This application is in response to RFA-DE-12-004, Functional Restoration of Salivary Glands (R01). Hypofunction of salivary gland is a common pathological condition in patients with Sjogren's syndrome or treated with radiotherapy for head and neck cancer. Current treatments can only temporarily relieve the symptoms, while regenerative therapies based on adult salivary gland stem cells have shown potential to restore salivary gland function in animal models but limited by technical hurdles and lack of understanding of molecular mechanisms. Hedgehog intercellular pathway is highly conserved during evolution and regulates regeneration or repair of various tissues after injury. We found previously that Hedgehog activity is marginal in adult salivary gland but significantly upregulatedduring their functional regeneration after physical injury; our preliminary data suggested that in salivary glands of both male and female mice, radiation impairs maintenance and differentiation of salivary stem/progenitor cells, and does not activate Hedgehog pathway, while transient Hedgehog activation after radiation in male mice significantly rescued salivary flow rates, possibly by both maintenance of salivary stem/progenitor cells and their differentiation after radiation. The goal of this project is understanding the mechanisms of Hedgehog-mediated rescue of hyposalivation, which will lead to optimization of this approach or development of more efficient and safer approaches to restore salivary function. To achieve this goal, we will: (1) determine the effects and mechanisms of transient Hedgehog activation on maintenance of salivary stem/progenitor cells after radiation; (2) determine the effects and mechanisms of transient Hedgehog activation on differentiation of salivary stem/progenitor cels after radiation; and (3) determine the effects of gender- or species-differences on Hedgehog mediated resuce of radiation-induced hyposalivation. Success of proposed experiments will open a new avenue for functional restoration of salivary glands after radiotherapy.