Metabolic effects of adipose lipogenesis

描述（由申请人提供）：我们对胰岛素抵抗和2型糖尿病的分子机制的认识存在重大差距。葡萄糖和脂质代谢的失调都起作用。该建议调查这些途径之间的机械联系。脂肪酸合成（从头脂肪生成，DNL）在肥胖和2型糖尿病的肝脏中升高，并且通常与胰岛素抵抗相关。相反，我们的新数据表明，脂肪组织中的DNL对代谢有益，因为它促进胰岛素敏感性，防止高脂肪饮食诱导的胰岛素抵抗。此外，在人类中，脂肪组织中脂肪生成酶表达的增加与胰岛素敏感性的增强有关。DNL的主要转录调节因子之一是碳水化合物反应元件结合蛋白（ChREBP），一种葡萄糖反应性转录因子。ChREBP主要在肝脏和胰腺细胞中进行研究，在那里它调节脂肪酸合成和糖酵解。ChREBP基因敲除小鼠具有轻度饮食相关的胰岛素抵抗。然而，敲低肥胖小鼠肝脏中升高的ChREBP表达可改善胰岛素敏感性和代谢综合征。尚未研究选择性ChREBP敲低在脂肪组织中的作用。我们最近的论文表明，脂肪组织ChREBP是人体和啮齿动物全身胰岛素敏感性和葡萄糖稳态的关键决定因素。 本申请的目的是整合整个动物和细胞研究，以确定脂肪组织中ChREBP促进胰岛素敏感性的生理，细胞和分子机制。我们将创建在脂肪细胞中选择性过表达或缺乏ChREBP的小鼠。目的1是确定ChREBP在脂肪细胞中选择性表达的增加是否足以增强全身胰岛素敏感性和改善葡萄糖稳态。目的2是确定脂肪细胞中ChREBP选择性缺失是否会导致全身性胰岛素抵抗。除了生理和代谢表征，在这两个目标中，我们将进行脂肪组织和血清的基因组学和脂质组学分析，以确定与胰岛素敏感性和胰岛素抵抗相关的途径。目的3是确定ChREBP调节脂肪细胞脂肪生成的细胞机制。分子、细胞生物学、生物化学和定量显微镜方法将用于确定脂肪细胞中ChREBP核质穿梭和活化的调节机制，以及胰岛素信号在脂肪-ChREBP活性调节中的潜在作用。总的来说，该项目将提供生理，分子和细胞的见解ChREBP调节。由于肥胖人群脂肪组织中ChREBP表达减少与胰岛素抵抗高度相关，因此了解脂肪细胞中ChREBP的调节机制可能会导致预防和治疗2型糖尿病的新治疗方法。

DESCRIPTION (provided by applicant): Major gaps exist in our knowledge of the molecular mechanisms underlying insulin resistance and type 2 diabetes. Dysregulation of both glucose and lipid metabolism play a role. This proposal investigates the mechanistic links between these pathways. Fatty acid synthesis (de novo lipogenesis, DNL) is elevated in liver in obesity and type 2 diabetes and is usually associated with insulin resistance. In contrast, our new data indicate DNL in adipose tissue is metabolically beneficial since it promotes insulin sensitivity an protects against high fat diet-induced insulin resistance. Furthermore, in humans, increased lipogenic enzyme expression in adipose tissue is associated with enhanced insulin sensitivity. One of the major transcriptional regulators of DNL is Carbohydrate responsive-element binding protein (ChREBP), a glucose-responsive transcription factor. ChREBP has been studied mainly in liver and pancreatic ¿ cells where it regulates fatty acid synthesis and glycolysis. ChREBP knockout mice have mild diet-related insulin resistance. However, knocking down the elevated ChREBP expression in liver of obese mice improves insulin sensitivity and metabolic syndrome. The effects of selective ChREBP knockdown in adipose tissue have not been studied. Our recent paper demonstrates that adipose tissue ChREBP is a key determinant of systemic insulin sensitivity and glucose homeostasis in humans and rodents. The goal of this application is to integrate whole animal and cellular studies to define the physiological, cellular and molecular mechanisms underlying the effects of ChREBP in adipose tissue to promote insulin sensitivity. We will create mice that overexpress or lack ChREBP selectively in adipocytes. Aim 1 is to determine whether increased expression of ChREBP selectively in adipocytes is sufficient to enhance systemic insulin sensitivity and improve glucose homeostasis. Aim 2 is to determine whether absence of ChREBP selectively in adipocytes causes systemic insulin resistance. In addition to physiological and metabolic characterization, in both aims we will perform genomic and lipidomic analyses of adipose tissue and serum to identify pathways associated with insulin sensitivity and insulin resistance. Aim 3 is to determine the cellular mechanisms by which ChREBP regulates de novo lipogenesis in adipocytes. Molecular, cell biological, biochemical and quantitative microscopy methods will be used to determine the mechanisms for regulation of ChREBP nuclear-cytoplasmic shuttling and activation in adipocytes, and the potential role of insulin signaling in regulation of adipose-ChREBP activity. Overall, this project will provide physiological, molecular, and cellular insights into ChREBP regulation. Because reduced ChREBP expression in adipose tissue of obese humans correlates highly with insulin resistance, understanding the mechanisms that regulate ChREBP in adipocytes could lead to novel therapeutic approaches to prevent and treat type 2 diabetes.