Corneal opacification affects millions of people and is the second leading cause of blindness in the world. The effective medical treatment of vision-threatening corneal opacification is a major unmet clinical challenge. Injury is a major cause of corneal opacification and can occur by a variety of mechanisms including infectious and noninfectious ulcers, incisional and laser surgery, and trauma. Following injury, proteinases regulate aspects of the repair process including inflammation, neovascularization, and remodeling. Excessive proteolysis resulting in corneal scarring has been associated with loss of corneal clarity. The matrix metalloproteinases (MMPs) represent the most prominent family of proteinases associated with corneal wound repair in humans. It has long been appreciated that tissue destruction and corneal pathology following corneal injury is associated with excessive proteolytic activity mediated by MMPs. However, potential protective effects of MMPs in the repair response are underappreciated. We have found that MMP12 (macrophage metalloelastase) is expressed in injured corneas and has a protective effect on corneal fibrosis during wound repair. Our preliminary data show that MMP12 protects against corneal stromal myofibroblast transformation, that MMP12 blunts the corneal angiogenic response to injury via regulation of VEGFA expression, and that MMP12 inhibits the accumulation of macrophages in wounded corneas via regulation of CCL2 expression. Collectively, these data demonstrate a protective role of MMP12 in the fibrotic, neovascular, and inflammatory responses to corneal injury. Furthermore, our findings suggest MMP12 as an important factor needed for the maintenance of corneal clarity following injury. Given these findings, we hypothesize that MMP12 regulation of CCL2 expression is a common mechanism by which MMP12 inhibits inflammation and neovascularization. This hypothesis will be addressed in the experiments of the following Specific Aims: (1) to define the role of MMP12 in the regulation of expression of CCL2 and CCR2;(2) to determine the interplay of MMP12 and CCL2 in the regulation of corneal neovascularization;and (3) to characterize MMP12 expression and activity levels in patient corneal samples. This combination of molecular and translational approaches will provide novel insight into the mechanisms by which MMP12 protects against corneal fibrosis and will open the possibility of developing novel modalities aimed at preventing and treating pathological fibrosis in human patients.
Corneal opacification due to corneal injury affects millions of people and is a leading cause of blindness worldwide. This research proposal examines a protective role of the matrix metalloproteinase MMP12 in the injury response through its effects on the inflammatory chemokine CCL2. Understanding the role of MMP12 in wounded corneas should further our understanding of the mechanisms important to the maintenance of corneal clarity and provide basic insights that could, in the long term, lead to better treatment of cornea opacification.