Differential regulation of vascular smooth muscle and endothelial cell proliferation in vitro and in vivo by cAMP/PKA-activated p85αPI3K

Abstract

cAMP inhibits proliferation in most cell types, triggering different and sometimes opposing molecular pathways. p85α (phosphatidylinositol 3-kinase regulatory subunit) is phosphorylated by cAMP/PKA in certain cell lineages, but its effects on vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) are unknown. In the present study, we evaluated 1) the role of p85α in the integration of cAMP/PKA-dependent signaling on the regulation of VSMC and EC growth in vitro; and 2) the effects of PKA-modified p85α on neointimal hyperplasia and endothelial healing after balloon injury in vivo. Plasmid constructs carrying wild-type and PKA-modified p85α were employed in VSMCs and ECs in vitro and after balloon injury in rat carotid arteries in vivo. cAMP/PKA reduced VSMC proliferation through p85α phosphorylation. Transfected PKA-activated p85α binds p21ras, reducing ERK1/2 activation and VSMC proliferation in vitro. In contrast, EC proliferation inhibition by cAMP is independent from PKA modification of p85α and ERK1/2 inhibition; indeed, PKA-activated p85α did not inhibit per se ERK1/2 activation and proliferation in ECs in vitro. Interestingly, cAMP reduced both VSMC and EC apoptotic death through p85α phosphorylation. Accordingly, PKA-activated p85α triggered Akt activation, reducing both VSMC and EC apoptosis in vitro. Finally, compared with controls, vascular gene transfer of PKA-activated p85α significantly reduced neointimal formation after balloon injury in rats, without inhibiting endothelial regeneration of the injured arterial segment. In conclusions, PKA-activated p85α integrates cAMP/PKA signaling differently in VSMCs and ECs. By reducing neointimal hyperplasia without inhibiting endothelial regeneration, it exerts a protective effect against restenosis after balloon injury.