The Change Of TSH Receptor Expression In Thyroid And Adipose Tissue Of Obese Rats

Objective:With the improvement of people’s living level and effects of environment factors, the incidence of metabolic syndrome and metabolic diseases such as type2diabetes, is rapidly growing, which is a serious threat to global health, insulin resistance is the common pathogenesis of type2diabetes and the metabolic syndrome, and an independent risk factor for coronary heart disease, stroke and other diseases. Therefore, the investigation of the pathogenesis of insulin resistance has become a hotspot of domestic and foreign scientific research. In recent years, it was shown by many studies that serum thyroid stimulating hormone (TSH) levels was positively correlated with insulin resistance and obesity but negatively correlated with insulin sensitivity index. However, the mechanism of the correlation between serum TSH levels and insulin resistance is unclear now. Researches have found out that TSHR not only express on the surface of thyroid follicular cell, but also express in the abdominal wall fat, ovary, adrenal gland and other organs.TSH can directly bind to TSHR in tissues outside of thyroid and play the effect outside of thyroid. Adipose tissue can not only store energy, but also secrete a variety of cytokines and inflammatory mediators which is closely related to the occurrence of insulin resistance, obesity is insulin resistance occurs. Obesity is the foundation of insulin resistance. but studies in the expression of TSHR in thyroid and adipose tissue of obese animals are seldomly seen now. This study was aimed to provide a theoretical basis for the further study of the pathogenesis of insulin resistance by observing the expression of TSHR in epididymal adipose tissue an d thyroid tissue of obese rats.Methods:22clean grade male SD rats that weighted at95to105grams were randomly divided into the control group which consist of8rats and daily fed with normal diet; obesity group which consist of14rats and fed with high fat diet.The two groups of rats ate and drank freely, and were taken weight once a week. After12weeks of feeding,8rats whose weight was20%higher than the conventional feeding group was selected as qualified obesity animal model. The blood samples were obtained through the femoral artery bleeding from the two groups of rats which were killed later. The samples of thyroid, epididymal adipose tissue were taken from the killed rats. TSH, blood glucose (GLU), total cholesterol (TC), triglyceride (TG), insulin (INS) were respectively measured from two groups of blood samples,and homeostasis model of insulin resistance index (HOMA-IR) was calculated; immunohistochemical staining of thyroid, epididymal adipose tissue as conducted to observe the percentage of TSHR staining and positive cells and the expression changes of TSHR under light microscope.Results:①the results of TSH level of rats:the TSH level in serum of obesity group rats was significantly higher than that in control group, the difference was statistically significant (P<0.01).②the results of metabolic indexes of rats:GLU, TC, TG and INS in serum of obese rats were significantly higher than those in the control group, the differences were statistically significant (P<0.01), HOMA-IR index of obesity obese rats was significantly higher than that of the rats in the control group, the difference was statistically significant (P<0.01). HLOMA-IR was significantly positively correlated with TSH (P<0.01)③The analysis of immunohistochemistry: the expression of TSHR in epididymal adipose tissue:the epididymal fat cells of obese rat was bigger than that of the control group. The expression of TSHR particles in epididymal adipose tissue were observed in obesity group and control group, expression site located in cytoplasm. The medium strength expression was showed in control group and a strong positive expression was observed in obesity group. A semi-quantitative method display:the expression of TSHR in obesity group was stronger than in control group, the difference was statistically significant (P<0.05). Expression of TSHR in thyroid tissue:the particles of TSHR expression were all visible in thyroid tissues of obese and control group of,the expression sites were mainly located in the cytoplasm, but the expression intensity was not same. Expression of TSHR in thyroid follicular epithelial cells of two groups were all strong positive A semi-quantitative method display that the TSHR expression in obesity group were significantly stronger than that in control group, the difference was statistically significant (P<0.01).Conclusions:(1) Serum TSH level in obese rats was significantly higher than that in control group, TSH was significantly positively correlated with HOMA-IR (2) The insulin resistance in obese rats was more significant when compared with control group rats.(3) The expression of TSHR in epididymal adipose tissue and thyroid tissue of obese group is significantly higher than that in normal group, revealing that TSH may be participated in the occurrence of insulin resistance through interaction with TSHR in adipose tissue.