The effects of L-type amino acid transporter 1 on milk protein synthesis in mammary glands of dairy cows

Weighted single step GWAS reveals genomic regions associated with economic traits in Murrah buffaloes

The objective of the present study was to identify genomic regions influencing economic traits in Murrah buffaloes using weighted single step Genome Wide Association Analysis (WssGWAS). Data on 2000 animals, out of which 120 were genotyped using a double digest Restriction site Associated DNA (ddRAD) sequencing approach. The phenotypic data were collected from NDRI, India, on growth traits, viz., body weight at 6M (month), 12M, 18M and 24M, production traits like 305D (day) milk yield, lactation length (LL) and dry period (DP) and reproduction traits like age at first calving (AFC), calving interval (CI) and first service period (FSP). The biallelic genotypic data consisted of 49353 markers post-quality check. The heritability estimates were moderate to high, low to moderate, low for growth, production, reproduction traits, respectively. Important genomic regions explaining more than 0.5% of the total additive genetic variance explained by 30 adjacent SNPs were selected for further analysis of candidate genes. In this study, 105 genomic regions were associated with growth, 35 genomic regions with production and 42 window regions with reproduction traits. Different candidate genes were identified in these genomic regions, of which important are OSBPL8, NAP1L1 for growth, CNTNAP2 for production and ILDR2, TADA1 and POGK for reproduction traits.

Prolactin upregulates amino acids uptake in dairy cow mammary epithelial cells via LAT1

The uptake of AA in mammary tissues is affected by prolactin (PRL). To investigate whether PRL-induced AA uptake is involved in L-type AA transporter 1 (LAT1), we analyzed the changes of AA in the medium of dairy cow mammary epithelial cells in the presence of PRL or PRL plus BCH, an inhibitor of LAT1. Then Western blot and luciferase assay were used to detect the regulation mechanism of PRL on LAT1 expression and function. Our results showed that Thr, Val, Met, Ile, Leu, Tyr, Lys, Phe, and His are LAT1 substrates and could be transported into mammary epithelial cells via LAT1. PRL stimulation increased the uptake of most AA into mammary epithelial cells of dairy cows, however, inhibition of LAT1 transport activity reduced PRL-induced AA uptake, suggesting that the effect of PRL on AA transport depends on LAT1 expression and function. PRL stimulation upregulated LAT1 expression and plasma membrane location not only in dairy cow mammary epithelial cells, but also in mouse mammary epithelial cell line HC11. Western blot showed that PI3K-AKT-mTOR signaling could be activated in PRL-stimulated mammary epithelial cells. Treatment of cells with LY294002 decreased PI3K-AKT-mTOR activation, as well LAT1 expression, that in turn decreased milk protein synthesis. Luciferase assay showed PRL treatment increased the promoter activity of LAT1 promoter fragment -419∼-86 bp. Treatment of cells with LY294002, an inhibitor of PI3K, or SC79, an activator of AKT abolished or promoted the transcriptional activity of this promoter fragment in the presence of PRL. These results suggested that the -419∼-86 bp fragment of LAT1 promoter mediates the action of PI3K-AKT-mTOR signaling on LAT1 transcription in mammary epithelial cells of dairy cows, which in turn increased LAT1 expression and AA uptake.

Leucine-Mediated SLC7A5 Promotes Milk Protein and Milk Fat Synthesis through mTOR Signaling Pathway in Goat Mammary Epithelial Cells

The SLC7A5 gene encodes a Na+ and pH-independent transporter protein that regulates cell growth by regulating the uptake of AA. This study, utilizing RNA-seq, aimed to explore the effect of SLC7A5 on the synthesis of milk proteins and fats in goat mammary epithelial cells (GMECs) through gene interference and overexpression techniques. The results demonstrated that the overexpression of SLC7A5 resulted in a significant increase in the expression of CSN1S1, SCD, CEBPB, ACACA, αS1-casein, p-S6K, and p-S6. The levels of p-S6K and p-S6 gradually increased as the AA/Leu stimulation time lengthened. The overexpression of SLC7A5 rescued the role of Torin1 in GMECs. In conclusion, SLC7A5 plays a crucial role in promoting the synthesis of milk proteins and milk fats through the mTOR signaling pathway in GMECs, providing a theoretical foundation for improving the quality of goat milk.

