Cholestasis and the Unfolded Protein Response

说明(申请人提供)：胆汁淤积性肝病在美国是进行性肝病的高度流行原因，也是肝移植的常见适应症。不幸的是，目前的医学疗法不能治愈，也可能无法阻止疾病的发展。在过去的十年中，未折叠蛋白反应(UPR)是一种对内质网(ER)应激的适应性细胞反应，与许多肝脏疾病的发病机制有关。然而，UPR在肝脏胆盐毒性和胆汁淤积性肝病中的作用尚不清楚。X-box结合蛋白1-剪接蛋白(XBP1s)是UPR的关键调控分子，我们的初步数据表明，XBP1s对胆盐损伤具有保护作用。该方案的核心假设是，XBP1s在胆汁淤积期对肝脏具有保护作用，而抑制XBP1s的肝脏表达会导致肝脏胆盐转运体表达减少，增加对肝脏胆盐肝损伤的易感性。因此，在这项提案中，我们将给小鼠喂食添加胆酸的饲料，并确定XBP 1及其下游靶点在肝脏胆盐损伤中的作用(具体目标1)。CYP7a1是胆盐合成的限速步骤，抑制其表达和活性可以作为一种负反馈机制来减少胆盐的合成。我们提供的初步数据表明，肝脏UPR的激活显著减少了表达 肝细胞色素P7a1，可能通过XBP1s介导的途径。因此，我们将确定未折叠蛋白反应和XBP1抑制肝脏Cyp7a1的表达、功能和胆盐合成(特定目标2)。最后，为了直接确定肝脏XBP1s表达减弱会增加对胆盐肝毒性的易感性，我们将开发肝脏特异缺失XBP1的转基因小鼠。我们将建立肝脏特异性XBP1(-/-)小鼠，以确定XBP1在肝脏胆盐损伤中的保护作用和保护机制(特定目标#3)。虽然这项建议侧重于肝脏XBP1，但长期目标是开发一系列研究，以确定UPR信号通路可以作为治疗淤胆性肝病的治疗靶点。这一建议利用最先进的小鼠遗传学、分子生物学和脂质生化技术来加深我们对XBP1在胆盐损伤和胆汁淤积中的保护作用的理解。明确XBP1s信号通路在胆盐诱导的肝损伤中的作用及其作用，可能为治疗淤胆性肝病的药物开发提供新的途径和潜在的靶点。 公共卫生相关性：胆汁淤积性肝病是进行性肝病的常见原因，可导致肝硬变和肝功能衰竭。不幸的是，几乎没有治疗淤胆性肝病的药物。我们将研究胆盐在肝损伤中的作用，以及 一种名为XBP1S的肝脏蛋白预防肝脏胆盐损伤的机制和保护作用

DESCRIPTION (provided by applicant): Cholestatic liver diseases are highly prevalent causes of progressive liver disease in the United States and are a common indication for liver transplantation. Unfortunately, current medical therapies are not curative and may not prevent disease progression. Over the past decade, the Unfolded Protein Response (UPR), an adaptive cellular response to Endoplasmic Reticulum (ER) stress, has been implicated in the pathogenesis of many liver diseases. The role of the UPR in hepatic bile salt toxicity and cholestatic liver disease, however, remains unexplored. X-box binding protein 1-spliced (XBP1s) is a key regulatory molecule of the UPR that our preliminary data indicates is protective from bile salt injury. The central hypothesis of this proposal is that XBP1s is protective to the live during cholestasis~ and attenuated hepatic expression of XBP1s results in diminished expression of liver bile salt transporters and increased susceptibility to hepatic bile salt liver injury. Thus, in this proposal we will feed diets supplemented with cholic acid to mice and define the role of XBP1s and downstream targets in hepatic bile salt injury (Specific Aim #1). CYP7a1 is the rate-limiting step in bile salt synthesis, and inhibition of CYP7a1 expression and activity can act as a negative feedback mechanism to reduce the bile salt pool. We present preliminary data indicating that activation of the hepatic UPR markedly reduces expression of hepatic CYP7a1, likely via a XBP1s- mediated pathway. Thus, we will determine that the Unfolded Protein Response and XBP1s suppress hepatic Cyp7a1 expression, function and bile salt synthesis (Specific Aim #2). Finally, in order to directly determine that attenuation of hepatic XBP1s expression increases susceptibility to bile salt hepatotoxicity, we will develop genetically-modified mice with a liver-specific deletion of XBP1. We will develop liver-specific XBP1(-/-) mice in order to confirm the protective role, and define the protective mechanisms, of XBP1s in liver bile salt injury (Specific Aim #3). While this proposal focuses on hepatic XBP1s, the long-term goal is to develop a line of research to identify UPR signaling pathways that can serve as therapeutic targets for the treatment of cholestatic liver diseases. This proposal utilizes state-of-the-art mouse genetics, molecular biology and lipid biochemical techniques to further our understanding of the protective role of XBP1s in bile salt injury and cholestasis. Investigations identifying the role of the XBP1s signaling pathway and its effects on bile salt-induced liver injury may identify a novel pathway and potential targets for drug development to treat cholestatic liver diseases. PUBLIC HEALTH RELEVANCE: Cholestatic liver diseases are common causes of progressive liver disease that can lead to cirrhosis and hepatic failure. Unfortunately, there are few medical therapies for cholestatic liver diseases. We will study role of bile salts in liver injury, and the mechanisms and protective effects of a liver protein named XBP1s in preventing hepatic bile salt injury.