Role of MMP-12 on tissue remodeling at early stage of radiation-induced pulmonary injury

Objective To explore the role of MMP-12 on tissue remodeling at early stage of radiationinduced pulmonary injury. Methods Wistar rats irradiated by 60Coγ-rays to the whole lungs were sacrificed at 1, 2, 4 weeks. MMP-12 mRNA expression was detected by RT-PCR. MMP-2, MMP-9, MMP-12 activities were determined by zymography. The degradation and collapse of elastin were determined by tissue elastin particular staining; the phenomenon between alveolar type Ⅱ cells and mesenchymal cells was observed under electron microscope; the expression of TGF-β1 and TNF-α in BALF was detected by ELISA. The expression of α-SMA was determined by immunohistochemistry. Results The mRNA expression of MMP-12 displayed a significant elevation at 1, 2, 4 weeks after irradiation. MMP-12 activity increased at 2, 4 weeks after irradiation. Elastin began to degrade and collapse at 1 week, which became worst 4 weeks after irradiation. The cross talking phenomenon was found under electron microscope. The expression of TGF-β1, TNF-α and α-SMA was increased gradually as time elapse after irradiation. Conclusions 60 Co γ-ray irradiation can promote pulmonary MMP-12 expression, initiate pulmonary tissue remodeling by degradation of elastin, and make the pulmonary injury develop towards pulmonary fibrosis eventually. Key words: Macrophnge metalloproteinase-12;  Radiation pulmonary injury;  Elastin;  Cross talking;  Tissue remodeling