Valine and nonessential amino acids affect bidirectional transport rates of leucine and isoleucine in bovine mammary epithelial cells

A more complete understanding of the mechanisms controlling AA transport in mammary glands of dairy cattle will help identify solutions to increase nitrogen feeding efficiency on farms. It was hypothesized that Ala, Gln, and Gly (NEAAG), which are actively transported into cells and exchanged for all branched-chain AA (BCAA), may stimulate transport of BCAA, and that Val may antagonize transport of the other BCAA due to transporter competition. Thus, we evaluated the effects of varying concentrations of NEAAG and Val on transport and metabolism of the BCAA Ala, Met, Phe, and Thr by bovine mammary epithelial cells. Primary cultures of bovine mammary epithelial cells were assigned to treatments of low (70% of mean in vivo plasma concentrations of lactating dairy cows) and high (200%) concentrations of Val and NEAAG (LVal and LNEAAG, HVal and HNEAAG, respectively) in a 2 × 2 factorial design. Cells were preloaded with treatment media containing [15N]-labeled AA for 24 h. The [15N]-labeled media were replaced with treatment media containing [13C]-labeled AA. Media and cells were harvested from plates at 0, 0.5, 1, 5, 15, 30, 60, and 240 min after application of the [13C]-labeled AA and assessed for [15N]- and [13C]-AA label concentrations. The data were used to derive transport, transamination, irreversible loss, and protein-synthesis fluxes. All Val fluxes, except synthesis of rapidly exchanging tissue protein, increased with the HVal treatment. Interestingly, the rapidly exchanging tissue protein, transamination, and irreversible-loss rate constants decreased with HVal, indicating that the significant flux increases were primarily driven by mass action with the cells resisting the flux increases by downregulating activity. However, the decreases could also reflect saturation of processes that would drive down the mass-action rate constants. This is supported by decreases in the same rate constants for Ile and Leu with HVal. This could be due to either competition for shared transamination and oxidation reactions or a reduction in enzymatic activity. Also, NEAAG did not affect Val fluxes, but influx and efflux rate constants increased for both Val and Leu with HNEAAG, indicating an activating substrate effect. Overall, AA transport rates generally responded concordantly with extracellular concentrations, indicating the transporters are not substrate-saturated within the in vivo range. However, BCAA transamination and oxidation enzymes may be approaching saturation within in vivo ranges. In addition, System L transport activity appeared to be stimulated by as much as 75% with high intracellular concentrations of Ala, Gln, and Gly. High concentrations of Val antagonized transport activity of Ile and Leu by 68% and 15%, respectively, indicating competitive inhibition, but this was only observable at HNEAAG concentrations. The exchange transporters of System L transport 8 of the essential AA that make up approximately 40% of milk protein, so better understanding this transporter is an important step for increased efficiency.

Effect of sodium butyrate treatment at the basolateral membranes on the tight junction barrier function via a monocarboxylate transporter in goat mammary epithelial cells

In lactating mammary glands, tight junctions (TJs) prevent blood from mixing with milk and maintain epithelial cell polarity, which is important for milk production. This study aimed to investigate the effect of sodium acetate and sodium butyrate (SB) stimulation direction on the TJ barrier function, which is measured with regard to transepithelial electrical resistance and fluorescein flux, in goat mammary epithelial cells. The expression and localization of the TJ proteins claudin-3 and claudin-4 were examined using Western blotting and immunofluorescence. SB treatment in the lower chamber of cell culture inserts adversely affected the TJ barrier function, whereas sodium acetate barely had any effect, regardless of stimulation direction. In addition, SB treatment in the lower chamber significantly upregulated claudin-3 and claudin-4, whereas TJ proteins showed intermittent localization. Moreover, SB induced endoplasmic reticulum (ER) stress. ARC155858, a monocarboxylate transporter-1 inhibitor, alleviated the adverse impact of SB on TJs and the associated ER stress. Interestingly, sodium β-hydroxybutyrate, a butyrate metabolite, did not affect the TJ barrier function. Our findings indicate that sodium acetate and SB influence the TJ barrier function differently, and excessive cellular uptake of SB can disrupt TJs and induce ER stress.

