Staphylococcus aureus and Escherichia coli elicit different innate immune responses from bovine mammary epithelial cells

Presence of pathogen DNA in milk harvested from quarters is associated to changes in cows' milk yield and composition

BACKGROUND

Intramammary infection is the result of invasion and multiplication of microorganisms in the mammary gland and commonly leads to mastitis in dairy animals. Although much has been done to improve cows' udder health, mastitis remains a significant and costly health issue for dairy farmers, especially if subclinical. In this study, quarter milk samples from clinically healthy cows were harvested to detect pathogens via quantitative PCR (qPCR) and evaluate changes in individual milk traits according to the number of quarters infected and the type of microorganism(s). A commercial qPCR kit was used for detection of Mycoplasma bovis, Mycoplasma spp., Staphylococcus aureus, coagulase-negative staphylococci (CNS), Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, Prototheca spp., Escherichia coli, Klebsiella spp., Enterococcus spp. and Lactococcus lactis ssp. lactis. Quarter and pooled milk information of 383 Holstein, 132 Simmental, 129 Rendena, and 112 Jersey cows in 9 Italian single-breed herds was available.

RESULTS

Among the cows with pathogen(s) present in at least 1 quarter, CNS was the most commonly detected DNA, followed by Streptococcus uberis, Mycoplasma bovis, and Streptococcus agalactiae. Cows negative to qPCR were 206 and had the lowest milk somatic cell count. Viceversa, cows with DNA isolated in ≥ 3 quarters were those with the highest somatic cell count. Moreover, when major pathogens were isolated in ≥ 3 quarters, milk had the lowest casein index and lactose content. In animals with pathogen(s) DNA isolated, the extent with whom milk yield and major solids were impaired did not significantly differ between major and minor pathogens.

CONCLUSIONS

The effect of the number of affected quarters on the pool milk quality traits was investigated in clinically healthy cows using a commercial kit. Results remark the important negative effect of subclinical udder inflammations on milk yield and quality, but more efforts should be made to investigate the presence of untargeted microorganisms, as they may be potentially dangerous for cows. For a smarter use of antimicrobials, analysis of milk via qPCR is advisable - especially in cows at dry off - to identify quarters at high risk of inflammation and thus apply a targeted/tailored treatment.

Lactococcus garvieae exerts a critical role in inducing inflammation in dairy mastitis by triggering NLRP3 inflammasome-mediated pyroptosis in MAC-T cells

Lactococcus garvieae (L. garvieae) is a pathogenic bacterium that is Gram-positive and catalase-negative (GPCN), and it is capable of growing in a wide range of environmental conditions. This bacterium is associated with significant mortality and losses in fisheries, and there are concerns regarding its potential as a zoonotic pathogen, given its presence in cattle and dairy products. While we have identified and characterized virulent strains of L. garvieae through phenotyping and molecular typing studies, their impact on mammary tissue remains unknown. This study aims to investigate the pathogenicity of strong and weak virulent strains of L. garvieae using in vivo mouse models. We aim to establish MAC-T cell model to examine potential injury caused by the strong virulent strain LG41 through the TLR2/NLRP3/NF-kB pathway. Furthermore, we assess the involvement of NLRP3 inflammasome-mediated pyroptosis in dairy mastitis by silencing NLRP3. The outcomes of this study will yield crucial theoretical insights into the potential mechanisms involved in mastitis in cows caused by the L. garvieae-induced inflammatory response in MAC-T cells.

Immunolocalization of antibacterial peptide S100A7 in mastitis goat mammary gland and lipopolysaccharide induces the expression and secretion of S100A7 in goat mammary gland epithelial cells via TLR4/NFκB signal pathway

The antimicrobial peptide S100A7, with antimicrobial activities for a broad spectrum of bacteria, has attracted more and more attention for the prevention and treatment of mastitis. However, there is little information about the expression and regulation mechanism of S100A7 in mastitis goats. This study revealed that S100A7 was mainly expressed in the stratified squamous epithelium of teat skin and streak canal, and S100A7 was present weakly in the healthy goat alveolus yet densely in the mastitis goat collapsed alveolus. Goat mammary epithelial cells (MECs) were isolated and treated with 2.5, 5, 10 and 20 µg/mL lipopolysaccharide (LPS) respectively for a different time, S100A7 mRNA expression and protein secretion were upregulated significantly with LPS treatment for 3 h, and the secretion level of S100A7 descended after 48 h treatment for all of these four groups. Moreover, after treatment with LPS, the mRNA levels of Toll-like receptor 4 (TLR4) and MyD88 were up-regulated, and the phosphorylation of p65 was up-regulated markedly. However, adding TLR4 inhibitor TAK-242 or/and NF-κB inhibitor QNZ significantly suppressed the phosphorylation of p65, and then inhibited the expression and secretion of S100A7 induced by LPS treatment. In conclusion, LPS induced the expression and secretion of S100A7 in goat MECs via TLR4/NF-κB signaling pathway.

Lnc-ANRIL modulates the immune response associated with NF-κB pathway in LPS-stimulated bovine mammary epithelial cells

BACKGROUND

The antisense noncoding RNA in the INK4 locus (ANRIL) has been confirmed related to multiple disease progression, but the role and exact mechanisms of lnc-ANRIL in lipopolysaccharide (LPS)-induced inflammation of bovine mammary epithelial cells (MAC-T) remain unclear.

