| Objective:Metabolic syndrome?MS?is the pathological state of abnormal aggregation of various metabolic components and it is a group of complex metabolic disorders that can increase the risk of diabetes and cardiovascular disease.Many recent studies have shown that adipose tissue can not only maintain energy balance,but also secrete a variety of adipokines and mediate the metabolic balance between various systems of the body through paracrine,autocrine and endocrine,which is closely related to metabolic diseases.Meanwhile,previous studies have confirmed that abnormal thyroid function is closely related to the occurrence and development of MS.Abnormally elevated thyroid-stimulating hormone?TSH?can alter the expression levels of multiple adipokines by combining with its TSH receptor?TSHR?on the surface of adipocytes,thereby affecting glucose metabolism and producing insulin resistance.It eventually participated in the development of a series of metabolic diseases such as hyperglycemia,dyslipidemia,hypertension,hyperuricemia and obesity.Angiotensin?type 1 receptor related protein?APJ?is a G-protein-coupled receptor with seven transmembrane helical structures.apelin is its endogenous ligand,mainly expressed in adipocytes,cardiac cells,and vascular interstitial cells.APJ is widely expressed in the surrounding tissues and central nervous system,so the apelin/APJ system can be involved in the regulation of multiple physiological functions.There are few studies on the effects of TSH on apelin expression levels.Therefore,this study aimed to identify serum apelin levels in patients with clinical or subclinical hypothyroidism through case-control study and to determine the changes of apelin expression levels in adipocytes when TSH levels rise and the possible mechanisms through in vitro cell experiments.Thereby explore whether apelin are involved in the occurrence and development of TSH mediated metabolic diseases.Methods:?1?This study included 36 patients with overt hypothyroidism,36 patients with subclinical hypothyroidism,and 36 patients that tested positive for isolated thyroid peroxidase antibody?TPOAb?.The healthy control group consisted of 36 age-matched and gender-matched individuals,with normal thyroid function.The serum apelin level,thyroid function,and glycolipid metabolism indexes of all subjects were measured.The correlation between the serum apelin level,and thyroid function and glycolipid metabolism indexes was investigated.?2?3T3-L1 cells were differentiated into mature adipocytes using the classical method,and were stimulated by exogenous TSH in different stimulation concentration and time.The stimulation time were 0h,2h,6h,12h,and 24h.The stimulated concentrations were 0mIU/mL,0.01mIU/mL,0.1mIU/mL,1mIU/mL and 10m IU/mL.The expression of apelin in the supernatant were determined by ELISA,and the mRNA expression of apelin were determined by Realtime qPCR.Stimulation dosing groups were phosphatidylinositol 3-kinase inhibitor?PI3-K?Wortmannin(10-6mol/L)intervention 30min,mitogen activated protein kinases?P38MAPK?inhibitor SB203580?10-5mol/L?intervention 30min and protein kinase A?PKA?inhibitor H89?0.0lmmol/L?intervention 15min,followed by TSH at optimum concentration stimulating for 6h.Meanwhile A blank control group and a simple TSH intervention group were established.The protein expression levels of apelin in adipocytes were determined by Western blotting.Results:Serum apelin levels of OH group,SCH group,Isolated TPOAb positivity group and HC group were?114.96±10.57?pg/L,?101.44±10.03?pg/L,?84.53±11.18?pg/L and?79.11±11.67?pg/L respectively.Compared with HC group,serum apelin levels in OH group and SCH group were significantly increased?P<0.01?,but serum apelin level in Isolated TPOAb positivity group was not significantly changed.After correction of multiple confounders,linear regression analysis indicated a positive correlation between the serum apelin level and levels of TSH and triglyceride?TG??P<0.01?for all the subjects.A negative correlation was indicated between the serum apelin level and free thyroxine?FT4??P<0.01?.?2?When TSH stimulation was given at different times,the expression levels of apelin mrna and apelin were significantly different compared with the baseline level?P<0.05 or P<0.001?and peaked at 6h.When TSH stimulation was given at different concentrations,the expression levels of apelin mrna and apelin increased with the increase of TSH levels compared with the blank control group?P<0.05or 0.001?.After adding three signal pathway inhibitors,the results showed that PI3K inhibitor Wortmannin and P38MAPK inhibitor could partially inhibit apelin expression,while PKA inhibitor could significantly inhibit apelin expression?P<0.05 or P<0.001?,but none of them could reverse the increase of apelin expression levels.Conclusion:?1?Clinical study show that serum apelin may be associated with lipid metabolic disorders that are mediated by high level of serum TSH.?2?The elevated TSH levels may promote the secretion of apelin mainly through PKA pathway in adipocytes.There may be other signaling pathways that mediate the effect of TSH on apelin expression levels.The results of in vitro cell experiment show that TSH can promote the synthesis and secretion of apelin.In addition to PKA signaling pathways,elevated TSH may also promote the synthesis and secretion of apelin through other signaling pathways,thus participating in the regulation of body metabolism. |
PDF Full Text Request