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International audience; Ileal interposition (IT) is a surgical procedure that increases the delivery of incompletely digested nutrients and biliary and pancreatic secretions to the distal intestinal mucosa. Here, we investigated the metabolic impact of this intervention in 2-mo-old prediabetic University of California, Davis type 2 diabetes mellitus rats by assessing liver gene expression at 1.5 mo post-IT surgery. Pathway analysis indicated decreased signaling via TGF-β/Smad (a family of proteins named mothers against decapentaplegic homologs), peroxisome proliferator-activated receptor (PPAR), and PI3K-Akt-AMPK–mechanistic target of rapamycin, likely targeting hepatic stellate cells because differentiation and activation of these cells is associated with decreased signaling via PPAR and TGF-β/Smad. IT surgery up-regulated the expression of genes involved in regulation of cholesterol and terpenoid syntheses and down-regulated those involved in glycerophospholipid metabolism [including cardiolipin (CL)], lipogenesis, and gluconeogenesis. Consistent with the down-regulation of the hepatic CL pathway, IT surgery produced a metabolic switch in liver, kidney cortex, and fat depots toward decreased mitochondrial fatty acid β-oxidation, the process required to fuel high energy–demanding pathways (e.g., gluconeogenesis and glyceroneogenesis), whereas opposite effects were observed in skeletal and cardiac muscles. This study demonstrates for the first time the presence of metabolic pathways that complement the effects of IT surgery to maximize its benefits and potentially identify similarly effective, durable, and less invasive therapeutic options for metabolic disease, including inhibitors of TGF-β signaling.—Hung, C., Napoli, E., Ross-Inta, C., Graham, J., Flores-Torres, A. L., Stanhope, K. L., Froment, P., Havel, P. J., Giulivi, C. Ileal interposition surgery targets the hepatic TGF-β pathway, influencing gluconeogenesis and mitochondrial bioenergetics in the UCD-T2DM rat model of diabetes.

Alaskan Husky encephalopathy (AHE(1) ) is a fatal brain disease associated with a mutation in SLC19A3.1 (c.624insTTGC, c.625C>A). This gene encodes for a thiamine transporter 2 with a predominately (CNS) central nervous system distribution. Considering that brain is particularly vulnerable to thiamine deficiency because of its reliance on thiamine pyrophosphate (TPP)-dependent metabolic pathways involved in energy metabolism and neurotransmitter synthesis, we characterized the impact of this mutation on thiamine status, brain bioenergetics and the contribution of oxidative stress to this phenotype. In silico modeling of the mutated transporter indicated a significant loss of alpha-helices resulting in a more open protein structure suggesting an impaired thiamine transport ability. The cerebral cortex and thalamus of affected dogs were severely deficient in TPP-dependent enzymes accompanied by decreases in mitochondrial mass and oxidative phosphorylation (OXPHOS) capacity, and increases in oxidative stress. These results along with the behavioral and pathological findings indicate that the phenotype associated with AHE is consistent with a brain-specific thiamine deficiency, leading to brain mitochondrial dysfunction and increased oxidative stress. While some of the biochemical deficits, neurobehavior and affected brain areas in AHE were shared by Wernicke's and Korsakoff's syndromes, several differences were noted likely arising from a tissue-specific vs. that from a whole-body thiamine deficiency.

