Regulation of MMP-9 production by human corneal epithelial cells

The matrix metalloproteinases. MMP-2 and MMP-9. are known to be critical extracellular-remodeling enzymes in wound healing and other diseases of the ocular surface. This study investigated the regulation of MMP-2 and MMP-9 in human corneal epithelial cells by growth factors and pro-inflammatory cytokines (IL-1β and TNF-α) they are exposed to, and by doxycycline, a medication used to treat ocular surface disease. Primary human corneal epithelial cell cultures were treated with one of the following cytokines (IL-1α, IL-1β, IL-6, IL-8, TNF-α) or growth factors (EGF, HGF, KGF, PDGF-BB, TGF-α, TGF-β), with or without their corresponding inhibitors. The conditioned media were collected after 24 hr for gelatin zymography and MMP-9 activity assay. Total RNA was extracted from the cells treated for 6 hr and was subjected to RT-PCR and Northern hybridization. Between the two gelatinases. MMP-2 and MMP-9, detected by zymography, the 92 kDa MMP-9 in the conditioned medium was markedly up-regulated by the pro-inflammatory cytokines. IL-1β and TNF-α. The MMP-9 protein and activity were dose-dependently stimulated by IL-1β or TNF-α at 0.1, 1.0 and 10 ng ml^-1. This upregulation was nearly abolished by neutralizing antibodies (IL-1β and TNF-α) and by IL-1 receptor antagonist. Semi-quantitative RT-PCR and Northern hybridization disclosed that the MMP-9 transcript was also markedly up-regulated in a dose-dependent manner by IL-1β and TNF-α. Doxycycline (10 μg ml^-1) suppressed MMP-9 protein level and activity, but not its mRNA, that was stimulated by IL-1β and TNF-α (1 ng ml^-1). In contrast, the 72 kDa MMP-2 was not significantly modulated by any of these cytokines. In conclusion, production of MMP-9 is stimulated by the pro-inflammatory cytokines, IL-1β and TNF-α. These factors may play a role in the pathogenesis of MMP-9 mediated corneal matrix degradation. The efficacy of doxycycline in treating ocular surface diseases may be related to its ability to suppress MMP-9 production in the corneal epithelium.