Mitochondrial Tricarboxylic Acid Cycle Research Articles

Plasma amino acids imbalance in cirrhotic patients disturbs the tricarboxylic acid cycle of dendritic cell

An imbalance of plasma amino acids (AA) is observed cirrhotic patients. Here we report that the imbalance suppresses the maturation of dendritic cells (DCs) by reducing the intracellular ATP due to interference with the mitochondrial tricarboxylic acid (TCA) cycle. We used serum-free culture medium consistent with the average concentration of the plasma AA from a healthy volunteer (HCM) and that from patients with advanced cirrhosis (ACM). We compared the function of DCs and the metabolism of glucose-amino acids under each medium. The maturation and intracellular ATP of immature DCs were lower under ACM in spite of the enhancement of mitochondrial respiratory chain complex genes. Metabolomics revealed that the TCA cycle metabolite, fumarate and 2-oxoglutarate were increased in DCs generated under ACM. Consistent with in vitro, In CD1c+ or CD14+ cells from cirrhotic patients, the gene expression of 2-oxoglutarate-succinate-fumarate transition enzymes were significantly different from the cells of healthy controls.

Mitochondrial metabolism of sexual and asexual blood stages of the malaria parasite Plasmodium falciparum

BackgroundThe carbon metabolism of the blood stages of Plasmodium falciparum, comprising rapidly dividing asexual stages and non-dividing gametocytes, is thought to be highly streamlined, with glycolysis providing most of the cellular ATP. However, these parasitic stages express all the enzymes needed for a canonical mitochondrial tricarboxylic acid (TCA) cycle, and it was recently proposed that they may catabolize glutamine via an atypical branched TCA cycle. Whether these stages catabolize glucose in the TCA cycle and what is the functional significance of mitochondrial metabolism remains unresolved.ResultsWe reassessed the central carbon metabolism of P. falciparum asexual and sexual blood stages, by metabolically labeling each stage with 13C-glucose and 13C-glutamine, and analyzing isotopic enrichment in key pathways using mass spectrometry. In contrast to previous findings, we found that carbon skeletons derived from both glucose and glutamine are catabolized in a canonical oxidative TCA cycle in both the asexual and sexual blood stages. Flux of glucose carbon skeletons into the TCA cycle is low in the asexual blood stages, with glutamine providing most of the carbon skeletons, but increases dramatically in the gametocyte stages. Increased glucose catabolism in the gametocyte TCA cycle was associated with increased glucose uptake, suggesting that the energy requirements of this stage are high. Significantly, whereas chemical inhibition of the TCA cycle had little effect on the growth or viability of asexual stages, inhibition of the gametocyte TCA cycle led to arrested development and death.ConclusionsOur metabolomics approach has allowed us to revise current models of P. falciparum carbon metabolism. In particular, we found that both asexual and sexual blood stages utilize a conventional TCA cycle to catabolize glucose and glutamine. Gametocyte differentiation is associated with a programmed remodeling of central carbon metabolism that may be required for parasite survival either before or after uptake by the mosquito vector. The increased sensitivity of gametocyte stages to TCA-cycle inhibitors provides a potential target for transmission-blocking drugs.

Abstract 1998: Exome sequencing and SNP array analysis of HLRCC syndromic uterine leiomyomas.

