Peroxisome proliferator-activated receptor α and γ ligands differentially affect smooth muscle cell proliferation and migration

Peroxisome proliferator-activated receptors (PPARs) alpha and gamma are expressed in smooth muscle cells (SMCs). This study was designed to compare the effects of PPAR alpha and PPAR gamma on SMC proliferation and migration and to determine how they operate. Treatment of SMCs from porcine coronary artery revealed that mitogen-stimulated DNA synthesis was blocked by the PPAR alpha ligand 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (WY14,643) and 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)) (a putative PPAR gamma agonist) but not by the PPAR gamma agonist rosiglitazone or the PPAR beta/delta ligand 2-methyl-4-((4-methyl-2-(4-trifluoromethylphenyl)1,3-thiazol-5-yl)-methylsulfanyl)phenoxy acetic acid (GW501516). Inhibition of DNA synthesis by clofibrate and 2-(4-(2-(1-cyclohexanebutyl-3-cyclohexylureido)ethyl)phenylthio)-2-methylproprionic acid (GW7647) confirmed that SMC proliferation is affected by PPAR alpha. This conclusion was supported by the fact that WY14,643 also inhibited the proliferation of H4IIE hepatoma cells (expressing only PPAR alpha) but not Ad10 SMCs (expressing only PPAR gamma 1). In contrast, the effective inhibition of all cell types with 15d-PGJ(2) indicated that this compound probably operates via a PPAR gamma-independent mechanism. Interestingly, rosiglitazone did not inhibit DNA synthesis of either H4IIE or A10 cells, suggesting that the activation of PPAR gamma does not influence cell proliferation. Phosphorylation of cyclin-dependent kinase 2 and expression of proliferating cell nuclear antigen were inhibited by WY14,643 but not by rosiglitazone or 15d-PGJ(2), indicating that PPAR alpha prevents progression into S phase. Although rosiglitazone did not block SMC proliferation, it (like WY14,643) reduced neointimal hyperplasia in vitro. This observation can be rationalized by the fact that both WY14,643 and rosiglitazone inhibit SMC migration, probably through matrix metalloproteinase 9. Our study therefore shows that selective interference with mediators of cell cycle progression and cell migration via activation of PPARs may prevent growth-related vascular diseases such as restenosis and atherosclerosis.