Differential Regulation of Vascular Smooth Muscle and Endothelial Cell Proliferation

37 cAMP inhibits proliferation in most cell types triggering different and sometimes opposing 38 molecular pathways. p85α (PI3K regulatory subunit) is phosphorylated by cAMP/PKA in certain 39 cell lineages but its effects on vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) 40 are unknown. In the present study we evaluated: i) the role of p85α in the integration of 41 cAMP/PKA-dependent signaling on the regulation of VSMC and EC growth in vitro and ii) the 42 effects of PKA-modified-p85α on neointimal hyperplasia and endothelial healing after balloon 43 injury in vivo.Plasmid constructs carrying wild type and PKA-modified p85α were employed in 44 VSMCs and ECs in vitro and after balloon injury in rat carotid arteries in vivo. cAMP/PKA reduced 45 VSMC proliferation through p85α phosphorylation. Transfected PKA-activated-p85α binds p21 46 reducing ERK 1/2 activation and VSMC proliferation in vitro. In contrast, EC proliferation 47 inhibition by cAMP is independent from PKA modification of p85α and ERK 1/2 inhibition; 48 indeed, PKA-activated-p85α did not inhibit per se ERK 1/2 activation and proliferation in ECs in 49 vitro. Interestingly, cAMP reduced both VSMC and EC apoptotic death through p85α 50 phosphorylation. Accordingly, PKA-activated-p85α triggered Akt activation reducing both VSMC 51 and EC apoptosis in vitro. Finally, compared to controls, vascular gene transfer of PKA-activated52 p85α significantly reduced neointimal formation after balloon injury in rats, without inhibiting 53 endothelial regeneration of the injured arterial segment. In conclusions, PKA-activated-p85α 54 integrates cAMP/PKA signaling differently in VSMCs and ECs. By reducing neointimal 55 hyperplasia without inhibiting endothelial regeneration, it exerts a protective effect against 56 restenosis after balloon injury. 57 58