Cellular milk production: Proteins and minerals in secretomes from cultivated bovine milk-derived mammary cells

This study explores the feasibility of utilizing in vitro cultivated milk-derived bovine mammary epithelial cells (bMECs) for the production of milk constituents. BMECs were isolated from milk and treated with various lactogenic agents in 3D transwell systems. By proteomics, >900 proteins were identified and quantified in the secretomes, including >100 milk-related proteins such as caseins and enzymes. Despite limited secretion of total proteins and major milk proteins, 110 proteins were found phosphorylated, including 27 involved in metal- or calcium-binding. Mineral analysis confirmed that 6-9 % of minerals in secretomes were associated with proteins. Notably, six proteins, including prolactin, were secreted into the basolateral side of bMECs without lactogenic treatment, suggesting their local de novo synthesis. This research advances our understanding of bMECs biology, as well as the compositional and functional features of their secretomes, highlighting their potential for sustainable production of functional milk proteins, meanwhile emphasizing the need for further optimization.