The anterior piriform cortex (APC) is activated by, and is the brain area most sensitive to, essential (indispensable) amino acid (IAA) deficiency. The APC is required for the rapid (20 min) behavioral rejection of IAA deficient diets and increased foraging, both crucial adaptive functions supporting IAA homeostasis in omnivores. The biochemical mechanisms signaling IAA deficiency in the APC block initiation of translation in protein synthesis via uncharged tRNA and the general amino acid control kinase, general control nonderepressing kinase 2. Yet, how inhibition of protein synthesis activates the APC is unknown. The neuronal K(+) Cl(-) cotransporter, neural potassium chloride co-transporter (KCC2), and GABAA receptors are essential inhibitory elements in the APC with short plasmalemmal half-lives that maintain control in this highly excitable circuitry. After a single IAA deficient meal both proteins were reduced (vs. basal diet controls) in western blots of APC (but not neocortex or cerebellum) and in immunohistochemistry of APC. Furthermore, electrophysiological analyses support loss of inhibitory elements such as the GABAA receptor in this model. As the crucial inhibitory function of the GABAA receptor depends on KCC2 and the Cl(-) transmembrane gradient it establishes, these results suggest that loss of such inhibitory elements contributes to disinhibition of the APC in IAA deficiency. The circuitry of the anterior piriform cortex (APC) is finely balanced between excitatory (glutamate, +) and inhibitory (GABA, -) transmission. GABAA receptors use Cl(-), requiring the neural potassium chloride co-transporter (KCC2). Both are rapidly turning-over proteins, dependent on protein synthesis for repletion. In IAA (indispensable amino acid) deficiency, within 20 min, blockade of protein synthesis prevents restoration of these inhibitors; they are diminished; disinhibition ensues. GCN2 = general control non-derepressing kinase 2, eIF2α = α-subunit of the eukaryotic initiation factor 2.

A number of studies have been conducted that link mitochondrial dysfunction (MD) to Huntington's disease (HD); however, contradicting results had resulted in a lack of a clear mechanism that links expression of mutant Huntingtin protein and MD. Mouse homozygous (HM) and heterozygous (HT) mutant striatal cells with two or one allele encoding for a mutant huntingtin protein with 111 polyGln repeats showed a significant impairment of the mitochondrial disulfide relay system (MDRS). This system (consisting of two proteins, Gfer and Mia40) is involved in the mitochondrial import of Cys-rich proteins. The Gfer-to-Mia40 ratio was significantly altered in HM cells compared with controls, along with the expression of mitochondrial proteins considered substrates of the MDRS. In progenitors and differentiated neuron-like HM cells, impairment of MDRS were accompanied by deficient oxidative phosphorylation, Complex I, IV and V activities, decreased mtDNA copy number and transcripts, accumulation of mtDNA deletions and changes in mitochondrial morphology, consistent with other MDRS-deficient biological models, thus providing a framework for the energy deficits observed in this HD model. The majority (>90%) of the mitochondrial outcomes exhibited a gene–dose dependency with the expression of mutant Htt. Finally, decreases in the mtDNA copy number, along with the accumulation of mtDNA deletions, provide a mechanism for the progressive neurodegeneration observed in HD patients.

Current medical countermeasures against organophosphate (OP) nerve agents are effective in reducing mortality, but do not sufficiently protect the CNS from delayed brain damage and persistent neurological symptoms. In this study, we examined the efficacy of neuregulin-1 (NRG-1) in protecting against delayed neuronal cell death following acute intoxication with the OP diisopropylfluorophosphate (DFP). Adult male Sprague Dawley rats were pretreated with pyridostigmine (0.1 mg/kg BW, i.m.) and atropine methylnitrate (20 mg/kg BW, i.m.) prior to DFP (9 mg/kg BW, i.p.) intoxication to increase survival and reduce peripheral signs of cholinergic toxicity but not prevent DFP-induced seizures or delayed neuronal injury. Pretreatment with NRG-1 did not protect against seizures in rats exposed to DFP. However, neuronal injury was significantly reduced in most brain regions by pretreatment with NRG-1 isoforms NRG-EGF (3.2 μg/kg BW, i.a) or NRG-GGF2 (48 μg/kg BW, i.a.) as determined by FluroJade-B labeling in multiple brain regions at 24 h post-DFP injection. NRG-1 also blocked apoptosis and oxidative stress-mediated protein damage in the brains of DFP-intoxicated rats. Administration of NRG-1 at 1 h after DFP injection similarly provided significant neuroprotection against delayed neuronal injury. These findings identify NRG-1 as a promising adjuvant therapy to current medical countermeasures for enhancing neuroprotection against acute OP intoxication.

