胆汁酸受体FXR/TGR5对断奶仔猪肠道屏障功能的调控作用及其机制

The high rates of diarrhea and mortality of weaned piglets are the major reasons for the low level and efficiency of pig breeding in our country. The intestinal barrier dysfunction is the fundamental cause of diarrhea in weaned piglets. The previous studies demonstrate that bile acid and its receptors FXR/TGR5 have an important role in the regulation of intestinal barrier function. However, the regulative effects and the mechanisms of bile acid receptors FXR/TGR5 on intestinal barrier function in weaned piglets remain unclear. In the present proposal, we firstly detect the bile acid level and the expression and localization of FXR/TGR5 in the gut of healthy and diarrheic piglets. Secondly, we investigate and elucidate the effects of bile acid on intestinal epithelial barrier such as the expression of tight junction protein, intestinal immune cell function such as the expression of inflammatory cytokines, and intestinal microflora composition of weaned piglets. Meanwhile, agonists, antagonists and gene editing technique (CRISPR/Cas9) were applied to explore the role of FXR/TGR5 in regulating of epithelial cells tight junction and inflammation in the intestine of weaned piglets, as well as the signaling pathways underlying these processes. Finally, through the feeding experiment of weaned piglets, we investigate the effects and mechanisms of bile acid or the FXR/TGR5 agonist on the intestinal barrier function and growth performance of weaned piglets. The results of the present project can not only reveal the regulative effects and mechanisms of bile acid and its receptors FXR/TGR5 on intestinal barrier function in weaned piglets, but also provide scientific basis for developing the nutritional control strategies to reduce diarrhea and improve gut health of weaned piglets.

断奶仔猪腹泻率和死亡率高是导致我国生猪养殖水平和效率低下的重要原因。肠道屏障功能损伤是仔猪腹泻的根本内因。研究表明，胆汁酸及其受体FXR/TGR5在肠道屏障功能的调节中具有重要作用，但其对仔猪肠道屏障的调控作用及机制尚不清楚。本项目首先检测健康与腹泻仔猪肠道胆汁酸水平及FXR/TGR5的表达与定位；其次，体外研究和阐明胆汁酸对猪肠道上皮细胞屏障（紧密连接蛋白表达）、免疫细胞功能（炎症因子表达）及肠道菌群结构的影响；同时，采用激动剂、阻断剂及基因编辑技术，揭示FXR/TGR5 在调控猪肠道上皮细胞紧密连接和肠道炎症反应中的作用及信号通路；最后，通过活体饲养试验，研究胆汁酸及其受体激动剂对断奶仔猪肠道屏障功能和生产性能的影响及机制。研究结果不仅能深入揭示胆汁酸及其受体FXR/TGR5对断奶仔猪肠道屏障功能的调控作用及其机制，同时可为研发降低断奶仔猪腹泻、提高肠道健康的营养调控技术提供科学依据。

断奶仔猪腹泻率和死亡率高是导致我国生猪养殖水平和效率低下的重要原因。因此，良好的肠道屏障功能对断奶仔猪肠道健康和存活率至关重要。本项目首先比较了正常与腹泻断奶仔猪血清及粪便中的胆汁酸的差异。结果发现，在正常与腹泻断奶仔猪的血清及粪便中，总胆汁酸、初级和次级胆汁酸比例、结合型和非结合型胆汁酸比例等方面均存在明显差异，提示胆汁酸可能在维持断奶仔猪肠道健康方面发挥重要作用。.在此基础上，项目进一步研究了不同胆汁酸对断奶仔猪、猪肠上皮细胞的屏障功能、细胞增殖及肠道菌群的调控作用和机制。结果表明，日粮添加鹅脱氧胆酸（CDCA）可显著提高断奶仔猪的肠道屏障功能和生产性能，同时CDCA可通过FXR-MLCK通路改善猪肠上皮细胞IPEC-J2和小鼠中LPS导致的肠屏障损伤；日粮添加猪脱氧胆酸（HDCA）会降低断奶仔猪生产性能，其机制可能是HDCA通过FXR-PI3K/Akt通路或调控肠道菌群组成及胆汁酸谱，分别直接或间接地抑制猪肠上皮细胞增殖；日粮添加牛磺熊脱氧胆酸（TUDCA）能够显著降低断奶仔猪腹泻率，此外TUDCA可通过TGR5-MLCK通路改善猪肠上皮细胞IPEC-J2和小鼠中E.coli或LPS诱导的肠屏障损伤。.总之，胆汁酸不仅是一种重要的消化液，还可作为信号分子调控肠道屏障功能。本项目研究结果深入揭示胆汁酸及其受体FXR/TGR5对断奶仔猪肠道屏障功能的调控作用及其机制，为研发降低断奶仔猪腹泻、提高肠道健康的营养调控技术提供科学依据。