Microglia and macrophages are increased in response to ischemia-induced retinopathy in the mouse retina.
OBJECTIVE
The ability of microglial cells (MG) and macrophages (MAC) to release cytokines, induce apoptosis, as well as perform phagocytic functions suggests a possible role in wound healing following oxygen-induced injury. This study was performed to determine the temporal and spatial expression of F4/80 (F4/80+) positive microglia/macrophages (MG/MAC) in areas of retinal damage in the mouse model of oxygen-induced retinopathy.


METHODS
C57BL/6 postnatal day 7 (P7) mice were exposed to 75% O2 for 5 days (P12) then allowed to recover in room air. Hyperoxia-exposed (O2) mice (O2 refers to hyperoxia exposure from P7 to P12 only) were sacrificed on P12, P14, P17, and P21 and their eyes were examined. Localization of F4/80+ cells in FITC-dextran-perfused retinas allowed coordinate visualization of retinal vessels and MG/MAC via fluorescence microscopy. BrdU, a cellular proliferation marker, was injected intraperitoneally 1 h prior to sacrifice. Immunostaining was performed for a microglia and macrophage-specific antigen (F4/80) and BrdU. CCL2 (monocyte chemoattractant protein-1; MCP-1) expression was examined by quantitative real time reverse transcriptase polymerase chain reaction (RT-PCR).


RESULTS
There was a marked increase (>500%) in MG/MAC in hyperoxia-exposed retinas on P17O2 and P21O2 compared to control retinas. At P17O2, MG/MAC were localized in areas of neovascularization (NV), revealing an intimate relationship between MG/MAC and neovascular tufts. However, P21O2 retinas demonstrated MG/MAC associated with avascular regions in the outer layers of the retina. Immunostaining for F4/80 and BrdU revealed rare co-localization in hyperoxia-exposed retinas. Real time RT-PCR results demonstrated increased expression of CCL2 in P14O2- and P17O2- exposed retinas.


CONCLUSIONS
Our results suggest that resident retinal microglia proliferation occurs at a low frequency in response to injury in this model. The substantial increase in total F4/80+ cells in hyperoxia-exposed retinas in conjunction with the upregulation of CCL2 is consistent with recruitment of hematogenous macrophages into the retina. The temporal and spatial localization of MG/MAC adjacent to neovascular tufts suggests these cells are modulating the retinal response to ischemia-induced retinopathy.
Davies
Michael H
MH
Department of Pediatrics, Casey Eye Institute, Oregon Health and Science University, Portland, OR 97239, USA.
Eubanks
Joshua P
JP
Powers
Michael R
MR
D000818:Animals; D000831:Animals, Newborn; D000943:Antigens, Differentiation / Q000378:metabolism; D049109:Cell Proliferation; D018932:Chemokine CCL2 / Q000235:genetics / Q000378:metabolism; D007511:Ischemia / Q000150:complications*; D008264:Macrophages / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000378:metabolism / Q000473:pathology*; D018919:Neovascularization, Physiologic; D010100:Oxygen; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000378:metabolism / Q000473:pathology; D012164:Retinal Diseases / Q000139:chemically induced / Q000209:etiology* / Q000473:pathology* / Q000503:physiopathology; D012171:Retinal Vessels; D013997:Time Factors; D014018:Tissue Distribution; D015854:Up-Regulation
D000943:Antigens, Differentiation; C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D012333:RNA, Messenger; C036763:monocyte-macrophage differentiation antigen; D010100:Oxygen