Modulating Wnt-Hedgehog Signaling to Protect/Restore Salivary Glands Function after Radiation

Objectives: Many head-and-neck cancer survivors treated with radiotherapy suffer from permanent impairment of their salivary gland function, for which few effective prevention or treatment options are available. We found previously that Wnt-Hedgehog signaling is activated during functional salivary gland regeneration after ligation of main excretory duct. This study explores the potential of transient activation of Wnt or Hedgehog signaling in protection or restoration of salivary function in mouse models.

Methods: Wnt reporter Axin2-lacZ and Hedgehog reporter Patched1-lacZ transgenic mice were exposed to 15Gy single dose radiation in head-and-neck area to evaluate the effects of radiation on Hedgehog activity in salivary gland. Transient over-expression of Wnt1 or Sonic Hedgehog (Shh) in basal epithelia was induced in Keratin5-rtTA/tetO-Wnt1 or Keratin5-rtTA/tetO-Shh transgenic mice 3 days before or after, 90 days after, in together with, or without local radiation, then saliva flow rate, histology, apoptosis, proliferation, stem cell activity and mRNA expression were evaluated.

Results: Radiation damage did not significantly affect activity of Wnt and Hedgehog pathways as physical damage did. Transient Wnt1 expression only activated Wnt pathway in submandibular glands of male mice, while transient Shh expression activated Hedgehog pathway in submandibular glands of both male and female mice. In Wnt1 treatment groups, only concurrent Wnt activation in male ameliorated hyposalivation; the mechanisms include inhibition of radiation-induced apoptosis and preserving of functional salivary stem/progenitor cells. In Shh treatment groups, Shh activation 3 days before radiation in female mice and 3 days after radiation in male mice ameliorated hyposalivation. Shh induction 90 days after radiation also significantly but transiently improved salivary function in male mice with established hyposalivation, but not in females. The mechanisms are under investigation now.

Conclusion: These results suggest that transient activation of Wnt or Hedgehog pathways could prevent radiation-induced salivary dysfunction or restore damaged salivary function in a gender-specific manner.