High iodine induces DNA damage in autoimmune thyroiditis partially by inhibiting the DNA repair protein MTH1.

This study aims to investigate the level of DNA damage in high iodine (HI)-induced autoimmune thyroiditis (AIT), and to explore the role of DNA repair protein MutT homolog-1 (MTH1) in this process. The levels of pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-8 were measured using qRT-PCR and ELISA. The apoptosis was evaluated using TUNEL staining. The pathological changes of thyroid tissues were evaluated using hematoxylin and eosin (HE) staining. The DNA damage was assessed by determining the expression of 8-hydroxy-2'deoxyguanosine (8-OHdG; an indicator of oxidative DNA damage) and performing the Comet assay. Our results showed that both the HI-treated NOD.H-2h4 mice (experimental AIT mice) and the HI-treated mouse thyroid follicular epithelial cells showed enhanced inflammation, apoptosis, and DNA damage level, accompanied by decreased MTH1 expression. Importantly, overexpression of MTH1 effectively abrogated the HI-induced enhancement of inflammation, apoptosis, and DNA damage in mouse thyroid follicular epithelial cells. In conclusion, HI treatment induces DNA damage in AIT, at least in part, by inhibiting the DNA repair protein MTH1.