OVER-EXPRESSION OF A GELATINASE A ACTIVITY IN KERATOCONUS

Keratoconus is an ocular disorder in which the central cornea becomes thin, conical and frequently scarred. We are exploring the possibility that this condition is induced and maintained by proteases that exist in the corneal matrix in an activated form, In this study, the activi ties of the proteases secreted in vitro and in vivo by keratocytes of normal, clear keratoconic, scarred keratoconic and traumatically scarr ed corneas have been compared and partially characterised. Data obtain ed by assaying acyl transferase activity showed that the matrix metall oproteinases account for a minimum of 95% of the total protease secret ed by cultured keratocytes, Their summated specific activity was consi stently and significantly higher in the culture medium of keratoconic keratocytes than in the medium of other keratocyte cultures, Analysis of the individual protease activities secreted by these corneal kerato cytes in vitro and in vivo by SDS-gelatin polyacrylamide gel electroph oresis showed that a gelatinase of molecular weight 65 000 is the majo r protease secreted by normal keratocytes. Whereas clear keratoconic a nd traumatically scarred corneal keratocytes secrete an additional act ivity of molecular weight 61 000, scarred keratoconic corneal keratocy tes generally produced little or none of this gelatinase activity, Bot h activities may be ascribed to gelatinase A, and although the 61 000 molecular weight form may be a significant feature of keratoconus, nei ther appears to be active as secreted.