BADERC-Raul Mostoslavsky

Raul Mostoslavsky, M.D., Ph.D.

Cells need to accurately maintain their nuclear DNA in order to function properly. Indeed, defects in DNA integrity are associated with cancer, aging, and immunodeficiency. Therefore, numerous DNA repair systems in mammalian cells function to endow us with long and relatively tumor-free lives. The DNA and the histones are arranged in the nucleus in a highly condensed structure known as chromatin. Cellular processes that unwind the double helix, such as transcription, replication and DNA repair, have to overcome this natural barrier to DNA accessibility. Multicellular organisms also need to control their use of cellular energy stores. The insulin signaling (IS) pathway plays a crucial role in metabolic homeostasis, influencing energy consumption, cell proliferation, stress resistance, and lifespan. Defective insulin signaling causes numerous diseases ranging from diabetes to an increased tendency to develop tumors. For cells to respond appropriately to changes in energy status or to DNA damage, there is likely to be a close coupling of DNA repair, chromatin remodelling and metabolic pathways.

Our lab is interested in understanding the influence of chromatin on DNA repair, and the relationship between the DNA damage response and the metabolic adaptation of cells. We focus on the study of a group of proteins called SIRTs, the mammalian homologues of the yeast Sir2. Sir2 is a chromatin silencer that functions as an NAD- dependent histone deacetylase to inhibit DNA transcription and recombination. We have found that one of the mammalian Sir2 homologues, SIRT6, binds to chromatin and regulates DNA repair through the Base Excision Repair pathway that removes oxidated and alkylated DNA bases. In addition, we have shown that SIRT6 regulates metabolic responses in cells, and that mice lacking SIRT6 exhibit severe metabolic defects, including a fatal hypoglycemia. SIRT6 appears to modulate glucose flux inside the cells, directing glucose away of glycolysis and into the mitochondria. In this regard, SIRT6 functions as a critical modulator of cellular stress, regulating glucose metabolism as a co-repressor of Hif1a. In the presence of nutrients, SIRT6 binds Hif1a and deacetylates H3K9 at Hif1a target promoters, thereby suppressing Hif1a-dependent transcriptional activation of these genes. Under conditions of nutrient stress, SIRT6 is inactivated, enabling a Hif1a-dependent response with increased glucose uptake, enhanced glycolysis and inhibition of mitochondrial respiration. Our current studies are directed at determining how SIRT6 regulates glucose flux at the molecular level. Understanding the role of SIRT6 in glucose homeostasis might pave the way for future therapeutic approaches in glucose-related diseases, such as diabetes and obesity. As well, understanding the link between the metabolic defects and the genomic instability in SIRT6 deficient cells would help define their relative contribution in age- related diseases, such as cancer and neurodegeneration.

References:

Chua, K.F.*, Mostoslavsky, R.*, Lombard, D.B., Pang, W.W., Saito, S., Franco, S., Kaushal, D., Cheng, H-L, Fischer, M.R., Stokes, N., Murphy, M., Apella, E., and Alt, F.W. Mammalian Sirt1 limits replicative life-span in response to chronic genotoxic stress. (2005). Cell Metabolism 2, 67-76.* Both authors contributed equally to this work.
Mostoslavsky, R., Chua, K.F, Lombard, D.L., Pang, W.W, Fischer, M.R., Gellon, L., Liu, P., Mostoslavsky, G., Franco, S., Murphy, M.M., Mills, K.D., Patel, P., Hsu, J., Hong, A.L., Ford, E., Cheng, H-L., Kennedy, C., Nunez, N., Bronson, R., Frendewey, D., Auerbach, W., Valenzuela, D., Karow, M., Hottiger, M.O., Hursting, S., Barrett, J.C., Guarente, L., Mulligan, R., Demple, B., Yancopolous, G.D., and Alt, F.W. Genomic instability and aging-like phenotype in the absence of mammalian SIRT6. (2006). Cell, 124, 315-329.
Haigis, M.C.*, Mostoslavsky, R.*, Haigis, K.M., Fahie, K., Christodoulou, D.C., Murphy, A.J., Valenzuela, D., Yancopoulos, G.D., Karow, M., Blander, G., Wolberger, C., Prolla, T.A., Weindruch, R., Alt, F.W., and Guarente, L. SIRT4 inhibits glutamate dehydrogenase and opposes the effects of calorie restriction in pancreatic b cells. (2006). Cell, 126, 941-954. *Both authors contributed equally to this work.
Gerhart-Hines, Z., Rodgers, J.T., Bare,O., Lerin, C., Kim, S-h, Mostoslavsky, R., Alt, F.W., Wu, Z., and Puigserver, P. Metabolic control of muscle mitochondrial function and fatty acid oxidation through SIRT1/PGC1a. (2007). EMBO J, 26, 1913-1926.
Potente, M., Ghaeni, L., Baldessari, D., Mostoslavsky, R., Rossig, L., Dequiedt, F., Haendeler, J., Mione, M., Dejana, E., Alt, F.W., Zeiher, A.M., and Dimmeler, S. (2007). Sirt1 controls endothelial angiogenic functions during postnatal vascular growth. Genes & Dev. 21, 2644-2658.
Lee, I.H., Cao, L., Mostoslavsky, R., Lombard, D.B., Liu, J., Bruns, N.E., Tsokos, M., Alt, F.W. and Finkel, T. (2008). A role for the NAD-dependent deacetylase Sirt1 in the regulation of autophagy. Proc. Natl. Acad. Sci. USA. 105, 3374-3379.
Asher, G., Gatfield, D., Stratmann, M., Reinke, H., Dibner, C., Kreppel, F., Mostoslavsky, R., Alt., F.W., and Schibler, U. (2008). SIRT1 regulates circadian clock gene expression through PER2 deacetylation. Cell 134, 317-328.
Oberdoerffer, P., Michan, S., McVay, M., Mostoslavsky, R., Hartlerode, A., Stegmuller, J., Vann, J., Park, S-K., Hafner, A., Loerch, P., Wright, S.M., Mills, K.D., Bonni, A., Yankner, B.A., Scully, R., Prolla, T.A., Alt, F.W., and Sinclair, D. (2008). DNA damage-induced alterations in chromatin contribute to genomic integrity and age-related changes in gene expression. Cell, 135, 907-918.
Van Gool, F., Galli, M., Gueydan, C., Kruys, V., Prevot, P-P, Bedalov, A., Mostoslavsky, R., Alt, F.W., De Smedt, T. and Leo, O. (2009). Intracellular NAD levels regulate tumor necrosis factor protein synthesis in a sirtuin-dependent manner. Nat. Med. 15, 206-210.

