Effects of Arginine concentration on the in vitro expression of Casein and mTOR pathway related genes in mammary epithelial cells from dairy cattle

Varying the ratio of Lys: Met through enhancing methionine supplementation improved milk secretion ability through regulating the mRNA expression in bovine mammary epithelial cells under heat stress

Introduction

The ratio of lysine (Lys) to methionine (Met) with 3.0: 1 is confirmed as the "ideal" profile for milk protein synthesis, but whether this ratio is suitable for milk protein synthesis under HS needs to be further studied.

Methods

To evaluate the molecular mechanism by which HS and Lys to Met ratios affect mammary cell functional capacity, an immortalized bovine mammary epithelial cell line (MAC-T) is incubated with 5 doses of Met while maintaining a constant concentration of Lys. The MAC-T cells was treated for 6 h as follow: Lys: Met 3.0: 1 (control 37°C and IPAA 42°C) or treatments under HS (42°C) with different ratios of Lys: Met at 2.0: 1 (LM20), 2.5: 1 (LM25), 3.5: 1 (LM35) and 4.0: 1 (LM40). RNA sequencing was used to assess transcriptome-wide alterations in mRNA abundance.

Results

The significant difference between control and other groups was observed base on PCA analysis. A total of 2048 differentially expressed genes (DEGs) were identified in the IPAA group relative to the control group. Similarly, 226, 306, 148, 157 DEGs were detected in the LM20, LM25, LM35 and LM40 groups, respectively, relative to the IPAA group. The relative mRNA abundance of HSPA1A was upregulated and anti-apoptotic genes (BCL2L1 and BCL2) was down-regulated in the IPAA group, compared to the control group (p < 0.05). Compared with the IPAA group, the relative mRNA abundance of anti-apoptotic genes and casein genes (CSN1S2 and CSN2) was up-regulated in the LM25 group (p < 0.05). The DEGs between LM25 and IPAA groups were associated with the negative regulation of transcription RNA polymerase II promoter in response to stress (GO: 0051085, DEGs of BAG3, DNAJB1, HSPA1A) as well as the mTOR signaling pathway (ko04150, DEGs of ATP6V1C2, WNT11, WNT3A, and WNT9A). Several DEGs involved in amino acids metabolism (AFMID, HYKK, NOS3, RIMKLB) and glycolysis/gluconeogenesis (AFMID and MGAT5B) were up-regulated while DEGs involved in lipolysis and beta-oxidation catabolic processes (ALOX12 and ALOX12B) were down-regulated.

Conclusion

These results suggested that increasing Met supply (Lys: Met at 2.5: 1) may help mammary gland cells resist HS-induced cell damage, while possibly maintaining lactation capacity through regulation of gene expression.

Alfalfa xeno-miR159a regulates bovine mammary epithelial cell proliferation and milk protein synthesis by targeting PTPRF

Milk protein content is an important index to evaluate the quality and nutrition of milk. Accumulating evidence suggests that microRNAs (miRNAs) play important roles in bovine lactation, but little is known regarding the cross-kingdom regulatory roles of plant-derived exogenous miRNAs (xeno-miRNAs) in milk protein synthesis, particularly the underlying molecular mechanisms. The purpose of this study was to explore the regulatory mechanism of alfalfa-derived xeno-miRNAs on proliferation and milk protein synthesis in bovine mammary epithelial cells (BMECs). Our previous study showed that alfalfa miR159a (mtr-miR159a, xeno-miR159a) was highly expressed in alfalfa, and the abundance of mtr-miR159a was significantly lower in serum and whey from high-protein-milk dairy cows compared with low-protein-milk dairy cows. In this study, mRNA expression was detected by real-time quantitative PCR (qRT-PCR), and casein content was evaluated by enzyme-linked immunosorbent assay (ELISA). Cell proliferation and apoptosis were detected using the cell counting kit 8 (CCK-8) assay, 5-ethynyl-2'-deoxyuridine (EdU) staining, western blot, and flow cytometry. A dual-luciferase reporter assay was used to determine the regulation of Protein Tyrosine Phosphatase Receptor Type F (PTPRF) by xeno-miR159a. We found that xeno-miR159a overexpression inhibited proliferation of BMEC and promoted cell apoptosis. Besides, xeno-miR159a overexpression decreased β-casein abundance, and increased α-casein and κ-casein abundance in BMECs. Dual-luciferase reporter assay result confirmed that PTPRF is a target gene of xeno-miR159a. These results provide new insights into the mechanism by which alfalfa-derived miRNAs regulate BMECs proliferation and milk protein synthesis.

The role of milk fat globule size in modulating the composition of postbiotics produced by Bacillus subtilis and their effect on mammary epithelial cells

Milk lipids are secreted into the milk collecting ducts as milk fat globule (MFG) where they are exposed to microflora of the udder. We hypothesized that MFG size modulates the metabolic fingerprint of B. subtilis. Accordingly, small and large (2.3 and 7.0 µm, respectively) MFG were isolated from cow milk and used as a substrate for B. subtilis. Small MFG enhanced growth, whereas large MFG enhanced biofilm formation. Bacteria incubated with small MFG had increased concentration of metabolites related to energy production whereas metabolome of the bacteria incubated with large MFG had reduced concentrations of metabolites important for biofilm formation. Postbiotics from bacteria grown on large MFG exacerbated the proinflammatory response of MEC to LPS, and changed the expression of key enzymes involved in lipid and protein synthesis. Our results suggest that MFG size modulate growth trajectories and metabolome of B. subtilis, and consequently the stress response of host cells.

Optimizing hormonal and amino acid combinations for enhanced cell proliferation and cell cycle progression in bovine mammary epithelial cells

OBJECTIVE

The number of bovine mammary epithelial cells (BMECs) is closely associated with the quantity of milk production in dairy cows; however, the optimal levels and the combined effects of hormones and essential amino acids (EAAs) on cell proliferation are not completely understood. Thus, the purpose of this study was to determine the optimal combination of individual hormones and EAAs for cell proliferation and related signaling pathways in BMECs.

METHODS

Immortalized BMECs (MAC-T) were treated with six hormones (insulin, cortisol, progesterone, estrone, 17β-estradiol, and epidermal growth factor) and ten EAAs (arginine, histidine, leucine, isoleucine, threonine, tryptophan, lysine, methionine, phenylalanine, and valine) for 24 h.

RESULTS

Cells were cultured in a medium containing 10% fetal bovine serum (FBS) as FBS supplemented at a concentration of 10% to 50% showed a comparable increase in cell proliferation rate. The optimized combination of four hormones (insulin, cortisol, progesterone, and 17β-estradiol) and 20% of a mixture of ten EAAs led to the highest cell proliferation rate, which led to a significant increase in cell cycle progression at the S and G2/M phases, in the protein levels of proliferating cell nuclear antigen and cyclin B1, cell nucleus staining, and in cell numbers.

CONCLUSION

The optimal combination of hormones and EAAs increased BMEC proliferation by enhancing cell cycle progression in the S and G/2M phases. Our findings indicate that optimizing hormone and amino acid levels has the potential to enhance milk production, both in cell culture settings by promoting increased cell numbers, and in dairy cows by regulating feed intake.

