The Role of Macrophage Class A Scavenger Receptors on CNV Formation in a Laser-induced Murine CNV Model

Abstract

Purpose: : Inflammatory mechanisms play a major role in laser-induced choroidal neovascularization (CNV), which mimics wet age related macular degeneration (AMD). Both Class A scavenger receptors, SR-A and MARCO, have been linked to inflammation. While SR-A is ubiquitously expressed on macrophages, MARCO is expressed only on a defined subset of macrophages. The goal of this study is to examine the role of different types of macrophage scavenger receptors on the formation of CNV.

Methods: : CNV was induced by laser photocoagulation in wild-type, SR-A knockout, MARCO knockout, and SR-A/MARCO knockout mice. To test if scavenger receptors affect CNV, mice were euthanized after 14 days of laser treatment and lesions were imaged by confocal microscopy. CNV volume was calculated using Volocity software. Moreover, mice were euthanized at different time points after laser injury to quantify the immune cell recruitment through immunostaining and confocal microscopy. Furthermore, flow cytometry was performed one day post laser injury to confirm the expression of immune cells.

Results: : CNV volume was significantly reduced in SR-A and MARCO single scavenger receptor knockout mice compared to wild-type mice. However, SR-A/MARCO double scavenger receptor mice’s inhibition of CNV was not as dramatic as single scavenger receptor knockout mice. Neutrophils infiltrated the sites of laser injury as early as 6 hours and peaked at 1 day after laser injury more substantially in wild type mice compared to SR-A knockout mice. After 3 days of laser treatment, there was no significant difference in the number of neutrophils between wild type mice and SR-A knockout mice since wild type mice dramatically decreased recruitment while SR-A knockout mice remained constant from 1 day after laser treatment. Neutrophils began to clear from the laser lesions in both groups after 4 days post laser injury. Flow cytometry confirmed the decreased presence of neutrophils and macrophage after 1 day post laser treatment in both single and double scavenger receptor knockout mice compared to wild type mice.

Conclusions: : The deficiency of scavenger receptors impairs the formation of CNV and immune cell recruitment. Thus, our data suggest that scavenger receptors may contribute to the formation of CNV and inflammation typically seen in AMD.

Keywords: age-related macular degeneration • choroid: neovascularization • inflammation