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Single Cell Transcriptomics Identifies Distinct Choroid Cell Populations Involved in Visually Guided Eye Growth

ABSTRACT: Postnatal ocular growth is regulated by a vision-dependent mechanism, termed emmetropization, which acts to minimize refractive error through coordinated growth of the ocular tissues. Many studies suggest that the ocular choroid participates in the emmetropization process via the production of scleral growth regulators that control ocular elongation and refractive development. To elucidate the role of the choroid in emmetropization, we used single-cell RNA sequencing (scRNA-seq) to characterize the cell populations in the chick choroid and compare gene expression changes in these cell populations during conditions in which the eye is undergoing emmetropization. UMAP clustering analysis identified 24 distinct cell clusters in all chick choroids. 7 clusters were identified as fibroblast subpopulations; 5 clusters represented different populations of endothelial cells; 4 clusters were CD45+ macrophages, T cells and B cells; 3 clusters were Schwann cell subpopulations; and 2 clusters were identified as melanocytes. Additionally, single populations of RBCs, plasma cells and neuronal cells were identified. Significant changes in gene expression between control and treated choroids were identified in 17 cell clusters, representing 95% of total choroidal cells. The majority of significant gene expression changes were relatively small (< 2 fold). The highest changes in gene expression were identified in a rare cell population (0.11% - 0.49% of total choroidal cells). This cell population expressed high levels of neuron-specific genes as well as several opsin genes suggestive of a rare neuronal cell population that is potentially light sensitive. Our results, for the first time, provide a comprehensive profile of the major choroidal cell types and their gene expression changes during the process of emmetropization as well as insights into the canonical pathways and upstream regulators that coordinate postnatal ocular growth.

ORGANISM(S): Gallus gallus

PROVIDER: GSE235684 | GEO | 2023/09/05

REPOSITORIES: GEO

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Project description:Purpose: The goals of this study were to identify cell specific expression patterns of the retinal pigment epithelium (RPE) and a variety of choroidal cell types originating from the macula and the periphery of human donor eyes, with a particular emphasis on identifying expression signatures of choroidal endothelial cells. Methods: Independent libraries were prepared for macular and peripheral samples of combined RPE/choroid from seven donors in two single cell sequencing experiments. In the first experiment, 8-mm macular and peripheral punches of RPE/choroid from Donors 1-3 were digested in papain prior to cryopreservation and subsequent GEM barcoding/library construction. Donors 1-2 had no noted ophthalmologic disease documented, while Donor 3 was diagnosed with age-related macular degeneration. In the second experiment, 12-mm macular and peripheral punches of RPE/choroid from Donors 4-7 were digested in collagenase II prior to cryopreservation, CD31-magentic bead enrichment and subsequent GEM barcoding/library construction. Donors 5-7 had no noted ophthalmologic disease documented, while Donor 4 was diagnosed with age-related macular degeneration. In both experiments, libraries were sequenced on a HiSeq4000. Sequenced reads were mapped to the human genome build hg19 will CellRanger(v3.0.1) and filters removed cells likely to be doublets or cells with a high proportion of mitochondrial reads. Clustering of cells with similar expression profiles was performed with Seurat (v3.0.2). Results: In the first experiment with unenriched RPE/choroid from donors 1-3, we recovered 4,355 cells post filtering with 40,177,477 corresponding reads. A total of 2,167 cells originated from the macula and 2,168 cells originated from the periphery. A total of 11 clusters were identified, and highly enriched genes in each cluster were used to classify clusters into their presumed dominant cell type. Differential expression analysis was performed between cells of macular and peripheral origin in each cluster and between donors with and without a history of age-related macular degeneration. Results: In the second experiment with CD31-enriched RPE/choroid from donors 4-7, we recovered 14,234 cells post filtering with 135,742,297 corresponding reads. A total of 7,647 cells originated from the macula and 6,587 cells originated from the periphery. A total of 8,521 of these cells were presumed endothelial cells. A total of 13 clusters were identified, and highly enriched genes in each cluster were used to classify clusters into their presumed dominant cell type(s). Differential expression analysis was performed between cells of macular and peripheral origin in each cluster and between donors with and without a history of age-related macular degeneration. Within each of the endothelial clusters (Clusters 5-8), differential expression analysis was performed between each cluster and the remaining endothelial cells. Conclusions: This study provides a large atlas of single-cell level gene expression patterns of the human retinal pigment epithelium and choroidal cell types. We identify expression patterns of most expected choroidal cell populations and describe macular versus peripheral regional differences. We additionally identify enriched transcripts in specific cell populations in age-related macular degeneration. We characterize gene expression patterns along the choroidal vascular tree, and identify populations of arterial, capillary, and venous endothelial cells. Our results show that single-cell sequencing can be performed on human RPE/choroid after cryopreservation, and that CD31 magnetic bead enrichment can be employed to enrich for endothelial cells for single-cell sequencing.

Project description:The choroid is the vascular layer situated between the outer sclera and the inner retina. Together with the ciliary body and the iris it forms the uvea. Because of its rich blood supply it is also called the nutritive layer and it supplies oxygen and nutrition to the retinal pigment epithelium and the outer retina. Due to its vascular nature it acts as a heat sink and helps in thermoregulation within the eye. It also contains a pigment “melanin”, which absorbs excess light within the eye and prevents scattering. . The human choroid is thickest posteriorly where it measures 0.2 mm, whereas anteriorly it measures 0.1 mm.. The aim of this study was to characterize the choroid proteome to generate a resource for future studies on the choroid . The method used in this study combined bRPLC and LC-MS/MS analysis of the proteins isolated from the three cadaver samples of healthy donors. Subsequently, we classified the proteins based on gene ontology and pathway analysis. A total of 5,249 non redundant proteins were identified in the human choroid. Gene ontology classification pinpointed proteins involved in protein metabolism, regulation of nucleobase, nucleoside, nucleotide and nucleic acid metabolism, transport, cell growth and/or maintenance and immune response. Several proteins identified in normal choroid have previously been identified in human choroid where these proteins are related to glaucoma, ocular inflammation, toxoplasmic retinochoroiditis, diabetic retinopathy, open-angle glaucoma and Grave’s disease. The top canonical pathway in which the choroid proteins participated are EIF2 signaling, integrin signalling, mitochondrial dysfunction, regulation of eIF4 and p70S6K signaling and clathrin-mediated endocytosis signalling. Around 800 choroid proteins were related to infectious diseases. The results of this study illustrate the largest number of proteins identified in human choroid and may serve as a valuable resource for future investigations of choroid biology and disease. Proteomic analysis of choroid proteins could provide versatile information to understand choroidal functions and the underlying pathogenesis of choroidal pathologies.

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Single Cell Transcriptomics Identifies Distinct Choroid Cell Populations Involved in Visually Guided Eye Growth

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