wouldn't contradict that until we have more evidence."
N-Acetylaspartate (NAA) is employed as a non-invasive marker for neuronal health using proton magnetic resonance spectroscopy (MRS). This utility is afforded by the fact that NAA is one of the most concentrated brain metabolites and that it produces the largest peak in MRS scans of the healthy human brain. NAA levels in the brain are reduced proportionately to the degree of tissue damage after traumatic brain injury (TBI) and the reductions parallel the reductions in ATP levels. Because NAA is the most concentrated acetylated metabolite in the brain, we have hypothesized that NAA acts in part as an extensive reservoir of acetate for acetyl coenzyme A synthesis. Therefore, the loss of NAA after TBI impairs acetyl coenzyme A dependent functions including energy derivation, lipid synthesis, and protein acetylation reactions in distinct ways in different cell populations. The enzymes involved in synthesizing and metabolizing NAA are predominantly expressed in neurons and oligodendrocytes, respectively, and therefore some proportion of NAA must be transferred between cell types before the acetate can be liberated, converted to acetyl coenzyme A and utilized. Studies have indicated that glucose metabolism in neurons is reduced, but that acetate metabolism in astrocytes is increased following TBI, possibly reflecting an increased role for non-glucose energy sources in response to injury. NAA can provide additional acetate for intercellular metabolite trafficking to maintain acetyl CoA levels after injury. Here we explore changes in NAA, acetate, and acetyl coenzyme A metabolism in response to brain injury
N-acetylaspartate (NAA) is one of the most abundant brain metabolites and is highly concentrated in neurons, but it remains to be determined why neurons synthesize so much of this particular acetylated amino acid. Early research implicated NAA in lipid synthesis in the brain, especially during postnatal myelination.
NAA is synthesized from acetyl CoA and aspartate, and because of the exceptionally high concentration in the human brain (~10 mM) some proportion of acetyl CoA must be utilized to maintain NAA levels
The primary mitochondrial aspartate-glutamate carrier expressed in brain, heart, skeletal muscle, and several other tissues is known as aralar1 (Del Arco et al., 2002), which is part of a larger complex that comprises the so-called mitochondrial malate-aspartate shuttle. The malate-aspartate shuttle functions to move reducing equivalents into the mitochondrial matrix in the form of malate, whereas the major mitochondrial output through this complex is aspartate. Specifically, aralar1 moves cytoplasmic glutamate into mitochondria, while moving mitochondrially synthesized aspartate out. Without aralar1, brain mitochondrial glutamate import and aspartate export are crippled. Studies with aralar1 knockout mice showed a dramatic drop in brain aspartate levels, with a concomitant reduction in NAA synthesis
The connection between a lack of aralar1 expression and dramatically reduced NAA synthesis has at least two potential explanations. First, as suggested by Jalil et al. (2005) it could be due to the lack of mitochondrial aspartate output, which in turn would limit substrate availability for microsomal Asp-NAT to synthesize NAA. The other possible explanation is that the lack of glutamate uptake into neuronal mitochondria prevents intramitochondrial aspartate synthesis via the aspartate aminotransferase reaction which converts glutamate and oxaloacetate into α-ketoglutarate and aspartate. In this case the lack of intramitochondrial aspartate synthesis would be the limiting factor in NAA synthesis, leading to decreases in NAA levels. It is also possible that both of these mechanisms are responsible for the large drop in NAA levels observed in aralar1-deficient mice.
One of the more interesting outcomes of aralar1 deficiency in addition to the large decrease in brain NAA levels is hypomyelination (Jalil et al., 2005; Wibom et al., 2009). The hypomyelination is hypothesized to result from the lack of availability of NAA and this conclusion is supported by the fact that galactocerebrosides, one of the myelin lipid classes that are reduced in Canavan disease
The more NAA the more creative?
A broadly accepted definition of creativity refers to the production of something both novel and useful within a given social context. Studies of patients with neurological and psychiatric disorders and neuroimaging studies of healthy controls have each drawn attention to frontal and temporal lobe contributions to creativity. Based on previous magnetic resonance (MR) spectroscopy studies demonstrating relationships between cognitive ability and concentrations of N-acetyl-aspartate (NAA), a common neurometabolite, we hypothesized that NAA assessed in gray and white matter (from a supraventricular slab) would relate to laboratory measures of creativity. MR imaging and divergent thinking measures were obtained in a cohort of 56 healthy controls. Independent judges ranked the creative products of each participant, from which a “Composite Creativity Index” (CCI) was created. Different patterns of correlations between NAA and CCI were found in higher verbal ability versus lower verbal ability participants, providing neurobiological support for a critical “threshold” regarding the relationship between intelligence and creativity. To our knowledge, this is the first report assessing the relationship between brain chemistry and creative cognition, as measured with divergent thinking, in a cohort comprised exclusively of normal, healthy participants.
