Transcriptional repression of PAI-1 gene expression by leptin receptor signal-mediated mechanisms.

肥胖患者有患心血管疾病的风险，这在一定程度上可以用止血和纤溶系统的紊乱来解释。最近，研究表明脂肪细胞本身能够产生一种主要的纤溶抑制物PAI-1，这可能是肥胖症患者PAI-1水平升高的原因。我们推测瘦素受体信号转导途径可能调节脂肪细胞PAI-1基因的表达，该信号转导通路可被脂肪细胞分泌的瘦素激活。重组瘦素治疗ob/ob遗传性肥胖小鼠6小时和24小时后，不仅降低了血浆PAI-1的水平，而且还抑制了腹脂、皮下脂肪和肺组织中PAI-1基因的表达。将5-PAI-1/Luc报告基因与瘦素表达载体共转染3T3-L1前脂肪细胞，发现PAI-1启动子活性被抑制，且呈剂量依赖关系。这些结果表明，外源性添加瘦素在体内和体外均能抑制PAI-1的表达。脂肪细胞至少表达两种瘦素受体：长型和短型。为确定瘦素受体(Lepr)在抑制PAI-1基因表达中的作用，将Leptin基因导入3T3-L1前脂肪细胞，构建Lepr短型和长型Lepr表达载体，孵育48h后检测荧光素酶活性。联合应用Leptin和Lepr短型表达载体可使PAI-1基因转录活性降低至对照的70%~75%，而Leptin和Lepr长型表达载体可使PAI-1基因转录活性上调1.8~2倍。这些结果提示，瘦素治疗降低PAI-1基因的表达是由于短形式的Lepr信号转导机制。

Obese patients are at risk for development of cardiovascular disease, which can in part be explained by disturbances in the haemostatic and fibrinolytic systems. Recently, it has been demonstrated that the adipocyte itself is able to produce a primary fibrinolytic inhibitor, PAI-1, possibly accounting for the elevated PAI-1 levels in obesity. We hypothesized that leptin receptor signal transduction pathway might regulate PAI-1 gene expression in adipocytes, which could be activated by leptin secreted from these cells. Administration of recombinant leptin to ob/ob genetic obese mice not only caused reduction of plasma levels of PAI-1 but also repression of PAI-1 gene expression in abdominal fat, subcutaneous fat tissues, and lung tissue after 6 hr and 24 hr treatments. Cotransfection of 3T3-L1 preadipocyte with 5-PAI-1/Luc reporter and leptin expression vectors revealed that PAI-1 promoter activities were repressed in a dose-dependent manner. These results suggested that exogenous addition of leptin caused repression of PAI-1 expression in vivo and in vitro. Adipocytes express at least two kinds of leptin receptors ; long-and short-form. To identify the leptin receptor (LepR) involved in repression of PAI-1 gene expression, 3T3-L1 preadipocyte were transfected with leptin, and either short-or long-form LepR expression vectors, and then luciferase activities were measured after 48-hr incubation. Transfection in combination with leptin and short-form LepR expression vectors reduced PAI-1 gene transcriptional activities to 70〜75% of control value, while the transcriptional activities were up-regulated 1.8〜2 fold by transfection with leptin and long-form LepR expression vectors. These results suggested that decreased PAI-1 gene expression by leptin treatment was due to the short-form LepR signaling-mediated mechanisms.