Dec1 DEFICIENCY RESTORES THE AGE-RELATED DYSFUNCTIONS OF SUBMANDIBULAR GLANDS

Age-related organ and tissue-specific cell kinetic and morphological alterations are associated with the incidence of numerous diseases in old age. Salivary dysfunction frequently appears in a wide range of older people and thus is a physiological and biological aspect of aging. The transcription factor Dec1 (differentiated embryo chondrocyte expressed gene 1) is essential for the regulation of cellular senescence. Here, we explored the morphological and physiological abnormalities and the microRNA (miRNA) expression profiles in the submandibular glands (SMGs) of young (3-month-old) and of aged (24-month-old) wild-type (WT) and Dec1KO mice. Hematoxylin-eosin (H-E) staining, Masson's Trichrome staining, immunohistochemistry, immunofluorescence, and quantitative real time PCR were employed. MicroRNA (miRNA) expression profiles were examined using an Agilent system with a Mouse 8x60K array. Immunohistochemical analysis revealed an increased oxidative stress response (8-OHdG), increased expression levels of type I collagen in the fibrotic tissues with substantial amounts of fibroblasts and collagen fibers, the presence of CCl-22-positive lymphocytes infiltrating the SMGs of aged WT mice and a subsequently enhanced expression of fibrosis-associated gene (MMP-2) in the aged SMGs. The water channel protein aquaporin-5 (AQP5) was expressed in the basal cytoplasmic regions of acini in young SMGs but showed a decreased expression in aged SMGs. Myoepithelial cell markers (p63 immunoreactivity and alpha-SMA immunofluorescence staining) were also decreased in aged SMGs. Quantitative real-time PCR revealed decreased mRNA expression levels of AQP5 and increased mRNA expression levels of Dec1 in aged WT mice. All those characteristics were attenuated in aged Dec1KO mice. There were no apparent differences between young WT and Dec1KO mice. Of the miRNAs analyzed, miR-181c-5p, miR-141-3p, miR-374c-5p and miR-466i-3p are proposed regulatory targets of Dec1 and AQP5 genes that are involved in SMG dysfunction in aged mice. We suggest that a Dec1 deficiency might alleviate the aging-induced hypofunction of SMGs and relevant alterations of Dec1 would be useful to keep SMGs healthy. This study provides clues for determining unique microRNAs concerned with SMG dysfunction. Subsequent activation of such diversely expressed miRNAs be of great value in clarifying the nature of age-related alterations in SMGs.