Abstract: Objective To explore the mechanism of BMP-9 in biliary atresia (BA) liver fibrosis. Methods Fourteen samples of BA cases were selected as the BA group and 5 samples of congenital biliary dilatation (CBD) cases were selected as the CBD group. Liver fibrosis was evaluated by HE staining, immunohistochemical staining was used to detect the expression levels of BMP-9 and p-SMAD1/5, and qPCR was used to detect the expression levels of BMP-9 and ID1 mRNA in liver. Human hepatic stellate cells (LX-2) were cultured and treated with rTGF-β1 and different concentrations of rBMP-9. The protein expression levels of α-SMA, SMAD1/5, p-SMAD1/5 and ID1 in cells were detected by Western blot assay, and the mRNA expressions of α-SMA and ID1 in cells were detected by qPCR. Results The expression levels of BMP-9 and p-SMAD1/5 proteins, BMP-9 and ID1 mRNA in liver were higher in the BA group than those of the CBD group. In the BA group, the expressions levels of BMP-9 protein, BMP-9 and ID1 mRNA were significantly higher in children with moderate and severe liver fibrosis than those in children with mild liver fibrosis (P＜0.05). After treatment with rTGF-β1 and rBMP-9, the expression levels of α-SMA protein and α-SMA mRNA were increased in LX-2 cells (P＜0.05). The expressions of p-SMAD1/5, SMAD1/5, ID1, α -SMA protein and ID1, α -SMA mRNA in the downstream pathway were increased after adding different concentrations of rBMP-9 in LX-2 cells compared with those of 0 μg/L group (P＜0.05). Conclusion The expression levels of BMP-9, p-SMAD1/5 and ID1 in the liver of BA children are increased than those of CBD children, which are positively correlated with the degree of liver fibrosis. BMP-9 can activate LX-2 cells through SMAD/ID1 signaling pathway and promote the progress of fibrosis.

Key words: liver cirrhosis, biliary atresia, bone morphogenetic proteins, SMAD proteins, actins, inhibitor of DNA binding 1