Matrix metalloproteinase 2 activation in cultured corneas

Corneas that are maintained in tissue culture medium shed their epithelial cells and repopulation following graft surgery is an essential facet of the healing process. Failure to do so may be a result of structural damage to the epithelial basement membrane of a donor cornea. The purpose of the present investigation was to ascertain whether MMP-2, the matrix metalloproteinase produced by corneal keratocytes, may be activated during storage and hence cleave the type IV collagen component of the epithelial cell basement membrane.

Fresh and transplant rejected corneas that had been stored in culture medium for varying time periods and of known donor age were collected. The soluble protein fractions of these corneas were obtained. Their MMP-2 proteins were visualised by zymography on SDS gelatin polyacrylamide gels and assayed for activity against nitrophenyl acetate and denatured [(3)H]type I collagen.

The stromal tissue of fresh, normal corneas produced inactive MMP-2 of M(r) 66,000. Although the cultured corneas did not up-regulate MMP-2 production, they contained additional MMP-2 activities of M(r) 62,000 and M(r) 43,000. The appearance of these additional MMP-2 activities correlated with corneal culture time but not donor age. The ability to cleave denatured [(3)H]type I collagen correlated with the appearance of the M(r) 43,000 activity but not the M(r) 62,000 activity.

Activated MMP-2 is produced in cultured corneas. For this reason the corneas donated for all graft procedures should not be held in culture medium for periods exceeding 4 weeks.