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.

Effects of L-arginine and arginine-arginine dipeptide on amino acids uptake and αS1-casein synthesis in bovine mammary epithelial cells

Arginine (Arg), as an important functional amino acids (AA), is essential for milk protein synthesis in lactating ruminants. Arg shares transporters with cationic and neutral AA in mammary epithelial cells. Therefore, competitive inhibition might exist among these AA in uptake by mammary epithelial cells. In this study, cultured bovine mammary epithelial cells (BMEC) were used as the model to investigate whether the availability of L-Arg (0.7, 1.4, 2.8, 5.6, and 11.2 mM) affects the uptake of other AA and if this related to αS1-casein synthesis, and whether Arginine-Arginine (Arg-Arg) substituting part of free L-Arg can alleviate competitive inhibition among Arg and other AA, so as to promote αS1-casein synthesis. Our results showed that 2.8 mM L-Arg generated the greatest positive effects on αS1-casein synthesis and the activation of mammalian target of rapamycin (mTOR) signaling pathway (P < 0.01). With L-Arg supply increasing from 0.7 to 11.2 mM, the net-uptake of other AA (except Glu and Ala) decreased linearly and quadratically (Plinear < 0.01; Pquadratic < 0.01). Compared with 2.8 mM, the net-uptake of essential amino acids (EAA) and total amino acids (TAA) were lower at 11.2 mM L-Arg group, while greater at 1.4 mM L-Arg group (P < 0.01). Arg-Arg dipeptide replacing 10% free L-Arg increased αS1-casein synthesis (P < 0.05), net-uptake of EAA and TAA, as well as phosphorylation level of mTOR and p70 ribosomal protein S6 kinase (P70S6K) and mRNA expression of oligopeptide transporter 2 (PepT2; P < 0.01). These observations suggested that the increased αS1-casein synthesis by 10% Arg-Arg dipeptide might be related to the increase of AA availability and the activation of mTOR signaling pathway in BMEC.

The effect of arginine on inhibiting amyloid fibril derived from β-casein and the binding studies with multi-spectroscopic techniques

In general, β-casein is a stable molecular chaperone. However, the fact that amyloid fibrils derived from β-casein has been reported in some cases, which were usually associated with some malignant breast diseases. As an important amino acid, arginine not only exhibits the significance in casein synthesis in mammary gland, but also has great potentiality in inhibiting the amyloid fibril formation. Therefore, the influence of arginine on the amyloid fibrils formed by β-casein and further molecular mechanism were studied firstly with multi-spectroscopic techniques in the present work. The results of Thioflavin T determination, particle size analysis, transmission electron microscope observation showed that arginine not only inhibited the aggregation of β-casein at the growth stage, but also depolymerized the mature amyloid fibrils at the saturation stage. The further fluorescence experiment results demonstrated that the complex was formed between β-casein and arginine. Besides, there was one binding site and 0.48 nm binding distance. The thermodynamic parameters like ΔG⁰, ΔS⁰, ΔH⁰ were all negative, showing their binding reaction was spontaneous, and hydrogen bond and van der Waals force were the possibly chief intermolecular forces. Furthermore, the synchronous fluorescence spectra showing that the conformation of β-casein was affected and its tyrosine residues were gradually buried inside the protein. Our research would provide new insights into the treatments for the breast amyloidosis.

Effects of Essential Amino Acid Deficiency on General Control Nonderepressible 2/Eukaryotic Initiation Factor 2 Signaling and Proteomic Changes in Primary Bovine Mammary Epithelial Cells

We hypothesized that the general control nonderepressible 2 (GCN2)/eukaryotic initiation factor 2 (eIF2) signaling pathway and intracellular protein synthesis (PS) are regulated to maintain milk PS in primary bovine mammary epithelial cells (MECs) under essential amino acid (EAA) starvation conditions. We cultured MECs with 0%, 2% (depletion), and 100% (control) EAA for two exposure times (8 and 24 h), followed by three refeeding (RF) times with 100% EAA (0, 8, and 24 h). Subsequently, we measured cell viability, total protein concentration, and proliferation. Western blotting was used to quantify the levels of casein and the expression of total GCN2 and eIF2, as well as phosphorylated GCN2 (GCN2P) and eIF2 (eIF2P). The ISOQuant method was used to assess MEC proteomes, and the resultant data were analyzed using the Kruskal−Wallis test, nonpaired Wilcoxon rank post-hoc test, and ANOVA−Tukey test, as well as principal component analyses and multiple regressions models. Differences in cell viability were observed between the control versus the depleted and repleted MECs, respectively, where 97.2−99.8% viability indicated low cell death rates. Proliferation (range, 1.02−1.55 arbitrary units (AU)) was affected by starvation for 12 and 24 h and repletion for 24 h, but it was not increased compared with the control. Total protein expression was unaffected by both depletion and repletion treatments (median 3158 µg/mL). eIF2P expression was significantly increased (p < 0.05) after treatment with 2% EAA for 8 and 24 h compared with 2% EAA with 8 h + 24 h RF and 2% EAA with 24 h + 8 h RF. GCN2P also showed significantly increased expression (p < 0.05) after treatment with 2% EAA for 24 h compared with the control and 2% EAA with 24 h + 8 h RF. Intracellular casein/α-tubulin expression was unaffected by 2% EAA compared with control (0.073 ± 0.01 AU versus 0.086 ± 0.02 AU, respectively). We studied 30 of the detected 1180 proteins, 16 of which were differentially expressed in starved and refed MECs. Cells faced with EAA deficiency activated the GCN2P/eIF2P pathway, and the lack of change in the levels of casein and other milk proteins suggested that the EAA deficit was mitigated by metabolic flexibility to maintain homeostasis.

Insulin signaling and antioxidant proteins in adipose tissue explants from dairy cows challenged with hydrogen peroxide are altered by supplementation of arginine or arginine plus methionine

