Background Myofibroblasts are activated fibroblasts mainly characterized by the expression of α-smooth muscle actin (α-SMA) playing a prominent role in the fibrotic process that characterizes some connective tissue diseases, in particular systemic sclerosis (SSc) (1). Recently, it was shown that myofibroblasts may arise by the transition from epithelial or endothelial cells, thus expressing α-SMA, vimentin and type I collagen. This mechanism mightbe induced by transforming growth factor β (TGF-β) and/or endothelin-1 (ET-1) (2-4).
Objectives To investigate the involvement of ET-1 in cell proliferation and entothelial-to-myofibroblast transition by evaluating α-SMA expression in cultures of human endothelial cells.
Methods Human umbilical vein endothelial cells (HUVEC) were cultured in collagen-coated dishes with completed endothelial cell basal medium (EGM-2) at 2% of fetal bovine serum and used between the third and fifth passages for the experiments. The cells were treated with ET-1 (100nM) for 24 hrs, 3 days and 6 days, whereas untreated cells were used as controls (cnt). Cell proliferation was evaluated by methyl-tetrazolium salt test (MTT) at 24 hrs whereas the α-SMA expression was evaluated at 3 and 6 days by immunocytochemistry (ICC), immunofluorescence (IF) and western blotting analysis (WB) according to a recent study (5). The data were obtained from four different experiments and statistical analysis was carried out by a non-parametric Friedman test.
Results ET-1 significantly increased the endothelial cell proliferation (p<0.01 vs. cnt) at 24 hrs from treatment, as detected by MTT test in cell cultures. In addition, ET-1 stimulated endothelial cells to express the myofibroblasts marker α-SMA after 6 days from treatment. The data were obtained by IF, ICC and confirmed by WB.
Conclusions Results showed that ET-1 may stimulate human endothelial cell growth supporting its mitogenic effects as already shown for other cell types involved in the fibrotic process (6). Interestingly, ET-1 induced the α-SMA expression in human endothelial cells, supporting a possible transition from endothelial to the myofibroblast phenotype (2, 5). The implications in the fibrotic process that characterize SSc are matter of further evaluations.
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Disclosure of Interest None Declared