Culture Models to Investigate Lactation and Mastitis in Bovine Mammary Epithelial Cells

Mammary epithelial cells (MECs) are the only cell types that produce milk components such as casein and milk fat. Synthesized milk components are secreted from the apical membranes of MECs; cell polarity is, thus, necessary for milk production in MECs. The enhanced milk production ability of MECs contributes to increased milk yield in lactating cows. MECs are confronted with mastitis-causing pathogens in mammary glands when cows afflicted with mastitis experience decreased milk production. Experiments have been conducted using lactating cows in vivo to explain the mechanisms of milk production and mastitis. However, considering costs, workers, and space constraints, setting a large sample size or treatment group for trials is difficult. In vitro culture models using bovine MECs (BMECs) have, therefore, been developed as an alternative. Previous culture models have been reported to produce several components of milk. However, limited information is available on culture models of BMECs with cell polarity. In contrast, our established culture model introduced in this study demonstrates cell polarity with milk component secretion and less-permeable tight junctions. This review introduces the establishment of a BMEC culture model and its application to investigate the mechanisms of milk production or mastitis, along with our research.