Inhibition of proliferation and apoptosis of vascular smooth muscle cells by ghrelin

To evaluate the possible role of ghrelin in the development of atherosclerosis, its effects on tumor necrosis factor (TNF)-alpha-induced proliferation and apoptosis of vascular smooth muscle cells (VSMCs) were investigated. Rat VSMCs were pretreated with different concentrations of ghrelin and then with TNF-alpha. VSMC proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and flow cytometry method. Apoptosis was detected using propidium iodide and Annexin-V labeling method. Exogenous ghrelin (10-1000 ng/ml) significantly inhibited TNF-alpha-induced proliferation of VSMCs in a concentration-dependent manner. Treatment with 1000 ng/ml ghrelin was most effective at inhibiting VSMC proliferation rate and the expression of proliferating cell nuclear antigen. However, treatment with des-acyl ghrelin affected neither proliferation nor PCNA expression. In contrast, TNF-alpha-induced apoptosis of VSMCs was inhibited by both ghrelin and des-acyl ghrelin in concentration-dependent manners, with maximal inhibition observed for both compounds at 1000 ng/ml. Taken together, our results suggested that ghrelin inhibited both the proliferation and apoptosis of rat VSMCs. Furthermore, the former effect is probably mediated by the growth hormone secretagogue receptor type la receptor, while the latter effect may be mediated through other receptors.