Characterizing the dynamic co-evolution of lung fibroblasts in the metastatic microenvironment during breast cancer metastasis

Mortality in breast cancer is almost exclusively a result of tumor metastasis, and Lungs are one of the main sites of breast cancer metastasis. Formation of a hospitable microenvironment in the target distant organ is required for the establishment of metastases. Cancer-associated fibroblasts (CAFs) are prominent players in the microenvironment of many primary tumors, including breast cancer. However, the role of CAFs in the formation of a permissive metastatic niche is still largely unresolved. To characterize the dynamic changes in CAFs during the formation of lung metastases, we combined the MMTV-PyMT model of mammary carcinogenesis with mice that express the fluorescent reporter YFP under the Collagen-1α gene promoter, thus creating PyMT-Col1α-YFP mice, which develop autochthonous mammary tumors followed by spontaneous lung metastasis, in which all fibroblasts are fluorescently labeled. Utilizing these mice, we isolated lung fibroblasts in an unbiased manner from normal mice, or from mice with micro- or macro-metastases and profiled their transcriptome by RNA-Seq. We used multiple bioinformatics tools in order to characterize the gene expression pattern and phenotype of the fibroblasts along the stages and found that it is dynamic, indicating that fibroblasts co-evolve during the process of pulmonary metastases formation. Characterization of the most prominent transcriptional programs indicated that the main tasks operative in metastases-associated CAFs include extracellular matrix deposition and remodeling, inflammation and stress response. Further functional studies of metastases-associated lung fibroblasts will uncover the contribution of these pathways to facilitating breast cancer lung metastasis.