Abstract
Purpose:
Subretinal microglia/macrophages have been identified in patients with AMD and retinal dystrophies, and also in multiple animal models of retinal degenerations. Yet, there is little known about the factors that regulate their accumulation in the subretinal space, and their level/type of activation. We have previously shown that the number of yellow fundus spots have a strong correlation with the number of Iba-1+ subretinal microglia/macrophages. Our aim was to study the gene expression profile of the retina, RPE and subretinal macrophage/microglia in eyes showing many vs. few subretinal yellow fundus spots.<br />
Methods:
Age-matched adult (12-15 m old) chimeric Cfh transgenic mice vs. C57BL/6J mice were photographed using a Micron III rodent fundus camera. Eyes were classified into 4 groups, using the genotype and a semiquantitative scale based on the density of yellow fundus spots: CfhTg/Hi, CfhTg/Lo, B6J/Hi and B6J/Lo. Eyes were enucleated and total RNA was isolated from the retina, and from the RPE/subretinal microglia. Two separate candidate gene approaches were used to identify genes of interest: 1. TaqMan Mouse Immune Arrays (Applied Biosystems) containing 92 immune-related genes, and 2. qPCR analysis of 62 candidate genes related to microglial chemotaxis, inflammation and oxidative stress.<br />
Results:
CfhTg mice had on average a significant increase (p=0.03) in the number of yellow fundus spots compared to B6J mice. However, there was a wide range of fundus spot density in each strain of mice. The qPCR analysis revealed that 14 RPE/subretinal microglia genes were up- or down-regulated with an increased number of fundus spots in CfhTg mice (5 in B6 mice). The array data also revealed a group of 14 RPE/subretinal microglia genes which were up- or down-regulated with a high number of subretinal spots in CfhTg mice (and another set of 14 genes in B6 mice). We were able to identify several gene families that appeared to be involved in the differential microglial subretinal infiltration. These include cytokines, chemokines and signal transduction genes.<br />
Conclusions:
A wide range of genes involving several pathways are differentially expressed in eyes with increased number of subretinal microglia. A better understanding of subretinal microglial behavior may offer new therapeutic approaches for a variety of retinal diseases.