Endostatin inhibits fibrosis by modulating the PDGFR/ERK signal pathway: an in vitro study

Accumulating evidence indicates that endostatin inhibits fibrosis. However, the mechanism is yet to be clarified. The aim of this study is to evaluate the effect of endostatin on platelet-derived growth factor-BB (PDGF-BB)-or transforming growth factor beta 1 (TGF-beta 1)-induced fibrosis in cultured human skin fibroblasts, and to further examine the molecular mechanisms involved. Human dermal fibroblasts were cultured in Dulbecco's modified Eagle's medium (DMEM) and serum-starved for 48 h before treatment. Cells were grouped as follows: PDGF-BB, PDGF-BB+ endostatin, TGF-beta 1, TGF-beta 1+endostatin, endostatin, and blank control. The fibroblasts were stimulated with either TGF-beta 1 or PDGF-BB for 72 h in order to set up the fibrosis model in vitro. The cells were co-cultured with either TGF-beta 1 or PDGF-BB and endostatin and were used to check the inhibiting effect of endostatin. A blank control group and an endostatin group were used as negative control groups. The biomarkers of fibrosis, including the expression of collagen I, hydroxyproline, and alpha-smooth muscle actin (alpha-SMA), were evaluated using an enzyme-linked immunosorbent assay (ELISA) and Western blot. The expression of phosphorylated PDGF receptor beta (p-PDGFR beta), PDGFR beta, phosphorylated extracellular signal-regulated kinase (p-ERK), and ERK was detected using Western blot and immunofluorescent staining was used to explore the mechanisms. Both PDGF-BB and TGF-beta 1 significantly up-regulated the expression of collagen I, hydroxyproline, and alpha-SMA. Endostatin significantly attenuated both the PDGF-BB- and TGF-beta 1-induced over-expression of collagen I, hydroxyproline, and alpha-SMA. PDGF-BB and TGF-beta 1 both promoted the expression of PDGFR, ERK, and p-ERK. Endostatin inhibited the expression of PDGFR and p-ERK but did not affect the expression of total ERK. Endostatin inhibited hypertrophic scar by modulating the PDGFR beta/ERK pathway. Endostatin could be a promising multi-target drug in future fibrosis therapy.