mTORC2-AKT-LAT1 signalling participates in methionine-induced β-CASEIN expression in mammary epithelial cells of dairy cows

This study investigated the role of the mammalian target of rapamycin complex 2 (mTORC2)-protein kinase B (AKT) signalling in methionine (Met)-induced L-type amino acid transporter 1 (LAT1) expression and milk protein production. Primary mammary epithelial cells (MECs) from mammary parenchymal tissues of three lactating cows and MAC-T bovine MECs were cultured with or without 0.6 mM Met. Rapamycin-insensitive companion of mTOR (RICTOR) siRNA, the mTORC1 inhibitor rapamycin and the AKT activator SC79 were used to evaluate the effects of mTORC2-AKT signalling on Met-induced LAT1 expression and function. Each experiment was performed three times. Data were analysed with a two-sided unpaired t test or ANOVA with the Bonferroni multiple-comparison test. Western blotting showed that Met stimulation increased RICTOR expression (~244.67%; p < 0.05; control, 0.15 ± 0.026; Met, 0.517 ± 0.109) and AKT-S473 levels (~281.42%; p < 0.01; control, 0.253 ± 0.067; Met, 0.965 ± 0.019) in both primary MECs and MAC-T cells. Rapamycin-induced mTORC1 signalling inhibition decreased only Met-induced β-CASEIN expression by ~21.24% (p < 0.01; Met, 0.777 ± 0.01; Met and rapamycin, 0.612 ± 0.04) and did not affect Met-stimulated AKT-S473 levels, suggesting that mTORC2-AKT activation upon Met stimulation also contributes to milk protein synthesis. LAT1 participates in Met-induced β-CASEIN expression. In dairy cow MECs, mTORC2 inhibition by RICTOR siRNA decreased LAT1 levels on the plasma membrane by ~45.13% (p < 0.01; control, 0.359 ± 0.006; siRICTOR, 0.197 ± 0.004). However, SC79-induced AKT activation had the opposite effect (p < 0.01). In primary MECs and MAC-T cells, Met stimulation increased cytosolic and plasma membrane LAT1 expression respectively (MECs, 113.98% and 58.43%; MAC-T, 165.85% and 396.39%; p < 0.05). However, RICTOR siRNA significantly reduced Met-induced plasma membrane LAT1 expression (~76.48%; Met, 0.539 ± 0.05; Met and siRICTOR, 0.127 ± 0.012; p < 0.05). Thus, Met increased LAT1 expression and function via mTORC2-AKT signalling, upregulating milk protein synthesis in dairy cow MECs.

The functional and regulatory entities underlying free and peptide-bound amino acid transporters in the bovine mammary gland

Free and peptide-bound AA act as building blocks and key regulators of milk protein. To improve milk protein production, mammary epithelial cells of lactating mammals require extensive AA movement across the plasma membrane via multiple transport systems. Recent studies on bovine mammary cells/tissues have expanded the number of AA transporter systems identified and the knowledge on their contribution to AA utilization for milk protein synthesis and the regulatory machinery. However, in lactating cows, the exact intracellular location of mammary AA transporters and the extent of mammary net AA utilization for milk protein production remain unclear. This review highlights the existing knowledge on various characteristics, such as substrate specificity, kinetics, their effects on AA uptake and utilization, and regulatory mechanism, of recently examined bovine mammary free and peptide-bound AA transporters.

