Promoting CD200R signalling inhibits laser-induced choroidal neovascularisation due to altered proangiogenic macrophage gene expression

Abstract

Purpose: Manipulating macrophage activation to prevent choroidal neovascularisation (CNV) may offer a new strategic approach for therapeutic intervention in AMD. The recruitment and infiltration of macrophages to the choroid are essential for the development of CNV, and whilst the exact mechanisms that drive CNV are still poorly defined, experimental evidence suggests macrophages initiate angiogenesis. The purpose of this study was to interrogate whether suppressing angiogenic macrophage phenotype (Arg-1+VEGF+) via targeting inhibitory myeloid CD200R modulates the early infiltrating macrophage phenotype and function, and thereby influence the clinical outcome of disease.

Methods: CNV was induced in B10.RIII, C57BL/6J, CD200-/- and CD200R-/- mice by laser photocoagulation. The agonist monoclonal rat anti-mouse CD200R antibody (DX109) or isotype control antibody was administered by intravitreal injection either at time of laser or on day 3 following induction of CNV (6 lesions per fundus). The effect of DX109 (a CD200R agonist) treatment on both size and permeability of induced CNV was assessed by digital image analysis of fundus fluorescein angiograms. Expression of macrophage activation-related mediators from choroid and retinal tissue was assessed by quantitative RT-PCR.

Results: In vivo assessment demonstrated that the local delivery of DX109 resulted in significant reduction in the mean CNV size at 2 weeks post-laser. Administration of DX109 led to reduced expression of the macrophage chemokine CCL2, as well as a proangiogenic phenotype including reduced Arginase-1 and IL-1β at day 3 post-laser. In further experiments examining the influence of CD200R ligation on modulating macrophage phenotype, DX109 was administered following CNV induction in CD200 and CD200R deficient mice. A corroborative reduction in gene expression was demonstrated in CD200-/- as in wild-type mice, whilst no effect was observed in CD200R-/- animals.

Conclusions: These results demonstrate that modulating macrophage activity via myeloid CD200R ligation can suppress the pro-angiogenic phenotype of recruited cells, and proffers mechanisms whereby laser-induced choroidal neovascularisation is inhibited. Approaches to target CD200R and promote such a change in function may prove beneficial for the treatment of AMD.

Keywords: 555 immunomodulation/immunoregulation • 453 choroid: neovascularization • 533 gene/expression