Abstract B035: Preneoplastic transformation of murine mammary stem cells by aging and inhibition by rapamycin
Authors: Sun Lu-Zhe , Bandyopadhyay Abhik , Dong Qiaoxiang , Gao Hui , Gu Xiang , Wang Danhan , Wu Anqi , Huang Changjiang 
Published: May 2015

Abstract
The number one risk fact for breast cancer is aging. Recent research implicated that adult mammary stem cells (MaSCs) might be responsible for the initiation and progression of certain types of breast cancer. We tested the hypothesis that aging-associated mammary tumorigenesis may be due to altered number and function of MaSCs using mouse models. MaSC-enriched basal cells, characterized by their immunophenotype (Lin-CD49fhighCD24med), were utilized for the evaluation of MaSC frequency and function during aging by in vitro mammosphere formation and 3D-ECM sphere differentiation assays and by in vivo cleared mammary fat pad transplantation (IVT) as we reported recently (Stem Cell Res. 2013). We found that the basal-to-luminal cell ratios analyzed by FACS and the frequency of MaSCs analyzed with in vitro assays increased steadily with increasing age in various strains of mice. Subsequent IVT using mammosphers or 3D-ECM structures formed by young (4 months) or old (28 months) MaSCs derived from C57BL/6 mice showed similar in vivo functional mammary gland regenerative capacity indicating similar self-renewal/differentiation ability between young and old MaSCs. However, we found that the regenerated glands from old MaSCs had significantly higher number of spontaneous hyperplastic and atypical ductal hyperplastic lesions than those from young MaSCs. These findings indicate that aged MaSCs can serve as the cell of origin for early neoplastic transformation in breast tissue. Because rapamycin treatment has been shown to ameliorate age-related pathologies including cancer in murine models, we fed old C57BL/6 mice with microencapsulated rapamycin-containing food or control diet to determine whether rapamycin treatment can inhibit the aging-associated alteration of MaSC number and function. Our findings indicate that short-term (5-10 days) or long-term (&gt; 2 year) rapamycin treatment reversed phenotypic changes associated with aged mammary gland, which were mainly characterized by decreased luminal-to-basal cell ratio and increased MaSC frequency. Histological analysis of regenerated glands by aged MaSCs derived from control and rapamycin-treated mice showed a significant decrease of early neoplastic lesions in rapamycin-treated group. Subsequent whole genome transcriptome analysis with the second generation sequencing revealed age-associated differential expression of genes involved in immune, inflammatory, and wounding responses in both mammosphere-forming cells and stromal cells suggesting that these may be the main cellular processes contributing to the altered MaSC phenotypes and inhibited by rapamycin. In conclusion, our findings suggest that aging causes MaSC to increase its pool and to form early neoplastic lesions, which can be inhibited by rapamycin treatment.
Citation Format: Lu-Zhe Sun, Abhik Bandyopadhyay, Qiaoxiang Dong, Hui Gao, Xiang Gu, Danhan Wang, Anqi Wu, Changjiang Huang. Preneoplastic transformation of murine mammary stem cells by aging and inhibition by rapamycin. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr B035.