Abstract Uterine leiomyomas (fibroids) affect approximately 70% of women by the age of 50 years and thus are the most frequent tumors of the female reproductive tract. Fibroids are benign tumors originating from the smooth muscle cells of the uterus. They may cause various symptoms including abdominal pain, abnormal bleeding, and pregnancy complication, and they are the most common cause for hysterectomy. Our recent study identified somatic mutations in mediator complex subunit 12 (MED12) in as many as 70% of sporadic fibroids. Traditionally, fibroids have been considered rather stable, although some recurrent cytogenetic rearrangements affecting mainly chromosomes 7q, 12q15, and 6p21 have been reported. Hereditary Leiomyomatosis and Renal Cell Cancer (HLRCC, OMIM 150800) is an autosomal dominant cancer syndrome which predisposes to cutaneous and uterine leiomyomas, and renal cell cancer. Syndrome is caused by heterozygous germline mutations in the tumor suppressor gene fumarate hydratase (FH) at 1q42.1. The gene encodes fumarase, which catalyzes the hydratation of fumarate to L-malate in mitochondrial tricarboxylic acid cycle. Cutaneous and uterine leiomyomas are the most prevalent lesions with the syndrome and present typically at the age of 25 to 30 years. The aim of this study was to systematically characterize the genomic profile of FH deficient fibroids. For this, we analyzed altogether 10 fibroids and their corresponding myometrial samples from two Finnish HLRCC-family members and one sporadic leiomyoma sample with two somatic changes in FH by exome sequencing and SNP array analyses. To identify somatic variants, exome data from the tumors was filtered against the data from the respective myometrial samples as well as 93 Finnish individuals from the 1000 Genomes Project, 62 in-house controls, and all known variants in the dbSNP database. Altogether only 18 validated somatic mutations were observed in the exome data. All the variants were unique; they were observed only in one sample and the respective genes did not harbor additional changes in other tumors. No variations in genes commonly mutated in malignant tumors e.g. TP53, Rb or PTEN were observed. Neither were MED12 mutations, suggesting that mutations in MED12 and biallelic FH inactivation are mutually exclusive. In the SNP array analysis most of the tumors were found to carry large (>5 Mb) aberrations. The only recurrent change was the deletions at the FH locus. Deletions at 7q, which are frequently observed in sporadic uterine leiomyomas, were not present in these FH deficient tumors. To summarize, exome sequencing and SNP array analyses of 11 FH deficient tumors did not reveal any recurrent somatic variations in addition to the changes at the site of FH at 1q42. Loss of FH function damages the tricarboxylic acid cycle and causes a severe metabolic stress for the cells. This may be sufficient to induce formation of these benign lesions of the uterus. Citation Format: Kati Kämpjärvi, Miika Mehine, Pia Vahteristo, Lauri A. Aaltonen. Exome sequencing and SNP array analysis of HLRCC syndromic uterine leiomyomas. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1998. doi:10.1158/1538-7445.AM2013-1998

Measuring mitochondrial metabolism in rat brain in vivo using MR Spectroscopy of hyperpolarized [2‐13C]pyruvate

Hyperpolarized [1-(13) C]pyruvate ([1-(13) C]Pyr) has been used to assess metabolism in healthy and diseased states, focusing on the downstream labeling of lactate (Lac), bicarbonate and alanine. Although hyperpolarized [2-(13) C]Pyr, which retains the labeled carbon when Pyr is converted to acetyl-coenzyme A, has been used successfully to assess mitochondrial metabolism in the heart, the application of [2-(13) C]Pyr in the study of brain metabolism has been limited to date, with Lac being the only downstream metabolic product reported previously. In this study, single-time-point chemical shift imaging data were acquired from rat brain in vivo. [5-(13) C]Glutamate, [1-(13) C]acetylcarnitine and [1-(13) C]citrate were detected in addition to resonances from [2-(13) C]Pyr and [2-(13) C]Lac. Brain metabolism was further investigated by infusing dichloroacetate, which upregulates Pyr flux to acetyl-coenzyme A. After dichloroacetate administration, a 40% increase in [5-(13) C]glutamate from 0.014 ± 0.004 to 0.020 ± 0.006 (p = 0.02), primarily from brain, and a trend to higher citrate (0.002 ± 0.001 to 0.004 ± 0.002) were detected, whereas [1-(13) C]acetylcarnitine was increased in peripheral tissues. This study demonstrates, for the first time, that hyperpolarized [2-(13) C]Pyr can be used for the in vivo investigation of mitochondrial function and tricarboxylic acid cycle metabolism in brain.

