Coenzyme A (CoA) is the predominant acyl carrier in mammalian cells and a cofactor that plays a key role in energy and lipid metabolism. CoA and its thioesters (acyl-CoAs) regulate a multitude of ...metabolic processes at different levels: as substrates, allosteric modulators, and via post-translational modification of histones and other non-histone proteins. Evidence is emerging that synthesis and degradation of CoA are regulated in a manner that enables metabolic flexibility in different subcellular compartments. Degradation of CoA occurs through distinct intra- and extracellular pathways that rely on the activity of specific hydrolases. The pantetheinase enzymes specifically hydrolyze pantetheine to cysteamine and pantothenate, the last step in the extracellular degradation pathway for CoA. This reaction releases pantothenate in the bloodstream, making this CoA precursor available for cellular uptake and de novo CoA synthesis. Intracellular degradation of CoA depends on specific mitochondrial and peroxisomal Nudix hydrolases. These enzymes are also active against a subset of acyl-CoAs and play a key role in the regulation of subcellular (acyl-)CoA pools and CoA-dependent metabolic reactions. The evidence currently available indicates that the extracellular and intracellular (acyl-)CoA degradation pathways are regulated in a coordinated and opposite manner by the nutritional state and maximize the changes in the total intracellular CoA levels that support the metabolic switch between fed and fasted states in organs like the liver.
The objective of this review is to update the contribution of these pathways to the regulation of metabolism, physiology and pathology and to highlight the many questions that remain open.
•Coenzyme A levels are regulated both at the level of synthesis and degradation.•Distinct hydrolases control CoA degradation outside and inside the cell.•Pantetheinases regulate the extracellular recycling of the CoA precursor pantothenate.•Nudix hydrolases regulate subcellular CoA pools.•CoA degradation contributes to metabolic adaptation.
CoA regulates energy metabolism and exists in separate pools in the cytosol, peroxisomes, and mitochondria. At the whole tissue level, the concentration of CoA changes with the nutritional state by ...balancing synthesis and degradation; however, it is currently unclear how individual subcellular CoA pools are regulated. Liver and kidney peroxisomes contain Nudt7 and Nudt19, respectively, enzymes that catalyze CoA degradation. We report that Nudt8 is a novel CoA‐degrading enzyme that resides in the mitochondria. Nudt8 has a distinctive preference for manganese ions and exhibits a broader tissue distribution than Nudt7 and Nudt19. The existence of CoA‐degrading enzymes in both peroxisomes and mitochondria suggests that degradation may be a key regulatory mechanism for modulating the intracellular CoA pools.
Background The study objectives were: provide longitudinal data on upper aerodigestive tract function and late complications following IMRT for nasopharyngeal carcinoma, and elucidate factors that ...might predict a worse outcome. The hypotheses were: (1) Despite advances such as IMRT, radiation will cause significant functional decline and late complications that often progress or arise years after treatment. (2) Larger radiation volume will be associated with poorer outcomes. Methods Longitudinal, observational cohort study of nasopharyngeal carcinoma patients with retrospective analysis of prospectively collected, population-based data. Late sequelae and validated measures of overall performance, speech, and swallowing were documented pre-treatment and 3,6,12, 24, 36 and greater than or equal to 60-months post-treatment. Results Forty-two patients treated curatively with radiation (N = 9) or chemoradiation (N = 33) were followed for a median 74 months. Functional outcomes showed an initial nadir at 3 months associated with acute effects of treatment, followed by initial recovery. There was subsequent functional decline years post-treatment with advancing dysphagia/aspiration, trismus, muscle spasm, and hypoglossal nerve palsy. Univariable regression analysis revealed that increasing high-dose radiation volumes (PTV 70 Gy) were associated with increased likelihood of less than solid diet (Performance Status Scale (PSS)--Normalcy of Diet score < 50; p = 0.04), and reduced PSS--Understandability of Speech (p = 0.005). The probability of poor outcome increased with time. Eleven percent of patients were tube feed dependent at greater than or equal to 5 years. Conclusions Despite improvements in radiation delivery, late effects of radiation remain common. Higher radiation volumes are associated with poorer outcomes that worsen over time. Graphical Keywords: Nasopharyngeal carcinoma, Functional outcomes, IMRT
