Mitochondrial-impaired ductal epithelium fuels TLS formation in Sjögren's disease.

Abstract

Progressive inflammatory cell infiltration within salivary glands is a defining feature of advanced Sjögren's disease (SjD) and is frequently accompanied by tertiary lymphoid structure (TLS) formation. However, the initial events driving this pathogenic trait in SjD progression are not fully understood. We collected 848 labial salivary gland (LSG) biopsies (668 SjD, 180 non-SjD) and profiled bulk transcriptomics, single cell RNA-sequencing (scRNA-seq), spatial transcriptomics, transmission electron microscopy (TEM), and histology. In vivo functional validation was performed in NOD/ShiLtj mice with spontaneous SjD via nicotinamide mononucleotide administration to restore mitochondrial function. Mitochondrial function was impaired in LSG tissues from SjD patients, with functional validation in NOD/ShiLtj mice showing attenuated ductal injury and reduced immune cell infiltration. scRNA-seq analyses revealed that each LSG cellular subset harbours a distinct mitochondrial transcriptional profile, which we identified here as a molecular fingerprint for individual cellular subsets. TEM established an ultrastructural atlas of human minor salivary glands, showing that striated duct (SD) cells are most enriched with mitochondria among all epithelial subtypes. In SjD LSGs, particularly those with TLSs, profound mitochondrial dysfunction and impaired oxidative phosphorylation were observed. A previously unrecognized proinflammatory SD subset, SD-C1 (marked by matrix metalloproteinase 7), was markedly expanded in SjD-TLS+ tissues and exhibited severe mitochondrial impairment. SD-C1 cells showed enhanced crosstalk with T cells, B cells, and macrophages via immune signalling pathways and were spatially colocalized with immune cell aggregates in periductal regions where TLSs formed. Mitochondrial injury in SD epithelial cells emerges as a trigger of TLS formation and progressive autoimmunity in SjD. Therapies that preserve mitochondrial integrity and functionality in ductal cells may mitigate salivary gland degeneration during SjD progression.