The Mammalian Longevity-associated Gene Product p66 Regulates Mitochondrial Metabolism

Abstract

Previous studies have determined that mice with a homozygous deletion in the adapter protein p66shc 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 p66shc؊/؊ mouse embryonic fibroblasts were lower than similarly maintained wild type cells. shc may extend life span by repartitioning metabolic energy conversion away from oxidative and toward glycolytic pathways.Generation of ATP in the mitochondria represents the most efficient pathway to meet the energetic needs of a cell. This process, however, requires the consumption of molecular oxygen with a corresponding production of reactive oxygen species (ROS).2 Generation of ROS appears to be one of the central mechanisms that contribute to aging in a wide range of organisms (1-3). In contrast, under aerobic conditions, energy generation can also be achieved through glycolytic pathways present in the cytosol. These cytosolic pathways are inherently less efficient but do not produce ROS. Each cell employs a different relative balance between these two major energetic pathways, although relatively little is known about how this partition is established or maintained.In lower organisms, such as Caenorhabditis elegans and Drosophila, a number of longevity-associated genes have been isolated. One prominent and well characterized aging pathway regulates the activity of the transcription factor DAF-16, a member of the Forkhead family of transcriptional regulators. Evidence suggests that DAF-16 is involved in responding to numerous environmental stresses (4). A rise in intracellular ROS is one particular stress that may be relevant to life span determination, and in this regard, it is of interest that both DAF-16 and its closest mammalian ortholog Foxo3a appear to regulate a number of cellular antioxidant proteins (5-9).In addition to the DAF-16 pathway, RNAi screens performed in C. elegans has identified a number of other putative longevity genes (10, 11). Interestingly, functional characterization of these longevity-associated genes have determined that a number of them appear to be important for mitochondrial function. Similarly, direct knockdown of components of the electron transport chain has also been shown to extend the life span of the worm (12). Analysis of these long lived mitochondrial mutants, as well as in depth energetic analysis of the previously characterized DAF-16-related mutants, has led to the proposal that many life span-extending mutants in C. elegans slow aging by decreasing mitochondrial metabolism (13). This hypothesis suggests that a shift away from trichloroacetic acid-based mitochondrial metabolism might extend life by a reduction in oxidative stress. Nonetheless, it should be mentioned that the relationship bet...

Mammalian life-span determinant p66 shcA mediates obesity-induced insulin resistance

“…S4A); however, microspectrofluorometric analysis of cellular autofluorescence (Fig. S4D) indicated that p66 slightly but significantly reduced cellular accumulation of NAD(P)H in cells exposed to glucose, in keeping with a role for this protein in accelerating NAD(P)H oxidation in mitochondria (28). Moreover, overexpression of p66shc and p66shc qq , a mutant p66shc reportedly devoid of prooxidant activity (15), activated S6K to a comparable extent in serum-stimulated 3T3L1 cells, while having no effect on the redox-sensitive stress kinase p38 MAPK (Fig.…”

Secrets of the lac Operon

“…However, it has now been demonstrated that the clk-1 mutation depresses complex I activity while sparing complex II activity [37], thus favoring the utilization of complex II at the expense of complex I. Similarly, in mice, ablation of the p66shc gene increases life span and reduces the production of reactive oxygen species, apparently by reducing NADH levels and thus the utilization of complex I [38]. Interestingly, a mutation in NADH dehydrogenase, a key enzyme in complex I, is also associated with increased longevity in humans [39].…”

Mitochondrial protein phosphorylation: instigator or target of lipotoxicity?

“…For example, the translocation of pro-and antiapoptotic Bcl-2 family members is frequently regulated by phosphorylation-dephosphorylation cycles [30]. In this respect, the Src-homology-2-domain-containing transforming protein 1 (p66Shc), which is predominantly localized in the cytosol [31] but also shown to interact with the mitochondrial heat-shock protein 70 [32], perhaps represents the most appealing factor. Under conditions of cytosolic oxidative stress, such as occurs under lipotoxic conditions or hyperglycemia, PKCβ phosphorylates cytosolic p66Shc, which then binds to Pin1 and translocates into the intermembrane space, where it is activated, perhaps via phosphatase PP2A-mediated dephosphorylation [33,34].…”