Publication date: 25th July 2016
For decades it has been largely recognized that mammary gland stroma plays a major role in regulation of development and homeostasis of mammary epithelium. However, despite major efforts in the area, the particular roles of the individual stromal components have not been fully elucidated.
We have focused on the role of fibroblasts and extracellular matrix (ECM) remodeling during pubertal mammary gland development. Our studies using mouse models revealed that modulation of receptor tyrosine kinase (RTK) signaling in mammary fibroblasts has an important role in regulation of epithelial branching morphogenesis. Using 3D cell cultures, including co-culture branching assay, organotypic invasion assay and time-lapse imaging we found that mammary fibroblasts induced epithelial branching and promoted epithelial invasion into ECM. These effects were mediated by EGFR- and FGFR-regulated paracrine signaling and ECM remodeling by fibroblasts. Using a 3D spheroid invasion assay we found that FGF2 induces an invasive phenotype in fibroblasts through its action on actomyosin cytoskeleton (via MLCK and small GTPases Rac1, Cdc42 and Rho). 3D organotypic co-cultures of mammary epithelial organoids with fibroblasts revealed that this invasive phenotype was also induced by mammary epithelium and represented an activated state of fibroblasts that regulated mammary epithelial morphogenesis.
Moreover, besides fibroblasts, mammary epithelial cells remodel ECM by themselves. Currently we are developing 3D culture systems to investigate epithelium-mediated ECM remodeling during mammary branching morphogenesis.
Taken together, our studies bring new insights into the mechanisms by which fibroblasts and ECM remodeling regulate mammary gland development and homeostasis, and deregulation of which could lead to tumor formation.
Acknowledgement: This work has been supported by grant GJ16-20031Y from Czech Science Foundation (GACR).