Elevated Levels Of acetyl-CoA Research Articles

Enhanced supply of acetyl-CoA by exogenous pantothenate kinase promotes synthesis of poly(3-hydroxybutyrate)

BackgroundCoenzyme A (CoA) is a carrier of acyl groups. This cofactor is synthesized from pantothenic acid in five steps. The phosphorylation of pantothenate is catalyzed by pantothenate kinase (CoaA), which is a key step in the CoA biosynthetic pathway. To determine whether the enhancement of the CoA biosynthetic pathway is effective for producing useful substances, the effect of elevated acetyl-CoA levels resulting from the introduction of the exogenous coaA gene on poly(3-hydroxybutyrate) [P(3HB)] synthesis was determined in Escherichia coli, which express the genes necessary for cyanobacterial polyhydroxyalkanoate synthesis (phaABEC).ResultsE. coli containing the coaA gene in addition to the pha genes accumulated more P(3HB) compared with the transformant containing the pha genes alone. P(3HB) production was enhanced by precursor addition, with P(3HB) content increasing from 18.4% (w/w) to 29.0% in the presence of 0.5 mM pantothenate and 16.3%–28.2% by adding 0.5 mM β-alanine. Strains expressing the exogenous coaA in the presence of precursors contained acetyl-CoA in excess of 1 nmol/mg of dry cell wt, which promoted the reaction toward P(3HB) formation. The amount of acetate exported into the medium was three times lower in the cells carrying exogenous coaA and pha genes than in the cells carrying pha genes alone. This was attributed to significantly enlarging the intracellular pool size of CoA, which is the recipient of acetic acid and is advantageous for microbial production of value-added materials.ConclusionsEnhancing the CoA biosynthetic pathway with exogenous CoaA was effective at increasing P(3HB) production. Supplementing the medium with pantothenate facilitated the accumulation of P(3HB). β-Alanine was able to replace the efficacy of adding pantothenate.

Loss of fatty acid degradation by astrocytic mitochondria triggers neuroinflammation and neurodegeneration.

Astrocytes provide key neuronal support, and their phenotypic transformation is implicated in neurodegenerative diseases. Metabolically, astrocytes possess low mitochondrial oxidative phosphorylation (OxPhos) activity, but its pathophysiological role in neurodegeneration remains unclear. Here, we show that the brain critically depends on astrocytic OxPhos to degrade fatty acids (FAs) and maintain lipid homeostasis. Aberrant astrocytic OxPhos induces lipid droplet (LD) accumulation followed by neurodegeneration that recapitulates key features of Alzheimer's disease (AD), including synaptic loss, neuroinflammation, demyelination and cognitive impairment. Mechanistically, when FA load overwhelms astrocytic OxPhos capacity, elevated acetyl-CoA levels induce astrocyte reactivity by enhancing STAT3 acetylation and activation. Intercellularly, lipid-laden reactive astrocytes stimulate neuronal FA oxidation and oxidative stress, activate microglia through IL-3 signalling, and inhibit the biosynthesis of FAs and phospholipids required for myelin replenishment. Along with LD accumulation and impaired FA degradation manifested in an AD mouse model, we reveal a lipid-centric, AD-resembling mechanism by which astrocytic mitochondrial dysfunction progressively induces neuroinflammation and neurodegeneration.

A mechanistic perspective on the health promoting effects of alcohol - A focus on epigenetics modification.

