Homeostatic mechanisms in mammals function to maintain blood glucose levels within a narrow range in response to hormones and nutrients. Glucose homeostasis is highly dysregulated in metabolic diseases such as obesity and diabetes as well as in dietary manipulations such as caloric restriction (CR). CR extends life span and causes many changes in glucose metabolism similar to fasting. However, how the metabolism of glucose might be connected to aging is largely unknown. One key component of glucose homeostasis in mammals is the transcriptional coactivator PGC-1alpha that controls glucose production in liver. Studies in yeast and worms have identified a Sir2 histone deacetylase protein as a possible link between caloric restriction and life span. Importantly, we have preliminary data showing that SIRT1 (mammalian Sir2 homolog) is regulated by insulin in hepatocytes. SIRT1 interacts with and deacetylates PGC-1alpha at specific lysine residues in an NAD+ dependent manner. In addition, in cultured hepatocytes SIRT1 regulates gluconeogenic/glycolytic genes and hepatic glucose output through PGC-lalpha. This application contains three large aims. First, we will identify the mechanisms of how insulinregulates SIRT1. Second, we will perform a detailed biochemical and cellular analysis of the physical and functional interaction between PGC-1alpha and SIRT1. We will focus on the regulatory mechanisms of SIRT1 on PGC-1alpha function on hepatic glucose metabolic genes. Finally, to bring the PGC-1alpha /SIRT1 mechanistic and cellular studies to the animal level we will perform a glucose-related gene expression and metabolic analysis using adenoviral delivery to the liver of mice. Taken together, the findings of these studies will allow us to identify the molecular mechanism by which two important regulated transcriptional components, PGC-1alpha and SIRT1 control glucose homeostasis in response to CR signals such as insulin. Understanding of these metabolically regulated molecular events could be used for anti-obesity, diabetes or aging drug development. These findings have strong implications for the basic pathways of energy homeostasis, diabetes and lifespan.
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