Examination of age-related changes in the submandibular glands of male mice

Salivary gland hypofunction adversely affects the oral environment and daily life by causing dry mouth (xerostomia). Senescence-related atrophy of salivary gland tissues is one cause of xerostomia, and it is particularly common among the elderly. However, the underlying mechanism is poorly understood, and no treatment has been established. Therefore, we examined age-related changes in senescence-associated secretory phenotype (SASP) factors, which regulate stemness and cellular senescence, in mouse submandibular glands. We analyzed the submandibular glands of 6-week-old (young group, n = 6) and 82-week-old mice (aged group, n = 6). We performed salivary flow rate measurements, histological analysis including immunohistochemistry, and quantitative real-time PCR. The salivary flow rate was significantly lower in the aged group than in the young group. In addition, immunostaining and quantitative real-time PCR illustrated that aquaporin-5 and α-amylase expressions were significantly decreased in aged mice, indicating salivary gland hypofunction. c-Kit and cytokeratin 5 expressions were also significantly decreased in this group, suggesting that the regenerative abilities of the submandibular glands were reduced because of decreased stem and progenitor cell counts. Furthermore, the levels of p16^INK4a and p21 (the senescence markers) and TGF-β1 and IL-6 (SASP factors) were significantly increased in mice, suggesting that senescence had been promoted. The decreased numbers of stem and progenitor cells and increased levels of SASP factors might be associated with age-related changes in mouse submandibular glands. These results might facilitate the development of treatments for senescence-related submandibular gland hypofunction.