Exactly how does variation in NAA concentration affect brain activity in normals? A rapidly growing literature links NAA to intelligence, working memory, attention, and memory both in health and disease (Ross and Sachdev, 2004), but the mechanisms underlying these relationships remain elusive. In the adult brain, there is substantial evidence that NAA is a marker of mitochondrial functioning, is involved in myelin lipid turnover, participates in axonglial signaling, and may be involved in brain nitrogen balance (Moffett et al., 2007). Substantial basic research has yet to unravel the complex role that NAA plays in higher cognitive functioning, including creativity, beyond mere correlation.
NAA is synthesized from acetyl CoA and aspartate, so you would not want to be short of either.
From your high school biology you may recall a process called aerobic respiration which is how you mitochondria convert Glucose (fuel) into ATP (energy).
As you can see one step in this process is the production of Acetyl CoA.
If you are breathing, you must be making Acetyl CoA. So perhaps a little extra aspartic acid might help produce more NAA.
In extreme cases a lack of the mitochondrial carrier protein Aralar1 will causes very low levels of NAA.
Canavan disease is a rare condition caused by too much NAA, a genetic error prevents the normal breakdown of NAA and this disrupts myelination leading to death in childhood.
Even after all that, we do not know for sure why supplementing Aspartate works for Tyler. Making more NAA would be a nice explanation but Aspartate does stimulate NMDA receptors.
Autism is a severe developmental disorder, whose pathogenetic underpinnings are still largely unknown. Temporocortical gray matter from six matched patient-control pairs was used to perform post-mortem biochemical and genetic studies of the mitochondrial aspartate/glutamate carrier (AGC), which participates in the aspartate/malate reduced nicotinamide adenine dinucleotide shuttle and is physiologically activated by calcium Ca2+. AGC transport rates were significantly higher in tissue homogenates from all six patients, including those with no history of seizures and with normal electroencephalograms prior to death. This increase was consistently blunted by the Ca2+ chelator ethylene glycol tetraacetic acid; neocortical Ca2+ levels were significantly higher in all six patients; no difference in AGC transport rates was found in isolated mitochondria from patients and controls following removal of the Ca2+-containing post mitochondrial supernatant. Expression of AGC1, the predominant AGC isoform in brain, and cytochrome c oxidase activity were both increased in autistic patients, indicating an activation of mitochondrial metabolism. Furthermore, oxidized mitochondrial proteins were markedly increased in four of the six patients. Variants of the AGC1-encoding SLC25A12 gene were neither correlated with AGC activation nor associated with autism-spectrum disorders in 309 simplex and 17 multiplex families, whereas some unaffected siblings may carry a protective gene variant. Therefore, excessive Ca2+ levels are responsible for boosting AGC activity, mitochondrial metabolism and, to a more variable degree, oxidative stress in autistic brains. AGC and altered Ca2+ homeostasis play a key interactive role in the cascade of signaling events leading to autism: their modulation could provide new preventive and therapeutic strategies.
Evidence linking altered energy metabolism to autistic disorder has been available for some time, including peripheral markers, such as increased plasma lactate levels, and rare instances of association between respiratory chain disorders and autism. Interest in assessing the role of mitochondria
in this disorder has been revitalized by the association between autism and variants of the SLC25A12 gene, which encodes the predominant isoform of the mitochondrial aspartate (asp)/glutamate (glu) carrier (AGC) in brain.15,16 AGC belongs to a family of integral proteins that catalyze the transport of metabolites and cofactors across the inner mitochondrial membrane.17 In particular, AGC is important in energy metabolism
by transporting glutamate into mitochondria in exchange for matrix aspartate, a key regulatory step in the malate/aspartate reduced nicotinamide adenine dinucleotide (NADH) shuttle.18,19 Its two
isoforms, AGC1 and AGC2, also named aralar(1) and citrin, are encoded by the SLC25A12 and SLC25A13 genes, located on human chromosomes 2q24 and 7q21.3, respectively.19 AGC1 and AGC2 expression overlaps during early prenatal life, but diverges beginning in late gestation and into adulthood, with AGC1 predominantly expressed in the brain, heart and skeletal muscle, whereas AGC2 is mainly expressed in liver and kidney.20,21 In the CNS, AGC1 is highly expressed in neurons, whereas glial cells express both isoforms at much lower levels.20,21 Importantly, AGC activity is regulated by intracellular calcium (Ca2+) through four ‘EF-hand’ domains22 located at its N-terminus, hanging into the intermembrane
space.18,19 As Ca2+ concentrations in the mitochondrial intermembrane space and cytosol are in equilibrium, cytosolic Ca2+ can rapidly activate AGC transport, thereby increasing the NADH/NAD ratio in the mitochondrial matrix and consequently boosting electron flow through the respiratory
chain and adenosine triphosphate (ATP) generation by oxidative phosphorylation.18,19,23 Through this mechanism, AGC1 is important in the transduction of small Ca2+ signals to neuronal mitochondria.19 An
excessive amplitude and/or duration of Ca2+ spikes leading to AGC activation can, however, contribute to the formation of reactive oxygen species (ROS) and to oxidative stress.24 Genetic and/or environmental
factors could thus interfere with neuronal ATP production and with oxidative stress by affecting the AGC1 carrier, either directly or through Ca2+ homeostasis.