While the detrimental effects of binge drinking are well recognized, low-to-moderate alcohol consumption may be beneficial to health, although the underlying mechanism(s) remains elusive. In this opinion article, we will examine the effects of low dose alcohol consumption from the perspective of epigenetic modulation. Biochemically, alcohol is metabolized into acetate and subsequently to acetyl-coA, which can modulate histone acetylation levels. While elevated levels of acetyl-CoA are detrimental for longevity, we argue that diminished acetyl-CoA also negatively affects fatty acid biosynthesis and histone acetylation, which play a critical role in gene expression and, ultimately, health span. Since mitochondrial function and glucose metabolism, which provide the main source of nucleocytoplasmic acetyl-CoA, are compromised with age, alcohol-derived acetate could be an alternative source of acetyl-CoA to compensate. Hence, the health benefits of low ethanol consumption may be more pronounced after midlife, since mitochondrial function and/or glucose metabolism are diminished in this phase of the life course. Indeed, various clinical alcohol consumption studies concur with this notion, and have shown that a low dose of regular alcohol intake after midlife brings about various health and survival benefits. The requirement for regular alcohol intake may also reflect the transient nature of ethanol-induced histone acetylation. Conversely, ethanol may also stimulate carcinogenesis by inhibiting DNA methylation, as it was shown to reduce various pathways leading to DNA and histone methylation. However, unlike acetylation, where ethanol directly increases the substrate for acetylation, this effect was only observed in the high alcohol exposure cohort. While alcohol-derived acetate may be beneficial for health after midlife, various detrimental effects of alcohol consumption remain, and hence, we do not advocate excessive drinking to increase acetate. This opinion article establishes a possible role of ethanol-derived acetate in achieving homeostasis and sustaining an organism's health span.

Hypoxia promotes osteogenesis by facilitating acetyl-CoA-mediated mitochondrial-nuclear communication.

Bone-derived mesenchymal stem cells (MSCs) reside in a hypoxic niche that maintains their differentiation potential. While hypoxia (low oxygen concentration) was reported to critically support stem cell function and osteogenesis, the molecular events triggering changes in stem cell fate decisions in response to normoxia (high oxygen concentration) remain elusive. Here, we study the impact of normoxia on mitochondrial-nuclear communication during stem cell differentiation. We show that normoxia-cultured murine MSCs undergo profound transcriptional alterations which cause irreversible osteogenesis defects. Mechanistically, high oxygen promotes chromatin compaction and histone hypo-acetylation, particularly on promoters and enhancers of osteogenic genes. Although normoxia induces metabolic rewiring resulting in elevated acetyl-CoA levels, histone hypo-acetylation occurs due to the trapping of acetyl-CoA inside mitochondria owing to decreased citrate carrier (CiC) activity. Restoring the cytosolic acetyl-CoA pool remodels the chromatin landscape and rescues the osteogenic defects. Collectively, our results demonstrate that the metabolism-chromatin-osteogenesis axis is perturbed upon exposure to high oxygen levels and identifies CiC as a novel, oxygen-sensitive regulator of the MSC function.

Acetyl-CoA Derived from Hepatic Peroxisomal β-Oxidation Inhibits Autophagy and Promotes Steatosis via mTORC1 Activation

Autophagy is activated by prolonged fasting but cannot overcome the ensuing hepatic lipid overload, resulting in fatty liver. Here, we describe a peroxisome-lysosome metabolic link that restricts autophagic degradation of lipids. Acyl-CoA oxidase 1 (Acox1), the enzyme that catalyzes the first step in peroxisomal β-oxidation, is enriched in liver and further increases with fasting or high-fat diet (HFD). Liver-specific Acox1 knockout (Acox1-LKO) protected mice against hepatic steatosis caused by starvation or HFD due to induction of autophagic degradation of lipid droplets. Hepatic Acox1 deficiency markedly lowered total cytosolic acetyl-CoA levels, which led to decreased Raptor acetylation and reduced lysosomal localization of mTOR, resulting in impaired activation of mTORC1, a central regulator of autophagy. Dichloroacetic acid treatment elevated acetyl-CoA levels, restored mTORC1 activation, inhibited autophagy, and increased hepatic triglycerides in Acox1-LKO mice. These results identify peroxisome-derived acetyl-CoA as a key metabolic regulator of autophagy that controls hepatic lipid homeostasis.

Cutting Edge: TCR Signal Strength Regulates Acetyl-CoA Metabolism via AKT.