Effect of hyperthermia on cell viability, amino acid transfer, and milk protein synthesis in bovine mammary epithelial cells

The reduction of milk yield caused by heat stress in summer is the main condition restricting the economic benefits of dairy farms. To examine the impact of hyperthermia on bovine mammary epithelial (MAC-T) cells, we incubated the MAC-T cells at thermal-neutral (37°C, CON group) and hyperthermic (42°C, HS group) temperatures for 6 h. Subsequently, the cell viability and apoptotic rate of MAC-T cells, apoptosis-related genes expression, casein and amino acid transporter genes, and the expression of the apoptosis-related proteins were examined. Compared with the CON group, hyperthermia significantly decreased the cell viability (p < 0.05) and elevated the apoptotic rate (p < 0.05) of MAC-T cells. Moreover, the expression of heat shock protein (HSP)70, HSP90B1, Bcl-2-associated X protein (BAX), Caspase-9, and Caspase-3 genes was upregulated (p < 0.05). The expression of HSP70 and BAX (pro-apoptotic) proteins was upregulated (p < 0.05) while that of B-cell lymphoma (BCL)2 (antiapoptotic) protein was downregulated (p < 0.05) by hyperthermia. Decreased mRNA expression of mechanistic target of rapamycin (mTOR) signaling pathway-related genes, amino acid transporter genes (SLC7A5, SLC38A3, SLC38A2, and SLC38A9), and casein genes (CSNS1, CSN2, and CSN3) was found in the heat stress (HS) group (p < 0.05) in contrast with the CON group. These findings illustrated that hyperthermia promoted cell apoptosis and reduced the transport of amino acids into cells, which inhibited the milk proteins synthesis in MAC-T cells.

Intracellular Staphylococcus aureus Infection Decreases Milk Protein Synthesis by Preventing Amino Acid Uptake in Bovine Mammary Epithelial Cells

Staphylococcus aureus (S. aureus) is one of the main pathogens in cow mastitis, colonizing mammary tissues and being internalized into mammary epithelial cells, causing intracellular infection in the udder. Milk that is produced by cows that suffer from mastitis due to S. aureus is associated with decreased production and changes in protein composition. However, there is limited information on how mastitis-inducing bacteria affect raw milk, particularly with regard to protein content and protein composition. The main purpose of this work was to examine how S. aureus infection affects milk protein synthesis in bovine mammary epithelial cells (BMECs). BMECs were infected with S. aureus, and milk protein and amino acid levels were determined by ELISA after S. aureus invasion. The activity of mTORC1 signaling and the transcription factors NF-κB and STAT5 and the expression of the amino acid transporters SLC1A3 and SLC7A5 were measured by western blot or immunofluorescence and RT-qPCR. S. aureus was internalized by BMECs in vitro, and the internalized bacteria underwent intracellular proliferation. Eight hours after S. aureus invasion, milk proteins were downregulated, and the level of BMECs that absorbed Glu, Asp, and Leu from the culture medium and the exogenous amino acids induced β-casein synthesis declined. Further, the activity of mTORC1 signaling, NF-κB, and STAT5 was impaired, and SLC1A3 and SLC7A5 were downregulated. Eight hours of treatment with 100 nM rapamycin inhibited NF-κB and STAT5 activity, SLC1A3 and SLC7A5 expression, and milk protein synthesis in BMECs. Thus mTORC1 regulates the expression of SLC1A3 and SLC7A5 through NF-κB and STAT5. These findings constitute a model by which S. aureus infection suppresses milk protein synthesis by decreasing amino acids uptake in BMECs.

Regulation of Milk Protein Synthesis by Free and Peptide-Bound Amino Acids in Dairy Cows

Milk protein (MP) synthesis in the mammary gland of dairy cows is a complex biological process. As the substrates for protein synthesis, amino acids (AAs) are the most important nutrients for milk synthesis. Free AAs (FAAs) are the main precursors of MP synthesis, and their supplies are supplemented by peptide-bound AAs (PBAAs) in the blood. Utilization of AAs in the mammary gland of dairy cows has attracted the great interest of researchers because of the goal of increasing MP yield. Supplying sufficient and balanced AAs is critical to improve MP concentration and yield in dairy cows. Great progress has been made in understanding limiting AAs and their requirements for MP synthesis in dairy cows. This review focuses on the effects of FAA and PBAA supply on MP synthesis and their underlying mechanisms. Advances in our knowledge in the field can help us to develop more accurate models to predict dietary protein requirements for dairy cows MP synthesis, which will ultimately improve the nitrogen utilization efficiency and lactation performance of dairy cows.

