Environmental toxins and stem cell epigenetic remodeling

描述（由申请人提供）：长期以来，流行病学研究表明，生命早期接触有毒环境与生命后期人类疾病的发展之间存在着关键的、但鲜为人知的联系。环境毒素在细胞中产生氧化应激，细胞中氧化应激和表观遗传变化之间的联系对多种人类疾病，包括癌症、不孕症和多种神经退行性疾病都有影响。尽管数据有限，但也有研究表明，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，还会影响整体基因组的稳定性。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建立，这是本提案的主要焦点。我们提出，在发育期间或在一生中易感关键窗口期暴露于常见的环境污染物可能导致发育/分化细胞的异常表观遗传、恶性前变化。预计这一易感性窗口与发育或细胞修复/再生期间谱系承诺所需的正常表观遗传重塑相吻合。为了验证这一观点，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诱导分化干细胞DNA甲基化变化的体外WOS。据推测，当干细胞在发育和组织再生过程中接收到主动重塑染色质的信号时，它们很容易受到表观遗传重塑错误的影响；特定目标2：研究暴露于百草枯是否会破坏肿瘤抑制基因启动子的干细胞转录抑制复合物的组成和/或功能募集。据推测，在活跃的表观遗传重塑窗口期间，DNA损伤剂的引入和细胞长期暴露于环境毒素可能导致多梳抑制复合物（PRC）、应激反应蛋白SIRT1和/或DNA甲基转移酶在DNA甲基化异常变化的基因启动子区域的破坏和/或异常募集；特异性目的3：确定低剂量、慢性、子宫内百草枯暴露是否会诱导发育中的小鼠大脑DNA甲基化变化，破坏神经细胞可塑性，和/或增强F1代神经干细胞的恶性潜能。还有一种假设是，胚胎发育过程中表观遗传重塑的动态性质可能使细胞特别容易受到环境毒素的影响。长时间暴露可能导致异常启动子相关DNA甲基化的积累，抑制神经干细胞正常分化的能力，并可能诱导这些细胞的恶性前病变，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.