Temporospatial distribution and transcriptional profile of retinal microglia in the oxygen-induced retinopathy mouse model.

Myeloid cells such as resident retinal microglia (MG) or infiltrating blood-derived macrophages (Mϕ) accumulate in areas of retinal ischemia and neovascularization (RNV) and modulate neovascular eye disease. Their temporospatial distribution and biological function in this process, however, remain unclarified. Using state-of-the-art methods, including cell-specific reporter mice and high-throughput RNA sequencing (RNA Seq), this study determined the extent of MG proliferation and Mϕ infiltration in areas with retinal ischemia and RNV in Cx3cr1CreERT2 :Rosa26-tdTomato mice and examined the transcriptional profile of MG in the mouse model of oxygen-induced retinopathy (OIR). For RNA Seq, tdTomato-positive retinal MG were sorted by flow cytometry followed by Gene ontology (GO) cluster analysis. Furthermore, intraperitoneal injections of the cell proliferation marker 5-ethynyl-2'-deoxyuridine (EdU) were performed from postnatal day (p) 12 to p16. We found that MG is the predominant myeloid cell population while Mϕ rarely appears in areas of RNV. Thirty percent of retinal MG in areas of RNV were EdU-positive indicating a considerable local MG cell expansion. GO cluster analysis revealed an enrichment of clusters related to cell division, tubulin binding, ATPase activity, protein kinase regulatory activity, and chemokine receptor binding in MG in the OIR model compared to untreated controls. In conclusion, activated retinal MG alter their transcriptional profile, exhibit considerable proliferative ability and are by far the most frequent myeloid cell population in areas of ischemia and RNV in the OIR model thus presenting a potential target for future therapeutic approaches.