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

肥胖患者有发生心血管疾病的风险，这可以部分解释为止血和纤溶系统的紊乱。最近，已经证明脂肪细胞本身能够产生主要的纤溶抑制剂派-1，这可能是肥胖症中派-1水平升高的原因。我们推测瘦素受体信号转导通路可能调控脂肪细胞派-1基因的表达，而脂肪细胞分泌的瘦素可激活PAI-1基因的表达。重组瘦素对ob/ob基因肥胖小鼠给药6小时和24小时后，不仅导致血浆派-1水平降低，而且还抑制了腹部脂肪、皮下脂肪组织和肺组织中派-1基因的表达。将5-派-1/Luc报告基因和瘦素表达载体共转染3 T3-L1前脂肪细胞，发现派-1启动子活性受到抑制，并呈剂量依赖性。这些结果表明，外源性添加瘦素引起抑制派-1的表达在体内和体外。脂肪细胞表达至少两种瘦素受体：长型和短型。为了鉴定参与抑制派-1基因表达的瘦素受体（LepR），用瘦素和短或长形式的LepR表达载体转染3 T3-L1前脂肪细胞，然后在48小时孵育后测量荧光素酶活性。Leptin和LepR短型表达载体联合转染可使派-1基因转录活性降低至对照值的70 ~ 75%，而Leptin和LepR长型表达载体联合转染可使PAI-1基因转录活性上调1.8 ~ 2倍。这些结果表明，派-1基因表达的减少瘦素治疗是由于短形式的LepR信号介导的机制。

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.