===================
Results
AGC activity is boosted by excessive Ca2+ levels in autistic brains
AGC activity, normalized by CS activity to adjust for differences in absolute mitochondria tissue content, displays a prominent threefold increase in neocortical homogenates from nonsyndromic autistic patients compared to matched controls in all six pairs (Wilcoxon’s test: Z=
2.201, P<0 .05="" 1a="" a="" agc1="" ca="" figure="" increase="" instead="" left="" levels="" modest="" nonsignificant="" only="" protein="" s1="" show="" sup="" upplementary="" very="">2+
chelation by EGTA reduces asp/glu exchange rates to a much larger extent in patients than in controls (2.1- vs 0.35-fold, respectively), reducing case–control differences to only 36.1% (Figure 1a, middle). No difference between patients and controls is anymore detectable upon reconstitution of protein extracts from isolated mitochondria (P=0.17; Figure 1a, right). These results strongly point toward excessive Ca2+ concentrations as most likely responsible for increased asp/glu exchange rates in the brains of autistic patients.
AGC activation increases mitochondrial metabolism and oxidative stress
By increasing the availability of reducing equivalents in the mitochondrial matrix through AGC, enhanced cytosolic Ca2+ can be predicted to steadily boost mitochondrial metabolism and oxidative phosphorylation.18,19,23 Indeed, transcript amounts of the mitochondrial phosphate carrier (PiC), AGC1, and AGC2 (expressed at much lower levels compared to AGC1), are all increased (Supplementary Figure S2). Also COX activity is elevated to a similar extent in all six autistic patients compared to their matched controls (P<0 .05="" 3a="" figure="" span="">
No evidence of SLC25A12 gene contributions to autism vulnerability
Sequencing of the AGC1-encoding SLC25A12 cDNA and genomic DNA in these same six case–control pairs does not detect any nonsynonymous coding mutation
Figure 2 Calcium levels measured directly in the post mitochondrial supernatant by fluorimetry. (a) Calcium concentrations are significantly higher in the neocortical tissue of autism-spectrum disorder (ASD) patients compared to matched controls
A SLC25A12 gene variant may confer protection in unaffected siblings
Single-marker analyses point toward the possible existence of a protective SLC25A12 gene variant preferentially transmitted from heterozygous parents to unaffected siblings of autistic patients.
The allele frequency of this haplotype is estimated at approximately 23–26% (Table 2b), making it a relatively common variant among unaffected siblings.
This study reports increased asp/glu exchange rates and significantly higher Ca2+ concentrations in postmortem neocortical tissue specimens of six nonsyndromic autistic patients compared to age-, sex- and PMI-matched controls. Altogether, our results strongly support excessive Ca2+ levels as primarily responsible for the observed activation of asp/glu exchange rates, whereas genetic contributions appear neither widespread nor necessary, at least in our postmortem and genetic samples.
Most importantly, direct measurements of neocortical Ca2+ concentrations clearly demonstrate a significant elevation of neocortical Ca2+ levels in all autistic patients compared to controls (Figure 2a)
Increased AGC transport rates, COX activities and Ca2+ levels consistently recorded in all six neocortical specimens from ASD patients crossvalidate each other, confirming the reliability and biological significance of these findings
In summary, altered Ca2+ homeostasis is the only factor shared by all autistic cortical tissue samples (Figure 2a), able to boost AGC activity,18,19,23 and previously linked to the pathogenesis of autism per se.
