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. Single-cell RNAseq of BALB/cJ, MRL/MpJ-Fas(lpr/lpr), NOD.H2b lacrimal glands. Processed and annotated data can also be accessed at: https://jacobheng.shinyapps.io/lacrimal/

泪腺（lacrimal gland）在眼科学研究中具有核心地位，既是泪液水相成分的来源，也是干燥综合征（Sjogren’s syndrome, SjS）背景下自身免疫病理损伤的发生位点。为系统性解析小鼠泪腺的细胞类型及其基因表达模式，我们对野生型（Balb/c）小鼠以及两种遗传型干燥综合征模型小鼠——MRL/lpr与NOD.H2b（非肥胖糖尿病，nonobese diabetic）的单细胞转录组（single-cell transcriptomes）进行了分析，并明确了多种细胞类型特异性蛋白及mRNA标志物的定位。本研究揭示了一种此前未被报道的细胞类型——Car6+细胞，该细胞群分布于腺泡与连接导管的交界处。腺泡细胞表达十余种可能作为泪液组成成分的分泌多肽，且其表达存在显著的性别差异。此外，本研究还鉴定出单一细胞类型内基因表达异质性的多个实例，包括沿导管系统全长分布的紧密连接蛋白4（Claudin4）表达梯度，以及腺泡细胞与肌上皮细胞中转录因子表达的细胞间异质性。腺泡细胞、Car6+细胞与导管细胞中离子通道、转运蛋白及泵蛋白的表达模式，为水与电解质分泌的机制提供了强有力的预测依据。在MRL/lpr与NOD.H2b小鼠的泪腺中，实质细胞基因表达与免疫细胞亚群均出现特征性改变：MRL/lpr模型呈现广泛的干扰素应答以及以T细胞为主的免疫浸润，而NOD.H2b模型则存在混合的B细胞与T细胞浸润。本研究对BALB/cJ、MRL/MpJ-Fas(lpr/lpr)、NOD.H2b小鼠的泪腺开展了单细胞RNA测序（single-cell RNA-seq）。经处理与注释的数据集亦可通过以下链接获取：https://jacobheng.shinyapps.io/lacrimal/