Nf1 Deficiency Increases Mammary Collagen Deposition and Restricts Adipocyte Differentiation Before Tumor Formation

BACKGROUND: The NF1 tumor suppressor gene is the main negative regulator of the RAS pathway and is frequently mutated in various cancers. Women with Neurofibromatosis Type I (NF1) – a tumor predisposition syndrome caused by a germline NF1 mutation – have an increased risk of developing aggressive breast cancer with poorer prognosis. The mechanisms by which NF1 mutation leads to breast cancer tumorigenesis are not well understood. Therefore, the objective of this work was to identify stromal alterations before tumor formation that result in the increased risk and poorer outcome seen among NF1 patients with breast cancer. METHODS: To accurately model the germline monoallelic NF1 mutations in NF1 patients, we utilized an Nf1-deficient rat model with accelerated mammary development and develops highly penetrant breast cancer. RESULTS: We identified increased collagen content in Nf1-deficient rat mammary glands before tumor formation that correlated with age of tumor onset. Additionally, gene expression analysis revealed that Nf1-deficient rat mammary mature adipocytes have increased collagen expression and shifted to a fibroblast and preadipocyte expression profile. This alteration in lineage commitment was also observed with in vitro differentiation but flow cytometry analysis did not show a change mammary adipose-derived mesenchymal stem cell abundance. CONCLUSION: Collectively, these studies uncovered the previously undescribed role of Nf1 in mammary collagen deposition and regulating adipocyte differentiation. In addition to unraveling the mechanism of tumor formation, further investigation of adipocytes and collagen modifications in preneoplastic mammary gland will create a foundation for developing early detection strategies of breast cancer among NF1 patients.研究背景：NF1肿瘤抑制基因（NF1 tumor suppressor gene）是RAS通路的主要负调控因子，在多种癌症中频繁发生突变。I型神经纤维瘤病（Neurofibromatosis Type I, NF1）是一种由生殖系NF1突变引发的肿瘤易感综合征，此类女性患者罹患侵袭性乳腺癌且预后不良的风险显著升高。目前，NF1突变诱发乳腺癌发生的分子机制尚未完全阐明。因此，本研究旨在鉴定肿瘤发生前的基质细胞改变，以解析NF1相关乳腺癌患者发病风险升高及预后不良的潜在机制。研究方法：为精准模拟NF1患者的生殖系单等位基因NF1突变，我们采用了一种乳腺发育加速且可高外显率诱发乳腺癌的Nf1缺陷型大鼠模型。研究结果：我们在肿瘤发生前的Nf1缺陷型大鼠乳腺组织中检测到胶原蛋白含量升高，且该变化与肿瘤发病年龄呈显著相关。此外，基因表达分析显示，Nf1缺陷型大鼠乳腺成熟脂肪细胞的胶原蛋白表达上调，并向成纤维细胞及前脂肪细胞的表达谱转变。这种细胞谱系定向改变在体外分化实验中得到了验证，但流式细胞术分析未发现乳腺脂肪来源间充质干细胞的丰度发生变化。研究结论：综上，本研究揭示了Nf1在乳腺胶原蛋白沉积及调控脂肪细胞分化中此前未被报道的作用。本研究不仅阐明了肿瘤发生的分子机制，同时对癌前乳腺组织中脂肪细胞及胶原蛋白修饰的进一步研究，将为开发NF1患者乳腺癌早期检测策略奠定理论基础。