Aberrant DNA methylation of the PDGF gene in homocysteine-mediated VSMC proliferation and its underlying mechanism

It is well established that homocysteine (Hcy) is an independent risk factor for atherosclerosis (AS), which is characterized by vascular smooth muscle cell (VSMC) proliferation. However, the molecular mechanism underlying AS in VSMCs is yet to be elucidated. The aim of this study was to investigate the potential involvement of aberrant DNA methylation of the platelet-derived growth factor (PDGF) gene in Hcy-mediated VSMC proliferation and its underlying mechanism. Cultured human VSMCs were treated with varying concentrations of Hcy. VSMC proliferation, PDGF mRNA and protein expression and PDGF promoter demethylation showed a dose-dependent increase with Hey concentration, suggesting an association among them. Cell cycle analysis revealed a decreased proportion of VSMCs in G(0)/G(1) and an increased proportion in S phase, indicating that VSMC proliferation was increased under Hey treatment. Furthermore, S-adenosylhomocysteine (SAH) levels were observed to increase and those of S-adenosylmethionine (SAM) were observed to decrease. The consequent decrease in the ratio of SAM/SAH may partially explain the hypomethylation of PDGF with Hey treatment. Folate treatment exhibited an antagonistic effect against Hey-induced VSMC proliferation, aberrant PDGF methylation and PDGF expression. These data suggest that Hey may stimulate VSMC proliferation through the PDGF signaling pathway by affecting the epigenetic regulation of PDGF through the demethylation of its promoter region. These findings may provide novel insight into the molecular association between aberrant PDGF gene demethylation and the proliferation of VSMCs in Hey-associated AS.