Exploration of the lactation function of protein phosphorylation sites in goat mammary tissues by phosphoproteome analysis

BACKGROUND

Protein phosphorylation plays an important role in lactation. Differentially modified phosphorylation sites and phosphorylated proteins between peak lactation (PL, 90 days postpartum) and late lactation (LL, 280 days postpartum) were investigated using an integrated approach, namely, liquid chromatography with tandem mass spectrometry (LC-MS/MS) and tandem mass tag (TMT) labeling, to determine the molecular changes in the mammary tissues during the different stages of goat lactation.

RESULTS

A total of 1,938 (1,111 upregulated, 827 downregulated) differentially modified phosphorylation sites of 1,172 proteins were identified (P values < 0.05 and fold change of phosphorylation ratios > 1.5). Multiple phosphorylation sites of FASN, ACACA, mTOR, PRKAA, IRS1, RPS6KB, EIF4EBP1, JUN, and TSC2 were different in PL compared with LL. In addition, the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the calcium signaling pathway, oxytocin signaling pathway and MAPK signaling pathway were enriched. The western blot results showed that the phosphorylation levels of ACACA (Ser80), EIF4EBP1 (Thr46) and IRS1 (Ser312) increased and JUN (Ser63) decreased in PL compared with LL. These results were consistent with the phosphoproteome results.

CONCLUSIONS

In this study, we identified for the first time the differentially modified phosphorylation sites in goat mammary tissues between PL and LL. These results indicate that the multiple differentially modified phosphorylation sites of FASN, ACACA, mTOR, PRKAA, IRS1, RPS6KB, EIF4EBP1, TSC2, and JUN and proteins involved in the calcium signaling pathway, oxytocin signaling pathway, and MAPK signaling pathway are worthy of further exploration.

Free threonine in human breast milk is related to infant intestinal microbiota composition

BACKGROUND

Accumulating evidence indicates that free amino acids (FAA) might be bioactive compounds with potential immunomodulatory capabilities. However, the FAA composition in human milk is still poorly characterized with respect to its correlation to maternal serum levels and its physiological significance for the infant. Studies addressing the relation of human milk FAA to the infants' intestinal microbiota are still missing.

METHODS

As part of a pilot study, maternal serum and breast milk FAA concentrations as well as infant intestinal microbiota (16S rRNA) were determined 2 months after birth. The study cohort consisted of 41 healthy mothers and their term delivered, healthy infants with normal birthweight. The relationship between maternal serum and milk FAA was determined by correlation analyses. Associations between (highly correlated) milk FAA and infant intestinal beta diversity were tested using PERMANOVA, LefSe and multivariate regression models adjusted for common confounders.

RESULTS

Seven breast milk FAA correlated significantly with serum concentrations. One of these, threonine showed a negative association with abundance of members of the class Gammaproteobacteria (R²adj = 17.1%, p = 0.006; β= - 0.441). In addition, on the level of families and genera, threonine explained 23.2% of variation of the relative abundance of Enterobacteriaceae (R²adj; p = 0.001; β = - 0.504) and 11.1% of variability in the abundance of Escherichia/Shigella (R²adj, p = 0.025; β  = - 0.368), when adjusted for confounders.

CONCLUSION

Our study is the first to suggest potential interactions between breast milk FAA and infant gut microbiota composition during early lactation. The results might be indicative of a potential protective role of threonine against members of the Enterobacteriaceae family in breast-fed infants. Still, results are based on correlation analyses and larger cohorts are needed to support the findings and elucidate possible underlying mechanisms to assess the complex interplay between breast milk FAA and infant intestinal microbiota in detail.

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.

