塑化剂DEHP干扰下丘脑-肝脏甲状腺激素代谢环路诱导肥胖的作用及分子机制研究

At present, there is a global epidemic trend for obesity. The widespread exposure of environmental obesogens plays key roles in the rapid increase of obesity morbidity. Bis(2-ethylhexyl)phthalate(DEHP) is a chemical characterized by high productivity, wide applicability and easy leakage. Previous studies have revealed its role in inducing obesity, however, the underlying molecular mechanism are not clear. The preliminary results of this study show that, DEHP exposure led to the disturbance of energy metabolism homeostasis, which might be resulted from the hypothyroidism caused by hypothalamic TRH inhibition and hepatic CAR activation. Based on the above results as well as the newest literature reports, the theoretical hypothesis that DEHP may induce obesity via interrupting hypothalamus-liver thyroid hormone metabolic loop was put forward by the applicant. The current project will elucidate the basic interference effect of DEHP on whole-body energy metabolism and thyroid hormone metabolism first, followed by two intervention experiments: one is to restore hypothalamic TRH by implantation of intracerebroventricular cannula into the lateral brain ventricle, and the other is to interfere the activation of hepatic CAR using CAR gene knockout mice. By the method of Quantification PCR, western blotting, and ELISA et al, the key molecular mechanism of DEHP in inducing obesity will be elucidated. This project will help to identify crucial reasons for DEHP to induce obesity, deepen the understanding of the basic theory of environmental factors in mediating obesity, and provide important theoretical evidence for prevention and treatment of obesity and other related metabolic disease.

目前，肥胖在全世界范围内高度流行。环境致肥胖化合物的广泛暴露是当前肥胖发病激增的重要原因。邻苯二甲酸二(2-乙基己)酯（DEHP）是一种产量高、应用广、易渗漏的化合物，既往研究表明其可诱导肥胖，但确切机制不明。申请人前期结果表明，DEHP能诱导显著的能量代谢失衡，而下丘脑TRH受抑制和肝脏CAR激活诱导甲状腺功能减退可能是其内在原因。基于上述结果并结合最新文献，申请人提出了DEHP干扰下丘脑-肝脏甲状腺激素代谢环路诱导肥胖的理论假设。本项目拟在明确DEHP干扰能量代谢和甲状腺激素代谢基本表型的基础上，分别利用侧脑室给药技术和CAR基因敲除小鼠，对下丘脑TRH和肝脏CAR进行干预，并结合Q-PCR、免疫印迹、ELISA等实验技术，最终阐明DEHP诱导肥胖的核心分子机制。本项目的研究成果将解析DEHP致肥胖的核心原因，丰富环境因素致肥胖的基础理论，为肥胖及相关代谢性疾病的防治提供重要理论依据。

项目背景：既往研究表明，塑化剂DEHP可诱导肥胖和甲状腺功能减退，但内在分子机制不明。本研究主要目的是阐明DEHP诱导肥胖症具体表型和相关分子机制。.项目主要研究内容：1）探索DEHP诱导能量代谢紊乱和肥胖的基本表型和分子机制，我们用0.5、5、50和200mg/kg BW/day的DEHP对雄性C3H/He小鼠进行了5周的灌胃染毒实验； 2）验证CAR在DEHP诱导的能量代谢紊乱和肥胖中的作用，我们用0、0.5和200mg/kg BW/day的DEHP对野生型小鼠和CAR基因敲除小鼠进行了5周的灌胃染毒实验；3）在实验中，我们定期监测了小鼠的体重、摄食量和体温等能量代谢关键参数，并对小鼠的下丘脑、肝脏、白色脂肪和褐色脂肪等脏器的关键分子变化情况进行了检测。.项目重要结果：DEHP暴露后，所有小鼠均出现显著的体重增加和脂肪蓄积，以0.5mg/kg组的表型最为显著。此外，DEHP暴露小鼠还出现了显著的摄食增加和日间平均体温降低，并伴随着小鼠能量代谢调控枢纽下丘脑的关键神经肽AgRP/NPY和POMC/CART的表达紊乱，和褐色脂肪组织UCP1表达减少。白色脂肪组织的脂质代谢在DEHP暴露后也出现了显著地紊乱，表现为DEHP暴露对脂肪代谢具备双向干扰作用，在低剂量时（0.5mg/kg）受甲状腺激素功能减退影响，脂肪代谢速率减慢，脂质蓄积增加。而在高剂量时（50和200mg/kg）时受甲减和PPARα激活的双重影响，脂肪代谢速率加快，脂肪蓄积速度减慢。此外， DEHP暴露还诱导小鼠出现了显著的甲状腺功能减退，主要机制为：1）DEHP可显著激活小鼠肝脏结构性雄烷受体（CAR），进而加速了甲状腺激素分解代谢；2）DEHP诱导了下丘脑炎症反应和瘦素抵抗，进而抑制下丘脑促甲状腺激素释放激素（TRH）的表达，加剧了甲减表型；CAR基因敲除实验证明，在DEHP诱导的肥胖中，该基因发挥核心作用。.项目的关键数据其科学意义：慢性DEHP暴露可以通过干扰机体的能量代谢稳态来诱导肥胖，而这与其诱导的甲状腺功能减退有密切关联，肝脏的CAR基因是关键因子。此外，低剂量的塑化剂DEHP（0.5mg/kg）有更强的致肥胖效应，高剂量的DEHP暴露反而会减弱这一趋势，这一发现具有重要的公共卫生意义。

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