Role of excess glycogenolysis in fasting hyperglycemia in obesity-associated T2DM

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DESCRIPTION (provided by applicant): Type 2 diabetes mellitus (T2DM) is getting epidemic threatening millions of people and its increase is tightly related with the rapid increase of obesity throughout the world. Insulin resistance may proceed decades before the onset of diabetes and it is common in obese individuals. My long term goal in research is finding primary cause(s) of insulin resistance and elucidating the interactions between glucose and lipid metabolism in T2DM, which are essential for strategy development to prevent the onset of diabetes and to fine a cure or better treatments for the disease. A key clinical observation for diagnosis of diabetes is fasting hyperglycemia. Hepatic glucose overproduction contributes fasting hyperglycemia, but controversial data have been reported about the roles of glycogenolysis and gluconeogenesis in T2DM. Recently I found that preserved liver glycogen in fasting resulted in excess glycogenolysis, and subsequently contributed fasting hyperglycemia in rodent models for obesity-associated T2DM. This observation could be important in understanding the failure of hepatic glucose autoregulation in obese T2DM patients because increased fasting hepatic glycogen was reported in obese humans and T2DM patients. Excess liver glycogen in fasting could be critical in fasting hyperglycemia in those individuals because endogenous glucose production is sensitive to the amount of hepatic glycogen available for hydrolysis. In this proposal, liver metabolic changes in obesity and in obesity-associated T2DM will be evaluated in the connection with systemic metabolic fluxes of whole animals. A short-term high-fat diet induced hepatic insulin resistance and the interaction between lipid and carbohydrate metabolism in obesity-associated T2DM will be evaluated focusing hepatic glycogen. It will be determined whether inhibition of glycogenolysis alters fasting hyperglycemia in rodent models of obesity-associated T2DM. The Advanced Imaging Research Center has pioneered in method development to evaluate comprehensive metabolic fluxes in vivo and to study intermediary metabolism using simultaneous administration of stable isotope tracers. The technologies with high field nuclear magnetic resonance (NMR) spectroscopy will be adapted in performing proposed research projects.