TCR signaling activates kinases including AKT/mTOR that engage metabolic networks to support the energetic demands of a T cell during an immune response. It is realized that CD4+ T cell subsets have different metabolic requirements. Yet, how TCR signaling is coupled to the regulation of intermediate metabolites and how changes in metabolite flux contribute to T cell differentiation are less established. We find that TCR signaling regulates acetyl-CoA metabolism via AKT in murine CD4+ T cells. Weak TCR signals promote AKT-catalyzed phosphorylation and inhibition of citrate synthase, elevated acetyl-CoA levels, and hyperacetylation of mitochondrial proteins. Genetic knockdown of citrate synthase promotes increased nuclear acetyl-CoA levels, increased histone acetylation at the FOXP3 promotor and induction of FOXP3 transcription. These data identify a circuit between AKT signaling and acetyl-CoA metabolism regulated via TCR signal strength and that transient fluctuations in acetyl-CoA levels function in T cell fate decisions.

Cytosolic acetyl-CoA promotes histone acetylation predominantly at H3K27 in Arabidopsis.

Acetyl-coenzyme A (acetyl-CoA) is a central metabolite and the acetyl source for protein acetylation, particularly histone acetylation that promotes gene expression. However, the effect of acetyl-CoA levels on histone acetylation status in plants remains unknown. Here, we show that malfunctioned cytosolic acetyl-CoA carboxylase1 (ACC1) in Arabidopsis leads to elevated levels of acetyl-CoA and promotes histone hyperacetylation predominantly at lysine 27 of histone H3 (H3K27). The increase of H3K27 acetylation (H3K27ac) is dependent on adenosine triphosphate (ATP)-citrate lyase which cleaves citrate to acetyl-CoA in the cytoplasm, and requires histone acetyltransferase GCN5. A comprehensive analysis of the transcriptome and metabolome in combination with the genome-wide H3K27ac profiles of acc1 mutants demonstrate the dynamic changes in H3K27ac, gene transcripts and metabolites occurring in the cell by the increased levels of acetyl-CoA. This study suggests that H3K27ac is an important link between cytosolic acetyl-CoA level and gene expression in response to the dynamic metabolic environments in plants.

Lysine acetyltransferase NuA4 and acetyl-CoA regulate glucose-deprived stress granule formation in Saccharomyces cerevisiae.

Eukaryotic cells form stress granules under a variety of stresses, however the signaling pathways regulating their formation remain largely unknown. We have determined that the Saccharomyces cerevisiae lysine acetyltransferase complex NuA4 is required for stress granule formation upon glucose deprivation but not heat stress. Further, the Tip60 complex, the human homolog of the NuA4 complex, is required for stress granule formation in cancer cell lines. Surprisingly, the impact of NuA4 on glucose-deprived stress granule formation is partially mediated through regulation of acetyl-CoA levels, which are elevated in NuA4 mutants. While elevated acetyl-CoA levels suppress the formation of glucose-deprived stress granules, decreased acetyl-CoA levels enhance stress granule formation upon glucose deprivation. Further our work suggests that NuA4 regulates acetyl-CoA levels through the Acetyl-CoA carboxylase Acc1. Altogether this work establishes both NuA4 and the metabolite acetyl-CoA as critical signaling pathways regulating the formation of glucose-deprived stress granules.

Novel role of serine racemase in anti-apoptosis and metabolism

BackgroundSerine racemase (SR) catalyzes the production of d-serine, a co-agonist of the N-methyl-d-aspartate receptor (NMDAR). A previous report shows the contribution of SR in the NMDAR-mediated neuronal cell death process. Methods and resultsTo analyze the intrinsic role of SR in the cell death process, we established the epithelial human embryonic kidney 293T (HEK293T) cell lines expressing wild-type SR (SR-WT), catalytically inactive mutant SR (SR-K56G), and catalytically hyperactive mutant SR (SR-Q155D). To these cell lines, staurosporine (STS), which induces apoptosis, was introduced. The cells expressing SR-WT and SR-Q155D showed resistance to STS-induced apoptosis, compared with nontransfected HEK293T cells and cells expressing SR-K56G. The SR-WT cells also showed a significant higher viability than the SR-QD cells. Furthermore, we detected elevated phosphorylation levels of Bcl-2 at serine-70 and Akt at serine-473 and threonine-308, which are related to cell survival, in the cells expressing SR-WT and SR-Q155D. From the results of metabolite analysis, we found elevated levels of acetyl CoA and ATP in cells expressing SR-WT. ConclusionBecause SR has two enzymatic activities, namely, racemization and α, β-elimination, and SR-Q155D shows enhanced racemization and reduced α, β-elimination activities, we concluded that the racemization reaction catalyzed by SR may have a more protective role against apoptosis than the α, β-elimination reaction. Moreover, both of these activities are important for maximal survival and elevated levels of acetyl CoA and ATP. General significanceOur findings reveal the NMDAR-independent roles of SR in metabolism and cell survival.

