Regenerative Capacity of Atrophic Submandibular Gland by Duct Ligation in Mice

Abstract

Function degeneracy of the salivary gland leads to reduced protection against infection and reduced physiological function of the oral cavity, considerably diminishing the patient’s quality of life. However, no method of treatment has yet been established to recover the secretory capacity of the salivary gland reduced by the degeneration or disappearance of the gland tissue. Ongoing salivary gland regeneration experiments using cell transplantation aim to introduce clinical regenerative treatment for the salivary gland. Because it is essential to understand the self-regenerative capacity that remains in the recipient’s salivary gland, it is essential to search for optimal conditions for transplantation and establish a salivary gland atrophy model. In this context, we performed duct ligation of the submandibular gland in groups of mice for 7-, 14-, and 21-day ligation periods, compared immunohistochemical staining using acinar cell and stem cell markers, detected apoptosis using TUNEL staining, and analyzed gene expression using RT-PCR to search for the expression of factors related to regenerative capacity that remain in the atrophic salivary gland. All 3 periods of ligation led to remarkable atrophy/disappearance of acinar cells and the dominant presence of duct-like structures. These structures expressed stem cell markers most intensively after 14 days of ligation, and double immunostaining revealed the expressions of PSCA and c-Kit that coincided with them. AQP5 expression was detected in acinar cells and the apical membrane of the intercalated ducts in the normal submandibular gland and was also detected after 21 days of ligation in the remnant acinar cells and intercalated ducts. Conversely, the number of TUNEL-positive apoptotic cells in the atrophic salivary gland was highest after 7 days of ligation. These results showed that the duct-like structures that exist after ligation expressed stem cell markers and AQP5, indicating the presence of a mechanism related to the regeneration of salivary gland tissue.