14-3-3γ affects mTOR pathway and regulates lactogenesis in dairy cow mammary epithelial cells

Genetics, environmental stress, and amino acid supplementation affect lactational performance via mTOR signaling pathway in bovine mammary epithelial cells

Mammary glands are known for their ability to convert nutrients present in the blood into milk contents. In cows, milk synthesis and the proliferation of cow mammary epithelial cells (CMECs) are regulated by various factors, including nutrients such as amino acids and glucose, hormones, and environmental stress. Amino acids, in particular, play a crucial role in regulating cell proliferation and casein synthesis in mammalian epithelial cells, apart from being building blocks for protein synthesis. Studies have shown that environmental factors, particularly heat stress, can negatively impact milk production performance in dairy cattle. The mammalian target of rapamycin complex 1 (mTORC1) pathway is considered the primary signaling pathway involved in regulating cell proliferation and milk protein and fat synthesis in cow mammary epithelial cells in response to amino acids and heat stress. Given the significant role played by the mTORC signaling pathway in milk synthesis and cell proliferation, this article briefly discusses the main regulatory genes, the impact of amino acids and heat stress on milk production performance, and the regulation of mTORC signaling pathway in cow mammary epithelial cells.

14-3-3β is essential for milk composition stimulated by Leu/IGF-1 via IGF1R signaling pathway in BMECs

The cell proliferation of bovine mammary epithelial cells (BMECs) and consequent milk synthesis are regulated by multiple factors. The purpose of this study was to examine the effect of 14-3-3β on cellular proliferation and milk fat/β-casein synthesis in BMECs and reveal its underlying mechanisms. In this study, we employed gene function analysis to explore the regulatory effect and molecular mechanisms of 14-3-3β on milk synthesis and proliferation in BMECs. We found that leucine and IGF-1 enhance cell proliferation and milk synthesis in a 14-3-3β-dependent manner and only exhibiting such effect in the presence of 14-3-3β. We further determined that 14-3-3β interacts with the IGF1R self-phosphorylation site and it additionally mediated leucine and IGF-1 to stimulate the synthesis of milk through the IGF1R-AKT-mTORC1 signaling pathway. In summary, our data indicated that 14-3-3β mediates the expression of milk fat and protein stimulated by leucine and IGF-1, leading to lactogenesis through IGF1R signaling pathway in BMECs.

Shotgun proteomics of homogenate milk reveals dynamic changes in protein abundances between colostrum, transitional and mature milk of swine

Milk is an easily digestible source of nutrients and bioactive factors, its composition reflects the neonate's needs, and changes from colostrum to transitional and mature milk. Our objective was to measure milk fat, lactose, total carbohydrate, and protein content in parallel with global proteome of homogenate milk samples to characterize changes across the three phases of swine lactation. Milk samples were collected from multiparous sows (n=9) on postnatal day 0 (D0; colostrum), 3 (D3; early transitional), 7 (D7; late transitional) and 14 (D14; mature). On D3, percent fat (16 ± 2.1) and lactose (3.8 ± 0.3) were higher (P<0.05) than on D0 (10 ± 3.9, and 1.5 ± 0.3; respectively). Levels of fat and lactose were not different between D3 and D14. Percent total protein decreased (P<0.05) between D0 (11 ± 2.1) and D3 (5 ± 0.7), but there was no significant change in percent protein between D3 and D14. Total carbohydrates increased (P<0.05) between D3 (944 ± 353 µg/ml) and D14 (1150 ± 462 µg/ml). Quantitative proteomic analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS) of homogenate D0, D3, and D14 milk samples (n=6) identified 772 protein groups which corresponded to 501 individual protein-coding genes. A total of 207 high confidence proteins were detected in n=3 sows/day. Of the high confidence proteins, 81 proteins were common amongst all three days of lactation. Among the proteins that decreased between the days (FDR < 0.05) were multiple apolipoproteins and XDH which decreased between D0 to D3. Proteins that increased across the days (FDR < 0.05) were complement factors and14-3-3 proteins (YWHAQ, YWHAE). Our data provide a good characterization of milk proteome changes that likely reflect mammary function as well as the neonate's phase-specific developmental needs. This data may be useful in developing approaches to enhance the health and welfare of swine.

The regulatory mechanism of amino acids on milk protein and fat synthesis in mammary epithelial cells: a mini review

Mammary epithelial cell (MEC) is the basic unit of the mammary gland that synthesizes milk components including milk protein and milk fat. MECs can sense to extracellular stimuli including nutrients such as amino acids though different sensors and signaling pathways. Here, we review recent advances in the regulatory mechanism of amino acids on milk protein and fat synthesis in MECs. We also highlight how these mechanisms reflect the amino acid requirements of MECs and discuss the current and future prospects for amino acid regulation in milk production.