AIMS

This manuscript focused on expounding the functional role of lnc-ANRIL through experiments performed in MAC-T.

METHODS

At the in vitro level, we established a Bovine mammary epithelial cell (BMEC) cell model of mastitis by LPS treatment. Transfection of siRNA was examined by immunofluorescence localization and RT-qPCR. CCK8, clonogenic assay and EdU were used to detect the proliferation ability of the cells. Cell cycle and apoptosis were detected by flow cytometry and Western blot. The levels of inflammatory factors and oxidative stress markers were detected by ELISA kits.

RESULTS

Cell Counting Kit-8, colony formation, and 5-ethynyl-20-deoxyuridine were adopted and the data illustrated that LPS could significantly suppress the cell proliferation, while knockdown of lnc-ANRIL expression obviously promoted MAC-T cell proliferation compared with LPS or LPS + si-NC group. Flow cytometry analysis demonstrated that lnc-ANRIL could induce MAC-T cell apoptosis. In addition, downregulation of lnc-ANRIL affected LPS-induced immune response by regulating inflammatory factor expressions and modulating the nuclear factor kappa B (NF-κB) axis in MAC-T cells.

CONCLUSION

Our results suggest that lnc-ANRIL is involved in the regulation of cell proliferation, cell cycle, and cell apoptosis of MAC-T cells, and plays an important role in the inflammatory and immune response of MAC-T cells through the regulation of the NF-κB pathway, proposing new therapeutic strategies for the treatment of innate immune response-related disease such as bovine mastitis.

Effects of Glucose Levels on Inflammation and Amino Acid Utilization in Lipopolysaccharide-Induced Bovine Mammary Epithelial Cells

Glucose and amino acids are important sources of nutrients in the synthetic milk of dairy cows, and understanding the fate of amino acids is essential to optimize the utilization of amino acids in milk protein synthesis, thereby reducing nutrient inefficiencies during lactation. The purpose of this study was to investigate the effects of LPS and different concentrations of glucose on (1) the expression of inflammatory factors and genes, (2) the glucose metabolism, and (3) amino acid utilization in BMECs. The results showed that there was an interaction (LPS × glucose, p < 0.05) between LPS and glucose content in the inflammatory cytokine genes (IL-6 and TNF-α) and the inflammatory regulatory genes (CXCL2, CXCL8, and CCL5). With the addition of LPS, the HG + LPS group caused downregulated (p < 0.05) expression of IL-6 and TNF-α, compared with the LG + LPS group. Interestingly, compared with the LG + LPS group, the HG + LPS group upregulated (p < 0.05) the expression of CXCL2, CXCL8, and CCL5. LPS supplementation increased (p = 0.056) the consumption of glucose and GLUT1 gene expression (p < 0.05) and tended to increase (p = 0.084) the LDHA gene expression of BMECs under conditions of different concentrations of glucose culture. High glucose content increased (p < 0.001) the consumption of glucose and enhanced (p < 0.05) the GLUT1, HK1, HK2, and LDHA gene expression of BMECs with or without LPS incubation, and there was an interaction (LPS × glucose, p < 0.05) between LPS and glucose concentrations in GLUT1 gene expression. In this study, LPS enhanced (p < 0.05) the consumption of amino acids such as tryptophan, leucine, isoleucine, methionine, valine, histidine, and glutamate, while high levels of glucose decreased (p < 0.01) consumption, except in the case of tyrosine. For histidine, leucine, isoleucine, and valine consumption, there was an interaction (LPS × glucose, p < 0.05) between LPS and glucose levels. Overall, these findings suggest that relatively high glucose concentrations may lessen the LPS-induced BMEC inflammatory response and reduce amino acid consumption, while low glucose concentrations may increase the demand for most amino acids through proinflammatory responses.

Expression, Regulation, and Function of β-Defensins in the Bovine Mammary Glands: Current Knowledge and Future Perspectives

β-Defensins are cationic antimicrobial peptides (AMPs) that play an important role in the innate immune defense of bovines. They are constitutively expressed in mammary glands and induced differently in response to pathogens. Their expression is influenced by various factors, including hormones, plant-derived compounds, and dietary energy imbalance. The toll-like receptors (TLRs)/nuclear factor-kappa B (NF-κB) pathway plays a crucial role in β-defensin induction, while alternative pathways such as mitogen-activated protein kinase (MAPK) and epigenetic regulation also make substantial contributions. β-Defensins exhibit bactericidal activity against a wide range of pathogens, including two major mastitis pathogens, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), primarily through membrane disruption. β-Defensins have low cytotoxicity to host cells and demonstrate immunomodulatory properties, and pathogens also display minimal resistance to these AMPs. Given the increasing concern in antimicrobial resistance, the potential of β-defensins as natural antimicrobials has garnered considerable attention. This article provides an overview of the characteristics of bovine β-defensins, their expression pathways, their mode of action, and factors influencing their expression in the mammary glands of cattle. Additionally, it identifies the current gaps in research within this field and suggests areas that require further investigation. Understanding the regulation and function of β-defensins offers valuable insights to develop effective strategies for strengthening the immune system of mammary glands, reducing the reliance on synthetic antimicrobials, and explore novel natural antimicrobial alternatives.