Arginine (Arg) and methionine (Met) can elicit anti-inflammatory and antioxidant effects in animals. Unlike Met, however, it is unknown if the supply of Arg can impact key aspects of adipose tissue (AT) function in dairy cows. Since Met and Arg metabolism are linked through the synthesis of polyamines, it is also possible that they have a complementary effect on aspects of AT function during a stress challenge. In this experiment, subcutaneous AT was harvested from four lactating multiparous Holstein cows (~27.0 kg milk per day, body condition score 3.38 ± 0.23) and used for incubations (4 h) with the following: control medium with an "ideal" profile of essential amino acids (IPAA; CTR; Lys:Met 2.9:1), IPAA plus 100 μM H2O2 (HP), H2O2 plus greater Arg supply (HPARG; Lys:Arg 1:1), or H2O2 plus greater Arg and methionine (Met) supply (HPARGMET; Lys:Met 2.5:1 and Lys:Arg 1:1). Western blotting was used to measure abundance of 18 protein targets associated with insulin and AA signaling, nutrient transport, inflammation, and antioxidant response. Reverse transcription polymerase chain reaction (RT-PCR) was used to assess effects on genes associated with Arg metabolism. Among the protein targets measured, although abundance of phosphorylated (p) AKT serine/threonine kinase (P = 0.05) and p-mechanistic target of rapamycin (P = 0.04) were lowest in HP explants, this effect was attenuated in HPARG and especially HPARGMET compared with CTR. Compared with HP, incubation with HPARG led to upregulation of the AA transporter solute carrier family 1 member 3 (L-glutamate transporter; P = 0.03), the reactive oxygen species detoxification-related enzyme glutathione S-transferase mu 1 (GSTM1; P = 0.03), and fatty acid synthase (P = 0.05). Those effects were accompanied by greater abundance of solute carrier family 2 member 4 (insulin-induced glucose transporter) in explants incubated with HPARG and also HPARGMET (P = 0.04). In addition, compared with other treatments, the peak response in abundance of the intracellular energy sensor 5'-prime-AMP-activated protein kinase was detected with HPARGMET (P = 0.003). There was no effect of Arg or Arg plus Met on the mRNA abundance of genes associated with Arg metabolism (ARG1, NOS2, AMD1, SMS, and SRM). Overall, supplementation of Arg alone or with Met partially alleviated the negative effects induced by H2O2. More systematic studies need to be conducted to explore the function of Arg supply with or without Met on AT function.

Arginine Regulates TOR Signaling Pathway through SLC38A9 in Abalone Haliotis discus hannai

Arginine plays an important role in the regulation of the target of the rapamycin (TOR) signaling pathway, and Solute Carrier Family 38 Member 9 (SLC38A9) was identified to participate in the amino acid-dependent activation of TOR in humans. However, the regulations of arginine on the TOR signaling pathway in abalone are still unclear. In this study, slc38a9 of abalone was cloned, and the slc38a9 was knocked down and overexpressed to explore its function in the regulation of the TOR signaling pathway. The results showed that knockdown of slc38a9 decreased the expression of tor, ribosomal s6 protein kinase (s6k) and eukaryotic translation initiation factor 4e (eif4e) and inhibited the activation of the TOR signaling pathway by arginine. Overexpression of slc38a9 up-regulated the expression of TOR-related genes. In addition, hemocytes of abalone were treated with 0, 0.2, 0.5, 1, 2 and 4 mmol/L of arginine, and abalones were fed diets with 1.17%, 1.68% and 3.43% of arginine, respectively, for 120 days. Supplementation of arginine (0.5–4 mmol/L) increased the expressions of slc38a9, tor, s6k and eif4e in hemocytes, and abalone fed with 1.68% of dietary arginine showed higher mRNA levels of slc38a9, tor, s6k and eif4e and phosphorylation levels of TOR, S6 and 4E-BP. In conclusion, the TOR signaling pathway of abalone can be regulated by arginine, and SLC38A9 plays an essential role in this regulation.

Amino Acids Supplementation for the Milk and Milk Protein Production of Dairy Cows

Simple Summary

The composition of milk not only has nutritional implications, but is also directly related to the income of dairy producers. As regards milk’s composition, concerns around milk protein have emerged from the increased consumption of casein products. The synthesis of proteins in milk is a highly complex and high-cost process, because the conversion efficiency of dietary protein to milk protein is very low in dairy cows. Thus, some studies have increased milk protein by using protein supplements or a single amino acid (AA) supply. AAs are the building blocks of protein, and can also stimulate the protein synthetic pathway. This review mainly concerns the use of AAs for producing milk protein in high-producing dairy cows, particularly with methionine, lysine, and histidine. Understanding the mechanisms of AAs will help to promote milk protein synthesis in the dairy industry.

Abstract

As the preference of consumers for casein products has increased, the protein content of milk from dairy cows is drawing more attention. Protein synthesis in the milk of dairy cows requires a proper supply of dietary protein. High protein supplementation may help to produce more milk protein, but residues in feces and urine cause environmental pollution and increase production costs. As such, previous studies have focused on protein supplements and amino acid (AA) supply. This review concerns AA nutrition for enhancing milk protein in dairy cows, and mainly focuses on three AAs: methionine, lysine, and histidine. AA supplementation for promoting protein synthesis is related to the mammalian target of rapamycin (mTOR) complex and its downstream pathways. Each AA has different stimulating effects on the mTOR translation initiation pathway, and thus manifests different milk protein yields. This review will expand our understanding of AA nutrition and the involved pathways in relation to the synthesis of milk protein in dairy cows.

Arginine Alters miRNA Expression Involved in Development and Proliferation of Rat Mammary Tissue

Simple Summary

MiRNAs are small noncoding RNAs that regulate a variety of developmental and physiological processes, with many having well-defined developmental and cell-type specific expression patterns. Aspects of the cell cycle such as cell differentiation, proliferation and apoptosis can be regulated by miRNA, underscoring an unexplored link between arginine supply and mammary tissue function during lactation. The specific objective of the present study was to determine miRNA profiles in mammary tissue at the end of lactation in response to enhanced dietary supply of arginine. Our results indicate that arginine may potentially be involved in the development of rat mammary glands through miRNA.

Abstract

This study was designed to determine the effects of dietary arginine on development and proliferation in rat mammary tissue through changes in miRNA profiles. Twelve pregnant Wistar rats were allocated randomly to two groups. A basal diet containing arginine or the control diet containing glutamate on an equal nitrogen basis as the arginine supplemented diet were used. The experiment included a pre-experimental period of four days before parturition and an experimental period of 17 days after parturition. Mammary tissue was collected for histology, RNA extraction and high-throughput sequencing analysis. The greater mammary acinar area indicated that arginine supplementation enhanced mammary tissue development (p < 0.01). MicroRNA profiling indicated that seven miRNA (miR-206-3p, miR-133a-5p, miR-133b-3p, miR-1-3p, miR-133a-3p, miR-1b and miR-486) were differentially expressed in response to Arginine when compared with the glutamate-based control group. In silico gene ontology enrichment and KEGG pathway analysis revealed between 240 and 535 putative target genes among the miRNA. Further verification by qPCR revealed concordance with the differential expression from the sequencing results: 17 of 28 target genes were differentially expressed (15 were highly expressed in arginine and 2 in control) and 11 target genes did not have significant difference in expression. In conclusion, our study suggests that arginine may potentially regulate the development of rat mammary glands through regulating miRNAs.

Effects of Hydroxytyrosol against Lipopolysaccharide-Induced Inflammation and Oxidative Stress in Bovine Mammary Epithelial Cells: A Natural Therapeutic Tool for Bovine Mastitis

Background: Bovine mastitis is a growing health problem, affecting both welfare of dairy cattle and milk production. It often leads to chronic infections, disturbing the quality of milk and resulting in cow death. Thus, it has a great economic impact for breeders. Methods: In this study, we evaluated the protective effect of hydroxytyrosol—a natural molecule which is the major constituent of many phyto-complexes—in an in vitro model of mastitis induced by LPS (1μg/mL). Results: Our results showed that hydroxytyrosol (10 and 25 μM) was able to prevent the oxidative stress induced by LPS (intracellular ROS, GSH and NOX-1) and the consequently inflammatory response (TNF-α, IL-1β and IL-6). The protective effect of hydroxytyrosol is also related to the enhancement of endogenous antioxidant systems (Nrf2, HO-1, NQO-1 and Txnrd1). Moreover, hydroxytyrosol showed an important protective effect on cell functionality (α-casein S1, α-casein S2 and β-casein). Conclusions: Taken together, our results showed a significant protective effect of hydroxytyrosol on oxidative stress and inflammatory response in MAC-T cells. Thus, we indicated a possible important therapeutic role for hydroxytyrosol in the prevention or management of bovine mastitis.