Septin6 regulates cell growth and casein synthesis in dairy cow mammary epithelial cells via mTORC1 pathway

This research paper addresses the hypothesis that Septin6 is a key regulatory factor influencing amino acid (AA)-mediated cell growth and casein synthesis in dairy cow mammary epithelial cells (DCMECs). DCMECs were treated with absence of AA (AA-), restricted concentrations of AA (AAr) or normal concentrations of AA (AA+) for 24 h. Cell growth, expression of CSN2 and Septin6 were increased in response to AA supply. Overexpressing or inhibiting Septin6 demonstrated that cell growth, expression of CSN2, mTOR, p-mTOR, S6K1 and p-S6K1 were up-regulated by Septin6. Furthermore, overexpressing or inhibiting mTOR demonstrated that the increase in cell growth and expression of CSN2 in response to Septin6 overexpression were inhibited by mTOR inhibition, and vice versa. Our hypothesis was supported; we were able to show that Septin6 is an important positive factor for cell growth and casein synthesis, it up-regulates AA-mediated cell growth and casein synthesis through activating mTORC1 pathway in DCMECs.

Cyclase-associated protein 1 is a key negative regulator of milk synthesis and proliferation of bovine mammary epithelial cells

Adenylyl cyclase-associated protein (CAP) is a highly conserved protein. Previous reports have suggested that CAP1 may be a negative regulator of cellular proliferation, migration, and adhesion and the development of cell carcinomas. The molecular mechanism of CAP1 regulation of downstream pathways, as well as how CAP1 is regulated by environmental stimuli and upstream signalling, is not well understood. In this present study, we assessed the role of CAP1 in milk synthesis and proliferation of bovine mammary epithelial cells. Using gene overexpression and silencing methods, CAP1 was found to negatively regulate milk synthesis and proliferation of cells via the PI3K-mTOR/SREBP-1c/Cyclin D1 signalling pathway. Hormones, such as prolactin and oestrogen, and amino acids, such as methionine and leucine, stimulate MMP9 expression and trigger CAP1 degradation, and thus, abrogate its inhibition of synthesis of milk protein, fat, and lactose by and proliferation of bovine mammary epithelial cells. The results of our study help deepen our understanding of the regulatory mechanisms underlying milk synthesis and aid in characterizing the molecular mechanisms of CAP1. Previous reports have suggested that CAP1 is a negative regulator of cellular proliferation and anabolism, but the molecular mechanisms are largely unknown. In this present study, we identified CAP1 as a negative regulator of milk synthesis and proliferation of bovine mammary epithelial cells. Our results will deepen our understanding of the regulatory mechanisms underlying milk synthesis and aid in exploring the molecular mechanisms of CAP1.

Proteomic Analysis of Lysosomal Membrane Proteins in Bovine Mammary Epithelial Cells Illuminates Potential Novel Lysosome Functions in Lactation

Lactation of bovine mammary epithelial cells (BMEC) is a complex biological process that involves in various organelles. Studies have shown that lysosome and lysosomal membrane proteins (LMP) plays an important role in lactation of BMEC. But the LMP of BMEC remains poorly understood. To obtain a global view of the LMP of BMEC and the affect of lysosome on lactation, the LMP of BMEC was identified using sequential windowed acquisition of all theoretical mass spectra (LC-SWATH/MS). 1214 LMP were identified and 559 were reported to be localized on lysosomal membrane for the first time in BMEC. Gene ontology annotation of these identified proteins showed that both previously reported casein synthesis-related LMP, such as LAMTOR1, 2, 3, and rRagC, and newly identified casein and milk fat synthesis-related LMP, such as EIF4E and ACAA1, were found. KEGG pathway analysis of these identified proteins showed that some pathways involved in lactation, such as PI3K-Akt, mTOR, insulin, PPAR, and JAK-STAT pathway, were found. The lysosomal location of five proteins (PRKCA, EIF4E, ACAA1, HRAS, and THBS1) was analyzed by laser confocal microscopy, and all five were associated with the lysosomal membrane. These findings help to elucidate lysosome functions in the regulation of lactation. The results implicate lysosomes as important organelles in regulation of lactation of BMEC that have been previously undervalued.

