Establishment and characterization of a lactating bovine mammary epithelial cell model for the study of milk synthesis

D-sodium lactate promotes the activation of NF-κB signaling pathway induced by lipopolysaccharide via histone lactylation in bovine mammary epithelial cells

Lactate is a glycolytic end product that is further metabolized as an energy source. This end product has been associated with certain diseases, including sepsis and tumors, and it can regulate the transition of macrophages to an anti-inflammatory state. This study aimed to explore the effects of lactate on the inflammatory responses of mammary gland epithelial cells, which constitute the first line of defense against pathogens in mammary glands. Bovine mammary epithelial cells (BMECs) were challenged with lipopolysaccharide (LPS) in the presence or absence of D-sodium lactate (D-nala). LPS exposure increased the concentration of lactate both inside and outside the cells. Further, inhibiting glycolysis diminished the LPS-induced production of proinflammatory cytokines. Treatment with LPS, exogenous D-nala, and their combination upregulated the expression levels of MCT1, increased the intracellular levels of lactate and histone H3 lysine 18 lactylation (H3K18la), and activated the nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) signaling pathway. The lactylation of H3K18 was mediated by p300/CBP. The p300/CBP inhibitor C646 decreased the level of H3K18la, reversing the activation of the NF-κB signaling pathway and release of proinflammatory cytokines. Therefore, LPS increased the intracellular level of lactate by upregulating MCT1 and glycolysis. D-nala exacerbated the LPS-induced inflammatory responses in BMECs. Moreover, intracellular lactate enhanced the activation of the NF-κB signaling pathway through the p300/CBP-mediated lactylation of H3K18. Thus, the findings of this study expand our understanding of lactate function in immune regulation.

Cellular milk production: Proteins and minerals in secretomes from cultivated bovine milk-derived mammary cells

This study explores the feasibility of utilizing in vitro cultivated milk-derived bovine mammary epithelial cells (bMECs) for the production of milk constituents. BMECs were isolated from milk and treated with various lactogenic agents in 3D transwell systems. By proteomics, >900 proteins were identified and quantified in the secretomes, including >100 milk-related proteins such as caseins and enzymes. Despite limited secretion of total proteins and major milk proteins, 110 proteins were found phosphorylated, including 27 involved in metal- or calcium-binding. Mineral analysis confirmed that 6-9 % of minerals in secretomes were associated with proteins. Notably, six proteins, including prolactin, were secreted into the basolateral side of bMECs without lactogenic treatment, suggesting their local de novo synthesis. This research advances our understanding of bMECs biology, as well as the compositional and functional features of their secretomes, highlighting their potential for sustainable production of functional milk proteins, meanwhile emphasizing the need for further optimization.

Current status and challenges for cell-cultured milk technology: a systematic review

Cellular agriculture is an innovative technology for manufacturing sustainable agricultural products as an alternative to traditional agriculture. While most cellular agriculture is predominantly centered on the production of cultured meat, there is a growing demand for an understanding of the production techniques involved in dairy products within cellular agriculture. This review focuses on the current status of cellular agriculture in the dairy sector and technical challenges for cell-cultured milk production. Cellular agriculture technology in the dairy sector has been classified into fermentation-based and animal cell culture-based cellular agriculture. Currently, various companies synthesize milk components through precision fermentation technology. Nevertheless, several startup companies are pursuing animal cell-based technology, driven by public concerns regarding genetically modified organisms in precision fermentation technology. Hence, this review offers an up-to-date exploration of animal cell-based cellular agriculture to produce milk components, specifically emphasizing the structural, functional, and productive aspects of mammary epithelial cells, providing new information for industry and academia.

Multi-omics dataset of bovine mammary epithelial cells stimulated by ten different essential amino acids

Application of high-throughput sequencing and screening help to detect the transcriptional and metabolic discrepancies in organs provided with various levels of nutrients. The influences of individual essential amino acid (EAA) administration on transcriptomic and metabolomic profilings of bovine mammary epithelial cells (BMECs) were systematically investigated. A RNA sequencing and liquid chromatography-tandem mass spectrometry generated a comprehensive comparison of transcriptomics, non-targeted metabolomics and targeted amino acids profilings of BMECs with individual EAA stimulation by turn. The sequencing data and raw LC-MS/MS data of samples were presented in the databases of Gene Expression Omnibus, MetaboLights and Figshare for efficient reuse, including exploring the divergences in metabolisms between different EAAs and screening valuable genes and metabolites regulating casein synthesis.

The Role of Progesterone in Elf5 Activation and Milk Component Synthesis for Cell-Cultured Milk Production in MAC-T Cells

Prolactin is essential for mammary gland development and lactation. Progesterone also induces ductal branching and alveolar formation via initial secretory differentiation within the mammary gland. Herein, we aimed to evaluate the role of progesterone as a prolactin substitute for the production of cell-cultured milk components in MAC-T cells. Cells were treated with various hormones such as prolactin (PRL), progesterone (P4), 17β-estradiol (E2), cortisol (COR), and insulin (INS) for 5 d. MAC-T cells cultured in a P4 differentiation media (2500 ng/mL of P4, 25 ng/mL of E2, 25 ng/mL of COR, and 25 ng/mL of INS) showed similar levels of E74-like factor 5 (Elf5) and milk component synthesis (α-casein, β-casein, α-lactalbumin, β-lactoglobulin, and triglycerides) compared to those cultured in a PRL differentiation media (5000 ng/mL of PRL, 500 ng/mL of CORT, and 50 ng/mL of INS). The levels of α-casein and triglycerides in the optimal P4 differentiation media were present at comparable levels to those in the PRL differentiation media. Our results demonstrated that P4 induces the activation of Elf5 and the synthesis of milk components in MAC-T cells, similar to PRL. Therefore, P4 may be used as an effective substitute of PRL for cell-cultured milk production in in vitro frameworks.

Effects of dietary folic acid supplementation on lactation performance and mammary epithelial cell development of dairy cows and its regulatory mechanism

The experiment investigated the impacts of FA on the proliferation of bovine mammary gland epithelial cells (BMECs) and to investigate the underlying mechanisms. Supplementation of 10 µM FA elevated the mRNA expression of proliferating cell nuclear antigen (PCNA), cyclin A2 and cyclin D1, and protein expression of PCNA and Cyclin A1. The mRNA and protein expression of B-cell lymphoma-2 (BCL2) and the BCL2 to BCL2 associated X 4 (BAX4) ratio elevated, while that of BAX, Caspase-3 and Caspase-9 reduced by FA. Both Akt and mTOR signaling pathways were activated by FA. Moreover, the stimulation of BMECs proliferation, the alteration of proliferative genes and protein expression, the change of apoptotic genes and protein expression, and the activation of mTOR signaling pathway caused by FA were obstructed by Akt inhibitor. Suppression of mTOR with Rapamycin reversed the FA-modulated promotion of BMECs proliferation and change of proliferous genes and protein expression, with no impact on mRNA or proteins expression related to apoptosis and FA-activated Akt signaling pathway. Supplementation of rumen-protected FA in cow diets evaluated milk yields and serum insulin-like growth factor-1 and estradiol levels. The results implied that the proliferation of BMECs was stimulated by FA through the Akt-mTOR signaling pathway.

