Expression of membrane-type 1 matrix metalloproteinase (MT1-MMP) and MMP-2 in normal and keratoconus corneas.
OBJECTIVE
To determine whether MT1-MMP and MMP-2 are expressed in normal and keratoconic corneas, and to investigate the ability of MT1-MMP, expressed on cultured keratocytes after stimulation with concanavalin A, to activate pro-gelatinase A (pro-MMP 2).


METHODS
Specimens of keratoconus corneas (n = 20), removed at corneal transplantation, were obtained from pathology archives, sections were cut, and were stained with an antibody to MT1-MMP, using peroxidase immunohistochemistry. Eye banked corneas served as controls (n = 14). Normal human keratocyte cultures were initiated from eye bank corneas, and after stimulation with con A, MMPs in the media were examined using gelatin zymography and immunoblotting, and MT1-MMP expression was analysed by flow cytometry and immunoblotting.


RESULTS
All corneas showed some expression of MT1-MMP and MMP-2, although the degree of staining varied greatly. The MMPs were present in the epithelium, endothelium and stroma. Expression of MT1-MMP, but not MMP-2, in the epithelium and stroma, was significantly elevated in keratoconus, compared to normal corneas. In vitro, keratocytes stimulated with con A expressed MT1-MMP and produced active MMP-2, detected by zymography. These responses to con A were concentration-dependent and MT1-MMP expression and MMP-2 activation correlated significantly (p = 0.0003) In addition, MMP inhibitors abolished MMP-2 activation, providing further evidence that MT1-MMP activated MMP-2.


CONCLUSIONS
The observation that MT1-MMP expression may be up-regulated in keratoconus corneas, taken together with the demonstration that human corneal cells can express this enzyme, which in turn can activate latent MMP-2, provide evidence for a possible role for MT1-MMP in the pathogenesis of keratoconus.
Collier
S A
SA
Department of Clinical Ophthalmology, University of Sydney, Sydney, NSW, Australia. scollier@eye.usyd.edu.au
Madigan
M C
MC
Penfold
P L
PL
D002478:Cells, Cultured; D003208:Concanavalin A / Q000494:pharmacology; D003315:Cornea / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007640:Keratoconus / Q000201:enzymology*; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D053504:Matrix Metalloproteinases, Membrane-Associated; D008666:Metalloendopeptidases / Q000378:metabolism*; D012016:Reference Values
D003208:Concanavalin A; D053504:Matrix Metalloproteinases, Membrane-Associated; D008666:Metalloendopeptidases; D020778:Matrix Metalloproteinase 2