The effects of iodine excess on thyroid function, antibody and TSHR gene expression in experimental autoimmune thyroiditis rats / 中华地方病学杂志

ABSTRACT

Objective:Experimental autoimmune thyroiditis (EAT) rat model was establish to observe the effects of iodine excess on thyroid function, antibody and thyrotropin receptor (TSHR) gene expression in EAT rats, and to explore the role of TSHR gene in autoimmune thyroiditis.Methods:According to body weight (80 - 180 g), 48 rats (4-week-old female Lewis) were randomly divided into control group, thyroglobulin (TG) group, TG + high iodine Ⅰ(TG + HⅠ) group, and TG + high iodine Ⅱ (TG + HⅡ) group, 12 rats per group. The iodine concentration in drinking water given to each group was 50 μg/L, 50 μg/L, 20 mg/L and 200 mg/L, respectively. At the same time, rats in TG, TG + HⅠ and TG + HⅡ groups were immunized once every two weeks for three times using pTg and CFA as immunoreagent. Paraffin embedded sections of thyroid tissues were used to observe the pathological changes of rats. The serum levels of thyroglobulin antibody (TgAb), thyroperoxidase autoantibody (TPOAb), free triiodothyronine (FT 3) and free thyroxine (FT 4) in rats were determined by radioimmunoassay. Serum TSHR content in rats was determined by enzyme linked immunosorbent assay (ELISA). The expression of TSHR mRNA in whole blood and thyroid tissue of rats was determined by RT-PCR. The expression of TSHR protein in thyroid tissue of rats was determined by immunohistochemistry (IHC). Results:Hematoxylin-eosin (HE) showed that the thyroid follicles in control group were complete in structure and regular in shape, and no lymphocyte infiltration was observed. A small number of lymphocytes were observed in TG group and scattered in distribution. Follicular structure destruction, fusion and interfollicular infiltration were observed in TG + HⅠ group and TG + HⅡ group. There were significant differences in serum TgAb, TPOAb, FT 3 and FT 4 levels among all groups ( H = 30.28, 21.99, 12.87, 26.69, P < 0.05). Compared to the control group [6.89 (6.32, 7.27), 11.02 (7.60, 12.53), 5.05 (2.71, 7.99), 7.51 (6.50, 9.24) pmol/L], the levels of TgAb [34.99 (25.39, 41.35), 37.70 (29.06, 43.99), 46.41 (38.52, 55.26)], TPOAb [22.87 (13.65, 31.82), 22.22 (14.82, 28.33), 14.61 (12.95, 19.34)], FT 3 [57.74 (24.56, 64.27), 43.64 (5.69, 80.03), 38.56 (17.73, 47.59) pmol/L], and FT 4 [62.16 (41.22, 91.57), 60.61 (35.52, 103.31), 47.96 (31.84, 112.71) pmol/L] were significantly higher in TG group, TG + HⅠ group, and TG + HⅡ group ( P < 0.05). Compared with the control group [(249.37 ± 38.12) μU/L], TG group [(225.33 ± 41.28) μU/L], and TG + HⅠ group [(218.15 ± 65.51) μU/L], TSHR expression level in TG + HⅡ group [(154.26 ± 25.95) μU/L] were significantly decreased ( P < 0.05). The mRNA expression levels of TSHR gene in the whole blood (0.89 ± 0.19, 0.89 ± 0.30, 0.85 ± 0.24) and thyroid tissue(0.63 ± 0.25, 0.46 ± 0.16, 0.51 ± 0.25) of TG group, TG + HⅠ group and TG + HⅡ group were significantly lower than that of control group (1.00 ± 0.05, 1.13 ± 0.21, P < 0.05). IHC showed that the positive intensity of TSHR protein in control group was significantly higher than that in TG group, TG + HⅠ group and TG + HⅡ group. Conclusions:Long-term exposure to high iodine will eventually lead to the damage of iodine-uptake function in thyroid gland and thyroid diseases. Abnormal expression of TSHR gene may lead to antigenicity of thyrotropin binding site in extracellular receptor region and autoimmune thyroid disease.