Dynamic expression of pulmonary YKL-40 protein in rats with bleomycin-induced pulmonary fibrosis

Objective To observe the expression of YKL-40 protein in the pulmonary tissues of rats with bleomycin-induced pulmonary fibrosis(PF).Methods The PF model group was induced with intratracheal instillation of bleomycin solution(7.5 mg/kg) and the control group was treated with normal saline.On day 7,14,21 after bleomycin challenge,rats were sacrificed and the pulmonary tissues were harvested.H-E staining,Masson staining and Szapiel score were employed to determine alveolitis and pulmonary fibrosis.Expressions of YKL-40 in lung tissues were detected by real-time RT-PCR,Western blotting analysis and immunohistochemistry method.Results Bleomycin instillation induced alveolitis in the lung of rats,with inflammation score being significantly higher on day 7(2.8±0.45,P0.01) and on day 21(1.8±0.84,P0.05) compared with that of control group(0.42±0.25).Pulmonary fibrosis degrees in model group was significantly higher on day 14(1.7±0.73,P0.05) and on day 21(2.9±0.56,P0.01) compared with that of control group(0.2±0.45).YKL-40 mRNA(YKL-40/β-actin) expression was significantly increased on day 7(3.71±0.25) after bleomycin treatment compared with the control group(P0.05).Western blotting analysis showed that YKL-40 protein expression was significantly increased on day 14(0.56±0.24,P0.05) and on day 21(1.15±0.19,P0.01) after bleomycin treatment compared with the control group(0.23±0.07).The results of immunohistochemistry showed that bleomycin up-regulated YKL-40 expression in a time-dependent manner,and YKL-40 expression was mainly located in the smooth muscle cells,alveolar macrophages,alveolar epithelium and fibroblasts.Conclusion YKL-40 expression may contribute to the pulmonary fibrosis,and may participate in the pathogenesis of pulmonary fibrosis.