肠道菌群代谢产物丁酸钠通过HDAC2调控肝脏GLP-1抵抗改善NASH机制研究

The morbidity of non-alcoholic steatohepatitis (NASH) is high which does great harm to health, and the pathogenesis of NASH is not fully elucidated and lack effective treatment strategies. Our previous studies found that total fecal microbiota transplantation could attenuate NASH via improving the dysbiosis of gut microbiota, and the abundance of butyrate-producing bacteria was significantly increased after transplantation by bacteria sequencing. Subsequently the butyrate-producing probiotic was used to transplant, which could alleviate NASH via enterohepatic immunoregulation, and further we found that sodium butyrate (NaB), one kind of short chain fatty acids, could mediate the effects mentioned above and regulate the gut-liver axis immunity. In addition, we also found that NaB could regulate the secretion of glucagon-like peptide-1 (GLP-1) and up-regulate the expression of hepatic GLP-1 receptor through the inhibition of histone deacetylase-2 (HDAC2), then enhance the hepatic GLP-1 sensitivity, and finally ameliorate NASH. Therefore, we hypothesize that liver-specific GLP-1 resistance may be existed in NASH and NaB could attenuate NASH by improving hepatic GLP-1 sensitivity which is dependent on the regulation of HDAC2. This study intends to confirm the existence of liver-specific GLP-1 resistance in clinical NASH patients and explore the onset of liver GLP-1 resistance via in vivo and vitro experiments. Furthermore we will elucidate the mechanism of NaB in improving liver GLP-1 resistance dependent on HDAC2. Ultimately the study aims to propose a new mechanism of NASH pathogenesis, to provide a new target or strategy for the clinical prevention and treatment of NASH.

非酒精性脂肪性肝炎（NASH）发病率高，危害大，发病机制尚未阐明，缺乏有效治疗手段。我们研究发现整体粪菌移植可以改善肠菌紊乱，通过菌群测序发现移植后产丁酸菌丰度提高；随后使用产丁酸益生菌移植，后者可恢复失衡的肠肝免疫改善NASH，进一步发现菌群代谢产物丁酸钠能够介导上述作用。我们还发现丁酸钠可以调控胰高血糖素样肽-1（GLP-1）的分泌，通过抑制组蛋白去乙酰化酶-2（HDAC2）上调肝脏GLP-1受体表达，增强肝脏对GLP-1敏感性。因此，我们推测NASH可能存在肝脏特异性GLP-1抵抗，丁酸钠依赖于调控HADC2提高肝脏GLP-1敏感性改善NASH。本研究拟通过临床样本证实肝脏特异性GLP-1抵抗的存在，通过体内外实验揭示肝脏GLP-1抵抗发生机制，利用基因调控技术阐述丁酸钠依赖HDAC2改善肝脏GLP-1抵抗，揭示NASH发病的可能新机制，为临床防治NASH提供新思路。

非酒精性脂肪性肝病（NAFLD）发病率逐年增高，造成极大的全球健康负担，因此，对NAFLD的发病机制研究、开发新的诊治靶标成为重中之重。既往研究提示肠道菌群及其代谢产物与NAFLD发病、诊治密切相关。本项目着重探索了肠道菌群代谢产物丁酸盐、三甲胺 N-氧化物(TMAO)对NAFLD进展的机制研究。研究结果提示NAFLD患者存在肝脏特异性胰高血糖素样肽-1（GLP-1）抵抗，丁酸盐可通过抑制组蛋白去乙酰化酶2（HDAC2）活性，而非通过作用于细胞表面G蛋白受体（GPR），提高肝细胞GLP-1受体表达，进而减轻脂肪变性肝细胞GLP-1抵抗，改善肝脏脂质代谢；随后通过肝脏特异性HDAC2敲除NAFLD模型，发现HDAC2的敲除显著改善高脂饮食诱导的肝脏病理损害，蛋白质组学、mRNA转录组学均提示HDAC2对多条脂代谢、炎症调控通路影响显著。而体外细胞学研究发现丁酸盐可促进脂肪变性肝细胞凋亡、抑制其增殖，内在机制与抑制GPR43/GPR109a-pAKT-mTOR信号通路相关。此外，通过TMAO干预高脂饮食诱导的NAFLD大鼠，结果提示TMAO干预显著减轻高脂饮食诱导的大鼠肝脏病理组织学损害，显著减轻脂肪变肝脏内质网应激和抑制肝细胞死亡通路，同时亦发现TMAO抑制肠道上皮胆固醇转运蛋白表达，减少胆固醇吸收，降低肝脏胆固醇负荷，改善肝细胞脂代谢。最终，本项目从肠道菌群代谢产物-肠肝轴角度，系统阐述了丁酸盐、TMAO对NAFLD发生发展的调控作用，为后续NAFLD诊治研究提供了新的思路和潜在干预靶点。