The First Transcriptomic Atlas of the Adult Lacrimal Gland Reveals Epithelial Complexity and Identifies Novel Progenitor Cells in Mice

Distinctive small molecules blend: Promotes lacrimal gland epithelial cell proliferation in vitro and accelerates lacrimal gland injury repair in vivo

PURPOSE

This study aims to develop a novel serum-free culture strategy containing only two small molecules, Y27632 and SB431542 (2C), for in vitro expansion of mouse lacrimal gland epithelial cells (LGECs) and investigate an innovative therapeutic approach for lacrimal gland (LG) injury.

METHODS

LGECs proliferative capacity was assessed by cell counting, crystal violet staining, qRT-PCR and immunofluorescence. Cell differentiation was achieved by manipulating culture conditions and assessed by qRT-PCR and AQP5 immunofluorescence. LGECs were seeded in Matrigel for three-dimensional culture and assessed by qRT-PCR and immunofluorescence. Secretory function of the cultures was assayed by ELISA. In vivo, 2C injection verified its reparative capacity in a mouse LG injury model. Corneal fluorescein staining, phenol red cotton thread, H&E, immunofluorescence and Western blot were used to assess LG injury repair.

RESULTS

LGECs cultured with 2C exhibited high expression of stemness/proliferation markers and maintained morphology and proliferative capacity even after the tenth passage. Removal of 2C was efficacious in achieving LGECs differentiation, characterized by the increased AQP5 expression and LTF secretion. 3D spheroids cultured with 2C demonstrated differentiation potential, forming microglandular structures containing multiple LG cell types with secretory functions after 2C removal. In vivo, 2C improved the structural integrity and function of the injured LG.

CONCLUSIONS

We present a small molecule combination, 2C, that promotes LGECs expansion and differentiation in vitro and accelerates LG injury repair in vivo. This approach has potential applications for providing a stable source of seed cells for tissue engineering applications, providing new sights for LG-related diseases treatment.

Single-cell RNA-sequencing reveals the transcriptional landscape of lacrimal gland in GVHD mouse model

PURPOSE

To investigate the global transcriptional landscape of lacrimal gland cell populations in the GVHD mouse model.

METHODS

Single-cell RNA sequencing and further bioinformatic analysis of dissociated lacrimal gland (LG) cells from the mouse model were performed. Parts of transcriptional results were confirmed by immunofluorescence staining.

RESULTS

We identified 23 cell populations belonging to 11 cell types. In GVHD LG, the proportion of acinar cells, myoepithelial cells, and endothelial cells was remarkably decreased, while T cells and macrophages were significantly expanded. Gene expression analysis indicated decreased secretion function, extracellular matrix (ECM) synthesis, and increased chemokines of myoepithelial cells. A newly described epithelial population named Lrg1high epithelial cells, expressing distinct gene signatures, was exclusively identified in GVHD LG. The fibroblasts exhibited an inflammation gene pattern. The gene pattern of endothelial cells suggested an increased ability to recruit immune cells and damaged cell-cell junctions. T cells were mainly comprised of Th2 cells and effective memory CD8+ T cells. GVHD macrophages exhibited a Th2 cell-linked pattern.

CONCLUSIONS

This single-cell atlas uncovered alterations of proportion and gene expression patterns of cell populations and constructed cell-cell communication networks of GVHD LG. These data may provide some new insight into understanding the development of ocular GVHD.

Crk mediates Csk-Hippo signaling independently of Yap tyrosine phosphorylation to induce cell extrusion

Src family kinases (SFKs), including Src, Fyn and Yes, play important roles in development and cancer. Despite being first discovered as the Yes-associated protein, the regulation of Yap by SFKs remains poorly understood. Here, through single-cell analysis and genetic lineage tracing, we show that the pan-epithelial ablation of C-terminal Src kinase (Csk) in the lacrimal gland unleashes broad Src signaling but specifically causes extrusion and apoptosis of acinar progenitors at a time when they are shielded by myoepithelial cells from the basement membrane. Csk mutants can be phenocopied by constitutively active Yap and rescued by deleting Yap or Taz, indicating a significant functional overlap between Src and Yap signaling. Although Src-induced tyrosine phosphorylation has long been believed to regulate Yap activity, we find that mutating these tyrosine residues in both Yap and Taz fails to perturb mouse development or alleviate the Csk lacrimal gland phenotype. In contrast, Yap loses Hippo signaling-dependent serine phosphorylation and translocates into the nucleus in Csk mutants. Further chemical genetics studies demonstrate that acute inhibition of Csk enhances Crk/CrkL phosphorylation and Rac1 activity, whereas removing Crk/CrkL or Rac1/Rap1 ameliorates the Csk mutant phenotype. These results show that Src controls Hippo-Yap signaling through the Crk/CrkL-Rac/Rap axis to promote cell extrusion.

Analysis of the heterogeneity and complexity of murine extraorbital lacrimal gland via single-cell RNA sequencing

PURPOSE

The lacrimal gland is essential for maintaining ocular surface health and avoiding external damage by secreting an aqueous layer of the tear film. However, a healthy lacrimal gland's inventory of cell types and heterogeneity remains understudied.

METHODS

Here, 10X Genome-based single-cell RNA sequencing was used to generate an unbiased classification of cellular diversity in the extraorbital lacrimal gland (ELG) of C57BL/6J mice. From 43,850 high-quality cells, we produced an atlas of cell heterogeneity and defined cell types using classic marker genes. The possible functions of these cells were analyzed through bioinformatics analysis. Additionally, the CellChat was employed for a preliminary analysis of the cell-cell communication network in the ELG.