Lipid metabolism requires CoA, an essential cofactor found in multiple subcellular compartments, including the peroxisomes. In the liver, CoA levels are dynamically adjusted between the fed and ...fasted states. Elevated CoA levels in the fasted state are driven by increased synthesis; however, this also correlates with decreased expression of Nudix hydrolase (Nudt)7, the major CoA-degrading enzyme in the liver. Nudt7 resides in the peroxisomes, and we overexpressed this enzyme in mouse livers to determine its effect on the size and composition of the hepatic CoA pool in the fed and fasted states. Nudt7 overexpression did not change total CoA levels, but decreased the concentration of short-chain acyl-CoAs and choloyl-CoA in fasted livers, when endogenous Nudt7 activity was lowest. The effect on these acyl-CoAs correlated with a significant decrease in the hepatic bile acid content and in the rate of peroxisomal fatty acid oxidation, as estimated by targeted and untargeted metabolomics, combined with the measurement of fatty acid oxidation in intact hepatocytes. Identification of the CoA species and metabolic pathways affected by the overexpression on Nudt7 in vivo supports the conclusion that the nutritionally driven modulation of Nudt7 activity could contribute to the regulation of the peroxisomal CoA pool and peroxisomal lipid metabolism.
Organelle interactions play a significant role in compartmentalizing metabolism and signaling. Lipid droplets (LDs) interact with numerous organelles, including mitochondria, which is largely assumed ...to facilitate lipid transfer and catabolism. However, quantitative proteomics of hepatic peridroplet mitochondria (PDM) and cytosolic mitochondria (CM) reveals that CM are enriched in proteins comprising various oxidative metabolism pathways, whereas PDM are enriched in proteins involved in lipid anabolism. Isotope tracing and super-resolution imaging confirms that fatty acids (FAs) are selectively trafficked to and oxidized in CM during fasting. In contrast, PDM facilitate FA esterification and LD expansion in nutrient-replete medium. Additionally, mitochondrion-associated membranes (MAM) around PDM and CM differ in their proteomes and ability to support distinct lipid metabolic pathways. We conclude that CM and CM-MAM support lipid catabolic pathways, whereas PDM and PDM-MAM allow hepatocytes to efficiently store excess lipids in LDs to prevent lipotoxicity.
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•CM are enriched in oxidative proteins and utilize FAs during fasting•PDM are enriched in lipid anabolism proteins and facilitate FA esterification•MAM around PDM and CM are unique and differentially regulate lipid metabolism•PLIN5 regulates the proteomes and functions of mitochondrial and MAM subpopulations
Najt et al. reveal that the proteomes and functions of subpopulations of hepatic mitochondria and MAM differ based on their interactions with LDs. FAs are selectively trafficked to and oxidized in CM, especially during fasting, whereas PDM and associated MAM facilitate FA esterification and LD expansion.
CoA is the major acyl carrier in mammals and a key cofactor in energy metabolism. Dynamic regulation of CoA in different tissues and organs supports metabolic flexibility. Two mammalian Nudix ...hydrolases, Nudt19 and Nudt7, degrade CoA in vitro. Nudt19 and Nudt7 possess conserved Nudix and CoA signature sequences and specifically hydrolyze the diphosphate bond of free CoA and acyl-CoAs to form 3′,5′-ADP and 4′-(acyl)phosphopantetheine. Limited information is available on these enzymes, but the relatively high abundance of Nudt19 and Nudt7 mRNA in the kidney and liver, respectively, suggests that they play specific roles in the regulation of CoA levels in these organs. Here, we analyzed Nudt19−/− mice and found that deletion of Nudt19 elevates kidney CoA levels in mice fed ad libitum, indicating that Nudt19 contributes to the regulation of CoA in vivo. Unlike what was observed for the regulation of Nudt7 in the liver, Nudt19 transcript and protein levels in the kidney did not differ between fed and fasted states. Instead, we identified chenodeoxycholic acid as a specific Nudt19 inhibitor that competed with CoA for Nudt19 binding but did not bind to Nudt7. Exchange of the Nudix and CoA signature motifs between the two isoforms dramatically decreased their kcat. Furthermore, substitutions of conserved residues within these motifs identified amino acids playing different roles in CoA binding and hydrolysis in Nudt19 and Nudt7. Our results reveal that the kidney and liver each possesses a distinct peroxisomal CoA diphosphohydrolase.
