PBDEs发育神经毒性的机制和生物标记物：基于胎盘脱碘酶3（Dio3）的研究

PBDEs are a new class of environmental persistent organic pollutants (POPs) that have been linked to developmental neurotoxicities and thyroid hormone disturbance, according to animal studies. However, due to lack of effective biomarkers to direct research in humans, it is not very clear whether PBDEs can exert toxicities similar to animal experiments. We previously demonstrated that in utero exposure to PBDES may lead to a decline in the expression of placental deiodinase 3 (Dio3), consistent with the developmental neurotoxicities in offspring mice, indicating that PBDEs may induce neurotoxicities through suppressing placental Dio3 and subsequent early fetal T3 disturbance. PBDEs have been known to modulate DNA methylation and miRNA expressions. Dio3 is a paternally expressed gene located in the Dlk1-Dio3 imprinting region and tightly regulated by the differential methylations in the IG-DMR alleles, and/or maternal mRNA expressions, which may underlie the PBDEs-mediated placental Dio3 inhibition. In the current project, by using human placenta trophoblast cells and placental Dio3-specific knockdown/knockout mouse models, we aim to prove the hypothesis that placental Dio3 is a key in utero molecular target of PBDEs developmental neurotoxicities, and identify the mechanisms through which PBDEs may regulate placental Dio3 expression. Our study will also aim to seek a potential biomarker, and validate in clinical human specimens, in hope of providing a new molecular target for large scale human epidemiological studies and early clinical screening and intervention of PBDEs developmental neurotoxicities in newborns.

PBDEs是环境持久性有机污染物，动物研究已证实其发育神经毒性，但机制不清。由于缺乏特异敏感的生物标记物指导人群研究，其对人体的类似危害则尚未确定。我们前期研究发现，PBDEs可诱导小鼠胎盘Dio3表达下调，并与其发育神经毒性效应有关，推测PBDEs可通过对胎盘Dio3抑制，诱导胚胎高T3毒症，导致神经发生发育损伤。有研究表明PBDEs具有影响DNA甲基化和miRNA的潜能，而Dio3是Dlk1-Dio3印记区父系表达基因，受控于该区IG-DMR等位基因甲基化状态和/或母系miRNA表达，推测两者可能是PBDEs对胎盘Dio3抑制的机制途径。本课题将用人胎盘滋养层细胞和胎盘特异性Dio3敲除/敲降小鼠，求证胎盘Dio3与PBDEs发育神经毒性的充要关系，及PBDEs对胎盘Dio3的影响机制，并从中发现潜在的生物标记物，通过临床初步验证，以期为流行病学研究和新生儿健康早期筛查提供分子新靶标。

PBDEs是环境持久性有机污染物，动物研究已证实其发育神经毒性，但机制不清。由于缺乏特异敏感的生物标记物指导人群研究，其对人体的类似危害则尚未确定。本项目是基于“PBDEs通过诱导小鼠胎盘Dio3表达下调，使胎脑处于高TH环境而引起发育神经毒性”的理论假设。我们以两种人胎盘滋养层细胞为体外生物体系、孕期BDE209大鼠模型以及神经元/神经胶质细胞共培养体系，探讨BDE209调控胎盘Dio3的机制途径。Dio3是Dlk1-Dio3印记区父系表达基因，受控于该区IG-DMR等位基因甲基化状态和/或母系miRNA表达，推测两者可能是PBDEs对胎盘Dio3抑制的机制途径。研究结果表明，低剂量BDE 209（包括环境相关剂量）可以干扰胎盘细胞Dio3表达，进而导致甲状腺激素干扰；其机制可能是通过改变胎盘细胞Dlk1-Dio3印记区miR379/656簇中miRNA表达谱，尤其是miR409-3p和miR668-3p表达抑制，及/或改变胎盘细胞DNA甲基化状态实现的，尤其是Dlk1-Dio3印记区IG-DMR和MEG3-DMR两个区域的甲基化状态改变。本项目结果将为胎盘Dio3可以作为BDE 209发育神经毒性机制研究的一个方向；miR409-3p和miR668-3p可能是孕期PBDEs暴露诱导的甲状腺激素干扰或其它发育毒性效应的分子靶点，为以后大规模人群流行病学研究提供新的无创生物标记物。