β-carotene targets IP3R/GRP75/VDAC1-MCU axis to renovate LPS-induced mitochondrial oxidative damage by regulating STIM1

Endoplasmic reticulum (ER) and mitochondria are the main sites for the storage and regulation of Ca2+ homeostasis. An imbalance of Ca2+ homeostasis can cause ER stress and mitochondrial dysfunction, thereby inducing apoptosis. The store-operated calcium entry (SOCE) is the main channel for extracellular calcium influx. Mitochondria-associated endoplasmic reticulum (MAM) is an important agent for Ca2+ transfer from the ER to the mitochondria. Therefore, regulation of SOCE and MAMs has potential therapeutic value for disease prevention and treatment. In this study, bovine mammary epithelial cells (BMECs) and mice were used as models to explore the mechanisms of β-carotene to relieve ER stress and mitochondrial dysfunction. BAPTA-AM, EGTA (Ca2+ inhibitor), and BTP2 (SOCE channel inhibitor) alleviated ER stress and mitochondrial oxidative damage induced by increased intracellular Ca2+ levels after lipopolysaccharide (LPS) stimulation. Furthermore, inhibition of ER stress by 4-PBA (ER stress inhibitor), 2-APB (IP3R inhibitor), and ruthenium red (mitochondrial calcium uniporter (MCU) inhibitor) restored mitochondrial function by reducing mitochondrial ROS. Our data also confirm that β-carotene targeted STIM1 and IP3R channels to repair LPS-induced ER stress and mitochondrial disorders. Consistent with the in vitro study, in vito experiments in mice further showed that β-carotene attenuated LPS-induced ER stress and mitochondrial oxidative damage by inhibiting the expression of STIM1 and ORAI1, and reducing the level of Ca2+ in mouse mammary glands. Therefore, ER stress-mitochondrial oxidative damage mediated by the STIM1-ER-IP3R/GRP75/VDAC1-MCU axis plays an vital role in the development of mastitis. Our results provided novel ideas and therapeutic targets for the prevention and treatment of mastitis.

Successful editing and maintenance of lactogenic gene expression in primary bovine mammary epithelial cells

In vitro investigation of bovine lactation processes is limited by a lack of physiologically representative cell models. This deficiency is most evident through the minimal or absent expression of lactation-specific genes in cultured bovine mammary tissues. Primary bovine mammary epithelial cells (pbMECs) extracted from lactating mammary tissue and grown in culture initially express milk protein transcripts at relatively representative levels. However, expression drops dramatically after only three or four passages, which greatly reduces the utility of primary cells to model and further examine lactogenesis. To investigate the effects of alternate alleles in pbMECs including effects on transcription, we have developed methods to deliver CRISPR-Cas9 gene editing reagents to primary mammary cells, resulting in very high editing efficiencies. We have also found that culturing the cells on an imitation basement membrane composed of Matrigel, results in the restoration of a more representative lactogenic gene expression profile and the cells forming three-dimensional structures in vitro. Here, we present data from four pbMEC lines recovered from pregnant cows and detail the expression profile of five key milk synthesis genes in these MECs grown on Matrigel. Additionally, we describe an optimised method for preferentially selecting CRISPR-Cas9-edited cells conferring a knock-out of DGAT1, using fluorescence-activated cell sorting (FACS). The combination of these techniques facilitates the use of pbMECs as a model to investigate the effects of gene introgressions and genetic variation in lactating mammary tissue.

Staphylococcus aureus induces mitophagy to promote its survival within bovine mammary epithelial cells

Mitophagy occurs in a variety of pathogenic infections. However, the role of mitophagy in the intracellular survival of Staphylococcus aureus (S.aureus) within bovine mammary epithelial cells (BMECs) and which molecules specifically mediate the induction of mitophagy remains unclear. Therefore, this study aims to investigate the role and mechanism of mitophagy in the intracellular survival of S.aureus. Here, we reported that S.aureus induced complete mitophagy to promote its survival within BMECs. The further mechanistic study showed that S. aureus induced mitophagy by activating the p38-PINK1-Parkin signaling pathway. These findings expand our knowledge of the intracellular survival mechanism of S.aureus in the host and provide a desirable therapeutic strategy against S.aureus and other intracellular infections.

A high-concentrate diet induces inflammatory injury via regulating Ca2+/CaMKKβ-mediated autophagy in mammary gland tissue of dairy cows

Introduction

Calmodulin-dependent protein kinase β (CaMKKβ) is closely related to Ca²⁺ concentration. An increase in Ca²⁺ concentration in the cytoplasm activates CaMKKβ, and activated CaMKKβ affects the activities of AMPK and mTOR and induces autophagy. A high-concentrate diet leads to Ca²⁺ disorder in mammary gland tissue.

Objectives

Therefore, this study mainly investigated the induction of mammary gland tissue autophagy by a high-concentrate diet and the specific mechanism of lipopolysaccharide (LPS)-induced autophagy in bovine mammary epithelial cells (BMECs).

Material and Methods

Twelve mid-lactation Holstein dairy cows were fed with a 40% concentrate diet (LC) and a 60% concentrate diet (HC) for 3 weeks. At the end of the trial, rumen fluid, lacteal vein blood, and mammary gland tissue were collected. The results showed that the HC diet significantly decreased rumen fluid pH, with a pH lower than 5.6 for more than 3 h, indicating successfully induction of subacute rumen acidosis (SARA). The mechanism of LPS-induced autophagy in BMECs was studied in vitro. First, the cells were divided into a Ctrl group and LPS group to study the effects of LPS on the concentration of Ca²⁺ and autophagy in BMECs. Then, cells were pretreated with an AMPK inhibitor (compound C) or CaMKKβ inhibitor (STO-609) to investigate whether the CaMKKβ-AMPK signaling pathway is involved in LPS-induced BMEC autophagy.

Results

The HC diet increased the concentration of Ca²⁺ in mammary gland tissue and pro-inflammatory factors in plasma. The HC diet also significantly increased the expression of CaMKKβ, AMPK, and autophagy-related proteins, resulting in mammary gland tissue injury. In vitro cell experiments showed that LPS increased intracellular Ca²⁺ concentration and upregulated protein expression of CaMKKβ, AMPK, and autophagy-related proteins. Compound C pretreatment decreased the expression of proteins related to autophagy and inflammation. In addition, STO-609 pretreatment not only reversed LPS-induced BMECs autophagy but also inhibited the protein expression of AMPK, thereby alleviating the inflammatory response in BMECs. These results suggest that inhibition of the Ca²⁺/CaMKKβ-AMPK signaling pathway reduces LPS-induced autophagy, thereby alleviating inflammatory injury of BMECs.

Conclusion

Therefore, SARA may increase the expression of CaMKKβ by increasing Ca²⁺ levels and activate autophagy through the AMPK signaling pathway, thereby inducing inflammatory injury in mammary gland tissue of dairy cows.

Lentinan inhibits oxidative stress and alleviates LPS-induced inflammation and apoptosis of BMECs by activating the Nrf2 signaling pathway

Lentinan (LNT) has been reported to have a wide range of functions, including anti-inflammatory, antioxidant and anticancer properties. LNT may provide a protective effect in dairy cow mastitis. In this study, we investigated the effect of LNT on lipopolysaccharide (LPS)-induced injury of bovine mammary epithelial cells (BMECs) and the possible mechanism. First, we treated BMECs with different concentrations of LPS to study the effects of LPS on oxidative stress and inflammation in BMECs. Then, we examined the effects of LNT by dividing the cells into seven groups: the control group (CON), LPS treatment group (LPS), Acetyl-l-cysteine (NAC) pretreatment group (NAC + LPS), LNT pretreatment group (LNT + LPS), ML385 and LNT pretreatment group (ML385 + LNT + LPS), LNT treatment group (LNT) and NAC treatment group (NAC). The results showed that LPS-triggered intracellular ROS production and the downregulation of Nrf-2 and HO-1 in BMECs were blocked by LNT pretreatment. LNT inhibited the expression of inflammatory genes and proteins by inhibiting of NF-κB and MAPK. In addition, LNT attenuated LPS induced-apoptosis in BMECs. However, ML385 reversed the protective effect of LNT. Taken together, LNT can be used as a natural protective agent against LPS-triggered BMECs damage through its anti-inflammatory, antioxidant and antiapoptotic effects through modulation of the Nrf2 pathway.

