Increased replicative longevity in Saccharomyces cerevisiae because of calorie restriction has been linked to enhanced mitochondrial respiratory activity. Here we have further investigated how mitochondrial respiration affects yeast life span. We found that calorie restriction by growth in low glucose increased respiration but decreased mitochondrial reactive oxygen species production relative to oxygen consumption. Calorie restriction also enhanced chronological life span. The beneficial effects of calorie restriction on mitochondrial respiration, reactive oxygen species release, and replicative and chronological life span could be mimicked by uncoupling agents such as dinitrophenol. Conversely, chronological life span decreased in cells treated with antimycin (which strongly increases mitochondrial reactive oxygen species generation) or in yeast mutants null for mitochondrial superoxide dismutase (which removes superoxide radicals) and for RTG2 (which participates in retrograde feedback signaling between mitochondria and the nucleus). These results suggest that yeast aging is linked to changes in mitochondrial metabolism and oxidative stress and that mild mitochondrial uncoupling can increase both chronological and replicative life span.The only intervention known to increase average and maximum life span in mammals is caloric restriction (CR), 1 a reduction of 25-60% in calorie intake without essential nutrient deficiency. This diet not only extends life span but also delays many unwanted effects of aging and age-related pathologies. CR is highly effective in a wide range of organisms, increasing life span by up to 50% in some species (reviewed in Refs. 1-3). Unfortunately, the mechanisms through which it results in increased life span are still controversial (see Ref. 4
for a critical review).A leading hypothesis on the mechanism through which CR prevents aging is that this process decreases reactive oxygen species (ROS) generation and, hence, the oxidation of cellular components (5-8). Indeed, aging is usually accompanied by oxidative damage of DNA, proteins, and lipids (9, 10). CR promotes a metabolic shift resulting in more efficient electron transport in the mitochondrial respiratory chain (1, 5). Faster and more efficient electron transport may lead to lower production of ROS by mitochondria, one of the major intracellular ROS sources. This occurs because of reduced leakage of electrons from the respiratory chain and/or lower oxygen concentrations in the mitochondrial microenvironment (11,12). Indeed, artificially increasing mitochondrial respiration using uncouplers such as 2,4-dinitrophenol (DNP) strongly prevents mitochondrial ROS release (11). Furthermore, CR decreases ROS release/O 2 consumed in isolated mammalian mitochondria (13), possibly because of enhanced expression of mitochondrial uncoupling proteins (14,15). Despite this evidence supporting a correlation between ROS-induced damage and aging, a clear cause-effect relationship has been hard to establish, and conflicting results are often p...