Paeoniflorin alleviates inflammation in bovine mammary epithelial cells induced by Staphylococcus haemolyticus through TLR2/NF-κB signaling pathways

Staphylococcus haemolyticus (S. haemolyticus) is one of the most common coagulase-negative staphylococci (CoNS) isolates from bovine mastitis. Paeoniflorin (PF) shows anti-inflammatory effects on different inflammatory diseases in vitro studies and in vivo animal experiments. In this study, the viability of bovine mammary epithelial cells (bMECs) was detected by the cell counting kit-8 experiment. Subsequently, bMECs were induced with S. haemolyticus, and the induction dosage was determined. The expression of pro-inflammatory cytokines and toll-like receptor (TLR2) and nuclear factor kappa-B (NF-κB) signaling pathway-related genes were investigated by quantitative real-time PCR. The critical pathway proteins were detected by western blot. The results showed that the multiplicity of infection (MOI; the ratio of bacteria to bMECs) 5:1 of S. haemolyticus for 12 h could cause cellular inflammation, which was selected to establish the inflammatory model. Incubation with 50 μg/ml PF for 12 h was the best intervention condition for cells stimulated by S. hemolyticus. Quantitative real-time PCR and western blot analysis showed that PF inhibited the activation of TLR2 and NF-κB pathway-related genes and the expression of related proteins. Western blot results showed that PF suppressed the expression of NF-κB unit p65, NF-κB unit p50, and MyD88 in bMECs stimulated by S. haemolyticus. The inflammatory response pathway and molecular mechanism caused by S. haemolyticus on bMECs are related to TLR2-mediated NF-κB signaling pathways. The anti-inflammatory mechanism of PF may also be through this pathway. Therefore, PF is expected to develop potential drugs against CoNS-induced bovine mastitis.

Candidate genes for mastitis resistance in dairy cattle: a data integration approach

BACKGROUND

Inflammation of the mammary tissue (mastitis) is one of the most detrimental health conditions in dairy ruminants and is considered the most economically important infectious disease of the dairy sector. Improving mastitis resistance is becoming an important goal in dairy ruminant breeding programmes. However, mastitis resistance is a complex trait and identification of mastitis-associated alleles in livestock is difficult. Currently, the only applicable approach to identify candidate loci for complex traits in large farm animals is to combine different information that supports the functionality of the identified genomic regions with respect to a complex trait.

METHODS

To identify the most promising candidate loci for mastitis resistance we integrated heterogeneous data from multiple sources and compiled the information into a comprehensive database of mastitis-associated candidate loci. Mastitis-associated candidate genes reported in association, expression, and mouse model studies were collected by searching the relevant literature and databases. The collected data were integrated into a single database, screened for overlaps, and used for gene set enrichment analysis.

RESULTS

The database contains candidate genes from association and expression studies and relevant transgenic mouse models. The 2448 collected candidate loci are evenly distributed across bovine chromosomes. Data integration and analysis revealed overlaps between different studies and/or with mastitis-associated QTL, revealing promising candidate genes for mastitis resistance.

CONCLUSION

Mastitis resistance is a complex trait influenced by numerous alleles. Based on the number of independent studies, we were able to prioritise candidate genes and propose a list of the 22 most promising. To our knowledge this is the most comprehensive database of mastitis associated candidate genes and could be helpful in selecting genes for functional validation studies.

Scavenger receptor B1 facilitates the endocytosis of Escherichia coli via TLR4 signaling in mammary gland infection

SCARB1 belongs to class B of Scavenger receptors (SRs) that are known to be involved in binding and endocytosis of various pathogens. SRs have emerging role in regulating innate immunity and host-pathogen interactions by acting in co-ordination with Toll-like receptors.Query Little is known about the function of SCARB1 in milk-derived mammary epithelial cells (MECs). This study reports the role of SCARB1 in infection and its potential association in TLR4 signaling on bacterial challenge in Goat mammary epithelial cells (GMECs). The novelty in the establishment of MEC culture lies in the method that aims to enhance the viability of the cells with intact characteristics upto a higher passage number. We represent MEC culture to be used as a potential infection model for deeper understanding of animal physiology especially around the mammary gland. On E.coli challenge the expression of SCARB1 was significant in induced GMECs at 6 h. Endoribonuclease-esiRNA based silencing of SCARB1 affects the expression of TLR4 and its pathways i.e. MyD88 and TRIF pathways on infection. Knockdown also affected the endocytosis of E.coli in GMECs demonstrating that E.coli uses SCARB1 function to gain entry in cells. Furthermore, we predict 3 unique protein structures of uncharacterized SCARB1 (Capra hircus) protein. Overall, we highlight SCARB1 as a main participant in host defence and its function in antibacterial advances to check mammary gland infections. Video Abstract.

