Wnt/beta-catenin Signaling Regulates Progenitor Cells and Regeneration of Salivary Gland

Methods: Wnt/beta-catenin signaling was visualized with BAT-gal Wnt reporter transgenic mice. Regeneration of submandibular gland (SMG) was induced by ligation of main secretory ducts. Epithelial Wnt signaling in adult salivary glands was inhibited in Keratin5-rtTA/tetO-Dkk1 mice or activated in Keratin5-rtTA/tetO-Cre/Ctnnb1(Ex3)fl mice upon doxycycline induction. Sca-1+/c-Kit+ salivary gland stem/progenitor cells were identified with immunohistochemistry and quantified by FACS.

Results: In SMG of newborn mice Wnt/beta-catenin signaling is active in a few cells at the basal layer of intercalated ducts, the putative location of salivary gland stem/progenitor cells. These Wnt-responsive cells disappeared gradually as mice grow up; however, during the regeneration of adult SMG after duct ligation, Wnt/beta-catenin signaling is remarkably activated in the ducts. Inhibition of epithelial Wnt/beta-catenin signaling in adult Keratin5-rtTA/tetO-Dkk1 mice impairs the homeostasis of SMG, probably via loss of duct-originated stem/progenitor cells. Conversely, forced activation of epithelial Wnt/beta-catenin signaling in adult Keratin5-rtTA/tetO-Cre/Ctnnb1(Ex3)fl mice promotes proliferation of ductal cells and expands the salivary gland stem/progenitor cell compartment; meanwhile, the expression of Sonic Hedgehog, an essential signaling molecule for embryonic development of salivary gland, is ectopically activated.

Conclusion: Wnt/beta-catenin signaling regulates the activity of salivary gland stem/progenitor cells during homeostasis and regeneration, thus modulating Wnt/beta-catenin and/or Hedgehog signal pathways may be potential approaches for functional restoration of salivary gland after irradiation.

This work is supported by NIH/NIDCR grant 1RC1DE020595-01.