Effects of a High-Grain Diet With a Buffering Agent on Milk Protein Synthesis in Lactating Goats

Chinese dairy industries have developed rapidly, providing consumers with high-quality sources of nutrition. However, many problems have also appeared during the development process, especially the low quality of milk. To improve milk quality, a large amount of concentrated feed is usually added to the diet within a certain period of time, which increases the milk production to a certain extent. However, long-term feeding with high-concentration feed can lead to subacute rumen acidosis. Therefore, the present study aimed to determine the effect of adding a buffer on subacute rumen acidosis, and the improvement of milk production and milk quality. We also aimed to study the mechanism of promoting mammary gland lactation. A total of 12 healthy mid-lactating goats were randomly divided into two groups, they were high-grain diet group (Control) and buffering agent group. To understand the effects of high-grain diets with buffers on amino acids in jugular blood and the effects of amino acids on milk protein synthesis, Milk-Testing™ Milkoscan 4000, commercial kits, and high-performance liquid chromatography (HPLC) measurements were integrated with the milk protein rate, the amino acid concentration in jugular venous blood samples, quantitative real-time PCR, comparative proteomics, and western blotting to study differentially expressed proteins and amino acids in mammary gland tissues of goats fed high-grain diets. Feeding lactating goats with buffering agent increased the percentage of milk protein in milk, significantly increased the amino acid content of jugular blood (p < 0.05), and increase the amino acid transporter levels in the mammary gland. Compared with the high-grain group, 2-dimensional electrophoresis technology, matrix-assisted laser desorption/ionization-time of flight/time of flight proteomics analyzer, and western blot analysis further verified that the expression levels of beta casein (CSN2) and lactoferrin (LF) proteins in the mammary glands of lactating goats were higher when fed a high-grain diets and buffers. The mechanism of increased milk protein synthesis was demonstrated to be related to the activation of mammalian target of rapamycin (mTOR) pathway signals.

Cell death-inducing DNA fragmentation factor-α-like effector C (CIDEC) regulates acetate- and β-hydroxybutyrate-induced milk fat synthesis by increasing FASN expression in mammary epithelial cells of dairy cows

Increasing acetate and β-hydroxybutyrate (BHB) supply to lactating cows will increase milk fat synthesis. However, the underlying molecular mechanism remains largely unknown. Cell death-inducing DNA fragmentation factor-α-like effector C (CIDEC) is a lipid droplet-associated protein that promotes intracellular triacylglycerol accumulation. In the present study, using gene overexpression and knockdown, we detected the contributions of CIDEC on milk fat synthesis in mammary epithelial cells of dairy cows in the presence of acetate and BHB. The results showed that knockdown of CIDEC decreased fatty acid synthase (FASN) expression and intracellular triacylglycerol content, whereas overexpression of CIDEC had the opposite effect. The transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) regulates cell growth and differentiation in the mammary gland. We demonstrated that the FASN promoter had a canonical C/EBPβ binding sequence. CEBPB overexpression upregulated FASN expression and milk fat synthesis, whereas CEBPB knockdown had the opposite effect. Moreover, knockdown of CEBPB attenuated the promoting effects of CIDEC on acetate- and BHB-induced FASN transcription. Taken together, our data showed that acetate and BHB induced FASN expression in mammary epithelial cells of dairy cows in a CIDEC-C/EBPβ-dependent manner, which provides new insights into the understanding of the molecular events involved in milk fat synthesis.

The market for amino acids: understanding supply and demand of substrate for more efficient milk protein synthesis

