Establishment and characterization of a lactating bovine mammary epithelial cell model for the study of milk synthesis.

This study sought to establish an in vitro lactating BMEC (bovine mammary epithelial cell) model, which may maintain the native function for a period of time. Mammary tissues of midlactation Holstein dairy cows were dispersed and cultured in a medium containing insulin, prolactin, hydrocortisone, transferrin, epidermal growth factor and fetal calf serum. After the cells migrating from the tissue reached approximately 80% of confluency, the tissues were removed, and secretory epithelial cells were enriched by digesting with 0.25% trypsin repeatedly to remove fibroblasts. The BMEC cells plated on plastic dishes displayed a monolayer, cobblestone, epithelial-like morphology and formed alveoli-like structures and island monolayer aggregates which are the typical characteristics of the mammary epithelial cells. The isolated cells were identified as of epithelial origin by staining with antibody against cytokeratin 18. A one-half logarithmically growth curve and abundant microvilli and cytoplasmic lipid droplets were observed in these cells. The transcription of the alphas1 casein gene and synthesis of alphas caseins were also detected in the model. Thus, our lactating BMEC model can be an effective model in vitro for studies of milk synthesis in the bovine mammary gland.