Prostacyclin and PPARα agonists control vascular smooth muscle cell apoptosis and phenotypic switch through distinct 14-3-3 isoforms.

Abstract

We hypothesized that prostacyclin (PGI2) protects vascular smooth muscle cell (VSMC) against apoptosis and phenotypic switch through peroxisome proliferator-activated receptor-α (PPARα) activation and 14-3-3 upregulation. Here we showed that transfection of rat aortic VSMC, A-10, with PGI2-producing vectors, Ad-COPI, resulted in attenuated H2O2-induced apoptosis accompanied by a selective increase in 14-3-3β and 14-3-3θ expression. Carbaprostacyclin (cPGI2) and Wy14,643 exerted a similar effect. The effects of PGI2 were abrogated by MK886, a PPARα antagonist, but not GSK3787, a PPARδ antagonist. PPARα transfection upregulated 14-3-3β and θ expression and attenuated H2O2-induced apoptosis. H2O2-induced 14-3-3β but not 14-3-3θ degradation was blocked by a caspase 3 inhibitor. Furthermore, 14-3-3β but not 14-3-3θ overexpression reduced, while 14-3-3β siRNA aggravated apoptosis. VSMC contractile proteins and serum response factor (SRF) were reduced in H2O2-treated A-10 cells which were concurrently prevented by caspase 3 inhibitor. By contrast, PGI2 prevented H2O2-induced SM22α and Calponin-1 degradation without influencing SRF. cPGI2 and Wy14,643 also effectively blocked VSMC phenotypic switch induced by growth factors (GFs). GFs suppressed 14-3-3β, θ, ε and η isoforms and cPGI2 prevented the decline of β, θ and η, but not ε. 14-3-3θ siRNA abrogated the protective effect of cPGI2 on SM22α and Calponin-1 while 14-3-3 θ or 14-3-3β overexpression partially restored SM22α. These results indicated that PGI2 protects VSMCs via PPARα by upregulating 14-3-3β and 14-3-3θ. 14-3-3β upregulation confers resistance to apoptosis whereas 14-3-3θ and β upregulation protects SM22α and Calponin-1 from degradation.