Arginine Supply Impacts the Expression of Candidate microRNA Controlling Milk Casein Yield in Bovine Mammary Tissue

Arginine, a semi-essential functional amino acid, has been found to promote the synthesis of casein in mammary epithelial cells to some extent. Data from mouse indicated that microRNA (miRNA) are important in regulating the development of mammary gland and milk protein synthesis. Whether there are potential links among arginine, miRNA and casein synthesis in bovine mammary gland is uncertain. The objective of the present work was to detect the effects of arginine supplementation on the expression of miRNA associated with casein synthesis in mammary tissue and mammary epithelial cells (BMEC). The first study with bovine mammary epithelial cells (BMEC) focused on screening for miRNA candidates associated with the regulation of casein production by arginine. The BMEC were cultured with three different media, containing 0, 1.6 and 3.2 mM arginine, for 24 h. The expression of candidate miRNA was evaluated. Subsequently, in an in vivo study, 6 Chinese Holstein dairy cows with similar BW (mean ± SE) (512.0 ± 19.6 kg), parity (3), BCS (4.0) and DIM (190 ± 10.3 d) were randomly assigned to three experimental groups. The experimental cows received an infusion of casein, arginine (casein plus double the concentration of arginine in casein), and alanine (casein plus alanine, i.e., iso-nitrogenous to the arginine group) in a replicated 3 × 3 Latin square design with 22 d for each period (7 d for infusion and 15 d for washout). Mammary gland biopsies were obtained from each cow at the end of each infusion period. Results of the in vitro study showed differences between experimental groups and the control group for the expression of nine miRNA: miR-743a, miR-543, miR-101a, miR-760-3p, miR-1954, miR-712, miR-574-5p, miR-468 and miR-875-3p. The in vivo study showed that arginine infusion promoted milk protein content, casein yield and the expression of CSN1S1 and CSN1S2. Furthermore, the expression of miR-743a, miR-543, miR-101a, miR-760-3p, miR-1954, and miR-712 was also greater in response to arginine injection compared with the control or alanine group. Overall, results both in vivo and in vitro revealed that arginine might partly influence casein yield by altering the expression of 6 miRNAs (miR-743a, miR-543, miR-101a, miR-760-3p, miR-1954, and miR-712).

High levels of fatty acids inhibit β-casein synthesis through suppression of the JAK2/STAT5 and mTOR signaling pathways in mammary epithelial cells of cows with clinical ketosis

Ketosis is a metabolic disease of dairy cows often characterized by high concentrations of ketone bodies and fatty acids, but low milk protein and milk production. The Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) and the mechanistic target of rapamycin (mTOR) signaling pathways are central for the regulation of milk protein synthesis. The effect of high levels of fatty acids on these pathways and β-casein synthesis are unknown in dairy cows with clinical ketosis. Mammary gland tissue and blood samples were collected from healthy (n = 15) and clinically-ketotic (n = 15) cows. In addition, bovine mammary epithelial cells (BMEC) were treated with fatty acids, methionine (Met) or prolactin (PRL), respectively. In vivo, the serum concentration of fatty acids was greater (P > 0.05) and the percentage of milk protein (P > 0.05) was lower in cows with clinical ketosis. The JAK2-STAT5 and mTOR signaling pathways were inhibited and the abundance of β-casein was lower in mammary tissue of cows with clinical ketosis (P > 0.05). In vitro, high levels of fatty acids inhibited the JAK2-STAT5 and mTOR signaling pathways (P > 0.05) and further decreased the β-casein synthesis (P > 0.05) in BMEC. Methionine or PRL treatment, as positive regulators, activated the JAK2-STAT5 and mTOR signaling pathways to increase the β-casein synthesis. Importantly, the high concentration of fatty acids attenuated the positive effect of Met or PRL on mTOR, JAK2-STAT5 pathways and the abundance of β-casein (P > 0.05). Overall, these data indicate that the high concentrations of fatty acids that reach the mammary cells during clinical ketosis inhibit mTOR and JAK2-STAT5 signaling pathways, and further suppress β-casein synthesis.

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.

Camellia (Camellia oleifera Abel.) seed oil promotes milk fat and protein synthesis-related gene expression in bovine mammary epithelial cells

Camellia (Camellia oleifera Abel.) seed oil is a commonly used edible oil of China. In ancient Chinese literature, it is mentioned to be helpful for postpartum repair and lactation in women. Research on camellia seed oil (CO) as a feed additive for dairy cattle is less. We investigated the effect of CO on the expression of milk fat and protein syntheses-related genes in differentiated bovine mammary epithelial cells (MAC-T) using soybean oil (SO) as the control. The results showed that CO increased the expression of genes related to de novo synthesis of fatty acids including sterol regulatory element-binding protein 1 (SREBP1), acetyl-CoA carboxylase 1 (ACC), fatty acid synthase (FASN), lipoprotein lipase (LPL), and stearoyl-CoA desaturase (SCD) (p < .05). Among the milk protein genes analyzed, CO increased β-casein mRNA expression (p < .05) and decreased αS1-casein mRNA expression (p < .05) in MAC-T cells. CO upregulated the pathways related to milk protein synthesis with increased mRNA levels of phosphoinositide 3-kinase (PI3K), RAC-alpha serine/threonine-protein kinase (AKT1), and mammalian target of rapamycin (mTOR) (p < .05) in MAC-T cells. Ribosomal protein S6 kinase beta-1 (S6K1) gene was upregulated, and eukaryotic initiation factor 4E (eIF4E) gene (p < .05) was downregulated with CO treatment. The mRNA expression levels of janus kinase 2 (JAK2), activator of transcription 5-β (STAT5-β), and E74-like factor 5 (ELF5) were elevated in MAC-T cells treated with CO (p < .05). Meanwhile, the protein expression levels of S6K1, STAT5-β, phosphorylated mTOR (p-mTOR), p-S6K1, and p-STAT5-β increased in MAC-T cells treated with CO (p < .05). In summary, CO promoted β-casein synthesis by regulating PI3K-mTOR-S6K1 and JAK2-STAT5 signaling pathways and influenced fatty acid synthesis by regulating SREBP1-related genes in MAC-T cells. We need to further confirm the function of CO using in vivo models.

