肠道菌群在β淀粉样蛋白代谢和阿尔茨海默病发生中的作用及机制研究

Periphery system has effects on the metabolism of amyloid beta (Aβ) and the pathogenesis of Alzheimer’s disease. Recently, we have found that periphery system facilitates the catabolism of 40% of brain derived Aβ; meanwhile, the intestine is essential for Aβ clearance; besides, the gut microbiota (GM) promotes the clearance and transport of brain injected Aβ while ameliorating the neuronal death induced by the toxicity of Aβ and expediting the release of 5-HT in the brain. It is well known that the 5-HT receptor subtype 4 (5-HT4R) is crucial in the association between 5-HT and Aβ metabolism as well as AD pathogenesis. Therefore, we propose that the GM may reduce the Aβ levels in the brain and influence the AD pathogenesis by acting on multiple pathways involved in Aβ metabolism, in which the 5-HT4R in the brain may play a mediating role. In this proposal, the GM depletion and GM reconstitution APP/PS1 transgenic mice will be employed. We plan to investigate the effects of the GM on the cognitive impairment in AD using a battery of animal behavioral tests. Then we intend to determine the influence of the GM on Aβ metabolism and AD-like pathology by means of the immunochemical and molecular biological methods. Finally, we will explore the role of the 5-HT4R signaling pathway in the association between the GM and Aβ metabolism as well as AD pathogenesis utilizing the selective 5-HT4R antagonist RS39604, and Lactobacillus Rhamnosus GG which was known to elevate the 5-HT level in the brain as a probiotic, respectively. The results from this proposal should be helpful to reveal the pathogenesis and new therapeutic targets of AD.

外周系统影响β淀粉样蛋白（Aβ）代谢和阿尔茨海默病（AD）发生。我们发现，整个外周系统清除40%脑内Aβ；肠道是清除Aβ的重要脏器；肠道菌群促进脑内外源性Aβ清除和转运，减轻Aβ毒性所致的神经元坏死，促进中枢5-羟色胺（5-HT）释放。而脑内5-HT受体4（5-HT4R）是5-HT作用于Aβ代谢和AD发生的重要位点。故推测，肠道菌群可能通过Aβ代谢的多个环节，降低脑内Aβ水平，影响AD发生，其中脑内5-HT4R可能起着介导作用。本项目拟采用肠道菌群抑制（GMD）和肠道菌群重建（GMR）动物模型；利用动物行为学实验，探讨肠道菌群对AD认知能力的影响；使用免疫化学和分子生物学等手段，明确肠道菌群对Aβ代谢和AD相关病理的影响；采用选择性5-HT4R拮抗剂和食用益生菌分别进行干预，揭示5-HT4R在肠道菌群与Aβ代谢和AD发生中的介导作用。本项目对探索AD发病机制和防治新靶点具有重要意义。

外周系统影响β淀粉样蛋白（Aβ）代谢和阿尔茨海默病（AD）发生。结合前期研究，我们推测，肠道菌群可能通过Aβ代谢的多个环节，降低脑内Aβ水平，影响AD发生，其中脑内5-HT4R可能起着介导作用。..本项目首先建立了肠道菌群抑制（GMD）和肠道菌群重建（GMR）小鼠模型，并在此基础上进一步建立了脑内5-HT4R抑制模型（RS小鼠）和提高脑内5-HT水平模型（LGG小鼠）。动物行为学实验显示，较AD-GMD小鼠而言，AD-GMR小鼠和LGG小鼠活动能力、探究能力、学习记忆能力均明显增强，上述指标在RS小鼠则均明显减低。上述结果提示，肠道菌群影响AD认知能力，其中脑内5-HT4R可能起着介导作用。..进一步发现，较AD-GMD小鼠而言，AD-GMR小鼠和LGG小鼠脑内Aβ负荷，包括刚果红染色显示的致密老年斑、特异性抗体显示的Aβ沉积、不同溶质下脑组织提取物内Aβ水平、脑内CAA的数量、脑内微出血数量等均明显减少，而上述指标在RS小鼠则明显增多。上述结果提示肠道菌群对AD脑内Aβ代谢的影响，其中脑内5-HT4R可能起着介导作用。同时，AD-GMD和AD-GMR两组间APP表达、Aβ代谢酶的表达以及Aβ转运酶的表达均无显著差异，提示肠道菌群可不通过影响Aβ的产生和中枢清除发挥减低脑内Aβ的作用。..进一步发现，较AD-GMD小鼠而言，AD-GMR和LGG小鼠脑内活化小胶质细胞、星形胶质细胞、过度磷酸化tau蛋白水平等均明显减少，而上述指标在RS小鼠则明显增多。上述结果提示肠道菌群对AD脑内相关病理特征的影响，其中其中脑内5-HT4R可能起着介导作用。..综上，本项目目前发现，肠道菌群可降低脑内Aβ水平，影响AD发生，其中脑内5-HT4R可能起着介导作用。本项目对探索AD发病机制和防治新靶点具有重要意义。..