胃旁路手术上调GLP-1分泌通过活化肝细胞自噬改善肝脂代谢机制研究

Decreased lipotoxicity in the liver may contribute to hepatic insulin sensitivity improvement after Roux-en-Y gastric bypass (RYGB). However, little has been performed to elucidate the exact mechanism of RYGB reducing hepatic lipid over-accumulation in response to environmental cues. Recently we reported that hepatocellular autophgy is activated by RYGB and might play a key role in regulating intracellular lipid degradation in the liver. Moreover, RYGB may induce hepatic autophagy through mechanisms beyond just starvation and weight loss. We also showed the marked increase of autophagy in liver after RYGB correlated well with the plasma glucagon-like peptide-1(GLP-1) level. Based on the data, we hypothesize that due to the regulation of GLP-1 after RYGB, hepatocellular autophagy is further activated, which sequesters, breaks down and deliveries lipid droplets (LDs) into lysosomes. Through lysosomal acid lipase (LIPA), the triglycerides stored in lipid droplets are degraded into fatty acids for energy. Furthermore, the marked increase in the autophagy-targeted LDs for LIPA degradation may contribute to the later decrease of hepatic lipid accumulation. Here, by combining pharmacological and genetic approaches, we will demonstrate the hypothesis, and make further investigate to clarify the molecular mechanisms of GLP-1 inducing the hepatocellular autophagy focusing on the contributions of AMPK-mTORC1-ULK1 complex and peroxisome proliferator activator receptor α. The study would have important implications for a deep understanding of the mechanisms of metabolic surgery improving lipid metabolism, and give new ideas to the therapeutic strategies of non-alcoholic fatty liver disease and type 2 diabetes.

胃旁路术（RYGB）减少肝脂蓄积，是术后肝胰岛素敏感性上调的关键因素。自噬是调控肝脂代谢主要途径之一，我们发现：RYGB术活化肝自噬，增强肝脂解，不能完全用摄食减少、体重下降解释，GLP-1可能与术后活化肝细胞自噬，上调脂肪酸氧化有关。本课题将首次1.利用特异性肝Atg7敲除鼠，研究肝细胞自噬在RYGB术后，调控肝脂代谢中的作用。2.采用药物阻断GLP-1受体，研究RYGB术后GLP-1在激活肝自噬，增强脂肪酸氧化中的作用。3.采用药物抑制/活化AMPK、mTORC1和PPARα，研究GLP-1激活肝细胞自噬的分子机制。我们推测：RYGB术后GLP-1通过活化肝自噬而改善肝脂代谢，AMPK-mTORC1-ULK1激酶复合可能是GLP-1激活肝细胞自噬的主要路径。探明RYGB手术改善肝脂代谢机制，为非创伤手段治疗非酒精性脂肪肝及2型糖尿病提供新靶点。

代谢性手术能够有效减少肥胖2型糖尿病患者肝脏脂肪蓄积，改善肝脏胰岛素抵抗，恢复血糖稳态，而其降低肝脂毒性的机制并不完全清楚。本课题旨在探讨代谢性手术改善肝脂代谢的神经内分泌机制，研究内容包括（1）RYGB术后不同时间点2、4、8周肥胖2型糖尿病大鼠肝脏脂肪三条主要代谢途径活性变化。（2）分别观察胃肠激素GLP-1、肝自噬及肝脏局部交感神经活性在术后肝脏脂肪分解代谢中的作用。（3）体内及体外实验，观察AMPK-mTORC1-P70S6K在RYGB术后GLP-1活化肝自噬中的作用。（4）观察术后肝外组织包括脂肪及下丘脑对能量代谢的调节。结果：（1）术后肝内脂肪分解增强对短期及长期肝脂蓄积减少起重要作用。肝内脂肪合成减少在术后早期肝脂沉积下降上发挥作用。（2）术后分泌增多的GLP-1可能通过AMPK-mTORC1-P70S6K通路活化肝自噬，上调脂肪分解。（3）术后肝脏局部交感神经活性增强与肝内脂肪分解增加有关。（4）代谢性手术促进白色脂肪棕色化，脂联素-SIRT1-AMPK通路，心房利钠肽受体NPRA与NPRC比率，PPARγ-FSP27 可能在此过程中发挥调节作用。（5）下丘脑内nesfatin-1-MC3/4R-ERK通路活性升高是导致术后摄食减少和体脂下降的原因之一。本研究科学意义在于（1）增强肝脏脂肪分解对治疗非酒精性脂肪肝及降低2型糖尿病肝脂毒性有意义。肝自噬及肝脏交感神经对增强肝脏局部脂肪分解有作用，可能会成为潜在治疗靶点。GLP-1可以激活肝自噬，上调肝脏脂肪分解，从而减少肝脏脂肪堆积。（2）探讨了胃肠道-下丘脑-靶器官（包括肝脏、肌肉及脂肪）作用链条在调节脂代谢中的作用。为研究能量代谢的神经内分泌调节提供了可靠的模型，并积累了一定的数据。