Molecular taxonomy of human ocular outflow tissues defined by single cell transcriptomics

Abstract

The conventional outflow pathway is a complex tissue responsible for maintaining intraocular pressure (IOP) homeostasis. The coordinated effort of multiple cells with differing responsibilities ensure healthy outflow function and IOP maintenance. Dysfunction of one or more resident cell type results in ocular hypertension and risk for glaucoma, a leading cause of blindness. In this study, single cell RNA sequencing was performed to generate a comprehensive cell atlas of human conventional outflow tissues. We obtained 17757 genes expression profiles from 8758 cells from eight eyes of four donors representing the outflow cell transcriptome. Upon clustering analysis, 12 distinct cell types were identified, and region-specific expression of candidate genes were mapped in human tissues. Significantly, we identified two distinct expression patterns (myofibroblast and fibroblast) from cells located in the trabecular meshwork (TM), the primary structural component of the conventional outflow pathway. We also located neuron and macrophage signatures in the TM.The second primary component structure, Schlemm's canal displayed a unique combination of lymphatic/blood vascular gene expression. Other expression clusters corresponded to cells from neighboring tissues, predominantly in the ciliary muscle/scleral spur, which together correspond to the uveoscleral outflow path. Importantly, the utility of our atlas was demonstrated by mapping glaucomarelevant genes to outflow cell clusters. Our study provides a comprehensive molecular and cellular classification of conventional and unconventional outflow pathway structures responsible for IOP homeostasis. Significance statementOcular hypertension is the primary, and only modifiable risk factor for glaucoma, the leading cause of irreversible blindness. Intraocular pressure is regulated homeostatically by resistance to aqueous humor outflow through an architecturally complex tissue, the conventional/trabecular pathway. In this study, we generated a comprehensive cell atlas of the human trabecular meshwork and neighboring tissues using single cell, RNA sequencing. We identified 12 distinct cell types, and mapped regionspecific expression of candidate genes. The utility of our atlas was demonstrated by mapping glaucoma-relevant genes to conventional outflow cell clusters. Our study provides a comprehensive molecular and cellular classification of tissue structures responsible for intraocular pressure homeostasis in health, and dysregulation in disease.