Matrix compositions and the development of breast acini and ducts in 3D cultures.

Breast epithelial cells develop into polarized and highly organized acinar and ductal structures in response to stromal cues, including extracellular matrix composition and density, which can in part be reproduced in 3D culture conditions. Here, we present the effects of various 3D in vitro stroma compositions (termed "matrices" or "substrates") on the ability of heterotypic cultures of epithelial and mesenchymal stem cells to organize into acinar and tubular structures. Normal murine mammary gland (NMuMG) cells were cultured, either alone or in combination (30:70) with mouse mesenchymal stem cells (D1), in 3D matrices generated by agarose, collagen, and Matrigel alone or by a combination thereof. After 3-5 d in culture, cell distribution, organization, and the presence of acinus-like and tubule-like structures were determined. The number of acinar structures was significantly higher in cultures grown in combination matrices of agarose with Matrigel or collagen I when compared with cultures grown in Matrigel or collagen I alone (p < 0.05). No tubular structures were formed when agarose was included in the matrix, regardless of the combination. In Matrigel, but not in collagen I/Matrigel microenvironment, the number of tubular structures was significantly increased in NMuMG/D1 coculture when compared with culture of NMuMG cells alone (p < 0.05). By immunohistochemical analysis, NMuMG cells cocultured with D1 cells were shown to form acinar structures with the NMuMG epithelial cells surrounding a lumen composed of dead cells while the D1 cells were mostly peripheral. Immunostaining for laminin indicated the presence of basement membrane when NMuMG cells were grown in Matrigel alone or cocultured with D1 cells in a combination of Matrigel and collagen I. These results indicate that the physical and biochemical properties of the matrix and cellular composition alter the organization of the mammary gland.