[Foxo1 mediates immune damage in autoimmune thyroiditis by regulating the differentiation and function of Th17 cells]

Objective To explore the roles and mechanisms of forkhead box protein O1(Foxo1) in the occurrence and immune injury of experimental autoimmune thyroiditis (EAT). Methods In vivo experiments, thirty female C57BL/6 mice were randomized into three groups: NC (normal control) group, EAT (pTg-induced model via multi-point subcutaneous injection) group, and EAT+AS (EAT mice administered AS1842856 intraperitoneally) group. At the end of the 8th week, the thyroid, serum and spleen tissues were collected. In vitro experiments, 0 nmol/L, 30 nmol/L and 60 nmol/L AS1842856 were used to interfere with the cytokine polarized spleen mononuclear cells(SMCs) for 24 hours, and the cells were collected for follow-up experiments. HE staining was used to evaluate the degree of inflammation in the thyroid tissue of mice; ELISA was used to detect the thyroglobulin antibody(TgAb) and interleukin 17A(IL-17A) concentrations in the serum; flow cytometry was used to detect the proportion of T helper 17(Th17) cells in SMCs; Western blot was used to detect the protein expression levels of Foxo1, phosphorylation Foxo1(p-Foxo1), retinoic acid-related orphan receptor γt(RORγt) and IL-17A; qPCR was used to detect the mRNA levels of RORγt and IL-17A. Results The thyroid showed varying degrees of follicular destruction and lymphocyte infiltration in the EAT group; the levels of serum TgAb and IL-17A were significantly increased; the total protein expression of Foxo1 had no significant change, while the p-Foxo1 protein was obviously increased; The proportion of Th17 cells in SMCs, spleen index, the protein and mRNA levels of RORγt and IL-17A were all increased remarkably, and all were positively correlated with the phosphorylation level of Foxo1. The degree of thyroid destruction and lymphocyte infiltration in the EAT+AS group was aggravated; the serum TgAb and IL-17A concentrations, the proportion of Th17 cells in SMCs, spleen index, and the protein and mRNA levels of RORγt and IL-17A were all significantly increased. Additionally, the proportion of Th17 cells and the expressions of RORγt and IL-17A increased in a concentration-dependent manner with the increase of the concentration of AS1842856 in vitro. Conclusion The enhanced phosphorylation-mediated inactivation of Foxo1 weakens its inhibitory effect on Th17 cells in EAT mice, and then promotes the differentiation of Th17 cells and the secretion of IL-17A, ultimately participating in the onset of EAT and the thyroid autoimmune damage.