A Novel TLR4-SYK Interaction Axis Plays an Essential Role in the Innate Immunity Response in Bovine Mammary Epithelial Cells

Mammary gland epithelium, as the first line of defense for bovine mammary gland immunity, is crucial in the process of mammary glands’ innate immunity, especially that of bovine mammary epithelial cells (bMECs). Our previous studies successfully marked SYK as an important candidate gene for mastitis traits via GWAS and preliminarily confirmed that SYK expression is down-regulated in bMECs with LPS (E. coli) stimulation, but its work mechanism is still unclear. In this study, for the first time, in vivo, TLR4 and SYK were colocalized and had a high correlation in mastitis mammary epithelium; protein−protein interaction results also confirmed that there was a direct interaction between them in mastitis tissue, suggesting that SYK participates in the immune regulation of the TLR4 cascade for bovine mastitis. In vitro, TLR4 also interacts with SYK in LPS (E. coli)-stimulated or GBS (S. agalactiae)-infected bMECs, respectively. Moreover, TLR4 mRNA expression and protein levels were little affected in bMECsSYK- with LPS stimulation or GBS infection, indicating that SYK is an important downstream element of the TLR4 cascade in bMECs. Interestingly, IL-1β, IL-8, NF-κB and NLRP3 expression in LPS-stimulated or GBS-infected bMECsSYK- were significantly higher than in the control group, while AKT1 expression was down-regulated, implying that SYK could inhibit the IL-1β, IL-8, NF-κB and NLRP3 expression and alleviate inflammation in bMECs with LPS and GBS. Taken together, our solid evidence supports that TLR4/SYK/NF-κB signal axis in bMECs regulates the innate immunity response to LPS or GBS.

Bta-miR-199a-3p Inhibits LPS-Induced Inflammation in Bovine Mammary Epithelial Cells via the PI3K/AKT/NF-κB Signaling Pathway

Mastitis is characterized by inflammatory damage to mammary gland tissue, which could decline milk production and quality and significantly affect the economic benefits of ranching. MicroRNAs (miRNAs), such as miR-199a-3p, are novel therapeutic targets in inflammation, and their regulation is an effective strategy for inflammation control. Despite its importance in humans and animals, the molecular mechanism of bovine miR-199a-3p (bta-miR-199a-3p) in dairy cow mastitis and bovine mammary epithelial cell (bMEC) inflammation is unclear. In our study, a bovine mammary epithelial cell line (MAC-T) induced by lipopolysaccharide (LPS) was used as an inflammatory cell model to investigate the molecular mechanism of bta-miR-199a-3p in the MAC-T inflammatory response. bta-miR-199a-3p was up-regulated in the LPS-induced MAC-T cells, while CD2-associated protein (CD2AP) was revealed as its target gene in a double luciferase reporter gene experiment. In addition, the overexpression of bta-miR-199a-3p negatively regulated the expression of CD2AP and the activation of the phosphatidylinositol 3-kinase (PI3K)/AKT/nuclear factor kappa-B (NF-κB) signaling pathway. These subsequently inhibited the secretion of related inflammatory factors (TNF-α, IL-1β, and IL-6) and the expression of apoptotic genes (CASP3 and CASP9), thereby alleviating the LPS-challenged inflammatory response in the MAC-T cells. Silencing of bta-miR-199a-3p, however, reversed the above effects. Thus, bta-miR-199a-3p inhibits LPS-induced inflammation in bMECs by directly targeting CD2AP and regulating the PI3K/AKT/NF-κB signaling pathway. This study reveals the potential regulatory mechanism of bta-miR-199a-3p in bMEC inflammatory immune response and may serve as a useful target for the treatment of mastitis.

Immune defenses of the mammary gland epithelium of dairy ruminants

The epithelium of the mammary gland (MG) fulfills three major functions: nutrition of progeny, transfer of immunity from mother to newborn, and its own defense against infection. The defense function of the epithelium requires the cooperation of mammary epithelial cells (MECs) with intraepithelial leucocytes, macrophages, DCs, and resident lymphocytes. The MG is characterized by the secretion of a large amount of a nutrient liquid in which certain bacteria can proliferate and reach a considerable bacterial load, which has conditioned how the udder reacts against bacterial invasions. This review presents how the mammary epithelium perceives bacteria, and how it responds to the main bacterial genera associated with mastitis. MECs are able to detect the presence of actively multiplying bacteria in the lumen of the gland: they express pattern recognition receptors (PRRs) that recognize microbe-associated molecular patterns (MAMPs) released by the growing bacteria. Interactions with intraepithelial leucocytes fine-tune MECs responses. Following the onset of inflammation, new interactions are established with lymphocytes and neutrophils recruited from the blood. The mammary epithelium also identifies and responds to antigens, which supposes an antigen-presenting capacity. Its responses can be manipulated with drugs, plant extracts, probiotics, and immune modifiers, in order to increase its defense capacities or reduce the damage related to inflammation. Numerous studies have established that the mammary epithelium is a genuine effector of both innate and adaptive immunity. However, knowledge gaps remain and newly available tools offer the prospect of exciting research to unravel and exploit the multiple capacities of this particular epithelium.