The existence of altered Ca2+ signaling in autism has been suggested in recent years by several lines of research.42 Gain-of-function mutations in the L-type voltage-gated Ca2+ channel Cav1.2 (CACNA1C) cause Timothy syndrome, a multisystem disorder including mental retardation and autism.43 Similarly, mutations in the L-type voltage-gated Ca2+ channel Cav1.4 (CACNA1F) cause the incomplete form of X-linked congenital stationary night blindness (CSNB2): gain-of-function mutations cause CSNB2 frequently accompanied by cognitive impairment and either autism or epilepsy, whereas CSNB2 due to lossof-function mutations is not accompanied by these symptoms.44 All of these gain-of-function mutations prevent voltage-dependent channel inactivation leading to excessive Ca2+ influx. Also mutations indirectly yielding increased cytosolic Ca2+ levels or amplifying intracellular Ca2+ signaling by hampering Ca2+-activated negative feedback mechanisms have been found associated with autism.42,45 The bioelectrical instability resulting from these mutations nicely parallels the high prevalence of seizures and/or EEG abnormalities present among autistic individuals
We are currently in the process of correlating AGC activity and levels of oxidative stress with markers of immune activation, measured in the same tissue specimens assessed in this study.
The present results can potentially pave the path to targeted preventive and therapeutic strategies. One important example is represented by thimerosal, an ethyl-mercury compound used as a preservative in vaccines.59,60 Thimerosal has drawn attention following initial anecdotal reports by some parents linking vaccinations to behavioral regression and to the onset of autism in their child within a matter of days or few weeks. Thimerosal is a Ca2+-mobilizing agent, capable of releasing Ca2+ from intracellular stores and increasing Ca2+ entry.61 Despite its short half-life compared to inorganic mercury, it undergoes preferential accumulation in the CNS, affecting the microglia and producing strain-dependent neurotoxic effects in rodents.62,63 This strain dependency, in conjunction with the present data, suggests that thimerosal could contribute to produce an unbalanced Ca2+ homeostasis in genetically vulnerable individuals. Indeed, a postnatal exposure to thimerosal is not reconcilable with the prenatal onset of neurodevelopmental anomalies leading to autism. Also large retrospective epidemiological studies confirm that thimerosal neither causes autism, nor provides large-scale contributions to its pathogenesis.2,60 However, our results suggest that thimerosal could conceivably precipitate an abrupt onset in a subset of children who would have otherwise developed autistic symptoms more insidiously. At the same time, we cannot exclude that thimerosal and other Ca2+-mobilizing environmental factors could also push genetically vulnerable individuals along the autism-spectrum toward more severe forms of the disease. On the basis of the present study, the elimination of thimerosal from vaccines, undertaken in the United States and Canada, is a well-justified safety measure.
Pharmacological treatments able to modulate extracellular Ca2+ entry, intracellular Ca2+ release from the endoplasmic reticulum or putative upstream immune mechanisms affecting either or both the pathways are, at least in principle, already available. However, caution should be exercised in translating the present findings into therapeutic interventions prior to at least one replication in an independent cohort of brain samples and to assessments of Ca2+ homeostasis in vivo.
Pharmacologically reducing Ca2+ entry into cells or blunting the oxidative damage produced by AGC activation seemingly represent more amenable and less dangerous therapeutic strategies. It is nonetheless difficult to predict the actual efficacy of treatments initiated during childhood on pathogenetic mechanisms active since early prenatal development. In this regard, the identification and functional characterization of protective SLC25A12 gene variants, if existent, could provide additional critical information on the contribution of AGC activation and oxidative stress to autism pathogenesis.
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This study reports increased asp/glu exchange rates and significantly higher Ca2+ concentrations in postmortem neocortical tissue specimens of six nonsyndromic autistic patients compared to age-, sex- and PMI-matched controls. Altogether, our results strongly support excessive Ca2+ levels as primarily responsible for the observed activation of asp/glu exchange rates, whereas genetic contributions appear neither widespread nor necessary, at least in our postmortem and genetic samples.
Our results point toward the possible existence of a protective SLC25A12 gene variant in a sizable group of unaffected siblings. This cannot be conclusively demonstrated with our sample size of 104 families including one or more unaffected sibling.
