Roles of matrix metalloproteinases in the cornea: A special focus on macular corneal dystrophy

Matrix metalloproteinases (MMPs) are endopeptidases that are responsible for the degradation of several components of the extracellular matrix (ECM) and some non-ECM proteins. MMPs are subdivided into 6 groups according to their structure and substrate specificity: collagenases, gelatinases, membrane-type MMPs, stromelysins, and matrilizines. Collagenases are important proteolytic tools during ECM remodeling, tissue regeneration, and organ development. MMPs, especially collagenases, have important roles in ocular processes such as retinal neurogenesis and corneal wound healing. MMP studies on eye research are limited, but there is growing evidence that MMP physiology is key for the ocular system, especially for the cornea. The cornea is predominantly composed of collagen fibrils, which form uniform lamellar lattices. Collagenase-driven ECM remodeling is essential for the cornea. Macular corneal dystrophy (MCD) is a rare inherited disease and characterized by progressive, insoluble accumulation of irregular substances in the corneal ECM. MCD can cause visual acuity loss up to blindness, and there is currently no treatment available. It has been recently reported that certain collagenases are downregulated in MCD disease progression. Here, we review the roles of MMPs in eye diseases and propose possible treatment strategies for MCD.