Role of glycosaminoglycans and collagen in the development of a fibronectin-rich extracellular matrix in cultured embryonic corneal epithelial cells

Corneal epithelial cells from 15-day chick embryos produce a fibronectin-rich extracellular matrix when cultured on glass, plastic and fibronectin-coated substrata. Cell culture in the presence of Streptomyces hyaluronidase or chondroitinase ABC resulted in considerable reduction of the matrix; collagenase had a lesser effect but nevertheless also reduced the matrix. In all enzyme treatments the cells attached and spread to form characteristic epithelial cell islands, but the marginal cells of these islands showed a marked reduction in the number of lamellipodia and focal contacts. Also, the immunofluorescent staining pattern for fibronectin was considerably reduced. Control cells cultured on a fibronectin-coated surface were able to reorganize the fibronectin into fibrils, whereas cells cultured in enzymes showed little or no ability to do so. The cellular reorganization of fibronectin could also be inhibited by the addition of L-azetidine-2-carboxylic acid (LACA), an inhibitor of collagen secretion. Cells plated out in the presence of LACA spread much better on collagen substrata than on plastic, glass or fibronectin. However, in all cases very little fibronectin matrix was detectable in the epithelial islands. The results suggest that components of the extracellular matrix (ECM) such as collagen, hyaluronic acid and chondroitin sulphates are not essential for the initial attachment and spreading of corneal epithelial cells in culture, but are important in the development of the ECM, and in maintaining a flattened morphology and spreading behaviour. It is suggested that fibronectin plays an important role in these interactions and that the ability of cells to organize fibronectin into fibrils is dependent on the presence of other ECM components such as glycosaminoglycans and collagen.