| Objective Methylation abnormalities in the promoter region of RASSF1 A gene have been proved to be related to various thyroid diseases.Excessive or insufficient iodine intake will result in the progression of thyroid diseases.However,it is still unknown whether different iodine nutrition levels will affect the methylation of RASSF1 A gene.This study aims to explore the relationship between methylation of RASSF1 A gene and iodine nutrition status.Methods Forty SPF grade female SD rats were randomly divided into five groups: low iodine group,suitable iodine group,5-fold high iodine group,10-fold high iodine group and20-fold high iodine group.Each group were fed by low iodine fodder and different KI content of deionized water,to build the animal model.The 24 hours urine samples of rats were collected every mouths,and MUI level was measured by ICP-MS method.The success of modeling was estimated by the positive connection between MUI and iodine intake.After 3 months feeding,the animals were sacrificed.Blood was collected from the inferior vena cava to collect serum.The thyroid glands were stripped and stored carefully.All serum samples were tested by chemiluminescent detection technology;The expressions of RASSF1 A protein in thyroid tissues were tested by immunohistochemical staining.The methylation rate of RASSF1 A gene promoter region was determined by BSP method.The results were analysed by SPSS20.0 software and expressed as mean ± standard.The correlation between iodine intake and dependent variables were assessed by Spearman analysis.The data between each groups were compared by ANOVA method,P<0.05 was determined as statistically significant.Results After feeding SD rats with different iodine concentrations for 3 months,(1)The median urine iodine of each group was positively correlated with the iodine intake,indicating that the model was successful.(2)Iodine intake and the serum FT3 value of rats appeared in a negative correlation(r=-0.345,P= 0.039),but FT4 and TSH values had no significant relationship with iodine(P > 0.05).The serum FT3 value of five groups had significant difference(P=0.006),but the FT4(P=0.622)and TSH(P=0.236)value had no statistical significance.The FT3 value of the LI group was lower than the NI group(P=0.032),with statistically significant difference(P < 0.05).The FT3 value of the 5HI(P=0.001),10HI(P=0.006)and 20HI(P=0.003)groups was lower than the NI group,with statistically significant difference(P<0.01).(3)Iodine intake and the expression level of RASSF1 A gene appeared in a positive correlation(r= +0.407,P= 0.005).The expression level of RASSF1 A in thyroid tissues of five groups(P=0.057)had significant difference(P<0.1).The expression level of RASSF1 A in thyroid tissues of the 20 HI group was higher than that of the NI group(P=0.014)and LI group(P=0.024),with statistically significant difference(P < 0.05),while there was no significant difference between LI group,5 HI group,10 HI group and NI group(P > 0.05).(4)There was no significant positive or negative correlation between iodine intake and the Cp G island methylation ratio(P > 0.05).The methylation rates of Cp G island 1(P=0.630),Cp G island 2(P=0.401)and total Cp G island(P=0.398)in the promoter region of RASSF1 A gene was not statistically significant among the groups(P > 0.05).Besides,the methylation rates of LI group,5 HI group,10 HI group and 20 HI group also had no significant difference compared with NI group(P > 0.05).Conclusion(1)Both excessive iodine or iodine deficiency can affect the serum thyroid hormone level in rats.(2)After 3 months iodine induction,there is no statistical difference in methylation rate of RASSF1 A gene promoter region between each groups.But the RASSF1 A gene protein expression is higher than that of the NI group.The mechanism need to be further explored. |
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