The Unfolded Protein Response in Fatty Liver

项目概要 非酒精性脂肪性肝病（NAFLD）是肝功能检查异常的最常见原因 在美国，它是肝硬化、肝细胞癌和死亡的主要原因。虽然脂肪肝 该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并不完美，因此过量的错误折叠或未折叠的蛋白质可能 累积，这种情况称为内质网应激。未折叠蛋白反应 (UPR) 是一种保护性信号传导 所有真核细胞中都存在反应，人类和动物研究表明 UPR 在 NAFLD 及其进展性非酒精性脂肪性肝炎 (NASH) 亚型。然而，角色和 UPR 信号传导在 NASH 发病机制中的机制仍知之甚少。普遍定期审议包括 ER 蛋白 IRE1α、PERK 和 ATF6 激活的三种途径。这些蛋白质同时服务于 作为内质网应激的传感器和信号通路的激活剂。在规范的自适应 IRE1α 中 途径，激活的 p-IRE1α 将 XBP1 剪接到活性转录因子 XBP1s 中，然后激活 保护性下游靶基因。最近的数据表明 IRE1α 在细胞命运中发挥着重要作用 测定，同时具有适应性 XBP1 途径和凋亡调节 Ire1α 依赖性衰变 (RIDD) 和 TRAF2 途径。此外，IRE1α 与 UPR 通路相互作用，涉及 eIF2α/ATF4/CHOP 信号传导和其他细胞应激信号传导途径。虽然肝脏失调 IRE1α 和 e-IF2α 通路与人类 NASH 及其致病和机制作用相关 IRE1α 在脂肪性肝炎发病机制中的作用仍知之甚少。这些的长期目标 研究旨在增强我们对 UPR 信号在发病机制和进展中的作用的理解 NASH 的。该拨款提案的目标是进一步明确肝脏 IRE1α 适应性和 非酒精性脂肪性肝炎发病机制中的细胞凋亡信号。我们之前已经演示过 当喂食高脂肪饮食时，肝细胞特异性缺失 Xbp1 的小鼠对以下疾病的易感性增加 发展 NASH。我们现在提出三个具体目标来进一步研究 IRE1α 信号在 脂肪性肝炎的发病机制：确定增强的肝脏 IRE1α 信号传导会增加 使用高饲喂肝脏特异性 XBP1(-/-) 和肝脏特异性 IRE1α(-/-) 小鼠患脂肪性肝炎的易感性 脂肪饮食（目标 1）；描述肝脏 IRE1α 通过 TRAF2、eIF2α 和 RIDD 对细胞凋亡的调节 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 IRE1α 信号在肝细胞脂毒性过程中细胞命运决定（目标 3）。通过更好的理解 这种 IRE1α 介导的肝脏适应性和凋亡信号传导，可能会改变肝脏中的平衡 细胞命运决定从细胞凋亡转向适应性 XBP1 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.