For dairy production systems, nitrogen is an expensive nutrient and potentially harmful waste product. With three quarters of fed nitrogen ending up in the manure, significant research efforts have focused on understanding and mitigating lactating dairy cows’ nitrogen losses. Recent changes proposed to the Nutrient Requirement System for Dairy Cattle in the US include variable efficiencies of absorbed essential AA for milk protein production. This first separation from a purely substrate-based system, standing on the old limiting AA theory, recognizes the ability of the cow to alter the metabolism of AA. In this review we summarize a compelling amount of evidence suggesting that AA requirements for milk protein synthesis are based on a demand-driven system. Milk protein synthesis is governed at mammary level by a set of transduction pathways, including the mechanistic target of rapamycin complex 1 (mTORC1), the integrated stress response (ISR), and the unfolded protein response (UPR). In tight coordination, these pathways not only control the rate of milk protein synthesis, setting the demand for AA, but also manipulate cellular AA transport and even blood flow to the mammary glands, securing the supply of those needed nutrients. These transduction pathways, specifically mTORC1, sense specific AA, as well as other physiological signals, including insulin, the canonical indicator of energy status. Insulin plays a key role on mTORC1 signaling, controlling its activation, once AA have determined mTORC1 localization to the lysosomal membrane. Based on this molecular model, AA and insulin signals need to be tightly coordinated to maximize milk protein synthesis rate. The evidence in lactating dairy cows supports this model, in which insulin and glucogenic energy potentiate the effect of AA on milk protein synthesis. Incorporating the effect of specific signaling AA and the differential role of energy sources on utilization of absorbed AA for milk protein synthesis seems like the evident following step in nutrient requirement systems to further improve N efficiency in lactating dairy cow rations.

Free Amino Acids in Human Milk: A Potential Role for Glutamine and Glutamate in the Protection Against Neonatal Allergies and Infections

Breastfeeding is indicated to support neonatal immune development and to protect against neonatal infections and allergies. Human milk composition is widely studied in relation to these unique abilities, which has led to the identification of various immunomodulating components in human milk, including various bioactive proteins. In addition to proteins, human milk contains free amino acids (FAAs), which have not been well-studied. Of those, the FAAs glutamate and glutamine are by far the most abundant. Levels of these FAAs in human milk sharply increase during the first months of lactation, in contrast to most other FAAs. These unique dynamics are globally consistent, suggesting that their levels in human milk are tightly regulated throughout lactation and, consequently, that they might have specific roles in the developing neonate. Interestingly, free glutamine and glutamate are reported to exhibit immunomodulating capacities, indicating that these FAAs could contribute to neonatal immune development and to the unique protective effects of breastfeeding. This review describes the current understanding of the FAA composition in human milk. Moreover, it provides an overview of the effects of free glutamine and glutamate on immune parameters relevant for allergic sensitization and infections in early life. The data reviewed provide rationale to study the role of free glutamine and glutamate in human milk in the protection against neonatal allergies and infections.

Regulatory Effects of Soy Isoflavones and Their Metabolites in Milk Production via Different Ways in Mice

Soy products contain abundant genistein and daidzein isoflavones. Orally ingested soy isoflavones are partially metabolized to isoflavan by enteric bacteria. Their levels in the blood increase after soy products are eaten. In this study, we investigated the influence of genistein, daidzein, and equol by intraperitoneal administration in lactating mice. Genistein decreased the secretion of α- and β-casein and downregulated the gene expression of Csn1, Csn2, Csn3, and Wap while inactivating the signal transducer and activator of transcription 5 (STAT5) and ERK1/2. In contrast, equol increased Csn1-3 expression while inactivating STAT3. Daidzein did not show inhibitory effects on milk production. The effects of genistein and equol were also confirmed in lactating mammary epithelial cells (MECs), which were cultured in the presence of soy isoflavones and equol at physiological concentrations for 7 days. These findings indicate that genistein, daidzein, and equol influence milk production in MECs in vivo and in vitro in distinctly different ways.

Amino acid transportation, sensing and signal transduction in the mammary gland: key molecular signalling pathways in the regulation of milk synthesis

The mammary gland, a unique exocrine organ, is responsible for milk synthesis in mammals. Neonatal growth and health are predominantly determined by quality and quantity of milk production. Amino acids are crucial maternal nutrients that are the building blocks for milk protein and are potential energy sources for neonates. Recent advances made regarding the mammary gland further demonstrate that some functional amino acids also regulate milk protein and fat synthesis through distinct intracellular and extracellular pathways. In the present study, we discuss recent advances in the role of amino acids (especially branched-chain amino acids, methionine, arginine and lysine) in the regulation of milk synthesis. The present review also addresses the crucial questions of how amino acids are transported, sensed and transduced in the mammary gland.

