Expression of collagenolytic/gelatinolytic metalloproteinases by normal cornea.

Members of the gelatinase subclass of the matrix metalloproteinase family have the capacity to degrade denatured collagens of all types and native types IV, V, and VII collagens. The authors identified the metalloproteinase species of the gelatinase class produced by the cells of rabbit corneal tissue. Two different molecular forms of gelatinase, visualized as enzymatic activities, that undergo electrophoresis with different mobilities on gelatin zymograms are synthesized by corneal cells in serum-free organ culture. The enzyme species that has the slower mobility is biochemically and immunologically related to a gelatinase synthesized by macrophages and neutrophils which has been called both type IV and type V collagenase. The second gelatinase species is related to a second enzyme, the product of a different gene, which has also been called type IV collagenase. The electrophoretic mobilities of these enzymes on polyacrylamide gels indicate the inactive proenzyme forms. The authors refer to these enzymes as 92-kilodalton (kD) gelatinase and 72-kD gelatinase based on their electrophoretic mobilities under sulfhydryl-reducing conditions. In primary cell culture, corneal epithelial cells were found to synthesize predominantly the 92-kD gelatinase species whereas the 72-kD gelatinase is synthesized mostly by stromal fibroblasts. However, each cell type can produce small amounts of the other enzyme. The 72-kD gelatinase, mostly in the proenzyme form, can be extracted from the normal corneal stroma without culturing, but expression of 92-kD gelatinase can only be detected in cell or organ culture. The substrate specificities of these enzymes suggests that they may be of central importance in the degradation of the epithelial basement membrane and in formation of the epithelial defect that precedes corneal ulceration.