International audience; Citrullinemia type I (CTLN1, OMIM# 215700) is an inherited urea cycle disorder that is caused by an argininosuccinate synthetase (ASS) enzyme deficiency. In this report, we describe two spontaneous hypomorphic alleles of the mouse Ass1 gene that serve as an animal model of CTLN1. These two independent mouse mutant alleles, also described in patients affected with CTLN1, interact to produce a range of phenotypes. While some mutant mice died within the first week after birth, others survived but showed severe retardation during postnatal development as well as alopecia, lethargy, and ataxia. Notable pathological findings were similar to findings in human CTLN1 patients and included citrullinemia and hyperammonemia along with delayed cerebellar development, epidermal hyperkeratosis, and follicular dystrophy. Standard treatments for CTLN1 were effective in rescuing the phenotype of these mutant mice. Based on our studies, we propose that defective cerebellar granule cell migration secondary to disorganization of Bergmann glial cell fibers cause cerebellar developmental delay in the hyperammonemic and citrullinemic brain, pointing to a possible role for nitric oxide in these processes. These mouse mutations constitute a suitable model for both mechanistic and preclinical studies of CTLN1 and other hyperammonemic encephalopathies and, at the same time, underscore the importance of complementing knockout mutations with hypomorphic mutations for the generation of animal models of human genetic diseases.

FXTAS (fragile X-associated tremor/ataxia syndrome) is a late-onset neurodegenerative disorder that affects individuals who are carriers of premutation expansions (55–200 CGG repeats) in the 5′ untranslated region of the FMR1 (fragile X mental retardation 1) gene. The role of MD (mitochondrial dysfunction) in FXTAS was evaluated in fibroblasts and brain samples from premutation carriers with and without FXTAS symptoms, with a range of CGG repeats. This study resulted in several important conclusions: (i) decreased NAD- and FAD-linked oxygen uptake rates and uncoupling between electron transport and synthesis of ATP were observed in fibroblasts from premutation carriers; (ii) a lower expression of mitochondrial proteins preceded both in age and in CGG repeats the appearance of overt clinical involvement; (iii) the CGG repeat size required for altered mitochondrial protein expression was also smaller than that required to produce brain intranuclear inclusions from individuals with the premutation who died, suggesting that MD is an incipient pathological process occurring in individuals who do not display overt features of FXTAS; and (iv) on the basis of the CGG repeats, MD preceded the increase in oxidative/nitrative stress damage, indicating that the latter is a late event. MD in carriers of small CGG repeats, even when the allele size is not sufficient to produce FXTAS, may predispose them to other disorders (e.g. Parkinson's disease) that are likely to involve MD, and to environmental stressors, which may trigger the development of FXTAS symptoms. Detection of MD is of critical importance to the management of FXTAS, since it opens up additional treatment options for this disorder.

Diets deficient in an indispensable amino acid are known to suppress food intake in rats. Few studies were focused at understanding how amino acid-deficient diets may elicit biochemical changes at the mitochondrial level. The goal of this study was to evaluate mitochondrial function in rats fed diets with 0.00, 0.18, 0.36, and 0.88% threonine (Thr) (set at 0, 30, 60, and 140% of Thr requirement for growth). Here, it is described for the first time that Thr-deficient diets induce a specific uncoupling of mitochondria in liver, especially with NADH-linked substrates, not observed in heart (except for Thr-devoid diet). The advantage of this situation would be to provide ATP to support growth and maintenance when high-quality protein food (or wealth of high-quality food in general) is available, whereas Thr-deficient diets (or deficient-quality protein food) promote the opposite, increasing mitochondrial uncoupling in liver. The uncoupling with NADH substrates would favor the use of nutrients as energy sources with higher FADH-to-NADH ratios, such as fat, minimizing the first irreversible NADH-dependent catabolism of many amino acids, including Thr, thus enhancing the use of the limiting amino acid for protein synthesis when a low quality protein source is available.

