Perinatal xenoestrogen exposure: epigenesis and neoplasia

描述(由申请人提供)： 在过去的50年里，在欧洲和美国人群中观察到的子宫肌瘤、睾丸和乳腺癌发病率的增加促使科学家们假设，产前暴露于环境雌激素可能是这些肿瘤的潜在原因。流行病学研究表明，胎儿环境中雌激素水平的波动会对成年后患乳腺癌的风险产生长期影响。实验室啮齿动物研究表明，围产期暴露于药理剂量的己烯雌酚(DES)会增加乳腺癌的发病率并缩短潜伏期，这一点得到了支持。在异种雌激素中，双酚-A被选为这些研究的原因是因为它的广泛使用，而且在疾控中心最近一项研究中分析的95%的尿样中发现了双酚-A。围产期暴露于环境相关剂量的异种雌激素双酚A(BPA)会改变啮齿动物乳腺的发育，导致青春期对雌激素的敏感性增加，成年后导管密度增加，以及发生癌症的结构数量增加。利用大鼠乳腺癌变模型，进行了一项先导性实验，显示围产期暴露于低剂量双酚A可诱导导管内增生。当被亚致癌剂量的亚硝基甲基脲激发时，只有暴露于BPA的动物发生了肿瘤。因此，可以假设，围产期给药的双酚A将通过改变特定基因的甲基化模式永久地改变特定组织的基因表达模式。这些变化反过来会影响BPA暴露后的发育，导致乳腺癌易感性增加。具体目标1将比较载体和双酚A暴露动物乳腺中DNA甲基化的全球模式，并构建染色体甲基化惯用图。具体目标2的三个组成部分是：1)通过DNA微阵列分析确定BPA处理的乳腺组织的mRNA表达谱，并将差异表达基因定位在大鼠染色体表意文字上；2)根据mRNA微阵列分析找出映射到BPA甲基化或去甲基化染色体区域的差异表达候选基因；以及3)通过生物信息学技术(分子通路和本体论分析)缩小候选基因集。最有希望的候选人(S)将通过甲基化的CpG二核苷酸的亚硫酸氢盐图谱进行详细的探索。如果发现围产期双酚A暴露与基因甲基化改变之间的因果联系，这项工作将提供可检验的假说，将双酚A诱导的基因标记与发生乳腺肿瘤的倾向联系起来。如果假设与结果一致，这将构成重点从成人接触到宫内接触的重大转变。这也将对我们研究风险因素和进行流行病学研究的方式产生重大影响，甚至可能影响预防乳腺癌的公共政策。

DESCRIPTION (provided by applicant): The increased incidence of uterine leiomyoma, testicular and breast cancer observed in European and US populations during the last 50 years prompted scientists to hypothesize that prenatal exposure to environmental estrogens may be the underlying cause of these neoplasms. Epidemiological studies suggest that fluctuating estrogen levels in the fetal environment have long-term consequences regarding the risk of developing breast cancer during adult life. This is supported by laboratory rodent studies showing that perinatal exposure to pharmacological doses of diethylstilbestrol (DES) increases the incidence and decreases the latency period of mammary cancer. Among the xenoestrogens, bisphenol-A was chosen for these studies because of its widespread use and because it is found in 95% of the urine samples analyzed in a recent CDC study. Perinatal exposure to environmentally relevant doses of the xenoestrogen bisphenol A (BPA) alters the development of the rodent mammary gland and results in outcomes such as increased sensitivity to estrogens at puberty, increased ductal density in adulthood, and an increase in the number of structures where cancer arises. Using a rat mammary carcinogenesis model a pilot experiment was performed that revealed that perinatal exposure to low BPA doses induces intraductal hyperplasias. When challenged with a subcarcinogenic dose of nitrosomethylurea, only the BPA exposed animals developed neoplasias. Thus it is hypothesized that BPA administered perinatally will permanently alter tissue-specific patterns of gene expression by altering the methylation pattern of specific genes. These alterations will, in turn, affect development beyond the period of exposure to BPA, leading to an increase in susceptibility to breast cancer. Specific Aim 1 will compare the global pattern of DNA methylation in the mammary glands of vehicle and BPA-exposed animals and to construct a chromosomal methylation idiogram. The three components of Specific Aim 2 are to: 1) Determine the mRNA expression profiles of the BPA-treated mammary glands by DNA microarray analysis and to map the loci of differentially expressed genes on the rat chromosomal ideogram; 2) Identify candidate genes that are differentially expressed according to the mRNA microarray analysis that map onto the BPA-methylated or demethylated chromosomal regions; and 3) Narrow the set of candidate genes by bioinformatics techniques (molecular pathway and ontology analysis). The most promising candidate(s) will be probed in detail using bisulfite mapping of the methylated CpG dinucleotides. If a causal link is found between perinatal BPA exposure and alterations in gene methylation, this work will provide testable hypotheses connecting BPA-induced gene marking and propensity to develop mammary gland neoplasia. If the hypothesis is consistent with the result, this will constitute a major shift in emphasis from adult exposures to in utero exposures. This will also have a great impact on the way we study risk factors and conduct epidemiological studies; it may even influence public policy about breast cancer prevention.