Effects of intravenous arginine infusion on inflammation and metabolic indices of dairy cows in early lactation

Enhancing the supply of arginine (Arg), a semi-essential amino acid, has positive effects on immune function in dairy cattle experiencing metabolic stress during early lactation. Our objective was to determine the effects of Arg supplementation on biomarkers of liver damage and inflammation in cows during early lactation. Six Chinese Holstein lactating cows with similar BW (508 ± 14 kg), body condition score (3.0), parity (4.0 ± 0), milk yield (30.6 ± 1.8 kg) and days in milk (20 ± days) were randomly assigned to three treatments in a replicated 3 × 3 Latin square design balanced for carryover effects. Each period was 21 days with 7 days for infusion and 14 days for washout. Treatments were (1) Control: saline; (2) Arg group: saline + 0.216 mol/day l-Arg; and (3) Alanine (Ala) group: saline + 0.868 mol/day l-Ala (iso-nitrogenous to the Arg group). Blood and milk samples from the experimental cows were collected on the last day of each infusion period and analyzed for indices of liver damage and inflammation, and the count and composition of somatic cells in milk. Compared with the Control, the infusion of Arg led to greater concentrations of total protein, immunoglobulin M and high density lipoprotein cholesterol coupled with lower concentrations of haptoglobin and tumor necrosis factor-α, and activity of aspartate aminotransferase in serum. Infusion of Ala had no effect on those biomarkers compared with the Control. Although milk somatic cell count was not affected, the concentration of granulocytes was lower in response to Arg infusion compared with the Control or Ala group. Overall, the biomarker analyses indicated that the supplementation of Arg via the jugular vein during early lactation alleviated inflammation and metabolic stress.

Moringa Extract Attenuates Inflammatory Responses and Increases Gene Expression of Casein in Bovine Mammary Epithelial Cells

Bovine mastitis is a common inflammatory disease in the udder of dairy cows that causes economic loss to dairy industries. The development of alternative strategies, especially the utilization of natural products, e.g. Moringa oleifera, has gained a lot of interests. The objective of the current study was to investigate the protective effects of moringa extract (ME) in bovine mammary epithelial cells (MAC-T) in in vitro settings. Radical scavenging capacities and anti-inflammatory properties of ME were examined using lipopolysaccharide (LPS)-challenged MAC-T cells. ME showed significant radical scavenging activities. In addition, ME decreased reactive oxygen species produced by LPS in cells. ME also attenuated inflammatory cyclooxygenase-2 expression induced by LPS by down-regulating NF-κB signaling cascade. Moreover, ME ameliorated LPS-induced pro-inflammatory cytokines including tumor necrosis factor-, interleukin-1, and interleukin-6. Furthermore, ME up-regulated mRNA expression levels of heme oxygenase-1, NAD(P)H: quinone oxidoreductase-1, and thioredoxin reductase 1. Importantly, ME promoted differentiated MAC-T cells by increasing mRNA expression levels of α-casein S1, α-casein S2, and β-casein. In conclusion, ME has beneficial effects in bovine mammary epithelial cells through its anti-inflammatory, antioxidant, and casein production properties. Our study provides evidence that ME could be a good candidate for a feed supplement to decrease inflammatory responses due to bovine mastitis.

Amino Acid Metabolism in Dairy Cows and their Regulation in Milk Synthesis

Background:

Reducing dietary Crude Protein (CP) and supplementing with certain Amino Acids (AAs) has been known as a potential solution to improve Nitrogen (N) efficiency in dairy production. Thus understanding how AAs are utilized in various sites along the gut is critical.

Objective:

AA flow from the intestine to Portal-drained Viscera (PDV) and liver then to the mammary gland was elaborated in this article. Recoveries in individual AA in PDV and liver seem to share similar AA pattern with input: output ratio in mammary gland, which subdivides essential AA (EAA) into two groups, Lysine (Lys) and Branchedchain AA (BCAA) in group 1, input: output ratio > 1; Methionine (Met), Histidine (His), Phenylalanine (Phe) etc. in group 2, input: output ratio close to 1. AAs in the mammary gland are either utilized for milk protein synthesis or retained as body tissue, or catabolized. The fractional removal of AAs and the number and activity of AA transporters together contribute to the ability of AAs going through mammary cells. Mammalian Target of Rapamycin (mTOR) pathway is closely related to milk protein synthesis and provides alternatives for AA regulation of milk protein synthesis, which connects AA with lactose synthesis via α-lactalbumin (gene: LALBA) and links with milk fat synthesis via Sterol Regulatory Element-binding Transcription Protein 1 (SREBP1) and Peroxisome Proliferatoractivated Receptor (PPAR).

Conclusion:

Overall, AA flow across various tissues reveals AA metabolism and utilization in dairy cows on one hand. While the function of AA in the biosynthesis of milk protein, fat and lactose at both transcriptional and posttranscriptional level from another angle provides the possibility for us to regulate them for higher efficiency.

Influence of arginine on enzymes related to arginine metabolism in bovine mammary epithelial cells in vitro

Bovine mammary epithelial cells were used to evaluate the effects of different levels of Arginine (Arg) on enzymes related to Arg metabolism. A series of seven Arg concentrations in the medium as treatments were T0 (0.00 mg L−1) as control group, and T0.25 (69.50 mg L−1), T0.5 (139.00 mg L−1), T1 (278.00 mg L−1), T2 (556.00 mg L−1), T4 (1112.00 mg L−1), and T8 (2224.00 mg L−1) as experiment groups, respectively. The quantitative polymerase chain reaction and enzyme-linked immunosorbent assay analysis showed that the nitric oxide concentration, the expressions of endothelial nitric oxide synthase in mRNA, and enzyme level were all increased in response to enhanced Arg doses such that the T8 was the greatest group (P < 0.05). Four-fold Arg concentration improved gene expression and synthesis of arginase which then deceased when excessive Arg was supplied (P < 0.05). The expressions of ornithine aminotransferase mRNA and enzyme in T1 and T2 groups were significantly greater than that in the other groups (P < 0.05). Two-fold Arg was the optimum level for ornithine decarboxylase gene expression and enzyme synthesis among all seven treatments (P < 0.05). These somewhat various effects of Arg concentrations on four kinds of enzymes in different Arg metabolic pathways suggest that Arg might participate in regulating bovine mammary physiological function with an optimum concentration by influencing the enzymes in related metabolic pathways.

