Docosahexaenoic Acid, a Peroxisome Proliferator-Activated Receptor-α Activator, Induces Apoptosis in Vascular Smooth Muscle Cells by Activation of P38 Mitogen-Activated Protein Kinase
Omega-3 fatty acids (n-3 FAs) exert a blood pressure-lowering effect in hypertension, possibly by influencing vascular structure. We previously demonstrated that n-3 FAs might induce vascular smooth muscle cell (VSMC) apoptosis, which could exert an effect on structure of blood vessels. This study investigated signaling pathways through which n-3 FAs mediate apoptosis in VSMCs. Cultured Mesenteric VSMCs from Sprague Dawley rats were stimulated with docosahexaenoic acid (DHA), a representative n-3 FA. Morphological changes of apoptosis and DNA fragmentation were examined by phase-contrast microscopy and fluorescence microscopy with Hoechst 33342 staining. To clarify possible pathways of apoptosis, expression of phosphorylated p38 mitogen-activated protein kinases (p38 MAPKs), bax, bcl-2, cytochrome C and peroxisome proliferator-activated receptors-α (PPARs-α) was evaluated by Western blot analysis. DHA treatment induced cell shrinkage, cell membrane blebbing and apoptotic bodies in VSMCs. DHA increased apoptosis (%) in a time-dependent manner to 1.5±0.1, 3.6±0.5, 7.1±0.4, 22.5±0.6, 50.8±1.8 and 61.4±0.9 after 0, 1, 3, 6, 17, and 24 h, respectively. DHA time-dependently activated p38 MAPKs, bax, PPARs-α and cytochrome C with maximal effects obtained after 5, 30 min, 1 h and 3 h, respectively to 551±42, 245±55, 310±12 and 407±14.7 % of controls, respectively. SB-203580 (10-5M) and SB-202190 (10-5M), selective p38 inhibitors, reduced DHA-elicited apoptosis and expression of PPARs-α, but had no effect on expression of bax or cytochrome C. The present results indicate that DHA induces apoptosis in VSMCs through at least two distinct mechanisms: (i) a p38-dependent pathway that regulates PPAR-α and (ii) a p38-independent pathway via dissipation of mitochondrial transmembrane potential. The death-signaling pathway mediated by DHA may involve an integration of these multiple pathways. By triggering VSMC apoptosis, DHA could play a pathophysiological role in vascular remodeling in cardiovascular disease.