Sitagliptin通过microbiota-gut-brain轴在2型糖尿病致阿尔茨海默样变中的脑保护作用机制

Type 2 diabetes mellitus increase risk for Alzheimer’s disease. It was reported that the gut microbiota of T2D patients was characterized with low level of SCFA-producing bacteria and high level of LPS .The current study showed the level of LPS and component of Coli were higher in AD brain compared to controls.Microbial production of SCFAs was reported to decrease blood-brain barrier permeability by upregulating expression of the tight junction proteins, which are known to control barrier function in endothelial tissues， and promote microglial immune response. Furthermore, amplification of regulatory T cells could restore cognitive funtions in AD model,which suggested that intestinal microbiome dysbiosis could be a key modulator of T2DM induced AD-like lesion. However,the molecular mechanism for this association remain unclear. Our previous studies showed Sitagliptin could attenuate brain injury in T2DM induced AD-like lesion model, accompanied with increased level of intestinal SCFA .We hypothesize Sitagliptin ameliorates brain injury in T2D induced AD-like lesion via microbiota-gut-brain axis triggered by SCFA-producing bacteria.. We will investigate the neuroprotective effect of Sitagliptin on T2DM induced AD-like lesion model by in vitro and in vivo experiments. The effect of Sitaglipin on gut microbiota and its neuroprotection will be first observed. Then, whether the effects of Sitaglipint are mediated by integrated blood brain barrier and activated microglia which controlled by Treg- TGFβ1 pathway trigerred by SCFA will be examed. Our project will explore the molecular mechanism of neuroprotection of Sitagliptin from a new sight and elucidate the multiple protective mechanisms of Sitagliptin on prevention and treatment of T2DM induced AD-like lesion.

2型糖尿病(T2DM)是阿尔茨海默病(AD)发病的高危因素。有研究发现T2DM患者肠道产短链脂肪酸(SCFA)菌明显减少,LPS明显增多,而AD患者大脑中发现大量LPS和Coli成分；SCFA可调控血脑屏障和小胶质细胞,并刺激肠道产生Treg细胞，后者可缓解AD认知障碍，提示肠道菌群失调可能是T2DM致AD样变的关键因素，但机制不清。我们前期实验发现Sitagliptin可改善T2DM致AD样变的脑损伤，并伴产SCFA菌明显增多。我们提出：Sitagliptin通过microbiota-gut-brain轴改善由2型糖尿病致AD样变的脑损伤。本项目拟先观察其对T2DM致AD样变的脑保护作用,再分析该作用是否通过产SCFA菌介导的Treg-TGFβ1通路对血脑屏障紧密连接蛋白和小胶质细胞的调控，最终揭示Sitagliptin对脑保护作用全新的分子机制，为防治T2DM致AD样变提供新策略。

2型糖尿病（T2DM）是阿尔茨海默病（AD）发病的高危因素。研究发现T2DM患者肠道产短链脂肪酸（SCFA）菌明显减少，LPS明显增多，而AD患者大脑中大量LPS和Coli成分；由于SCFA可控制血脑屏障和小胶质细胞，并刺激肠道产生Treg细胞，后者可缓解AD认知障碍，但机制不清。本项目主要通过高脂饲喂链脲佐菌素（STZ）腹腔注射SD大鼠、C57小鼠构建2型糖尿病致AD样变的动物模型，运用Morris水迷宫、16S技术、免疫荧光、Evasblue法、菌群移植等多种实验方法，以及血脑屏障体外模型和Treg细胞Transwell共培养证实了：1）2型糖尿病模型鼠可出现明显的认知功能障碍，脑内存在大量LPS和Aβ的共表达，Sitagliptin可明显减少LPS和Aβ的共表达，明显缓解期认知障碍，同时肠内伴有肠道菌群结构的改变。2）菌群移植实验首次证实Sitagliptin可依赖其诱导的产SCFA菌减少脑内LPS和Aβ的共表达，发挥脑保护作用。3）体外实验证实Sitagliptin通过产SCFA诱导的Treg-TGFβ1信号通路作用于血脑屏障而发挥脑保护作用，从而证实了Sitagliptin依赖microbiota-gut-brain轴在2型糖尿病致AD样变中发挥脑保护作用的新机制。另外，在该基金的支持下，我们证实了：4）脑红蛋白对AD转基因小鼠有脑保护作用，可能与脑红蛋白减少Aβ42生成以及激活PI3K/AKt信号通路进而抑制caspase依赖的细胞凋亡途径有关。5）Curcumin明显减少AD转基因小鼠脑内Aβ的沉积，同时激活了RXR-α-LXR-β-ABCA1-apoA1信号通路促进胆固醇转运从而改善其认知障碍。6）LXR信号通路在改善AD认知障碍的过程中，小凹蛋白Caveolin-1在其中起重要作用。综上，我们的研究为2型糖尿病致AD样变和AD的防治提供了新的治疗靶点。