Nutrigenomic Role of Acetate and β-Hydroxybutyrate in Bovine Mammary Epithelial Cells

Acetate and β-hydroxybutyrate (BHBA) are the predominant substrates for de novo fatty acid (FA) synthesis in mammary gland of dairy cow. To investigate the nutrigenomic role of acetate and BHBA in bovine mammary epithelial cells during milk fat production, RNA sequencing (RNA-seq) transcriptomic analysis was used to identify differentially expressed genes (DEGs) between acetate- and BHBA-treated cells (high-milk fat cells) and control cells. A total of 625 DEGs (358 upregulated and 267 downregulated) were identified between the high-milk fat cells and control cells. Gene ontology enrichment analysis revealed that the upregulated genes in high-milk fat cells were mainly involved in lipid biosynthetic process, steroid biosynthetic process, oxidation-reduction process, receptor binding, and vesicle and small molecule biosynthetic process. The downregulated genes were mainly associated with immune response, cytokine production, negative regulation of biological process, and peptidyl-threonine modification. Pathway analysis indicated that FA metabolism and steroid biosynthesis were significantly enriched for the upregulated genes in the high-milk fat cells, while apoptosis was enriched for the downregulated genes. This work provides a profile of gene expression changes that occur during acetate- and BHBA-induced milk fat synthesis in bovine mammary epithelial cells, which furthers our understanding of the molecular regulation of lipid metabolism.

Meta-analysis of mammary RNA seq datasets reveals the molecular understanding of bovine lactation biology

A better understanding of the biology of lactation, both in terms of gene expression and the identification of candidate genes for the production of milk and its components, is made possible by recent advances in RNA seq technology. The purpose of this study was to understand the synthesis of milk components and the molecular pathways involved, as well as to identify candidate genes for milk production traits within whole mammary transcriptomic datasets. We performed a meta-analysis of publically available RNA seq transcriptome datasets of mammary tissue/milk somatic cells. In total, 11 562 genes were commonly identified from all RNA seq based mammary gland transcriptomes. Functional annotation of commonly expressed genes revealed the molecular processes that contribute to the synthesis of fats, proteins, and lactose in mammary secretory cells and the molecular pathways responsible for milk synthesis. In addition, we identified several candidate genes responsible for milk production traits and constructed a gene regulatory network for RNA seq data. In conclusion, this study provides a basic understanding of the lactation biology of cows at the gene expression level.

U2AF65 enhances milk synthesis and growth of bovine mammary epithelial cells by positively regulating the mTOR-SREBP-1c signalling pathway

U2 snRNP auxiliary factor 65 kDa (U2AF65) is a splicing factor that promotes prespliceosome assembly. The function of U2AF65 in alternative splicing has been identified; however, the essential physiological role of U2AF65 remains poorly understood. In this study, we investigated the regulatory role of U2AF65 in milk synthesis and growth of bovine mammary epithelial cells (BMECs). Our results showed that U2AF65 localizes in the nucleus. Treatment with amino acids (Met and Leu) and hormones (prolactin and β-estradiol) upregulated the expression of U2AF65 in these cells. U2AF65 overexpression increased the synthesis of β-casein, triglycerides, and lactose; increased cell viability; and promoted proliferation of BMECs. Furthermore, our results showed that U2AF65 positively regulated mTOR phosphorylation and expression of mature mRNA of mTOR and SREBP-1c. Collectively, our findings demonstrate that U2AF65 regulates the mRNA expression of signalling molecules (mTOR and SREBP-1c) involved in milk synthesis and growth of BMECs, possibly via controlling the splicing and maturation of these mRNAs. U2 snRNP auxiliary factor 65 kDa (U2AF65) is a splicing factor that promotes prespliceosome assembly. The essential physiological role of U2AF65 remains poorly understood. In the present study, we confirmed that U2AF65 functions as a positive regulator of milk synthesis in and proliferation of bovine mammary epithelial cells via the mTOR-SREBP-1c signalling pathway. Therefore, our study uncovers the regulatory role of U2AF65 in milk synthesis and cell proliferation.