On the other hand, our results would provide further support for key contributions of Ca2+-triggered AGC1 activity to autism pathogenesis. Increased asp/glu exchange rates provide more reducing equivalents (that is, NADH) to the respiratory chain and could foster oxidative stress,24 which was previously found increased measuring peripheral markers in autism.55 Also overexpression of AGC1 in cell culture has been recently found associated with a biphasic response, characterized initially by enhanced neurite outgrowth, which subsequently slows down and ends in early cell death.56 This response is seemingly compatible with an initial overproduction of ATP paralleled by a progressive build up of oxidative stress leading to cell damage. Oxidative stress, in addition to lipid and protein oxidation,55 can also produce genomic instability and stimulate cell cycle progression, pathophysiological events likely to be important in autism pathogenesis9,57,58 In this regard, the interindividual variability in oxidative damage reported in our study is not at all surprising, as the balance between ROS production and antioxidant agents leaves ample room for genetic and environmental influences
The present results can potentially pave the path to targeted preventive and therapeutic strategies. One important example is represented by thimerosal, an ethyl-mercury compound used as a preservative in vaccines.59,60 Thimerosal has drawn attention following initial anecdotal reports by some parents linking vaccinations to behavioral regression and to the onset of autism in their child within a matter of days or few weeks. Thimerosal is a Ca2+-mobilizing agent, capable of releasing Ca2+ from intracellular stores and increasing Ca2+ entry.61 Despite its short half-life compared to inorganic mercury, it undergoes preferential accumulation in the CNS, affecting the microglia and producing strain-dependent neurotoxic effects in rodents.62,63 This strain dependency, in conjunction with the present data, suggests that thimerosal could contribute to produce an unbalanced Ca2+ homeostasis in genetically vulnerable individuals. Indeed, a postnatal exposure to thimerosal is not reconcilable with the prenatal onset of neurodevelopmental anomalies leading to autism.
Also large retrospective epidemiological studies confirm that thimerosal neither causes autism, nor provides large-scale contributions to its pathogenesis. 2,60 However, our results suggest that thimerosal could conceivably precipitate an abrupt onset in a subset of children who would have otherwise developed autistic symptoms more insidiously. At the same time, we cannot exclude that thimerosal and other Ca2+-mobilizing environmental factors could also push genetically vulnerable individuals along the autism-spectrum toward more severe forms of the disease. On the basis of the present study, the elimination of thimerosal from vaccines, undertaken in the United States and Canada, is a well-justified safety measure.
Pharmacological treatments able to modulate extracellular Ca2+ entry, intracellular Ca2+ release from the endoplasmic reticulum or putative upstream immune mechanisms affecting either or both the pathways are, at least in principle, already available. However, caution should be exercised in translating the present findings into therapeutic interventions prior to at least one replication in an independent cohort of brain samples and to assessments of Ca2+ homeostasis in vivo. In particular, our findings in no way support the use of Ca2+ chelation as a therapeutic approach in autism. Ca2+ chelation has not only been purported of benefit in few anecdotal reports and small-sized open trials, but also carries a substantial risk to produce hypocalcemia, resulting in recent deaths of autistic children.64,65 Pharmacologically reducing Ca2+ entry into cells or blunting the oxidative damage produced by AGC activation seemingly represent more amenable and less dangerous therapeutic strategies. It is nonetheless difficult to predict the actual efficacy of treatments initiated during childhood on pathogenetic mechanisms active since early prenatal development. In this regard, the identification and functional characterization of protective SLC25A12 gene variants, if existent, could provide additional critical information on the contribution of AGC activation and oxidative stress to autism pathogenesis.
Solute carrier family 1 (glial high-affinity glutamate transporter), member 3, also known as SLC1A3, is a protein that, in humans, is encoded by the SLC1A3 gene.[5] SLC1A3 is also often called the GLutamate ASpartate Transporter (GLAST) or Amino Acid Transporter 1 (EAAT1) Excitatory.
GLAST is predominantly expressed in the plasma membrane, allowing it to remove glutamate from the extracellular space.[6] It has also been localized in the inner mitochondrial membrane as part of the malate-aspartate shuttle.[7]
VERY thorough but rather complex
N-Acetylaspartate (NAA) is employed as a non-invasive marker for neuronal health using proton magnetic resonance spectroscopy (MRS). This utility is afforded by the fact that NAA is one of the most concentrated brain metabolites and that it produces the largest peak in MRS scans of the healthy human brain. NAA levels in the brain are reduced proportionately to the degree of tissue damage after traumatic brain injury (TBI) and the reductions parallel the reductions in ATP levels. Because NAA is the most concentrated acetylated metabolite in the brain, we have hypothesized that NAA acts in part as an extensive reservoir of acetate for acetyl coenzyme A synthesis. Therefore, the loss of NAA after TBI impairs acetyl coenzyme A dependent functions including energy derivation, lipid synthesis, and protein acetylation reactions in distinct ways in different cell populations. The enzymes involved in synthesizing and metabolizing NAA are predominantly expressed in neurons and oligodendrocytes, respectively, and therefore some proportion of NAA must be transferred between cell types before the acetate can be liberated, converted to acetyl coenzyme A and utilized. Studies have indicated that glucose metabolism in neurons is reduced, but that acetate metabolism in astrocytes is increased following TBI, possibly reflecting an increased role for non-glucose energy sources in response to injury. NAA can provide additional acetate for intercellular metabolite trafficking to maintain acetyl CoA levels after injury. Here we explore changes in NAA, acetate, and acetyl coenzyme A metabolism in response to brain injury.
