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

描述(由申请人提供)：胰岛素抵抗是2型糖尿病的一个潜在原因，也是代谢综合征的一个重要特征。我们已经证明，雌激素提供了对已知的导致男性胰岛素抵抗的代谢和遗传干扰的保护，这种保护随着年龄的增长和更年期的到来而消失。与雌激素的作用类似，噻唑烷二酮类化合物(TZDS)激活PPAR-γ(G)可引起胰岛素敏化，其机制是参与葡萄糖和脂肪酸代谢以及炎症的基因转录。我们之前已经证明，选择性骨骼肌PPAR-g缺失(MKO)会导致年轻和老年雄性小鼠的葡萄糖耐量异常和严重的胰岛素抵抗。令人惊讶的是，在雌性MKO小鼠身上的初步研究表明，骨骼肌PPAR-g的缺失会增强葡萄糖耐量和胰岛素敏感性，这与雄性小鼠的表型相反。随后，我们用TZD或雌二醇(E2)治疗雄性MKO小鼠，虽然TZD对骨骼肌胰岛素敏感性没有影响，但E2治疗引起的胰岛素作用高于WT对照组小鼠，这意味着PPAR-g和雌激素受体之间存在串扰。在目标1中，我们将验证PPAR-g降低雌激素动物骨骼肌ER作用的假设。我们将评估在存在或不存在骨骼肌PPAR-g(MKO)的情况下，用或不用E2处理的雄性和雌性小鼠的胰岛素敏感性(FL/FL对照)。在目标2中，我们将验证一种假设，即罗格列酮激活PPAR-g可以降低雌性大鼠因卵巢切除和或高脂饮食而导致的胰岛素抵抗的E2的胰岛素增敏作用。在这两个目标中，我们将进行葡萄糖钳夹研究，以评估胰岛素敏感性，并辅之以体外研究，以探讨导致表型表达的分子机制。为此，将对夹闭动物的组织进行Western印迹和定量RT-PCR分析，以评估肌肉和脂肪中胰岛素信号转导和基因转录的变化。这些研究对老年糖尿病妇女具有重要的临床意义，因为这些激动剂对基因转录的相互作用尚不清楚。此外，我们的目标是阐明核受体串扰在基因转录调控中的重要性，并表明异常串扰是胰岛素抵抗和肥胖的潜在机制。

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.