Mitochondrial redox regulation and myocardial ischemia-reperfusion injury.

Mitochondrial reactive oxygen species (ROS) have emerged as an important mechanism of disease and redox signaling in the cellular system. Under basal or pathological conditions, electron leakage for ROS production is primarily mediated by complexes I and III of the electron transport chain (ETC) and by the proton motive force (PMF), consisting of a membrane potential (ΔΨ) and a proton gradient (ΔpH). Several factors control redox status in mitochondria, including ROS, the PMF, oxidative posttranslational modifications (OPTM) of the ETC subunits, SOD2, and cytochrome c heme lyase (HCCS). In the mitochondrial PMF, increased ΔpH-supported backpressure due to diminishing electron transport and chemiosmosis promotes a more reductive mitochondrial physiological setting. OPTM by protein cysteine sulfonation in complex I and complex III has been shown to affect enzymatic catalysis, the proton gradient, redox status, and enzyme-mediated ROS production. Pathological conditions associated with oxidative or nitrosative stress, such as myocardial ischemia and reperfusion (I/R), increase mitochondrial ROS production and redox dysfunction via oxidative injury to complexes I and III, intensely enhancing protein cysteine sulfonation and impairing heme integrity. The physiological conditions of reductive stress induced by gains in SOD2 function normalize I/R-mediated ROS overproduction and redox dysfunction. Further insight into the cellular mechanisms by which HCCS, biogenesis of c-type cytochrome, and OPTM regulate PMF and ROS production in mitochondria will enrich our understanding of redox signal transduction and identify new therapeutic targets for cardiovascular diseases in which oxidative stress perturbs normal redox signaling.