Ganoderma lucidum polysaccharides ameliorates D-galactose-induced aging salivary secretion disorders by upregulating the rhythm and aquaporins

Abstract

Longer-term deterioration in saliva secretion has been observed to occur in response to aging. The functional deterioration of the salivary gland damages swallowing and chewing abilities and consequently reduces life quality of the elderly. There are, however, only a few proven effective treatments for aging salivary secretion disorders. Ganoderma lucidum polysaccharide (GLP) has been applied to treat various diseases because of its safety, efficacy, and low cost. We investigated the protective effect of GLP on the submandibular gland (SMG) during aging. D-galactose (D-gal) was used to treat the aging mice, and the body weight, water consumption, saliva secretion, and flow rate were measured after 6 weeks of modeling. Micromorphological changes of the SMG were assessed by hematoxylin-eosin staining and transmission electron microscopy. RT-qPCR and Western blot were used to detect the expression of apoptotic proteins and inflammatory cytokines. Aquaporins (AQPs) and rhythmic protein expression were analyzed by immunohistochemistry and immunofluorescence. The results showed that GLP effectively promoted the expression of AQP5, AQP4, and AQP1, inhibited the release of TNF-α, IL-6, and Bax, and reduced inflammation and apoptosis. Further experiments showed that GLP promoted the up-regulation of core clock genes and proteins and restored the co-localized expression of CLOCK and AQP5 that were weakened during aging, helping to attenuate aging-induced weight loss, decreased salivation, and structural and functional damage. The findings of this work contribute to understanding the nature of age-related modifications in SMG by identifying changes in AQP5 expression and regulatory mechanisms linked to SMG dysfunction during aging. GLP is a potential drug for maintaining healthy salivary gland (SG) status and preventing SG deficiency in the elderly.