The Unfolded Protein Response in Fatty Liver

项目摘要 非酒精性脂肪性肝病（NAFLD）是肝功能检查异常的最常见原因， 是美国肝硬化、肝细胞癌和死亡的主要原因。虽然脂肪肝 尽管疾病与代谢综合征有关，但其发病机制仍知之甚少。在 在肝脏中，蛋白质折叠的保真度是不完美的，因此过量的错误折叠或未折叠的蛋白质可能 积累，这种情况称为ER应激。未折叠蛋白反应（Unfolded Protein Response，UPR）是一种保护性信号传导机制。 在所有真核细胞中存在的反应，人类和动物研究表明，UPR在 NAFLD及其进行性亚型非酒精性脂肪性肝炎（NASH）。然而，角色和 UPR信号传导在NASH发病机制中的机制仍然知之甚少。普遍定期审议包括： ER蛋白IRE 1 α、PERK和ATF 6激活的三条通路。这些蛋白质既可以 作为ER应激的传感器和其信号传导通路的激活剂。在规范自适应IRE 1 α中， 激活的p-IRE 1 α将XBP 1剪接成活性转录因子XBP 1 s，然后激活 保护性下游靶基因。最近的数据表明，IRE 1 α在细胞命运中起着重要作用 用适应性XBP 1通路和凋亡调节的Ire 1 α依赖性衰变测定 （RIDD）和TRAF 2途径。此外，IRE 1 α与UPR通路相互作用， eIF 2 α/ATF 4/CHOP信号通路和其他细胞应激信号通路。虽然肝脏的失调 IRE 1 α和e-IF 2 α通路与人类NASH相关，其致病和机制作用 IRE 1 α在脂肪性肝炎发病机制中的作用尚不清楚。这些长期目标 这些研究旨在加深我们对UPR信号在发病机制和进展中的作用的理解， 关于NASH本资助提案的目标是进一步定义肝脏IRE 1 α适应性和 非酒精性脂肪性肝炎发病机制中的凋亡信号传导。之前我们已经证实 当喂食高脂饮食时，肝细胞特异性缺失Xbp 1的小鼠对 出现NASH。我们现在提出了三个具体的目的，以进一步研究IRE 1 α信号转导在细胞凋亡中的作用。 脂肪性肝炎的发病机制：确定增强的肝脏IRE 1 α信号传导增加了 使用肝脏特异性XBP 1（-/-）和肝脏特异性IRE 1 α（-/-）小鼠高喂养对脂肪性肝炎的易感性 目的1：阐明肝脏IRE 1 α通过TRAF 2、eIF 2 α和RIDD对细胞凋亡的调节作用 途径（目标2）;并利用肝脏特异性细胞培养物和培养的肝细胞来确定 IRE 1 α信号在肝细胞脂毒性过程中的细胞命运决定（目的3）。通过更好地了解 这种IRE 1 α介导的适应性和凋亡信号在肝脏中的作用，可能会改变肝脏的平衡。 细胞命运决定远离凋亡并朝向适应性XBP 1信号传导，具有潜在的治疗作用， 影响

Project Summary Non-alcoholic fatty liver disease (NAFLD) is the most common cause of abnormal liver function tests in the United States and is a major cause of cirrhosis, hepatocellular carcinoma and death. Although fatty liver disease is associated with the metabolic syndrome, the pathogenesis remains poorly understood. In the liver, the fidelity for protein folding is imperfect, and therefore excess misfolded or unfolded proteins may accumulate, a condition termed ER stress. The Unfolded Protein Response (UPR) is a protective signaling response present in all eukaryotic cells, and human and animal studies indicate that the UPR is important in NAFLD and its progressive sub-type of non-alcoholic steatohepatitis (NASH). However, the role and mechanisms of UPR signaling in the pathogenesis of NASH remains poorly understood. The UPR consists of three pathways that are activated by the ER proteins IRE1α, PERK and ATF6. These proteins serve both as sensors of ER stress and activators of their signaling pathways. In the canonical adaptive IRE1α pathway, activated p-IRE1α splices XBP1 into the active transcription factor XBP1s, which then activates protective downstream target genes. More recent data indicates that IRE1α has a major role in cell fate determination, with both the adaptive XBP1 pathway, and apoptotic Regulated Ire1α-Dependent Decay (RIDD) and TRAF2 pathways. In addition, IRE1α interacts with the UPR pathway involved with eIF2α/ATF4/CHOP signaling and other cellular stress signaling pathways. Although dysregulation of liver IRE1α and e-IF2α pathways have been associated with human NASH, the causative and mechanistic role of IRE1α in the pathogenesis of steatohepatitis remain poorly understood. The long-term goals of these studies are to enhance our understanding of the role of UPR signaling in the pathogenesis and progression of NASH. The objectives of this grant proposal are to further define the role of hepatic IRE1α adaptive and apoptotic signaling in the pathogenesis of non-alcoholic steatohepatitis. We have previously demonstrated that when fed a high fat diet, mice with hepatocyte-specific deletion of Xbp1 have increased susceptibility to develop NASH. We now propose three Specific Aims to further investigate the role of IRE1α signaling in the pathogenesis of steatohepatitis: to determine that enhanced hepatic IRE1α signaling increases the susceptibility to develop steatohepatitis using liver-specific XBP1(-/-) and liver-specific IRE1α(-/-) mice fed high fat diets (Aim 1); to delineate the regulation of apoptosis by hepatic IRE1α via the TRAF2, eIF2α and RIDD pathways (Aim 2); and to utilize liver-specific cell cultures and cultured hepatocytes to determine the role of IRE1α signaling in cell fate determination during hepatocyte lipotoxicity (Aim 3). By better understanding this IRE1α-mediated adaptive and apoptotic signaling in the liver, it may be possible to shift the balance of cell fate determination away from apoptosis and toward adaptive XBP1 signaling, with potential therapeutic implications.