Reversed argininosuccinate lyase activity in fumarate hydratase-deficient cancer cells

BackgroundLoss of function of fumarate hydratase (FH), the mitochondrial tumor suppressor and tricarboxylic acid (TCA) cycle enzyme, is associated with a highly malignant form of papillary and collecting duct renal cell cancer. The accumulation of fumarate in these cells has been linked to the tumorigenic process. However, little is known about the overall effects of the loss of FH on cellular metabolism.MethodsWe performed comprehensive metabolomic analyses of urine from Fh1-deficient mice and stable isotopologue tracing from human and mouse FH-deficient cell lines to investigate the biochemical signature of the loss of FH.ResultsThe metabolomics analysis revealed that the urea cycle metabolite argininosuccinate is a common metabolic biomarker of FH deficiency. Argininosuccinate was found to be produced from arginine and fumarate by the reverse activity of the urea cycle enzyme argininosuccinate lyase (ASL), making these cells auxotrophic for arginine. Depleting arginine from the growth media by the addition of pegylated arginine deiminase (ADI-PEG 20) decreased the production of argininosuccinate in FH-deficient cells and reduced cell survival and proliferation.ConclusionsThese results unravel a previously unidentified correlation between fumarate accumulation and the urea cycle enzyme ASL in FH-deficient cells. The finding that FH-deficient cells become auxotrophic for arginine opens a new therapeutic perspective for the cure of hereditary leiomyomatosis and renal cell cancer (HLRCC).

Superoxide Triggers an Acid Burst in Saccharomyces cerevisiae to Condition the Environment of Glucose-starved Cells

Although yeast cells grown in abundant glucose tend to acidify their extracellular environment, they raise the pH of the environment when starved for glucose or when grown strictly with non-fermentable carbon sources. Following prolonged periods in this alkaline phase, Saccharomyces cerevisiae cells will switch to producing acid. The mechanisms and rationale for this "acid burst" were unknown. Herein we provide strong evidence for the role of mitochondrial superoxide in initiating the acid burst. Yeast mutants lacking the mitochondrial matrix superoxide dismutase (SOD2) enzyme, but not the cytosolic Cu,Zn-SOD1 enzyme, exhibited marked acceleration in production of acid on non-fermentable carbon sources. Acid production is also dramatically enhanced by the superoxide-producing agent, paraquat. Conversely, the acid burst is eliminated by boosting cellular levels of Mn-antioxidant mimics of SOD. We demonstrate that the acid burst is dependent on the mitochondrial aldehyde dehydrogenase Ald4p. Our data are consistent with a model in which mitochondrial superoxide damage to Fe-S enzymes in the tricarboxylic acid (TCA) cycle leads to acetate buildup by Ald4p. The resultant expulsion of acetate into the extracellular environment can provide a new carbon source to glucose-starved cells and enhance growth of yeast. By triggering production of organic acids, mitochondrial superoxide has the potential to promote cell population growth under nutrient depravation stress.

Differential induction of mitochondrial machinery by light intensity correlates with changes in respiratory metabolism and photorespiration in rice leaves

The light responsiveness of mitochondrial function was investigated through changes in mitochondrial composition and metabolism in rice (Oryza sativa) shoots. The mitochondrial proteome and metabolite abundances under low light, (LL, 100 μmol m(-2) s(-1) ), and high light (HL, 700 μmol m(-2) s(-1) ) were measured along with information on shoot photosynthetic, respiratory and photorespiratory activity. Specific steps in mitochondrial tricarboxylic acid (TCA) cycle metabolism were decreased under HL, correlating with lower respiration rate under HL. The abundance of mitochondrial enzymes in branch chain metabolism was reduced under HL/LL, and correlated with a decrease in the abundance of a range of amino acids in the HL/LL. Mitochondrial nucleoside diphosphate kinase was increased under LL/HL treatments. Significant accumulation of glycine decarboxylase P, T subunits and serine hydroxymethyltransferase occurred in response to light. The abundance of the glycine decarboxylase (GDC) H subunit proteins was not changed by HL/LL treatments, and the abundance of GDC L subunit protein was halved under HL, indicating a change in the stoichiometry of GDC subunits, while photorespiration was fourfold higher in LL- than in HL-treated plants. Insights into these light-dependent phenomena and their importance for understanding the initiation of photorespiration in rice and adaptation of mitochondria to function in photosynthetic cells are discussed.

