胶原三螺旋重复蛋白1(Cthrc1)在肝纤维化发生发展中的作用及机制

Liver fibrosis，a adaptive response to a variety of chronic liver injury factors, is characterized by excessive deposition of extracellular matrix in liver. Imbalance of profibrotic and antifibrotic mechanisms contributes to the activation of hepatic stellate cells. Collagen triple helix repeat containing 1 (Cthrc1), a secreted protein, is involved in tissue injury and repair. It could inhibit TGF-β1 induced collagen deposition in the process of adventitia repairing through negative feedback. The relationship between Cthrc1 and liver fibrosis has not been reported. In primary experiments, we found that Cthrc1 expression was significantly increased in liver tissues from patients and mice model with liver fibrosis. TGF-β1 promoted the synthesis of Cthrc1 in hepatic stellate cell line. Forced expression of Cthrc1 gene in hepatic stellate cell line, inhibited the expression of collagen typeⅠ,Ⅲ and α- SMA. We assume confidently that Cthrc1, as a negative feedback regulation mechanism, can attenuate liver fibrosis. We will focus on the following important scientific problems: Firstly, what efects of Cthrc1 on hepatic stellate cells, and what is the mechanism? Secondly, which factors regulate the expression of Cthrc1 in liver fibrosis? Finally, is it possible that liver fibrosis could be attenuated or even reversed by modifying the expression of Cthrc1

肝纤维化是肝脏对多种慢性损伤因素的修复反应，以促纤维化和抗纤维化机制失衡，肝星状细胞活化，细胞外基质过多沉积为特征。胶原三螺旋重复蛋白1（Cthrc1）是一种分泌性蛋白，主要参与机体生长发育及组织损伤修复等过程，可负反馈抑制血管损伤修复过程中TGF-β1导致的胶原沉积。目前尚未见到Cthrc1与肝纤维化关系的研究报道。我们预实验发现，人和小鼠肝纤维化组织中Cthrc1表达均明显增高；TGF-β1促进肝星状细胞合成Cthrc1；有趣的是，过表达Cthrc1可抑制肝星状细胞Ⅰ、Ⅲ型胶原以及α-SMA的表达。我们假设，Cthrc1作为机体抗纤维化过程的重要介质，减缓肝纤维化进程。本研究致力于阐明的主要科学问题：①肝纤维化时，Cthrc1对肝星状细胞发挥哪些作用及其机制？②在肝纤维化中，上调肝内Cthrc1表达的因素及其机制。③通过调节Cthrc1的表达缓解甚至阻断肝纤维化的发生发展。

胶原三螺旋重复蛋白1(Cthrc1)是一个TGF-β信号通路特定抑制剂，因此我们假设敲入/敲除Cthrc1基因以改变胆汁淤积小鼠淤胆型肝纤维化的自然进程。我们建立了两种小鼠肝纤维化模型，其一是胆总管结扎法，另一种是DDC饮食法。在每个模型，我们都分别在建模前或建模后注射表达Cthrc1的腺病毒或包含抑制Cthrc1表达的shRNA的腺病毒。我们观察到Cthrc1基因过表达可使肝纤维化明显病理评分明显减低，肝纤维化基因表达显著下降。相反，当Cthrc1基因被抑制时，肝纤维化的程度明显加重。为探明敲入/敲除Cthrc1基因所产生的显著效果的机制，我们接下来研究了在大鼠肝星状细胞HSC和人肝星状细胞LX-2中Cthrc1基因的交互作用。我们证明TGF-β可通过磷酸化smad3绑定Cthrc1启动子从而激活转录，诱导Cthrc1表达。另外，我们发现Cthrc1可通过加速磷酸化smad3降解来负反馈抑制TGF-β信号通路。重要的是，Cthrc1去顶端片段也有肝纤维化作用。总之，我们的研究表明TGF-β可诱导Cthrc1表达，Cthrc1反之通过加速磷酸化smad3降解负反馈抑制TGF-β，从而达到抑制肝纤维化的作用。