Mechanism of Gdf3 action to limit insulin sensitivity in obesity

项目摘要 噻唑烷二酮类(TZD)是一种有效的抗糖尿病药物，其在治疗2型糖尿病方面的应用有限 由副作用引起。这项提议的目标是对 将TZDS降低血糖的积极代谢作用与其特征良好的负面作用分开 效果。PPARγ是TZDS的一个分子靶点，通过促进 新的脂肪细胞。然而，我们发现TZD对PPARγ有第二个生化功能，以阻断 丝氨酸273(PS273)的磷酸化。我们发现PPARγ在第273位丝氨酸的磷酸化促进胰岛素 在不影响脂肪生成的情况下进行抵抗。用药物或基因逆转这种磷酸化 抑制足以促进胰岛素敏感性，增加对寒冷的生热反应。我们建议 PPARγ丝氨酸第273位的磷酸化促进胰岛素抵抗的主要机制之一是 通过增加生长分化因子3(GDF3)的表达。GDF3是转化生长因子-2中的一种分泌型蛋白。 /骨形态发生蛋白超家族和骨形态发生蛋白信号的负调控因子。在脂肪组织中，BMP蛋白有助于 胰岛素敏感性和生热作用。因此，我们认为肥胖患者体内GDF3水平升高是其原因。 PPARγS273磷酸化介导的胰岛素抵抗。事实上，我们展示了异乎寻常的表达 GDF3足以引起瘦小鼠的胰岛素抵抗。在本提案中，我们考察了GDF3的贡献 与肥胖和胰岛素抵抗的发病机制有关。我们预测，阻断GDF3水平或活动将恢复 全身对胰岛素敏感，促进生热。我们将询问GDF3在葡萄糖中的作用 使用急性功能获得和功能丧失模型的动态平衡和肥胖。我们将利用创新 无线连续血糖监测新技术与间接量热法同步实现高血糖 精确测量胰岛素抵抗、能量平衡和循环营养供应。我们会 确定GDF3是否是PPARγS273磷酸化与胰岛素抵抗之间的联系机制。我们会 还要确定GDF3是否需要通过Smad1/5/8蛋白传递BMP信号。最后，我们将执行一个 利用全基因组CRISPR/Cas9对GDF3信号转导途径的无偏研究 淘汰屏。这一假说提出了一种新的治疗方式，它利用一种特定的益处 与TZD相关的副作用无关的TZD治疗方面。这项提案的结果将是 明确确定GDF3是否是促进代谢健康的合适靶点。

Project Summary The thiazolidinediones (TZDs) are powerful anti-diabetic drugs whose use in treating type 2 diabetes is limited by adverse side effects. The goal of this proposal is a biochemical investigation into the mechanism that separates the positive metabolic effects of TZDs to lower glucose from their well-characterized negative side effects. PPARγ, a molecular target of the TZDs, regulates systemic insulin sensitivity by promoting formation of new adipocytes. However, we show that the TZDs have a second biochemical function on PPARγ, to block phosphorylation of serine 273 (pS273). We find that phosphorylation of PPARγ at serine 273 promotes insulin resistance without affecting adipogenesis. Reversing this phosphorylation with pharmacological or genetic inhibition is sufficient to promote insulin sensitivity and increase thermogenic responses to cold. We propose that one of the main mechanisms by which phosphorylation of PPARγ at serine 273 promotes insulin resistance is through increased expression of growth differentiation factor 3 (Gdf3). Gdf3 is a secreted protein in the TGF- /BMP superfamily and a negative regulator of BMP signaling. In adipose tissue, BMP proteins contribute to insulin sensitivity and thermogenesis. We therefore propose that elevated levels of Gdf3 in obesity are the cause of insulin resistance mediated by PPARγ S273 phosphorylation. Indeed, we show that ectopic expression of Gdf3 is sufficient to cause insulin resistance in lean mice. In this proposal we examine the contribution of Gdf3 to the pathogenesis of obesity and insulin resistance. We predict that blocking Gdf3 levels or activity will restore whole-body insulin sensitivity and promote thermogenesis. We will interrogate the role of Gdf3 on glucose homeostasis and obesity using both acute gain-of-function and loss-of-function models. We will utilize innovative new wireless continuous glucose monitoring technology concurrently with indirect calorimetry to achieve high- precision measurements of insulin resistance, energy balance, and circulating nutrient availability. We will determine whether Gdf3 is the mechanism linking PPARγ S273 phosphorylation and insulin resistance. We will also determine whether Gdf3 requires BMP signaling through SMAD1/5/8 proteins. Finally, we will perform an unbiased investigation into the pathways required for Gdf3 signaling using a genome-wide CRISPR/Cas9 knockout screen. This hypothesis suggests a new therapeutic modality which harnesses a specific beneficial aspect of TZD treatment which is independent of TZD-associated side effects. The results from this proposal will definitively determine if Gdf3 is a suitable target for promoting metabolic health.