Uncoupling the mechanisms that facilitate cell survival in hormone-deprived bovine mammary explants

Abstract

Mammary explants can be hormonally stimulated to mimic the biochemical changes that occur during lactogenesis. Previous studies using mammary explants concluded that the addition of exogenous macromolecules were required for mammary epithelial cells to remain viable in culture. The present study examines the survival of mammary explants from the dairy cow using milk protein gene expression as a functional marker of lactation and cell viability. Mammary explants cultured from late pregnant cows mimicked lactogenesis and showed significantly elevated milk protein gene expression after 3 days of culture with lactogenic hormones. The subsequent removal of exogenous hormones from the media for 10 days resulted in the down-regulation of milk protein genes. During this time, the mammary explants remained hormone responsive, the alveolar architecture was maintained and the expression of milk protein genes was re-induced after a second challenge with lactogenic hormones. We report that a population of bovine mammary epithelial cells have an intrinsic capacity to remain viable and hormone responsive for extended periods in chemically defined media without any exogenous macromolecules. In addition, we found mammary explant viability was dependent on de novo protein and RNA synthesis. Global functional microarray analysis showed that differential expression of genes involved in energy production, immune responses, oxidative stress and apoptosis signalling might contribute to cell survival. As the decline in milk production in dairy cattle after peak lactation results in considerable economic loss, the identification of novel survival genes may be used as genetic markers for breeding programmes to improve lactational persistency in dairy cows.

Dispersal of an ancient retroposon in the TP53 promoter of Bovidae: phylogeny, novel mechanisms, and potential implications for cow milk persistency

“…Mammary involution proceeds with little loss of epithelial cells, and no disengagement of epithelial cells from the basement membrane [ 62 ]. Mammary explants from pregnant dairy cows have the capacity to maintain a population of surviving mammary epithelial cells that remain hormone-responsive, are capable of milk protein gene expression, and maintain alveolar architecture without exposure to exogenous macromolecules during culture [ 63 ]. This intrinsic capacity was attributed to expression of genes which lead to avoidance of cell death pathways [ 63 ].…”

“…Mammary explants from pregnant dairy cows have the capacity to maintain a population of surviving mammary epithelial cells that remain hormone-responsive, are capable of milk protein gene expression, and maintain alveolar architecture without exposure to exogenous macromolecules during culture [ 63 ]. This intrinsic capacity was attributed to expression of genes which lead to avoidance of cell death pathways [ 63 ]. It was proposed that identification of genes that may contribute to cell survival in bovine mammary explants may constitute a significant financial advantage for the dairy industry, due to improved persistence of lactation [ 64 ].…”

Evolution of Lactation: Ancient Origin and Extreme Adaptations of the Lactation System

“…This variability in copy number may be responsible in part for the variability in milk composition. The regulation of transcription and other physiological energy partitioning processes may also play a role, and studies on the transcriptional regulation of genes in epithelial cell culture, mammary explants, or mammary gland tissue from a number of animal models are starting to address factors influencing gene expression (13,50,(57)(58)(59)82). A number of genus-specific milk proteins have also been identified, especially in marsupials.…”

Identification and characterization of bovine mammary peptide transporters in response to tripeptide and lactogenic hormone treatment

“…The tyrosine kinases Janus kinase (JAK)2 and JAK3 also influence PepT1 and PepT2 Warsi et al 2013). Lactogenic hormones (prolactin, hydrocortisone, and insulin) play major roles in pregnancy, milk protein synthesis, postpartum development of the mammary gland, and lactation (Brennan et al 2008;Lee et al 2009). Prolactin enhances the production of total protein and casein in the mammary glands and also affects mammary differentiation and milk production after birth (Oakes et al 2008).…”