Bta-miR-223 Targeting the RHOB Gene in Dairy Cows Attenuates LPS-Induced Inflammatory Responses in Mammary Epithelial Cells

Bovine mammary epithelial cells (bMECs) are part of the first line of defense against pathogens. In recent studies, bta-miR-223 has been reported to activate congenital and innate immunity against inflammatory damage during the pathogenesis of mastitis in dairy cows. The purpose of this study was to identify the regulatory mechanism of bta-miR-223 and its downstream target genes in inflammatory bMECs. A double luciferase reporter gene assay demonstrated that ras homolog family member B (RHOB) was the target gene of bta-miR-223. To further elucidate the role of bta-miR-223 in congenital immune responses, bta-miR-223 mimics (mimic/inhibitor) were transfected into bMECs stimulated with lipopolysaccharide (LPS), which activates the Toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) signaling pathway. Real-time quantitative PCR (qPCR) and Western blot were used to detect the expression of related genes and proteins, and enzyme-linked immunosorbent assay (ELISA) was used to detect secreted inflammatory factors. Results showed that bta-miR-223 expression during inflammation in bMECs reduced the secretion of inflammatory factors by targeting RHOB and deactivation of NF-κB gene activity. Silencing RHOB inhibited LPS-induced inflammatory response in bMECs. Overall, bta-miR-223 attenuated LPS-induced inflammatory response, and acted as a negative feedback regulator via targeting RHOB, providing a novel avenue for mastitis treatment.

Prediction of potential molecular markers of bovine mastitis by meta-analysis of differentially expressed genes using combined p value and robust rank aggregation

Bovine mastitis causes significant economic loss to the dairy industry by affecting milk quality and quantity. Escherichia coli and Staphylococcus aureus are the two common mastitis-causing bacteria among the consortia of mastitis pathogens, wherein E. coli is an opportunistic environmental pathogen, and S. aureus is a contagious pathogen. This study was designed to predict molecular markers of bovine mastitis by meta-analysis of differentially expressed genes (DEG) in E. coli- or S. aureus-infected mammary epithelial cells (MECs) using p value combination and robust rank aggregation (RRA) methods. High-throughput transcriptome of bovine MECs, infected with E. coli or S. aureus, were analyzed, and correlation of z-scores were computed for the expression datasets to identify the lineage profile and functional ontology of DEGs. Key pathways enriched in infected MECs were deciphered by Gene Set Enrichment Analysis (GSEA), following which combined p value and RRA were used to perform DEG meta-analysis to limit type I error in the analysis. The miRNA-gene networks were then built to uncover potential molecular markers of mastitis. Lineage profiling of MECs showed that the gene expression levels were associated with mammary tissue lineage. The up-regulated genes were enriched in immune-related pathways, whereas down-regulated genes influenced the cellular processes. GSEA analysis of DEGs deciphered the involvement of Toll-like receptor (TLR), and NF-kappa B signaling pathway during infection. Comparison after meta-analysis yielded with genes ZC3H12A, RND1, and MAP3K8 having significant expression levels in both E. coli and S. aureus dataset, and on evaluating miRNA-gene network, 7 pairs were common to both sets identifying them as potential molecular markers.

Effects of the interaction of Notch and TLR4 pathways on inflammation and heart function in septic heart

We investigated the role of the interaction between the Notch and Toll-like receptor 4 (TLR4) pathways in septic myocardial injury. The sepsis model was induced in rats with lipopolysaccharide (LPS). Rats were divided into control, LPS, LPS + TAK242 ((6R)-6-[N-(2-chloro-4-fluorophenyl)sulfamoyl]cyclohex-1-ene-1-carboxylate) and LPS + DAPT (N-[N-(3,5-difluorophenacetyl)-l-alanyl]-s-phenylglycinetbutylester) groups. Heart function was evaluated with a Cardiac Doppler ultrasound. Myocardial morphological changes were detected by hematoxylin-eosin staining (H&E). Apoptosis was assessed by a TUNEL assay. The mRNA and protein levels were detected with real-time PCR, Western blot, and immunohistochemistry analysis. We found that heart function in the LPS + TAK242 group was significantly improved, but not in the LPS + DAPT group. LPS + TAK242 had a lower level of degeneration and necrosis of cardiomyocytes and inflammatory cell infiltration, as well as lower apoptosis and caspase-3 expression than the LPS group. Compared with the LPS group, the inflammatory cell infiltration was reduced in the LPS + DAPT group, while the degeneration and necrosis of cardiomyocytes were not obviously improved. Additionally, the expression levels of tumor necrosis factor-α and Interleukin-6, the protein contents of Notch intracellular domain and Hes1, and the P65 nuclear factor kappa-B (NF-κB) to P-P65 NF-κB ratio in LPS + TAK242 group and LPS + DAPT group were significantly lower than those in LPS group. Conclusively, the interaction between TLR4 and Notch signaling pathways enhances the inflammatory response in the septic heart by activating NF-κB. Blocking the TLR4 pathway with TAK242 can improve heart dysfunction and myocardial damage in sepsis, while blocking the Notch pathway with DAPT cannot effectively prevent heart dysfunction and myocardial damage in sepsis.

