Abstract 14982: Rap1 Mediates Thrombin-Induced Vascular Smooth Muscle Cell Proliferation via an Integrin-Dependent Pathway
Introduction: Neointimal hyperplasia plays an important role in atherosclerosis and restenosis. Vascular smooth muscle cell (SMC) proliferation represents a major contributor to neointimal hyperplasia. Thrombin and its receptor, protease activated receptor-1 (PAR-1), are upregulated at sites of vascular injury and promote SMC proliferation via an αvβ 3-integrin-dependent mechanism. Rap1, a member of the Ras family of small GTP-binding proteins, regulates αIIβ 3 function in platelets.
Hypothesis: Thrombin stimulates SMC proliferation via a Rap1 and integrin αvβ 3-dependent pathway.
Results: In rat aortic SMC, thrombin (2 U/mL) or thrombin receptor activating peptide (TRAP-6) activated Rap1 (Rap1-GTP) and this effect was abolished by the PAR-1 antagonist varopaxar, demonstrating that thrombin-activated Rap1 is mediated through PAR1 receptors. Treatment with thrombin increased the activation of ERK1/2 and JNK1, two MAP kinase (MAPK) pathways which ultimately result in SMC proliferation. Overexpression of GTPase-activating protein II (Rap1GAP-II) significantly attenuated Rap1 activation and decreased thrombin activation of ERK1/2 and JNK1. Thrombin-induced activation of ERK1/2 and JNK1 was also inhibited by a Rap1 isoform-specific siRNA knock-down approach (Rap1a + Rap1b). Taken together, these data strongly suggest that thrombin-mediated MAPK activation in SMC was mediated through Rap1 activation. Lastly, we demonstrated that inhibition of integrin αvβ 3 with echistatin prevented thrombin-induced activation of Rap1, ERK1/2 and JNK1. In association with our prior studies demonstrating that echistatin inhibits thrombin-induced proliferation, these studies demonstrate that αvβ 3 plays an essential role in thrombin-mediated activation of Rap1 and MAPK, and ultimately SMC proliferation.
Conclusions: In rat aortic SMC, thrombin activates Rap1 via an αvβ 3-dependent pathway, and that leads to the activation of ERK1/2 and JNK1 pathways, and SMC proliferation.
Author Disclosures: B. Jiang: None. J. Huang: None. G.A. Stouffer: None.
- © 2016 by American Heart Association, Inc.