Purpose. To determine if genetic ablation of the chemokine receptor CCR2 (involved in leukocyte and endothelial chemotaxis) inhibits the development of corneal neovascularization.
Methods. Wild-type C57BL/6J mice, as well as species-specific counterparts with targeted homozygous disruption of the CCR2, underwent chemical and mechanical denudation of corneal and limbal epithelium. Corneas were harvested 2 weeks after injury. Neovascularization was quantified by CD31 immunostaining.
Results. The mean percentages of neovascularized corneal area in control mice and CCR2-deficient mice 2 weeks after denudation were 58.3% and 38.8% (P = 0.047), respectively.
Conclusions. Development of corneal neovascularization is inhibited in CCR2-deficient mice.
Corneal neovascularization (KNV) is a central feature in the pathogenesis of many blinding corneal disorders and a major sight-threatening complication in corneal infections, chemical injury, and following keratoplasty, in which neovascularization adversely impacts corneal graft survival. 1
Although the molecular mechanisms underlying KNV have not been fully deciphered, vascular endothelial growth factor (VEGF) seems to play an indispensable role. It induces KNV when applied exogenously 2 and is the principal endogenous angiogenic force in the neovascularization that follows limbal injury. 3 Transmigrating and invading corneal leukocytes appear to provide much of the requisite VEGF that drives KNV. 3
The recruitment of leukocytes to inflammatory sites is mediated by chemokines. Chemokines bind to specific receptors, which, despite some redundancy, show specificity for individual chemokines. Evidence is emerging that individual chemokines attract specific leukocyte populations through processes determined by ligand specificity and the expression patterns of the corresponding receptors. 4 C-C chemokine receptor 2 (CCR2) is the principal receptor for the monocyte chemoattractant proteins (MCPs) 1-5, which are potent chemoattractants for monocytes 5,6.
Endothelial cell migration and proliferation are also essential to angiogenesis, and these processes are influenced by vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). 7,8 Further, endothelial cell chemotaxis and/or proliferation can be stimulated by chemokines, including MCP-1. 9-11
Previous work has confirmed that corneal angiogenesis is driven in large part by inflammatory mediators. 12,13 MCP-1 induces KNV when implanted into the cornea, 14 directs monocyte infiltration near areas of endothelial denudation, and increases vessel growth after femoral artery occlusion. 15,16 CCR2 has been identified in both vascular smooth muscle cells and endothelial cells 12,13,17,18 and, along with its ligand MCP-1, is involved in the promotion of endothelial migration after wound injury. 12,18 MCP-1 has also been implicated in tumor angiogenesis. 19
We therefore examined the role of CCR2 in a clinically relevant ocular model of corneal injury by studying the neovascular response of animals genetically deficient in these molecules.