SINGLE CELL ATLAS OF THE ADULT LACRIMAL GLAND UNCOVERS CELLULAR COMPLEXITY, PROGENITOR-LIKE CELLS AND SEXUAL DIMORPHISM

Abstract

Purpose : The lacrimal gland (LG) secretes the aqueous layer of the tear film. Lineage tracing and single cell RNA-sequencing (scRNA-seq) experiments on the developing mouse LG have provided insights into the cell lineage relationships during embryogenesis and postnatal development. However, little is known about the cell types composing the adult LG and their progenitors. Using scRNA-seq, we established a comprehensive cell atlas of the adult mouse LG to investigate cell hierarchy, their secretory repertoire and sex differences.

Methods : Using the 10X platform, we generated scRNA-seq data of LGs from nine 2 months old C57BL/6J mice (7056 female and 9216 male LG cells). Unsupervised clustering and gene expression analysis were done with R/Seurat. Immunostaining and fluorescent reporter mice were used for validation. To connect our findings with sex-biased tear composition, we used the published data on the mouse tear proteome.

Results : The epithelial compartment recapitulated known subtypes: myoepithelial, acinar and ductal cells. Epithelium subclustering identified two main clusters of mature acinar cells, and two novel acinar subpopulations identified by high expression of Tfrc (transferrin receptor) and Car6 (carbonic anhydrase 6), respectively. The ductal compartment contained basal and luminal ductal cells, and a cluster marked by Ltf (lactoferrin) composed of luminal cells, intercalated duct cells, and an Aldh1a1+ subpopulation reminiscent of pancreatic centroacinar/terminal duct cells. Kit-expressing cells were mainly found in the Ltf+ and the Car6^high clusters, suggesting that they may contain acinar and ductal progenitors. Comparison of our data with the tear proteome showed that acinar cells synthesize lipocalins like female-specific Obp1b and male-specific Mup4, but also many male-biased androgen-binding secretoglobins, while ductal cells secrete male-biased antimicrobial LTF. In addition, analysis of the LG stromal cells identified multiple clusters of vascular cells (pericytes and endothelial cells), fibroblasts, and of resident lymphoid and myeloid cell populations.

Conclusions : We identified subpopulations previously uncharacterized and putative epithelial progenitors for the ductal and acinar compartments. Moreover, our study improves our understanding of LG function by identifying the cell types responsible for the secretion of major and sex-biased tear products.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.