Metabolic effects of adipose lipogenesis

描述（由申请人提供）：我们在胰岛素抵抗和2型糖尿病的分子机制方面的知识存在重大空白。葡萄糖和脂质代谢失调都起作用。本提案研究了这些途径之间的机制联系。肥胖和2型糖尿病患者肝脏中脂肪酸合成（de novo lipogenesis， DNL）升高，通常与胰岛素抵抗有关。相反，我们的新数据表明，脂肪组织中的DNL在代谢方面是有益的，因为它可以促进胰岛素敏感性，防止高脂肪饮食引起的胰岛素抵抗。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响应元件结合蛋白（ChREBP），一种葡萄糖响应转录因子。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基因敲除小鼠有轻微的饮食相关胰岛素抵抗。然而，抑制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。选择性敲除ChREBP在脂肪组织中的作用尚未被研究。我们最近的论文表明，脂肪组织ChREBP是人类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。本应用程序的目标是整合全动物和细胞研究，以确定ChREBP在脂肪组织中促进胰岛素敏感性作用的生理、细胞和分子机制。我们将在脂肪细胞中选择性地过度表达或缺乏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是确定脂肪细胞选择性缺失ChREBP是否会导致全身性胰岛素抵抗。除了生理和代谢特征外，在这两个目标中，我们将对脂肪组织和血清进行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调节脂肪细胞新生脂肪生成的细胞机制。将采用分子、细胞生物学、生化和定量显微镜方法来确定脂肪细胞中ChREBP核胞质穿梭和激活的调节机制，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，该项目将为ChREBP调控提供生理、分子和细胞方面的见解。由于肥胖人群脂肪组织中ChREBP表达的降低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.