Reviews and Chapters

Lombard, D.B., Chua, K.F., Mostoslavsky, R., Franco, S., Gostissa, M., and Alt, F.W. (2005) DNA repair, genomic stability, and aging. Cell 120, 497-512.
Lombard, D.B., Schwer, B., Alt., F.W. and Mostoslavsky, R. (2008). SIRT6 in DNA repair, metabolism and ageing. J. Intern. Med. 263, 128-141.
Mostoslavsky, R. (2008). DNA repair, insulin signaling and sirtuins: at the crossroads between cancer and aging. Front. Biosci. 13, 6966-6990.






			Raul Mostoslavsky, M.D., Ph.D. Cells need to accurately maintain their nuclear DNA in order to function properly. Indeed, defects in DNA integrity are associated with cancer, aging, and immunodeficiency. Therefore, numerous DNA repair systems in mammalian cells function to endow us with long and relatively tumor-free lives. The DNA and the histones are arranged in the nucleus in a highly condensed structure known as chromatin. Cellular processes that unwind the double helix, such as transcription, replication and DNA repair, have to overcome this natural barrier to DNA accessibility. Multicellular organisms also need to control their use of cellular energy stores. The insulin signaling (IS) pathway plays a crucial role in metabolic homeostasis, influencing energy consumption, cell proliferation, stress resistance, and lifespan. Defective insulin signaling causes numerous diseases ranging from diabetes to an increased tendency to develop tumors. For cells to respond appropriately to changes in energy status or to DNA damage, there is likely to be a close coupling of DNA repair, chromatin remodelling and metabolic pathways. Our lab is interested in understanding the influence of chromatin on DNA repair, and the relationship between the DNA damage response and the metabolic adaptation of cells. We focus on the study of a group of proteins called SIRTs, the mammalian homologues of the yeast Sir2. Sir2 is a chromatin silencer that functions as an NAD- dependent histone deacetylase to inhibit DNA transcription and recombination. We have found that one of the mammalian Sir2 homologues, SIRT6, binds to chromatin and regulates DNA repair through the Base Excision Repair pathway that removes oxidated and alkylated DNA bases. In addition, we have shown that SIRT6 regulates metabolic responses in cells, and that mice lacking SIRT6 exhibit severe metabolic defects, including a fatal hypoglycemia. SIRT6 appears to modulate glucose flux inside the cells, directing glucose away of glycolysis and into the mitochondria. In this regard, SIRT6 functions as a critical modulator of cellular stress, regulating glucose metabolism as a co-repressor of Hif1a. In the presence of nutrients, SIRT6 binds Hif1a and deacetylates H3K9 at Hif1a target promoters, thereby suppressing Hif1a-dependent transcriptional activation of these genes. Under conditions of nutrient stress, SIRT6 is inactivated, enabling a Hif1a-dependent response with increased glucose uptake, enhanced glycolysis and inhibition of mitochondrial respiration. Our current studies are directed at determining how SIRT6 regulates glucose flux at the molecular level. Understanding the role of SIRT6 in glucose homeostasis might pave the way for future therapeutic approaches in glucose-related diseases, such as diabetes and obesity. As well, understanding the link between the metabolic defects and the genomic instability in SIRT6 deficient cells would help define their relative contribution in age- related diseases, such as cancer and neurodegeneration. References: Chua, K.F., Mostoslavsky, R.,** Lombard, D.B., Pang, W.W., Saito, S., Franco, S., Kaushal, D., Cheng, H-L, Fischer, M.R., Stokes, N., Murphy, M., Apella, E., and Alt, F.W. Mammalian Sirt1 limits replicative life-span in response to chronic genotoxic stress. (2005). Cell Metabolism 2, 67-76.