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Serine Catabolism Feeds NADH when Respiration Is Impaired.

ABSTRACT: NADH provides electrons for aerobic ATP production. In cells deprived of oxygen or with impaired electron transport chain activity, NADH accumulation can be toxic. To minimize such toxicity, elevated NADH inhibits the classical NADH-producing pathways: glucose, glutamine, and fat oxidation. Here, through deuterium-tracing studies in cultured cells and mice, we show that folate-dependent serine catabolism also produces substantial NADH. Strikingly, when respiration is impaired, serine catabolism through methylene tetrahydrofolate dehydrogenase (MTHFD2) becomes a major NADH source. In cells whose respiration is slowed by hypoxia, metformin, or genetic lesions, mitochondrial serine catabolism inhibition partially normalizes NADH levels and facilitates cell growth. In mice with engineered mitochondrial complex I deficiency (NDUSF4-/-), serine's contribution to NADH is elevated, and progression of spasticity is modestly slowed by pharmacological blockade of serine degradation. Thus, when respiration is impaired, serine catabolism contributes to toxic NADH accumulation.

SUBMITTER: Yang L

PROVIDER: S-EPMC7397714 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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Serine Catabolism Feeds NADH when Respiration Is Impaired.

Yang Lifeng L Garcia Canaveras Juan Carlos JC Chen Zihong Z Wang Lin L Liang Lingfan L Jang Cholsoon C Mayr Johannes A JA Zhang Zhaoyue Z Ghergurovich Jonathan M JM Zhan Le L Joshi Shilpy S Hu Zhixian Z McReynolds Melanie R MR Su Xiaoyang X White Eileen E Morscher Raphael J RJ Rabinowitz Joshua D JD

Cell metabolism 20200317 4

NADH provides electrons for aerobic ATP production. In cells deprived of oxygen or with impaired electron transport chain activity, NADH accumulation can be toxic. To minimize such toxicity, elevated NADH inhibits the classical NADH-producing pathways: glucose, glutamine, and fat oxidation. Here, through deuterium-tracing studies in cultured cells and mice, we show that folate-dependent serine catabolism also produces substantial NADH. Strikingly, when respiration is impaired, serine catabolism ...[more]

PMID: 32187526

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Project description:Type 2 NADH dehydrogenase (Ndh-2) is an oxidative phosphorylation enzyme discussed as a promising drug target in different pathogens, including Plasmodium falciparum and Mycobacterium tuberculosis ( Mtb ). To kill Mtb , Ndh-2 needs to be inactivated together with the alternative enzyme type 1 NADH dehydrogenase (Ndh-1), but the mechanism of this synthetic lethality remained unknown. Here, we provide insights into the biology of NADH dehydrogenases and a mechanistic explanation for Ndh-1 and Ndh-2 synthetic lethality in Mtb . NADH dehydrogenases have two main functions: maintaining an appropriate NADH/NAD+ ratio by converting NADH into NAD+ and providing electrons to the respiratory chain. Heterologous expression of a water forming NADH oxidase (Nox), which catalyzes the oxidation of NADH, allows to distinguish between these two functions and show that Nox rescues Mtb from Ndh-1/Ndh-2 synthetic lethality, indicating that NADH oxidation is the essential function of NADH dehydrogenases for Mtb viability. Quantification of intracellular levels of NADH, NAD, ATP, and oxygen consumption revealed that preventing NADH oxidation by Ndh-2 depletes NAD(H) and inhibits respiration. Finally, we show that Ndh-1/ Ndh-2 synthetic lethality can be achieved through chemical inhibition.ImportanceIn 2022, it is estimated that 10.6 million people fell ill, and 1.6 million people died from Tuberculosis (TB). Available treatment is lengthy and requires a multi-drug regimen, which calls for new strategies to cure Mycobacterium tuberculosis ( Mtb ) infections more efficiently. We have previously shown that simultaneous inactivation of type 1 (Ndh-1) and type 2 (Ndh-2) NADH dehydrogenase kills Mtb . NADH dehydrogenases play two main physiological roles: NADH oxidation and electron entry to the respiratory chain. Here, we show that this bactericidal effect is a consequence of impaired NADH oxidation. Importantly, we demonstrate that Ndh-1/Ndh-2 synthetic lethality can be achieved through simultaneous chemical inhibition, which could be exploited by TB drug development programs.

Project description:BackgroundEfficiently utilizing all available carbon from lignocellulosic feedstock presents a major barrier to the production of economically feasible biofuel. Previously, to enable xylose utilization, we introduced a cofactor-dependent xylose reductase (XR) and xylitol dehydrogenase (XDH) pathway, or a cofactor-independent xylose isomerase (XI) pathway, into Saccharomyces cerevisiae. The resulting strains metabolized xylose with high efficiency. However, in both pathway recombinant strains, the cofactor imbalance caused accumulation of the byproducts glycerol and/or xylitol and reduced the ethanol production efficiency.ResultsIn this study, we introduced NADH oxidase from Lactococcus lactis into both XI and XR-XDH pathway recombinant strains. To reduce byproduct accumulation while maintaining xylose metabolism, we optimized the expression level of NADH oxidase by comparing its expression under the control of different promoters and plasmids. In recombinant XI strains, NADH oxidase was expressed at different levels, regulated by the GPD2 promoter or TEF1 promoter in the 2 μ plasmid. The expression under the control of GPD2 promoter decreased glycerol production by 84% and increased the ethanol yield and specific growth rate by 8% and 12%, respectively. In contrast, in the recombinant XR-XDH strains, such expression level was not efficient enough to decrease the byproduct accumulation. Therefore, higher NADH oxidase expression levels were tested. In the strain expressing NADH oxidase under the control of the TEF1 promoter in the centromeric plasmids, xylitol and glycerol production were reduced by 60% and 83%, respectively, without significantly affecting xylose consumption.ConclusionsBy fine-tuning NADH oxidase expression, we decreased the glycerol or/and xylitol production in both recombinant XI and XR-XDH xylose-metabolizing yeast strains. The optimal NADH oxidase expression levels depend on metabolic pathways. Similar cofactor engineering strategies could maximize the production of other redox dependent metabolites.

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Serine Catabolism Feeds NADH when Respiration Is Impaired.

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Serine Catabolism Feeds NADH when Respiration Is Impaired.

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