Inhibition of ATGL-Mediated Lipolysis by G0S2

描述（由申请人提供）：脂肪组织甘油三酯（TAG）是高等真核生物的主要能量来源。脂肪细胞在需要时从TAG储存中动员游离脂肪酸（FFAs）的能力对生存至关重要。在人类和啮齿类动物中，游离脂肪酸释放率的改变与肥胖和2型糖尿病的发生密切相关。脂解是TAG被水解为游离脂肪酸和甘油的过程，几十年来一直是研究的热点，主要集中在激素敏感脂肪酶（HSL）上。随着脂肪甘油三酯脂肪酶（ATGL）在脂肪分解中作为限速酶的发现，对TAG动员的分子过程有了更清晰的认识。虽然最近的研究确定CGI-58是ATGL的共激活剂，但调节ATGL酶作用的机制仍然不够清楚。在这方面，我们的初步研究已经发现了控制atgl介导的脂肪分解的新机制。我们已经获得了令人信服的证据，证明G0/G1开关基因2 （G0S2）编码的蛋白质是ATGL的选择性调节因子。G0S2在脂肪组织和分化的脂肪细胞中高表达。它特异性地与ATGL相互作用，导致其TAG脂肪酶活性的抑制。敲低和过表达实验表明，G0S2在脂肪细胞和非脂肪细胞中都具有减弱atgl介导的脂肪分解的功能。本课题的总体目标是进一步探索G0S2抑制ATGL的分子细节，更重要的是，在各种功能设置的背景下，G0S2在TAG脂解中的生理作用。这一目标将通过以下途径实现：(1)确定G0S2调控ATGL活性的生化机制；(2)验证G0S2和CGI-58在atgl介导的脂肪分解中发挥相反作用的假设；(3)评估脂肪过表达G0S2对能量代谢和胰岛素敏感性的影响。在目标1中，我们将进行酶动力学研究和底物相互作用分析。我们还将在ATGL中绘制G0S2结合的精确序列基序。对于目标2，我们将在不同的细胞环境中控制G0S2和CGI-58的相对水平，并检查atgl介导的脂肪分解和相关功能后果的影响。目的3将通过使用特异性过表达G0S2脂肪的转基因动物模型进行饮食治疗研究来完成。这些研究将有助于我们对TAG代谢的理解，并有助于开发针对肥胖和2型糖尿病的新治疗策略。

DESCRIPTION (provided by applicant): Adipose tissue triacylglycerol (TAG) is the major source of energy in higher eukaryotes. The ability of adipocytes to mobilize free fatty acids (FFAs) from TAG stores during times of demand is essential for survival. The altered rates of FFA release are strongly associated with the development of obesity and type 2 diabetes, both in humans and in rodents. Lipolysis, the process in which TAG is hydrolyzed to FFAs and glycerol, has been a subject of intense investigation for decades, with much focus on hormone-sensitive lipase (HSL). With the discovery of adipose triglyceride lipase (ATGL) as the rate-limiting enzyme in lipolysis, a clearer understanding of the molecular processes governing TAG mobilization emerged. Although recent studies identified CGI-58 as a co-activator of ATGL, the mechanisms that regulate the ATGL enzyme action remain insufficiently understood. In this regard, our preliminary studies have uncovered a novel mechanism for the control of ATGL-mediated lipolysis. We have obtained compelling evidence that a protein encoded by G0/G1 switch gene 2 (G0S2) is a selective regulator of ATGL. G0S2 is highly expressed in adipose tissue and differentiated adipocytes. It specifically interacts with ATGL, leading to the inhibition of its TAG lipase activity. Knockdown and overexpression experiments demonstrate that G0S2 functions to attenuate ATGL-mediated lipolysis in both adipocytes and nonadipocyte cells. The overall goal of this proposal is to further explore the molecular details of ATGL inhibition by G0S2, and more importantly, the physiologic roles of G0S2 in TAG lipolysis in the context of various functional settings. The goal will be accomplished by (1) determining the biochemical mechanisms by which ATGL activity is regulated by G0S2; (2) testing the hypothesis that G0S2 and CGI-58 play opposing roles in ATGL-mediated lipolysis; and (3) evaluating the effects of adipose overexpression of G0S2 on energy metabolism and insulin sensitivity. In aim 1, we will perform both enzyme kinetic studies and substrate interaction assays. We will also map the precise sequence motif(s) in ATGL for G0S2 binding. For aim 2, we will manipulate relative levels of G0S2 and CGI-58 in various cellular setting and examine the effects on ATGL-mediate lipolysis and the related functional consequences. Aim 3 will be accomplished through diet treatment studies using a transgenic animal model overexpressing G0S2 fat specifically. These studies will contribute to our understanding of TAG metabolism, and to the development of new therapeutic strategies against obesity and type 2 diabetes. PUBLIC HEALTH RELEVANCE: Obesity is a prevalent disorder of energy balance in which excess energy, in the form of triacylglycerol, accumulates in adipose tissue. Despite a need for therapeutic approaches to treat obesity, little is known about the mechanisms that control fat storage and release from adipose tissue. The proposed study will focus on investigating the important role of a new protein that regulates ATGL, the key enzyme for fat mobilization in adipose tissue.