Early senescence in salivary glands: A multimodal analysis across parotid, submandibular, and sublingual glands

OBJECTIVES: To elucidate the early-stage mechanisms of aging in salivary glands by focusing on the epigenetic regulator Jmjd3, proliferation marker proliferating cell nuclear antigen (PCNA), and senescence marker p16INK4a in adult and middle-aged mice of both sexes. METHODS: Male and female C57BL/6JJcl mice at 18 weeks (adult) and 48 weeks (middle-aged) of age (n ≥ 5 per group) were used. The parotid, submandibular, and sublingual glands were collected, weighed, and analyzed by histology (hematoxylin and eosin, Alcian blue, periodic acid-Schiff staining), immunohistochemistry (for Jmjd3, PCNA, and p16INK4a), quantitative image analysis, and real-time polymerase chain reaction. Statistical analysis was performed using analysis of variance or Kruskal-Wallis with appropriate post hoc tests (α = 0.05). RESULTS: Body weight increased with age, but the salivary gland weight relative to body weight remained unchanged. Histologically, at 48 weeks, the parotid and submandibular glands exhibited lymphocytic infiltration, whereas the sublingual glands did not. Jmjd3 was mainly localized in the acinar and striated duct cells and decreased with age in the parotid gland. PCNA-positive cells (acinar and ductal) were abundant at 18 weeks, but decreased after 48 weeks. p16INK4a expression increased from 18 to 48 weeks, with initial staining in ductal cells and extension to some acinar cells by 48 weeks. p16INK4a levels were higher in females than in males across all three glands. CONCLUSIONS: By middle age, salivary glands exhibit early senescent changes, senescent cell accumulation, altered proliferative capacity, and shifts in Jmjd3-mediated epigenetic regulation, which occur in parallel with histological changes.