ACS DIVISION OF BIOLOGICAL CHEMISTRY

January 22nd, 2014 by Shao, D., Fry, J. L., Han, J., Hou, X., Pimentel, D. R., Matsui, R., Cohen, R. A., Bachschmid, M. M.

Sirtuin-1 (SirT1), a member of the NAD+-dependent class III histone deacetylase family, is inactivated in vitro by oxidation of critical cysteine thiols. In a model of metabolic disease, SirT1 activation attenuated apoptosis of hepatocytes and improved liver function including insulin and lipid metabolism. We show in SirT1 overexpressing HepG2 cells that oxidants (nitrosocysteine or hydrogen peroxide) or metabolic stress (high palmitate and high glucose) inactivate SirT1 by reversible oxidative post-translational modifications (OPTM) on cysteines. Mutating these oxidation-sensitive cysteines to serine preserves SirT1 activity and abolishes reversible OPTMs. Overexpressed mutant SirT1 maintains deacetylase activity and attenuates proapoptotic signaling, while overexpressed wild type SirT1 is less protective in metabolically or oxidant stressed cells. To prove that OPTMs of SirT1 are glutathione (GSH) adducts, glutaredoxin-1 (Glrx) was overexpressed to remove this modification. Glrx overexpression maintains endogenous SirT1 activity and prevents proapoptotic signaling in metabolically stressed HepG2 cells. The in vivo significance of oxidative inactivation of SirT1 was investigated in livers of high fat diet-fed C57/B6J mice. SirT1 deacetylase activity was decreased in the absence of changes in SirT1 expression and associated with a marked increase in OPTMs. These results indicate that glutathione adducts on specific SirT1 thiols may be responsible for dysfunctional SirT1 associated with liver disease in metabolic syndrome.