Regional atrophy, cellular plasticity, and regenerative potential in irradiated murine salivary glands

Radiotherapy of head and neck cancer may cause detrimental late side effects such as fibrosis and hyposalivation. We investigated mouse salivary glands after fractionated irradiation, with the aim to elucidate cellular plasticity and potential regeneration.

12-week-old female C57BL/6JRj mice were irradiated with X-rays to a total dose of 66 Gy, given in 10 fractions over 5 days. The radiation field covered the oral cavity and major salivary glands. The submandibular (SMG), sublingual (SLG), and parotid glands (PG) were dissected at day 100 after finishing irradiation. Using different histological staining techniques, morphological, cellular, and molecular changes were investigated in irradiated and control SMG, SLG, and PG.

Atrophy of acinar cells was observed in irradiated SMG and SLG, but not in PG. Surprisingly, the acinar atrophy was confined to one region of each irradiated gland. These atrophic regions showed distinct cellular and molecular compositions compared to non-atrophic regions and control glands. Increased expression of the ductal cell markers keratin 5 and 19 (K5 and K19), along with increased percentages of proliferating myofibroblasts, fibroblasts, leukocytes, and acinar cells (Nkcc1+) were observed in the atrophic regions compared to controls. In addition, some of the K19+ and K5+ duct-like cells also co-expressed Nkcc1.

Through a detailed histological assessment of the cellular and molecular changes in the major salivary glands of irradiated mice, we observed signs of cellular plasticity where ductal cells adopt an acinar cell phenotype upon irradiation. This suggests a regenerative potential of salivary glands after irradiation.