Linking the Metabolic State and Mitochondrial DNA in Chronic Disease, Health, and Aging

Abstract

Physical inactivity and overeating leading to obesity and diabetes are both linked to increased risk of age-related chronic diseases. By contrast, caloric restriction and physical activity promote health. However, the cellular mechanisms that link the metabolic state to long-term health outcomes have remained unclear. Damage to mitochondrial DNA (mtDNA), which accumulates with aging in diseased human tissues and with diabetes complications, has been shown in animal models to recapitulate several features of aging. Importantly, mitochondrial morphology, function, and the integrity of mtDNA directly respond to the metabolic state. The oversupply of cells with excess lipids and glucose (i.e., hyperglycemia) fragments mitochondria, increases mitochondrial reactive oxygen species production, and promotes the accumulation of mtDNA damage. In turn, the limited supply of energy substrates promotes fusion and elongation of mitochondria and limits accumulation of mtDNA damage. Here we propose a model in which mitochondrial dynamics (fusion/fission) integrate systemic metabolic information and control the stability of the mitochondrial genome, thus helping to mediate the effects of physical activity, inactivity, and calorie intake on health outcomes. It is well established both epidemiologically and clinically that physical inactivity and behaviors leading to weight gain are associated with elevated risk of most age-related diseases as well as mortality (1). However, the underlying mechanisms mediating these effects are not fully explained. Conversely, the health promoting and life-extending effects of caloric restriction and physical activity are well described (2,3). Nonetheless, the exact mechanisms underlying the health benefits of these interventions, including the reduced risk of most age-related metabolic diseases and diabetes complications, have not been fully elucidated. Here we present a common mechanism that may account for the combined long-term effects of physical activity/inactivity and diet on health outcomes and aging. Improved understanding of the acute cellular events initiated by fluctuations in the metabolic state may …