The Effects of Endocrine and Mechanical Stimulation on Stage I Lactogenesis in Bovine Mammary Epithelial Cells

Abstract

The study objective was to evaluate the effect of endocrine and mechanical (gel release) signaling on bovine mammary epithelial cell ultrastructure and gene expression. Cultures receiving only one stimulus demonstrated partially differentiated ultrastructure, which included abundant polysomes, limited rough endoplasmic reticulum, and absence of secretory products, whereas the 2 stimuli together induced a more complete lactogenic phenotype that included increased rough endoplasmic reticulum, abundant lipid droplets, and secretory vesicles containing casein micelles. The structural data indicated that although synthesis of milk components was initiated, the copious synthesis and secretion associated with stage II lactogenesis was not evident. Microarray analysis revealed that both prolactin and gel release independently regulated several genes linked to a wide array of cellular activities. In combination, they regulated fewer genes targeted to lactogenesis. Genes regulated by the combination treatment included claudin 7, multiple caseins, xanthine oxidoreductase, and several protein synthesis, packaging, and transport genes. Genes related to structural activity including keratin 15 (morphogenesis), alpha-spectrin (cell shape via actin cytoskeleton), and chitinase-like protein 1 (tissue remodeling) were up-regulated by the combination treatment as was the transcription factor Kruppel-like factor 2 (KLF-2). However, Snail 2, which down-regulates and inhibits tight junction components, was repressed in response to the combination treatment. These results suggest coordination between endocrine and physical signals at the genomic level that produces a more specific and targeted transcriptional response associated with stage I lactogenesis. A molecular pathway analysis of the differentially expressed genes revealed that genes regulating cell signaling were linked to those regulating cell structure and adhesion.

Acute milk yield response to frequent milking during early lactation is mediated by genes transiently regulated by milk removal

“…In agreement, CHI3L-1, which is a secreted protein, has been previously reported to be upregulated during mammary involution and remodeling in dairy cows (28,44), goats (29,40), and sheep (46). More recently, differential expression of CHI3L-1 mRNA was linked to lactogenic changes in mammary cells in culture (47). In other tissues, CHI3L-1 is involved in cellular differentiation and remodeling (3,7,26) and in the cellular response to mechanical stimuli and pressure (49,60,61).…”

In vivo inhibition followed by exogenous supplementation demonstrates galactopoietic effects of prolactin on mammary tissue and milk production in dairy cows

“…The downregulation of milk protein gene expression with QN treatment was previously observed in bovine mammary tissue and in milk-purified MEC (Boutinaud et al, 2012). The effect of QN on milk protein transcripts could be due to the inhibition of milking-induced PRL release, because PRL is known to stimulate milk protein expression in bovine MEC (Choi et al, 1988;Stiening et al, 2008).…”

“…Also in primary bovine MEC cultures, PRL has been shown to upregulate the mRNA levels of several caseins (Choi et al, 1988). A high number of other genes are under the control of PRL stimulation, as has been shown in bovine MEC using microarray analyses (Stiening et al, 2008;Riley et al, 2010). In association with its role in MEC differentiation, PRL is also known to promote DNA synthesis and cell proliferation, as has been demonstrated in rabbit and bovine MEC (Suard et al, 1983;Olazabal et al, 2000).…”

Milk Protein Synthesis in the Lactating Mammary Gland: Insights from Transcriptomics Analyses

“…The endocrine and mechanical cues independently stimulate expression of a plethora of genes involved in mammary differentiation and lactation in mice; but, apparently, the combination of those cues are more important in stimulating the expression of caseins, xanthine oxidoreductase, and several genes involved in milk protein synthesis, as well as genes coding for proteins involved in packaging and transport [138]. Finally, the recognized differences among species prompts a call for caution when extrapolating findings in one species to another [139].…”