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日粮中胆汁酸对改善大口黑鲈肠道屏障和肠道微生物介导的影响

The direct and gut microbiota-mediated effects of dietary bile acids on the improvement of gut barriers in largemouth bass (Micropterus salmoides)

作者：Rui Xia, Qingshuang Zhang, Dongmei Xia, Qiang Hao, Qianwen Ding, Chao Ran, Yalin Yang, Aizhi Cao, Zhen Zhang, Zhigang Zhou.

发布期刊：Animal Nutrition. 2023 Apr 20;14:32-42.

鱼类肠道屏障的损伤，是集约化养殖模式中关注的一个重要问题。本研究旨在探讨胆汁酸对大口黑鲈肠道屏障的影响。采用无菌斑马鱼模型，来阐明胆汁酸的直接作用和肠道菌群介导的间接调节对肠道屏障的影响。分别添加 0、150、300 和 450 mg/kg 的胆汁酸配制4种日粮，分别为：对照组、胆汁酸150、胆汁酸300 和胆汁酸450。经5周试验，胆汁酸300组的成活率显著提高（P < 0.05）。组织学分析显示胆汁酸150 组和胆汁酸300 组的肠道结构完整性有所改善。与对照组相比，胆汁酸150组和胆汁酸300组化学屏障（黏蛋白、溶菌酶和补体1）和物理屏障（occludin和claudin-4）相关基因的表达量显著增加（P < 0.05），胆汁酸300组免疫屏障相关基因（白细胞介素[IL]-6、肿瘤生长因子b、IL-10、巨噬细胞半乳糖型凝集素和免疫球蛋白M[IgM]）的表达显著增加（P < 0.05），但胆汁酸450组与化学屏障和免疫屏障（IL-1b、肿瘤坏死因子-a、IL-6和精氨酸酶）相关基因的表达量显著降低（P < 0.05）。肠道菌群宏基因组分析显示，胆汁酸150组和胆汁酸300组中厚壁菌门的细菌丰度显著增加（P < 0.05），而放线菌门和变形菌门的丰度呈下降趋势（P > 0.05）。肠道菌群转移试验的结果表明，从胆汁酸300组转移的肠道菌群可上调肠道屏障相关基因，与对照组相比，包括免疫球蛋白 Z/T (IgZ/T)、IL-6、IL-1b 和 IL-10基因的表达量显著上调（P < 0.05）。直接给无菌斑马鱼饲喂 BA300 日粮可增强 IgM、IgZ/T、溶菌酶、occludin-2、IL-6 和 IL-10 的表达（P < 0.05）。总之，胆汁酸可以通过肠道微生物群介导的直接和间接作用来改善鱼类的肠道屏障。

Fish gut barrier damage under intensive culture model is a significant concern for aquaculture industry. This study aimed to investigate the effects of bile acids (BAs) on gut barriers in Micropterus salmoides. A germ-free (GF) zebrafish model was employed to elucidate the effects of the direct stimulation of BAs and the indirect regulations mediated by the gut microbiota on gut barrier functions. Four diets were formulated with BAs supplemented at 0, 150, 300 and 450 mg/kg, and these 4 diets were defined as control, BA150, BA300 and BA450, respectively. After 5 weeks of feeding experiment, the survival rate of fish fed with BA300 diet was increased (P < 0.05). Histological analysis revealed an improvement of gut structural integrity in the BA150 and BA300 groups. Compared with the control group, the expression of genes related to chemical barrier (mucin, lysozyme and complement 1) and physical barrier (occludin and claudin-4) was increased in the BA150 and BA300 groups (P < 0.05), and the expression of genes related to immunological barrier (interleukin [IL]-6, tumor growth factor β, IL-10, macrophage galactose-type lectin and immunoglobulin M [IgM]) was significantly increased in the BA300 group (P < 0.05), but the expression of genes related to chemical barrier (hepcidin) and immunological barrier (IL-1β, tumor necrosis factor-α, IL-6 and arginase) was significantly decreased in the BA450 group (P < 0.05). Gut microbiota composition analysis revealed that the abundance of Firmicutes was augmented prominently in the BA150 and BA300 groups (P < 0.05), while that of Actinobacteriota and Proteobacteria showed a downward trend in the BA150 and BA300 groups (P > 0.05). The results of the gut microbiota transferring experiment demonstrated an upregulation of gut barrier-related genes, including immunoglobulin Z/T (IgZ/T), IL-6, IL-1β and IL-10, by the gut microbiota transferred from the BA300 group compared with the control (P < 0.05). Feeding the BA300 diet directly to GF zebrafish resulted in enhanced expression of IgM, IgZ/T, lysozyme, occludin-2, IL-6 and IL-10 (P < 0.05). In conclusion, BAs can improve the gut barriers of fish through both direct and indirect effects mediated by the gut microbiota.

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