Successful silencing of plasminogen activator inhibitor-1 in human vascular endothelial cells using small interfering RNA.

Clinical as well as experimental evidence suggests that vascular overexpression of plasminogen activator inhibitor (PAI)-1, the primary physiological inhibitor of both urokinase and tissue-type plasminogen activator, may be involved in the pathophysiology of atherosclerosis and cardiovascular disease. We investigated the feasibility, efficacy and functional effects of PAI-1 gene silencing in human vascular endothelial cells using small interfering RNA. Double-stranded 21 bp-RNA molecules targeted at sequences within the human PAI-1 gene were constructed. Successful siRNA transfection of HUVEC was confirmed using fluorescence microscopy and flow cytometry. One of five candidate siRNA sequences reduced PAI-1 mRNA and protein in a concentration- and time-dependent manner. Suppression of PAI-1 mRNA was detected up to 72 hours after transfection. Moreover, siRNA treatment reduced the activity of PAI-1 released from HUVEC, and prevented the oxLDL- or LPS-induced upregulation of PAI-1 secretion. Importantly, siRNA treatment did not affect the expression of other endothelial-cell markers. Moreover, downregulation of PAI-1 significantly enhanced the ability of endothelial cells to adhere to vitronectin, and this effect could be reversed upon addition of recombinant PAI-1. SiRNA-mediated reduction of PAI-1 expression may be a promising strategy for dissecting the effects of PAI-1 on vascular homeostasis.

Enhanced thrombosis in atherosclerosis-prone mice is associated with increased arterial expression of plasminogen activator inhibitor-1.

OBJECTIVE: This study was undertaken to investigate the origin and pathophysiological importance of plasminogen activator inhibitor (PAI-1) in atherosclerosis. METHODS AND RESULTS: We used the ferric chloride model to induce carotid artery injury in apolipoprotein E knockout (apoE-/-) and wild-type (WT) mice. ApoE-/- mice fed high-fat diet for 4 months developed severe hypercholesterolemia and had significantly elevated plasma PAI-1 levels (2.3+/-0.3 versus 0.6+/-0.1 ng/mL in WT mice; P<0.05). These mice exhibited a prothrombotic phenotype with shortened times to thrombotic arterial occlusion (8.6 versus 11.5 minutes; P<0.001) and reduced recanalization rates (12% versus 51%; P<0.0001) compared with WT mice. In situ hybridization, reverse transcriptase-polymerase chain reaction, and immunohistochemistry showed a significantly upregulated PAI-1 expression in P-selectin-positive (activated) endothelial cells lining normal-appearing arterial segments and within the advanced atherosclerotic lesions of apoE-/- mice. No significant upregulation of PAI-1 expression was found in the other organs studied, and only trace amounts of PAI-1 mRNA were detected in murine platelets. Importantly, deletion of the PAI-1 gene reversed the prothrombotic tendency and reduced neointimal growth after injury in apoE-/- mice despite the persistence of excessive hypercholesterolemia. CONCLUSIONS: These results suggest that increased vascular expression of PAI-1 may contribute to the elevated circulating levels of the inhibitor and be responsible, at least in part, for the prothrombotic phenotype in apoE-/- mice.