Abstract 1224: Epac 1 is Upregulated After Mechanical Vascular Injury and Promotes Smooth Muscle Cell Migration
Background Vascular remodeling after mechano-injury, such as stenting, largely depends upon the migration of vascular smooth muscle cells (VSMC). However, the role of cat-echolamines, in particular, beta-adrenergic receptor signal, in regulating such migration remains controversial. Recently, a new molecule downstream of beta-adrenergic receptor/ cAMP signal, Epac, has been identified, which does not depend upon the classical PKA activation.
Hypothesis The role of Epac in regulating VSMC migration and intimal thickening is different from that of the classic PKA.
Methods We have examined changes in Epac expression in neointimal thickening after vascular injury. We have also compared the role of Epac from that of PKA in regulating VSMC migration and proliferation by the use of cAMP analogs selective to PKA or Epac, and adenovirus-mediated gene transfer of Epac (Adv. Epac) or PKA (Adv. PKA).
Results When mouse femoral artery was injured transluminally in vivo, the expression of Epac 1 mRNA was transiently but significantly increased (1.82+/−0.1 fold, p<0.01, n=4) with the progress of neointimal thickening. Epac1 protein was also positively stained in neointimal formation. pCPT-cAMP, a cAMP analog selective to PKA, decreased VSMC migration (0.38+/−0.01 fold, p<0.001) as determined by the Boyden chamber method. However, 8-cCPT-2′-O-Me-cAMP, which is selective to Epac, enhanced cell migration (1.8+/−0.07 fold, p<0.001). Targeted disruption of Epac 1 by siRNA negated this enhancement. Adv. Epac 1 dramatically enhanced cell migration (3.7+/−0.06 fold, p<0.001), which was further enhanced in the presence of Epac-stimulation (4.41+/−0.06 fold, p<0.001), while it was inhibited in the presence of PKA-stimulation (0.63+/−0.01 fold, p<0.001). VSMC showed a star-like formation upon PKA-stimulation while they became round shape with Epac-stimulation. Further, Adv. Epac 1 enhanced VSMC proliferation (1.4+/−0.02 fold, p<0.05) while Adv. PKA inhibited proliferation (0.82+/−0.01 fold, p<0.05).
Conclusion Epac 1 plays an opposite role from PKA in regulating VSMC migration and proliferation although both are activated by cAMP. Up-regulation of Epac upon vascular injury may play an important role in advancing vascular remodeling and re-stenosis.