Lactobacillus plantarum 17-5 attenuates Escherichia coli-induced inflammatory responses via inhibiting the activation of the NF-κB and MAPK signalling pathways in bovine mammary epithelial cells

Background

Mastitis is one of the most prevalent diseases and causes considerable economic losses in the dairy farming sector and dairy industry. Presently, antibiotic treatment is still the main method to control this disease, but it also brings bacterial resistance and drug residue problems. Lactobacillus plantarum (L. plantarum) is a multifunctional probiotic that exists widely in nature. Due to its anti-inflammatory potential, L. plantarum has recently been widely researched in complementary therapies for various inflammatory diseases. In this study, the apoptotic ratio, the expression levels of various inflammatory mediators and key signalling pathway proteins in Escherichia coli-induced bovine mammary epithelial cells (BMECs) under different doses of L. plantarum 17–5 intervention were evaluated.

Results

The data showed that L. plantarum 17–5 reduced the apoptotic ratio, downregulated the mRNA expression levels of TLR2, TLR4, MyD88, IL1β, IL6, IL8, TNFα, COX2, iNOS, CXCL2 and CXCL10, and inhibited the activation of the NF-κB and MAPK signalling pathways by suppressing the phosphorylation levels of p65, IκBα, p38, ERK and JNK.

Conclusions

The results proved that L. plantarum 17–5 exerted alleviative effects in Escherichia coli-induced inflammatory responses of BMECs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03355-9.

RNA-Seq Reveals the Role of miR-29c in Regulating Inflammation and Oxidative Stress of Bovine Mammary Epithelial Cells

Healthy mammary gland is essential for milk performance in dairy cows. MicroRNAs (miRNAs) are the key molecules to regulate the steady state of mammary gland in dairy cows. This study investigated the potential role of miR-29c in bovine mammary epithelial cells (bMECs). RNA sequencing (RNA-seq) was used to measure the transcriptome profile of bovine mammary epithelial cells line (MAC-T) transfected with miR-29c inhibitor or negative control (NC) inhibitor, and then differentially expressed genes (DEGs) were screened. The results showed that a total of 42 up-regulated and 27 down-regulated genes were found in the miR-29c inhibitor group compared with the NC inhibitor group. The functional enrichment of the above DEGs indicates that miR-29c is a potential regulator of oxidative stress and inflammatory response in bMECs through multiple genes, such as forkhead box O1 (FOXO1), tumor necrosis factor-alpha (TNF-α), and major histocompatibility complex, class II, DQ alpha 5 (BoLA-DQA5) in the various biological process and signaling pathways of stress-activated mitogen-activated protein kinase (MAPK) cascade, Epstein-Barr virus infection, inflammatory bowel disease, etc. The results imply that miR-29c plays an important role in a steady state of bMECs or cow mammary gland and may be a potential therapeutic target for mastitis in dairy cows.

Cis-9, Trans-11 CLA Alleviates Lipopolysaccharide-Induced Depression of Fatty Acid Synthesis by Inhibiting Oxidative Stress and Autophagy in Bovine Mammary Epithelial Cells

Lipopolysaccharide (LPS) is the dominating endotoxin of Gram-negative bacteria, which can cause mastitis. Bovine mammary epithelial cells (BMECs), as major components of the mammary gland, usually suffer LPS challenge. Cis-9, trans-11 conjugated linoleic acid (CLA) has been reported to have anti-inflammatory characteristics, while its anti-oxidative ability to maintain cellular homeostasis in BMECs under LPS challenge is limited. Therefore, we studied whether cis-9, trans-11 CLA can restore the disturbance of cellular homeostasis indicated by the redox status and autophagy level caused by LPS and have an effect on cellular function- milk fat metabolism. For oxidative stress, LPS challenge promoted the formation of reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS) and decreased the concentration of glutathione. Anti-oxidative signaling regulated by transcription factor nuclear factor, erythroid 2 like 2 (Nrf2) was also depressed by LPS at the mRNA and protein level. However, cis-9, trans-11 CLA pretreatment downregulated the formation of ROS and TBARS and upregulated the expression of antioxidative enzymes. As a part of innate immunity, autophagy was also motivated by LPS challenge, while CLA decreased the autophagy level. LPS and H₂O₂ inhibited milk fat synthesis-related transcription factor sterol regulatory element binding protein (SREBP1), peroxisome proliferator activated receptor gamma (PPARG) and their downstream enzymes. Furthermore, 50 uM cis-9, trans-11 CLA promoted the mRNA and protein abundance of milk fat synthesis-related genes and lipid droplet formation in BMECs. In conclusion, LPS challenge disturbed the cellular homeostasis and depressed milk fat synthesis in BMECs; while cis-9, trans-11 CLA alleviated oxidative stress and decreased autophagy level, thus promoting milk fat synthesis, which offers a natural therapeutic strategy for mastitis.

Selenium and Taurine Combination Is Better Than Alone in Protecting Lipopolysaccharide-Induced Mammary Inflammatory Lesions via Activating PI3K/Akt/mTOR Signaling Pathway by Scavenging Intracellular ROS

Mastitis is mainly induced by gram-negative bacterial infections, causing devastating economic losses to the global cattle industry. Both selenium (Se) and taurine (Tau) exhibit multiple biological effects, including reducing inflammation. However, no studies have reported the protective effect of the combined use of Se and Tau against mastitis, and the underlying mechanisms remain unclear. In this study, lipopolysaccharide (LPS), the vital virulence factor of gram-negative bacteria, was used to construct the in vivo and vitro mastitis models. The results of in vivo model showed that Se and Tau combination was more effective than either substance alone in reducing tissue hyperemia, edema, and neutrophil infiltration in the mammary acinar cavity, improving the blood-milk barrier in LPS-induced mice mastitis, and decreasing the expression of proinflammatory factors and the activity of MPO. Moreover, Se and Tau combination significantly increased the levels of LPS-induced reduction in PI3K/Akt/mTOR, but the expressions of TLRs and NLRP3 were not significantly changed in the mammary tissue. In the in vitro experiments, the effects of Se and Tau combination or alone on inflammatory factors, inflammatory mediators, MPO activity, and blood-milk barrier were consistent with those in vivo. The Se and Tau combination has also been found to increase the survival rate of BMECs compared with each substance alone via promoting cellular proliferation and inhibiting apoptosis. Also, it has been confirmed that this combination could restore the LPS-induced inhibition in the PI3K/Akt/mTOR signaling pathway. Inhibition of mTOR by Rapamycin counteracted the combined protection of SeMet and Tau against LPS-induced inflammatory damage, the inhibition of PI3K by LY294002 blocked the activation of mTOR, and the accumulation of ROS by the ROS agonist blocked the activation of PI3K. In conclusion, these findings suggested that Se and Tau combination was better than either substance alone in protecting LPS-induced mammary inflammatory lesions by upregulating the PI3K/Akt/mTOR signaling pathway.