Protein Profiling of Blood Samples from Patients with Hereditary Leiomyomatosis and Renal Cell Cancer by Surface-Enhanced Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an extremely rare syndrome with autosomal dominant inheritance. HLRCC is characterized by a predisposition to leiomyomas of the skin and the uterus as well as renal cell carcinoma. The disease-related gene has been identified as fumarate hydratase (fumarase, FH), which encodes an enzyme involved in the mitochondrial tricarboxylic acid cycle. Protein profiling may give some insight into the molecular pathways of HLRCC. Therefore, we performed protein profiling of blood samples from HLRCC patients, their family members, and healthy volunteers, using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) coupled with IMAC-Cu chips. For hierarchical clustering analysis, we used the 45 peaks that revealed significant differences in single-marker analysis over the range from 1500 to 15,000 m/z. Heat map analysis based on the results of clustering distinguished the HLRCC kindred from non-HLRCC subjects with a sensitivity of 94% and a specificity of 90%. SELDI-TOF MS profiling of blood samples can be applied to identify patients with HLRCC and to assess specific molecular mechanisms involved in this condition.

Parkin prevents cortical atrophy and Aβ-induced alterations of brain metabolism: 13C NMR and magnetic resonance imaging studies in AD models

Alzheimer’s disease (AD) is a neurodegenerative aging disorder characterized by extracellular Aβ plaques and intraneuronal neurofibrillary tangles. We conducted longitudinal studies to examine the effects of Aβ on brain amino acid metabolism in lentiviral Aβ1–42 gene transfer animals and transgenic AD mice. We also performed lentiviral parkin gene delivery to determine the effects of Aβ clearance in AD models. Aβ1–42 activated mTOR signaling, and increased 4E-BP phosphorylation. Aβ1–42 increased the synthesis of glutamate and aspartate, but not glutamine, leucine and isoleucine, but an increase in leucine and isoleucine levels was concurrent with diminution of neurotransmitters. Additionally, Aβ1–42 attenuated mitochondrial tricarboxylic acid (TCA) cycle activity and decreased synthesis of its by-products. Glutamate levels increased prior to lactate accumulation, suggesting oxidative stress. Importantly, parkin reversed the effects of Aβ1–42 on amino acid levels, prevented TCA cycle impairment and protected against glutamate toxicity. Cortical atrophy was observed in aged 3xTg-AD mice, while parkin expression was associated with reduced atrophy. Similarly, Aβ1–42 resulted in significant cell loss, pronounced astrogliosis and cortical atrophy and parkin reduced astrogliosis and reversed Aβ1–42 effects on cell loss and cortical atrophy. Taken together these data suggest that parkin prevents amyloid-induced alteration of brain metabolism and may be used as a therapeutic target to limit neuronal loss in AD.

Pyruvate dehydrogenase phosphatase1 mRNA expression is divergently and dynamically regulated between rat cerebral cortex, hippocampus and thalamus after traumatic brain injury: A potential biomarker of TBI-induced hyper- and hypo-glycaemia and neuronal vulnerability

Cerebral pyruvate depletion and lactate acidosis are common metabolic characteristics of patients with traumatic brain injury (TBI) and are associated with poor prognosis. Pyruvate dehydrogenase (PDH) is the rate-limiting enzyme coupling glycolysis to mitochondrial tricarboxylic acid (TCA) cycle. Brain PDH activity is regulated by its phosphorylation status and other effectors. Phosphorylation of PDH E1α1 subunit by PDH kinase inhibits PDH activity while dephosphorylation of phosphorylated PDHE1α1 by PDH phosphatase (PDP1) restores PDH activity. In situ hybridization showed that PDP1 mRNA is highly expressed in the cerebral cortex, hippocampus and thalamus of rat. Controlled cortical impact (CCI) induced a significant increase in PDP1 mRNA expression in ipsilateral cerebral cortex at 4h (P<0.05) and 24h post CCI (P<0.01) that returned to basal level 72h post CCI. PDP1 mRNA level increased transiently in ipsilateral hippocampal dentate gyrus and CA1-3 subfields 4h post CCI (P<0.01) but decreased significantly 24h and 72h (P<0.01) post CCI, coinciding with a marked increase in neuronal apoptosis in ipsilateral hippocampus 24h post CCI. PDP1 mRNA expression in thalamus and other subcortical regions decreased persistently post CCI. Contralateral CCI and craniotomy showed similar effects on PDP1 mRNA expression as ipsilateral CCI. Because GFAP mRNA expression was induced in brain regions where PDP1 expression was altered, further study should determine the potential relationship between astrocyte activation, PDP1 alteration, and pyruvate metabolism following TBI.

