Differences in the distribution,phenotype and gene expression of subretinal microglia/macrophages in C57BL/6N (Crb1rd8/rd8) versus C57BL6/J (Crb1wt/wt) mice

Microglia/macrophages (mg/mφ) are found in the subretinal space in both mice and humans. our goal was to study the spatial and temporal distribution,the phenotype,and gene expression of subretinal mg/mφ in mice with normal retinas and compare them to mice with known retinal pathology. methods: we studied c57bl/6 mice with (c57bl/6n),or without (c57bl/6j) the rd8 mutation in the crb1 gene (which,in the presence of yet unidentified permissive/modifying genes,leads to a retinal degeneration),and documented their fundus appearance and the change with aging. immunostaining of retinal pigment epithelium (rpe) flat mounts was done for 1) ionized calcium binding adaptor (iba)-1,2) fcγiii/ii receptor (cd16/cd32,abbreviated as cd16),and 3) macrophage mannose receptor (mmr). reverse-transcription quantitative pcr (rt-qpcr) was done for genes involved in oxidative stress,complement activation and inflammation. results: the number of yellow fundus spots correlated highly with subretinal iba-1+ cells. the total number of subretinal mg/mφ increased with age in the rd8 mutant mice,but not in the wild-type (wt) mice. there was a centripetal shift in the distribution of the subretinal mg/mφ with age. old rd8 mutant mice had a greater number of cd16+ mg/mφ. cd16+ cells had morphological signs of activation,and this was most prominent in old rd8 mutant mice (p <1×10-8 versus old wt mice). subretinal mg/mφ in rd8 mutant mice also expressed inos and mhc-ii,and had ultrastructural signs of activation. finally,rd8 mutant mouse rpe/ mg/mφ rna isolates showed an upregulation of ccl2,cfb,c3,nf-kβ,cd200r and tnf-alpha. the retinas of rd8 mutant mice showed upregulation of ho-1,c1q,c4,and nrf-2. conclusions: when compared to c57bl/6j mice,c57bl/6n mice demonstrate increased accumulation of subretinal mg/mφ,displaying phenotypical,morphological,and gene-expression characteristics consistent with a pro-inflammatory shift. these changes become more prominent with aging and are likely due to the combination of the rd8 mutation and yet unidentified permissive/modulatory genes in the c57bl/6n mice. in contrast,aging leads to a scavenging phenotype in the c57bl/6j subretinal microglia/macrophages. © aredo et al.; licensee biomed central.