Docosahexaenoic acid, a peroxisome proliferator-activated receptor-alpha ligand, induces apoptosis in vascular smooth muscle cells by stimulation of p38 mitogen-activated protein kinase

Omega-3 fatty acids (n-3 FAs) have been shown to exert a blood pressure-low ering effect in hypertension, possibly in part by influencing vascular stru cture. We previously demonstrated that n-3 FAs induce vascular smooth muscl e cell (VSMC) apoptosis, which could exert an effect on the structure of bl ood vessels. In the present study, we investigated signaling pathways throu gh which n-3 FAs mediate apoptosis in VSMCs. Cultured mesenteric VSMCs from Sprague-Dawley rats were stimulated with docosahexaenoic acid (DHA), a rep resentative n-3 FAs. Morphological changes in apoptosis and DNA fragmentati on were examined with phase-contrast microscopy and fluorescence microscopy with Hoechst 33342 staining. To clarify possible pathways of apoptosis, we evaluated the expression of phosphorylated p38 mitogen-activated protein k inases, bar, bcl-2, cytochrome c, and peroxisome proliferator-activated rec eptor-alpha (PPAR-alpha) with Western blot analysis. DHA treatment induced cell shrinkage, cell membrane blebbing, and apoptotic bodies in VSMCs, DNA time-dependently activated p38 mitogen-activated protein kinases, bar, PPAR -alpha, and cytochrome c, with maximal effects obtained after 5 and 30 minu tes and 1 and 3 hours, respectively. SB-203580 and SB-202190, selective p38 inhibitors, reduced DHA-elicited apoptosis and expression of PPAR-alpha bu t had no effect on the expression of bar or cytochrome c. The present resul ts indicate that DHA induces apoptosis in VSMCs through greater than or equ al to2 distinct mechanisms: (1) a p38-dependent pathway that regulates PPAR -alpha and (2) a p38-independent pathway via dissipation of mitochondrial m embrane potential and cytochrome c release. The death-signaling pathway sti mulated by DHA may involve an integration of these multiple pathways. By tr iggering VSMC apoptosis, DHA may play a pathophysiological role in vascular remodeling in cardiovascular disease.