Simultaneous measurement of the TCA cycle and respiration in isolated mitochondria and intact cells with the XF24‐3 Analyzer

Measuring mitochondrial dysfunction is increasingly important in the study of neurodegenerative and cardiovascular disease, metabolic syndrome, diabetes, cancer, and aging. Mitochondrial function is usually measured by oxygen consumption rates using respirometry methods. However, a critical aspect of mitochondrial function may be overlooked when only O2 consumption is employed: the tricarboxylic acid (TCA) or Krebs cycle, a central metabolic pathway. Measuring the TCA cycle function requires monitoring the flux of an additional analyte, such as carbon dioxide (CO2). The reported method describes simultaneous monitoring of carbon dioxide evolution rates (CDER) and oxygen consumption rates (OCR) using isolated mitochondria and intact cells, in real‐time, using the XF24‐3 Analyzer. This technology employs fluorescent sensors specific for CO2 and O2, which operate reversibly, and reveal details of mitochondrial respiration and TCA cycle activities. Results indicate that O2 consumption and CO2 evolution may be monitored simultaneously, and that data agrees with attributes of TCA cycle and mitochondrial function obtained by other methods. Differential rates of O2 and CO2 flux can be identified relative to substrate utilization and interdependency among the TCA cycle, electron transport, and oxidative phosphorylation systems. Support for this research is provided by Seahorse Bioscience.

Alternative Splicing Regulates Targeting of Malate Dehydrogenase in Yarrowia lipolytica

Alternative pre-mRNA splicing is a major mechanism contributing to the proteome complexity of most eukaryotes, especially mammals. In less complex organisms, such as yeasts, the numbers of genes that contain introns are low and cases of alternative splicing (AS) with functional implications are rare. We report the first case of AS with functional consequences in the yeast Yarrowia lipolytica. The splicing pattern was found to govern the cellular localization of malate dehydrogenase, an enzyme of the central carbon metabolism. This ubiquitous enzyme is involved in the tricarboxylic acid cycle in mitochondria and in the glyoxylate cycle, which takes place in peroxisomes and the cytosol. In Saccharomyces cerevisiae, three genes encode three compartment-specific enzymes. In contrast, only two genes exist in Y. lipolytica. One gene (YlMDH1, YALI0D16753g) encodes a predicted mitochondrial protein, whereas the second gene (YlMDH2, YALI0E14190g) generates the cytosolic and peroxisomal forms through the alternative use of two 3′-splice sites in the second intron. Both splicing variants were detected in cDNA libraries obtained from cells grown under different conditions. Mutants expressing the individual YlMdh2p isoforms tagged with fluorescent proteins confirmed that they localized to either the cytosolic or the peroxisomal compartment.

D-Pinitol a low-molecular cyclitol prevents 7,12-Dimethylbenz [a] anthracene induced experimental breast cancer through regulating anti-apoptotic protein Bcl-2, mitochondrial and carbohydrate key metabolizing enzymes

Compounds of dietary origin have always been considered as a paramount entity due to their popular belief of the absence of adverse side effects and also for their extraordinary efficacy against many diseases among which cancer is most important. The present investigation was aimed to evaluate the modulatory effect of d-Pinitol a compound from dietary origin, on the key mitochondrial tricarboxylic acid cycle, carbohydrate metabolizing enzymes and anti-apoptotic protein Bcl-2 against 7, 12-Dimethylbenz [a] anthracene (DMBA) induced mammary carcinoma in female Sprague Dawley rats. Breast caner was induced by intragastric administration of single dose of 20mg/kg body weight of DMBA. The results revealed that the levels of TCA cycle enzymes and carbohydrate metabolizing enzymes were drastically altered in both breast and liver tissues of cancer-bearing animals when compared to controls. Further, the anti-apoptotic protein Bcl-2 was found to be expressed during breast cancer. Interestingly, the oral administration of d-Pinitol at a dosage of 200mg/kg body weight for 45days to breast cancer-bearing rats were found to be significantly brought back the altered enzymes status to near normal range. This therapeutic activity may be due to the antioxidant property of d-Pinitol, which ultimately results in the mitochondrial compartment. Thus, our results clearly confirmed that d-Pinitol has some key modulatory property in mitochondrial and carbohydrate metabolizing enzymes through its antioxidant nature and also regulatory role in the proteins of anti-apoptotic cascade against the free radicals involved oxidative stress-mediated diseases, and which results in the consideration of the compound as safe and more effective in the treatment of mammary carcinoma in the near future.

