Corneal stimulation of MMP-1, -9 and uPA by platelet-activating factor is mediated by cyclooxygenase-2 metabolites

This study was undertaken to evaluate the significance of cyclooxygenase-2 (COX-2) activity on urokinase plasminogen activator (uPA) and matrix metalloproteinases (MMPs)-1 and -9 induction in cornea following platelet-activating factor (PAF) treatment.

Corneal organ cultures were pre-treated with increasing concentrations of COX-2-specific inhibitors NS398 or nimesulide prior to PAF stimulation. To determine the effect of exogenous prostaglandins (PGs) on uPA, MMP-1 and MMP-9 levels, corneas were pre-treated with COX-2 inhibitors followed by the addition of 2.5 microM PGD2, PGE2 or PGF2alpha. The levels of uPA and MMP-9 were assayed by casein and gelatin zymography, respectively. MMP-1 levels were determined by Western Blot analysis.

The increase in uPA, MMP-9 and MMP-1 levels detected in corneal organ cultures treated with 100 nM cPAF was blocked by 5 microM NS398 and 10 microM nimesulide, concentrations at which these inhibitors selectively inhibit COX-2 activity. Furthermore, pre-incubation with COX-2 inhibitors, followed by supplementation with PGD2, PGE2 or PGF 2alpha, increases uPA, MMP-9 and MMP-1 levels in corneas similar to and in some cases greater than that produced by cPAF treatment alone.

During corneal injury and inflamation, PAF is an important factor in the activation of proteolytic cascades, which could lead to corneal epithelial defects and ultimately ulceration. One important goal in treating these defects is to modulate the activity of enzymes that destroy the extracellular matrix. Our results suggest that COX-2 induction following PAF stimulation and subsequent eicosanoid release may play a crucial role in the induction of uPA, MMP-1 and MMP-9 enzymes. Specific COX-2 inhibition could therefore block the actions of PAF when inflammation is sustained.