Downregulation of osteopontin in the mouse salivary gland after X-ray irradiation

Objectives Radiation-induced xerostomia is a frequent consequence of radiotherapy for head and neck cancer, but its mechanisms remain unclear. Osteopontin (OPN), a highly phosphorylated glycoprotein, has been shown to be involved in the modulation of inflammatory and tissue repair processes and to be expressed in the salivary gland. Methods In this study, using a murine model of radiation-induced xerostomia, expression of OPN in the mouse sublingual gland (SLG) and submandibular gland (SMG) after irradiation was determined by quantitative RT-PCR (qRT-PCR) and western blotting. To explore the cellular location of OPN and its relationships with matrix metalloproteinase 3 (MMP3)-positive and CD11b-positive cells, both of which are also involved in radiation-induced tissue responses, immunofluorescence analysis was performed with anti-OPN, anti-MMP3, and anti-CD11b antibodies. Results In both the SLG and SMG, a transient increase in OPN mRNA expression was observed on day 5 post-irradiation; this subsequently decreased by day 10 post-irradiation. Western blotting and immunofluorescence analysis revealed downregulation of OPN and MMP3 in duct cells on day 10 post-irradiation, whereas CD11b-positive cells, which were not detected in non-irradiated mice, were increased in the stroma after irradiation. Conclusions The downregulation of OPN and MMP3, together with the concomitant increase in CD11b-positive cells, may modulate radiation-induced inflammatory responses, resulting in salivary gland dysfunction at a later stage after irradiation.