Fumarase: a paradigm of dual targeting and dual localized functions

The enzyme fumarase is a conserved protein in all organisms with regard to its sequence, structure and function. This enzyme participates in the tricarboxylic acid cycle in mitochondria which is essential for cellular respiration in eukaryotes. However, a common theme conserved from yeast to humans is the existence of a cytosolic form of fumarase; hence this protein is dual localized. We have coined identical (or nearly identical) proteins situated in different subcellular locations 'echoforms' or 'echoproteins'. Fumarase was the first example of a dual localized protein whose mechanism of distribution was found to be based on a single translation product. Consequently, fumarase has become a paradigm for three unique eukaryotic cellular phenomena related to protein dual localization: (a) distribution between mitochondria and the cytoplasm involves reverse translocation; (b) targeting to mitochondria involves translation coupled import; and (c) there are two echoforms possessing distinct functions in the respective subcellular compartments. Here we describe and discuss these fumarase related phenomena and in addition point out approaches for studying dual function of distributed proteins, in particular compartment-specific depletion. In the case of fumarase, the cytoplasmic function was only recently discovered; the enzyme was found to participate in the cellular response to DNA double strand breaks. Strikingly, upon DNA damage the protein is transported from the cytosol to the nucleus, where by virtue of its enzymatic activity it participates in the DNA damage response.

Ellagic acid protects mitochondria from β-adrenergic agonist induced myocardial damage in rats; evidence from in vivo, in vitro and ultra structural study

This study aimed to evaluate the protective role of ellagic acid against mitochondrial damage in beta adrenergic agonist (isoproterenol)-induced myocardial infarction in Wistar rats in order to provide a scientific basis for the use of ellagic acid in preventing myocardial infarction. Mitochondria were isolated from the heart tissue of rats from all the groups. Lipid profile, lipid peroxidation, antioxidant enzyme activities and mitochondrial enzyme activities were measured. The structure of mitochondria was analysed by transmission electron microscopy. Isoproterenol-induced rats showed a significant increase in mitochondrial lipid peroxidation products and alterations in mitochondrial lipid profile. Significant decreases in mitochondrial antioxidants and tricarboxylic acid cycle enzymes were also found in the heart mitochondria of isoproterenol-induced myocardial infarcted rats. The protective effect of ellagic acid on the heart mitochondrial structure was evidenced by transmission electron microscopic study. Free radical scavenging and metal chelating activities of ellagic acid which are confirmed by in vitro studies may be the mechanism, responsible for the protective action against mitochondrial damage in myocardial infarction. The results support the importance of ellagic acid in regular diet to prevent myocardial infarction.

Up‐regulation of the mitochondrial malate dehydrogenase by oxidative stress is mediated by miR‐743a

These experiments reveal for the first time that microRNAs (miRNAs) mediate oxidant regulated expression of a mitochondrial tricarboxylic acid cycle gene (mdh2). mdh2 encoded malate dehydrogenase (MDH) is elevated by an unknown mechanism in brains of patients that died with Alzheimer's disease. Oxidative stress, an early and pervasive event in Alzheimer's disease, increased MDH activity and mRNA level of mdh2 by 19% and 22%, respectively, in a mouse hippocampal cell line (HT22). Post-transcriptional events underlie the change in mRNA because actinomycin D did not block the elevated mdh2 mRNA. Since miRNAs regulate gene expression post-transcriptionally, the expression of miR-743a, a miRNA predicted to target mdh2, was determined and showed a 52% reduction after oxidant treatment. Direct interaction of miR-743a with mdh2 was demonstrated with a luciferase based assay. Over-expression or inhibition of miR-743a led to a respective reduction or increase in endogenous mRNA and MDH activity. The results demonstrate that miR-743a negatively regulates mdh2 at post-transcriptional level by directly targeting the mdh2 3'UTR. The findings are consistent with the suggestion that oxidative stress can elevate the activity of MDH through miR-743a, and provide new insights into possible roles of miRNA in oxidative stress and neurodegeneration.