No studies have been performed on the mitochondria of malaria vector mosquitoes. This information would be valuable in understanding mosquito aging and detoxification of insecticides, two parameters that have a significant impact on malaria parasite transmission in endemic regions. In the present study, we report the analyses of respiration and oxidative phosphorylation in mitochondria of cultured cells [ASE (Anopheles stephensi Mos. 43) cell line] from A. stephensi, a major vector of malaria in India, South-East Asia and parts of the Middle East. ASE cell mitochondria share many features in common with mammalian muscle mitochondria, despite the fact that these cells are of larval origin. However, two major differences with mammalian mitochondria were apparent. One, the glycerol–phosphate shuttle plays as major a role in NADH oxidation in ASE cell mitochondria as it does in insect muscle mitochondria. In contrast, mammalian white muscle mitochondria depend primarily on lactate dehydrogenase, whereas red muscle mitochondria depend on the malate–oxaloacetate shuttle. Two, ASE mitochondria were able to oxidize proline at a rate comparable with that of α-glycerophosphate. However, the proline pathway appeared to differ from the currently accepted pathway, in that oxoglutarate could be catabolized completely by the tricarboxylic acid cycle or via transamination, depending on the ATP need.

The anterior piriform cortex (APC) has been shown to be an essential brain structure for the detection of dietary indispensable amino acid (IAA) deficiency, but little has been known about possible molecular detection mechanisms. Increased phosphorylation of the α-subunit of the eukaryotic initiation factor 2α (eIF2α) has been directly linked to amino acid deficiency in yeast. Recently, we have shown increased phosphorylation of eIF2α (p-eIF2α) in the rat APC 20 minutes after ingestion of an IAA-deficient meal. We suggest that if phosphorylation of eIF2α is an important mechanism in detection of IAA deficiency, then APC neurons that show p-eIF2α should also show molecular evidence of potentiation. The present research demonstrates increased expression and co-localization of p-eIF2α and phosphorylated extracellular signal-regulated protein kinase 1/2 (p-ERK1/2) in APC neurons, but not in the primary motor or agranular insular cortices in response to an IAA-deficient diet. ERK1/2 is an element of the mitogen-activated protein kinase cascade, an intraneuronal signaling mechanism associated with neuronal activation. The region of the APC that responds to IAA deficiency with increased p-eIF2α and p-ERK1/2 labeling ranges from 3.1 to 2.5 mm rostral of bregma. Within this region, only a few neurons respond to IAA deficiency with co-localization of abundant p-eIF2α and p-ERK1/2. These chemosensory neurons probably detect IAA deficiency and generate neuronal signaling to other portions of the brain, changing feeding behavior. J. Comp. Neurol. 494:485–494, 2006. © 2005 Wiley-Liss, Inc.

Alaskan Husky encephalopathy (AHE(1) ) is a fatal brain disease associated with a mutation in SLC19A3.1 (c.624insTTGC, c.625CA). This gene encodes for a thiamine transporter 2 with a predominately (CNS) central nervous system distribution. Considering that brain is particularly vulnerable to thiamine deficiency because of its reliance on thiamine pyrophosphate (TPP)-dependent metabolic pathways involved in energy metabolism and neurotransmitter synthesis, we characterized the impact of this mutation on thiamine status, brain bioenergetics and the contribution of oxidative stress to this phenotype. In silico modeling of the mutated transporter indicated a significant loss of alpha-helices resulting in a more open protein structure suggesting an impaired thiamine transport ability. The cerebral cortex and thalamus of affected dogs were severely deficient in TPP-dependent enzymes accompanied by decreases in mitochondrial mass and oxidative phosphorylation (OXPHOS) capacity, and increases in oxidative stress. These results along with the behavioral and pathological findings indicate that the phenotype associated with AHE is consistent with a brain-specific thiamine deficiency, leading to brain mitochondrial dysfunction and increased oxidative stress. While some of the biochemical deficits, neurobehavior and affected brain areas in AHE were shared by Wernicke's and Korsakoff's syndromes, several differences were noted likely arising from a tissue-specific vs. that from a whole-body thiamine deficiency.

