Objective

To investigate the dynamic trends of activities of matrix metalloproteinase (MMP)-2/9 and protein expressions of their inhibitors-tissue inhibitor of matrix metalloproteinase (TIMP)-1/2 during the progression of pulmonary fibrosis in rats so as to get insight of the roles played by MMP-2 /9 in lung injury and fibrogenesis.

Methods

Forty-eight SD rats were randomly divided into normal control group (n=18) and bleomycin (BLM)-treated group (n=30). The pulmonary fibrosis was induced by intratracheal injection of BLM once. At the consecutive time of 1 day, 3 days, 1 week, 2, 3, and 4 weeks after intoxication, the lung-to-body weight ratio was calculated and the inflammation and collagen deposition in lung tissue were checked by HE and Masson stainings respectively. Meanwhile, the content of hypdroxyproline (Hyp) in lung tissue was assayed with Jamall’s method, the protein expressions of MMP-2/9, TIMP-1/2 were examined by Western blotting, and the activities of MMP-2/9 were detected by gelatin zymography.

Results

The histopathological changes in lung tissue in the BLM-treated group from 1 day to 2 weeks after intoxication presented local lesions, broadened alveolar wall and septum, infiltration with lots of inflammatory cells and few of fibroblasts inside alveolar space and septum. At this early stage in the BLM-treated group, the lung-to-body weight ratio was increased significantly, the protein expressions and activities of MMP-2/9 were obviously increased especially for activity of active MMP-2, and the protein expressions of TIMP-1/2 were also increased gradually, as compared with those in the normal control group. From 3 to 4 weeks after intoxication in the BLM-treated group, the alveolar structure was damaged, parts of the alveolar space collapsed and replaced by collagens and fibroblasts, and the alveolar wall and septum obviously widened with remarkable fibrotic characteristics, as compared with those in the normal control group. Meanwhile, the lung-to-body weight ratio and the activities of MMP-2/9 were decreased in the BLM-treated group as compared with those in the same group at 2 weeks after intoxication, but the content of Hyp and the protein expressions of TIMP-1/2 were both increased dramatically, especially at 4 weeks after intoxication.

Conclusions

During the lung fibrogenesis induced by BLM in rats, the alveolar inflammation is the most important alteration with enhanced MMP-2/9 activities in the early stage. While in the late stage, the main change is displayed as pulmonary fibrosis, characterized by increased TIMP-1/2 and declined MMP-2/9 activities.

Key words: Bleomycin, Alveolitis, Pulmonary fibrosis, MMP-2, MMP-9, TIMP-1, TIMP-2