The Role of Sel1L and ER Quality Control in Adipocytes

 描述(由申请人提供)：我们的长期目标是描述通过三个关键质量控制系统维持内质网(ER)稳态的潜在分子机制和生理意义，ERAD、自噬和未折叠蛋白反应(UPR)。尽管最近的研究表明UPR可能在肥胖和2型糖尿病的发病机制中发挥作用，但脂肪细胞内ER稳态的维持及其生理意义仍然是个谜。我们最近的数据表明，Sel1L是哺乳动物ERAD中E3连接酶Hrd1的关键适配子蛋白，在脂肪细胞和代谢调节中发挥着关键作用。脂肪细胞特异性Sel1L缺陷小鼠(Sel1LΔADIPO)通过升高的UPR和自噬保护饮食诱导的肥胖，但在WAT中不耦合炎症和细胞死亡。此外，我们的数据表明，Sel1L对脂蛋白脂酶(Lpl)的分泌是至关重要的，这可能是Sel1LΔ脂肪小鼠餐后高甘油三酯血症的原因。因此，我们的数据表明，Sel1L在脂肪细胞功能中在肥胖发病机制中发挥着不可或缺的作用。然而，Sel1L影响脂肪细胞功能和肥胖的潜在分子机制(S)仍很不清楚。我们假设Sel1L通过Hrd1/ERAD依赖和非依赖的机制，以及通过脂肪细胞中三个ER质量控制系统(Sel1L-Hrd1 ERAD、UPR和自噬)之间的串扰来调节脂肪细胞的功能和代谢。利用一系列脂肪细胞特异性基因敲除小鼠模型，结合体外机制研究，我们将从机制上确定Se1L如何调节脂肪细胞的功能和代谢，重点是在Aim 1中对Hrd1/ERAD的依赖，以及在Aim 2中脂肪细胞中三个ER质量控制系统之间的串扰。几个具有不同水平ER应激的脂肪细胞特异性双基因敲除小鼠模型的产生和特征将不仅阐明关键ER质量控制机制之间的功能串扰，而且还将阐明ER稳态扰动在肥胖症和2型糖尿病发病机制中的细胞和病理后果。最后，本研究可能确定Sel1L-Hrd1ERAD复合体的一个新的内源底物，并建立一个新的机制，在Sel1L-Hrd1ERAD和IRE1ERAD信号之间建立反馈调控环。与人类健康相关：蛋白质错误折叠对细胞有害，并与几种人类疾病的发病机制有关。尽管经过近十年的努力，脂肪细胞中的内质网稳态在肥胖发病机制中的作用仍然不清楚。我们的初步数据表明，脂肪细胞Sel1L是ER动态平衡和新陈代谢的关键调节因子。这项研究的成功完成将对我们理解内质网质量控制系统的生理意义以及在饮食诱导肥胖的背景下维持脂肪细胞内的内质网稳态产生强大的影响。

 DESCRIPTION (provided by applicant): Our long-term goal is to delineate the underlying molecular mechanisms and physiological significance of the maintenance of endoplasmic reticulum (ER) homeostasis by three key quality-control systems, ERassociated degradation (ERAD), autophagy and unfolded protein response (UPR). Although recent studies have implied a possible role of UPR in the pathogenesis of obesity and type-2 diabetes, the maintenance and physiological significance of ER homeostasis in adipocytes remains enigma. Our recent data demonstrate that Sel1L, a key adaptor protein for the E3 ligase Hrd1 in mammalian ERAD, plays a critical role in adipocytes and metabolic regulation. Adipocyte-specific Sel1L-deficient mice (Sel1LΔadipo) are protected against diet-induced obesity with elevated UPR and autophagy, but uncoupled from inflammation and cell death in WAT. Moreover, our data demonstrate a critical requirement of Sel1L for the secretion of lipoprotein lipase (LPL), which may account for postprandial hypertriglyceridemia of Sel1LΔadipo mice. Thus, our data point to an indispensable role of Sel1L in adipocyte function in the pathogenesis of obesity. However, underlying molecular mechanism(s) by which Sel1L affects adipocyte function and obesity remain largely unclear. We hypothesize that Sel1L regulates adipocyte function and metabolism via both Hrd1/ERAD-dependent and -independent mechanisms, and via the crosstalk among three ER qualitycontrol systems (Sel1L-Hrd1 ERAD, UPR and autophagy) in adipocytes. Using an array of adipocytespecific knockout mouse models coupled with in vitro mechanistic studies, we will determine mechanistically how Se1L regulates adipocyte function and metabolism with a particular emphasis on Hrd1/ERAD dependency in Aim 1 and on the crosstalk among three ER quality-control systems in adipocytes in Aim 2. The generation and characterization of several adipocyte-specific double knockout mouse models with various levels of ER stress will elucidate not only the functional crosstalk among key ER quality-control machineries, but also the cellular and pathological consequences of perturbed ER homeostasis in the pathogenesis of obesity and type-2 diabetes. Finally, this study may identify a novel endogenous substrate of the Sel1L-Hrd1 ERAD complex and establish a novel mechanism underlying a feedback regulatory loop between Sel1L-Hrd1 ERAD and IRE1αsignaling. RELEVANCE TO HUMAN HEALTH: Protein misfolding is detrimental to the cell and has been linked to the pathogenesis of several human diseases. Despite nearly a decade of effort, the role of ER homeostasis in adipocytes in the pathogenesis of obesity remains vague. Our preliminary data point to adipocyte Sel1L as a key regulator in ER homeostasis and metabolism. A successful completion of this study will have a powerful impact on our understanding of the physiological significance of ER quality-control systems and the maintenance of ER homeostasis in adipocytes in the context of diet-induced obesity.