Liver Pathobiology: insights through the lens of rare diseases

项目总结/摘要 慢性肝病（CLD）是一个主要的全球健康问题，影响全球超过10亿人， 每年有200万人死亡。慢性肝损伤通常是无声的，但如果持续下去，可能会导致肝纤维化， 其可发展为肝硬化和临床上显著的门静脉高压并发症（如腹水， 食管静脉曲张出血和肝性脑病）。这些临床症状是最常见的 CLD的死亡原因，肝移植是唯一可用的治疗干预。以来 对肝移植的需求仍然远远超过可用供体器官的供应， 疾病是全球第11大死亡原因。因此，分子理解的进步 肝损伤和病理生物学的研究对于开发新的诊断、预后和治疗工具至关重要， 目的是减少未来肝移植的需求。几年来，我的研究集中在 研究病因不明的罕见肝脏表型个体，作为发现新的 可能与以下疾病的发病机制和治疗相关的肝脏病理学的分子机制 常见的肝脏疾病作为这项持续努力的一部分，我们最近发现，在一个小的隐性基因型， GT3，命名为GIMAP 5，引起肝窦内皮细胞毛细血管化和肝功能障碍。以 一个可用的Gimap 5功能丧失（LOF）突变小鼠模型的优点，它概括了 在Gimap 5缺陷的人中观察到的窦状内皮细胞毛细血管化表型，我们证明， Gimap 5在肝内皮细胞中表达，其在这些细胞中的选择性缺失导致肝窦状隙 内皮细胞（LSEC）去分化为毛细血管化内皮细胞（CEC）。此外，单细胞RNA- 从Gimap 5缺陷和Gimap 5充足小鼠分离的分选的肝内皮细胞的测序分析 显示CEC几乎完全取代健康的LSEC。重要的是，LSEC去分化为CEC 是肝纤维化中描述的一种事件，通常与肝损伤的病因无关。在此，我们建议 确定维持LSEC身份和防止肝窦内皮细胞 通过完成以下两个目标来实现毛细作用：（1）识别发出信号的细胞外部线索 通过GIMAP 5来维持LSEC身份;和（2）表征肝脏中的Gimap 5信号转导途径 内皮细胞总的来说，这项提议产生的知识有可能发现新的 治疗目标是将CEC恢复为健康的LSEC，并以这种方式开发新的非侵入性肝脏治疗方法 肝纤维化、肝硬化和门静脉高压，这代表了一个主要的未满足的医疗需求。

PROJECT SUMMARY/ABSTRACT Chronic liver disease (CLD) is a major global health problem that affects over 1 billion people globally and leads up to 2 million deaths annually. Chronic liver injury is typically silent, but when persistent may lead to liver fibrosis, which can progress to cirrhosis and clinically significant portal hypertension complications (such as ascites, esophageal variceal hemorrhage, and hepatic encephalopathy). These clinical signs are the most common cause of mortality from CLD, and for which liver transplantation is the only available curative intervention. Since the demands for liver transplantation still far exceeds the supply of available donor organs, end-stage liver disease represents the 11th leading cause of death worldwide. Hence, advances in the molecular understanding of liver injury and pathobiology are critical to develop novel diagnostic, prognostic and therapeutic tools, with the goal to decrease the demand for liver transplantation in the future. For several years, my research has focused on the study of individuals with rare liver phenotypes of unknown etiology as a roadmap to uncover novel molecular mechanism(s) underlying liver pathology that may be relevant to the pathogenesis and treatment of common liver diseases. As part of this ongoing effort, we recently found that recessive genotypes in a small GTPase, named GIMAP5, cause liver sinusoidal endothelial cell capillarization and liver dysfunction. Taking advantage of an available Gimap5 loss-of-function (LOF) mutant mouse model, which recapitulates the sinusoidal endothelial cell capillarization phenotype seen in Gimap5-deficient humans, we demonstrate that Gimap5 is expressed in liver endothelial cells and its selective deletion in these cells lead to liver sinusoidal endothelial cell (LSEC) de-differentiation into capillarized endothelial cells (CECs). Furthermore, single cell RNA- sequencing analysis of sorted liver endothelial cells isolated from Gimap5-deficient and Gimap5-sufficient mice shows a near complete replacement of healthy LSECs by CECs. Importantly, LSEC de-differentiation into CECs is an event described in liver fibrosis, in general, independent of the etiology of liver injury. Here, we propose to define the key contributors in maintaining LSEC identity and preventing hepatic sinusoidal endothelial cell capillarization through the completion of the following two aims: (1) identify the cell extrinsic cues that signal through GIMAP5 to maintain LSEC identity; and (2) characterize the Gimap5 signal transduction pathway in liver endothelial cells. Collectively, the knowledge generated by this proposal has the potential to identify novel therapeutic targets to revert CECs into healthy LSECs, and this way develop new non-invasive therapies for liver fibrosis, cirrhosis and portal hypertension, which represent a major unmet medical need.