瘦素在肝星状细胞中调控miRNA-122的机制及后者与抑制肝星状细胞激活关键因子SREBP-1c关系

Obesity is often accompanied by hyperleptinemia while obesity patients are more apt to develop liver fibrosis. Accumulating evidence indicate 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 factors that control gene expression. Our previous researches demonstrated that, in HSCs, leptin strongly down-regulated expression of sterol regulatory element binding protein-1c (SREBP-1c), a crucial transcription factor in inhibiting HSC activation. The new mechanisms of regulation of gene expression by microRNA have attracted extensive attention. Recently, miRNA122, the most abundant liver-specific microRNA, has been shown to inhibit liver fibrosis in rodents and in human. Only recently, we found that leptin significantly reduced miRNA122 and over expression of activated SREBP-1c up-regulated miRNA122 in cultured HSCs. Based on the above-mentioned data, the present research program aimed to detect the effect of leptin on miRNA122 expression, elucidate the complex mechanisms underlying the effect of leptin on miRNA122 expression in HSCs in vitro and in vivo (ob/ob mice) by using real-time PCR, plasmid construction, promoter mutation, and other techniques. Furtherly, the relationship between the effect of leptin on miRNA122 and leptin-induced HSC activatin and liver fibrosis and the the relationship between miRNA122 and SREBP-1c will also be examined. The results 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瘦素及高肝纤维化发生率。大量研究表明肥胖基因产物瘦素与肝纤维化关联。肝星状细胞(HSC)激活为肝纤维化发生的关键，此过程基础是HSC中调控基因表达的关键因子改变。申请者表明瘦素在HSC中下调抑制HSC激活的关键转录因子SREBP1c 表达。全新领域的miRNA对基因的调控引起关注。最近显示肝中表达最丰富且肝特异性miRNA122在鼠及人体中与抑制肝纤维化密切关联。申请者发现HSC中瘦素显著抑制miRNA122表达而SREBP1c上调miRNA122。该项目旨在依据以上基础，通过HSC培养及ob/ob肥胖鼠，利用real-time PCR，质粒构建，启动子位点突变等多种技术揭示仍未知的瘦素对HSC中miRNA122的调控与机制，miRNA122与SREBP1c的关系及与瘦素促HSC激活及肝纤维化的关系。该项目有益于阐明肥胖症患者高肝纤维化发生率的复杂分子机制。

肥胖症患者常具血清高浓度瘦素及高肝纤维化发生率。对人及鼠的肝纤维化研究表明瘦素促肝纤维化的发生。肝星状细胞(HSC)的激活为肝纤维化发生的关键，此过程的内在基础是HSC中调控基因表达的关键因子改变。申请者先前研究表明瘦素在HSC中下调抑制HSC激活的关键转录因子固醇调节元件结合蛋白1c (SREBP1c) 表达。microRNA（miRNA）是调控基因表达的重要机制之一。最近显示肝中表达最丰富且肝特异性miRNA122在鼠及人体中与抑制肝纤维化密切关联。在以上背景基础上，我们利用鼠及HSC研究了瘦素是否调控miRNA122表达，瘦素调控miRNA122表达机制，以及miRNA122对瘦素诱导肝纤维化发生的影响。同时也检测SREBP1c与miRNA122之间的关系。结果提示：瘦素能体内体外抑制HSC中miRNA122表达。介导瘦素作用的主要信号通路包括Hedgehog, JNK, Akt信号通路，而其中Akt通路介导瘦素磷酸化转录因子foxO1，使其失活。foxO1可结合于miRNA122启动子－56位点，促进miRNA122启动子活性及促进miRNA122表达。因此，瘦素激活Akt通路，后者磷酸化foxO1，从而抑制了miRNA122表达。同时显示SREBP1c与miRNA122在HSC中可以互为促进表达。利用ob/ob肥胖模型显示miRNA122抑制瘦素对HSC激活及肝纤维化的促进。以上实验结果显示了肥胖基因产物瘦素与在肝中表达最丰富的miRNA122在HSC中的关系，以及瘦素促肝纤维化发生的新机制。希望能为阐明肥胖症患者高肝纤维化发生率的复杂分子机制带来一丝亮光。

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