The Roles of Cell Proliferation and Cell Death in Regeneration of Salivary Glands

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【Introduction】The present research aimed to clarify the proliferation and apoptosis of parenchymal cells such as acinar, duct, myoepithelial cells during regeneration of rat salivary glands following atrophy induced by duct ligation.【Methods】Atrophy of the right submandibular gland was induced by excretory duct ligation near its hilum with metal clips, which were removed one week (day 0) after ligation. The right submandibular glands were collected from 0 to day 14 after removal of clips and investigated with PCNA as a marker of proliferating cells, TUNEL as a marker of apoptotic cells, actin-PCNA double immunohistochemistry as a marker of proliferating myoepithelial cells, and transmission electron microscopy.【Results】After one week of ligation, there were many remaining ducts and a few acini in the atrophic glands. At day 3 after discontinuing the ligation, newly formed acini appeared and thereafter increased in number and maturity. many residual and newly formed acinar cells showed positive reaction to PCNA especially at day 4 and 5. The PCNA-positive duct cells decreased in number with the regeneration. Double-positive cells, PCNA-positive myoepithelial cells were also observed, especially between days 2 and 4. A few TUNEL-positive acinar and duct cells were identified during regeneration. Some mitosis and a few apoptosis of acinar and duct cells were also identified by transmission electron microscopy. In addition, a mitotic figure of myoepithelial cell was first identified ultrastructurally.【Conclusions】During regeneration of the submandibular gland after atrophy, both residual and newly formed acinar cells proliferate actively. There is also apoptosis of duct and acinar cells, which participates in remodeling the structure of salivary gland tissue after parenchymal cell proliferation. In addition, it is confirmed that myoepithelial cells are able to proliferate and participate in the regeneration of salivary glands.