Germline BRCA1 mutation reprograms breast epithelial cell metabolism towards mitochondrial-dependent biosynthesis: evidence for metformin-based "starvation" strategies in BRCA1 carriers.

We hypothesized that women inheriting one germline mutation of the BRCA1 gene (“one-hit”) undergo cell-type-specific metabolic reprogramming that supports the high biosynthetic requirements of breast epithelial cells to progress to a fully malignant phenotype. Targeted metabolomic analysis was performed in isogenic pairs of nontumorigenic human breast epithelial cells in which the knock-in of 185delAG mutation in a single BRCA1 allele leads to genomic instability. Mutant BRCA1 one-hit epithelial cells displayed constitutively enhanced activation of biosynthetic nodes within mitochondria. This metabolic rewiring involved the increased incorporation of glutamine- and glucose-dependent carbon into tricarboxylic acid (TCA) cycle metabolite pools to ultimately generate elevated levels of acetyl-CoA and malonyl-CoA, the major building blocks for lipid biosynthesis. The significant increase of branched-chain amino acids (BCAAs) including the anabolic trigger leucine, which can not only promote protein translation via mTOR but also feed into the TCA cycle via succinyl-CoA, further underscored the anabolic reprogramming of BRCA1 haploinsufficient cells. The anti-diabetic biguanide metformin “reversed” the metabolomic signature and anabolic phenotype of BRCA1 one-hit cells by shutting down mitochondria-driven generation of precursors for lipogenic pathways and reducing the BCAA pool for protein synthesis and TCA fueling. Metformin-induced restriction of mitochondrial biosynthetic capacity was sufficient to impair the tumor-initiating capacity of BRCA1 one-hit cells in mammosphere assays. Metabolic rewiring of the breast epithelium towards increased anabolism might constitute an unanticipated and inherited form of metabolic reprogramming linked to increased risk of oncogenesis in women bearing pathogenic germline BRCA1 mutations. The ability of metformin to constrain the production of mitochondrial-dependent biosynthetic intermediates might open a new avenue for “starvation” chemopreventive strategies in BRCA1 carriers.

Life span extension by targeting a link between metabolism and histone acetylation in Drosophila.

Old age is associated with a progressive decline of mitochondrial function and changes in nuclear chromatin. However, little is known about how metabolic activity and epigenetic modifications change as organisms reach their midlife. Here, we assessed how cellular metabolism and protein acetylation change during early aging in Drosophila melanogaster. Contrary to common assumptions, we find that flies increase oxygen consumption and become less sensitive to histone deacetylase inhibitors as they reach midlife. Further, midlife flies show changes in the metabolome, elevated acetyl‐CoA levels, alterations in protein—notably histone—acetylation, as well as associated transcriptome changes. Based on these observations, we decreased the activity of the acetyl‐CoA‐synthesizing enzyme ATP citrate lyase (ATPCL) or the levels of the histone H4 K12‐specific acetyltransferase Chameau. We find that these targeted interventions both alleviate the observed aging‐associated changes and promote longevity. Our findings reveal a pathway that couples changes of intermediate metabolism during aging with the chromatin‐mediated regulation of transcription and changes in the activity of associated enzymes that modulate organismal life span.

