Single-cell Transcriptome Analyses Reveal Unique Microglia Types Associated with Retinal Pathological Angiogenesis

We used single cell RNA-seq to comprehensively map all retinal microglia populations in a mouse model of oxygen-induced PR. We unveiled several unique types of PR-associated microglia (PRAM) and identified markers, signaling pathways, and regulons associated with these cells. Among these microglial subpopulations, we found a highly proliferative subset of cells with a high self-renewal capacity and a subset of cells with hypermetabolism that expresses high levels of activating microglia markers, glycolytic enzymes, and pro-angiogenic insulin-like growth factor 1. Immunohistochemical staining shows that PRAMs were spatially located within neovascular tufts. These unique microglial subtypes have the potential to promote retinal angiogenesis, which may have important implications for the future treatment of PR and other ocular diseases characterized by pathological angiogenesis. Overall design: The objective of this study was to investigate heterogeneity of mononuclear phagocytes (MPs) recruited to areas of neovascularization that drive aberrant retinal angiogenesis in proliferative retinopathies (PRs). We first generated a mouse model of oxygen-induced retinopathy (OIR). We collected retinas from OIR mice and control room air (RA) mice. We sorted out F4/80 and CD11b positive cells and performed scRNAseq of these cells. We identified two unique PR-associated microglia (PRAM) subtypes. We analyzed detailed gene signatures, signaling pathways, transcription factor regulons, transcriptional dynamics, and metabolic characteristics in PRAM. Further we unraveled the spatial location of PRAM adjacent to pathological neovascularization tufts by immunostaining mouse whole mounts of retinas with fluorescent antibodies. Collectively, our study provides a comprehensive perspective that defines the contributions of retinal microglia to PR at the single-cell level.