RESULTS

Over 37 subclasses of cells were identified, including seven types of glandular epithelial cells, three types of fibroblasts, ten types of myeloid-derived immune cells, at least eleven types of lymphoid-derived immune cells, and five types of vascular-associated cell subsets. The cell-cell communication network analysis revealed that fibroblasts and immune cells play a pivotal role in the dense intercellular communication network within the mouse ELG.

CONCLUSIONS

This study provides a comprehensive transcriptome atlas and related database of the mouse ELG.

Single-Nuclei Characterization of Lacrimal Gland in Scopolamine-Induced Dry Eye Disease

Purpose

The lacrimal gland (LG) is the main organ responsible for tear secretion and an important pathogenic site for dry eye disease (DED). This study aimed to comprehensively characterize LG cellular heterogeneity under normal and DED conditions using single-nucleus RNA sequencing (snRNA-seq).

Methods

Single LG nuclei isolated from mice with or without DED induced by scopolamine (SCOP)/desiccating stress (DS) were subjected to snRNA-seq using the 10x Genomics platform. These cells were clustered and annotated using the t-distributed stochastic neighbor embedding (t-SNE) method and unbiased computational informatic analysis. Cluster identification and functional analysis were performed based on marker gene expression and bioinformatic data mining.

Results

The snRNA-seq analysis of 30,351 nuclei identified eight major cell types, with acinar cells (∼72.6%) being the most abundant cell type in the LG. Subclustering analysis revealed that the LG mainly contained two acinar cell subtypes, two ductal cell subclusters, three myoepithelial cell (MECs) subtypes, and four immunocyte subclusters. In the SCOP-induced DED model, three major LG parenchymal cell types were significantly altered, characterized by a reduced proportion of acinar cells with a lowered secretion potential and an augmented proportion of ductal cells and MECs. LG immunocytes in DED scenarios showed an intensified inflammatory response and dysregulated intercellular communication with three major LG parenchymal cells.

Conclusions

Overall, this study offers a systemic single-nucleus transcriptomic profile of LGs in both normal and DED conditions and an atlas of the complicated interactions of immunocytes with major LG parenchymal cells. The findings also facilitate understanding the pathogenesis of DED.

Exploring Immune Cell Diversity in the Lacrimal Glands of Healthy Mice: A Single-Cell RNA-Sequencing Atlas

The lacrimal gland is responsible for maintaining the health of the ocular surface through the production of tears. However, our understanding of the immune system within the lacrimal gland is currently limited. Therefore, in this study, we utilized single-cell RNA sequencing and bioinformatic analysis to identify and analyze immune cells and molecules present in the lacrimal glands of normal mice. A total of 34,891 cells were obtained from the lacrimal glands of mice and classified into 18 distinct cell clusters using Seurat clustering. Within these cell populations, 26 different immune cell subpopulations were identified, including T cells, innate lymphocytes, macrophages, mast cells, dendritic cells, and B cells. Network analysis revealed complex cell-cell interactions between these immune cells, with particularly significant interactions observed among T cells, macrophages, plasma cells, and dendritic cells. Interestingly, T cells were found to be the main source of ligands for the Thy1 signaling pathway, while M2 macrophages were identified as the primary target of this pathway. Moreover, some of these immune cells were validated using immunohistological techniques. Collectively, these findings highlight the abundance and interactions of immune cells and provide valuable insights into the complexity of the lacrimal gland immune system and its relevance to associated diseases.

A closer look into the cellular and molecular biology of myoepithelial cells across various exocrine glands

Myoepithelial cells (MECs) are a unique subset of epithelial cells that possess several smooth muscle cell characteristics, such as a high number of actin-myosin filaments and the ability to contract. These cells are primarily located around the secretory cells of exocrine glands, including the salivary, mammary, lacrimal, and sweat glands. Their primary functions involve the construction of the basement membrane and help with secretion of gland products through contraction. So far, no comparative analysis of MECs in different exocrine glands had ever evaluated their differences. In this review, we took advantage of the various publicly available scRNAseq data from mouse exocrine glands to identify their shared and unique characteristics. The aim of this review is to compare the role of MECs in maintaining healthy glandular function, their involvement in disease states, and their regenerative capacity, with a particular emphasis on the latest research findings in these areas.

Normal and Sjogren's syndrome models of the murine lacrimal gland studied at single-cell resolution

The lacrimal gland is of central interest in ophthalmology both as the source of the aqueous component of tear fluid and as the site of autoimmune pathology in the context of Sjogren's syndrome (SjS). To provide a foundational description of mouse lacrimal gland cell types and their patterns of gene expression, we have analyzed single-cell transcriptomes from wild-type (Balb/c) mice and from two genetically based SjS models, MRL/lpr and NOD (nonobese diabetic).H2b, and defined the localization of multiple cell-type-specific protein and mRNA markers. This analysis has uncovered a previously undescribed cell type, Car6+ cells, which are located at the junction of the acini and the connecting ducts. More than a dozen secreted polypeptides that are likely to be components of tear fluid are expressed by acinar cells and show pronounced sex differences in expression. Additional examples of gene expression heterogeneity within a single cell type were identified, including a gradient of Claudin4 along the length of the ductal system and cell-to-cell heterogeneity in transcription factor expression within acinar and myoepithelial cells. The patterns of expression of channels, transporters, and pumps in acinar, Car6+, and ductal cells make strong predictions regarding the mechanisms of water and electrolyte secretion. In MRL/lpr and NOD.H2b lacrimal glands, distinctive changes in parenchymal gene expression and in immune cell subsets reveal widespread interferon responses, a T cell-dominated infiltrate in the MRL/lpr model, and a mixed B cell and T cell infiltrate in the NOD.H2b model.