Protective effects of matrix metalloproteinase-12 following corneal injury

Corneal scarring due to injury is a leading cause of blindness worldwide and results from dysregulated inflammation and angiogenesis during wound healing. Here we demonstrate that the extracellular matrix metalloproteinase MMP12 (macrophage metalloelastase) is an important regulator of these repair processes. Chemical injury resulted in higher expression of the fibrotic markers α-smooth muscle actin and type I collagen, and increased levels of angiogenesis in corneas of MMP12−/− mice compared with corneas of wild-type mice. In vivo, we observed altered immune cell dynamics in MMP12−/− corneas by confocal imaging. We determined that the altered dynamics owed to an altered inflammatory response, with delayed neutrophil infiltration during the first day and excessive macrophage infiltration six days later, mediated by altered expression levels of chemokines CCL2 and CXCL1, respectively. Corneal repair returned to normal upon inhibition of these chemokines. Taken together, these data show that MMP12 has a protective effect on corneal fibrosis during wound repair via regulation of immune cell infiltration and angiogenesis.