Prolonged cellular hypoxia leads to energetic failure and death. However, sublethal hypoxia can trigger an adaptive response called hypoxic preconditioning. While prolyl-hydroxylase (PHD) enzymes and ...hypoxia-inducible factors (HIFs) have been identified as key elements of oxygen-sensing machinery, the mechanisms by which hypoxic preconditioning protects against insults remain unclear. Here, we perform serum metabolomic profiling to assess alterations induced by two potent cytoprotective approaches, hypoxic preconditioning and pharmacologic PHD inhibition. We discover that both approaches increase serum kynurenine levels and enhance kynurenine biotransformation, leading to preservation of NAD+ in the post-ischemic kidney. Furthermore, we show that indoleamine 2,3-dioxygenase 1 (Ido1) deficiency abolishes the systemic increase of kynurenine and the subsequent renoprotection generated by hypoxic preconditioning and PHD inhibition. Importantly, exogenous administration of kynurenine restores the hypoxic preconditioning in the context of Ido1 deficiency. Collectively, our findings demonstrate a critical role of the IDO1-kynurenine axis in mediating hypoxic preconditioning.
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•Hypoxia and PHD inhibition increase serum kynurenine•Ido1 deficiency blunts the increase in serum kynurenine by hypoxia and PHD inhibition•The IDO1-kynurenine axis is required in renoprotection by hypoxic preconditioning•Hypoxia and PHD inhibition activate the kynurenine pathway in the post-ischemic kidney
Torosyan et al. show that two potent cytoprotective strategies, hypoxic preconditioning and PHD inhibition, enhance kidney tissue resilience against ischemic injury by activating the kynurenine metabolic pathway. Specifically, they promote systemic kynurenine increase and enhance kynurenine metabolism, leading to preservation of NAD+ and generation of kynurenic acid in the post-ischemic kidney.
Stromal vascular fraction (SVF) cells, and the adipose-derived mesenchymal stem cells they contain, have shown enhanced wound healing in vitro and in vivo, yet their clinical application has been ...limited. In this regard, understanding the mechanisms that govern SVF-enhanced wound healing would improve their application in the clinic. Here, we show that the SVF cells and keratinocytes engage in a paracrine crosstalk during wound closure, which results in a new cytokine profile that is distinct from the cytokines regularly secreted by either cell type on their own. We identify 11 cytokines, 5 of which are not regularly secreted by the SVF cells, whose expressions are significantly increased during wound closure by the keratinocytes. This new cytokine profile could be used to accelerate wound closure and initiate re-epithelialization without the need to obtain the SVF cells from the patient.
The scratch assay is an in vitro assay that allows for high-throughput quantification of wound closure by keratinocytes and fibroblasts with relative ease. However, this assay is amenable to ...experimental variables, which can result in false-positive and false-negative data, making the interpretation of such data difficult. Also, data variability decreases the sensitivity of the scratch assay. Here, we identify important sources of data variation in the scratch assay and provide rational mitigation strategies that enable robust and highly reproducible quantification of scratch width and area, and ultimately the scratch closure rates. By eliminating these sources of variability, the sensitivity of the scratch assay is enhanced, thereby allowing for identification of dependent variables with wide-ranging impacts on wound closure in a robust and standardized manner.
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