Single Cell Transcriptomics Reveals a Tumor Promoting Mammary Cell Niche in Brca1 Heterozygous Breast Cancer Mouse Model

Women carrying BRCA1 (B1) mutations face an elevated risk of developing breast cancer, yet effective preventive strategies remain limited. To design innovative strategies, it is critical to understand the early events driving tumorigenesis. Here we present a unique mouse model which is conditionally heterozygous for B1 and deleted for Trp53, specifically in the mammary epithelial cells, and forms triple-negative mammary tumors under replication stress. Our single-cell RNA sequencing analysis, spanning various stages of mammary tumorigenesis in this model, reveals early tumor-promoting transcriptomic alterations. We identify a distinct, proliferative bi-potent cell population expressing both luminal progenitor and basal epithelial markers, uniquely enriched in Brca1 heterozygous mammary tissue upon replication stress. Notably, the transcriptomic changes in this population correlate with poor outcomes in human breast cancer. Transcriptomic analysis, combined with transcription factor analysis, along the trajectory from normal to precancerous and tumor stages, implicates the AP-1 complex, specifically the FRA-1 transcription factor, as an early driver in BRCA1 mutant breast cancer. Furthermore, pseudo-time analysis along this trajectory identifies alveolar luminal progenitor cells as the likely cell-of-origin. Luminal cells also show reduced efficiency of DNA damage repair when compared to basal cells. In conclusion, we have established the first Brca1 heterozygous mouse model for studying the effects of DNA replication stress on breast cancer and have identified early precancerous transcriptomic changes stemming from BRCA1 haploinsufficiency and replication stress. This study provides critical insights into the molecular mechanisms that drive breast cancer in BRCA1 mutation carriers. Mouse mammary glands from replication stress driven Brca1 heterozygous model. Samples for submission include 12x vehicle or 600mg/mL or tumor sample.

携带BRCA1（缩写B1）突变的女性罹患乳腺癌的风险显著升高，但当前有效的乳腺癌预防策略仍较为匮乏。若要开发创新性的防治方案，阐明驱动肿瘤发生的早期事件是核心前提。本研究构建并报道了一种独特的小鼠模型：该模型在乳腺上皮细胞中呈Brca1（BRCA1，缩写B1）条件性杂合状态且敲除Trp53，在复制应激条件下可形成三阴性乳腺肿瘤。我们针对该模型中乳腺肿瘤发生的多个阶段开展了单细胞RNA测序（single-cell RNA sequencing）分析，揭示了早期促肿瘤发生的转录组改变。本研究鉴定出一类独特的增殖性双潜能细胞群：该细胞群同时表达腔祖细胞（luminal progenitor）和上皮基底细胞标志物（basal epithelial markers），在复制应激条件下于BRCA1杂合型乳腺组织中特异性富集。值得注意的是，该细胞群的转录组改变与人类乳腺癌的不良预后显著相关。通过对从正常组织到癌前病变再到肿瘤阶段的轨迹进行转录组学分析并结合转录因子分析，本研究证实AP-1复合物（AP-1 complex），尤其是FRA-1转录因子（FRA-1 transcription factor），是BRCA1突变型乳腺癌的早期驱动因素。此外，沿该轨迹开展的拟时间分析（pseudo-time analysis）表明，肺泡腔祖细胞（alveolar luminal progenitor cells）是该类肿瘤的潜在细胞起源。与基底细胞相比，腔上皮细胞的DNA损伤修复（DNA damage repair）效率显著降低。综上，本研究构建了首个用于研究DNA复制应激对乳腺癌影响的BRCA1杂合型小鼠模型，并鉴定出由BRCA1单倍剂量不足（haploinsufficiency）和复制应激引发的早期癌前转录组改变。本研究为阐明BRCA1突变携带者乳腺癌发生的分子机制提供了关键见解。本数据集包含来自复制应激诱导的BRCA1杂合型小鼠模型的乳腺组织样本。提交的样本包括12份载体对照样本、600mg/mL处理组样本以及肿瘤样本。