Impact of transplacental PAH exposure on the epigenome

描述(申请人提供)：多环芳烃(PAHs)对人类健康构成“重新出现”的威胁。尽管美国通过烟草烟雾接触多环芳烃的量在减少，但人类每天接触多环芳烃的量却在增加，这可能是由于中国和美国煤电行业的大规模扩张所致。人们非常担心怀孕期间胎儿接触环境化学物质可能与成人癌症有关。环境中的多环芳烃二苯并[a，L]芘(DBP)和苯并[a]芘(Bap)都是小鼠经胎盘的致癌物质，在成年后代中引起肺癌的高发。表观基因组的改变被认为与许多癌症有关。肿瘤中的表观遗传学变化主要导致基因启动子区域的异常高甲基化和不适当的基因沉默，从而赋予肿瘤细胞选择性优势。在人类和小鼠肺癌中发现了肿瘤抑制基因的高甲基化，包括细胞周期蛋白依赖性激酶抑制因子2A(CDKN2a)、维甲酸受体β(RARB)、死亡相关蛋白激酶(Dapk1)、O-6-甲基鸟嘌呤DNA甲基转移酶(MGMT)和H-钙粘素(Cadh13)。来自体外细胞培养研究的新证据表明，BaP改变了基因特异性启动子甲基化的模式。然而，目前尚不清楚体内暴露于多环芳烃是否会改变表观基因组，从而增加癌症风险。为了解决这一重大的知识差距，我们建议在一个经胎盘的肺化学致癌模型中调查妊娠期多环芳烃暴露的影响。这项建议的主要目的是确定孕期暴露于多环芳烃对小鼠肺中胎儿和成年后代表观基因组的影响。工作假设是，经胎盘暴露于多环芳烃会改变关键肿瘤抑制基因启动子区域的DNA甲基化，从而增加成年人患肺癌的风险。我们计划通过以下具体目标来实现我们的初步目标：(1)确定经胎盘暴露于DBP和BaP对新生小鼠肺中CDKN2a、Rarb、Dapk1、MGMT和Cadh13基因启动子区甲基化的影响；评估宫内暴露对新生小鼠肺DNA甲基转移酶基因1、3a和3b表达的影响。(2)通过测量成年小鼠(15至45周)癌前病变发展为肺腺癌时的基因启动子甲基化，评估妊娠期多环芳烃暴露导致肿瘤抑制基因沉默的时间；从功能上将改变的DNA甲基化与改变的基因和蛋白表达联系起来。这项拟议研究的成功完成将提供有关多环芳烃对表观基因组影响的新知识，并在胎儿暴露和成人疾病之间建立潜在的表观遗传学联系。如果这一假设得到支持，这将是第一次证明胎儿暴露于多环芳烃会导致表观基因组的持续变化，从而增加成人的癌症风险。 公共卫生相关性：非常需要了解孕期环境暴露与成人疾病之间的关系。新的科学表明，环境因素可能会修改表观基因组(即影响基因表达的特定DNA结构模式和修饰)，以增加癌症风险。一生中接触化学致癌物的很大一部分发生在怀孕和整个母乳喂养期间，胎儿可能特别容易受到改变表观基因组的化学物质的影响。

DESCRIPTION (provided by applicant): Polycyclic aromatic hydrocarbons (PAHs) represent a "re-emerging" threat to human health. Even though exposure to PAHs via tobacco smoke is decreasing in the U.S., daily human exposures to PAHs are on the rise, likely due to the vast expansion of the coal power industry in China and the U.S. There is great concern that fetal exposure to environmental chemicals during pregnancy could be linked to adult cancers. The environmental PAHs dibenzo[a,l]pyrene (DBP) and benzo[a]pyrene (BaP) are both transplacental carcinogens in mice causing a high incidence of lung tumors in adult offspring. Alterations of the epigenome have been implicated in many cancers. Epigenetic changes in tumors mostly result in aberrant hypermethylation of gene promoter regions and inappropriate gene silencing, thus conferring a selective advantage to neoplastic cells. Hypermethylation of tumor suppressor genes has been shown in human and mouse lung cancers, including cyclin-dependent kinase inhibitor 2A (Cdkn2a), retinoic acid receptor beta (Rarb), death-associated protein kinase (Dapk1), O-6-methylguanine DNA methyltransferase (Mgmt) and H-cadherin (Cadh13). New evidence from in vitro cell culture studies suggests that BaP alters patterns of gene-specific promoter methylation. However, it is not known whether in vivo exposure to PAHs alters the epigenome to increase cancer risk. To address this significant knowledge gap, we propose to investigate the impact of gestational PAH exposure in a transplacental model of lung chemical carcinogenesis. The primary objective of this proposal is to determine the impact of gestational exposure to PAHs on the fetal and adult offspring epigenome in the mouse lung. The working hypothesis is that transplacental exposure to PAHs alters DNA methylation in the promoter region of key tumor suppressor genes leading to increased risk of lung cancer in the adult. We plan to accomplish our primary objective by pursuing the following specific aims: (1) Determine the impact of transplacental exposure to DBP and BaP on methylation of the promoter regions of the Cdkn2a, Rarb, Dapk1, Mgmt and Cadh13 genes in neonate mouse lung; assess impact of in utero exposure to PAHs on expression of DNA methyltransferase genes 1, 3a and 3b in neonate lung. (2) Assess the timing of tumor suppressor gene silencing resulting from gestational PAH exposure by measuring gene promoter methylation in adult mice (aged 15 to 45 weeks) as preneoplastic lesions develop into lung adenocarcinomas in the adults; functionally link altered DNA methylation to altered gene and protein expression. Successful completion of the proposed research will provide new knowledge about the impact of PAHs on the epigenome and establish potential epigenetic links between fetal exposure and adult disease. Should the hypothesis be supported, this would be the first demonstration that fetal exposure to PAHs causes persistent changes in the epigenome leading to increased cancer risk in the adult. PUBLIC HEALTH RELEVANCE: There is great need to understand how environmental exposures during pregnancy may be linked to adult disease. New science suggests that environmental agents may modify the epigenome (that is, specific patterns of DNA structure and modifications that influence gene expression) to increase cancer risk. A significant portion of lifetime exposure to chemical carcinogens occurs during gestation and throughout breast feeding, and the fetus may be particularly susceptible to chemicals that alter the epigenome.