The impact of PPAR-gamma and estrogen receptor crosstalk on insulin action

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DESCRIPTION (provided by applicant): Insulin resistance is an underlying cause of type 2 diabetes and a defining feature of the Metabolic Syndrome. We have shown that estrogen provides protection from metabolic and genetic perturbations known to cause insulin resistance in males and this protection is lost with age and coinciding with menopause. Similar to the effects of estrogen, PPAR-gamma (g) activation by thiazolidinediones (TZDs) causes insulin sensitization via alterations is transcription of genes involved in glucose and fatty acid metabolism as well as inflammation. We have previously shown that selective skeletal muscle PPAR-g deletion (MKO) causes glucose intolerance and severe insulin resistance in young and aged male mice. Surprisingly, preliminary studies in female MKO mice show that loss of skeletal muscle PPAR-g yields enhanced glucose tolerance and insulin sensitivity, a phenotype opposite of that described for males. Subsequently we have treated male MKO mice with a TZD or estradiol (E2), and while the TZD was without effect on skeletal muscle insulin sensitivity, E2 treatment caused increased insulin action above that observed for WT control mice which implicates a crosstalk between PPAR-g and the estrogen receptor. In Aim 1, we will test the hypothesis that PPAR-g decreases ER action in skeletal muscle from estrogenized animals. We will assess insulin sensitivity in male and female mice treated with or without E2 in the presence (fl/fl Control) or absence of skeletal muscle PPAR-g (MKO). In Aim 2 we will test the hypothesis that PPAR-g activation by Rosiglitazone diminishes the insulin sensitizing effects of E2 in female rats rendered insulin resistant by ovariectomy and or high fat diet. In both aims we will perform glucose clamp studies to assess insulin sensitivity complemented by in vitro studies to investigate the molecular mechanisms leading to phenotypic expression. To this end, Western blot and quantitative RT-PCR analyses will be performed on tissues harvested from clamped animals to assess alterations in insulin signal transduction and gene transcription in muscle and fat. These studies are of clinical importance for diabetic women of advanced age as the interaction of these agonists on gene transcription is unknown. Additionally our goal is to elucidate the importance of nuclear receptor crosstalk in the regulation of gene transcription and show that aberrant crosstalk is an underlying mechanism of insulin resistance and obesity.