Desiccating stress stimulates expression of matrix metalloproteinases by the corneal epithelium

PURPOSE. To determine the effects of experimental dryness on production of matrix metalloproteinases (MMPs) and their physiological inhibitors (TIMPs) by the corneal epithelium. METHODS. Experimental dry eye (EDE) was created in two strains of mice: BALB/c and C57BL/6. Real-time PCR was performed with MMP and TIMP probes, and the results were analyzed by the comparative C-T method, selecting the relative mRNA levels in untreated control samples as calibrator. Immunofluorescent staining with specific antibodies immunolocalized MMP proteins in situ. MMP enzymatic activity was evaluated in tears and corneal lysates. Corneal permeability to Oregon green dextran (OGD) and sodium fluorescein was measured. Corneal smoothness was evaluated by graded regularity of a ring reflected off the corneal surface. RESULTS. Desiccating stress significantly increased levels of MMP-1, -3, -9, and -10 transcripts in the corneal epithelium in C57BL/6 mice, but had no effect on levels of MMP transcripts in the corneal epithelium of BALB/c mice. There was no change in levels of TIMP transcripts except for TIMP-4 which significantly increased on day 10 in C57BL/6 mice. The MMP-1, -3, and -9 concentration in tears significantly increased compared with control levels after EDE for 4 and 6 days, respectively, in C57BL/6 and BALB/c. Changes in MMP protein expression detected by immunofluorescent staining were similar to changes in gene transcripts for most MMPs. EDE increased corneal permeability to OGD and fluorescein and corneal surface irregularity. CONCLUSIONS. Corneal dryness stimulates production of certain MMPs in a strain-dependent fashion and causes the disruption of the corneal barrier, thus increasing permeability and corneal irregularity.