No abstract

Consistent with this evidence, exogenously administered PDGF-BB into the rat carotid artery after endothelial denudation increased neointimal lesions. 2,4 In addition, genetic deletion of PDGFR-β decreased SMC accumulation in atherosclerotic lesions. 2,5 This accumulating evidence suggests that PDGF-BB and PDGFR-β signaling play a prominent role in vascular SMC migration into the neointima after vascular injury and during the development of atherosclerosis. 2It has been suggested that PDGF-BB-mediated cell migration is attributed to the activation of intracellular signal transduction pathways, including phosphatidylinositol 3-kinase, mitogen-activated protein kinase cascade, and © 2015 American Heart Association, Inc. Objective-Vascular smooth muscle cell (SMC) migration causes neointima, which is related to vascular remodeling after mechanical injury and atherosclerosis development. We previously reported that an exchange protein activated by cAMP (Epac) 1 was upregulated in mouse arterial neointima and promoted SMC migration. In this study, we examined the molecular mechanisms of Epac1-induced SMC migration and the effect of Epac1 deficiency on vascular remodeling in vivo. Approach and Results-Platelet-derived growth factor-BB promoted a 2-fold increase in SMC migration in a primary culture of aortic SMCs obtained from Epac1 +/+ mice (Epac1 +/+ -ASMCs), whereas there was only a 1.2-fold increase in Epac1 −/− -ASMCs. The degree of platelet-derived growth factor-BB-induced increase in intracellular Ca 2+ was smaller in Fura2-labeled Epac1 −/− -ASMCs than in Epac1 +/+ -ASMCs. In Epac1 +/+ -ASMCs, an Epac-selective cAMP analog or platelet-derived growth factor-BB increased lamellipodia accompanied by cofilin dephosphorylation, which is induced by Ca 2+ signaling, whereas these effects were rarely observed in Epac1−/− -ASMCs. Furthermore, 4 weeks after femoral artery injury, prominent neointima were formed in Epac1 +/+ mice, whereas neointima formation was significantly attenuated in Epac1 −/− mice in which dephosphorylation of cofilin was inhibited. The chimeric mice generated by bone marrow cell transplantation from Epac1 +/+ into Epac1 −/− mice and vice versa demonstrated that the genetic background of vascular tissues, including SMCs rather than of bone marrow-derived cells affected Epac1-mediated neointima formation. Conclusions-These data suggest that Epac1 deficiency attenuates neointima formation through, at least in part, inhibition of SMC migration, in which a decrease in Ca 2+ influx and a suppression of cofilin-mediated lamellipodia formation occur. 6,7 In addition to these signaling pathways, it has been recognized that PDGF-BB increases intracellular cAMP via a G protein-coupled receptor transactivation mechanism. 8,9 However, the role of PDGF-BB-induced cAMP in SMC migration remains unknown.A major second messenger cAMP activates protein kinase A (PKA) and an exchange protein activated by cAMP (Epac). 10Epac has 2 isoforms, Epac1 and Epac2, both of which are activated in living cells by physiol...