MicroRNA-432 inhibits milk fat synthesis by targeting SCD and LPL in ovine mammary epithelial cells

The microRNA (miR)-432 is differentially expressed in the mammary gland of two breeds of lactating sheep with different milk production traits, and between the non-lactating and peak-lactation periods, but there have been no reports describing the molecular mechanisms involved. In this study, the effect of miR-432 on the proliferation of ovine mammary epithelial cells (OMECs) and the target genes of miR-432 were investigated. The effects of miR-432 on the expression of the target genes and the content of triglycerides in the OMECs were also analyzed. Transfection with a miR-432 mimic was found using CCK8 and Edu assays, to inhibit the viability of OMECs and reduce the number of proliferated OMECs. In contrast, a miR-432 inhibitor had the opposite effect to the miR-432 mimic, and together these results suggest that miR-432 inhibits the proliferation of OMECs. A dual luciferase assay revealed that the genes for stearoyl-CoA desaturase (SCD) and lipoprotein lipase (LPL) are targeted by miR-432. The transfection of miR-432 mimic into OMECs resulted in decreases in the expression of SCD and LPL, and three other milk fat synthesis marker genes; FABP4, LPIN1 and ACACA. The mimic also decreased the content of triglycerides. The miR-432 inhibitor had the opposite effect to the mimic on the expression of these genes and the level of triglycerides. This is the first study to reveal the biological mechanisms by which miR-432 inhibits milk fat synthesis in sheep.

EEF1D facilitates milk lipid synthesis by regulation of PI3K-Akt signaling in mammals

Mammal's milk is an abundantly foremost source of proteins, lipids, and micronutrients for human nutrition and health. Understanding the molecular mechanisms underlying synthesis of milk components provides practical benefits to improve the milk quality via systematic breeding program in mammals. Through RNAi with EEF1D in primary bovine mammary epithelial cells, we phenotypically observed aberrant formation of cytoplasmic lipid droplets and significantly decreased milk triglyceride level by 37.7%, and exploited the mechanisms by which EEF1D regulated milk lipid synthesis via insulin (PI3K-Akt), AMPK, and PPAR pathways. In the EEF1D CRISPR/Cas9 knockout mice, incompletely developed mammary glands at 9th day postpartum with small or unformed lumens, and significantly decreased triglyceride concentration in milk by 23.4% were observed, as well as the same gene expression alterations in the three pathways. For dairy cattle, we identified a critical regulatory mutation modifying EEF1D transcription activity, which interpreted 7% of the genetic variances of milk lipid yield and percentage. Our findings highlight the significance of EEF1D in mammary gland development and milk lipid synthesis in mammals.

In vitro culture and evaluation of bovine mammary epithelial cells from Ukraine dairy cows

BACKGROUND

Mammary epithelial cells (MECs) have been widely-used over the years as models to understand the physiological function of mammary disease.

AIMS

This study aimed to establish a culture system and elucidate the unique characteristics of bovine mammary epithelial cells (BMECs) from the milk of Ukraine Holstein dairy cows in order to develop a general in vitro model.

METHODS

The milk from a three-year-old lactating dairy cow was used as a source of the epithelial cell, characteristics of BMECs were examined using real time cell assay (RTCA), immunocytochemistry (ICC), reverse transcription-polymerase chain reaction (RT-PCR), and Western blot (WB).

RESULTS

The results showed that BMECs can be recovered from milk, grown in culture, and exhibit the characteristic cobblestone morphology of epithelial cells.

CONCLUSION

The established BMECs retained MEC characteristics and secreted β-caseins even when grew on plastic substratum. Thus, the established cell line had normal morphology, growth characteristics, as well as secretory characteristics, and it could be considered as a model system and useful tool for understanding the biology of dairy cow mammary glands.

ASCT2 Is Involved in SARS-Mediated β-Casein Synthesis of Bovine Mammary Epithelial Cells with Methionine Supply

The methionine (Met) uptake into mammary cells depends upon the corresponding amino acid (AA) transporters, which play a regulatory role in the mammary protein production beyond transport. Our previous studies have identified that seryl-tRNA synthetase (SARS) could be a novel mediator to regulate essential AA-stimulated casein synthesis in primary bovine mammary epithelial cells (BMECs). However, the regulatory mechanisms of Met in milk protein production in dairy cows remain further clarified. Here, we aimed to investigate the effects of Met on milk protein synthesis in BMECs and explore the underlying mechanism. The effects of Met on the AA transporter, casein synthesis, and the related signaling pathway were evaluated in the BMECs treated with 0.6 mM Met for 6 h combined with or without the inhibition of AA transporter (ASCT2, a neutral AA transporter) activity by the corresponding inhibitor (GPNA). Besides, the effects of SARS on the cells were mainly evaluated in the BMECs treated with 0.6 mM Met for 6 h together with or without SARS knockdown by RNAi interference. The gene expression of AA transporters and pathway-related genes were analyzed by the real-time quantitative polymerase chain reaction method, and the protein expression of related proteins were determined by the western blot assay. Results showed that 0.6 mM Met remarkably enhanced cell growth and β-casein synthesis compared to the supply of other Met concentrations. Among 13 amino acid transporters, 0.6 mM Met highly increased ASCT2 expression. This Met-stimulated ASCT2 expression and the enhanced mammary intracellular Met uptake were both decreased by the addition of 500 μM GPNA, an inhibitor of ASCT2. In the presence of 0.6 mM Met, the inhibition of ASCT2 activity (by GPNA) and SARS expression (by RNAi) both reduced β-casein synthesis. Additionally, 0.6 mM Met increased the gene expression of mTOR, S6K1, 4EBP1, and Akt; in contrast, the inhibition of ASCT2 by GPNA lowered the gene expression of these four genes. Collectively, this work suggests that ASCT2 is involved in the SARS-mediated Met stimulation of β-casein synthesis through enhancing mammary Met uptake and activating the mTOR signaling pathway in BMECs.

Myricetin protects against H2 O2 -induced oxidative damage and apoptosis in bovine mammary epithelial cells

High-producing dairy cows are prone to oxidative stress due to their high secretion and strong metabolism, and excessive oxidative stress may cause the apoptosis of bovine mammary epithelial cells (bMECs). Myricetin (Myr) has been shown to have a wide range of pharmaceutical activities. The aim of this study was to evaluate the effect of Myr on hydrogen peroxide (H₂ O₂ )-induced oxidative stress and apoptosis in bMECs and to clarify the underlying mechanism. bMECs were pretreated with or without Myr and then stimulated with H₂ O₂ . The results showed that Myr significantly increased the total antioxidant capacity and superoxide dismutase levels and decreased the malondialdehyde (MDA) and reactive oxygen species (ROS) levels in a model of oxidative stress induced by H₂ O₂ in bMECs. Mechanistic studies found that Myr inhibited H₂ O₂ -induced oxidative stress in bMECs through the adenosine monophosphate-activated protein kinase/nuclear factor erythroid-2 related factor 2 (AMPK/NRF2) signaling pathway. Additional research found that Myr could also inhibit H₂ O₂ -induced apoptosis in bMECs through NRF2. These data suggest that Myr effectively alleviated oxidative stress and apoptosis in H₂ O₂ -induced bMECs through the activation of the AMPK/NRF2 signaling pathway.

