Complementation of mitochondrial electron transport chain by manipulation of the NAD ⁺/NADH ratio

Abstract

A decline in electron transport chain (ETC) activity is associated with many human diseases. Although diminished mitochondrial ATP production is recognized as a source of pathology, the contribution of the associated reduction in the ratio of the amount of oxidized nicotinamide adenine dinucleotide (NAD ⁺) to that of its reduced form (NADH) is less clear. We used a water-forming NADH oxidase from L. brevis ( LbNOX) as a genetic tool for inducing a compartment-specific increase of the NAD ⁺/NADH ratio in human cells. We used LbNOX to demonstrate the dependence of key metabolic fluxes, gluconeogenesis, and signaling on the cytosolic or mitochondrial NAD ⁺/NADH ratios. Expression of LbNOX in the cytosol or mitochondria ameliorated proliferative and metabolic defects caused by an impaired ETC. The results underscore the role of reductive stress in mitochondrial pathogenesis and demonstrate the utility of targeted LbNOX for direct, compartment-specific manipulation of redox state.

One Sentence Summary

We developed a genetically encoded tool for raising NAD ⁺/NADH ratios and showed it can complement an impaired electron transport chain in human cells.