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Bogale Aredo, kaiyan Zhang, Rafael L. Ufret-Vincenty; Change In The Distribution And Phenotype Of Subretinal Macrophages With Aging In C57BL/6 Mice. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1659.
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The role of subretinal microglia in maintaining homeostasis and/or inducing disease is not well understood. For instance, there is significant debate surrounding the role of macrophages-microglia in age-related macular degeneration (AMD). In order to better understand subretinal microglia, we decided to explore the natural history of their distribution and phenotype in wild type, B6-pigmented mice.
Naïve C57BL/6 (B6) mice of different ages were used for this experiment. Eyes were dilated and retinal images were taken using a Micron III rodent fundus camera (Phoenix Research Laboratories). Yellow spots in the central fundus (5 disc radius from the center of optic disc) were counted. Eyes were enucleated and fixed in 4% paraformaldehyde. Posterior segment flat mounts (sclera-choroid-RPE complex) were prepared and were single, double, or triple stained for ionized calcium binding adaptor molecule 1 (Iba-1), mouse Macrophage Mannose Receptor (MMR) or mouse FcγIII/II Receptor (CD16/CD32). Microglia cells (Iba-1+, MMR+, and/or CD16/CD32+) were counted on choroid-RPE flat mount images for both the central region (within a 5 disc diameter radius from the optic nerve), and for the total RPE.
The yellow fundus spots seen on B6 mice change in distribution at different ages. Iba-1+ microglial cells seen in immmunohistochemistry of flatmounts show a similar distribution pattern. In young mice (1-8 m), the fundus spots and the corresponding microglial cells on RPE flatmounts are frequently located at the anterior (far peripheral) retina. As the mice age, the distribution of cells is more posterior. In addition, an increasing proportion of the microglial cells also stain for MMR as mice age. Moreover, the microglial cell population becomes increasingly MMR+CD16/CD32- with advancing age.
As B6 mice age, although there is no significant change in the total amount of microglial cells in the sub-retinal space, the location of these cells seems to shift. Furthermore, progressively more cells become MMR+CD16/Cd32-. Further studies are needed to understand what triggers the changes in subretinal microglial cell distribution and phenotype, and how that may differ in mice under oxidative stress or inflammation.
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