PLATELET-ACTIVATING-FACTOR INDUCES THE EXPRESSION OF METALLOPROTEINASE-1 AND METALLOPROTEINASE-9, BUT NOT METALLOPROTEINASE-2 OR METALLOPROTEINASEX-3, IN THE CORNEAL EPITHELIUM

Purpose. The inflammatory mediator platelet-activating factor (PAF) in duces the expression of interstitial collagenase (metalloproteinase-1) messenger RNA in rabbit corneal epithelium. In this study, the author s investigated the effect of PAF on gene expression and protein activi ty of other matrix metalloproteinases (MMPs) in the cornea. Methods. R abbit corneas were incubated in an organ culture with 100 nM of cPAF ( a nonhydrolyzable PAF analog), PAF, or lyso-PAF, an inactive metabolit e of PAF. In some experiments, the corneas were preincubated for 1 hou r with 10 mu M BN50730, a PAF antagonist, before cPAF was added to the medium. Corneal epithelial cells and/or conditioned medium were colle cted at different times for analysis. Also, in vivo experiments were d one by injecting 2 mu g of cPAF intrastromally into rabbit eyes and co llecting the epithelium 8 hours rater for study. Northern blot analysi s and zymography were performed to determine the mRNA abundance and/or enzyme activity of 92 kd gelatinase (MMP-9), 72 kd gelatinase (MMP-2) , and stromelysin (MMP-3). The activity of MMP-1 was tested by collage nase assays. Results. cPAF induced the expression of MMP-9 mRNA, but n ot MMP-3 mRNA. The message was induced at 4 hours and remained elevate d at 48 hours, with a peak at 36 hours. In corneas preincubated with B N50730, MMP-9 mRNA activation by cPAF was inhibited. In vivo injection of cPAF also induced the expression of MMP-9. Furthermore, cPAF incre ased MMP-9 activity in the epithelial cells and in the conditioned med ia. The effect was blocked by BN50730. cPAF did not affect MMP-2 activ ity. Finally, cPAF also increased MMP-1 collagenolytic activity of the corneal epithelium, which waS blocked by the PAF antagonist. Conclusi on These results suggest a novel mechanism by which PAF activates MMPs . The lipid mediator selectively enhances the expression of MMP-1 and MMP-9 in rabbit corneal epithelium. This activation by PAF may be invo lved in the remodeling mechanisms of the cornea after injury and, when overexpressed, may lead to the formation of corneal ulcers. Specific PAF antagonists could therapeutically deter corneal ulcer formation an d facilitate corneal wound healing.