Novel mechanisms of UPR sensing and nonalcoholic fatty liver disease

 描述（由申请人提供）：该项目涉及未折叠蛋白反应（UPR）和非酒精性脂肪性肝病（NAFLD）的机制。当未折叠或错误折叠的蛋白质在内质网（ER）腔中积累时，真核细胞采用保守且根本上重要的UPR途径来开启主要ER分子伴侣和参与ER相关降解的蛋白质的表达以减轻应激。这种关键的蛋白质质量控制机制是通过三种ER跨膜UPR传感器传递的，包括IRE 1，PERK和ATF 6。普遍定期审议研究的意义在医学上具有深远意义; 2014年授予森一敏博士和彼得·沃尔特博士的阿尔伯特·拉斯克奖强调和支持了这一点。然而，UPR传感器被触发的机制仍然是激烈争论的主题，鉴于UPR在生理学和疾病中的普遍意义，解决这一问题非常重要。目前的模型包括错误折叠的蛋白质和Grp 78从ER传感器的腔域的解离的ER传感器的直接结合。这两种模型都没有充分解释系统的灵敏度和高效率，该系统允许细胞真实的时间对压力做出反应和适应。我们已经产生了一个令人兴奋的证据，暗示CNPY 2，一个以前未知的ER蛋白在UPR中，在激活所有三个UPR传感器响应ER压力。CNPY 2在稳定状态下在肝脏中高度表达，并且可以通过CHOP的直接反式激活由UPR进一步诱导。敲除（KO）小鼠cnpy 2沉默UPR途径，阻断CHOP表达，并保护细胞免受UPR诱导的细胞死亡。值得注意的是，KO小鼠对高脂饮食（HFD）诱导的ER应激和非酒精性脂肪肝病（NAFLD）具有高度保护作用。反过来，CNPY 2过表达增加ER应激诱导后细胞中的UPR和凋亡信号。因此，涉及CNPY 2的UPR传感的新模型正在出现。我们假设CNPY 2是肝脏中一般UPR的关键阳性起始物，并且它是ER应激诱导的NAFLD所需的。我们提出了两个具体的目标来解决我们的假设。目的1将通过生物化学、生物物理学和结构学方法，确定CNPY 2调控UPR起始的分子机制。目的2通过系统研究CNPY 2在脂肪生成和脂质代谢、调节脂蛋白分泌和LDL受体生物合成、调节钙稳态和ER信号转导等方面的作用，阐明CNPY 2在肝脂肪变性调控中的作用机制。总的来说，这一建议将对理解UPR感知机制和NAFLD的发病机制产生重大影响。

 DESCRIPTION (provided by applicant): This project addresses the mechanism of unfolded protein response (UPR) and non-alcoholic fatty liver disease (NAFLD). Upon accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum (ER), eukaryotic cells adopt a conserved and fundamentally important UPR pathway to turn on the expression of major ER chaperones and proteins involved in ER-associated degradation to alleviate stress. This critical protein quality control mechanism is transmitted by three ER trans-membrane UPR sensors including IRE1, PERK and ATF6. The significance of UPR research is far-reaching in medicine; it is highlighted and supported by the 2014 Albert Lasker Prize awarded to Drs. Kazutoshi Mori and Peter Walter. The mechanism whereby UPR sensors are triggered however remains a subject of intense debate, which is important to resolve given the ubiquitous implication of UPR in physiology and diseases. Present models include direct binding of ER sensors by misfolded proteins and dissociation of Grp78 from the luminal domains of ER sensors. Neither of the models sufficiently explains the exquisite sensitivity and high efficiency of the system which allows cells to react and adapt to stress in real time. We have produced an exciting body of evidence implicating CNPY2, a previously unknown ER protein in UPR, in activating all three UPR sensors in response to ER stress. CNPY2 is highly expressed in the liver in the steady state and can be further induced by UPR via direct transactivation by CHOP. Knockout (KO) of cnpy2 from mice silences UPR pathways, blocks CHOP expression, and protects cells from UPR-induced cell death. Remarkably, the KO mice are rendered highly protective against high fat diet (HFD)-induced ER stress and non-alcoholic fatty liver disease (NAFLD). In turn, CNPY2 overexpression increases the UPR and apoptotic signals in cells upon ER stress induction. Thus, a novel model of UPR sensing that involves CNPY2 is emerging. We hypothesize that CNPY2 is a critical positive initiator for general UPR in the liver, and that it i required for ER stress-induced NAFLD. We propose two specific aims to address our hypothesis. Aim 1 will determine the molecular mechanism of CNPY2- regulated UPR initiation, using biochemical, biophysical and structural approaches. Aim 2 will be focused on untangling the mechanisms of CNPY2 in regulating hepatosteatosis by systemically studying the roles of CNPY2 in: 1) lipogenesis and lipid metabolism; 2) regulating lipoprotein secretion and the biogenesis of LDL receptor; 3) controlling calcium homeostasis related to mitochondria-ER cross-talk. Collectively, this proposal shall have a significant impact in understanding the mechanism of UPR sensing, and the pathogenesis of NAFLD.