Comparative transcriptome analysis of mammary epithelial cells at different stages of lactation reveals wide differences in gene expression and pathways regulating milk synthesis between Jersey and Kashmiri cattle

Jersey and Kashmiri cattle are important dairy breeds that contribute significantly to the total milk production of the Indian northern state of Jammu and Kashmir. The Kashmiri cattle germplasm has been extensively diluted through crossbreeding with Jersey cattle with the goal of enhancing its milk production ability. However, crossbred animals are prone to diseases resulting to unsustainable milk production. This study aimed to provide a comprehensive transcriptome profile of mammary gland epithelial cells at different stages of lactation and to find key differences in genes and pathways regulating milk traits between Jersey and Kashmiri cattle. Mammary epithelial cells (MEC) isolated from milk obtained from six lactating cows (three Jersey and three Kashmiri cattle) on day 15 (D15), D90 and D250 in milk, representing early, mid and late lactation, respectively were used. RNA isolated from MEC was subjected to next-generation RNA sequencing and bioinformatics processing. Casein and whey protein genes were found to be highly expressed throughout the lactation stages in both breeds. Largest differences in differentially expressed genes (DEG) were between D15 vs D90 (1,805 genes) in Kashmiri cattle and, D15 vs D250 (3,392 genes) in Jersey cattle. A total of 1,103, 1,356 and 1,397 genes were differentially expressed between Kashmiri and Jersey cattle on D15, D90 and D250, respectively. Antioxidant genes like RPLPO and RPS28 were highly expressed in Kashmiri cattle. Differentially expressed genes in both Kashmiri and Jersey were enriched for multicellular organismal process, receptor activity, catalytic activity, signal transducer activity, macromolecular complex and developmental process gene ontology terms. Whereas, biological regulation, endopeptidase activity and response to stimulus were enriched in Kashmiri cattle and, reproduction and immune system process were enriched in Jersey cattle. Most of the pathways responsible for regulation of milk production like JAK-STAT, p38 MAPK pathway, PI3 kinase pathway were enriched by DEG in Jersey cattle only. Although Kashmiri has poor milk production efficiency, the present study suggests possible physicochemical and antioxidant properties of Kashmiri cattle milk that needs to be further explored.

Jugular arginine supplementation increases lactation performance and nitrogen utilization efficiency in lactating dairy cows

Background

Enhancing the post-ruminal supply of arginine (Arg), a semi-essential amino acid (AA), elicits positive effects on milk production. Our objective was to determine the effects of Arg infusion on milk production parameters and aspects of nitrogen (N) absorption and utilization in lactating dairy cows. Six lactating Chinese Holstein cows of similar body weight (508 ± 14 kg), body condition score (3.0 ± 0), parity (4.0 ± 0), milk yield (30.6 ± 1.8 kg) and days in milk (20 ± 2 d) were randomly assigned to 3 treatments in a replicated 3 × 3 Latin square design with 21 d for each period (1 week for infusion and 2 weeks for washout). Treatments were 1) Control: saline; 2) Arg group: saline + 9.42 g/L L-Arg; 3) Alanine (Ala) group: saline + 19.31 g/L L-Ala (iso-nitrogenous to the Arg group). Milk production and composition, dry matter intake, apparent absorption of N, profiles of amino acids (AA) in blood, urea N in urine, milk, and blood, and gene expression of AA transporters were determined.

Results

Compared with the Control or Ala group, the infusion of Arg led to greater expression of AA transporters (SLC7A2 and SLC7A8) and apparent uptake of free AA in the mammary gland, and was accompanied by greater milk yield, milk protein yield and milk efficiency (calculated by dividing milk yield over feed intake), together with lower concentration of urea N [regarded as an indicator of N utilization efficiency (NUE)] in blood and milk. Furthermore, in the cows infused with Arg, the NUE was higher and the concentration of urea N in urine was lower than those in the Ala group, although no differences were detected in NUE and urea N in urine between the Control and Arg group. The infusion of Ala had no effect on those indices compared with the Control.

Conclusions

Overall, enhancing the post-ruminal supply of Arg via the jugular vein had a positive effect on the synthesis of milk protein at least in part by increasing gene expression of some AA transporters and uptake of free AA by mammary gland.

Perspectives on the Therapeutic Benefits of Arginine Supplementation in Cancer Treatment

BACKGROUND

Arginine is considered a semi-essential amino acid in healthy adults and the elderly. This amino acid seems to improve the immune system, stimulate cell growth and differentiation, and increase endothelial permeability, among other effects. For those reasons, it has been theorized that arginine supplementation may be used as an adjuvant to conventional cancer therapy treatments.

OBJECTIVE

This review aims to evaluate the existing knowledge of the scientific community on arginine supplementation in order to improve the efficacy of current cancer treatment.

RESULTS

Despite the continued efforts of science to improve treatment strategies, cancer remains one of the greatest causes of death on the planet in adults and elderly people. Chemo and radiotherapy are still the most effective treatments but at the cost of significant side effects.

CONCLUSION

Thus, new therapeutic perspectives have been studied in recent years, to be used in addition to traditional treatments or not, seeking to treat or even cure the various types of cancer with fewer side effects.

Enhanced supply of methionine or arginine alters mechanistic target of rapamycin signaling proteins, messenger RNA, and microRNA abundance in heat-stressed bovine mammary epithelial cells in vitro

Heat stress (HS) causes reductions in milk production, but it is unclear whether this effect is due to reduced number or functional capacity (or both) of mammary cells. Methionine supplementation improves milk protein, whereas Arg is taken up in excess by mammary cells to produce energy and nonessential AA that can be incorporated into milk protein. To evaluate molecular mechanisms by which mammary functional capacity is affected by HS and Met or Arg, mammary alveolar (MAC-T) cells were incubated at thermal-neutral (37°C) or HS (42°C) temperatures. Treatments were optimal AA profiles (control; Lys:Met = 2.9:1.0; Lys:Arg = 2.1:1.0), control plus Met (Lys:Met = 2.5:1.0), or control plus Arg (Lys:Arg = 1.0:1.0). After incubation for 6 h, cells were harvested and RNA and protein were extracted for quantitative real-time PCR and Western blotting. Protein abundance of mechanistic target of rapamycin (MTOR), eukaryotic initiation factor 2a, serine-threonine protein kinase (AKT), 4E binding protein 1 (EIF4EBP1), and phosphorylated EIF4EBP1 was lower during HS. The lower phosphorylated EIF4EBP1 with HS would diminish translation initiation and reduce protein synthesis. Both Met and Arg had no effect on MTOR proteins, but the phosphorylated EIF4EBP1 decreased by AA, especially Arg. Additionally, Met but not Arg decreased the abundance of phosphorylated eukaryotic elongation factor 2, which could be positive for protein synthesis. Although HS upregulated the heat shock protein HSPA1A, the apoptotic gene BAX, and the translation inhibitor EIF4EBP1, the mRNA abundance of PPARG, FASN, ACACA (lipogenesis), and BCL2L1 (antiapoptotic) decreased. Greater supply of Met or Arg reversed most of the effects of HS occurring at the mRNA level and upregulated the abundance of HSPA1A. In addition, compared with the control, supply of Met or Arg upregulated genes related to transcription and translation (MAPK1, MTOR, SREBF1, RPS6KB1, JAK2), insulin signaling (AKT2, IRS1), AA transport (SLC1A5, SLC7A1), and cell proliferation (MKI67). Upregulation of microRNA related to cell growth arrest and apoptosis (miR-34a, miR-92a, miR-99, and miR-184) and oxidative stress (miR-141 and miR-200a) coupled with downregulation of fat synthesis-related microRNA (miR-27ab and miR-221) were detected with HS. Results suggest that HS has a direct negative effect on synthesis of protein and fat, mediated in part by coordinated changes in mRNA, microRNA, and protein abundance of key networks. The positive responses with Met and Arg raise the possibility that supplementation with these AA during HS might have a positive effect on mammary metabolism.