Protein 14-3-3ε Regulates Cell Proliferation and Casein Synthesis via PI3K-mTOR Pathway in Dairy Cow Mammary Epithelial Cells

Cell proliferation and casein synthesis of dairy cow mammary epithelial cells (DCMECs) are regulated by many factors. This research aimed to investigate the effect of 14-3-3ε on cell proliferation and casein synthesis in DCMECs and to reveal the underlying mechanism. Overexpressing or inhibiting 14-3-3ε demonstrated that cell proliferation; casein synthesis; expression of mTOR, p-mTOR, S6K1, and p-S6K1; and lysosomal localization of mTOR were all up-regulated by 14-3-3ε overexpressing and down-regulated by 14-3-3ε inhibiting. In addition, inhibiting mTOR demonstrated that the up-regulation of cell proliferation and casein synthesis in response to 14-3-3ε overexpressing was removed by inhibiting mTOR. Furthermore, the regulatory mechanism of 14-3-3ε was analyzed by coimmunoprecipitation, and we found that 14-3-3ε could interact with PI3K and activate mTORC1 pathway via PI3K. In addition, DCMECs were treated with insulin and prolactin, and the result showed that the cell proliferation and the expression of CSN2 and 14-3-3ε were all up-regulated by these hormones. In conclusion, the current research showed that 14-3-3ε is an important positive regulatory factor for cell proliferation and casein synthesis in DCMECs, as it up-regulates cell proliferation and casein synthesis via activating PI3K-mTOR pathway.

Kisspeptin-10 Induces β-Casein Synthesis via GPR54 and Its Downstream Signaling Pathways in Bovine Mammary Epithelial Cells

Kisspeptins (Kps) play a key role in the regulation of GnRH axis and as an anti-metastasis agent by binding with GPR54. Recently, we observed that the expression of GPR54 was higher in the lactating mammary tissues of dairy cows with high-quality milk (0.81 ± 0.13 kg/day of milk protein yield; 1.07 ± 0.18 kg/day of milk fat yield) than in those with low-quality milk (0.51 ± 0.14 kg/day of milk protein yield; 0.67 ± 0.22 kg/day of milk fat yield). We hypothesized that Kp-10 might regulate the milk protein, β-casein (CSN2) synthesis via GPR54 and its downstream signaling. First, we isolated the bovine mammary epithelial cells (bMECs) from lactating Holstein dairy cows, and treated them with different concentrations of Kp-10. Compared with the control cells, the synthesis of CSN2 is significantly increased at a concentration of 100 nM of Kp-10. In addition, the increased effect of CSN2 synthesis was blocked when the cells were pre-treated with the selective inhibitor of GPR54 Peptide-234 (P-234). Mechanistic study revealed that Kp-10 activated ERK1/2, AKT, mTOR and STAT5 in bMECs. Moreover, inhibiting ERK1/2, AKT, mTOR and STAT5 with U0126, MK2206, Rapamycin and AG490 could block the effects of Kp-10. Together, these results demonstrate that Kp-10 facilitates the synthesis of CSN2 via GPR54 and its downstream signaling pathways mTOR, ERK1/2, STAT5 and AKT.

Biological characterization of bovine mammary epithelial cell lines immortalized by HPV16 E6/E7 and SV40T

Primary bovine mammary epithelial cells are not ideal models for long-term studies, because primary cells undergo a limited number of proliferations in vitro and enter into a growth-arrest stage called cell replicative senescence; we therefore must establish the immortalized bovine mammary epithelial cells (BMECs) in vitro. More importantly, the mechanisms of the relationship between immortalized and apoptotic cell remain unknown in BMECs. We therefore sought to elucidate the mechanisms of which immortalized cells escape the pathway of apoptotic signal. These cells were successfully immortalized without any signs of senescence. The maximum number of BMEC and E6E7 immortalized cells were reached after 6 d of culture. At this point, there were significantly more E6E7 immortalized cells than primary BMECs (P < 0.01). The population-doubling times of the E6E7 and SV40T immortalized cells were lowest at 48 and 72 h. We failed to detect the expression of the epithelial cell marker E-cadherin in BMECs; however, immortalized cells had low expression of E-cadherin. The expression of β-catenin was markedly expressed in immortalized cells than in BMECs (P < 0.01). Caspase-3, caspase-9, and poly ADP-ribose polymerase (PARP) were detected; however, the cleavage of caspase-3 and PARP was not observed. Our data demonstrate that the expressions of caspase-9, caspase-3, and PARP are not sufficient for the apoptosis of immortalized cells and suggest that E-cadherin and β-catenin might be an important indicator of the development of cancer.