Culture Models to Investigate Mechanisms of Milk Production and Blood-Milk Barrier in Mammary Epithelial Cells: a Review and a Protocol

Abstract

Mammary epithelial cells (MECs) are the only cell type that produces milk during lactation. MECs also form less-permeable tight junctions (TJs) to prevent the leakage of milk and blood components through the paracellular pathway (blood-milk barrier). Multiple factors that include hormones, cytokines, nutrition, and temperature regulate milk production and TJ formation in MECs. Multiple intracellular signaling pathways that positively and negatively regulate milk production and TJ formation have been reported. However, their regulatory mechanisms have not been fully elucidated. In addition, unidentified components that regulate milk production in MECs likely exist in foods, for example plants. Culture models of functional MECs that recapitulate milk production and TJs are useful tools for their study. Such models enable the elimination of indirect effects via cells other than MECs and allows for more detailed experimental conditions. However, culture models of MECs with inappropriate functionality may result in unphysiological reactions that never occur in lactating mammary glands in vivo. Here, I briefly review the physiological functions of alveolar MECs during lactation in vivo and culture models of MECs that feature milk production and less-permeable TJs, together with a protocol for establishment of MEC culture with functional TJ barrier and milk production capability using cell culture inserts.

Cellular characteristics and milk component productivity of primary bovine mammary cells for cell-cultured milk component production

“…Previous studies have reported that mammary gland involution occurs in two distinct physiological phases in the absence of lactogenic hormone secretion [30,34]. Early apoptosis and the loss of TJs occurred in the first phase, and anoikis was irreversibly induced with a massive loss of mammary ECs after disruption of the basement membrane through the activation of MMPs in the second phase [35]. In contrast, the presence of hormones, such as PRL and CORT, enhanced the TJs formation and milk production by mammary ECs [36].…”

Comparison of miR-106b, miR-191, and miR-30d expression dynamics in milk with regard to its composition in Holstein and Ayrshire cows

“…Milk is produced by epithelial cells of the mammary gland, which under the influence of both exogenous and endogenous factors undergo numerous physiological changes throughout lactation. Ultimately, these changes determine the intensity of milk component synthesis and, hence, milk composition [5]. Functional genomics studies based on gene network analysis revealed the complexity of molecular adaptation of the mammary gland to lactation.…”

Studying Mammary Physiology and Pathology in Domestic Species Benefits Both Humans and Animals

“…Kobayashi describes the biology and dysfunction of mammary epithelial tight junctions and provides a detailed protocol describing culture of mammary epithelial cells in a manner that is compatible with milk production. This article also touches upon some of the challenges that may be encountered when working with non-traditional species, such as the fact that the optimal culture conditions for mammary epithelial cells may be species-specific [ 14 ].…”