Mice deficient in the Polycomb repressor Bmi1 develop numerous abnormalities including a severe defect in stem cell self-renewal, alterations in thymocyte maturation and a shortened lifespan. Previous work has implicated de-repression of the Ink4a/Arf (also known as Cdkn2a) locus as mediating many of the aspects of the Bmi1–/– phenotype. Here we demonstrate that cells derived from Bmi1–/– mice also have impaired mitochondrial function, a marked increase in the intracellular levels of reactive oxygen species and subsequent engagement of the DNA damage response pathway. Furthermore, many of the deficiencies normally observed in Bmi1–/– mice improve after either pharmacological treatment with the antioxidant N-acetylcysteine or genetic disruption of the DNA damage response pathway by Chk2 (also known as Chek2) deletion. These results demonstrate that Bmi1 has an unexpected role in maintaining mitochondrial function and redox homeostasis and indicate that the Polycomb family of proteins can coordinately regulate cellular metabolism with stem and progenitor cell function.

Cellular longevity is a complex process relevant to age-related diseases including but not limited to chronic illness such as diabetes and metabolic syndromes. Two gene families have been shown to play a role in the genetic regulation of longevity; the Sirtuin and FOXO families. It is also established that nuclear Sirtuins interact with and under specific cellular conditions regulate the activity of FOXO gene family proteins. Thus, we hypothesize that a mitochondrial Sirtuin (SIRT3) might also interact with and regulate the activity of the FOXO proteins. To address this we used HCT116 cells overexpressing either wild-type or a catalytically inactive dominant negative SIRT3. For the first time we establish that FOXO3a is also a mitochondrial protein and forms a physical interaction with SIRT3 in mitochondria. Overexpression of a wild-type SIRT3 gene increase FOXO3a DNA-binding activity as well as FOXO3a dependent gene expression. Biochemical analysis of HCT116 cells over expressing the deacetylation mutant, as compared to wild-type SIRT3 gene, demonstrated an overall oxidized intracellular environment, as monitored by increase in intracellular superoxide and oxidized glutathione levels. As such, we propose that SIRT3 and FOXO3a comprise a potential mitochondrial signaling cascade response pathway.

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...