Etiology of aberrant social behavior consistently points to a strong polygenetic component involved in fundamental developmental pathways, with the potential of being enhanced by defects in bioenergetics. To this end, the occurrence of social deficits and mitochondrial outcomes were evaluated in conditional Pten (Phosphatase and tensin homolog) haplo-insufficient mice, in which only one allele was selectively knocked-out in neural tissues. Pten mutations have been linked to Alzheimer's disease and syndromic autism spectrum disorders, among others. By 4-6 weeks of age, Pten insufficiency resulted in the increase of several mitochondrial Complex activities (II-III, IV and V) not accompanied by increases in mitochondrial mass, consistent with an activation of the PI3K/Akt pathway, of which Pten is a negative modulator. At 8-13 weeks of age, Pten haplo-insufficient mice did not show significant behavioral abnormalities or changes in mitochondrial outcomes, but by 20-29 weeks, they displayed aberrant social behavior (social avoidance, failure to recognize familiar mouse, and repetitive self-grooming), macrocephaly, increased oxidative stress, decreased cytochrome c oxidase (CCO) activity (50%) and increased mtDNA deletions in cerebellum and hippocampus. Mitochondrial dysfunction was the result of a downregulation of p53-signaling pathway evaluated by lower protein expression of p21 (65% of controls) and the CCO chaperone SCO2 (47% of controls), two p53-downstream targets. This mechanism was confirmed in Pten-deficient striatal neurons and, HCT 116 cells with different p53 gene dosage. These results suggest a unique pathogenic mechanism of the Pten-p53 axis in mice with aberrant social behavior: loss of Pten (via p53) impairs mitochondrial function elicited by an early defective assembly of CCO and later enhanced by the accumulation of mtDNA deletions. Consistent with our results, (i) SCO2 deficiency and/or CCO activity defects have been reported in patients with learning disabilities including autism and (ii) mutated proteins in ASD have been found associated with p53-signaling pathways.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder that affects individuals who are carriers of small CGG premutation expansions in the fragile X mental retardation 1 (FMR1) gene. Mitochondrial dysfunction was observed as an incipient pathological process occurring in individuals who do not display overt features of FXTAS ( 1). Fibroblasts from premutation carriers had lower oxidative phosphorylation capacity (35% of controls) and Complex IV activity (45%), and higher precursor-to-mature ratios (P:M) of nDNA-encoded mitochondrial proteins (3.1-fold). However, fibroblasts from carriers with FXTAS symptoms presented higher FMR1 mRNA expression (3-fold) and lower Complex V (38%) and aconitase activities (43%). Higher P:M of ATPase β-subunit (ATPB) and frataxin were also observed in cortex from patients that died with FXTAS symptoms. Biochemical findings observed in FXTAS cells (lower mature frataxin, lower Complex IV and aconitase activities) along with common phenotypic traits shared by Friedreich's ataxia and FXTAS carriers (e.g. gait ataxia, loss of coordination) are consistent with a defective iron homeostasis in both diseases. Higher P:M, and lower ZnT6 and mature frataxin protein expression suggested defective zinc and iron metabolism arising from altered ZnT protein expression, which in turn impairs the activity of mitochondrial Zn-dependent proteases, critical for the import and processing of cytosolic precursors, such as frataxin. In support of this hypothesis, Zn-treated fibroblasts showed a significant recovery of ATPB P:M, ATPase activity and doubling time, whereas Zn and desferrioxamine extended these recoveries and rescued Complex IV activity.

