环境雌激素双酚A增加乳腺癌风险的作用机制

The plastic monomer and plasticizer bisphenol A (BPA) is an environmental xenoestrogen that is ubiquitous in human body. The structure similarity between BPA and the 17β-estradiol (E2) has prompted researchers to suspect that BPA is one of the main causative factors for the continuous increase of breast cancer incidence. Previous research using mouse or rat has shown that in utero exposure to low dose BPA can increase lateral branching, hyperplastic lesion and mammary tumor susceptibility in adult mammary glands. Yet, the underlying mechanisms responsible for these changes remain unknown. Our preliminary findings of pubertal low dose BPA exposure with Balb/c mice indicated that mammary stem cell was one of the potential transformation targets responsible for BPA induced abnormalities. Our current proposal will take advantage of a transgenic DSR-C57BL6 mouse model and further explore this hypothesis. In details, we will use an in vitro mammary stem cell qualification and quantification method that developed in our laboratory in conjunction with the traditional in vivo regeneration method and take the advantage of the modern molecular techniques such as next generation sequence to reveal the underlying mechanism for BPA-induced mammary gland morphogenetic changes and tumor susceptibility. The specific objectives are to 1) identify whether regenerated glands from pubertal low dose BPA exposed luminal progenitors or mature luminal cells will exhibited similar preneoplastic lesions as the glands regenerated from BPA exposed mammary stem cells; 2) explore whether those preneoplastic lesions observed in regenerated glands from BPA exposed cells are correlate to any particular breast cancer subtypes in gene expression level; 3) elucidate the cell type (epithelial vs. stromal cells) and molecular receptors (estrogen vs. progesterone receptors) that mediated BPA induced preneoplastic lesions in regenerated glands. The findings of our research will not only reveal the underlying molecular mechanisms responsible for BPA induced preneoplastic lesions and tumor susceptibility, but also provide strong scientific evidence for human breast cancer risk assessment of xenoestrogens in general.

环境雌激素双酚A（BPA）因其在人体内普遍存在被认为是可能导致现代人类乳癌增加的主要环境因素之一。虽然许多动物实验都已证明在敏感窗口期暴露于低剂量BPA可导致成年乳腺发生病变，但至今对其内在机制仍一无所知。我们的前期研究表明乳腺干细胞是BPA的主要靶细胞之一，故拟在此基础上以转基因红色小鼠来继续深入验证这一假说。本项目将采用自己开发的乳腺干细胞体外定性和定量法，并结合干细胞体内移植再生技术和深度测序，通过低剂量BPA的青春期暴毒来：1）识别经BPA暴毒后的乳腺干／祖／分化细胞是否对BPA引发的再生乳腺癌前病变具有不同的敏感性；2）探索经BPA暴毒后所得再生乳腺的癌前病变是否与不同乳癌亚型存在关联；3）阐释BPA在敏感窗口期暴毒所引发的乳腺组织癌变风险的介质媒体及其分子作用受体。研究结果能诠释以BPA为代表的环境雌激素的乳癌诱发作用机制，也可为此类化合物的健康风险评价提供重要的科学依据。

环境雌激素双酚A（BPA）因其在人体内普遍存在被认为是可能导致现代人类乳癌增加的主要环境因素之一。虽然许多动物实验都已证明在敏感窗口期暴露于低剂量BPA可导致成年乳腺发生病变，但至今对其内在机制仍一无所知。我们的前期研究表明乳腺干细胞是BPA的主要靶细胞之一，故拟在此基础上继续深入验证这一假说。本项目采用自己开发的乳腺干细胞体外定性和定量法，并结合干细胞体内移植再生技术和深度测序，通过低剂量BPA的青春期暴毒，明确了青春期BPA暴露的敏感浓度，及其对小鼠乳腺生长发育相关激素水平的影响，甄别出导致再生乳腺癌前病变的敏感靶细胞，探索了青春期BPA暴露对乳腺干细胞的影响，研究了BPA诱导再生乳腺癌前病变的基因表达变化以及诱导再生乳腺癌前病变的介质媒体和分子受体。研究发现，BPA青春期暴露的敏感浓度为400 μg/kg/day，该浓度导致小鼠乳腺生长发育及相关激素水平的紊乱。在乳腺发育的早期阶段，乳腺管腔细胞中成熟管腔细胞群受BPA的影响最大，故而我们推测其上一级的管腔干细胞极有可能是BPA的主要作用靶细胞。去乳脂垫乳腺干细胞移植再生的交叉实验表明BPA既可以直接作用于乳腺上皮细胞，也可以通过基质细胞间接影响乳腺干细胞的癌变潜能，其诱导再生乳腺癌前病变的介质媒体为管腔干细胞。对导致再生乳腺癌前病变潜能的初步探索显示BPA可能通过激活STAT5信号通路，进一步促进炎症反应标志物COX2表达增加从而影响乳腺干细胞的功能，引起乳腺导管结构改变，增加乳腺癌的发生风险。此外，我们还发现在乳腺发育的青春期窗口暴露BPA会使得乳腺干细胞对雌激素缺乏诱导的转化敏感度增加。综上所述，本项目的研究结果不仅诠释了以BPA为代表的环境雌激素的乳癌诱发作用机制，而且为此类化合物的健康风险评价提供了重要的科学依据。