Corticosteroid and doxycycline suppress MMP-9 and inflammatory cytokine expression, MAPK activation in the corneal epithelium in experimental dry eye

We investigated the effects of corticosteroid and doxycycline on expression of matrix metalloproteinase (MMP)-9 and inflammatory cytokines and activation of mitogen-activated protein kinase (MAPK) signaling pathways, c-jun N-terminal kinases (JNK), extracellular-regulated kinases (ERK) and p38, in experimental murine dry eye. Experimental dry eye (EDE) was created in C57BL6 mice, with or without or topical treatment consisting of 1% methylprednisolone, 0.025% doxycycline or balanced salt solution four times per day. MMP-9 expression in the cornea epithelia was evaluated by laser scanning confocal microscopy. Gelatinase activity in the cornea was evaluated by in situ zymography and MMP-9 activity in tear washings was evaluated by gelatin zymography. Total and phosphorylated MAPKs (JNK1/2, ERK1/2, p38) were detected by Luminex immunobead assay. Levels of MMP-9, interleukin (IL)-1α, IL-1β and tumor necrosis factor (TNF)-α RNA transcripts were evaluated by real-time PCR. MMP-9 immunoreactivity was localized to the apical corneal epithelial cell membranes in normal control eyes. Desiccating stress significantly increased production of MMP-9 by the corneal epithelium and increased its activity in the corneal epithelium and tear fluid. Dryness also increased expression of IL-1α, IL-1β and TNF-α mRNA and stimulated phosphorylation of JNK1/2, ERK1/2 and p38 MAPKs in the corneal epithelium. Both methylprednisolone and doxycycline reduced expression and activity of MMP-9, decreased levels of inflammatory cytokines transcripts and reduced activation of MAPKs in the corneal epithelium in response to EDE. Desiccating stress stimulates expression of MMP-9, IL-1α, IL-1β and TNF-α mRNA , as well as activates MAPK signaling pathways in the corneal epithelium. Both corticosteroid and doxycycline suppressed this molecular stress response.