Cholestasis and the Unfolded Protein Response

描述（由申请人提供）：胆汁淤积性肝病是美国进展性肝病非常普遍的原因，也是肝移植的常见适应症。不幸的是，目前的医学疗法无法治愈，也可能无法预防疾病的进展。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，已被认为与许多肝脏疾病的发病机制有关。然而，UPR在肝胆盐毒性和胆汁淤积性肝病中的作用仍未被探索。X-box结合蛋白1-剪接（XBP1s）是UPR的关键调控分子，我们的初步数据表明它对胆盐损伤具有保护作用。本研究的中心假设是XBP1s对胆汁淤积期的活体具有保护作用，而XBP1s在肝脏中的表达减弱导致肝脏胆盐转运体表达减少，增加了对肝胆盐肝损伤的易感性。因此，在本提案中，我们将给小鼠喂食添加胆酸的饲料，并确定XBP1s和下游靶点在肝胆盐损伤中的作用（Specific Aim #1）。CYP7a1是胆盐合成的限速步骤，抑制CYP7a1的表达和活性可以作为减少胆盐池的负反馈机制。我们提出的初步数据表明，激活肝UPR显著降低表达

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.