γ-Secretase inhibitor ameliorates thyroid autoimmune damage via blocking Notch1 signaling and reducing γδT17 cells in EAT mice.

In order to explore if γ-secretase inhibitor can regulate γδT17 cells by blockading Notch1 signaling pathway and then affect thyroid autoimmune damage in experimental autoimmune thyroiditis (EAT) mice. Twenty-four female C57BL/6 mice, 6 to 8-week-old, were randomly divided into NC and EAT groups, and EAT group included EAT-A (pTg treated) and EAT-B (treated with DAPT before pTg) subgroups. HE staining was conducted to observe the pathological changes of thyroid tissue. ELISA was adopted to measure the concentrations of thyroglobulin antibody (TgAb) and interleukin 17A (IL-17A) in serum. The proportions of γδT17 cells were analysed by flow cytometry. The mRNA expressions of Notch1, hairy and split 1 (Hes1) and IL-17A were measured by RT-qPCR and the protein levels of Notch intracellular domain (NICD), Hes1 and IL-17A were examined by Western Blot. The titers of TgAb and IL-17A in serum, the proportions of γδT17 cells in spleen mononuclear cells (SMCs) and thyroid mononuclear cells (TMCs), the Notch1, Hes1, IL-17A mRNA and protein expressions in EAT-A mice were all increased significantly compared with NC group (all p < 0.001). However, in EAT-B group, the above indexes were all reduced significantly than those in EAT-A group (all p < 0.05), as well as the degrees of lymphocyte infiltration in thyroid were alleviated remarkably compared with EAT-A group. Additionally, γδT17 cells percentages of EAT mice were positively correlated with TgAb titers, IL-17A concentrations and Notch1 mRNA expressions. γ-secretase inhibitor is speculated to alleviate thyroid autoimmune injury in EAT by downregulating γδT17 cells via inhibition of the Notch1/Hes1 signaling pathway.