Niacin Alleviates Dairy Cow Mastitis by Regulating the GPR109A/AMPK/NRF2 Signaling Pathway

Mastitis is one of three bovine diseases recognized as a cause of substantial economic losses every year throughout the world. Niacin is an important feed additive that is used extensively for dairy cow nutrition. However, the mechanism by which niacin acts on mastitis is not clear. The aim of this study is to investigate the mechanism of niacin in alleviating the inflammatory response of mammary epithelial cells and in anti-mastitis. Mammary glands, milk, and blood samples were collected from mastitis cows not treated with niacin (n = 3) and treated with niacin (30 g/d, n = 3) and healthy cows (n = 3). The expression of GPR109A, IL-6, IL-1β, and TNF-α in the mammary glands of the dairy cows with mastitis was significantly higher than it was in the glands of the healthy dairy cows. We also conducted animal experiments in vivo by feeding rumen-bypassed niacin. Compared with those in the untreated mastitis group, the somatic cell counts (SCCs) and the expression of IL-6, IL-1β, and TNF-α in the blood and milk were lower. In vitro, we isolated the primary bovine mammary epithelial cells (BMECs) from the mammary glands of the healthy cows. The mRNA levels of IL-6, IL-1β, TNF-α, and autophagy-related genes were detected after adding niacin, shRNA, compound C, trans retinoic acid, 3-methyladenine to BMECs. Then GPR109A, AMPK, NRF-2, and autophagy-related proteins were detected by Western blot. We found that niacin can activate GPR109A and phosphorylate AMPK, and promote NRF-2 nuclear import and autophagy to alleviate LPS-induced inflammatory response in BMECs. In summary, we found that niacin can reduce the inflammatory response of BMECs through GPR109A/AMPK/NRF-2/autophagy. We also preliminarily explored the alleviative effect of niacin on mastitis in dairy cows.

Establishment of an in vitro culture model to study milk production and the blood–milk barrier with bovine mammary epithelial cells

This study attempted to establish a culture model to recreate the milk production pathway in bovine mammary epithelial cells (BMECs). BMECs were isolated from Holstein cows (nonlactating, nonpregnant, and parous) and were stored by cryopreservation. To separate the apical and basolateral compartments, BMECs were cultured on a cell culture insert with a collagen gel in the presence of bovine pituitary extract and dexamethasone to induce milk production and tight junction (TJ) formation. The culture model showed the secretion of the major milk components, such as β-casein, lactose, and triglyceride, and formed less-permeable TJs in BMECs. Moreover, the TJs were distinctly separated from the apical and basolateral membranes. Glucose transporter-1, which transports glucose into the cytoplasm through the basolateral membrane, localized in the lateral membrane of BMECs. Toll-like receptor-4, which binds to lipopolysaccharide in the alveolar lumen in mastitis, localized in the apical membrane. Beta-casein was mainly localized near the Golgi apparatus and the apical membrane. Moreover, milk components were almost secreted into the upper chamber of the cell culture insert. These findings indicate that this model has clear cell polarity as well as in vivo and is effective to study of milk production and the blood-milk barrier in lactating BMECs.

Seryl-tRNA synthetase is involved in methionine stimulation of β-casein synthesis in bovine mammary epithelial cells

Despite the well-characterised mechanisms of amino acids (AA) regulation of milk protein synthesis in mammary glands (MG), the underlying specific AA regulatory machinery in bovine MG remains further elucidated. As methionine (Met) is one of the most important essential and limiting AA for dairy cows, it is crucial to expand how Met exerts its regulatory effects on dairy milk protein synthesis. Our previous work detected the potential regulatory role of seryl-tRNA synthetase (SARS) in essential AA (EAA)-stimulated bovine casein synthesis. Here, we investigated whether and how SARS participates in Met stimulation of casein production in bovine mammary epithelial cells (BMEC). With or without RNA interference against SARS, BMEC were treated with the medium in the absence (containing all other EAA and devoid of Met alone)/presence (containing 0·6 mm of Met in the medium devoid of Met alone) of Met. The protein abundance of β-casein and members of the mammalian target of rapamycin (mTOR) and general control nonderepressible 2 (GCN2) pathways was determined by immunoblot assay after 6 h treatment, the cell viability and cell cycle progression were determined by cell counting and propidium iodide-staining assay after 24 h treatment, and protein turnover was determined by l-[ring-3H5]phenylalanine isotope tracing assay after 48 h treatment. In the absence of Met, there was a general reduction in cell viability, total protein synthesis and β-casein production; in contrast, total protein degradation was enhanced. SARS knockdown strengthened these changes. Finally, SARS may work to promote Met-stimulated β-casein synthesis via affecting mTOR and GCN2 routes in BMEC.

Effects of Free Fatty Acids with Different Chain Lengths and Degrees of Saturability on the Milk Fat Synthesis in Primary Cultured Bovine Mammary Epithelial Cells

How short-chain fatty acids (FAs) affect cell membrane morphology and milk fat biosynthesis in mammary epithelial cells (MECs) is yet unclear. This study investigated the primary bovine MEC response to different FAs. We observed that the cell surface ultrastructures were influenced by chain length and degree of saturability of FAs. The CD36, FATP1, and FABP3 gene expression was affected independent of the type of FA. FASN, LPIN1, PPARα, and PPARγ transcripts were more sensitive to the short-chain FAs (acetic and β-hydroxybutyric acids). Furthermore, short-chain FAs inclined to regulate FA degradation-, elongation-, and metabolism-associated pathways, while long-chain FAs (stearic and trans-10,cis-12 conjugated linolenic acids) modulated extracellular matrix-receptor interaction-, transcriptional misregulation-, microRNA-, and ribosome biogenesis-related pathways. However, triacylglycerol accumulation in the cytoplasm was not changed by all of the FAs. Overall, FAs with different chain lengths and degrees of saturability could differentially alter primary bovine MEC cell morphology and influence protein profiles involved in milk fat synthesis pathways.

Isolation, characterization, and SREBP1 functional analysis of mammary epithelial cell in buffalo

Compared to cow milk, buffalo milk contains more protein, fat, and vitamin. Buffalo milk is an ideal food in human life. Sterol regulatory element-binding protein 1 (SREBP1), an important transcription factor, regulates the expression and activity of enzyme and protein involved in milk fat synthesis to influence on the synthesis and secretion of triglyceride in mammary epithelial cells. In the present study, we successfully isolated buffalo mammary epithelial cell by using enzymatic digestion, and then described the growth characteristics and expression characteristics of mammary epithelial cells. Moreover, we cloned the SREBP1 gene from total RNA isolated from milk fat globule and analyzed the function of the SREBP1 gene. After infected with shRNA-SREBP1 lentiviral particle and treated with fatty acid, the expression trend of ACACA, FABP3, FAS, SCD, ERK1, ERK2, PPARy, and Insigl genes was consistent with the expression trend of SREBP1 gene. These results suggested that SREBP1 gene is a central transcription factor in regulating milk fat synthesis and SREBP1 gene may act on ERK1/ERK2 signaling pathway to regulate the expression of PPARy gene. The current study will provide a theoretical basis for further reveal the molecular mechanism of milk fat synthesis in buffalo mammary epithelial cells. PRACTICAL APPLICATIONS: This study aim to separate and analysis characterization of mammary epithelial cell in buffalo. Compared to cow milk, buffalo milk contains more protein, fat, and vitamin. Buffalo milk is an ideal food in human life. This study will provide a theoretical basis for further research on the molecular mechanism of milk fat synthesis in buffalo mammary epithelial cells.

