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. Overall design: Transcriptome profiling of 80 samples from Rattus norvegicus. Samples include primary tumor from three Nf1-mutated rat lines and flow sorted normal tissue types from these same lines and wildtype rats. Normal tissues include whole mammary pad, adipocytes, fibroblasts, and mammary epithelial cells.