Oxidized low-density lipoprotein increases the proliferation and migration of human coronary artery smooth muscle cells through the upregulation of osteopontin

Smooth muscle cell (SMC) proliferation and migration are known to play a critical role in the development of atherosclerosis. Oxidized low-density lipoprotein (oxLDL) is involved in the generation of atherosclerotic lesions. Recent studies have indicated that oxLDL is a well-established risk factor for atherosclerosis that induces vascular smooth muscle cell (VSMC) proliferation and migration; however, the exact mechanisms involved have not been fully elucidated. In this study, the proliferation of human coronary artery smooth muscle cells (HCASMCs) was detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cell migration was determined by Transwell assay. Osteopontin (OPN), matrix metaloproteinase-9 (MMP-9) and alpha v beta 3 integrin expression were measured by mRNA and western blot analysis. OPN and MMP-9 knockdown cells were established through transfection with OPN siRNA or MMP-9 siRNA, respectively. Our results revealed that oxLDL makredly promoted HCASMC proliferation and migration in a dose-dependent manner. Further experiments demonstrated that oxLDL upregulated the expression of OPN and oxLDL. Cell proliferation and migration were markedly reduced following the knockdown of the OPN gene in the HCASMCs. We then found that treatment with oxLDL induced a concentration-dependent increase in MMP-9 mRNA and protein levels in the HCASMCs. These effects were partially abrogated by silencing OPN expression or blocking the alpha v beta 3 integrin pathway. Moreover, cells treated with MMP-9 siRNA or alpha v beta 3 antibody showed lower proliferation and migration rates. This study provides direct in vitro evidence that the exposure of HCASMCs to oxLDL induces the activation of OPN, leading to higher protein levels of MMP-9, and to an increased proliferation and migration of HCASMCs.