Imbalance between apoptosis and proliferation causes late radiation damage of salivary gland in mouse

Abstract

Severe xerostomia is a common late radiation consequence, which occurs after irradiation of head and neck malignancies. The aim of the present study was to analyze apoptosis and proliferation and their relationship during the late post-irradiation phase. C57BL/6 mice were locally irradiated in head and neck region with a single dose of 7.5 or 15 Gy and their submandibular glands were collected at 40 and 90 days after irradiation. To identify apoptotic cells, the TUNEL method was employed and immunohistochemistry with proliferating cell nuclear antigen (PCNA) was used for detecting proliferation. Histological changes at day 40 were mild in contrast to day 90 when glands of irradiated mice showed severe atrophy, vacuolization and mononuclear infiltration. Acinar cells, granular and intercalated duct cells of mice irradiated with 7.5 and 15 Gy expressed higher apoptotic index than cells of non-irradiated, control glands at both examined time points. At 40 days, a higher proliferation index in granular and intercalated duct cells was detected only in group irradiated with 7.5 Gy. At 90 days, proliferation index for all cell types in both irradiated groups was similar to the controls. According to our results, the imbalance between apoptosis and proliferation caused by X-irradiation may be the reason for gland impairment during the late post-irradiation phase.

Long-term functional regeneration of radiation-damaged salivary glands through delivery of a neurogenic hydrogel

“…Given the proliferative response of irradiated acinar cells to CV, we next asked whether a single dose of CV or ALG+CV at 14 days post-IR could maintain saliva secretion and salivary gland architecture over a 10-week time period. This 10-week time frame was chosen based on rodent models showing extensive salivary gland degeneration 8-12 weeks after radiation exposure ( 7 ). Mice were irradiated at day 0 and treated with ALG+CV, free CV, ALG only or saline (control) 14 days later, and physiological levels of citrate-driven (nerve-mediated) saliva output being measured each week through gustatory stimulation ( Fig.3A ).…”

“…We next proceeded to analyze salivary glands for alterations in tissue structure and function by measuring changes in secretory cell number and secreted protein synthesis. Given the submandibular gland is responsible for at least 60% of saliva secretion in rodents ( 38 ) and its serous acini are severely damaged by IR ( 7 ), we first focused on acinar cell architecture and protein biosynthesis within this gland type by immunostaining for the water channel aquaporin 5 (AQP5) and the secreted protein mucin 10 (MUC10). Consistent with the known degeneration of irradiated submandibular glands 8-12 weeks after IR exposure ( 7 ), saline-and ALG-treated tissue showed extensive destruction of functional acini at 70 days (10 weeks) post-IR ( Fig.…”

“…Given the submandibular gland is responsible for at least 60% of saliva secretion in rodents ( 38 ) and its serous acini are severely damaged by IR ( 7 ), we first focused on acinar cell architecture and protein biosynthesis within this gland type by immunostaining for the water channel aquaporin 5 (AQP5) and the secreted protein mucin 10 (MUC10). Consistent with the known degeneration of irradiated submandibular glands 8-12 weeks after IR exposure ( 7 ), saline-and ALG-treated tissue showed extensive destruction of functional acini at 70 days (10 weeks) post-IR ( Fig. S3A ), with a 50% decrease in both the number of AQP5 + ( P <0.0001; Fig.3D, E ) and MUC10 + acinar cells ( P <0.0001; Fig.3F, G ).…”

“…Loss of saliva production after IR therapy has been primarily attributed to the destruction of the major secretory cell type, the acinar cell (6,7). Both serous and mucous acini belonging to the 3 major salivary glands (i.e., parotid, submandibular and sublingual) secrete a fluid containing water, electrolytes, mucus and proteins e.g.…”

“…enzymes and immunoglobulins, into the ductal system for deposition within the oral cavity. Numerous studies have demonstrated these cells to be gradually destroyed after IR exposure, with rodents and humans exhibiting extensive loss of serous acinar cells within 2-3 months ( 7, 8 ). Unfortunately, no regenerative treatments are currently available to promote the repopulation of acinar cells and repair organ function post-IR.…”