肠道菌群调控 FXR-FGF15 信号通路参与短肠综合征肠衰竭相关性肝损害发病的机制研究

Intestinal failure associated liver disease (IFALD) is a major complication in patients with short bowel syndrome (SBS), its essential pathophysiological change is disturbance of bile acid metabolism. The negative feedback pathway of FXR-FGF15 mediated by bile acid is of great importance in maintaining hepatic bile acids balance. Our previous study showed that the SBS rats developed IFALD confirmed by liver pathology, and the relative abundance of bacteria involved in bile acids metabolism decreased significantly, which further resulted in the imbalance between primary and secondary bile acids. Based on these findings, we conjecture that the disturbance of intestinal bile acid metabolism resulting from SBS intestinal dysbiosis causes IFALD through inhibiting the activation of FXR-FGF15 signaling. In this project, we will regulate the expression of FXR in enterocyte in vitro to explore the effects of different bile acids on the activation of intestinal FXR. Additionally, we will establish intestinal-specific FXR knock-out SBS mice and give them oral gavage of different bile acids. Through performance liquid chromatography and immunology and molecular biology technologies, we aim to study the effects of altered FXR-FGF15 signaling on the development of IFALD resulting from SBS associated intestinal bile acid disturbance. Our results could provide a new perspective on modulating FXR-FGF15 signaling of SBS patients by altering the intestinal microbial composition, which may primarily contribute to the development of targeted strategies for prevention and management of IFALD.

肠衰竭相关性肝损害(IFALD)是短肠综合征(SBS)的严重并发症，其核心病理生理改变是肝脏胆汁酸代谢紊乱。经肠道胆汁酸活化的FXR-FGF15负反馈通路是维持肝脏胆汁酸稳态的重要途径，但其在IFALD发病中的作用尚未阐明。我们的前期研究发现，SBS大鼠的肝功能和肝脏病理符合IFALD改变，其肠道中具有胆汁酸代谢酶活性的细菌显著减少，并进一步影响肠道胆汁酸正常代谢。我们推测，SBS肠道菌群紊乱所致的肠道胆汁酸失衡可通过干扰FXR-FGF15信号通路的活化参与IFALD的发生。基于此，我们将在体外实验中利用慢病毒系统调控肠上皮细胞FXR的表达，探究不同胆汁酸组成对FXR-FGF15活化的影响;同时构建特异性肠上皮细胞FXR基因敲除的SBS小鼠模型，经不同胆汁酸灌胃后，通过液相色谱以及免疫学和分子生物学技术研究FXR-FGF15信号通路在SBS肠道胆汁酸代谢紊乱所致的IFALD发病中的作用。本项目的研究结果将为通过改变SBS患者的肠道菌群来调控FXR-FGF15信号通路的表达提供了新的思路，并为IFALD的预防和治疗提供新的靶点。

肠衰竭相关性肝损害(IFALD)是短肠综合征(SBS)的严重并发症，也是SBS患者死亡的重要原因。肝脏胆汁淤积和纤维化是IFALD的重要病理变化，胆汁酸的肠-肝循环紊乱在IFALD的发病中发挥重要作用；而胆汁酸代谢与肠道菌群密切相关。因此，本项目的研究目标是探究SBS肠道菌群的变化及其在IFALD发病中的作用。通过建立SBS大鼠模型，我们发现其回盲部内容物的菌群多样性和丰富度较假手术大鼠显著降低，菌群组成结构也发生明显变化，表现为常驻菌群相对丰度的下降和机会致病菌（如肠杆菌科）相对丰度的显著升高。此外，我们还发现具有胆汁酸代谢酶活性的细菌在SBS大鼠回盲部中显著减少；进一步的代谢组学分析也证实，SBS大鼠回盲部内容物中初级胆汁酸含量升高而次级胆汁酸含量减少。通过体外细胞实验，我们发现次级胆汁酸对FXR-FGF15信号通路的活化作用明显强于初级胆汁酸，而FXR-FGF15信号通路是调节胆汁酸肠-肝循环的重要通路。分别利用脱氧胆酸（DCA）、生理盐水和多种混合抗生素灌胃SBS大鼠后，我们发现DCA组大鼠的肝脏脂质沉积明显减轻，肝脏胆汁酸合成酶的表达也明显降低，且末端回肠FXR-FGF15通路相关分子表达量显著上调；而抗生素组SBS大鼠的相关结果则正好相反。结合上述研究结果，我们发现：小肠大部切除可显著降低肠道菌群的多样性并改变其菌落组成。SBS大鼠肠道内胆汁酸代谢相关细菌的相对丰度减少，使得DCA等次级胆汁酸含量下降；后者进一步导致末端回肠 FXR-FGF15负反馈信号通路活化减弱，引起肝脏Cyp7a1等胆汁酸合成酶表达上调，肝脏的胆汁酸过度合成并出现胆汁淤积，最终发生IFALD。本项目的研究结果将为寻找IFALD的潜在治疗靶点提供实验依据，从而改善SBS患者的预后。