N6-Methyladenosine-Modified circRNA in the Bovine Mammary Epithelial Cells Injured by Staphylococcus aureus and Escherichia coli

Mastitis is a common disease that hinders the development of dairy industry and animal husbandry. It leads to the abuse of antibiotics and the emergence of super drug-resistant bacteria, and poses a great threat to human food health and safety. Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) are the most common pathogens of mastitis in dairy cows and usually cause subclinical or clinical mastitis. CircRNAs and N⁶-methyladenosine (m⁶A) play important roles in immunological diseases. However, the mechanisms by which m⁶A modifies circRNA in bovine mammary epithelial cells remain poorly understood. The aim of our study was to investigate m⁶A-modified circRNAs in bovine mammary epithelial cells (MAC-T cells) injured by S. aureus and E. coli. The profile of m⁶A-modified circRNA showed a total of 1,599 m⁶A peaks within 1,035 circRNAs in the control group, 35 peaks within 32 circRNAs in the S. aureus group, and 1,016 peaks within 728 circRNAs in the E. coli group. Compared with the control group, 67 peaks within 63 circRNAs were significantly different in the S. aureus group, and 192 peaks within 137 circRNAs were significantly different in the E. coli group. Furthermore, we found the source genes of these differentially m⁶A-modified circRNAs in the S. aureus and E. coli groups with similar functions according to GO and KEGG analyses, which were mainly associated with cell injury, such as inflammation, apoptosis, and autophagy. CircRNA–miRNA–mRNA interaction networks predicted the potential circRNA regulation mechanism in S. aureus- and E. coli-induced cell injury. We found that the mRNAs in the networks, such as BCL2, MIF, and TNFAIP8L2, greatly participated in the MAPK, WNT, and inflammation pathways. This is the first report on m⁶A-modified circRNA regulation of cells under S. aureus and E. coli treatment, and sheds new light on potential mechanisms and targets from the perspective of epigenetic modification in mastitis and other inflammatory diseases.

C4BPA: A Novel Co-Regulator of Immunity and Fat Metabolism in the Bovine Mammary Epithelial Cells

The C4b binding protein alpha (C4BPA) chain primarily engages in critical inflammatory and coagulation processes. The previous transcriptomic analysis showed that C4BPA is a differentially expressed gene in lower and higher fat content mammary gland cell lines from Chinese Holstein. This study aimed to investigate the effects of C4BPA on the inflammation and milk fat synthesis in bMECs by C4BPA knockdown and overexpression. The results highlighted that knockdown of C4BPA in bMECs could suppress the mRNA and protein expression of IL-6, IL-8, IL-12, and the TLR-4/NF-κB pathway-related genes and promote the expression of complement and coagulation cascade pathways related genes as well as TNF-α. Moreover, knockdown of C4BPA expression in bMECs reduced the content of triglyceride (TG) and cholesterol (CHOL) in bMECs, increased NEFA content, reduced mRNA and protein expression of ACSL1 and PPARA, and increased the mRNA and protein expression of ELOVL6, FADS1, and LPL. The bMECs, with the overexpression of C4BPA, showed the enhanced expression of TLR-4/NF-κB linked genes, IL-6, IL-8, IL-12, and mRNA and protein level while reduced mRNA expression of TNF-α, compliment, and coagulation cascade related genes was observed. In bMECs, overexpression of C4BPA enhanced the content of TG and CHOL while reducing NEFA and stimulated the mRNA and protein expression of ACSL1, PPARA, and PPARG genes while inhibiting the mRNA and protein expression of FADS1 and LPL genes. Our results show that C4BPA not only regulates the lipid metabolism through the PPAR signaling pathway in bMECs but also contributes to the inflammatory response through TLR-4/NF-κB and the complement and coagulation cascade pathways. This study, for the first time, provides the primary basis for understanding the role of C4BPA in immunity and fat metabolism, which enables the researchers for innovative direction to investigate genes associated with fat metabolism and immunity. This study also advocates that the breeders must pay attention to such type of genes with multiple functions during animal breeding.

Nanocurcumin alleviates inflammation and oxidative stress in LPS-induced mastitis via activation of Nrf2 and suppressing TLR4-mediated NF-κB and HMGB1 signaling pathways in rats

Coliform mastitis is a worldwide serious disease of the mammary gland. Curcumin is a pleiotropic polyphenol obtained from turmeric, but it is hydrophobic and rapidly eliminated from the body. However, nanoformulation of curcumin significantly improves its pharmacological activity by enhancing its hydrophobicity and oral bioavailability. Our study aimed to investigate the possible antioxidant and anti-inflammatory effects of nanocurcumin as a prophylactic against LPS-induced coliform mastitis in rat model, where LPS was extracted from a field strain of Escherichia coli (bovine mastitis isolate). The study was conducted on twenty lactating Wistar female rats divided into four equal groups, and the mastitis model was initiated by injection of LPS through the duct of the mammary gland. The results showed that nanocurcumin significantly attenuated the lipid peroxidation (MDA), oxidized glutathione, the release of pro-inflammatory cytokines (TNF-α and IL-1β), and the gene expression of TLR4, NF-κB p65, and HMGB1. Meanwhile, it improved the reduced glutathione level and Nrf2 activity and preserved the normal alveolar architecture. These findings suggested that nanocurcumin supplementation can be a promising potential protective approach for coliform mastitis.

