Contribution of Interleukin-4-Induced Epithelial Cell Senescence to Glandular Fibrosis in IgG4-Related Sialadenitis

IgG4-related sialadenitis (IgG4-RS) is a chronic fibroinflammatory disease characterized by glandular fibrosis and hyposalivation. This study was undertaken to explore the role of cellular senescence in the pathogenesis of IgG4-RS-related fibrosis.

The expression of senescence markers and proinflammatory cytokines in the submandibular glands (SMGs) of IgG4-RS patients (n = 18) and controls (n = 14) was determined by proteomics, real-time polymerase chain reaction, Western blotting, and immunohistochemistry. After interleukin-4 (IL-4) treatment, high-throughput RNA sequencing was performed to identify the differentially expressed genes in SMG-C6 cells. A glandular fibrosis model was established by the intraglandular injection of IL-4 into mouse SMGs (n = 8 per group).

Salivary acinar and ductal epithelial cells underwent senescence in IgG4-RS patients, as indicated by the elevated activity of senescence-associated β-galactosidase, lipofuscin accumulation, enhanced expression of senescence markers (p53 and p16^INK4A ), and up-regulation of senescence-associated secretory phenotype factors. Moreover, there was a significant increase in IL-4 levels in SMGs from IgG4-RS patients (P < 0.01), which positively correlated with p16^INK4A expression and the fibrosis score. Incubation with IL-4 exacerbated salivary epithelial cell senescence by increasing the expression of p16^INK4A through the reactive oxygen species (ROS)/p38 MAPK pathway. Supernatant collected from IL-4-induced senescent SMG-C6 cells enhanced fibroblast activation and matrix protein production (P < 0.05). Furthermore, injecting mice with IL-4 promoted fibrosis and senescence phenotypes in SMGs in vivo.

The cellular senescence induced by IL-4 through the ROS/p38 MAPK-p16^INK4A pathway promotes fibrogenesis in IgG4-RS. Our data suggest that cellular senescence could serve as a novel therapeutic target for treating IgG4-RS.