BDNF介导的孕期乙醇暴露致子代成年抑郁症易感的宫内表观遗传机制

Epidemiological surveys have shown that prenatal ethanol exposure is closely related to depression susceptivity in adult offspring, which hints depression may have developmental origin in fetal stage. Deficiency of brain-derived neurotrophic factor (BDNF) in hippocampus induces depression，which is mainly due to DNA methylation of the promoter region of the BDNF gene. However, it is unclear that regulation mechanism of expression of BDNF in fetal hippocampus with ethanol exposure during pregnancy and its relationship with depression susceptivity in adult offspring. Our previous studies indicated that prenatal ethanol exposure results in overexposure to maternal glucocorticoid (GC) in fetal hippocampus, and down-regulates the expression of BDNF; depressive behavior is investigated following the unpredictable chronic stress.Therefore, we put forward the research hypothesis that the prenatal ethanol exposure increases the expression of glucocorticoid receptor (GR) in fetal hippocampus dur to overexposure to maternal GC, then GR/GRE/DNMTs have been activited, which leads to DNA methylation in the promoter region of the BDNF gene. It inhibites the expression of BDNF, neurogenesis and synaptic plasticity in fetal hippocampus, following depression susceptivity in adult offspring. Our goals for this project are to prove that prenatal ethanol exposure can cause depression susceptivity in adult offspring, and further to clarify the epigenetic mechanism of BDNF in the fetal hippocampus induced by prenatal ethanol exposure both in vivo and in vitro. This project will provide a new perspective to the pathogenesis of depression.

流行病学调查表明，孕期乙醇暴露与子代成年后抑郁症易感密切相关，提示抑郁症存在宫内起源。海马脑源性神经营养因子（BDNF）缺乏可诱导抑郁症发生，这主要归因于该基因启动子区DNA甲基化。然而，孕期乙醇暴露对胎海马BDNF的表达调控机制及其与子代抑郁症易感的关系并不清楚。我们前期发现，孕期乙醇暴露可引起胎鼠母源性糖皮质激素（GC）过暴露，胎海马BDNF表达降低，成年后慢性刺激可诱导抑郁行为。综合文献，我们推测：孕期乙醇暴露所致胎海马GC过暴露，可通过过度活化GR/GRE/DNMTs而引起BDNF启动子区甲基化修饰，抑制BDNF基因的表达，使海马神经发生减少和突触可塑性改变，最终导致抑郁症易感性增加。本项目拟利用整体动物实验证实孕期乙醇暴露所致的子代成年抑郁症易感，进一步在细胞水平阐明BDNF介导的孕期乙醇暴露子代成年抑郁症的宫内表观遗传机制，为抑郁症的发病机制研究提供新的视角。

流行病学调查表明，孕期乙醇暴露与子代成年后抑郁症易感密切相关，提示情感障碍性疾病存在宫内起源。然而，其发生机制尚不明确。本项目成功建立孕期乙醇暴露（PEE）模型，发现其雌性子代大鼠成年后出现抑郁、焦虑双相情感障碍易感；慢性应激后，PEE雌性子代对应激的反应性明显，更容易受到损害，主要表现为海马细胞凋亡增加、细胞周期失调、突触可塑性下降以及BDNF表达下降。进一步发现，PEE所致的海马糖皮质激素受体（GR）高表达可调控谷氨酸脱羧酶67（GAD67）表达增加，后者使谷氨酸向γ氨基丁酸（GABA）的转化增加，由此可减弱海马对HPA轴的负调控作用，导致下丘脑的潜在兴奋性增加，慢性应激后HPA轴的敏感性增加。追溯到宫内，发现胎海马形态、功能以及BDNF表达变化不明显，但胎海马GR及GAD67高表达及GAD67启动子区甲基化降低。在体外培养的胎海马H19-7细胞系上发现，乙醇和皮质酮均可抑制BDNF的表达，且皮质酮还可上调GR、GAD67表达及GAD67启动子去甲基化，降低谷氨酸能神经元活性而增加GABA能神经元活性。提示，高糖皮质激素（GC）可能通过上调GAD67表达，介导兴奋性/抑制性神经元活性的失衡，导致HPA轴高应激敏感性。综上，PEE作为“第一次打击”，可引起胎海马多途径损伤及损伤/代偿机制并存。乙醇的直接作用和高GC的间接作用共同导致海马细胞BDNF表达下降，细胞周期调控紊乱，突触可塑性相关基因表达减少；同时GC通过高GR介导GAD67表遗传修饰异常及表达增加（为代偿机制），使兴奋性/抑制性神经元和递质失衡，导致HPA轴高应激敏感性，后者可增加子代成年后的焦虑抑郁双相情感障碍易感。成年后的慢性应激作为“第二次打击”可加重海马的损伤及焦虑抑郁双相情感障碍发生。这是一个多途径、多靶点、多因素共同参与的宫内编程机制。本研究为焦虑抑郁双相情感障碍的发病机制研究提供新的视点，并为其早期防治提供理论及实验依据。本项目在国际药理与毒理学杂志Toxicol Lett、Toxicol Res以及国际分子医学杂志Int J Mol Med上发表SCI论文3篇，待发表SCI论文1篇。