The Role of microRNAs in the Mammary Gland Development, Health, and Function of Cattle, Goats, and Sheep

Milk is an integral and therefore complex structural element of mammalian nutrition. Therefore, it is simple to conclude that lactation, the process of producing milk, is as complex as the mammary gland, the organ responsible for this biochemical activity. Nutrition, genetics, epigenetics, disease pathogens, climatic conditions, and other environmental variables all impact breast productivity. In the last decade, the number of studies devoted to epigenetics has increased dramatically. Reports are increasingly describing the direct participation of microRNAs (miRNAs), small noncoding RNAs that regulate gene expression post-transcriptionally, in the regulation of mammary gland development and function. This paper presents a summary of the current state of knowledge about the roles of miRNAs in mammary gland development, health, and functions, particularly during lactation. The significance of miRNAs in signaling pathways, cellular proliferation, and the lipid metabolism in agricultural ruminants, which are crucial in light of their role in the nutrition of humans as consumers of dairy products, is discussed.

Escherichia coli and Staphylococcus aureus Differentially Regulate Nrf2 Pathway in Bovine Mammary Epithelial Cells: Relation to Distinct Innate Immune Response

Escherichia coli and Staphylococcus aureus are major mastitis causing pathogens in dairy cattle but elicit distinct immune and an inflammatory response in the udder. However, the host determinants responsible for this difference remains largely unknown. Our initial studies focused on the global transcriptomic response of primary bovine mammary epithelial cells (pbMECs) to heat-killed E. coli and S. aureus. RNA-sequencing transcriptome analysis demonstrates a significant difference in expression profiles induced by E. coli compared with S. aureus. A major differential response was the activation of innate immune response by E. coli, but not by S. aureus. Interestingly, E. coli stimulation increased transcript abundance of several genes downstream of Nrf2 (nuclear factor erythroid 2-related factor 2) that were enriched in gene sets with a focus on metabolism and immune system. However, none of these genes was dysregulated by S. aureus. Western blot analysis confirms that S. aureus impairs Nrf2 activation as compared to E. coli. Using Nrf2-knockdown cells we demonstrate that Nrf2 is necessary for bpMECs to mount an effective innate defensive response. In support of this notion, nuclear Nrf2 overexpression augmented S. aureus-stimulated inflammatory response. We also show that, unlike E. coli, S. aureus disrupts the non-canonical p62/SQSTM1-Keap1 pathway responsible for Nrf2 activation through inhibiting p62/SQSTM1 phosphorylation at S349. Collectively, our findings provide important insights into the contribution of the Nrf2 pathway to the pathogen-species specific immune response in bovine mammary epithelial cells and raise a possibility that impairment of Nrf2 activation contributes to, at least in part, the weak inflammatory response in S. aureus mastitis.

Differential Expression Profiles of lncRNA Following LPS-Induced Inflammation in Bovine Mammary Epithelial Cells

Bovine mastitis is an inflammatory response of mammary glands caused by pathogenic microorganisms such as Escherichia coli (E. coli). As a key virulence factor of E. coli, lipopolysaccharide (LPS) triggers innate immune responses via activation of the toll-like-receptor 4 (TLR4) signaling pathway. However, the molecular regulatory network of LPS-induced bovine mastitis has yet to be fully mapped. In this study, bovine mammary epithelial cell lines MAC-T were exposed to LPS for 0, 6 and 12 h to assess the expression profiles of long non-coding RNAs (lncRNAs) using RNA-seq. Differentially expressed lncRNAs (DElncRNAs) were filtered out of the raw data for subsequent analyses. A total of 2,257 lncRNAs, including 210 annotated and 2047 novel lncRNAs were detected in all samples. A large proportion of lncRNAs were present in a high abundance, and 112 DElncRNAs were screened out at different time points. Compared with 0 h, there were 22 up- and 25 down-regulated lncRNAs in the 6 h of post-infection (hpi) group, and 27 up- and 22 down-regulated lncRNAs in the 12 hpi group. Compared with the 6 hpi group, 32 lncRNAs were up-regulated and 25 lncRNAs were down-regulated in the 12 hpi group. These DElncRNAs are involved in the regulation of a variety of immune-related processes including inflammatory responses bMECs exposed to LPS. Furthermore, lncRNA TCONS_00039271 and TCONS_00139850 were respectively significance down- and up-regulated, and their target genes involve in regulating inflammation-related signaling pathways (i.e.,Notch, NF-κB, MAPK, PI3K-Akt and mTOR signaling pathway), thereby regulating the occurrence and development of E. coli mastitis. This study provides a resource for lncRNA research on the molecular regulation of bovine mastitis.

Genome-Wide Analysis of LncRNA in Bovine Mammary Epithelial Cell Injuries Induced by Escherichia Coli and Staphylococcus Aureus

Escherichia coli and Staphylococcus aureus are two common pathogenic microorganisms that cause mastitis in dairy cows. They can cause clinical mastitis and subclinical mastitis. In recent studies, lncRNAs have been found to play an important role in the immune responses triggered by microbial inducers. However, the actions of lncRNAs in bovine mastitis remain unclear. The purpose of this study was to investigate the effects of bovine mammary epithelial cell injuries induced by treatment with E. coli and S. aureus, and to explore the lncRNA profile on cell injuries. The lncRNA transcriptome analysis showed a total of 2597 lncRNAs. There were 2234 lncRNAs differentially expressed in the E. coli group and 2334 in the S. aureus group. Moreover, we found that the E. coli and S. aureus groups of maternal genes targeted signaling pathways with similar functions according to KEGG and GO analyses. Two lncRNA-miRNA-mRNA interaction networks were constructed in order to predict the potential molecular mechanisms of regulation in the cell injuries. We believe that this is the first report demonstrating the dysregulation of lncRNAs in cells upon E. coli and S. aureus infections, suggesting that they have the potential to become important diagnostic markers and to provide novel insights into controlling and preventing mastitis.

