The control of matrix metalloproteinase-2 expression in normal and keratoconic corneal keratocyte cultures

PURPOSE. Early phase keratoconic corneas and their cultured keratocytes abn ormally produce the M-r 62,000 form of the matrix metalloproteinase-2 (MMP- 2). It is known that platelet derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) are involved in the regulation of MMP activi ty and tissue inhibitor of metalloproteinase (TIMP) production in non-ocula r tissues. The purpose of this enquiry was to determine whether these growt h factors also play a role in the activity and/or production of corneal MMP -2 and TIMP, and whether their activity could account for the existence of the M-r 62,000 form of MMP-2 in keratoconic corneas. METHODS. Confluent cultures of normal and early-phase keratoconic corneal k eratocytes were established and incubated in serum-free media in the presen ce or absence of PDGF and TGF-beta. The proteins secreted by these cells ov er periods of 7 days were harvested for analysis. The fetal protein produce d was determined spectrophotometrically. MMP-2 was visualised by SDS-gelati n polyacrylamide gel electrophoresis and assayed using radiolabelled type I V collagen as substrate. The enzyme inhibitors, TIMP-1 and TIMP-2, were qua ntified by dot blot immunoassay. RESULTS. The addition of PDGF or TGF-beta to the culture medium of keratoco nic corneal keratocytes had no significant effect on overall protein produc tion, MMP-2 activity or on the amounts of TIMP-1 and TIMP-2 secreted. These observations also applied to normal corneal keratocytes, with the exceptio n that PDGF induced expression of the M-r 62,000 species of MMP-2. CONCLUSIONS. PDGF may be involved in the production of the M-r 62,000 speci es of MMP-2 that is abnormally produced by early-phase keratoconic corneal keratocytes.