FXR与ERS信号交互作用介导白桦脂酸改善非酒精性脂肪肝的机制研究

Both FXR agonism and alleviation of endoplasmic reticulum stress (ER stress, ERS) have been the key strategies for non-alcoholic fatty liver disease (NAFLD) treatment. However, the potential cross talk between FXR and ERS signaling is still unknown. In vitro, our preliminary results show FXR silencing promotes ER stress progress in hepatocyte, but OCA incubation exerts converse effect. Additionally, betulinic acid (BA), a potential FXR agonist also inhibits hepatocellular ER stress and lipids accumulation in vitro. Thereby, it is hypothesized that FXR activation could mediate hepatic ER stress reduction. BA could ameliorate NAFLD via FXR agonism mediating hepatic ER stress alleviation. In condition that positive FXR agonism or FXR deletion, we will clarify the in vivo regulatory mechanism that FXR activation mediating hepatic ER stress alleviation via analyzing the liver pathology phenotype of hepatic steatosis and ER stress, biochemistry levels of lipid and glucose metabolism, FXR and ER stress signaling in model mice which have NAFLD accompanied by hepatic ER stress. Based on such molecular mechanism, we will further verify the active pharmacologic action of BA treatment on improving NAFLD in vivo. Our research points to uncover a new regulatory mechanism of FXR and discover the potentially therapeutic agent of NAFLD.

法尼醇X受体（FXR）激活和内质网应激（ERS）缓解是治疗非酒精性脂肪肝的两种重要策略，而FXR与ERS是否存在信号交互尚不清楚。我们的体外预实验结果显示: FXR沉默促进了肝细胞ERS进程，而OCA（FXR阳性激动剂）干预则发挥了相反的效果。另外，白桦脂酸（BA）作为潜在的FXR激动剂也抑制了肝细胞的ERS进程和脂质堆积。据此我们假设：FXR激活可抑制肝脏ERS；BA可通过FXR激活介导的ERS抑制机制改善非酒精性脂肪肝。本研究将在FXR阳性激活或FXR敲除条件下，通过对模型小鼠（脂肪肝合并ERS表型）的肝脏脂肪变性和ERS病理分析、糖脂代谢生化分析、FXR和ERS信号检测来明确FXR激活介导肝脏ERS改善的体内调节机制。基于此机制，我们将进一步验证BA改善非酒精性脂肪肝的体内药效。本研究有望揭示新的FXR调控机制和脂肪肝治疗药物。

非酒精性脂肪肝 (NAFLD) 是常见的肝脏疾病，但现今仍缺乏治疗药物。法尼醇 X 受体 (FXR)信号通路和内质网应激（ERS）都参与了NAFLD的进展；然而，尚不清楚这两种途径的作用是否相互依赖。此外，酸枣仁的有效成分白桦脂酸（BA）在调控代谢综合征和 NAFLD 中的作用仍然未知。本研究通过FXR激活和沉默、肝细胞内质网信号通路检测并结合FXR-/-小鼠阐明FXR激活抑制肝脏ERS的机制。通过报告基因和TR-FRET技术验证BA是新的FXR激动剂，随后在高脂餐诱导的肥胖、蛋氨酸胆碱缺乏饲料诱导的NASH、衣霉素诱导的ERS模型小鼠和ob/ob小鼠中观察BA对小鼠体重、糖脂代谢和脂肪肝的影响来阐述白桦脂酸改善肥胖和脂肪肝的药效。最后通过FXR-/-小鼠验证BA经FXR-ERS信号通路发挥抗NAFLD的机制。研究结果显示FXR激活通过抑制Perk/eif2α信号改善肝细胞的ERS；我们BA 鉴定为 FXR 激动剂，并有效减缓 NAFLD 和代谢紊乱的进展；通过激活FXR 信号通路恢复了肝细胞 ER 稳态。而在FXR-/- 和ob/ob小鼠中BA 的作用被减弱，说明FXR激活介导了BA改善ERS和NAFLD，而且需要瘦素信号的参与。本研究初步揭示了肝脏FXR-ERS交互的机制，发现BA通过激活FXR-ERS信号改善脂肪肝的药效，可能为开拓中药防治脂肪肝提供了新的理论基础。