Previous studies have determined that mice with a homozygous deletion in the adapter protein p66 shc have an extended life span and that cells derived from these mice exhibit lower levels of reactive oxygen species. Here we demonstrate that a fraction of p66 shc localizes to the mitochondria and that p66 shc؊/؊ fibroblasts have altered mitochondrial energetics. In particular, despite similar cytochrome content, under basal conditions, the oxygen consumption of spontaneously immortalized p66

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... /؊ mouse embryonic fibroblasts were lower than similarly maintained wild type cells. Differences in oxygen consumption were particularly evident under chemically uncoupled conditions, demonstrating that p66 shc؊/؊ cells have a reduction in both their resting and maximal oxidative capacity. We further demonstrate that reconstitution of p66 shc expression in p66 shc؊/؊ cells increases oxygen consumption. The observed defect in oxidative capacity seen in p66 shc؊/؊ cells is partially offset by augmented levels of aerobic glycolysis. This metabolic switch is manifested by p66 shc؊/؊ cells exhibiting an increase in lactate production and a stricter requirement for extracellular glucose in order to maintain intracellular ATP levels. In addition, using an in vivo NADH photobleaching technique, we demonstrate that mitochondrial NADH metabolism is reduced in p66 shc؊/؊ cells. These results demonstrate that p66 shc regulates mitochondrial oxidative capacity and suggest that p66 shc may extend life span by repartitioning metabolic energy conversion away from oxidative and toward glycolytic pathways. . 2 The abbreviations used are: ROS, reactive oxygen species; MEF, mouse embroyo fibroblast; FCCP, carbonylcyanide 4-(trifluoromethoxy)phenylhydrazone; ED-FRAP, enzyme-dependent fluorescence recovery after photobleaching.