ACTIVATION OF NUCLEAR RECEPTORS REGULATES ANITI THROMBOTIC ENVIRONMENT ON THE VASCULAR WALL

组织因子(Tf)是一种跨膜糖蛋白，似乎是动脉粥样硬化斑块血栓形成的关键决定因素，而动脉粥样硬化斑块是引发急性冠状动脉综合征的重要因素。我们发现，用过氧化物酶体增殖物激活受体-a(PPAR)α的配体，如苯扎贝特和Wy14643来预处理人脐静脉内皮细胞，可显著减弱肿瘤坏死因子-α(肿瘤坏死因子-α)诱导的细胞内转铁蛋白活性的增强。在用PPARγ配体预处理的细胞中没有观察到这样的效果。启动子分析表明，苯扎贝特或Wy14643降低Tf的表达与降低序列依赖的转录激活有关。在凝胶迁移率改变分析中，苯扎贝特和Wy14643减少了Jun/Fos异源二聚体与AP-1基本序列的相互作用，这一现象不仅归因于Jun/Fos相关核蛋白水平的降低，也归因于细胞内RAR/RXR异源二聚体形成减少而导致RAR/JunB异二聚体的形成增加。瞬时表达研究表明，RXRα和PPARα在细胞中的共表达降低了TF对AP-1依赖的启动子活性。这些结果表明，PPARa的配体可能通过改变核受体蛋白的异二聚体对来抑制不同炎症条件下人内皮细胞依赖Tf的血栓形成。另一方面，在本研究中，我们还发现他汀类药物通过抑制Rho家族的小G蛋白Rac/CDc42来调节血栓调节蛋白(TM)的表达。他汀类药物对内皮细胞TM表达的上调可能有助于他汀类药物对内皮细胞功能的有益影响。

Tissue factor (TF), a transmembrane glycoprotein, appeared to be a critical determinant of atherosclerotic plaque thrombogenicity that is important for triggering acute coronary syndromes. We demonstrated that pretreatment of human umbilical vein endothelial cells with ligands for peroxisome-proliferator activating receptor-a (PPARα), such as bezafibrate and Wy14643, greatly diminished the tumor necrosis factor-α (TNFα)-induced enhancement of TF activity in the cells. Such an effect was not observed in cells pretreated with ligands for PPARγ. Promoter assay using a reporter plasmid containing the AP-1 consensus sequence of TF showed that the reduction of TF expression by bezafibrate or Wy14643 is associated with a decrease in the sequence-dependent transcriptional activation. On electrophoretic mobility shift assay, bezafibrate and Wy14643 decreased the interaction between Jun/Fos heterodimer and the AP-1 elementary sequence, and this phenomenon was ascribed not only to a decrease in the levels of Jun/Fos-related nuclear proteins, but also to an increase in formation of RAR/JunB heterodimer that results from the decrease in RAR/RXR heterodimer formation in the cells. A transient expression study showed that coexpression of RXRα and PPARα in the cells decreased the AP-1-dependent promoter activity of TF. These results suggest that ligands for PPARa may serve as repressors of TF-dependent thrombosis of human endothelial cells under various inflammatory conditions through alteration of the heterodimeric partners of nuclear receptor proteins. In the present study, on the other hand, we also found that statins regulate thrombomodulin (TM) expression via inhibition of small G proteins of Rho family; Rac/Cdc42. A statinmediated increase in TM expression by endothelial cells may contribute the beneficial effects of statins on endothelial function.