肝脏再生过程细胞可塑性的分子调控机制研究

Liver is a pivotal organ possessing strong regenerative capability. The regenerative capability diminishes in the chronic liver diseases. A deep understanding of liver regeneration not only sheds new light on the regulation of tissue homeostasis and regeneration, but also provides new strategy to treat end-stage liver diseases. Classically, it is hold that liver regenerates by either direct duplication of hepatocytes or differentiation of liver progenitor cells (LPC). Notably, latest studies showed compelling evidence of a new paradigm that liver regenerates through hepatocyte dedifferentiation into LPCs. Apparently, it is compelling to delineate the underlying molecular regulation of hepatocyte dedifferentiation in vivo. In this study, we wish to characterize the change of hepatocyte identity during injury-induced liver regeneration using mouse models and clinical human samples. Given the importance of chromatin remodeling complex in cell reprogramming, we will focus on the chromatin remodeler protein Arid1a. Arid1a is a key component of the SWI/SNF complex and is highly mutated during tumorigenic transformation of human liver cells. We will delineate the role of Arid1a in regulating dedifferentiation of hepatocytes and consequently in liver regeneration by applying genetic modified mouse line. Next, we will identify by which molecular pathway Arid1a involves in the process of dedifferentiation. Finally, by characterization of human samples with chronic liver diseases, we wish to reveal whether Arid1a and chromatin remodeling has a role in human liver pathologies. By answering these questions, we hope to provide new knowledge about injury-induced reprogramming of hepatocytes and also, suggest likely strategies to promote regeneration in livers with chronic injury.

肝脏是人体重要器官，具很强再生能力。但在长期的肝损伤条件下，肝脏会失去再生能力，造成肝功能丧失，甚至肝衰竭。因此，深入了解肝脏再生不仅对于组织稳态维持和再生非常重要，而且对于肝脏疾病治疗也能提供新策略。传统认为肝脏再生由肝细胞自身复制或者肝干细胞增殖分化完成，但最近的系列研究明确指出在肝脏损伤再生过程中，存在以肝细胞去分化为基础的再生。显然对这一现象的分子调控机制的解析，将为促进肝脏再生提供全新思路。本项目我们拟利用肝损伤再生小鼠模型和人类病理样品，研究肝脏再生过程中细胞属性转换及其分子调控机制。鉴于SWI/SNF等染色体重塑复合物在细胞属性转换过程的重要功能，我们将聚焦SWI/SNF核心调控蛋白Arid1a，阐明其对肝细胞属性转换调控及其对肝脏再生的作用；鉴定Arid1a在此过程中调控的重要信号通路；并揭示与人类肝脏再生的相关性，从而为利用肝细胞属性转换促进肝脏再生提供新的思路。

当哺乳动物的上皮组织在受到损伤时，以往的研究发现，存在于组织中的干细胞会通过增殖和分化的方式补充受损的细胞来促进组织的再生。近些年通过对组织损伤再生中细胞的来源进行深入的研究发现，组织中除了存在干细胞为基础的再生方式，还存在一种体细胞可塑性介导的组织再生。体细胞可塑性是指终末分化的体细胞通过转分化或者去分化方式，重编程成其它类型的细胞来促进组织的再生。尽管体细胞可塑性已在多种上皮组织中被发现，关于体细胞可塑性在组织再生中的重要性及其内在分子调控机制仍待进一步研究。在本研究中，以肝细胞的可塑性作为研究对象，探索了在门静脉肝损伤修复的模型中，肝细胞可塑性在肝脏损伤再生中的作用及其分子调控机制。研究发现SWI/SNF染色体重塑复合体的重要亚基Arid1a，特异的调控门静脉肝损伤过程中肝细胞的重编程。在肝细胞中缺失Arid1a会抑制肝细胞到肝干细胞的重编程，并导致损伤修复后的肝脏出现了脂肪变性和肝功能障碍。进一步通过对机制的探索发现，Arid1a通过染色体重塑调控，使肝细胞重编程基因在静息状态处于预打开的状态。当肝脏在受到损伤时，Arid1a介导的肝细胞重编程基因的预打开帮助了转录因子Yap迅速地结合到肝细胞重编程基因上，启动肝细胞重编程基因的表达，促进肝细胞重编程的发生。综上所述，通过对Arid1a介导的肝细胞重编程调控机制的研究，我们揭示了肝细胞的可塑性在肝脏损伤再生至关重要的作用，同时揭示Arid1a介导肝细胞重编程基因的预打开可能是肝细胞具备重编程能力的内在分子基础。