Multifaceted role of plasminogen activator inhibitor-1 in regulating early remodeling of vein bypass grafts.

OBJECTIVE: The role of plasminogen activator inhibitor-1 (PAI-1) in vein graft (VG) remodeling is undefined. We examined the effect of PAI-1 on VG intimal hyperplasia and tested the hypothesis that PAI-1 regulates VG thrombin activity. METHODS AND RESULTS: VGs from wild-type (WT), Pai1(-/-), and PAI-1-transgenic mice were implanted into WT, Pai1(-/-), or PAI-1-transgenic arteries. VG remodeling was assessed 4 weeks later. Intimal hyperplasia was significantly greater in PAI-1-deficient mice than in WT mice. The proliferative effect of PAI-1 deficiency was retained in vitronectin-deficient mice, suggesting that PAI-1's antiproteolytic function plays a key role in regulating intimal hyperplasia. Thrombin-induced proliferation of PAI-1-deficient venous smooth muscle cells (SMC) was significantly greater than that of WT SMC, and thrombin activity was significantly higher in PAI-1-deficient VGs than in WT VGs. Increased PAI-1 expression, which has been associated with obstructive VG disease, did not increase intimal hyperplasia. CONCLUSIONS: Decreased PAI-1 expression (1) promotes intimal hyperplasia by pathways that do not require vitronectin and (2) increases thrombin activity in VG. PAI-1 overexpression, although it promotes SMC migration in vitro, did not increase intimal hyperplasia. These results challenge the concept that PAI-1 drives nonthrombotic obstructive disease in VG and suggest that PAI-1's antiproteolytic function, including its antithrombin activity, inhibits intimal hyperplasia.

C-reactive protein enhances tissue factor expression by vascular smooth muscle cells: mechanisms and in vivo significance.

OBJECTIVE: We examined the impact of C-reactive protein (CRP) on vascular smooth muscle cell (VSMC) expression of tissue factor (TF) and TF pathway inhibitor (TFPI). METHODS AND RESULTS: TF mRNA, protein, and activity levels were significantly higher in VSMCs isolated from CRP-transgenic (Tg) mice than from wild-type (WT) mice. TFPI expression was significantly downregulated in CRP-Tg versus WT VSMCs. Transfection of human VSMCs with CRP expression plasmid significantly increased TF expression and decreased TFPI expression. Gene silencing of Fc gamma receptor IIIa (Fc gammaRIIIa) blocked the effect of CRP on VSMC TF expression. CRP activated p44/42, but not p38 or JNK MAP kinase (MAPK), and the effect of CRP on TF expression was blocked by pharmacological inhibitor of p44/42, but not p38 or JNK MAPK. Reactive oxygen species (ROS) scavengers blocked CRP-induced upregulation of VSMC TF expression. In vivo analyses revealed significant increases in TF expression and decreases in TFPI expression in carotid arteries of CRP-Tg mice versus WT mice. CONCLUSIONS: CRP increases TF and decreases TFPI expression by VSMCs in vitro and in vivo. Induction of TF expression by CRP is mediated by Fc gammaRIIIa, p44/42 MAPK, and ROS generation. These data offer important insights into the role of CRP in the pathogenesis of arterial thrombosis.