Sestrin2 Negatively Regulates Casein Synthesis through the SH3BP4-mTORC1 Pathway in Response to AA Depletion or Supplementation in Cow Mammary Epithelial Cells

Sestrin2 (SESN2) negatively regulates the mammalian target of rapamycin complex 1 (mTORC1) pathway and casein synthesis in response to amino acid (AA) depletion in cow mammary epithelial cells (CMECs); however, the underlying mechanism is unclear. In the current study, the regulation of SESN2 on AA-mediated β-casein (CSN2) synthesis in CMECs and its mechanism were investigated. Overexpression and silencing of SESN2 demonstrated that SESN2 negatively regulated AA-mediated expression of CSN2 and mTORC1 pathway. Co-immunoprecipitation analysis showed that SESN2 interacted with SH3 domain-binding protein 4 (SH3BP4). Overexpression and silencing of SH3BP4 demonstrated that SH3BP4 negatively regulated AA-mediated expression of CSN2 and mTORC1 pathway and that SESN2 negatively regulated expression of CSN2 and mTORC1 pathway through the SH3BP4 in the presence and absence of AA. The absence or presence of AA demonstrated that AA negatively regulated expression and nuclear localization of activating transcription factor 4 (ATF4). Overexpression and silencing of ATF4 demonstrated that AA negatively regulated SESN2 expression through ATF4. Together, these results indicate that SESN2 negatively regulates the mTORC1 pathway and subsequent CSN2 synthesis through the SH3BP4 in response to AA absence or presence in CMECs.

Protective Effects of Inorganic and Organic Selenium on Heat Stress in Bovine Mammary Epithelial Cells

When dairy cows are exposed to high-temperature environment, their antioxidant capacity and productive performance decrease, leading to economic losses. Emerging evidence has shown that selenium (Se) can effectively alleviate heat stress in dairy cows; however, the cellular mechanism underlying this protection is not clear. The purpose of this study was to investigate and compare the protective effects of inorganic Se (sodium selenite, SS) and organic Se (selenite methionine, SM) in MAC-T (mammary alveolar cells-large T antigen, a bovine mammary epithelial cell (BMEC) line) cells during heat stress. MAC-T cells were treated in 4 ways unless otherwise described: (i) cells in the heat treatment (HT) group were cultured at 42.5°C for 1 h and then recovered in 37°C for another 12 h; (ii) the SM group was pretreated with organic Se for 2 h, cultured at 42.5°C for 1 h, and then recovered in 37°C for 12 h; (iii) the SS group was treated similarly to the SM group except that the cells were pretreated with inorganic Se instead of organic Se; and (iv) the control group was continuously cultured in 37°C and received no Se treatment. The results showed that heat shock at 42.5°C for 1 h triggered heat shock response, sabotaged the redox balance, and reduced cell viability in MAC-T cells; and pretreatment of cells with SM or SS effectively alleviated the negative effects of heat shock on the cells. However, the cells were much more sensitive to SS treatment but more tolerant to SM. In addition, two forms of Se appeared to affect the expression of different genes, including nuclear factor erythroid 2-related factor 2 (Nrf2) and inducible nitric oxide synthase (iNOS) in the SM group and thioredoxin reductase 1 (TXNRD1) in the SS group in Nrf2-ARE (antioxidant response element) antioxidant pathway and inflammation response. In summary, results showed the mechanistic differences in the protective effects of organic and inorganic Se on heat stress in BMECs.

Identification and functional analysis of candidate gene VPS28 for milk fat in bovine mammary epithelial cells

In a previous genome-wide association study on milk production traits in Chinese Holstein population, we revealed VPS28 gene was highly expressed in mammary gland tissue and a -58C > T mutation in 5'-UTR of it was significantly associated with milk fat content traits. In this study, we explored the effect of this -58C > T mutation on VPS28, and found it could significantly decrease promoter activity of VPS28 by reducing transcription factor binding sites. To identify the potential functional SNP involved, we performed RNAi experiment in BMECs, the results showed that VPS28 knockdown could increase the expression of ADFP and CD36, lead accumulation of ubiquitinated proteins, long chain fatty acids and triglyceride, and decrease the proteasome activity. Therefore, our study demonstrates that the -58C > T mutation could facilitate milk fat synthesis in two ways. The one is involved in ESCRTs signaling, it could directly lead an accumulation of ubqiuitinated membrane proteins to promote the long chain fatty acids uptake to incorporation into TG. The other is involved in ubiquitination-proteasome system, it could indirectly lead a dysfunction of proteasome to accumulate the ubqiuitinated proteins to promote TG synthesis. In conclusion, our study demonstrates that VPS28 could be a strong candidate gene for milk fat content traits, and in particular, the -58C > T mutation in 5'-UTR of VPS28 could be a functional mutation for its effects on milk fat content.

Proteomic analyses reveal GNG12 regulates cell growth and casein synthesis by activating the Leu-mediated mTORC1 signaling pathway

In cow mammary epithelial cells (CMECs), cell growth and casein synthesis are regulated by amino acids (AAs), and lysosomes are important organelles in this regulatory process, but the mechanisms remain unclear. Herein, lysosomal membrane proteins (LMPs) in CMECs in the presence (Leu+) and absence (Leu-) of leucine were quantitatively analysed using Sequential Windowed Acquisition of All Theoretical Fragment Ion (SWATH) mass spectrometry. In identified LMPs, Guanine nucleotide-binding protein subunit gamma-12 (GNG12) was a markedly up-regulated protein in Leu+ group. CMECs were treated with Leu+ or Leu-, expression and lysosomal localization of GNG12 were decreased in response to Leu absence. Overexpressing or inhibiting GNG12 demonstrated that cell growth, casein synthesis and activation of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway were all up-regulated by GNG12. Cell growth, casein synthesis and mTORC1 signaling pathway were decreased in response to Leu absence, but these decreases were partially restored by GNG12 overexpression, and those effects were partially reversed by inhibiting GNG12. Co-immunoprecipitation analysis showed that GNG12 activates the mTORC1 pathway via interaction with Ragulator. Taken together, these results suggest that GNG12 is a positive regulator of the Leu-mediated mTORC1 signaling pathway in CMECs that promotes cell growth and casein synthesis.

SESN2 negatively regulates cell proliferation and casein synthesis by inhibition the amino acid-mediated mTORC1 pathway in cow mammary epithelial cells

Amino acids (AA) are one of the key nutrients that regulate cell proliferation and casein synthesis in cow mammary epithelial cells (CMEC), but the mechanism of this regulation is not yet clear. In this study, the effect of SESN2 on AA-mediated cell proliferation and casein synthesis in CMEC was assessed. After 12 h of AA starvation, CMECs were cultured in the absence of all AA (AA-), in the presences of only essential AA (EAA+), or of all AA (AA+). Cell proliferation, casein expression, and activation of the mammalian target of rapamycin complex 1 (mTORC1) pathway were increased; but SESN2 expression was decreased in response to increased EAA or AA supply. Overexpressing or inhibiting SESN2 demonstrated that cell proliferation, casein expression, and activation of the mTORC1 pathway were all controlled by SESN2 expression. Furthermore, the increase in cell proliferation, casein expression, and activation of the mTORC1 pathway in response to AA supply was inhibited by overexpressing SESN2, and those effects were reversed by inhibiting SESN2. These results indicate that SESN2 is an important inhibitor of mTORC1 in CMEC blocking AA-mediated cell proliferation and casein synthesis.

