Developmental Exposure to Low-dose Bisphenol A and Human Prostate Cancer Suscepti

描述（由申请人提供）：先前对大鼠的研究提供了证据，表明生命早期以环境相关剂量短暂暴露于双酚A （BPA）会通过表观遗传修饰导致前列腺的发育重编程，从而增强生命后期的致癌易感性。虽然正在进行啮齿动物模型的剂量反应谱、双酚a药代动力学和暴露途径研究来验证这些发现，但目前迫切需要研究双酚a对发育中的人类前列腺的影响。国家毒理学规划2008年的报告摘要指出，“在实验动物身上进行的研究仅提供有限的证据证明对发育的不利影响，需要进行更多的研究，以便更好地了解它们对人类健康的影响”。为了满足这一需求，研究人员利用人类前列腺祖细胞开发了新的模型，可以直接检测低剂量BPA暴露在体外和体内形成前列腺样结构时的影响。拟议研究的目的是确定在人类前列腺发育的早期阶段暴露于环境相关水平的双酚a是否会增加以后生活中前列腺癌的易感性，并确定这种重编程事件的潜在机制。据推测，前列腺上皮祖细胞是早期腺体形成过程中BPA作用的直接靶点。此外，据预测，bpa诱导的重编程是通过改变的DNA甲基化和组蛋白修饰的组合介导的，这些修饰可作为祖细胞自我更新而遗传，在个体的整个生命周期中传递改变的表观基因组信息。因此，提出的研究代表了一种新的范式，即人类前列腺癌的发生可能在生命早期就开始了，这是对表观遗传改变祖细胞的不利环境影响的反应。我们将利用一种创新的方法来验证这一假设，并通过两种模型系统直接检测BPA对人前列腺祖细胞的影响：1)与人原代前列腺上皮/基质细胞的三维共培养系统在体外形成前列腺球；2)将重组体与大鼠泌尿生殖窦间充质移植到小鼠肾胶囊中，在体内形成嵌合前列腺样组织1-3个月。这些新方法将允许检查人类前列腺上皮细胞的分化缺陷（Aim 1）和癌变（Aim 2）作为发育性BPA暴露的功能。这些研究将通过使用人类基因启动子阵列和Solexa ChIP-seq分析进行DNA甲基化模式和遗传性染色质修饰的全基因组研究（Aim 3）。利用综合生物信息学，有望识别BPA重编程候选基因，这些候选基因可能作为人类流行病学研究中早期BPA暴露的生物标志物。为了确定bpa重编程候选基因与人类前列腺癌的潜在相关性，人类前列腺癌的组织微阵列（TMAs）将被用于筛选候选基因的错误表达，作为疾病分期、进展和种族的功能。从拟议的研究中获得的信息将在以下方面对科学、医学和监管界产生重大影响：1)为双酚a对人类的负面影响提供强有力的证据；2)建立发育重编程的机制框架；3)确定双酚a重编程的候选基因用作生物标志物；5)验证筛选其他内分泌干扰物质的有用模型系统，6)为研究BPA在其他器官系统和疾病中的作用奠定基础。

DESCRIPTION (provided by applicant): Previous studies in rats have provided evidence that brief, early-life exposures to bisphenol A (BPA) at environmentally relevant doses results in developmental reprogramming of the prostate gland via epigenetic modifications that enhance carcinogenic susceptibility later in life. While dose-response profiles, BPA pharmacokinetics and route of exposure studies in rodent models are underway to validate these findings, there is a current and compelling need for research on BPA effects in the developing human prostate gland. The National Toxicology Program 2008 report summarily stated that "studies in laboratory animals provide only limited evidence for adverse effects on development and more research is needed to better understand their implications for human health". In response to this need, novel models have been developed with human prostate progenitor cells that permit a direct examination of the impact of low-dose BPA exposures as they form prostate-like structures in vitro and in vivo. The goals of the proposed studies are to determine if exposure to environmentally relevant levels of BPA during the early stages of human prostate development increases susceptibility to prostate carcinogenesis later in life and to identify the underlying mechanism of this reprogramming event. It is hypothesized that prostate epithelial progenitor cells are the direct targets of BPA action during early gland formation. Further, it is predicted that BPA-induced reprogramming is mediated through a combination of altered DNA methylation and histone modifications that are heritable as progenitor cells self renew, transmitting altered epigenomic information throughout the lifespan of the individual. The proposed research thus represents a new paradigm that human prostate carcinogenesis may begin early in life in response to adverse environmental influences that epigenetically alter progenitor cells. An innovative approach will be exploited to test this hypothesis and directly examine BPA effects on human prostate progenitor cells using two model systems: 1) a 3-D co-culture system with human primary prostate epithelial/stromal cells to form prostaspheres in vitro, and 2) as recombinants with rat urogenital sinus mesenchyme grafted to murine kidney capsules for 1-3 months to form chimeric prostate-like tissues in vivo. These novel approaches will permit an examination of differentiation defects (Aim 1) and carcinogenesis (Aim 2) in the human prostate epithelial cells as a function of developmental BPA exposures. These studies will be informed by genome-wide studies of DNA methylation patterns and heritable chromatin modifications using human gene promoter arrays and Solexa ChIP-seq analysis (Aim 3). Using integrative bioinformatics, it is expected to identify BPA reprogrammed gene candidates that may serve as biomarkers for early-life BPA exposures in human epidemiology studies. To determine the potential relevance of BPA-reprogrammed candidate genes to human prostate cancer, tissue microarrays (TMAs) of human prostate cancer will be utilized to screen for misexpression of gene candidates as a function of disease stage, progression and ethnicity. The information gained from the proposed studies will be of high impact on the scientific, medical and regulatory communities in terms of 1) providing strong and compelling evidence for negative effects of BPA in humans, 2) establishing a mechanistic framework for developmental reprogramming, 3) identifying BPA-reprogrammed candidate genes for use as biomarkers, 4) ascertaining relevance of BPA-genes to human prostate cancer, 5) validating a useful model system for screening other endocrine disrupting chemicals, and 6) establishing a basis for studies on BPA in other organ systems and diseases. PUBLIC HEALTH RELEVANCE: There is increasing evidence in rodent models that brief, early-life exposures to bisphenol A (BPA) at dose levels typically found in humans results in developmental reprogramming of the prostate gland and increases susceptibility to prostate cancer later in life. The present proposal will test for this possibility in human prostate tissue using newly developed model systems with human prostate progenitor cells. Identification of epigenetic marks and BPA-reprogrammed genes may serve as biomarkers for developmental BPA exposures and provide molecular insight into the epigenomic plasticity that predisposes to prostate cancer with aging. The findings will be of high value to the medical and regulatory communities and serve as a model for human exposures to prevalent environmental endocrine disruptors with suspected carcinogenic potential.