Excessive iodine promotes the occurrence and development of experimental autoimmune thyroiditis in mice through p38 and intercellular adhesion molecule-1 / 中华地方病学杂志

ABSTRACT

Objective:To investigate the molecular mechanism of excessive iodine induced experimental autoimmune thyroiditis (EAT) in mice.Methods:Sixty female non-obese diabetic (NOD) mice were selected and divided into 5 groups according to body weight [(25 ± 3) g] via the random number table method, with 12 mice in each group control group (group A), 10-fold high iodine group (group B), 100-fold high iodine group (group C), 1 000-fold high iodine group (group D) and 1 000-fold high iodine combined with polyinosinic acid-polycytidylic acid [Poly (IC)] group (group E). The experiment period was 16 weeks. Mice in each group drank purified water with sodium iodine (NaI) content of 0.000, 0.005, 0.050, 0.500 and 0.500 mg/L, respectively; mice in group E were intraperitoneally injected with Poly (IC) at week 7 and week 15, respectively. At the end of the 16th week, mice were dissected and blood samples and thyroid tissue were taken. The levels of serum thyroid function indexes [thyroid stimulating hormone (TSH), free triiodothyronine (FT 3), free thyroxine (FT 4), and thyroid peroxidase antibody (TPOAb)] were detected by enzyme-linked immunosorbent assay (ELISA); the pathological changes of thyroid tissue were observed after hematoxylin-eosin (HE) staining; differentially expressed genes in thyroid tissue were detected by RNA-sequencing (RNA-seq), and analyzed by KEGG pathway; mRNA and protein levels of p38, intercellular adhesion molecule-1 (ICAM-1) and chemokine 10 (CXCL10) in thyroid tissue were detected by real-time fluorescence quantitative PCR (qPCR) and Western blotting, respectively. Results:There were statistically significant differences in serum levels of TSH (ng/ml 6.53 ± 0.86, 6.61 ± 0.82, 7.68 ± 0.55, 7.93 ± 0.60, 8.73 ± 1.60), FT 3 (pg/ml 59.35 ± 10.16, 53.73 ± 10.96, 46.19 ± 8.03, 41.01 ± 8.67, 34.21 ± 11.75), FT 4 (pg/ml 136.74 ± 10.06, 124.33 ± 14.34, 101.80 ± 6.78, 91.37 ± 6.75, 73.29 ± 17.31), and TPOAb (U/ml 130.81 ± 24.53, 145.47 ± 28.89, 166.52 ± 41.59, 199.78 ± 42.19, 201.99 ± 44.03) among the 5 groups of mice ( F = 4.77, 4.96, 23.12, 3.68, P < 0.05). Compared with group A, the serum TSH levels of mice in groups C, D and E were higher, the levels of FT 3 and FT 4 in groups B, C, D and E were lower, and the levels of TPOAb in groups D and E were higher, and the differences were statistically significant ( P < 0.05). HE staining showed that the thyroid follicle lesion in groups D and E was serious, and the EAT phenotype appeared in both groups. The differentially expressed genes were analyzed by KEGG pathway. Compared with group A, 8 metabolic pathways related to thyroid autoimmunity and inflammation were found in groups B, C, D and E. Further analysis found that 3 genes appeared in multiple pathways, namely p38, ICAM-1 and CXCL10. There were significant differences in the mRNA levels of p38, ICAM-1 and CXCL10 in thyroid tissue of the 5 groups of mice ( F = 14.77, 12.76, 16.39, P < 0.05); compared with group A, the mRNA levels of p38 in groups B, C, D and E were higher, and the mRNA levels of ICAM-1 and CXCL10 in groups C, D and E were higher ( P < 0.05). There were significant differences in the protein levels of p38, ICAM-1 and CXCL10 in thyroid tissue of the 5 groups of mice ( F = 7.97, 73.86, 18.02, P < 0.05); compared with group A, the protein levels of ICAM-1 and CXCL10 in groups B, C, D and E were higher ( P < 0.05). Conclusion:Excessive iodine promotes the occurrence and development of EAT in mice by up-regulating the expressions of p38 and ICAM-1 genes that are closely related to thyroid autoimmune and inflammatory responses.