Cellular and molecular effects of iodine deficiency and ionizing radiation on non-cancerous thyroid cells

Abstract

Ionizing radiation (IR) and iodine deficiency (ID) are risk factors for thyroid cancer development. There are uncertainties about the combined effects of ID and IR exposure on thyroid cells. We hypothesize that IR and ID both stress thyroid cells by an enhanced production of reactive oxygen species (ROS), affecting proliferation and survival. Rat thyroid cells were cultured in iodine-deficient or- sufficient conditions and irradiated with low (0 Gy, 0.05 Gy, 0.1 Gy), intermediate (0.1 Gy) and high (3 Gy) radiation doses. We performed Western blot to examine protein expression of (p)STAT3, NFkBp52, (p)AKT1; a BrdU/7-AAD assay to determine cell cycle distribution (6h, 24h, 48h post-treatment); immunocytochemistry against yH2AX and 53BP1 foci to determine double strand breaks (30min, 1h, 4h, 24h post-treatment) and CM-H2DCFDA fluorescent imaging to examine ROS production (24h post-treatment). We concluded that intermediate and high dose radiation enhance ROS production in co-treated cells. DNA repair is different after low-dose irradiation than after high-dose irradiation in which the presence of a DNA damage threshold is suggested in order to achieve efficient DDR pathway activation. Thyroid cells are relatively radioresistant exhibiting a G1 arrest only after exposure to 3Gy, 24 hours post-treatment. Co-treatment makes thyroid cells less sensitive for a G1 arrest and enhances proliferation 24h post-treatment. 6h post-irradiation there were no significant differences in protein expression between the different groups.