Single-Cell Analysis Explains Differences Between Lacrimal and Submandibular Gland Structure and Function

Abstract

Purpose : Both lacrimal (LG) and submandibular (SMG) glands secrete fluids that protect mucosal membranes, but saliva is related to digestion, while the LG provides multiple components to the tear film that sustains the ocular surface. Both glands are also affected by aging and Sjögren’s syndrome although they respond differently to stress, injury, and disease. We compared cell types between LG and SMG at single-cell resolution for better understanding the specific features and function of these two glands.

Methods : For LG dataset, we performed scRNA sequencing of 2 months old (2M) C57BL/6J mice (males and females). For SMG dataset we used publicly available data from GSE175649 and GSE150327. All data were analyzed with SEURAT v4 using R Studio (v1.4) software.

Results : Principal component analysis (PCA) and Uniform Manifold Approximation and Projection (UMAP) identified 12 main cell clusters that were further sub-clustered to determine specific cell types/populations. As expected within ductal compartments we identified three SMG-unique ductal clusters that were not present in the LG: granular ducts (GCT) containing recently identified ionocytes (expressing Foxi1, Ascl3 and Fgf10) and two striated cell ductal clusters: Klk1+/Egf+ also containing ionocytes, and Klk1+/Egf- cluster. Cftr (that we previously showed as mainly expressed by ionocytes) was found in the GCT cluster and the Egf+ striated duct cluster. Both glands have basal ductal cell clusters with slightly different gene expression and Kit+ intercalated ducts . Both glands also shared two acinar clusters: one enriched in secretoglobins and another Pigr+/Kcnn4+ that was also enriched in Aqp5 and Bhlha15, while LG also had two more unique acinar clusters. One other striking difference was that in the SMG Car6 was expressed at higher level in a large population of mature acinar cells, while in the LG the Car6^high cells also formed a small cluster of putative committed acinar progenitors. In addition, only LG had a cluster of Fgf10+ fibroblasts.

Conclusions : Our data outlines common and unique features in LG and SMG functions that may explain differences in ECM deposition and organization between the two glands.

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