Serial changes in the proliferation and differentiation of adipose-derived stem cells after ionizing radiation

Background: Adipose-derived stem cells (ASCs) are important to homeostasis and the regeneration of subcutaneous fat. Hence, we examined the proliferation and differentiation capacity of irradiated ASCs over time. Methods: Two female pigs received a single 18 Gy dose of ionizing radiation to an 18 x 8 cm area on the dorsal body skin via a 6 MeV electron beam. After irradiation, the ASCs were cultured from adipose tissue harvested from a non-irradiated area and an irradiated area at 2, 4, and 6 weeks. The proliferation capacity of ASCs was evaluated by a colony-forming units-fibroblasts (CFUs-Fs) assay, a cholecystokinin (CCK) test with 10 % fetal bovine serum (FBS), and a 1 % FBS culture test. The senescence of ASCs was evaluated through morphological examination, immunophenotyping, and beta-galactosidase activity, and the multipotent differentiation potential of ASCs was evaluated in adipogenic, osteogenic, and chondrogenic differentiation media. Results: Irradiated ASCs demonstrated significantly decreased proliferative capacity 6 weeks after irradiation. As well, the cells underwent senescence, which was confirmed by blunted morphology, weak mesenchymal cell surface marker expression, and elevated beta-galactosidase activity. Irradiated ASCs also exhibited significant losses in the capacity for adipocyte and chondrocyte differentiation. In contrast, osteogenic differentiation was preserved in irradiated ASCs. Conclusions: We observed decreased proliferation and senescence of irradiated ASCs compared to non-irradiated ASCs 6 weeks after irradiation. Furthermore, irradiated ASCs demonstrated impaired adipocyte and chondrocyte differentiation but retained their osteogenic differentiation capacity. Our results could shed light on additional pathogenic effects of late irradiation, including subcutaneous fibrosis and calcinosis.