High expression of cell death-inducing DFFA-like effector a (CIDEA) promotes milk fat content in dairy cows with clinical ketosis

High blood concentrations of nonesterified fatty acids (NEFA) during ketosis represent a source of fatty acids for milk fat synthesis and explain the increase in milk fat content in ketotic cows. Cell death-inducing DFFA-like effector a (CIDEA) is a lipid droplet coat protein with important roles in the regulation of milk fat synthesis and secretion in mice. Whether ketosis alters the expression of CIDEA in mammary gland tissue and the extent to which it may contribute to regulation of milk fat synthesis and secretion are unknown. Mammary gland tissue and blood samples were collected from healthy (n = 15) and clinically ketotic (n = 15) cows. Mammary epithelial cells isolated from cows were infected with CIDEA overexpression adenovirus for 48 h, treated with 0, 0.3, 0.6, or 1.2 mM NEFA for 24 h, or infected with CIDEA-silencing adenovirus for 48 h and treated with 1.2 mM NEFA for 24 h. Serum concentrations of NEFA and β-hydroxybutyrate were greater in cows with clinical ketosis, and milk production and dry matter intake were lower in cows with clinical ketosis. However, compared with healthy cows, the content of milk fat of cows with clinical ketosis was greater. Compared with healthy cows, abundance of mRNA and protein of CIDEA, fatty acid synthase (FASN), acetyl-coA carboxylase 1 (ACACA), butyrophilin (BTN1A1), and xanthine dehydrogenase (XDH) was greater in mammary tissue of cows with clinical ketosis. Overexpression of CIDEA in cultured mammary epithelial cells increased the abundance of FASN, ACACA, XDH, and BTN1A1, and increased triacylglycerol (TAG) content in mammary epithelial cells. Exogenous NEFA increased the abundance of CIDEA, FASN, ACACA, XDH, and BTN1A1, and increased TAG content in mammary epithelial cells. Importantly, knockdown of CIDEA reversed the upregulation of FASN, ACACA, XDH, and BTN1A1 abundance and TAG content induced by NEFA treatment. Overall, these data suggest that high levels of NEFA stimulate the expression of CIDEA and enhance de novo fatty acid synthesis and milk fat secretion. As such, these mechanisms explain in part the elevation of milk fat content in dairy cows with clinical ketosis.

Transcriptional regulation of milk lipid synthesis by exogenous C16:0 and C18 fatty acids in bovine mammary epithelial cells

The objective of this study was to examine the effects of removing one fatty acid from a combination of long-chain fatty acids (LCFA) on milk lipogenesis in bovine mammary epithelial cells. The incubation concentration of LCFA was determined, and 100 μmol L−1 of C16:0, 5 μmol L−1 of C18:0, 100 μmol L−1 of cis-9 C18:1, 25 μmol L−1 of n-6 C18:2, and 1.2 μmol L−1 of n-3 C18:3 were used in the study. Treatments were C16:0, C18:0, C18:1, C18:2, and C18:3 combinations as control; control absent of C16:0 as A-C16:0; control absent of C18:0 as A-C18:0; control absent of C18:1 as A-C18:1; control absent of C18:2 as A-C18:2; control absent of C18:3 as A-C18:3. Results showed that compared with control, fatty acid synthetase expression was reduced by A-C18:0 and A-C18:1. Palmitic acid decreased expression of lipoprotein lipase. Compared with control, the expression of stearoyl-coenzyme A desaturase-1 and cluster of differentiation 36 was reduced by all treatments. Peroxisome proliferator-activated receptor-α expression was down-regulated by A-C16:0, A-C18:0, A-C18:1, and A-C18:2. Sterol regulatory element binding factor-1 was decreased when treated with A-C18:0, A-C18:1, and A-C18:2. Cells lack of 18-carbon fatty acid synthesized lower amount of intracellular triglyceride compared with control.

Rapid Communication: Period2 gene silencing increases the synthesis of αs-casein protein in bovine mammary epithelial cells

(), a core clock gene, encodes a circadian rhythm protein which has been shown to control mammary metabolism in rodents. Whether regulates milk component synthesis such as α-casein protein in bovine mammary cells is unknown. Thus, we used gene silencing technology to determine if silencing could affect α-casein synthesis and cell growth in cultured primary bovine mammary epithelial cells (BMEC). The BMEC were established by enzymatic digestion of mammary tissue from mid-lactation cows. A transient-transfection technique was used to insert a small interfering RNA (siRNA) oligonucleotide specific for to inhibit transcription. Control and siRNA-transfected cells were cultured for 48 h. qRT-PCR and ELISA analysis showed that silencing enhanced the synthesis of 2 kinds of α-casein ( < 0.05) through upregulating the mRNA level of and ( < 0.01). Furthermore, the 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) results demonstrated that cell proliferation was not affected ( > 0.05). These data led us to hypothesize that PER2 protein may potentially play an important role in the control of milk protein synthesis and, hence, represents a target that can be used to regulate protein synthesis rate during lactation.

Inhibition of arginase via jugular infusion of Nω-hydroxy-nor-l-arginine inhibits casein synthesis in lactating dairy cows

A previous in vitro study revealed that Arg elicits positive effects on casein synthesis through alterations of the Arg-ornithine pathway in bovine mammary epithelial cells. The main purpose of this work was to determine the effects of arginase inhibition using N^ω-hydroxy-nor-l-arginine (nor-NOHA) on milk protein synthesis in vivo. Six healthy Chinese Holstein cows with similar body weight (550.0 ± 20 kg; means ± standard deviation), parity (4), body condition score (3.0), milk yield (21.0 ± 1.0 kg), and days in milk (80 ± 2) were selected and randomly assigned to 3 treatments in a replicated 3 × 3 Latin square design with 22 d for each period (7 d for infusion and 15 d for washout). The treatments were (1) control: saline infusion; (2) nor-NOHA: infusion of 125 mg/L of nor-NOHA; (3) nor-NOHA + Arg: infusion of 125 mg/L of nor-NOHA with 9.42 g/L of Arg. The activity of enzymes related to Arg metabolism, milk protein synthesis, and expression of AA transporters was determined. The infusion of nor-NOHA decreased the activity of arginase but had no effect on the activity of ornithine decarboxylase and nitric oxide synthase in serum, and these responses were the same at the gene expression level in mammary gland. In addition, the infusion of nor-NOHA also reduced protein and fat synthesis in milk but had no effect on milk yield. When Arg was infused with nor-NOHA, the activity of total arginase, ornithine decarboxylase, and nitric oxide synthase, and the concentration of casein, protein, and fat in milk did not change compared with the nor-NOHA group, but the milk protein yield, the expression of some Arg transporters (SLC7A5 and SLC7A8), and milk yield increased. Overall, results verified previous in vitro findings indicating that synthesis of casein protein is closely regulated by the Arg-ornithine pathway in bovine mammary gland.

