Molecular mechanisms of the antiproliferative effect of beraprost, a prostacyclin agonist, in murine vascular smooth muscle cells

Prostacyclin (PGI₂) has been shown to inhibit proliferation in vascular smooth muscle cells. To clarify the underlying molecular mechanism, we investigated the vasoprotection of beraprost (a PGI₂ agonist) both in vivo and in vitro. Beraprost eliminated increases in proliferation of rat aortic smooth muscle cells (RASMCs) by 12-O-tetradecanoylphorbol 13-acetate, and enhanced the peroxisome proliferator-activated receptor-delta (PPARδ) and inducible nitric oxide synthetase (iNOS) expressions, which were associated with the antiproliferative action of beraprost according to inhibition experiments by [³H]thymidine incorporation. Additionally, elimination of iNOS activity by PPARδ antagonists suggested that iNOS is the downstream target of PPARδ. Furthermore, beraprost increased both consensus PPARδ-responsive element (PPRE)-driven luciferase activity and the binding activity of the PPARδ to the putative PPRE in the iNOS promoter; nevertheless, it was abolished by PPARδ antagonists. Deletion of PPRE (-1,349/-1,330) in the iNOS promoter region (-1,359/+2) strongly reduced promoter-driven activity, representing a novel mechanism of iNOS induction by beraprost. Consistent with this, PPARδ and the concomitant iNOS induction by beraprost were also evident in vivo. Beraprost-mediated protection in a murine model of balloon angioplasty was significantly attenuated by 13S-HODE, a PPARδ antagonist. Taken together, the results suggest that the causal relationship between PPARδ and iNOS contributes to the vasoprotective action of beraprost in RASMCs.