Xu Xue-Ling, Zhao Yue, Chen Ming-Ming, Li Yan, Li Yao, Wu Su-Jun, Zhang Jin-Long, Zhang Xiao-Sheng, Yu Kun, Lian Zheng-Xing
Beijing Key Laboratory for Animal Genetic Improvement, National Engineering Laboratory for Animal Breeding, Key Laboratory of Animal Genetics and Breeding of the Ministry of Agriculture, College of Animal Science and Technology, China Agricultural University, Beijing, China.
Institute of Animal Husbandry and Veterinary Medicine, Tianjin Institute of Animal Sciences, Tianjin, China.
Front Microbiol. 2023 Feb 15;14:1075164. doi: 10.3389/fmicb.2023.1075164. eCollection 2023.
Toll-like receptor 4 (TLR4) identifies Gram-negative bacteria or their products and plays a crucial role in host defense against invading pathogens. In the intestine, TLR4 recognizes bacterial ligands and interacts with the immune system. Although TLR4 signaling is a vital component of the innate immune system, the influence of TLR4 overexpression on innate immune response and its impact on the composition of the intestinal microbiota is unknown.
Here, we obtained macrophages from sheep peripheral blood to examine phagocytosis and clearance of Salmonella Typhimurium () in macrophages. Meanwhile, we characterized the complex microbiota inhabiting the stools of TLR4 transgenic (TG) sheep and wild-type (WT) sheep using 16S ribosomal RNA (rRNA) deep sequencing.
The results showed that TLR4 overexpression promoted the secretion of more early cytokines by activating downstream signaling pathways after stimulation by . Furthermore, diversity analysis demonstrated TLR4 overexpression increased microbial community diversity and regulated the composition of intestinal microbiota. More importantly, TLR4 overexpression adjusted the gut microbiota composition and maintained intestinal health by reducing the ratio of Firmicutes/Bacteroidetes and inflammation and oxidative stress-producing bacteria (Ruminococcaceae, Christensenellaceae) and upregulating the abundance of Bacteroidetes population and short-chain fatty acid (SCFA)-producing bacteria, including Prevotellaceae. These dominant bacterial genera changed by TLR4 overexpression revealed a close correlation with the metabolic pathways of TG sheep.
Taken together, our findings suggested that TLR4 overexpression can counteract invasion as well as resist intestinal inflammation in sheep by regulating intestinal microbiota composition and enhancing anti-inflammatory metabolites.
Toll样受体4（TLR4）可识别革兰氏阴性菌及其产物，在宿主抵御入侵病原体的防御过程中发挥关键作用。在肠道中，TLR4识别细菌配体并与免疫系统相互作用。尽管TLR4信号传导是先天免疫系统的重要组成部分，但TLR4过表达对先天免疫反应的影响及其对肠道微生物群组成的影响尚不清楚。
在此，我们从绵羊外周血中获取巨噬细胞，以检测巨噬细胞对鼠伤寒沙门氏菌（Salmonella Typhimurium）的吞噬作用和清除能力。同时，我们使用16S核糖体RNA（rRNA）深度测序对TLR4转基因（TG）绵羊和野生型（WT）绵羊粪便中的复杂微生物群进行了表征。
结果表明，TLR4过表达通过在受到刺激后激活下游信号通路，促进了更多早期细胞因子的分泌。此外，多样性分析表明，TLR4过表达增加了微生物群落多样性并调节了肠道微生物群的组成。更重要的是，TLR4过表达通过降低厚壁菌门/拟杆菌门的比例以及减少产生炎症和氧化应激的细菌（瘤胃球菌科、克里斯滕森菌科），并上调拟杆菌门菌群和产生短链脂肪酸（SCFA）的细菌（包括普雷沃氏菌科）的丰度，从而调节肠道微生物群组成并维持肠道健康。TLR4过表达导致的这些优势细菌属的变化与TG绵羊的代谢途径密切相关。
综上所述，我们的研究结果表明，TLR4过表达可以通过调节肠道微生物群组成和增强抗炎代谢产物来抵抗绵羊体内的（Salmonella Typhimurium）入侵以及抵御肠道炎症。