Metabolic surgery profoundly influences gut microbial–host metabolic cross-talk

Background and aimsBariatric surgery is increasingly performed worldwide to treat morbid obesity and is also known as metabolic surgery to reflect its beneficial metabolic effects especially with respect to improvement...

The hexosamine biosynthetic pathway couples growth factor-induced glutamine uptake to glucose metabolism

Glucose and glutamine serve as the two primary carbon sources in proliferating cells, and uptake of both nutrients is directed by growth factor signaling. Although either glucose or glutamine can potentially support mitochondrial tricarboxylic acid (TCA) cycle integrity and ATP production, we found that glucose deprivation led to a marked reduction in glutamine uptake and progressive cellular atrophy in multiple mammalian cell types. Despite the continuous presence of growth factor and an abundant supply of extracellular glutamine, interleukin-3 (IL-3)-dependent cells were unable to maintain TCA cycle metabolite pools or receptor-dependent signal transduction when deprived of glucose. This was due at least in part to down-regulation of IL-3 receptor α (IL-3Rα) surface expression in the absence of glucose. Treatment of glucose-starved cells with N-acetylglucosamine (GlcNAc) to maintain hexosamine biosynthesis restored mitochondrial metabolism and cell growth by promoting IL-3-dependent glutamine uptake and metabolism. Thus, glucose metabolism through the hexosamine biosynthetic pathway is required to sustain sufficient growth factor signaling and glutamine uptake to support cell growth and survival.

The genetic basis of kidney cancer: a metabolic disease.

Kidney cancer is not a single disease but comprises a number of different types of cancer that occur in the kidney, each caused by a different gene with a different histology and clinical course that responds differently to therapy. Each of the seven known kidney cancer genes, VHL, MET, FLCN, TSC1, TSC2, FH and SDH, is involved in pathways that respond to metabolic stress or nutrient stimulation. The VHL protein is a component of the oxygen and iron sensing pathway that regulates hypoxia-inducible factor (HIF) levels in the cell. HGF-MET signaling affects the LKB1-AMPK energy sensing cascade. The FLCN-FNIP1-FNIP2 complex binds AMPK and, therefore, might interact with the cellular energy and nutrient sensing pathways AMPK-TSC1/2-mTOR and PI3K-Akt-mTOR. TSC1-TSC2 is downstream of AMPK and negatively regulates mTOR in response to cellular energy deficit. FH and SDH have a central role in the mitochondrial tricarboxylic acid cycle, which is coupled to energy production through oxidative phosphorylation. Mutations in each of these kidney cancer genes result in dysregulation of metabolic pathways involved in oxygen, iron, energy or nutrient sensing, suggesting that kidney cancer is a disease of cell metabolism. Targeting the fundamental metabolic abnormalities in kidney cancer provides a unique opportunity for the development of more-effective forms of therapy for this disease.

Ethyl pyruvate stabilizes hypoxia-inducible factor 1 alpha via stimulation of the TCA cycle

Ethyl pyruvate is a simple derivative of the endogenous metabolite pyruvate. Pyruvate is the starting substrate for the tricarboxylic acid (TCA) cycle and plays a central role in intermediary metabolism. The present study was to determine whether ethyl pyruvate affects the expression of hypoxia-inducible factor 1 alpha (HIF-1α) and to explore the mechanism of HIF-1α regulation. We found that ethyl pyruvate increased HIF-1α stability via inhibition of pVHL-mediated degradation. Furthermore, ethyl pyruvate enhanced the reactive oxygen species (ROS) generated through the TCA cycle in mitochondria. Taken together, our results support a novel role for ethyl pyruvate in HIF-1α stabilization by which high rates of the TCA cycle can promote ROS production.