锌alpha2糖蛋白对非酒精性脂肪肝的保护作用及机制研究

Nonalcoholic fatty liver disease (NAFLD) caused by obesity is rapidly becoming a worldwide public health problem. Recently accumulated evidence indicates that Zinc alpha2 glycoprotein (ZAG) could be a new candidate involved in the pathogenesis of obesity by regulating lipolysis and reducing fat accumulation. We have demonstrated firstly that expression of ZAG is decreased in the liver of obesity mice. The effects and mechanisms of ZAG on NAFLD remain unclear. Lipid metabolic disorders and inflammation are closely associated and contribute to the pathogenesis of NAFLD. The ''first hit'' is the initial excess lipid accumulation in the form of triglycerides, free fatty acid and free cholesterol in hepatocytes. In the ''second hit,'' excess lipids in hepatocytes lead to cell injury, setting off inflammatory changes. The fundamental pathophysiological change of NAFLD is the accumulation of TG in hepatocytes. Inflammatory signaling pathways activation plays a crucial role in the aggravation of NAFLD. Therefore, decreasing hepatic lipid levels and repressing the inflammatory response are the keys to NAFLD therapy. To ascertain the role of ZAG in NAFLD, we will design overexpression or silence expression of ZAG on cell and NAFLD mice. TG accumulation, steatosis and inflammation in the liver will be observed.The objective of the study is to investigate the effects of ZAG through which metabolic nuclear receptors and downstream lipid metabolic gene and to reveal how ZAG regulates inflammation in the liver by JNK and NF-κB signal pathways. The mechanisms of ZAG on occurrence and development of NAFLD would be clear and definite after this project which provides evidence for ZAG as a novel molecular therapeutic target for NAFLD.

肥胖所致的非酒精性脂肪性肝病（NAFLD）已成为严重的公共卫生问题，对人类健康构成严重威胁。锌α2糖蛋白(ZAG)是一种以减少脂肪积聚为特点的脂肪细胞因子，我们首次证实肥胖的小鼠肝脏ZAG表达减少，但ZAG在NAFLD中的作用和确切机制尚不清楚。肝脏脂质代谢紊乱及炎症与NAFLD病理机制密切相关，其中肝脏中甘油三酯（TG）异常积聚是NAFLD的发病基础，肝脏炎症信号通路的激活是NAFLD进展的重要机制。本课题从细胞和动物水平研究过表达及沉默ZAG表达后，肝脏TG沉积、脂肪变性和炎症状态的变化，阐明ZAG通过何种代谢性核受体及脂代谢基因调控肝脏TG代谢，揭示JNK和NF-κB信号通路如何参与ZAG调节肝脏的炎症反应。本项目的实施将阐明ZAG阻止NAFLD发生和发展的机制，为NAFLD治疗提供新的靶点和实验依据。

非酒精性脂肪性肝病（NAFLD）是肥胖和代谢综合征累及肝脏的表现，肝脏甘油三酯（TG）异常积聚是NAFLD发病的基础，而炎症信号通路激活是NAFLD进展的重要机制。近年的研究表明，脂肪细胞因子通过参与调节肝脏TG代谢等途径影响NAFLD的发生和发展。锌alpha2糖蛋白（Zinc alpha2 glycoprotein, ZAG）是近年证实的一种能强烈地促进脂肪分解，以减少脂肪积聚为特点的脂肪细胞因子。ZAG在肥胖性肝病中的作用机制不清楚。. 我们发现高脂饲料喂养的NAFLD小鼠肝脏中ZAG水平显著下降，通过腺相关病毒载体转载 ZAG 干预NAFLD小鼠，过表达ZAG能减轻肝脏重量，减少肝脏脂滴数量，降低肝脏TG、TC、FC、CE、CE/TC%水平，改善NAFLD。其机制是ZAG通过抑制肝脏TG合成及摄取相关因子SREBP1c、LXR、CD36、FATP4、FABP、SCD1、FAS的表达，促进脂肪酸β氧化相关因子PPARａ、FXR、CPT1、UCP-1的表达进而改善肝脏脂质沉积。体外研究发现，过表达ZAG能通过增加代谢性核受体FXR、PPARα的表达和降低SREBP1c、LXRα的表达，从而增加β氧化相关基因CPT1A的表达及降低脂肪酸合成基因FAS、ACC的表达，减少棕榈酸诱导的HepG2细胞内甘油三酯的沉积。我们还发现ZAG能够改善蛋氨酸-胆碱缺乏性饮食（MCD）诱导的非酒精性脂肪性肝炎（NASH）小鼠肝脏脂肪变及炎症反应，可能与ZAG调节肝脏脂代谢相关基因的表达以及抑制炎症因子的表达有关。ZAG可降低HepG2细胞中的炎症因子TNF-α及IL-1β蛋白表达，ZAG能降低p-JNK、C-jun及p-cjun蛋白的表达。ZAG还可以抑制磷酸化P65的入核来抑制NF-κB炎症信号通路炎症反应的发生。总之，我们的研究首次证实：（1）ZAG可能通过调节代谢性核受体及下游脂质代谢基因的表达而抑制肝脏TG异常积聚；（2）ZAG通过抑制JNK和（或）NF-κB通路，降低肝脏代谢性炎症，对NAFLD有保护作用。