肥胖基因产物瘦素对抑制肝星状细胞激活的关键因子PPARgamma表达的调控机制

Leptin is a product of the ob gene. Obesity is often accompanied by hyperleptinemia while obesity patients are more apt to develop liver fibrosis. Earlier studies have indicated that leptin is closely associated with liver fibrosis. Hepatic stellate cell (HSC) activation is the key step during the process of liver fibrosis and the process of HSC activation is based on the alterations in the expressions and activities of important transcription factors. Transcription factor peroxisome-proliferator activated receptor-gamma (PPARγ) was found to play a key role in inhibition of HSC activation. Our previous researches showed that leptin strongly inhibited PPARγ expression in HSCs. Based on this result, the present research program aimed to elucidate the complex mechanisms underlying the inhibitory effect of leptin on PPARγ expression in HSCs in vitro and in vivo (ob/ob mice) by using plasmid construction, promoter mutation, electrophoretic mobility shift assay, chromatin immunoprecipitation, and other techniques. The results from this research program will reveal the transcription factors mediating leptin's inhibition of PPARγexpression, the signaling pathways by which leptin affects those transcription factors, the effect of leptin on the stability of PPARγ protein, and the influence of leptin-induced inhibition of PPARγ through correlated mechanisms on HSC activation. The mechanisms underlying leptin inhibition of PPARγare still unknown. The data from the researches may have potential implications for clarifying the mechanisms of liver fibrogenesis associated with hyperleptinemia such as in obesity patients.

肥胖症患者常具血清高浓度的肥胖基因产物瘦素，且更易发生肝纤维化。已表明瘦素与肝纤维化密切关联。肝星状细胞(HSC)的激活为肝纤维化发生的关键，此过程的基础是HSC中重要转录因子表达及活性的改变，研究已显示转录因子过氧化物酶体增殖物激活受体γ(PPARγ)为抑制HSC激活的关键因子。申请者发现在HSC中瘦素强烈抑制PPARγ表达。该项目旨在此研究基础上，利用体外HSC培养及ob/ob肥胖鼠(缺正常瘦素)的体内实验，以及质粒构建，启动子突变，凝胶阻滞实验，染色质免疫沉淀等技术系统阐明瘦素抑制PPARγ表达的复杂机制，包括：筛查出介导瘦素调控PPARγ表达的转录因子；瘦素影响相关转录因子所利用的信号途径；瘦素对PPARγ稳定性的影响；瘦素通过以上相关机制对HSC激活的作用。深入到瘦素对抑制HSC激活的关键因子的详细调控研究，无报道。该项目有益于阐明肥胖症患者易于发生肝纤维化的复杂分子机理。

肥胖症患者常具血清高浓度的肥胖基因产物瘦素，更易发生肝纤维化。已表明瘦素与肝纤维化密切关联。肝星状细胞（Hepatic stellate cell， HSC）的激活为肝纤维化发生的关键，此过程的基础是HSC中重要转录因子表达的改变，研究已显示转录因子过氧化物酶体增殖物激活受体gamma (PPARgamma)为抑制HSC激活的关键因子。HSC中瘦素强烈抑制PPARgamma表达。该项目在此研究基础上，利用体外及ob/ob肥胖鼠(缺正常瘦素)的体内实验，以及利用启动子突变，染色质免疫沉淀等多种分子技术较为详细阐明HSC中瘦素抑制PPARgamma1（HSC中主要表达形式）表达的复杂机制。该研究筛查出三种转录因子GATA-2 (GATA binding protein-2)，GATA-3 (GATA binding protein-3) 以及Sox9 (Sex-determining region Y-box 9) 参与瘦素抑制HSC中PPARgamma1表达；多个信号途径包括β-Catenin，Sonic hedgehog，NADPH oxidase，及Deltalike homolog1（DLK1）等介导瘦素调控相应三种转录因子的表达；进一步显示其中部分信号途径之间存在互通，特别是NADPH oxidase信号途径能激活上述其它信号途径，提示该途径在瘦素促纤维化中应发挥更重要作用，因而如果从信号途径中寻找作用于HSC药物靶点时对此应有考虑。结果显示GATA-2与GATA-3能相互作用共同调控PPARgamma1；研究也表明以上转录因子及信号途径在瘦素抑制HSC中PPARgamma1表达的功能意义，即在瘦素促HSC激活及肝纤维化中发挥介导作用。同时结果也显示了瘦素并不影响HSC中PPARgamma蛋白的降解。.此项目揭示了瘦素在HSC中调控PPARgamma1表达的较为详细的分子事件。基于PPARgamma为抑制HSC激活的关键因子，此课题的研究结果应有益于阐明肥胖症患者易于发生肝纤维化的复杂分子机制。课题揭示的介导瘦素抑制HSC中PPARgamma表达，以促进HSC激活及肝纤维化发生的转录因子GATA-2，GATA-3 及Sox-9，以及显示的影响三种因子的相关信号途径特别是NADPH oxidase途径，为具高浓度瘦素的肥胖症患者肝纤维化治疗寻找靶点提供参考。