基于肠-肝轴FXR-FGF19反馈环路探究结肠炎性胆汁淤积的发病机制及特异性标志物

Ulcerative colitis(UC)-related hepatobiliary abnormality has been one of the serious complications of UC, the underlying mechanism has close correlation with intrahepatic cholestasis. Previous study showed that intestinal inflammation altered bile acids synthesis and transport in the liver and ileum, and thus resulted in intrahepatic cholestasis, but the mechanism has not been identified. FXR-FGF19 feedback loop of gut-liver axis plays an important role in regulating bile acids synthesis and transport. Our previous study showed that intestinal inflammation inhibited FXR-FGF19 signaling and thus induced intrahepatic cholestasis. Based on above evidence, we hypothesize that altered bile acids synthesis and transport may contribute to the pathogenisis of UC-related cholestasis via FXR-FGF19 feedback loop inhibition. To test this hypothesis, we will fistly investigate the effect of intestinal inflammation on bile acids synthesis, transport, and Fxr-Fgf15 signaling pathway using UC rat model. Meanwhile, the effect of pro-inflammatory cytokines and endotoxin on FXR-FGF19 signaling pathway and the molecular mechanism will be further investigated using in vitro study. Finally, the altered biomolecules in the serum of UC rats will be selected as potential biomarkers of UC-related cholestasis. Clarify the mechanism of UC-related cholestasis may provide clues for dignosis and therapy of UC-related hepatobiliary abnormality, and the discovered serum specific biomarkers may provide information for early dignosis of UC-related cholestasis.

溃疡性结肠炎（UC）相关性肝病是UC最常见肠外表现之一，其发生与肝内胆汁淤积密切相关。肠道炎症可影响胆汁酸的合成及转运并引起胆汁淤积，但机制不清。肠-肝轴FXR-FGF19反馈环路是调节胆汁酸合成与转运的关键信号，课题组发现肠道炎症可引起肝内胆汁淤积和FXR-FGF19信号通路抑制。基于此，课题组提出“肠-肝轴FXR-FGF19反馈环路抑制参与UC胆汁淤积发生”这一设想。本研究拟首先考察UC大鼠模型中胆汁酸合成、转运及Fxr-Fgf15信号通路变化及FXR激活对其影响；并在细胞水平研究炎症因子及内毒素对FXR-FGF19信号的影响及其分子机制；探究UC模型中特异性变化的血清生物分子有望发现UC胆汁淤积早期标志物。阐明UC胆汁淤积发病机制可为UC相关性肝病的防治提供线索；血清特异性标志物的发现可为UC胆汁淤积的早期准确诊断提供参考。

肝脏是胆汁酸合成场所，回肠是其重吸收的主要部位，肠-肝轴FXR-FGF19反馈环路是调控其合成、转运并维持平衡的关键信号。目前，UC相关性胆汁淤积的具体发病机制目前尚不明确，课题组基于前期研究发现提出“炎症因子通过肠-肝轴FXR-FGF19环路介导UC胆汁淤积发生”这一设想。研究应用TNBS制备UC大鼠模型研究UC发生中胆汁酸合成、转运及Fxr-Fgf15反馈环路的变化，并应用肝脏HepaRG细胞研究促炎因子对胆汁酸合成酶及转运体的影响，最后动态检测UC模型动物血清中早期特异性变化的生物分子。结果显示：①UC模型动物存在明显肝内胆汁淤积，表现为肝脏胆汁酸合成酶表达增高及胆汁酸合成增加，并伴有胆汁酸外排转运体表达减少及胆汁酸向胆管排泌减少；②UC模型存在回肠Asbt表达下调及胆汁酸重吸收减少，并引起肠道Fgf15表达减少及血清Fgf15含量降低，从而导致肠-肝轴“Fxr-Fgf15”负反馈通路抑制；③UC模型存在血清炎症因子TNF-α及IFN-γ升高，而TNF-α及IFN-γ可诱导肝脏HepaRG细胞中胆酸合成酶增高及胆汁酸外排转运体减少；④UC造模后5 d出现典型胆淤表现，造模后1 d即已出现血清甘氨酸结合型胆汁酸增高，造模后3 d出现血清6-酮醇石胆酸升高及Fgf15降低，提示血清甘氨酸结合型胆汁酸有望成为UC胆淤早期诊断标志物。由此可见，UC胆汁淤积的发生与肠-肝轴FXR-FGF19反馈环路抑制及循环炎症因子的调控作用有关，其结果可使肝脏胆汁酸合成增多而胆汁酸外排减少，最终引发肝内胆汁淤积。本研究发现可为UC胆汁淤积的发病机制提供依据，为UC胆汁淤积的治疗提供新思路，并有望为该病的早期准确诊断提供参考。