Regulation of Lipid Storage by mTORC1

 描述（由申请人提供）：肥胖是一种全球性的公共卫生流行病，影响了近三分之一的美国成年人。几种毁灭性的合并症与肥胖有关，包括胰岛素抵抗/II型糖尿病和非酒精性脂肪性肝炎/非酒精性脂肪性肝病。奇怪的是，在肥胖状态下，尽管对胰岛素作用有抵抗，但脂质储存没有受到抑制。这一发现对肥胖及其并发症的管理具有重要意义。一种将肥胖与过度脂质储存联系起来的新兴分子机制是mTORC 1/SREBP 1c通路，我们的研究小组和其他人已经确定该通路在肥胖时被激活，并且是脂肪生成和新脂肪细胞形成的关键调节因子。本研究将检验肥胖状态下mTORC 1激活升高脂质水平的假设，这是由于脂肪生成和脂肪生成两者的激活。为了实现这一目标，我们开发了几个新的创新模型来测试这一假设的特定方面。首先，我们已经产生了脂肪特异性Tsc 1敲除小鼠作为慢性脂肪mTORC 1激活的模型。这些小鼠中mTORC 1信号传导的慢性升高与脂肪量升高和肝脂肪变性增加相关，可能是由于脂肪组织中从头脂肪生成增强。我们将确定慢性mTORC 1升高引起的分子变化，并确定这些mTORC 1依赖性脂质储存增加的分子机制。肥胖可能是由脂肪生成增加引起的，因此我们将确定mTORC 1积极调节脂肪生成的分子机制。我们将专门评估mTORC 1通过miRNA依赖性机制调节PPARγ mRNA稳定性的假设。为了测试mTORC 1在肝脏中的作用，我们将通过分别在成年小鼠肝脏中消融必需的mTORC 1组分Rptor和Tsc 1来研究该激酶的激活和抑制。这种方法将使我们能够首次评估mTORC 1对于成人肝组织中肝脂肪变性的发展和维持是否必要和足够。这是我们所知的一个重要的gp，因为在肥胖相关的肝病中，mTORC 1在发育过程中不被激活，但与肥胖的升高同时发生。我们将使用基因组编辑的大鼠探索SREBP 1c中正反馈回路的生理意义。这个关键的mTORC 1靶点在从头脂肪生成中起着重要作用，并且已经提出通过转录前馈回路放大SREBP 1c作用是饮食诱导的肝脂肪变性和肥胖的重要组成部分。通过删除内源性Srebf 1位点的相关SRE，我们可以以受控和直接的方式测试该电路的重要性。重要的是，这些大鼠还将使我们能够将mTORC 1和其他信号对SREBP 1c的直接激活与正反馈的混杂效应分开。这些研究将共同回答有关mTORC 1和SREBP 1c如何调节脂肪生成和脂肪生成的基本机制问题，为肥胖和肝脏疾病的潜在治疗干预途径提供见解。

 DESCRIPTION (provided by applicant): Obesity is a public health epidemic wordwide and affects nearly a third of adult Americans. Several devastating co-morbidities are associated with obesity, including insulin resistance/type II diabetes and non-alcoholic steatohepatitis/non-alcoholic fatty liver disease. Paradoxically, in obese states, lipid storage is not suppressed, in spite of resistance to insulin action. This finding that has important consequences for the management of obesity and its complications. An emerging molecular mechanism linking obesity to excessive lipid storage is the mTORC1/SREBP1c pathway, which our group and others have identified as both activated with obesity, and as a key regulator of lipogenesis and new adipocyte formation. This study will test the hypothesis that mTORC1 activation in the obese state elevates lipid levels, due to activation of both adipogenesis and lipogenesis. To accomplish this, we have developed several new innovative models to test specific aspects of this hypothesis. First, we have generated adipose-specificTsc1 knockout mice as a model of chronic adipose mTORC1 activation. The chronic elevations in mTORC1 signaling in these mice are associated with elevated fat mass and increased hepatic steatosis, likely due to enhanced de novo lipogenesis in adipose tissue. We will determine the molecular changes resulting from chronic mTORC1 elevation, and identify the molecular mechanisms underlying these mTORC1-dependent increases in lipid storage. Elevated adiposity may is caused by increased adipogenesis, so we will determine the molecular mechanisms by which mTORC1 positively regulates adipogenesis. We will specifically evaluate the hypothesis that mTORC1 regulates PPARγ mRNA stability via a miRNA-dependent mechanism. To test the role of mTORC1 in the liver, we will study both activation and inhibition this kinase via ablation of the essential mTORC1 component Rptor, and Tsc1 respectively in adult mouse livers. This approach will allow us to evaluate whether mTORC1 is necessary and sufficient for the development and maintenance of hepatic steatosis in adult liver tissues for the first time. This is an important gp in our knowledge, since in obesity-associated liver disease, mTORC1 is not activated during development, but co-incident with elevations in adiposity. We will explore the physiological significance of a positive feedback loop in SREBP1c using genome-edited rats. This key mTORC1 target plays an important role in de novo lipogenesis and the amplification of SREBP1c action by a transcriptional feed-forward circuit has been proposed to be an important component of both diet-induced hepatic steatosis and obesity. By deleting only the relevant SRE at the endogenous Srebf1 locus, we can test the importance of this circuit in a controlled and direct manner. Importantly, these rats will also allow us to separate the direct activation of SREBP1c by mTORC1 and other signals, from the confounding effects of positive feedback. Together these studies will answer fundamental mechanistic questions regarding how mTORC1 and SREBP1c regulate adipogenesis and lipogenesis, providing insights into potential routes of therapeutic intervention for obesity and liver disease.