Fattman C L, Chu C T, Kulich S M, Enghild J J, Oury T D
Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA 15261, USA.
Free Radic Biol Med. 2001 Nov 15;31(10):1198-207. doi: 10.1016/s0891-5849(01)00699-2.
The antioxidant enzyme extracellular superoxide dismutase (EC-SOD) is highly expressed in the extracellular matrix of lung tissue and is believed to protect the lung from oxidative damage that results in diseases such as pulmonary fibrosis. This study tests the hypothesis that proteolytic removal of the heparin-binding domain of EC-SOD results in clearance of the enzyme from the extracellular matrix of pulmonary tissues and leads to a loss of antioxidant protection. Using a polyclonal antibody to mouse EC-SOD, the immunodistribution of EC-SOD in normal and bleomycin-injured lungs was examined. EC-SOD labeling was strong in the matrix of vessels, airways, and alveolar surfaces and septa in control lungs. At 2 d post-treatment, a slight increase in EC-SOD staining was evident. In contrast, lungs examined 4 or 7 d post-treatment, showed an apparent loss of EC-SOD from the matrix and surface 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 mice, suggesting that EC-SOD is being removed from the extracellular matrix through proteolysis. However, loss of EC-SOD through proteolysis did not correlate with a decrease in overall pulmonary EC-SOD activity. The negligible effect on EC-SOD activity may reflect the large influx of intensely staining inflammatory cells at day 7. These results indicate that injuries leading to pulmonary fibrosis have a significant effect on EC-SOD distribution due to proteolytic removal of the heparin-binding domain and may be important in enhancing pulmonary injuries by altering the oxidant/antioxidant balance in alveolar interstitial spaces.
抗氧化酶细胞外超氧化物歧化酶（EC-SOD）在肺组织的细胞外基质中高度表达，据信可保护肺部免受导致诸如肺纤维化等疾病的氧化损伤。本研究检验了以下假设：蛋白水解去除EC-SOD的肝素结合结构域会导致该酶从肺组织的细胞外基质中清除，并导致抗氧化保护作用丧失。使用针对小鼠EC-SOD的多克隆抗体，检测了EC-SOD在正常和博来霉素损伤肺中的免疫分布。在对照肺中，血管、气道、肺泡表面和间隔的基质中EC-SOD标记很强。治疗后2天，EC-SOD染色略有增加。相比之下，治疗后4天或7天检查的肺显示肺泡间隔的基质和表面明显丧失EC-SOD。值得注意的是，治疗后7天，在博来霉素处理小鼠的支气管肺泡灌洗液中发现了截短形式的EC-SOD，这表明EC-SOD正通过蛋白水解作用从细胞外基质中被清除。然而，通过蛋白水解作用导致的EC-SOD丧失与肺总体EC-SOD活性的降低并无关联。对EC-SOD活性的可忽略不计的影响可能反映了第7天大量强烈染色的炎性细胞的大量涌入。这些结果表明，导致肺纤维化的损伤由于蛋白水解去除肝素结合结构域而对EC-SOD分布有显著影响，并且可能通过改变肺泡间质空间中的氧化剂/抗氧化剂平衡在加重肺损伤方面起重要作用。
