Prostaglandin D2 stimulates phenotypic changes in vascular smooth muscle cells

Since chronic inflammation is associated with the pathogenesis of atherosclerosis, inflammatory cytokines might contribute to the phenotypic modulation of vascular smooth muscle cells (VSMCs). Tumor necrosis factor a (TNF alpha) facilitated the transformation of contractile VSMCs to the synthetic phenotype, as determined by the expression of marker proteins and a collagen gel contraction assay. Western blot analysis and a cyclooxygenase-2 (COX2) promoter assay revealed that TNFa stimulation resulted in the induction of COX2. The overexpression, silencing, or pharmacological inhibition of COX2 significantly affected TNF alpha-induced phenotypic conversion, and of the tested prostaglandins, only PGD(2) significantly induced phenotypic conversion. ERK was significantly activated by PGD(2) stimulation, and the pharmacological inhibition of ERK blocked the PGD(2)-induced phenotypic conversion of VSMCs. However, antagonists or agonists of PGD(2) receptors did not affect VSMC conversion. In contrast, spontaneously dehydrated forms of PGD(2), such as PGJ(2), Delta(12)- PGJ(2), and 15-d-PGJ(2), strongly induced phenotypic conversion. A reporter gene assay showed that TNF alpha, PGD2, and 15-d-PGJ(2) significantly activated the peroxisome proliferator-responsive element (PPRE) promoter. In addition, the overexpression or silencing of peroxisome proliferator-activated receptor delta (PPAR delta) significantly influenced 15-d-PGJ(2)-induced phenotypic conversion. Finally, atherosclerotic neointima formation was significantly suppressed in mice lacking TNF alpha. In addition, mice fed celecoxib exhibited complete inhibition of carotid artery ligation-induced neointima formation. This study shows that PGD(2) regulates the phenotypic conversion of VSMCs by generating an endogenous ligand of PPAR, and that this leads to neointima formation in occlusive arterial disease.