S1PR2信号通路调控胆汁淤积性肝纤维化进展的机制研究

Cholestasis has been shown to be an important stimulus for the development of fibrosis, which is associated with accumulation of bile acids, but the mechanism is still unclear. Sphingosine 1-phosphate receptor 2 (S1PR2) is a recently identified and widely expressed G-protein coupled, cell surface bile acid receptor. Our previous work found that S1PR2 expression was upregulated in fibrotic liver and bile acid-activated HSC cell, and S1PR2 deficiency significantly reduced BDL-induced liver fibrosis in mice. In addition, we found that JTE-013, a specific inhibitor of S1PR2, could prevent TCA-induced YAP activation which is a key regulator of HSC activation. We hypothesized that bile acids activated YAP signaling pathway via S1PR2, which induces HSC activation and participates in the progression of cholestasis liver fibrosis. In order to verify the hypothesis, this study explored the role of S1PR2 signaling pathway in regulation of HSC activation and cholestasis-induced liver fibrosis by HSC cell model in vitro and bile duct ligation induced-hepatic fibrosis model in vivo at molecular, cellular and animal levels. The results of the study elucidate the pathogenesis of cholestasis induced-fibrosis and represent a novel therapeutic target.for cholestasis liver fibrosis.

胆汁淤积是诱发肝纤维化的一个重要因素，通常认为与淤积的胆汁酸有关，但机制尚未完全阐释。1-磷酸鞘氨醇受体2(S1PR2)是近年来新发现的胆汁酸G蛋白偶联受体，我们前期发现其在纤维化的肝脏和胆汁酸活化的肝星状细胞（HSC）中表达升高，而且S1PR2敲除后可减缓肝纤维化的进程；另外，YAP激活是HSC活化的关键调节因子，我们发现S1PR2特异性抑制剂JTE-013能阻止牛磺胆汁酸诱导YAP活化的作用。由此推测：胆汁淤积时，胆汁酸通过S1PR2激活YAP信号通路，引起HSC活化，参与肝纤维化的进展。本研究拟通过体外活化HSC细胞模型及体内胆管结扎诱导的小鼠肝纤维化模型，利用S1PR2转基因小鼠，分别从分子、细胞和动物水平探讨S1PR2信号通路在调控HSC活化以及胆汁淤积性肝纤维化进程中的作用。研究结果有望阐明胆汁淤积进展为肝纤维化的病理过程，为防治胆汁淤积性肝纤维化提供新的理论基础和治疗靶点。

胆汁淤积是诱发肝纤维化的一个重要因素，通常认为与淤积的胆汁酸有关，但机制尚未完全阐释。1-磷酸鞘氨醇受体2(S1PR2)是近年来发现的胆汁酸G蛋白偶联受体，在细胞迁移、增殖、分化和存活调控中占有重要地位，但其在肝纤维化和肝星状细胞（HSC）中的表达和作用还有待考察。本研究利用3,5-二乙氧基羰基-1,4-二氢吡啶（DDC）饮食诱导的小鼠胆汁淤积性肝纤维化模型和体外牛磺胆酸（TCA）诱导HSC活化模型，应用荧光定量PCR、DNA凝胶和免疫荧光染色等方法检测S1PR2及肝纤维化相关基因的表达，证实S1PR2在肝纤维化进程中HSC表达量持续上调。接着，利用shRNA干扰等技术手段，阐明S1PR2与YAP信号通路的上下游关系，证实TCA通过S1PR2调控YAP信号通路介导HSC的增殖、迁移、收缩和细胞外基质的分泌。最后，在DDC诱导的肝纤维化模型中利用S1PR2特异性抑制剂JTE-013和腺相关病毒（AAV-shS1PR2）抑制小鼠肝脏S1PR2的活性，证实S1PR2抑制或敲低后可显著减轻了小鼠的肝组织病理学损伤、胶原积累和纤维化相关基因的表达。综上可知，胆汁淤积时，以TCA为代表的结合型胆汁酸可直接诱导S1PR2/p38MAPK/YAP信号通路的激活，从而调节HSC活化参与肝纤维化的进展。