Development and validation of immortalized bovine mammary epithelial cell line as an in vitro model for the study of mammary gland functions

This study aimed to develop a bovine mammary epithelial (BME) cell line model, which provides a possibility to determine functional properties of the bovine mammary gland. The primary cell culture was derived from bovine mammary gland tissues and processed enzymatically to obtain cell colonies with epithelial-like morphology. The cultures of BME cells were purified and optimally cultured at 37 °C in DMEM/F12 medium supplemented with 10% fetal bovine serum. The BME cells were identified as epithelial cell line by the evaluating the expression of keratin-18 using immunofluorescence staining. A novel gene expression system strongly enhances the expression of telomerase, has been used to immortalize BME cell line termed hTBME cell line. Interestingly, telomerase remained active even after over 60 passages of hTBME cell line, required for immortalization of BME cells. In addition, the hTBME cell line was continuously subcultured with a spontaneous epithelial-like morphology, with a great proliferation activity, and without evidence of apoptotic and necrotic effects. Further characterization showed that hTBME cell line can be continuously propagated in culture with constant chromosomal features and without tumorigenic properties. Finally, established hTBME cell line was evaluated for mammary gland specific functions. Our results demonstrated that the hTBME cell line was able to retain functional-morphological structure, and functional differentiation by expression of beta (β)-casein as in the bovine mammary gland in vivo. Taken together, our findings suggest that the established hTBME cell line can serve as a valuable tool for the study of bovine mammary gland functions.

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

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

Host-pathogen interactions in bovine mammary epithelial cells and HeLa cells by Staphylococcus aureus isolated from subclinical bovine mastitis

Staphylococcus aureus is a common pathogen that causes subclinical bovine mastitis due to several virulence factors. In this study, we analyzed S. aureus isolates collected from the milk of cows with subclinical mastitis that had 8 possible combinations of bap, icaA, and icaD genes, to determine their capacity to produce biofilm on biotic (bovine primary mammary epithelial cells and HeLa cells) and abiotic (polystyrene microplates) surfaces, and their ability to adhere to and invade these cells. We also characterized isolates for microbial surface components recognizing adhesive matrix molecules (MSCRAMM) and agr genes, and for their susceptibility to cefquinome sulfate in the presence of biofilm. All isolates adhered to and invaded both cell types, but invasion indexes were higher in bovine primary mammary epithelial cells. Using tryptic soy broth + 1% glucose on abiotic surfaces, 5 out of 8 isolates were biofilm producers, but only the bap⁺icaA⁺icaD⁺ isolate was positive in Dulbecco's Modified Eagle's medium. The production of biofilm on biotic surfaces occurred only with this isolate and only on HeLa cells, because the invasion index for bovine primary mammary epithelial cells was too high, making it impossible to use these cells in this assay. Of the 5 biofilm producers in tryptic soy broth + 1% glucose, 4 presented with the bap/fnbA/clfA/clfB/eno/fib/ebpS combination, and all were protected from cefquinome sulfate. We found no predominance of any agr group. The high invasive potential of S. aureus made it impossible to observe biofilm in bovine primary mammary epithelial cells, and we concluded that cells with lower invasion rates, such as HeLa cells, were more appropriate for this assay.

An explant of heifer mammary gland to study the immune response of the organ

Continuous or primary epithelial cell lines have been extensively used to study the mammary gland immune response, but they are constituted by a single cell population. Our aim was to test whether an explant of heifer gland, where the tissue structure is maintained, might be a valid model to investigate the innate immune response to infection. The study was carried out on 2mm³-sections of heifer udders, in 2 consecutive trials, using LPS or LTA in the first trial and two different concentrations of Staphylococcus aureus (Staph. aureus) in the second. Treated and untreated sections were collected after 1h, 3h and 6h incubation; in the first trial, a final time-point at 18h was considered. The mRNA expression of TNFα, IL-1β, IL-6, IL-8 and LAP was analyzed by quantitative real-time PCR. Histological examination showed well-preserved morphology of the tissue, and apoptosis only showed a slight, not significant increase throughout the experiment. IL-1β and IL-6 were significantly up-regulated, in response to LPS or Staph. aureus, while TNF-α and IL-8 significantly increased only under LPS treatment. LAP expression showed a significant late increase when stimulated by LPS. The immunochemical staining of the sections demonstrated a higher number of T lymphocytes within the alveolar epithelium, in comparison with interstitial localization. Since the explants belonged to pubertal non-pregnant heifers, T cells may be regarded as resident cells, suggesting their participation in the regulation of mammary homeostasis. Therefore, applying our model would give new insights in the investigation of udder pathophysiology.

Impact of Heat Stress on Cellular and Transcriptional Adaptation of Mammary Epithelial Cells in Riverine Buffalo (Bubalus Bubalis)

The present study aims to identify the heat responsive genes and biological pathways in heat stressed buffalo mammary epithelial cells (MECs). The primary mammary epithelial cells of riverine buffalo were exposed to thermal stress at 42°C for one hour. The cells were subsequently allowed to recover at 37°C and harvested at different time intervals (30 min to 48 h) along with control samples (un-stressed). In order to assess the impact of heat stress in buffalo MECs, several in-vitro cellular parameters (lactate dehydrogenase activity, cell proliferation assay, cellular viability, cell death and apoptosis) and transcriptional studies were conducted. The heat stress resulted in overall decrease in cell viability and cell proliferation of MECs while induction of cellular apoptosis and necrosis. The transcriptomic profile of heat stressed MECs was generated using Agilent 44 K bovine oligonucleotide array and at cutoff criteria of ≥3-or ≤3 fold change, a total of 153 genes were observed to be upregulated while 8 genes were down regulated across all time points post heat stress. The genes that were specifically up-regulated or down-regulated were identified as heat responsive genes. The upregulated genes in heat stressed MECs belonged to heat shock family viz., HSPA6, HSPB8, DNAJB2, HSPA1A. Along with HSPs, genes like BOLA, MRPL55, PFKFB3, PSMC2, ENDODD1, ARID5A, and SENP3 were also upregulated. Microarray data revealed that the heat responsive genes belonged to different functional classes viz., chaperons; immune responsive; cell proliferation and metabolism related. Gene ontology analysis revealed enrichment of several biological processes like; cellular process, metabolic process, response to stimulus, biological regulation, immune system processes and signaling. The transcriptome analysis data was further validated by RT-qPCR studies. Several HSP (HSP40, HSP60, HSP70, HSP90, and HSPB1), apoptotic (Bax and Bcl2), immune (IL6, TNFα and NF-kβ) and oxidative stress (GPX1 and DUSP1) related genes showed differential expression profile at different time points post heat stress. The transcriptional data strongly indicated the induction of survival/apoptotic mechanism in heat stressed buffalo MECs. The overrepresented pathways across all time points were; electron transport chain, cytochrome P450, apoptosis, MAPK, FAS and stress induction of HSP regulation, delta Notch signaling, apoptosis modulation by HSP70, EGFR1 signaling, cytokines and inflammatory response, oxidative stress, TNF-alpha and NF- kB signaling pathway. The study thus identified several genes from different functional classes and biological pathways that could be termed as heat responsive in buffalo MEC. The responsiveness of buffalo MECs to heat stress in the present study clearly suggested its suitability as a model to understand the modulation of buffalo mammary gland expression signature in response to environmental heat load.

