Role of ocular matrix metalloproteinases in peripheral ulcerative keratitis

Abstract

Aim-Peripheralulcerative keratitis (PUK) is an ocular manifestation of rheumatoid arthritis and other similar systemic diseases. The purpose of this inquiry was to investigate the involvement of matrix metalloproteinases (MMPs) in the induction and/or maintenance of PUK. Methods-Substrate gel electrophoresis was used to characterise the MMP activities secreted by primary cultures of keratocytes derived from normal and perforated pathological corneal specimens, and those present in tears of normal subjects and patients with PUK. Substrate specificity and the in vivo activity status of the secreted MMPs was assessed by SDS-polyacrylamide gel electrophoresis of standard collagens incubated in the presence or absence of the various enzyme preparations. Results-In addition to MMP-2 of M r 66 000, cultured keratocytes derived from perforated corneas of patients with PUK abnormally produce the MMP-2 of apparent M r 62 000. Other MMPs and in particular MMP-9 of M r 92 000, also occur in the tears of these patients. Their visualisation on substrate polyacrylamide gels correlated with clinical manifestations of disease activity; during periods of disease quiescence they were barely detectable. The steroid prednisolone, frequently used in systemic therapy, had no eVect on the in vitro activity of MMP-2, or on its production by cultured corneal keratocytes. Although the in vitro activity of MMP-2 was inhibited by both Cu 2+ and Zn 2+, Cu 2+ apparently induced the keratocytes to produce activated enzyme and Zn 2+ irreversibly inhibited their production of MMP-2. Conclusion-Overexpression of corneal MMP-2 and tear film MMP-9 are characteristic features of patients with PUK and their activation may be a crucial facet of disease initiation or progression. Although eVective in systemic therapy for PUK, prednisolone had no direct control over corneal MMP-2 production or activity. Zn 2+ on the other hand inhibited both MMP-2 production and MMP-2 activity and may, therefore, be of therapeutic value if suitably formulated and used in conjunction with systemic steroid treatment. (Br J Ophthalmol 1999;83:1376-1383

Matrix Metalloproteinase 2 Activation in Cultured Corneas

“…The M r 62,000 species is generally considered to represent the activated form of MMP-2 generated by the loss of an Nterminal peptide [16,17] through the action of membrane-bound MMPs [18,19]. Despite these reports, and in agreement with our previous findings [10,11,20], the transformation of the M r 66,000 species into the M r 62,000 species did not generate activated enzyme capable of hydrolysing denatured [ 3 H]type 1 collagen. Hydrolysis of this substrate was catalyed only by the soluble protein preparations that also contained the M r 43,000 zymographic activity and were generally those that had been maintained in culture medium for periods exceeding 30 days.…”

“…In addition to supporting the hypothesis that MMP-2 can become activated in organ cultured corneas, these observations also suggested that the M r 43,000 form of MMP-2 is the catalytically active species present, perhaps because it cannot effectively bind the tissue inhibitors of metalloproteinases 2 and 1 that are co-secreted by keratocytes [9,11,21]. With respect to the activity status of the M r 62,000 form of corneal MMP-2, this has been questioned previously [10,11,20]. However, if it is capable of catalysing peptide bond hydrolysis, it must remain complexed with tissue inhibitors of metalloproteinases, and thus inhibited, in corneal tissue.…”

Suppression by an RAR-γ Agonist of Collagen Degradation Mediated by Corneal Fibroblasts

“…The production of matrix metalloproteinases (MMPs) by corneal fibroblasts is responsible in part for the remodeling of collagen fibrils in the corneal stroma. 3,4 The production of tissue inhibitors of MMPs is also a determinant of collagen remodeling associated with corneal disease. 5,6 Proinflammatory cytokines such as interleukin (IL)-1b and IL-6 also contribute to the pathogenesis of inflammatory corneal disease.…”

The corneal melting point

“…Such studies show the progression of corneal melting to be influenced by the elaboration of excessive tissue degradative proteases. [6][7] One group of these proteases are the matrix metalloproteinases (MMPs). MMPs are regularly shown to have a role both in infectious and noninfectious causes of corneal tissue destruction.…”

“…MMPs are regularly shown to have a role both in infectious and noninfectious causes of corneal tissue destruction. [6][7][8] From animal and laboratory studies, a variety of agents or surgical approaches are proposed as potential inhibitors of MMPs. Some of these have been used in human patients.…”