In humans with NIDDM the inability of insulin to suppress hepatic gluconeogenesis is a major defect. However, a single bout of endurance exercise improves this defect significantly in NIDDM subjects. The mechanisms for chronic elevation of gluconeogenesis in animal models of NIDDM are unknown, but may involve a defect in the insulin receptor and an unknown postreceptor defect at the level of gene expression. The applicant will test the hypothesis that hormonal regulation of liver gene expression is dramatically altered during exercise, reflecting metabolic processes that subsequently enhance the ability of insulin to suppress gluconeogenesis at the level of gene transcription. This research will use the hepatic PEPCK gene promotor as a model to link the mechanism by which exercise and NIDDM act at the insulin receptor level to a signal transduction event on the promoter.
In specific aim 1, a novel stable isotope technique will be used to establish the impact of prior exercise on hepatic gluconeogenesis and insulin resistance in the genetically obese db/db mouse.
In aim 2, the investigators will analyze the effects of prior exercise on insulin receptor binding, tyrosine kinase activity, and the ability of insulin to stimulate IRS-1 phosphorylation in liver.
In aim 3, transgenic mice with mutations in the glucocorticoid receptor binding site, insulin regulatory element and cAMP regulatory site of the PEPCK promoter will be used to determine whether exercise modifies the insulin signal through a specific target sequence on the promoter.
Specific aim 4 will be to cross-breed genetically obese db/db mice with the transgenic mice carrying a series of mutations in the PEPCK promoter to determine the role of hormone signaling elements and their potential transcription factors in inducing PEPCK gene expression and gluconeogenesis during the onset of type II diabetes. The outcome of these studies will provide new insights linking the mechanism by which exercise and NIDDM act at the receptor level to signal transduction event on the promoter, and should aid in understanding the role of exercise in altering insulin signaling to control gluconeogenesis in type II diabetes.
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