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Dale S Gregerson, Neal D Heuss, Scott W McPherson; Replacement of retinal microglia with donor bone marrow-derived macrophages yields microglia-like cells. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1490.
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Brain microglia were reported to be long-lived and self-renewing, suggesting that they may perform unique, essential functions. Self-renewal in retina is more difficult to demonstrate. To address questions about potential differences in the properties of microglia versus recruited macrophages we replaced microglia with bone marrow-derived macrophages and examined their properties as "pseudo-microglia".
Radiation bone marrow chimeras were made by grafting CD45.2 CD11cDTR/GFP bone marrow, or CD45.2 beta-actin GFP bone marrow into irradiated CD45.1 B6/J recipients. CD45 allotypes were used to avoid confusion with potential local microglia progenitors. From 1200 to 1800 R irradiation was used as specified to clear host microglia and local progenitors. Diphtheria toxin was used in some eyes to ablate retinal CD11cGFPhi macrophages. An optic nerve crush (ONC) injury was done to stimulate macrophage activation. Retinas were examined by flow cytometry, immunofluorescence microscopy, and fundus imaging.
Repopulation of the retinal macrophage niche in wt B6J mice after radiation and bone marrow grafting with CD11cDTR/GFP bone marrow led to engraftment with donor-derived macrophages. Donor-derived macrophages accounted for 22% of macrophages at 40 days post-grafting, and 27% at 47 days post-grafting. An optic nerve crush at 40 days led to 95% repopulation with donor macrophages, where 45% of those macrophages were CD11cGFPhi. Some donor-derived CD11cGFPhi macrophages lined up on nerve fibers, while those in the OPL were dendritiform. Similar experiments done by grafting beta-actin GFP+ bone marrow showed the morphology of the donor macrophages in retina, and revealed a substantial number dividing CD11b+ donor cells in retina post-ONC. Conversely, few dividing host-derived cells were found.
An ONC in normal mice did not recruit macrophages to the retina from the circulation. Conversely, in radiation BM chimeras an ONC promoted near total microglia replacement by donor cells. BM-derived retinal macrophages are much like MG in phenotype and morphology. Functionally, an optic nerve crush stimulus induces CD11cGFP expression, and the donor-derived CD11cGFPhi cells were found on the nerve fibers. The retinal environment exerts an important influence on the properties expressed by macrophages entering the retina.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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