Altered expression of extracellular superoxide dismutase in mouse lung after bleomycin treatment

The antioxidant enzyme extracellular superoxide dismutase (EC-SOD) is highl y expressed in the extracellular matrix of lung tissue and is believed to p rotect the lung from oxidative damage that results in diseases such as pulm onary fibrosis. This study tests the hypothesis that proteolytic removal of the heparin-binding domain of EC-SOD results in clearance of the enzyme fr om the extracellular matrix of pulmonary tissues and leads to a loss of ant ioxidant protection. Using a polyclonal. antibody to mouse EC-SOD, the immu nodistribution of EC-SOD in normal and bleomycin-injured lungs was examined . EC-SOD labeling was strong in the matrix of vessels, airways, and alveola r surfaces and septa in control lungs. At 2 d post-treatment, a slight incr ease in EC-SOD staining was evident. In contrast, lungs examined 4 or 7 d p ost-treatment, showed an apparent loss of EC-SOD from the matrix and surfac e of alveolar septa. Notably, at 7 d post-treatment, the truncated form of EC-SOD was found in the bronchoalveolar lavage fluid of bleomycin-treated m ice, suggesting that EC-SOD is being removed from the extracellular matrix through proteolysis. However, loss of EC-SOD through proteolysis did not co rrelate with a decrease in overall pulmonary EC-SOD activity. The negligibl e effect on EC-SOD activity may reflect the large influx of intensely stain ing inflammatory cells at day 7. These results indicate that injuries leadi ng to pulmonary fibrosis have a significant effect on EC-SOD distribution d ue to proteolytic removal of the heparin-binding domain and may be importan t in enhancing pulmonary injuries by altering the oxidant/antioxidant balan ce in alveolar interstitial spaces. (C) 2001 Elsevier Science Inc.