Protein synthesis requires a continuous supply of all of the indispensable (essential) amino acids (IAAs). If any IAA is deficient, animals must obtain the limiting amino acid by diet selection. Sensing of IAA deficiency requires an intact anterior piriform cortex (APC), but does it act alone? Shortly after rats begin eating an IAA-deficient diet, the meal ends and EPSPs are activated in the APC; from there, neurons project to feeding circuits; the meal ends within 20 min. Within the APCin vivo, uncharged tRNA activates the general amino acid control non-derepressing 2 (GCN2) enzyme system increasing phosphorylation of eukaryotic initiation factor (P-eIF2α), which blocks general protein synthesis. If this paleocortex is sufficient for sensing IAA depletion, both neuronal activation and P-eIF2α should occur in an isolated APC slice. We used standard techniques for electrophysiology and immunohistochemistry. After rats ate IAA-devoid or -imbalanced diets, their depleted slices responded to different stimuli with increased EPSP amplitudes. Slices from rats fed a control diet were bathed in artificial CSF replete with all amino acids with or without the IAA, threonine, or a tRNA synthetase blocker,l-threoninol, or its inactive isomer,d-threoninol. Thr depletionin vitroincreased both EPSP amplitudes and P-eIF2α.l(but notd)-threoninol also increased EPSP amplitudes relative to control. Thus, we show independent excitation of the APC with responses parallel to those knownin vivo. These data suggest a novel idea: in addition to classical processing of peripheral sensory input, direct primary sensing may occur in mammalian cortex.

Context Impaired mitochondrial function may influence processes highly dependent on energy, such as neurodevelopment, and contribute to autism. No studies have evaluated mitochondrial dysfunction and mitochondrial DNA (mtDNA) abnormalities in a well-defined population of children with autism. Objective To evaluate mitochondrial defects in children with autism. Design, Setting, and Patients Observational study using data collected from patients aged 2 to 5 years who were a subset of children participating in the Childhood Autism Risk From Genes and Environment study in California, which is a population-based, case-control investigation with confirmed autism cases and age-matched, genetically unrelated, typically developing controls, that was launched in 2003 and is still ongoing. Mitochondrial dysfunction and mtDNA abnormalities were evaluated in lymphocytes from 10 children with autism and 10 controls. Main Outcome Measures Oxidative phosphorylation capacity, mtDNA copy number and deletions, mitochondrial rate of hydrogen peroxide production, and plasma lactate and pyruvate. Results The reduced nicotinamide adenine dinucleotide (NADH) oxidase activity (normalized to citrate synthase activity) in lymphocytic mitochondria from children with autism was significantly lower compared with controls (mean, 4.4 [95% confidence interval {CI}, 2.8-6.0] vs 12 [95% CI, 8-16], respectively; P = .001). The majority of children with autism (6 of 10) had complex I activity below control range values. Higher plasma pyruvate levels were found in children with autism compared with controls (0.23 mM [95% CI, 0.15-0.31 mM] vs 0.08 mM [95% CI, 0.04-0.12 mM], respectively; P = .02). Eight of 10 cases had higher pyruvate levels but only 2 cases had higher lactate levels compared with controls. These results were consistent with the lower pyruvate dehydrogenase activity observed in children with autism compared with controls (1.0 [95% CI, 0.6-1.4] nmol × [min × mg protein] −1 vs 2.3 [95% CI, 1.7-2.9] nmol × [min × mg protein] −1 , respectively; P = .01). Children with autism had higher mitochondrial rates of hydrogen peroxide production compared with controls (0.34 [95% CI, 0.26-0.42] nmol × [min × mg of protein] −1 vs 0.16 [95% CI, 0.12-0.20] nmol × [min × mg protein] −1 by complex III; P = .02). Mitochondrial DNA overreplication was found in 5 cases (mean ratio of mtDNA to nuclear DNA: 239 [95% CI, 217-239] vs 179 [95% CI, 165-193] in controls; P = 10 −4 ). Deletions at the segment of cytochrome b were observed in 2 cases (ratio of cytochrome b to ND1: 0.80 [95% CI, 0.68-0.92] vs 0.99 [95% CI, 0.93-1.05] for controls; P = .01). Conclusion In this exploratory study, children with autism were more likely to have mitochondrial dysfunction, mtDNA overreplication, and mtDNA deletions than typically developing children.

