Single-cell transcriptomics of the human retinal pigment epithelium and choroid in health and macular degeneration

Significance The retinal pigment epithelium and the choroid are complex tissues whose dysfunction can lead to irreversible visual loss. In this study, single-cell RNA sequencing of both of these tissues was performed to characterize gene expression patterns specific to the retinal pigment epithelium and all major choroidal cell populations. Unique gene expression signatures of arterial, venous, and choriocapillaris vascular beds within the choroid were identified. RGCC, a gene that responds to complement and has been shown to induce endothelial apoptosis, was specifically expressed in choriocapillaris endothelial cells. This study provides potential insight into the molecular mechanisms of choroidal vascular disease and its contribution to age-related macular degeneration. The human retinal pigment epithelium (RPE) and choroid are complex tissues that provide crucial support to the retina. Disease affecting either of these supportive tissues can lead to irreversible blindness in the setting of age-related macular degeneration. In this study, single-cell RNA sequencing was performed on macular and peripheral regions of RPE-choroid from 7 human donor eyes in 2 independent experiments. In the first experiment, total RPE/choroid preparations were evaluated and expression profiles specific to RPE and major choroidal cell populations were identified. As choroidal endothelial cells represent a minority of the total RPE/choroidal cell population but are strongly implicated in age-related macular degeneration (AMD) pathogenesis, a second single-cell RNA-sequencing experiment was performed using endothelial cells enriched by magnetic separation. In this second study, we identified gene expression signatures along the choroidal vascular tree, classifying the transcriptome of human choriocapillaris, arterial, and venous endothelial cells. We found that the choriocapillaris highly and specifically expresses the regulator of cell cycle gene (RGCC), a gene that responds to complement activation and induces apoptosis in endothelial cells. In addition, RGCC was the most up-regulated choriocapillaris gene in a donor diagnosed with AMD. These results provide a characterization of the human RPE and choriocapillaris transcriptome, offering potential insight into the mechanisms of choriocapillaris response to complement injury and choroidal vascular disease in age-related macular degeneration.

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