肠道菌群-FXR轴在次级胆汁酸介导的肠炎发生中的功能及其机制研究

Bile acid dysmetabolism and intestinal dysbiosis are associated with development of intestinal inflammation. Studies have revealed that increased bile acids pool was found in the intestinal lumen of individuals with intestinal inflammation, which might through the negative activity of intestinal FXR feedback signaling. It was also demonstrated that some strains of probiotics could express the bile salt hydrolase (BSH), thus modulates the bile acid metabolism and intestinal FXR signaling. Our preliminary results have demonstrated that deoxycholic acid (DCA), a secondary bile acid, could significantly upregulated the level of intestinal inflammatory cytokines. In vivo, we found the abundance of BSH-producing bacteria (Lactobacillus and Bifidobacterium) were decreased and the expression of intestinal Fxr was repressed during the progression of colitis mediated by DCA. Based on these preliminary studies, we hypothesize that DCA induces intestinal dysbiosis, and collectively repressed the intestinal FXR feedback signaling, which contributes to the aggravation of intestinal inflammation. Our proposal is firstly to determine how DCA induces changes of bile acid composition and intestinal microbiota during the development of intestinal inflammation. We also analyze the intestinal FXR signaling and the downstream targets in this process. Secondly, we will use antibiotics cocktail to modulate the intestinal microbiota generally to explore its effects on the intestinal inflammation development, changes of gut microbiota and bile acid metabolism. Lastly, we will evaluate the effects of BSH- producing bacteria and the gut-restricted FXR agonist fexaramine (Fex) on the intestinal inflammation mediated by DCA and activation of bile acid-related FXR signaling. Results from our project will provide new insights in the prevention and treatment of bile acid related intestinal inflammatory diseases.

胆汁酸代谢紊乱和肠道微生态失衡与肠道炎症发生关系密切。研究表明炎症相关性肠病个体肠腔中胆汁酸池（pool）增加可能是由肠道FXR负反馈作用减弱所致，且肠道某些产胆盐水解酶（BSH）菌可影响胆汁酸代谢及抑制肠道FXR表达。我们发现脱氧胆酸（DCA）可显著促进肠上皮细胞炎症因子分泌，且体内研究证明DCA可使肠道产BSH菌群（产乳酸菌及双歧杆菌属）丰度减少，肠道Fxr表达下降并伴随肠炎发生。故我们推测“DCA诱导肠道微生态失衡，并协同抑制肠道FXR反馈作用加重结肠炎”。本研究首先评价DCA介导的肠炎发生过程中肠腔胆汁酸组成、肠道菌群组成改变、FXR及其下游分子表达变化；采用抗生素整体调控肠道菌群探讨DCA诱导肠炎进展情况、肠道菌群及胆汁酸变化；最后探讨产BSH菌及肠道特异性FXR激动剂对DCA介导的肠炎小鼠肠FXR-FGF15轴及肠道炎症的影响。预期成果将为胆汁酸相关性肠炎的防治提供一种新思路。

炎症性肠病发病率逐年上升，与我国饮食西方化密切相关。高脂饮食引起机体肠道高水平次级胆汁酸，包括脱氧胆酸（deoxycholic acid，DCA），具有细胞毒性，可促进炎性相关肠癌发生。肠道菌群被认为机体一个特殊功能器官，易受饮食等环境影响。证据表明肠道菌群失衡可促进IBD发生、发展，但机制尚不明确。本研究首先应用 16S rRNA 测序检测 DCA 介导的结肠炎症发生过程中粪便和组织的菌群变化，分析 DCA 诱 导的肠道微生态功能性改变；进一步应用抗生素“鸡尾酒”方式整体水平调控 肠道菌群，应用病理组织学、色谱技术及 Western blot 方法评估 DCA 饲养的小鼠肠道炎症、肠道菌群结构、粪便胆汁酸水平及胆汁酸相关信号通路、炎性介质分泌情况，探讨肠道菌群在 DCA 诱导肠道炎症过程中发挥的重要作用；最后探索额外补充肠特异性 FXR 激动剂是否能够减少肠道胆汁酸池容量、恢复肠道菌群及改善肠道炎症。我们发现，24周的DCA干预可诱导小鼠末端回肠及结肠粘膜炎症，肠道炎症病理组织学评分较对照组明显升高，同时粪便菌群多样性明显降低，菌门水平中厚壁菌门百分比下降；在菌属水平上，DCA组产胆盐水解酶菌属-梭菌属XlVa丰度显著下降。色谱分析显示DCA组小鼠肠道胆汁酸池增大，粪便中总胆汁酸浓度升高，其中次级胆汁酸浓度和非结合胆汁酸浓度明显升高。DCA组胆汁酸转运基因Ostβ，及胆汁酸信号分子FXR转录明显减少，肝脏胆汁酸合成限速酶基因较对照组转录增加。进一步应用抗生素鸡尾酒联合DCA干预小鼠，发现应用抗生素后可缓解小鼠回肠及结肠炎症。同时发现经抗生素干预后肠道菌群多样性减少。最后，通过补充肠道特异性FXR激动剂Fexaramine，可以改善DCA诱导的肠道菌群失衡，同时抑制肠道FXR-FGF15信号通路，拮抗肝脏胆汁酸合成，缩小胆汁酸池容量，进而缓解小鼠肠道炎症。本研究将为胆汁酸相关性肠炎的防治提供一种新思路。