Environmental toxins and stem cell epigenetic remodeling

描述(由申请人提供)：流行病学研究长期以来一直表明，生命早期接触有毒环境与晚年人类疾病的发展之间存在关键但知之甚少的联系(S)。环境毒素在细胞内产生氧化应激，细胞中氧化应激与表观遗传学变化之间的联系可能导致多种人类疾病，包括癌症、不孕症和多种神经退行性疾病。尽管数据有限，但也有人认为，环境毒素可能会破坏DNA甲基化模式和染色质结构，这不仅会导致基因表达的遗传变化，还会影响整个基因组的稳定性。然而，环境毒素、氧化损伤和表观遗传变化之间的直接联系尚未确定，这是本提案的主要重点。有人认为，在发育过程中或在关键的易感窗口(WOS)期间暴露于常见的环境污染物可能会导致发育/分化细胞中异常的表观遗传学和癌前病变。预计这一易感窗口与发育或细胞修复/再生期间的血统承诺所需的正常表观遗传重塑相吻合。为了验证这一想法，提出了以下三个具体目标：具体目标1：确定环境毒素百草枯在体外诱导分化干细胞DNA甲基化变化的WOS。假设干细胞在接收到主动重塑其染色质的信号时，即在发育和组织再生期间，容易受到表观遗传重塑错误的影响；具体目标2：研究百草枯暴露是否扰乱了干细胞转录抑制复合体的组成和/或功能募集到肿瘤抑制基因启动子。据推测，在活跃的表观遗传重塑窗口期间，引入DNA损伤剂并长期暴露于环境毒素可能会导致多梳抑制复合体(PRC)、应激反应蛋白SIRT1和/或DNA甲基转移酶异常募集到DNA甲基化异常的基因启动子区域；具体目标3：确定低剂量的、长期的宫内暴露百草枯是否会诱导发育中的小鼠大脑DNA甲基化变化，破坏神经细胞的可塑性，和/或增强F1代神经干细胞的恶性潜能。它还假设，胚胎发育过程中表观遗传重塑的动态性质可能会使细胞特别容易受到环境毒素的影响。长期暴露可能导致异常的、启动子相关的DNA甲基化积累，抑制神经干细胞正常分化的能力，并可能导致这些细胞的癌前病变，包括异常高的有丝分裂率、核异型性或局灶性坏死。

DESCRIPTION (provided by applicant): Epidemiological studies have long suggested a critical, but poorly understood, link between toxic environmental exposures early in life and the development of human disease(s) later in life. Environmental toxins produce oxidative stress in cells, and a link between oxidative stress and epigenetic changes in a cell has implications for a variety of human diseases including cancer, infertility, and multiple neurodegenerative disorders. Though limited data exists, it has also been suggested that environmental toxins may disrupt both DNA methylation patterns and chromatin structure, which can confer not only heritable changes in gene expression, but also affect overall genomic stability. However, a direct link between environmental toxins, oxidative damage and epigenetic changes has not yet been established and is the primary focus of this proposal. It is proposed that exposure to common environmental contaminants during development or during key windows of susceptibility (WOS) throughout a lifetime may induce abnormal epigenetic, pre-malignant changes in developing/differentiating cells. It is expected that this window of susceptibility coincides with the normal epigenetic remodeling required for lineage commitment during development or periods of cellular repair/regeneration. To test this idea the following three specific aims are proposed: Specific Aim 1: Determine the in vitro WOS during which the environmental toxin paraquat induces DNA methylation changes in differentiating stem cells. It is hypothesized that stem cells are vulnerable to errors in epigenetic remodeling when they receive a signal to actively remodel their chromatin, i.e. during development and tissue regeneration; Specific Aim 2: Investigate whether paraquat exposure disrupts the composition and/or functional recruitment of stem cell transcriptional repressive complexes to tumor suppressor gene promoters. It is postulated that the introduction of DNA damaging agents and prolonged exposure of cells to environmental toxins during a window of active epigenetic remodeling may cause disruption and/or abnormal recruitment of polycomb repressive complexes (PRC), the stress response protein SIRT1, and/or DNA methyltransferases to gene promoter regions with abnormal DNA methylation changes; and Specific Aim 3: Determine whether low-dose, chronic, in utero paraquat exposure induces DNA methylation changes in the developing mouse brain, disrupts neural cell plasticity, and/or enhances the malignant potential of neural stem cells in the F1 generation. It is also hypothesized that the dynamic nature of epigenetic remodeling during embryonic development may leave cells particularly vulnerable to the effects of environmental toxins. Prolonged exposure may result in the accumulation of abnormal, promoter associated DNA methylation, inhibit the ability of neuronal stem cells to properly differentiate, and may induce pre-malignant changes including abnormally high mitotic rates, nuclear atypia, or focal necrosis in these cells.