Malignant hyperthermia (MH) and central core disease in humans have been associated with mutations in the skeletal ryanodine receptor (RyR1). Heterozygous mice expressing the human MH/central core disease RyR1 R163C mutation exhibit MH when exposed to halothane or heat stress. Considering that many MH symptoms resemble those that could ensue from a mitochondrial dysfunction (e.g. metabolic acidosis and hyperthermia) and that MH-susceptible mice or humans have a higher than normal cytoplasmic Ca(2+) concentration at rest, we evaluated the role of mitochondria in skeletal muscle from R163C compared with wild type mice under basal (untriggered) conditions. R163C skeletal muscle exhibited a significant increase in matrix Ca(2+), increased reactive oxygen species production, lower expression of mitochondrial proteins, and higher mtDNA copy number. These changes, in conjunction with lower myoglobin and glycogen contents, Myh4 and GAPDH transcript levels, GAPDH activity, and lower glucose utilization suggested a switch to a compromised bioenergetic state characterized by both low oxidative phosphorylation and glycolysis. The shift in bioenergetic state was accompanied by a dysregulation of Ca(2+)-responsive signaling pathways regulated by calcineurin and ERK1/2. Chronically elevated resting Ca(2+) in R163C skeletal muscle elicited the maintenance of a fast-twitch fiber program and the development of insulin resistance-like phenotype as part of a metabolic adaptation to the R163C RyR1 mutation.

Mitochondria can synthesize a limited number of proteins encoded by mtDNA (mitochondrial DNA) by using their own biosynthetic machinery, whereas most of the proteins in mitochondria are imported from the cytosol. It could be hypothesized that the mitochondrial pool of amino acids follows the frequency of amino acids in mtDNA-encoded proteins or, alternatively, that the profile is the result of the participation of amino acids in pathways other than protein synthesis (e.g. haem biosynthesis and aminotransferase reactions). These hypotheses were tested by evaluating the pool of free amino acids and derivatives in highly-coupled purified liver mitochondria obtained from rats fed on a nutritionally adequate diet for growth. Our results indicated that the pool mainly reflects the amino acid composition of mtDNA-encoded proteins, suggesting that there is a post-translational control of protein synthesis. This conclusion was supported by the following findings: (i) correlation between the concentration of free amino acids in the matrix and the frequency of abundance of amino acids in mtDNA-encoded proteins; (ii) the similar ratios of essential-to-non-essential amino acids in mtDNA-encoded proteins and the mitochondrial pool of amino acids; and (iii), lack of a correlation between codon usage or tRNA levels and amino-acid concentrations. Quantitative information on the mammalian mitochondrial content of amino acids, such as that presented in the present study, along with functional studies, will help us to better understand the pathogenesis of mitochondrial diseases or the biochemical implications in mitochondrial metabolism.

Recognizing a deficiency of indispensable amino acids (IAAs) for protein synthesis is vital for dietary selection in metazoans, including humans. Cells in the brain's anterior piriform cortex (APC) are sensitive to IAA deficiency, signaling diet rejection and foraging for complementary IAA sources, but the mechanism is unknown. Here we report that the mechanism for recognizing IAA-deficient foods follows the conserved general control (GC) system, wherein uncharged transfer RNA induces phosphorylation of eukaryotic initiation factor 2 (eIF2) via the GC nonderepressing 2 (GCN2) kinase. Thus, a basic mechanism of nutritional stress management functions in mammalian brain to guide food selection for survival.