MicroRNA-214 regulates immunity-related genes in bovine mammary epithelial cells by targeting NFATc3 and TRAF3

In human, microRNA-214 (miR-214) plays crucial roles in mechanisms of immunity. However, the potential importance of miR-214 in immune mechanisms in dairy cows has not been investigated. In this study, we assessed potential immunity-related functions of miR-214 in human 293A cells and in bovine mammary epithelial cells (BMECs). We found that NFATc3 and TRAF3 could be targeted by miR-214 in both 293A cells and BMECs. We also found that miR-214 indirectly inhibited the expression of MAP3K14, TBK1 and inflammatory cytokines IL-6 and IL-1β. Taken together, our data revealed miR-214 regulated immunity-related genes by targeting NFATc3 and TRAF3, which provides insight into the molecular basis of immunity.

Optimal ratios of essential amino acids stimulate β-casein synthesis via activation of the mammalian target of rapamycin signaling pathway in MAC-T cells and bovine mammary tissue explants

Amino acids are the building blocks of proteins and serve as key molecular components upstream of the signaling pathways that regulate protein synthesis. The objective of this study was to systematically investigate the effect of essential AA ratios on milk protein synthesis in vitro and to elucidate some of the underlying mechanisms. Triplicate cultures of MAC-T cells and bovine mammary tissue explants (MTE) were incubated with the optimal AA ratio (OPAA; Lys:Met, 2.9:1; Thr:Phe, 1.05:1; Lys:Thr, 1.8:1; Lys:His, 2.38:1; and Lys:Val, 1.23:1) in the presence of rapamycin (control), OPAA, a Lys:Thr ratio of 2.1:1, a Lys:Thr ratio of 1.3:1, a Lys:His ratio of 3.05:1, or a Lys:Val ratio of 1.62:1 for 12 h; the other AA concentrations were equal to OPAA. In some experiments, the cells were cultured with OPAA with or without rapamycin (100 ng/mL) or with mammalian target of rapamycin (mTOR) small interference RNA, and the MTE were exposed to OPAA with rapamycin for β-casein expression. Among the treatments, the expression of β-casein was greatest in the MTE cultured with OPAA. In MAC-T cells, the OPAA upregulated the mRNA expression of SLC1A5 and SLC7A5 but downregulated the expression of IRS1, AKT3, EEF1A1, and EEF2 compared with the control. The OPAA had no effect on the mTOR phosphorylation status but increased the phosphorylation of S6K1 and RPS6. When the MTE were treated with rapamycin in the presence of OPAA, the expression of β-casein was markedly decreased. The phosphorylation of RPS6 and 4EBP1 also was reduced in MAC-T cells. A similar negative effect on the expression of RPS6KB1 and EIF4EBP1 was detected when the cells were cultured with either rapamycin or mTOR small interference RNA. The optimal AA ratio stimulated β-casein expression partly by enhancing the transport of AA into the cells, cross-talk with insulin signaling and a subsequent enhancement of mTOR signaling, or translation elongation in both MAC-T cells and bovine MTE.

Establishment of primary bovine intestinal epithelial cell culture and clone method

The aim of this study was to establish bovine intestinal epithelial cell (BIEC) line and provide a novel clone cell method. Although various strategies of bovine cell culture and clone techniques have been reported, these methods remain not established. Here, we culture successfully primary BIECs and establish a novel clone cell method. Our result showed that BIECs could be successfully cultured and passaged about generation 5. These cellular aggregates and clusters were adherent loosely at day 2 of culture. Cell aggregates and clusters start to proliferate after approximately 4 d. The BIECs showed positive reaction against cytokeratin 18, E-cadherin, and characteristics of epithelial-like morphology. In addition, the fatty acid-binding proteins (FABPs), villin, and intestinal peptidase (IP) band were positive in BIECs. Our results suggest that the establishment of culturing and clone BIEC methods will apply to isolate and clone other primary cells. These BIECs could therefore contribute to the study of bovine intestinal nutrient absorption and regulation, immune regulation, and the pathogenesis of the bovine intestinal disease, which will provide intestinal cell model in vitro.

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.

Biosynthesis of milk fat, protein, and lactose: roles of transcriptional and posttranscriptional regulation

The demand for high-quality milk is increasing worldwide. The efficiency of milk synthesis can be improved by taking advantage of the accumulated knowledge of the transcriptional and posttranscriptional regulation of genes coding for proteins involved in the synthesis of fat, protein, and lactose in the mammary gland. Research in this area is relatively new, but data accumulated in the last 10 years provide a relatively clear picture. Milk fat synthesis appears to be regulated, at least in bovines, by an interactive network between SREBP1, PPARγ, and LXRα, with a potential role for other transcription factors, such as Spot14, ChREBP, and Sp1. Milk protein synthesis is highly regulated by insulin, amino acids, and amino acid transporters via transcriptional and posttranscriptional routes, with the insulin-mTOR pathway playing a central role. The transcriptional regulation of lactose synthesis is still poorly understood, but it is clear that glucose transporters play an important role. They can also cooperatively interact with amino acid transporters and the mTOR pathway. Recent data indicate the possibility of nutrigenomic interventions to increase milk fat synthesis by feeding long-chain fatty acids and milk protein synthesis by feeding amino acids. We propose a transcriptional network model to account for all available findings. This model encompasses a complex network of proteins that control milk synthesis with a cross talk between milk fat, protein, and lactose regulation, with mTOR functioning as a central hub.

Arginine Relieves the Inflammatory Response and Enhances the Casein Expression in Bovine Mammary Epithelial Cells Induced by Lipopolysaccharide

As one of functional active amino acids, L-arginine holds a key position in immunity. However, the mechanism that arginine modulates cow mammary inflammatory response in ruminant is unclear. Therefore, this study was conducted to investigate the effects of L-arginine on inflammatory response and casein expression after challenging the bovine mammary epithelial cells (BMECs) with lipopolysaccharide (LPS). The cells were divided into four groups, stimulated with or without LPS (10 μg/mL) and treated with or without arginine (100 μg/mL) for 12 h. The concentration of proinflammatory cytokines, inducible nitric oxide synthase (iNOS), mammalian target of rapamycin (mTOR), and Toll-like receptor 4 (TLR4) signaling pathways as well as the casein was determined. The results showed that arginine reduced the LPS-induced production like IL-1β, IL-6, TNF-α, and iNOS. Though the expression of NF-κB was attenuated and the mTOR signaling pathway was upregulated, arginine had no effect on TLR4 expression. In addition, our results show that the content of β-casein and the total casein were enhanced after arginine was supplemented in LPS-induced BMECs. In conclusion, arginine could relieve the inflammatory reaction induced by LPS and enhance the concentration of β-casein and the total casein in bovine mammary epithelial cells.

Recent advances on the circadian gene PER2 and metabolic rhythm of lactation of mammary gland

Due to regulation by circadian rhythm, the lactation of the mammary gland has rhythmicity. As one of prominent members of period protein family which regulates biological rhythms, PER2 plays an important role in developing the milk duct and maintaining the polarity and the morphology of the mammary epithelium; at the same time, it is also closely related with the metabolism of milk protein and milk fat. This paper summarized recent researches on PER2 gene and related researches on mammary gland development and metabolism to provide some information for the studies of the theory and technology on physiological functions of the mammary gland and milk quality control.