Three-dimensional culture system can induce expression of casein in immortalized bovine mammary epithelial cells

Primary bovine mammary epithelial cells (BMECs) are not ideal models for long-term studies of lactation mechanisms because these cells in a monolayer culture system cannot be polarized to simulate the physiological functions in vitro. We investigate the effects of different culture models and karyotypes on casein expression in a three-dimensional (3D) culture system. The immortalized cells' karyotypes were analyzed at passages 10, 20, 30 and 40 to detect the effects of chromosome stability. Western blotting examined that whether or not the immortalized cells at passages 5, 10, 20, 30, 40 and 50 could induce expression of casein in a 3D culture system. The proper polarization of the acinar structures was monitored. BMECs were successfully immortalized. The cell karyotype at passage 30 remained at 60 chromosomes and the average value was 57.1 ± 0.40 after passage 40. The polarized protein's levels were up-regulated in 3D culture compared to 2D culture. Expression of αs1, β and κ-casein could be detectable in a passage range in 3D culture. Expression of αs2-casein was undetectable in all experimental groups. However, all casein expressions were barely detectable in traditional 2D culture system. Therefore, 3D culture system is an important tool for the long-term study of lactation mechanisms in vitro.

Baicalin attenuates lipopolysaccharide induced inflammation and apoptosis of cow mammary epithelial cells by regulating NF-κB and HSP72

Baicalin is the main ingredient of traditional Chinese herbal medicine, Scutellaria baicalensis, which has been widely used clinically as an anti-inflammatory agent. However, molecular mechanism of action of this drug is not yet clear. In the present study, the protective mechanism of baicalin against lipopolysaccharide (LPS) induced inflammatory injury in cow mammary epithelial cells (CMECs) was explored. For this purpose, in vitro cultured CMECs were treated with baicalin (10μg/mL) and LPS (10μg/mL) for 24 and 12h, respectively, and the cell viability was measured by using cell counting kit-8 (CCK-8). The results revealed that LPS induced inflammatory responses, as p-p65/p65 and p-IκBα/IκBα ratios and TNF-α and IL-1β production was increased in the CMECs. Both Bcl-2/Bax ratio and cell viability were decreased and caspase-3 cleaved following LPS treatment, indicating apoptosis of CMECs. Moreover, both LPS and baicalin increased HSP72 expression of the CMECs. However, cellular inflammatory responses and apoptosis were significantly reduced in baicalin treated CMECs. In conclusion, baicalin ameliorated inflammation and apoptosis of the CMECs induced by LPS via inhibiting NF-κB activation and up regulation of HSP72.

Comparison of the effect of recombinant bovine wild and mutant lipopolysaccharide-binding protein in lipopolysaccharide-challenged bovine mammary epithelial cells

Lipopolysaccharide (LPS)-binding protein (LBP) plays a crucial role in the recognition of bacterial components, such as LPS that causes an immune response. The aim of this study was to compare the different effects of recombinant bovine wild LBP and mutant LBP (67 Ala → Thr) on the LPS-induced inflammatory response of bovine mammary epithelial cells (BMECs). When BMECs were treated with various concentrations of recombinant bovine lipopolysaccharide-binding protein (RBLBP) (1, 5, 10, and 15 μg/mL) for 12 h, RBLBP of 5 μg/mL increased the apoptosis of BMECs induced by LPS without cytotoxicity, and mutant LBP resulted in a higher cell apoptosis than wild LBP did. By gene-chip microarray and bioinformatics, the data identified 2306 differentially expressed genes that were changed significantly between the LPS-induced inflamed BMECs treated with 5 μg/mL of mutant LBP and the BMECs only treated with 10 μg/mL of LPS (fold change ≥2). Meanwhile, 1585 genes were differently expressed between the inflamed BMECs treated with 5 μg/mL of wild LBP and 10 μg/mL of LPS-treated BMECs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that these differentially expressed genes were involved in different pathways that regulate the inflammation response. It predicted that carriers of this mutation increase the risk for a more severe inflammatory response. Our study provides an overview of the gene expression profile between wild LBP and mutant LBP on the LPS-induced inflammatory response of BMECs, which will lead to further understanding of the potential effects of LBP mutations on bovine mammary glands.

14-3-3γ regulates cell viability and milk fat synthesis in lipopolysaccharide-induced dairy cow mammary epithelial cells

Our previous study demonstrated that 14-3-3γ overexpression was able to inhibit the production of lipopolysaccharide (LPS)-induced cytokines in dairy cow mammary epithelial cells (DCMECs) by inhibiting the activation of nuclear factor-κB (NF-κB) signaling pathways. However, the association between 14-3-3γ overexpression and milk fat synthesis in LPS-induced DCMECs remains unclear. Therefore, the present study investigated the effect of 14-3-3γ on cell viability and milk fat synthesis in LPS-induced DCMECs. The results of the MTT assay and lactate dehydrogenase activity assay demonstrated that 14-3-3γ overexpression was able to attenuate LPS-induced cytotoxicity in DCMECs, and increase the viability of the cells. In addition, the results of reverse transcription-quantitative polymerase chain reaction suggested that mRNA expression levels of genes associated with milk fat synthesis, including sterol regulatory element binding protein (SREBP1), peroxisome proliferator-activated receptor-γ (PPARG), cluster of differentiation 36, acetyl-coA carboxylase (ACC), fatty acid synthase (FAS) and fatty acid binding protein-3, were significantly upregulated in cells overexpressing the 14-3-3γ protein. In addition, as compared with the LPS-treated group, the activities of FAS and ACC were significantly increased. Furthermore, western blotting demonstrated that 14-3-3γ overexpression enhanced the protein expression levels of phosphorylated SREBP1 and PPARG. These results suggested that high levels of 14-3-3γ protein were able to attenuate LPS-induced cell damage and promote milk fat synthesis in LPS-induced DCMECs by increasing the cell viability and upregulating the expression levels of transcription factors associated with milk fat synthesis.

Can widely used cell type markers predict the suitability of immortalized or primary mammary epithelial cell models?

Background

Mammary cell cultures are convenient tools for in vitro studies of mammary gland biology. However, the heterogeneity of mammary cell types, e.g., glandular milk secretory epithelial or myoepithelial cells, often complicates the interpretation of cell-based data. The present study was undertaken to determine the relevance of bovine primary mammary epithelial cells isolated from American Holstein (bMEC_US) or Swiss Holstein–Friesian (bMEC_CH) cows, and of primary bovine mammary alveolar epithelial cells stably transfected with simian virus-40 (SV-40) large T-antigen (MAC-T) for in vitro analyses. This was evaluated by testing their expression pattern of cytokeratin (CK) 7, 18, 19, vimentin, and α-smooth muscle actin (α-SMA).

Results

The expression of the listed markers was assessed using real-time quantitative PCR, flow cytometry and immunofluorescence microscopy. Characteristic markers of the mesenchymal (vimentin), myoepithelial (α-SMA) and glandular secretory cells (CKs) showed differential expression among the studied cell cultures, partly depending on the analytical method used. The relative mRNA expression of vimentin, CK7 and CK19, respectively, was lower (P < 0.05) in immortalized than in primary mammary cell cultures. The stain index (based on flow cytometry) of CK7 and CK19 protein was lower (P < 0.05) in MAC-T than in bMECs, while the expression of α-SMA and CK18 showed an inverse pattern. Immunofluorescence microscopy analysis mostly confirmed the mRNA data, while partly disagreed with flow cytometry data (e.g., vimentin level in MAC-T). The differential expression of CK7 and CK19 allowed discriminating between immortal and primary mammary cultures.

Conclusions

The expression of the selected widely used cell type markers in primary and immortalized MEC cells did not allow a clear preference between these two cell models for in vitro analyses studying aspects of milk composition. All tested cell models exhibited to a variable degree epithelial and mesenchymal features. Thus, based on their characterization with widely used cell markers, none of these cultures represent an unequivocal alveolar mammary epithelial cell model. For choosing the appropriate in vitro model additional properties such as the expression profile of specific proteins of interest (e.g., transporter proteins) should equally be taken into account.