EXPRESSION OF DEGRADATIVE ENZYMES AND PROTEASE INHIBITORS IN CORNEAS WITH KERATOCONUS

PURPOSE. Keratoconus is characterized by thinning and scarring of the central region of the cornea. Previous research showed that, in cornea s obtained from patients with keratoconus, lysosomal enzyme activities are elevated, whereas levels of protease inhibitors such as alpha 1-p roteinase inhibitor are reduced. This study was undertaken to examine further the expression of a spectrum of proteolytic enzymes and protea se inhibitors. METHODS. Corneal buttons were collected from patients w ith keratoconus, healthy subjects, and patients with other corneal dis eases. Immunohistochemical staining was performed on paraffin sections . Enzymatic assays and western blot analysis were carried out for cath epsins B and G. in addition, an in situ zymography procedure was used to examine the gelatin and casein-digesting activities in corneas with keratoconus. RESULTS. An enhanced staining was found with antibodies to cathepsins B and G. Enzymatic assays and western blotting confirmed that the levels of these two enzymes were elevated in corneas with ke ratoconus. No alteration was noted with any of the matrix metalloprote inase (MMP) family members and other enzymes and inhibitors examined, although in situ zymography did indicate an increase in net gelatin- a nd casein-digesting activities in corneas with keratoconus. These acti vities were mostly abolished by inhibitors for serine and cysteine pro teinases, but not by those for MMPs and aspartic proteinases. CONCLUSI ONS. Levels of cathepsins B and G are increased in corneas with kerato conus. These enzymes may contribute to the heightened in situ gelatin- and casein-digesting activities, leading to abnormalities in keratoco nus.