Modulation of Rertinal Pigment Epithelium (RPE) Wound Healing by Blocking Macrophage Migration Inhibitory Factor (MIF): A Novel Target for Age-related Macular Degeneration (AMD) Treatment

Abstract

Purpose: : To determine the effect of MIF neutralization on RPE differention and wound healing properties in animal models of chemical RPE debridement and laser-induced choroidal neovascularization (CNV).

Methods: : CNV was induced in C57BL/6 mice (n = 18) using a double-frequency YAG laser (532 nm; 600 mW; 0.1 sec; 50 µm; 8-12 spots/eye). The experimental group (n=6) received 500 µg/in 5 µl of a MIF inhibitor (ACT-003) in the posterior subtenon space 24 hours before laser application. 10 days later animals were sacrificed and induced CNV (i.e. yield) was determined. Another group of animals received MIF-inhibitor 6 days after laser treatment to determine the effect of MIF-neutralization on established CNV. RPE loss was also mimicked in 12 C57BL/6 mice by patchy debridement of RPE using intraperitoneal sodium iodate injection (25 mg/kg). Seven days later animals received the subtenon MIF inhibitor and RPE resurfacing was determined on day 21 by morphometric image analysis. In all experiments, MIF -/- animals and wild-type animals that received the solvent (DMSO/Corn oil) and/or PBS were used as controls.

Results: : MIF-neutralization significantly lowered the CNV yield compared to the controls regardless of the application time; from 72.1% and 80% for PBS and the solvent, respectively to 10.7% and 12.9% for pre- and post-laser (p=0.0001). This decrease was comparable to the CNV yield in MIF-/- animals (12.5%, p=0.76). MIF-neutralization also resulted in significantly higher surface coverage by RPE cells compared to controls (93.8 ± 6.3% vs. 60.9 ± 19.0%, p=0.001). Proliferating RPE cells in MIF-neutralized animals maintained differentiated cuboidal morphology and expressed E-and N-cadherin and RPE-65.

Conclusions: : MIF neutralization enhances the ability of RPE cells to proliferate and maintain differentiated features. This results in the inhibition of CNV by rapid sealing of the damaged subretinal space and repopulation of the denuded Bruch’s membrane.

Keywords: age-related macular degeneration • retinal pigment epithelium • wound healing