Loss of caveolin-1 alters extracellular matrix protein expression and ductal architecture in murine mammary glands

The extracellular matrix (ECM) is abnormal in breast tumors and has been reported to contribute to breast tumor progression. One factor, which may drive ongoing matrix synthesis in breast tumors, is the loss of stromal caveolin-1 (cav-1), a scaffolding protein of caveolae, which has been linked to breast tumor aggressiveness. To determine whether loss of cav-1 results in the abnormal expression of matrix proteins, mammary glands from cav-1-/- and cav-1 +/+ mice were investigated for differences in expression of several ECM proteins. In addition, the presence of myofibroblasts, changes in the vessel density, and differences in duct number and size were assessed in the mammary glands of both animal models. Using immunohistochemistry, expression of fibronectin, tenascin-C, collagens and alpha SMA were significantly increased in the mammary glands of cav-1-/- mice. Second harmonic generation revealed more organized collagen fibers in cav-1-/- glands and supported immunohistochemical analyses of increased collagen abundance in the glands of cav-1-/- mice. Analysis of the ductal structure demonstrated a significant increase in the number of proliferating ducts in addition to significant increases in the duct circumference and area in cav1 -/- glands compared to cav-1 +/+ glands. Differences in microvessel density weren't apparent between the animal models. In summary, we found that the loss of cav-1 resulted in increased ECM and alpha-SMA protein expression in murine mammary glands. Furthermore, we found that an abnormal ductal architecture accompanied the loss of cav-1. These data support a role for cav-1 in maintaining mammary gland structure.