Epigenetic Changes in the Glucocorticoid Receptor Gene Due to Arsenic Exposure

描述（由申请人提供）：砷是最常见的自然环境污染物之一，虽然大多数研究都集中在其致癌潜力上，但少数研究表明砷对认知发育有不利影响。砷已被证明扰乱下丘脑-垂体-肾上腺轴（HPA）。这个轴的一个参数，糖皮质激素受体（GR），已被证明被砷直接改变。GRs特别集中在对认知至关重要的区域（海马体、杏仁核和额叶皮质）。砷降低糖皮质激素受体功能的机制尚未阐明，但一些研究表明，砷可能改变GR基因的表观遗传修饰。表观遗传机制，包括DNA甲基化、组蛋白修饰和非编码rna介导的过程，在发育和细胞功能中发挥着重要作用。由于表观遗传变化可以在体细胞中通过有丝分裂遗传，也可以通过种系遗传，因此它们可能是将环境损伤印记到哺乳动物基因组上的一种手段，从而对发育中的大脑中的基因表达产生长期影响。利用我们的产前小鼠模型，我们发现中度砷暴露（50 ppb）会降低小鼠在各种学习和记忆、焦虑和抑郁相关任务中的表现，并显著改变下丘脑-垂体-肾上腺轴（HPA）功能。进一步的研究表明，糖皮质激素受体水平下降，一些启动子含有糖皮质激素反应元件（GREs）并被GR结合激活的蛋白质减少。甲基化特异性DNA测序显示，在产前砷后代中，GR启动子的一个转录结合位点的甲基化程度更高。我们的战略是开发一种创新的、综合的方法，利用我们实验室的分子遗传学（Dr. Zhao）、神经药理学和行为学（Allan）专业知识。为这个项目开发的具体目标集中在证明：(1)产前砷增加GR启动子甲基化；(2)导致GR表达降低；(3)这些产前表观遗传变化持续到出生后发育；(4)这些变化是认知能力下降的原因。了解pae诱导的认知缺陷的分子基础对于开发环境损害的治疗方法至关重要。

DESCRIPTION (provided by applicant): Arsenic is one of the most common naturally occurring environment contaminants, and while most studies have focused on its carcinogenic potential, a few studies have shown that arsenic adversely affects cognitive development. Arsenic has been shown to perturb the hypothalamic-pituitary-adrenal (HPA) axis. One parameter of this axis, the glucocorticoid receptor (GR), has been shown to be directly altered by arsenic. The GRs are particularly concentrated in areas of central importance for cognition (hippocampus, amygdala and frontal cortex). The mechanism through which arsenic decreases glucocorticoid receptor function has not yet been elucidated, but several studies suggest that arsenic may alter epigenetic modifications to the GR gene. Epigenetic mechanisms, including DNA methylation, histone modification, and noncoding RNA-mediated processes, are known to play significant roles in development and cellular functions. Because epigenetic changes can be inherited mitotically in somatic cells as well as through germ-line, they can be a means to imprint environmental insults onto the mammalian genome, which leads to long-lasting effects on gene expression in the developing brain. Using our prenatal mouse model, we have found that moderate arsenic-exposure (50 ppb) reduced performance on a variety of learning and memory, anxiety and depression associated tasks and significantly altered the hypothalamic-pituitary-adrenal axis (HPA) function. Further studies showed that there was a decrease in glucocorticoid receptor level and a decrease in several proteins whose promoters contain glucocorticoid response elements (GREs) and are activated by GR binding. Methylation specific DNA sequencing of the GR promoter showed greater methylation at one of the transcription binding sites in the prenatal arsenic offspring. Our strategy is to develop an innovative, integrated approach that capitalizes on the molecular genetic (Dr. Zhao), neuropharmacological and behavioral (Allan) expertise of our laboratories. The specific aims developed for this project are focused on demonstrating that: (1) prenatal arsenic increases GR promoter methylation; (2) this leads to a decreased GR expression; (3) these prenatal epigenetic changes persist into postnatal development; and (4) these changes are responsible for the decrease in cognition. Understanding the molecular basis of PAE-induced cognitive deficits will be critical in developing treatments for environmental insults.