* Both authors contributed equally to this work. Mostoslavsky, R., Chua, K.F, Lombard, D.L., Pang, W.W, Fischer, M.R., Gellon, L., Liu, P., Mostoslavsky, G., Franco, S., Murphy, M.M., Mills, K.D., Patel, P., Hsu, J., Hong, A.L., Ford, E., Cheng, H-L., Kennedy, C., Nunez, N., Bronson, R., Frendewey, D., Auerbach, W., Valenzuela, D., Karow, M., Hottiger, M.O., Hursting, S., Barrett, J.C., Guarente, L., Mulligan, R., Demple, B., Yancopolous, G.D., and Alt, F.W. Genomic instability and aging-like phenotype in the absence of mammalian SIRT6. (2006). Cell, 124, 315-329. Haigis, M.C., Mostoslavsky, R.,** Haigis, K.M., Fahie, K., Christodoulou, D.C., Murphy, A.J., Valenzuela, D., Yancopoulos, G.D., Karow, M., Blander, G., Wolberger, C., Prolla, T.A., Weindruch, R., Alt, F.W., and Guarente, L. SIRT4 inhibits glutamate dehydrogenase and opposes the effects of calorie restriction in pancreatic b cells. (2006). Cell, 126, 941-954. Both authors contributed equally to this work. Gerhart-Hines, Z., Rodgers, J.T., Bare,O., Lerin, C., Kim, S-h, Mostoslavsky, R.,* Alt, F.W., Wu, Z., and Puigserver, P. Metabolic control of muscle mitochondrial function and fatty acid oxidation through SIRT1/PGC1a. (2007). EMBO J, 26, 1913-1926. Potente, M., Ghaeni, L., Baldessari, D., Mostoslavsky, R., Rossig, L., Dequiedt, F., Haendeler, J., Mione, M., Dejana, E., Alt, F.W., Zeiher, A.M., and Dimmeler, S. (2007). Sirt1 controls endothelial angiogenic functions during postnatal vascular growth. Genes & Dev. 21, 2644-2658. Lee, I.H., Cao, L., Mostoslavsky, R., Lombard, D.B., Liu, J., Bruns, N.E., Tsokos, M., Alt, F.W. and Finkel, T. (2008). A role for the NAD-dependent deacetylase Sirt1 in the regulation of autophagy. Proc. Natl. Acad. Sci. USA. 105, 3374-3379. Asher, G., Gatfield, D., Stratmann, M., Reinke, H., Dibner, C., Kreppel, F., Mostoslavsky, R., Alt., F.W., and Schibler, U. (2008). SIRT1 regulates circadian clock gene expression through PER2 deacetylation. Cell 134, 317-328. Oberdoerffer, P., Michan, S., McVay, M., Mostoslavsky, R., Hartlerode, A., Stegmuller, J., Vann, J., Park, S-K., Hafner, A., Loerch, P., Wright, S.M., Mills, K.D., Bonni, A., Yankner, B.A., Scully, R., Prolla, T.A., Alt, F.W., and Sinclair, D. (2008). DNA damage-induced alterations in chromatin contribute to genomic integrity and age-related changes in gene expression. Cell, 135, 907-918. Van Gool, F., Galli, M., Gueydan, C., Kruys, V., Prevot, P-P, Bedalov, A., Mostoslavsky, R., Alt, F.W., De Smedt, T. and Leo, O. (2009). Intracellular NAD levels regulate tumor necrosis factor protein synthesis in a sirtuin-dependent manner. Nat. Med. 15, 206-210. Reviews and Chapters Lombard, D.B., Chua, K.F., Mostoslavsky, R., Franco, S., Gostissa, M., and Alt, F.W. (2005) DNA repair, genomic stability, and aging. Cell 120, 497-512. Lombard, D.B., Schwer, B., Alt., F.W. and Mostoslavsky, R. (2008). SIRT6 in DNA repair, metabolism and ageing. J. Intern. Med. 263, 128-141. Mostoslavsky, R. (2008). DNA repair, insulin signaling and sirtuins: at the crossroads between cancer and aging. Front. Biosci. 13, 6966-6990.