N-acetylaspartate (NAA) is one of the most abundant brain metabolites and is highly concentrated in neurons, but it remains to be determined why neurons synthesize so much of this particular acetylated amino acid. Early research implicated NAA in lipid synthesis in the brain, especially during postnatal myelination.
Subsequently it was discovered that mutations in the gene for the enzyme that deacetylates NAA, known as aspartoacylase or ASPA, lead to the fatal neurodegenerative disorder known as Canavan disease.
One line of research has focused on the lack of catabolism leading to a toxic buildup of NAA in the brain as the primary etiological component. Another line of research has suggested that the lack of catabolism results in an acetate deficiency in oligodendrocytes during brain development that subsequently limits acetyl coenzyme A (acetyl CoA) availability during this critical period of myelination. There is experimental support for both mechanisms, and it is possible that both are operative.
The loss of NAA after TBI is paralleled by a loss of ATP, acetyl CoA, and other metabolites associated with energy metabolism (Vagnozzi et al., 2007) indicating a substantial impact on neuroenergetics. The connections between NAA and brain energy metabolism are not entirely clear
NAA is synthesized from acetyl CoA and aspartate, and because of the exceptionally high concentration in the human brain (~10 mM) some proportion of acetyl CoA must be utilized to maintain NAA levels, and that proportion may change with brain injury. Signoretti and colleagues have shown that severe brain injury results in a very rapid drop in NAA levels that is paralleled by a similar reduction in ATP levels, suggesting that NAA is utilized rapidly in response to injury
NAA Synthesis and the Mitochondrial Malate-Aspartate Shuttle
The malate-aspartate shuttle functions to move reducing equivalents into the mitochondrial matrix in the form of malate, whereas the major mitochondrial output through this complex is aspartate. Specifically, aralar1 moves cytoplasmic glutamate into mitochondria, while moving mitochondrially synthesized aspartate out. Without aralar1, brain mitochondrial glutamate import and aspartate export are crippled.
The connection between a lack of aralar1 expression and dramatically reduced NAA synthesis has at least two potential explanations. First, as suggested by Jalil et al. (2005) it could be due to the lack of mitochondrial aspartate output, which in turn would limit substrate availability for microsomal Asp-NAT to synthesize NAA. The other possible explanation is that the lack of glutamate uptake into neuronal mitochondria prevents intramitochondrial aspartate synthesis via the aspartate aminotransferase reaction which converts glutamate and oxaloacetate into α-ketoglutarate and aspartate. In this case the lack of intramitochondrial aspartate synthesis would be the limiting factor in NAA synthesis, leading to decreases in NAA levels. It is also possible that both of these mechanisms are responsible for the large drop in NAA levels observed in aralar1-deficient mice. One of the more interesting outcomes of aralar1 deficiency in addition to the large decrease in brain NAA levels is hypomyelination
NAA and Lipid Synthesis
Neurons provide key metabolites to their ensheathing oligodendrocytes for the purposes of myelination, myelin maintenance, and myelin sheath repair, including choline, palmitate, acetate, phosphate, and ethanolamine (Ledeen, 1984). NAA is among the trophic neuronally derived metabolites that are transferred to oligodendrocytes for use in myelination and myelin repair.
The synthesis of NAA requires the utilization of existing acetyl CoA and therefore NAA synthesis consumes a portion of brain acetyl CoA stores. Therefore NAA may be acting as a storage and transport form of acetate in the CNS that can be used for subsequent de novo synthesis of acetyl CoA, especially in oligodendrocytes
Inhibit AGC1?
The mitochondrial aspartate-glutamate carrier isoform 1 (AGC1) catalyzes a Ca2+-stimulated export of aspartate to the cytosol in exchange for glutamate, and is a key component of the malate-aspartate shuttle which transfers NADH reducing equivalents from the cytosol to mitochondria. By sustaining the complete glucose oxidation, AGC1 is thought to be important in providing energy for cells, in particular in the CNS and muscle where this protein is mainly expressed. Defects in the AGC1 gene cause AGC1 deficiency, an infantile encephalopathy with delayed myelination and reduced brain N-acetylaspartate (NAA) levels, the precursor of myelin synthesis in the CNS. Here, we show that undifferentiated Neuro2A cells with down-regulated AGC1 display a significant proliferation deficit associated with reduced mitochondrial respiration, and are unable to synthesize NAA properly. In the presence of high glutamine oxidation, cells with reduced AGC1 restore cell proliferation, although oxidative stress increases and NAA synthesis deficit persists. Our data suggest that the cellular energetic deficit due to AGC1 impairment is associated with inappropriate aspartate levels to support neuronal proliferation when glutamine is not used as metabolic substrate, and we propose that delayed myelination in AGC1 deficiency patients could be attributable, at least in part, to neuronal loss combined with lack of NAA synthesis occurring during the nervous system development.
