TH-DNMTs-BDNF通路在孕期五溴联苯醚（BDE-99）暴露对子代大鼠神经毒性中的作用机制研究

Polybrominated diphenyl ethers (PBDEs) are brominated flame retardants (BFRs) that are produced and applied extensively in China. Previous studies suggested that PBDEs may result in neurodevelopmental deficits, whereas potential mechanisms for the neurodevelopmental toxicity of PBDEs have not been fully elucidated. Our previous studies have demonstrated much higher PBDEs exposure levels among pregnant women from one of the major BFRs production areas in China, and we found that BDE-99 was the dominated PBDE congener. Additionally, prenatal exposure to BDE-99 was associated with lower language domain DQs in young children, suggested an adverse effect of BDE-99 on child neurodevelopment. Thyroid hormone (TH) disruption has been frequently proposed as an important potential pathway linking exposures to PBDEs and neurodevelopment deficits. It has been proved that TH is critical to promote the neurodevelopmental process of fetus and infants via the maintaining of brain-derived neurotrophic factor (BDNF) levels. The down regulation of DNA methyltransferase (DNMTs) activities by TH is believed to be responsible for a down regulated methylation of BDNF gene, which in turn induce BDNF production. Several studies have demonstrated that exposure to PBDEs may disrupt TH functions and thyroid homeostasis by interfering with homeostatic mechanisms including binding of thyroid hormones with their receptors (thyroid hormone receptors, TRs) and transporter proteins, which interferes with the homeostasis of BDNF and do harassment to neuron developments. Yet the exact relations between BDE-99 and DNMTs as well BDNF remain unclear. In our subsequent trials, rat dams were exposed to BDE-99 from gestation day 0.5 to gestation day19.5, and were treated with or without TH in vivo. In vitro, hippocampal neurons were isolated and exposed to BDE-99, and they were treated with or without TH as well as DNMTs inhibitor-SGI-1027. When pups were weaning, they were assessed by neurobehavioral testing for learning and memory function. Intracellular levels of TH, TRs, DNMTs and BDNF, and methylation levels of BDNF genes, were respectively assessed in hippocampal neurons. In conclusion, this study aims at revealing the neurotoxicity of PBDEs and the underlying mechanisms.

多溴联苯醚（PBDEs）作为我国广泛使用的阻燃剂，已被发现具有神经毒性但其机制不明。申请者前期研究发现，BDE-99是我国PBDEs生产源区孕妇血及脐带血中检出率最高的PBDEs同族体，且对幼儿神经发育有不良影响。PBDEs通过竞争性抑制甲状腺激素（TH）与其受体（TRs）结合，引起DNA甲基转移酶（DNMTs）活性增高，上调脑源性神经营养因子（BDNF）基因甲基化，引起BDNF水平下降，阻遏神经发育，是其神经毒性的可能机制。本项目选取BDE-99为受试物，以人群暴露水平为染毒剂量，在体内外分别对大鼠及其海马神经元进行BDE-99染毒，并分别以TH及DNMTs抑制剂SGI-1027干预。通过观察子鼠的神经行为变化，检测海马神经元TH、TRs、DNMTs及BDNF水平，BDNF甲基化水平，深入探讨BDE-99对子代神经行为发育的影响及其机制，为揭示PBDEs暴露的神经发育毒性提供科学依据。

多溴联苯醚（PBDEs）作为我国广泛使用的阻燃剂，已被发现具有神经毒性但其机制不明。申请者前期研究发现，BDE-99是我国PBDEs生产源区孕妇血及脐带血中检出率最高的PBDEs同族体，且对幼儿神经发育有不良影响。PBDEs通过竞争性抑制甲状腺激素（TH）与其受体（TRs）结合，引起DNA甲基转移酶（DNMTs）活性增高，上调脑源性神经营养因子（BDNF）基因甲基化，引起BDNF水平下降，阻遏神经发育，是其神经毒性的可能机制。.本项目选取BDE-99为受试物，以人群暴露水平为染毒剂量，在体内外分别对大鼠及其海马神经元进行BDE-99染毒，并分别以TH及DNMTs抑制剂SGI-1027干预。动物实验结果发现，与对照组相比，各染毒组仔鼠出生后体重均明显低于对照组，给予T3干预的染毒组仔鼠出生后体重均大于单纯染毒组，与对照组相比未发现体重存在明显差异。通过观察子鼠的神经行为变化结果发现，各个剂量组雌性子代大鼠的逃避潜伏期时间在第2,5天存在差异，而雄性子代大鼠仅在第1天中发现各组间逃避潜伏期时间存在差异，其余几天各组的逃避潜伏期基本一致，差异无统计学意义，但仍然发现随着染毒剂量的增加，各组子代大鼠逃避潜伏期时间增加；矿场实验结果则未发现各组幼鼠运动能力存在差异。结合体外染毒实验进一步检测海马神经元TH、TRs、DNMTs及BDNF表达水平，结果发现TRs、DNMTs及BDNF均下调，提示BDE-99可以通过竞争性结合TRs受体，干扰DNMTs活性，抑制神经营养因子BDNF的表达，产生一定的神经毒性。 .本项目首次确定BDE-99可通过调节TRs-DNMTs-BDNF信号通路，进而调节神经元内BDNF蛋白表达水平，实验成果为揭示PBDEs暴露的神经发育毒性提供科学依据。