Division of Gastrointestinal Pathophysiology, University of Toyama, Toyama, Japan.
Departments of Pathology and Cell Biology, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, United States.
Front Immunol. 2024 Nov 13;15:1372670. doi: 10.3389/fimmu.2024.1372670. eCollection 2024.
It has recently become clear that the gut microbiota influence intestinal motility, intestinal barrier function, and mucosal immune function; therefore, the gut microbiota are deeply involved in the maintenance of intestinal homeostasis. The effects of the gut microbiota on the enteric nervous system (ENS) in the adult intestine, however, remain poorly understood. In the current study, we investigated the effects of the gut microbiota on the ENS. Male C57BL/6 SPF mice at 12 weeks of age were given a cocktail of four antibiotics (ABX) orally to induce dysbiosis (ABX mice). As early as six hours after ABX administration, the weight of the cecum of ABX mice increased to be significantly greater than that of vehicle-treated animals; moreover, ABX-induced dysbiosis reduced the density of enteric nerve fibers (marked by tubulin-β3 immunoreactivity) in the lamina propria of the proximal colon to approximately 60% that of control. TAK242, a TLR4 antagonist, significantly lowered the nerve fiber density in the lamina propria of the proximal colonic mucosa to approximately 60% that of vehicle-treated SPF mice. We thus developed and tested the hypothesis that mucosal glia expressing TLR4 are activated by enteric bacteria and release neurotrophic factors that contribute to the maintenance of enteric neural circuits. Neurotrophic factors in the mucosa of the SPF mouse proximal colon were examined immunohistochemically. Ciliary neurotrophic factor (CNTF) was abundantly expressed in the lamina propria; most of the CNTF immunoreactivity was observed in mucosal glia (marked by S100β immunoreactivity). Administration of CNTF (subcutaneously, 0.3 mg/kg, 3 doses, 2 hours apart) to ABX mice significantly increased mucosal nerve fiber density in the ABX mouse proximal colon to nearly control levels. The effect of CNTF on enteric mucosal nerve fibers was examined in isolated preparations of proximal colon of ABX mice. As it did , exposure to CNTF significantly increased enteric mucosal nerve fiber density in the ABX-treated colon. In conclusion, our evidence suggests that gut microbiota constitutively activate TLR4 signaling in enteric mucosal glia, which secrete CNTF in response. The resulting bacterial-driven glial release of CNTF helps to maintain the integrity of enteric mucosal nerve fibers.
最近已经清楚的是，肠道微生物群会影响肠道蠕动、肠道屏障功能和黏膜免疫功能；因此，肠道微生物群深度参与了肠道内环境稳定的维持。然而，肠道微生物群对成年肠道内肠神经系统（ENS）的影响仍知之甚少。在目前的研究中，我们研究了肠道微生物群对肠神经系统的影响。12 周龄的雄性 C57BL/6 SPF 小鼠口服给予四种抗生素（ABX）混合物以诱导肠道菌群失调（ABX 小鼠）。在 ABX 给药后仅 6 小时，ABX 小鼠的盲肠重量增加到明显大于对照动物；此外，ABX 诱导的菌群失调使近端结肠固有层的肠神经纤维密度（用微管蛋白-β3 免疫反应性标记）降低至约对照的 60%。TLR4 拮抗剂 TAK242 使近端结肠黏膜固有层的神经纤维密度显著降低至约对照 SPF 小鼠的 60%。因此，我们提出并测试了以下假设：表达 TLR4 的黏膜神经胶质细胞被肠道细菌激活，并释放神经营养因子，有助于维持肠神经回路。通过免疫组织化学检查 SPF 小鼠近端结肠黏膜中的神经营养因子。睫状神经营养因子（CNTF）在固有层中大量表达；大部分 CNTF 免疫反应性观察到在黏膜神经胶质细胞（用 S100β 免疫反应性标记）中。向 ABX 小鼠皮下给予 CNTF（0.3mg/kg，3 剂，间隔 2 小时）可使 ABX 小鼠的近端结肠黏膜神经纤维密度显著增加至接近对照水平。在 ABX 小鼠的离体近端结肠标本中研究了 CNTF 对肠黏膜神经纤维的作用。正如预期的那样，暴露于 CNTF 可显著增加 ABX 处理的结肠中的肠黏膜神经纤维密度。总之，我们的证据表明，肠道微生物群持续激活肠黏膜神经胶质细胞中的 TLR4 信号，后者对其作出反应分泌 CNTF。由此产生的细菌驱动的神经胶质细胞 CNTF 释放有助于维持肠黏膜神经纤维的完整性。
