Collagen metabolism in experimental lung silicosis. A trimodal behavior of collagenolysis

In spite of several studies, both in vivo and in vitro, the pathogenesis of silicosis remains unclear, mainly in those mechanisms related to fibrogenesis. In this study, we analyzed the concentration, biosynthesis, and degradation of collagen in silica-treated rats 7, 15, 30, 45, and 60 days after instillation. Our results showed a significant increase in collagen content and biosynthesis from the 15th day onward. However, our most remarkable finding was related to collagenolytic activity. In this sense, the silicotic rats presented a trimodal behavior: some animals showed an increased degradation, others had similar values to those of the controls, and others exhibited a decrease of collagenolytic activity. Altogether, these results suggest that collagen deposition in silicotic lungs is due to a rise in biosynthesis and, at least in some animals, to a decrease in degradation. Nevertheless, the steps of collagenolysis must be studied in more detail.