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Low glucose stress decreases cellular NADH and mitochondrial ATP in colonic epithelial cancer cells: Influence of mitochondrial substrates.

ABSTRACT: In this study, we investigated how colonic epithelial cells maintained pyridine nucleotide (NADH/NAD+) redox homeostasis upon acute metabolic variation imposed by glucose deprivation or supplementation with mitochondrial substrates, succinate and malate/glutamate (M/G). Our results showed that low glucose caused cellular NADH/NAD+ redox imbalance that diminished lactate dehydrogenase (LDH) activity and resulted in lower lactate contents. The concurrent activation of malic enzyme (ME) suggested a role for malate in preserving cellular pyruvate that remained unchanged at low glucose. Mitochondrial substrates restored cellular NADH/NAD+ redox homeostasis at low glucose in association with specific compartmental catabolism of mitochondrial substrates. As compared with normal glucose, M/G and low glucose promoted glycolytic ATP production but inhibited mitochondrial-derived ATP generation in association with decreased glucose availability for mitochondrial respiration. At normal glucose, succinate and M/G enhanced mitochondrial respiratory activity, but had minimal impact on mitochondrial-derived ATP production. Collectively, these results are consistent with low glucose-induced NADH/NAD+ redox imbalance in association with decreased aerobic glycolysis that is reversed by supplementation with M/G but not succinate.

SUBMITTER: Circu ML

PROVIDER: S-EPMC5345695 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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Low glucose stress decreases cellular NADH and mitochondrial ATP in colonic epithelial cancer cells: Influence of mitochondrial substrates.

Circu Magdalena L ML Maloney Ronald E RE Aw Tak Yee TY

Chemico-biological interactions 20170110

In this study, we investigated how colonic epithelial cells maintained pyridine nucleotide (NADH/NAD<sup>+</sup>) redox homeostasis upon acute metabolic variation imposed by glucose deprivation or supplementation with mitochondrial substrates, succinate and malate/glutamate (M/G). Our results showed that low glucose caused cellular NADH/NAD<sup>+</sup> redox imbalance that diminished lactate dehydrogenase (LDH) activity and resulted in lower lactate contents. The concurrent activation of malic e ...[more]

PMID: 28087461

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Project description:Aims: Glucose-stimulated insulin secretion (GSIS) in pancreatic β cells was expected to enhance mitochondrial superoxide formation. Hence, we elucidated relevant redox equilibria. Results: Unexpectedly, INS-1E cells at transitions from 3 (11 mM; pancreatic islets from 5 mM) to 25 mM glucose decreased matrix superoxide release rates (MitoSOX Red monitoring validated by MitoB) and H2O2 (mitoHyPer, subtracting mitoSypHer emission). Novel double-channel fluorescence lifetime imaging, approximating free mitochondrial matrix NADHF, indicated its ∼20% decrease. Matrix NAD+F increased on GSIS, indicated by the FAD-emission lifetime decrease, reflecting higher quenching of FAD by NAD+F. The participation of pyruvate/malate and pyruvate/citrate redox shuttles, elevating cytosolic NADPHF (iNAP1 fluorescence monitoring) at the expense of matrix NADHF, was indicated, using citrate (2-oxoglutarate) carrier inhibitors and cytosolic malic enzyme silencing: All changes vanished on these manipulations. 13C-incorporation from 13C-L-glutamine into 13C-citrate reflected the pyruvate/isocitrate shuttle. Matrix NADPHF (iNAP3 monitored) decreased. With decreasing glucose, the suppressor of Complex III site Q electron leak (S3QEL) suppressor caused a higher Complex I IF site contribution, but a lower superoxide fraction ascribed to the Complex III site IIIQo. Thus, the diminished matrix NADHF/NAD+F decreased Complex I flavin site IF superoxide formation on GSIS. Innovation: Mutually validated methods showed decreasing superoxide release into the mitochondrial matrix in pancreatic β cells on GSIS, due to the decreasing matrix NADHF/NAD+F (NADPHF/NADP+F) at increasing cytosolic NADPHF levels. The developed innovative methods enable real-time NADH/NAD+ and NADPH/NADP+ monitoring in any distinct cell compartment. Conclusion: The export of reducing equivalents from mitochondria adjusts lower mitochondrial superoxide production on GSIS, but it does not prevent oxidative stress in pancreatic β cells.

Project description:IntroductionAutophagy is an adaptive response to extracellular and intracellular stress by which cytoplasmic components and organelles, including damaged mitochondria, are degraded to promote cell survival and restore cell homeostasis. Certain genes involved in autophagy confer susceptibility to Crohn's disease. Reactive oxygen species and pro-inflammatory cytokines such as tumor necrosis factor α (TNFα), both of which are increased during active inflammatory bowel disease, promote cellular injury and autophagy via mitochondrial damage. Prohibitin (PHB), which plays a role in maintaining normal mitochondrial respiratory function, is decreased during active inflammatory bowel disease. Restoration of colonic epithelial PHB expression protects mice from experimental colitis and combats oxidative stress. In this study, we investigated the potential role of PHB in modulating mitochondrial stress-related autophagy in intestinal epithelial cells.MethodsWe measured autophagy activation in response to knockdown of PHB expression by RNA interference in Caco2-BBE and HCT116 WT and p53 null cells. The effect of exogenous PHB expression on TNFα- and IFNγ-induced autophagy was assessed. Autophagy was inhibited using Bafilomycin A(1) or siATG16L1 during PHB knockdown and the affect on intracellular oxidative stress, mitochondrial membrane potential, and cell viability were determined. The requirement of intracellular ROS in siPHB-induced autophagy was assessed using the ROS scavenger N-acetyl-L-cysteine.ResultsTNFα and IFNγ-induced autophagy inversely correlated with PHB protein expression. Exogenous PHB expression reduced basal autophagy and TNFα-induced autophagy. Gene silencing of PHB in epithelial cells induces mitochondrial autophagy via increased intracellular ROS. Inhibition of autophagy during PHB knockdown exacerbates mitochondrial depolarization and reduces cell viability.ConclusionsDecreased PHB levels coupled with dysfunctional autophagy renders intestinal epithelial cells susceptible to mitochondrial damage and cytotoxicity. Repletion of PHB may represent a therapeutic approach to combat oxidant and cytokine-induced mitochondrial damage in diseases such as inflammatory bowel disease.

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Low glucose stress decreases cellular NADH and mitochondrial ATP in colonic epithelial cancer cells: Influence of mitochondrial substrates.

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Low glucose stress decreases cellular NADH and mitochondrial ATP in colonic epithelial cancer cells: Influence of mitochondrial substrates.

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