S.28.05 D-Serine acting at the glycine site of NMDA receptor in psychiatric disorders

Serine racemase (SR) catalyzes the production of d-serine, a co-agonist of the N-methyl-d-aspartate receptor (NMDAR). A previous report shows the contribution of SR in the NMDAR-mediated neuronal cell death process.To analyze the intrinsic role of SR in the cell death process, we established the epithelial human embryonic kidney 293T (HEK293T) cell lines expressing wild-type SR (SR-WT), catalytically inactive mutant SR (SR-K56G), and catalytically hyperactive mutant SR (SR-Q155D). To these cell lines, staurosporine (STS), which induces apoptosis, was introduced. The cells expressing SR-WT and SR-Q155D showed resistance to STS-induced apoptosis, compared with nontransfected HEK293T cells and cells expressing SR-K56G. The SR-WT cells also showed a significant higher viability than the SR-QD cells. Furthermore, we detected elevated phosphorylation levels of Bcl-2 at serine-70 and Akt at serine-473 and threonine-308, which are related to cell survival, in the cells expressing SR-WT and SR-Q155D. From the results of metabolite analysis, we found elevated levels of acetyl CoA and ATP in cells expressing SR-WT.Because SR has two enzymatic activities, namely, racemization and α, β-elimination, and SR-Q155D shows enhanced racemization and reduced α, β-elimination activities, we concluded that the racemization reaction catalyzed by SR may have a more protective role against apoptosis than the α, β-elimination reaction. Moreover, both of these activities are important for maximal survival and elevated levels of acetyl CoA and ATP.Our findings reveal the NMDAR-independent roles of SR in metabolism and cell survival.

A shift in myocardial substrate, improved endothelial function, and diminished sympathetic activity may contribute to the anti-anginal impact of very-low-fat diets

A new category of anti-anginal drug – exemplified by ranolazine – is believed to work by partially inhibiting cardiac oxidation of fatty acids; oxidation of glucose requires less oxygen per mol of ATP generated, and thus is preferable to fat oxidation when oxygen availability is limiting in underperfused cardiac tissue. Unfortunately, there is no reason to believe that these drugs inhibit fat oxidation selectively in the heart; thus, chronic use of these drugs can be expected to increase body fat stores until the original rate of fat oxidation is restored by mass action – presumably negating the therapeutic benefit in angina, while exacerbating the manifold adverse effects of insulin resistance syndrome. The rational way to decrease cardiac metabolic reliance on fatty acids is to consume a very-low-fat quasi-vegan diet (i.e., 10% fat calories). Indeed, such diets are known to have a rapid and substantial therapeutic impact on anginal symptoms, while concurrently benefiting insulin sensitivity, markedly improving serum lipid profile, promoting leanness, and lessening coronary risk. A reduction in diurnal insulin secretion might also be achieved, which would be expected to decrease sympathetic activity. While reduced myocardial demand for oxygen doubtless contributes to the beneficial impact of such diets on angina, it is likely that improved cardiac perfusion consequent to improved endothelium-dependent vasodilation also plays a role in this regard. Supplemental carnitine, also beneficial in angina, appears to improve utilization of glucose in the ischemic myocardium by lowering elevated acetyl-coA levels and thereby disinhibiting pyruvate dehydrogenase. Certain other nutraceuticals may aid control of angina by improving endothelial function. In the longer term, these measures have the potential to slow or reverse the progression of stenotic lesions that underlie most cases of angina. These safe and relatively inexpensive nutritional strategies for coping with angina deserve far more attention than orthodox medical practice has thus far accorded them.

