Regulation of Energy Metabolism in Human Cells in Aging and Diabetes: FoF1, mtDNA, UCP, and ROS

Abstract

Recent advances in bioenergetics consist of discoveries related to rotational coupling in ATP synthase (FoF1), uncoupling proteins (UCP), reactive oxygen species (ROS) and mitochondrial DNA (mtDNA). As shown in cloned sheep, mammalian genomes are composed of both nuclear DNA (nDNA) and maternal mtDNA. Oxidative phosphorylation (oxphos) varies greatly depending on cellular activities, and is regulated by both gene expression and the electrochemical potential difference of H+ (Δ μH+). The expression of both mtDNA (by mtTFA) and nDNA for oxphos and UCP (by NRFs, etc.) is coordinated by a factor called PGC-1. The Δ μH+ rotates an axis in FoF1 that is regulated by inhibitors and ATP-sensitive K+-channels. We cultured human ρo cells (cells without mtDNA) in synthetic media and elucidated relationships among mtDNA, nDNA, Δ μH+, UCPs, ROS, and apoptosis. These cells lack oxphos-dependent ROS formation and survive under conditions of high O2. Cells cultured in the absence of ROS scavengers have proliferated for 40 years. UCPs lower Δ μH+ and prevent ROS formation and resulting apoptosis. These results were applied to diabetology and gerontology. The pancreatic ρo cells did not secrete insulin, and mtDNA mutations caused diabetes, owing to the deficient Δ μH+. Insulin resistance was closely related to UCPs and other energy regulators. The resulting high-glucose environment caused glycation of proteins and ROS-mediated apoptosis in vascular cells involved in diabetic complications. Telomeres, oxphos, and ROS are determinants in cellular aging. Cell division and ROS shortened telomeres and accelerated aging. In aged cells, Δ μH+ was reduced by the slow respiration, and this change induced apoptosis. Cybrids made from aged cytoplasts and ρo cells showed that both decreased expression of nDNA, and somatic mutations of mtDNA are involved in the slowing of respiration in aged cells.