激素协同衰老诱发乳腺干细胞癌变的潜在风险及其分子机制

Aging is the number one risk factor for breast cancer as only 5% of all breast cancers occurring in women under 40 years old. Hormone is another important factor in breast cancer etiology, for example, serum estradiol levels are strongly associated with increased breast cancer risk in postmenopausal women. Hormonal replacement therapy (HRT) using estrogen plus progestin has been demonstrated to increase breast cancer risk. Prolactin promotes mammary tumor formation in various animal models, and has been recently shown to be associated with increased breast cancer risk among the postmenopausal HRT users. Together, all these findings indicate the important roles of aging and hormone in breast cancer etiology, yet there is no study employing an aged animal model to study hormone induced breast cancer. More recently, mammary stem/progenitor cells have been implicated as the cellular origins of various subtypes of breast cancer, and our own new findings revealed that old basal stem cells are more susceptible to spontaneous neoplastic lesion formation when they were transplanted into young recipient hosts, suggesting a transformation potential of old stem cells. Based on these observations, we hypothesized that hormone(s) induced breast cancer risk in aged women may be mediated through aberrant stem cells associated with aging. To test this hypothesis, we will administer estrogen, estrogen plus progestin, and prolactin (in the form of pituitary xenograft in renal kidney capsule) to 18-month old FVB-GFP transgenic mice to assess the effect of hormones on stem cell phenotypic and functional changes. 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 to reveal the underlying mechanisms responsible for hormone-induced breast cancer risk mediated by aged stem/progenitor cells. Our specific aims are to 1) explore whether hormone exposure will further increase or catalyze the transformation potential of aged stem cells, and 2) identify the particular stem cells that are most sensitive to hormone-induced tumorigenesis in aged hosts. The findings of our research will fill knowledge gap and make a breakthrough in our understanding of the cellular and molecular mechanisms that mediate hormone-induced transformation potential of mammary stem cells during progressive aging. It will set a foundation for future development of novel biomarkers for early detection and novel interventions in preventing aging-related breast cancer, which will particularly benefit the population at high risk for breast cancer.

基于乳腺癌发病率与年龄存在显著正相关以及使用激素是老年妇女乳腺癌病发的主要诱因之一，结合本课题组有关衰老乳腺干细胞异常增殖、功能衰退、且具有癌变潜能这一最新发现，本课题提出老年人群自发性乳腺癌高发的要因可能是激素协同衰老共同作用于乳腺干细胞而使之发生癌变的科学假说。本课题将以转基因绿色FVB小鼠为材料，利用自己开发的乳腺干细胞体外定性和定量分析方法，结合干细胞体内移植再生技术，通过激素处理老龄小鼠来：1）评价激素增加衰老乳腺干细胞发生癌变的风险；2）甄别易受激素诱发而产生癌变的乳腺干细胞群；3）阐释激素诱导衰老乳腺干细胞发生癌变的分子作用机制。由于本项目模拟自发性乳腺癌病发的真实生理环境，研究结果将有助于诠释乳腺肿瘤在老龄人群的真实发生机理，从而为开发乳腺癌早期诊断分子标记物和有效的癌症预防干预提供重要的科学依据。

基于乳腺癌发病率与年龄存在显著正相关以及使用激素是老年妇女乳腺癌病发的主要诱因之一，结合本课题组有关衰老乳腺干细胞异常增殖、功能衰退、且具有癌变潜能这一最新发现，本课题提出老年人群自发性乳腺癌高发的要因可能是激素协同衰老共同作用于乳腺干细胞而使之发生癌变的科学假说。本课题利用自己开发的乳腺干细胞体外定性和定量分析方法，结合干细胞体内移植再生技术，通过激素处理老龄小鼠来，评价了激素增加衰老乳腺干细胞发生癌变的风险，并甄别出易受激素诱发而产生癌变的乳腺干细胞群。研究发现，雌激素或雌孕激素联合处理2个月可导致乳腺上皮细胞发生癌前病变，增加老龄小鼠乳腺管腔细胞Ki67和ERα的表达水平，引起老龄小鼠乳腺干细胞数量的改变并影响老龄小鼠乳腺干细胞的分化潜能。其中雌孕激素联合处理显著增加了基底细胞群在乳腺上皮细胞中的比例。通过脑垂体移植的催乳素处理小鼠乳腺形态在3周后发生明显变化，其中年轻小鼠较老龄小鼠乳腺更易受到催乳素影响。体外集落实验可以用来研究乳腺干细胞不同亚群的分布频率和功能变化，这些实验的研究结果表明催乳素处理后不同干细胞亚群的分布频率发生了变化，且由这些干细胞分化所形成的集落的特性也发生了改变。这可能是因为催乳素通过PRL-Jak2-Stat5信号通路影响作用于乳腺干细胞。此外，由催乳素处理的小鼠乳腺干细胞形成的再生乳腺导管非典型性增生比例较对照组再生乳腺有增加的趋势，确证乳腺干细胞是激素诱导的乳腺导管非典型增生的介质媒体。综上所述，本项目的研究表明激素可以协同衰老进一步影响乳腺干细胞不同干细胞亚群的组成比例及其功能特性和癌变潜能，这些变化机制极有可能同样存在于自发性乳腺癌的老龄人群。故而该研究结果为今后开发乳腺癌早期诊断分子标记物和有效的癌症预防干预提供重要的科学依据。