Mutagenic analysis of 2,3-diaminophenazine and 2-amino-3-hydroxyphenazine in Salmonella strains expressing different levels of O-acetyltransferase with and without plant and mammalian activation

2,3-Diaminophenazine (DAP) and 2-amino-3-hydroxyphenazine (AHP) are products generated from oxidative-type phenylenediamine hair dyes and are also present in pesticide formulations as contaminants. Earlier studies demonstrated that DAP and AHP were mutagenic in Salmonella typhimurium strains after mammalian microsomal activation. Plant systems can activate structurally similar arylamines. S. typhimurium strains have been developed that express elevated levels of acetyl-CoA: N-hydroxyarylamine O-acetyltransferase (OAT). O-acetyltransferase expression is necessary for the generation of the ultimate arylamine promutagen after plant activation. A number of arylamines including 2-aminofluorene, benzidine and 4-aminobiphenyl were activated by plant cells into mutagens in the OAT over-expressing S. typhimurium strain, YG1024. The objectives of this research were to examine the mutagenicity of DAP and AHP with mammalian or plant activation in Salmonella strains with different acetyltransferase activities. The hypothesis tested was whether and to what degree a metabolite of DAP or AHP could serve as a substrate for bacterial O-acetyltransferase and induce mutation in Salmonella. DAP and AHP without activation induced both frameshift and base pair substitution mutations in S. typhimurium strains that exhibited elevated levels of O-acetyltransferase activity. The mutagenicity of DAP and AHP were greatly enhanced with mammalian hepatic microsomal activation resulting in a preferential induction of frameshift mutations. With the hisD3052 allele as the gene target, S9-activated DAP induced frameshift mutations in YG1024 and TA98 as well as the OAT deficient strain TA98/1,8-DNP 6. S9-activated AHP induced mutation only in the OAT over-expressing strain, YG1024. With the hisG46 allele, O-acetyltransferase activity was necessary for the metabolism of DAP and AHP to products that induce base pair substitution mutations. An intriguing finding of this work was the

Prostaglandin H synthase-dependent formation of the direct-acting mutagen 2-nitro-3-methylimidazo[4,5- f]quinoline (nitro-IQ) from IQ

The mutagenic effects of 2-amino-3-methylimidazo[4,5- f]quinoline (IQ) following activation by ram seminal vesicle microsomes (RSVM, a source of prostaglandin H synthase, PHS) were studied in Salmonella typhimurium tester strains possessing elevated levels of acetyl-CoA:arylamine N-acetyltransferase (NAT). The metabolites formed by RSVM were extracted and fractionated by high pressure liquid chromatography (HPLC). One isolable product accounted for most of the direct-acting mutagenicity observed in the extracts. The metabolite was identified as 2-nitro-3-methylimidazo[4,5- f]quinoline (nitro-IQ). Since nitro-IQ is a potent direct-acting mutagen, its role in IQ genotoxicity warrants further study.

Control of gluconeogenesis by acetyl CoA in rats treated with glucagon and anti-insulin serum

Glucagon has recently been shown to have a direct lipolytic action on liver (Bewsher and Ashmore 1966). Increased hepatic lipolysis, plus enhanced availability of plasma fatty acids, causes an elevation of acetyl CoA and fatty acyl CoA levels (Williamson, Herczeg, Coles and Danish 1966). Such elevated levels of acetyl CoA presumably account for the increased rate of ketogenesis observed with glucagon. Acute effects of insulin deficiency, induced by administration of guinea pig anti-insulin serum (AIS) to rats, are similar to effects produced by glucagon: elevation of plasma glucose, free fatty acid, and ketone levels, plus an increased rate of gluconeogenesis (Wagle and Ashmore, 1963; Wagle and Ashmore, 1964; Tarrant, Mahler, and Ashmore, 1964). These findings have led to the suggestion that the early metabolic changes in experimental insulin deficiency may be induced by hormones with actions normally counterbalanced by insulin (Wright, 1965). Such hormones are glucagon, epinephrine, ACTH and corticosteroids (Mahler, Stafford, Tarrant and Ashmore, 1964; Jungas and Ball, 1963). Data presented in this paper supports the concept that the lipolytic, ketogenic, and gluconeogenic effects of glucagon are revealed in the insulin-deficient rat. It is suggested that stimulation of gluconeogenesis, both with glucagon and with AIS, is secondary to enhanced lipolysis and is mediated through facilitation of pyruvic carboxylase by elevated hepatic levels of acetyl CoA.