Abstract
Ca2+ signaling in mitochondria is important to tune mitochondrial function to a variety of extracellular stimuli. The main mechanism is Ca2+ entry in mitochondria via the Ca2+ uniporter followed by Ca2+ activation of three dehydrogenases in the mitochondrial matrix. This results in increases in mitochondrial NADH/NAD ratios and ATP levels and increased substrate uptake by mitochondria. We review evidence gathered more than 20 years ago and recent work indicating that substrate uptake, mitochondrial NADH/NAD ratios, and ATP levels may be also activated in response to cytosolic Ca2+ signals via a mechanism that does not require the entry of Ca2+ in mitochondria, a mechanism depending on the activity of Ca2+-dependent mitochondrial carriers (CaMC). CaMCs fall into two groups, the aspartate-glutamate carriers (AGC) and the ATP-Mg/Pi carriers, also named SCaMC (for short CaMC). The two mammalian AGCs, aralar and citrin, are members of the malate-aspartate NADH shuttle, and citrin, the liver AGC, is also a member of the urea cycle. Both types of CaMCs are activated by Ca2+ in the intermembrane space and function together with the Ca2+ uniporter in decoding the Ca2+ signal into a mitochondrial response.
www.uniprot.org/uniprot/Q12482
Calcium-dependent mitochondrial aspartate and glutamate carrier. Transport of glutamate in mitochondria is required for mitochondrial transamination reactions and ornithine synthesis. Plays also a role in malate-aspartate NADH shuttle, which is critical for growth on acetate and fatty acids.
The aspartate/glutamate carrier isoform 1 is an essential mitochondrial transporter that exchanges intramitochondrial aspartate and cytosolic glutamate across the inner mitochondrial membrane. It is expressed in brain, heart and muscle and is involved in important biological processes, including myelination. However, the signals that regulate the expression of this transporter are still largely unknown. In this study we first identify a CREB binding site within the aspartate/glutamate carrier gene promoter that acts as a strong enhancer element in neuronal SH-SY5Y cells. This element is regulated by active, phosphorylated CREB protein and by signal pathways that modify the activity of CREB itself and, most noticeably, by intracellular Ca2+ levels. Specifically, aspartate/glutamate carrier gene expression is induced via CREB by forskolin while it is inhibited by the PKA inhibitor, H89. Furthermore, the CREB-induced activation of gene expression is increased by thapsigargin, which enhances cytosolic Ca2+, while it is inhibited by BAPTA-AM that reduces cytosolic Ca2+ or by STO-609, which inhibits CaMK-IV phosphorylation. We further show that CREB-dependent regulation of aspartate/glutamate carrier gene expression occurs in neuronal cells in response to pathological (inflammation) and physiological (differentiation) conditions. Since this carrier is necessary for neuronal functions and is involved in myelinogenesis, our results highlight that targeting of CREB activity and Ca2+ might be therapeutically exploited to increase aspartate/glutamate carrier gene expression in neurodegenerative diseases.
Studies in animal models have highlighted the relevance of AGC1 in the physiology of neurons. AGC1 knockout mice showed a dramatic drop in brain aspartate levels, with a concomitant reduction in N-acetylaspartate (NAA) synthesis and hypomyelination (Jalil et al., 2005). The connection between lack of AGC1 and drop in NAA synthesis may due to the lack of mitochondrial aspartate output, which in turn would limit availability of NAA-derived acetate needed for lipid biosynthesis resulting in hypomyelination. Numerous studies have indeed demonstrated that acetate moieties of NAA are incorporated into brain lipids during the development of the central nervous system, hence strongly suggesting that AGC1 may be crucially involved in the myelination). In support of this conclusion, children harboring mutations of the SLC25A12 gene display severe developmental delay, epilepsy, hypotonia hallmarked by hypomyelination and decreased NAA in the brain (Wibom et al., 2009; Falk et al., 2014). The chromosomal region containing the gene encoding AGC1 has also been identified as a putative autism susceptibility locus (Ramoz et al., 2004; Turunen et al., 2008; Palmieri et al., 2010). In addition, interest in the involvement of mitochondria in neurodegenerative and neuroinflammamtory disorders, such as Parkinson's and Alzheimer's disease, and multiple sclerosis is emerging (Lin and Beal, 2006)
Despite the well-established role of NAA in myelin biosynthesis, it is still unknown in which subcellular compartment the biosynthesis occurs. Different studies have provided evidence that the aspartate-N-acetyltransferase (Asp-NAT), the enzyme that catalyzes the biosynthesis of NAA, is localized in the mitochondria (Patel and Clark, 1979; Madhavarao et al., 2003; Arun et al., 2009). However, other studies performed in primary neuronal cultures established that Asp-NAT is located in the endoplasmic reticulum as well (Wiame et al., 2009; Tahay et al., 2012). A colocalization was reported by other authors (Lu et al., 2004; Ariyannur et al., 2010).
