Regulation of Hepatic Lipid Accumulation and Insulin Resistance

 描述（申请人提供）：非酒精性脂肪性肝病（NAFLD）和进行性非酒精性脂肪性肝炎（NASH）通常与肥胖、胰岛素抵抗和冠状动脉疾病相关。大多数关于肝脂肪变性的研究都集中在参与从头脂肪生成的酶。然而，新出现的数据也指出了调节肝内脂解的蛋白质的关键贡献，包括关键的甘油三酯水解物ATGL（脂肪甘油三酯脂肪酶）沿着其共激活物CGI-58（比较基因鉴定-58）。我们先前的研究已经确定G 0/G1开关基因2（G 0/G1 Switch Gene 2）是ATGL的内源性抑制剂，并提供了令人信服的证据，表明G 0 S2的差异表达在调节脂肪脂解、脂肪-肝脏FA通量和肝脏脂质含量中起着至关重要的作用。有趣的是，我们已经获得了初步证据，G 0 S2也独立于ATGL在甘油磷酸途径中用于TG合成。本申请的目的是进一步探索G 0 S2在肝脏脂质和能量代谢中的作用，以及肥胖相关的肝脂肪变性和胰岛素抵抗的发展。该研究假设G 0 S2作用于肝脏X受体-α（LXRα）的下游，是一种具有脂解抑制剂和溶血磷脂酸酰基转移酶（LPAAT）活性的双功能蛋白。虽然这两种功能在禁食期间以及响应于高脂肪和高碳水化合物喂养而促成肝脂肪变性，但G 0 S2作为LPAAT的作用促进肝脏中磷脂酸（PA）和二酰基甘油（DG）的合成，并且是其在饮食诱导的肥胖症（DIO）小鼠中的有害作用的原因。 这项研究的基本原理是，确定G 0 S2在介导肝脏脂质蓄积中的作用将为NAFLD和相关疾病的病因学提供重要的见解，从而促进营养或药物治疗的发展。将使用三个特定目的检验该假设：1）表征LXRα-G 0 S2轴及其在肝脏脂质代谢中的作用; 2）确定G 0 S2作为LPAAT在促进肝脏TG蓄积中的生理相关性; 3）确定G 0 S2在饮食诱导的胰岛素抵抗中的ATGL非依赖性作用。我们将通过将我们实验室建立的细胞生物学和生理学方法与现有的G 0 S2、LXRα或ATGL缺陷的独特动物模型相结合，进行功能获得和功能丧失研究。这些研究具有创新性，因为它们关注的是TG合成和水解的独特双功能调节剂在肝脂肪变性和胰岛素抵抗发展中的作用。了解肝脏TG代谢如何调节是重要的，因为它不仅影响NAFLD的治疗，而且还将推进与肥胖相关的能量代谢领域。

 DESCRIPTION (provided by applicant): Non-alcoholic fatty liver disease (NAFLD) and the progressive non-alcoholic steatohepatitis (NASH) are often associated with obesity, insulin resistance and coronary artery diseases. Most studies on hepatic steatosis have focused on enzymes involved in de novo lipogenesis. However, emerging data also point to critical contributions of proteins regulating intrahepatic lipolysis, including the key triglyceride hydrolae ATGL (adipose triglyceride lipase) along with its coactivator CGI-58 (Comparative Gene Identification-58). Our previous studies have identified G0S2 (G0/G1 Switch Gene 2) as an endogenous inhibitor of ATGL, and have provided compelling evidence that differential expression of G0S2 plays a crucial role in regulating adipose lipolysis, adipose-liver FA flux and hepatic lipid content. Interestingly, we have obtained preliminary evidence that G0S2 also functions independently of ATGL in the glycerol phosphate pathway for TG synthesis. The objective of this application is to further explore the roles of G0S2 in hepatic lipid and energy metabolism, and the development of obesity-associated hepatic steatosis and insulin resistance. The hypothesis of the proposed studies is that by acting downstream of the liver X receptor-α (LXRα), G0S2 is a dual-function protein that possesses activities of both a lipolytic inhibitor and a lysophosphatidic acid acyltransferase (LPAAT). While both functions contribute to hepatic steatosis during fasting and in response to high-fat and high-carbohydrate feeding, G0S2's role as a LPAAT promotes synthesis of phosphatidic acid (PA) and diacylglycerol (DG) in the liver and is responsible for its detrimental effect in mice with diet-induced obesity (DIO). The rationale for the proposed research is that identifying the role of G0S2 in mediating hepatic lipid accumulation will provide significant insight into the etiology of NAFLD and related disorders, thereby advancing the possibilities for development of nutritional or pharmaceutical therapies. The hypothesis will be tested using three specific aims: 1) to characterize the LXRα-G0S2 axis and its role in hepatic lipid metabolism; 2) to determine the physiologic relevance of G0S2 as a LPAAT in promoting hepatic TG accumulation; and 3) to determine the ATGL-independent role of G0S2 in diet-induced insulin resistance. We will perform both gain- and loss-of- function studies by combining the usage of cell biological and physiological approaches established in our laboratory with unique animal models deficient in G0S2, LXRα or ATGL that are available. These studies are innovative because they focus on the roles of a unique dual-function regulator of TG synthesis and hydrolysis in the development of hepatic steatosis and insulin resistance. Understanding how hepatic TG metabolism is regulated is significant because it not only impacts the treatment of NAFLD, but also will advance the field of energy metabolism as it relates to obesity.