Gut microbiota-derived metabolites mediates the neuroprotective effect of melatonin in cognitive impairment induced by sleep deprivation

Background: Sleep loss is a serious global health concern, displaying not only well-known memory deficits but also gastrointestinal dysfunctions. Our previous research proved that melatonin can effectively improve cognitive impairment and intestinal microbiota disturbance caused by sleep deprivation (SD). Present study further explored the mechanism whereby exogenous melatonin prevented SD-induced cognitive impairment. Here, we established fecal microbiota transplantation, Aeromonas colonization and LPS or butyrate supplementation tests to evaluate the role of intestinal microbiota and its metabolites in melatonin alleviating SD-induced memory impairment.Results: We found that transplantation of the SD-gut microbiota into normal mice induced microglia overactivation and neuronal apoptosis in hippocampus, cognitive decline and colonic microbiota disorder, manifesting as an increase in Aeromonas and LPS levels and decrease in Lachnospiraceae_NK4A136 and butyrate levels. However, the above events were reversed as the transplanting the SD+melatonin-gut microbiota. Colonization of Aeromonas and addition of LPS caused inflammatory response in hippocampus and spatial memory impairment in the mice, whereas supplementation of melatonin reversed these changes accompanied by decreased in Aeromonas and LPS levels. Additionally, administration of butyrate was given to sleep-deprived mice, and the inflammatory responses and memory impairment was restored. In vitro, the supplementation of LPS caused inflammatory response in BV2 cells, but was improved by butyrate supplementation. In contrast, this ameliorative effect of butyrate was blocked with pretreatments of MCT1 inhibitor and HDAC3 agonist but was mimicked by TLR4 and p-P65 antagonists.Conclusions: Our studies demonstrated that gut microbial and their metabolites mediate the ameliorative effect of melatonin on SD-induced cognitive impairment. A feasible mechanism is that melatonin down-regulated the levels of Aeromonas and its LPS and up-regulated the levels of Lachnospiraceae_NK4A136 and its butyrate in colon, thereby improving inflammatory response and neuronal apoptosis in hippocampus by role of crosstalk between TLR4/NF-kB and MCT1/ HDAC3 signaling pathways.

背景：睡眠缺失是一项严峻的全球性公共卫生问题，其不仅会引发公认的记忆缺陷，还会导致胃肠道功能紊乱。本团队前期研究证实，褪黑素（melatonin）可有效改善睡眠剥夺（Sleep Deprivation, SD）所致的认知损伤与肠道菌群失调。本研究进一步探究了外源性褪黑素拮抗SD诱导认知损伤的潜在机制。本实验通过构建粪便菌群移植（fecal microbiota transplantation）、气单胞菌（Aeromonas）定植以及脂多糖（Lipopolysaccharide, LPS）或丁酸（butyrate）干预实验，以评估肠道菌群及其代谢产物在褪黑素缓解SD诱导的记忆损伤中发挥的作用。
结果：研究发现，将SD小鼠的肠道菌群移植至正常小鼠体内后，可诱发其海马体（hippocampus）小胶质细胞（microglia）过度激活与神经元凋亡（neuronal apoptosis）、认知功能下降以及结肠菌群失调，具体表现为气单胞菌与脂多糖水平升高，毛螺菌科NK4A136群（Lachnospiraceae_NK4A136）与丁酸水平降低。而移植经SD+褪黑素处理小鼠的肠道菌群后，上述异常现象均得到逆转。气单胞菌定植与LPS干预可诱发小鼠海马体炎症反应与空间记忆损伤（spatial memory impairment），而褪黑素干预可逆转此类变化，同时伴随气单胞菌与LPS水平下调。此外，对睡眠剥夺小鼠施加丁酸干预后，其炎症反应与记忆损伤均得到恢复。体外实验（in vitro）中，LPS干预可诱导BV2细胞（BV2 cells）产生炎症反应，而丁酸干预可改善这一状况；相反，丁酸的这种改善效应可被单羧酸转运蛋白1（Monocarboxylate Transporter 1, MCT1）抑制剂与组蛋白去乙酰化酶3（Histone Deacetylase 3, HDAC3）激动剂预处理所阻断，却可被Toll样受体4（Toll-like Receptor 4, TLR4）与磷酸化P65（phosphorylated P65, p-P65）拮抗剂模拟。
结论：本研究证实，肠道菌群及其代谢产物介导了褪黑素对SD诱导认知损伤的改善作用。其潜在可行机制为：褪黑素可下调结肠内气单胞菌及其产物LPS的水平，同时上调毛螺菌科NK4A136群及其代谢产物丁酸的水平，进而通过TLR4/NF-κB与MCT1/HDAC3信号通路的交叉对话，改善海马体的炎症反应与神经元凋亡。