3.1. AGC1 expression is downregulated by inflammatory cytokines
3.3. The decrease in AGC1 expression in neuroinflammation is most likely caused by the downregulation of CREB
3.4. Cytosolic Ca2+ level affects AGC1 gene expression via CREB
Because Ca2+ is a well-known CREB inducer (Sheng and Greenberg, 1990) and is also known to stimulate AGC1 activity (Palmieri et al., 2001; Lasorsa et al., 2003; Contreras et al., 2007), we investigated whether alterations in the pool of intracellular Ca2 affect AGC1 gene expression.
Glutamate is the only amino acid extracted by healthy myocardium in net amounts, with uptake further increased during hypoxic or ischemic conditions. Glutamate supplementation provides cardioprotection from hypoxic and reperfusion injury through several metabolic pathways that depend upon adequate transport of glutamate into the mitochondria. Glutamate transport across the inner mitochondrial membrane is a key component of the malate/aspartate shuttle. Glutamate transport in the brain has been well characterized since the discovery of the excitatory amino acid transporter (EAAT) family.
Increased expression of the glutamate transporters EAAT1 and EAAT2 in the cerebellum of post-mortem tissue from autism patients has also been reported. Because EAAT expression is controlled in part by the extracellular concentration of glutamate, it is possible that the EAAT overexpression is due to the increased glutamate concentration seen in plasma and spectroscopic studies, as reviewed above.
Fig. 2 The malate – aspartate shuttle (MAS) and A TP generation. MAS is the main pathway for the transfer of reducing equivalents in the form of NADH from the cytosol into the mitochondria. Cytoplasmic malate dehydrogenase reduces oxaloacetate to malate while oxidizing
A reminder of what belongs where in a cell:-
Components of a typical animal cell:
2. Nucleus
3. Ribosome (little dots)
4. Vesicle
6. Golgi apparatus (or "Golgi body")
7. Cytoskeleton
10. Vacuole
12. Lysosome
13. Centrosome
14. Cell membrane
Conclusion
I hope some people made it to the end of this post. Since it was written on two computers, there may be some duplication.
It appears that most people with autism would benefit from less calcium in their brains, but this is more complex than it sounds. We need to block voltage gated calcium channels that are open, when they should be closed. We need to reduce IP3 to keep calcium locked up in the endoplasmic reticulum.
If we cannot reduce the level of Ca2+, we need to look at CREB which is mediating much of the damage. We can modify CREB via drugs that increase or decrease PKA. The only problem here is that for most people that would mean decreasing PKA, but PKA also does some other good things. At least in Alzheimer’s things do not conflict you want more CREB and more PKA.
The amino acid transporters AGC1, EAAT1 and EAAT2 are likely over activated in much autism. So we should expect lots of problems with glutamate, aspartate and indeed mitochondrial function.
It looks like most young people with autism would benefit from more NAA. One study showed that the omega 3 oil EPA can increase NAA. At least that is simple.
More NAA may well help correct impaired myelination.
Ideas that may potentially help in some cases of autism:-
· L-aspartic acid / L-aspartate
· High EPA fish oil to increase NAA
· PDE4 inhibitors (Ibudilast or Daxas)
· PKA inhibitors (not easy)
· IP3R blocker (only caffeine seems currently viable and is suboptimal)
Interactions of antagonists with subtypes of inositol 1,4,5-trisphosphate (IP3) receptor
Interactions of antagonists with subtypes of inositol 1,4,5-trisphosphate (IP3) receptor
· Verapamil in those with over-active (open) L-type calcium channels
Does oral L-aspartic acid actually reach the brain? Just try some. It tastes odd, like a homemade sweet/sour flavoring gone wrong and does not dissolve in water. It should be harmless in moderation.