Integrative Analysis of miRNA and mRNA Expression Profiles in Mammary Glands of Holstein Cows Artificially Infected with Staphylococcus aureus

Staphylococcus aureus- induced mastitis is one of the most intractable problems for the dairy industry, which causes loss of milk yield and early slaughter of cows worldwide. Few studies have used a comprehensive approach based on the integrative analysis of miRNA and mRNA expression profiles to explore molecular mechanism in bovine mastitis caused by S. aureus. In this study, S. aureus (A1, B1 and C1) and sterile phosphate buffered saline (PBS) (A2, B2 and C2) were introduced to different udder quarters of three individual cows, and transcriptome sequencing and microarrays were utilized to detected miRNA and gene expression in mammary glands from the challenged and control groups. A total of 77 differentially expressed microRNAs (DE miRNAs) and 1625 differentially expressed genes (DEGs) were identified. Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that multiple DEGs were enriched in significant terms and pathways associated with immunity and inflammation. Integrative analysis between DE miRNAs and DEGs proved that miR-664b, miR-23b-3p, miR-331-5p, miR-19b and miR-2431-3p were potential factors regulating the expression levels of CD14 Molecule (CD14), G protein subunit gamma 2 (GNG2), interleukin 17A (IL17A), collagen type IV alpha 1 chain (COL4A1), microtubule associated protein RP/EB family member 2 (MAPRE2), member of RAS oncogene family (RAP1B), LDOC1 regulator of NFKB signaling (LDOC1), low-density lipoprotein receptor (LDLR) and S100 calcium binding protein A9 (S100A9) in bovine mastitis caused by S. aureus. These findings could enhance the understanding of the underlying immune response in bovine mammary glands against S. aureus infection and provide a useful foundation for future application of the miRNA–mRNA-based genetic regulatory network in the breeding cows resistant to S. aureus.

Dynamics of intramammary infections in suckler ewes during early lactation

Mastitis is an important problem in meat-producing sheep, but few studies have investigated the transmission dynamics of mastitis pathogens in these animals. The objective of this study was to describe the pathogens causing intramammary infections (IMI) in suckler ewes, their effect on somatic cell count, and the dynamics of these IMI in early lactation. We enrolled 15 sheep flocks early after lambing and selected ewes in each flock that were sampled twice with a 3-wk interval. Milk samples from both glands of each ewe were bacteriologically cultured, and somatic cell count was measured. Non-aureus Staphylococcus spp. were the most prevalent culture results. Somatic cell counts were most strongly increased in ewes infected with Mannheimia haemolytica, whereas staphylococci, including Staphylococcus aureus, were associated with a moderate increase in somatic cell count. The proportion of udder halves that remained culture-positive with Staphylococcus spp. during the 3-wk sampling interval was moderate, but M. haemolytica infections were stable during this time period. A substantial number of new infections were seen in the early lactation study period for non-aureus Staphylococcus spp., Staph. aureus, and Corynebacterium spp., but not for M. haemolytica or Streptococcus spp. The number of new IMI of Staph. aureus was associated with the number of Staph. aureus-infected udder halves in the flock at the first sampling moment, indicative of contagious transmission. Altogether, we show that substantial transmission happens in early lactation in suckler ewes, but that the dynamics differ between pathogen species. More research is needed to further describe transmission in different stages of lactation and to identify transmission routes, to develop effective interventions to control mastitis.

Heat inactivation partially preserved barrier and immunomodulatory effects of Lactobacillus gasseri LA806 in an in vitro model of bovine mastitis

Probiotics could help combat infections and reduce antibiotic use. As use of live bacteria is limited in some cases by safety or regulatory concerns, the potential of inactivated bacteria is worth investigating. We evaluated the potential of live and heat-inactivated Lactobacillus gasseri LA806 to counteract Staphylococcus aureus and Escherichia coli infection cycles in an in vitro model of bovine mastitis. We assessed the ability of live and inactivated LA806 to impair pathogen colonisation of bovine mammary epithelial cells (bMECs) and to modulate cytokine expression by pathogen-stimulated bMECs. Live LA806 induced a five-fold decrease in S. aureus adhesion and internalisation (while not affecting E. coli colonisation) and decreased pro-inflammatory cytokine expression by S. aureus-stimulated bMECs (without interfering with the immune response to E. coli). The ability of inactivated LA806 ability to diminish S. aureus colonisation was two-fold lower than that of the live strain, but its anti-inflammatory properties were barely impacted. Even though LA806 effects were impaired after inactivation, both live and inactivated LA806 have barrier and immunomodulatory properties that could be useful to counteract S. aureus colonisation in the bovine mammary gland. As S. aureus is involved in various types of infection, LA806 potential would worth exploring in other contexts.

Antibacterial and immunomodulatory effects of Pheromonicin-NM on Escherichia coli-challenged bovine mammary epithelial cells

Mastitis affects cows in all regions of the world and Escherichia coli (E. coli) is by far the most common reason of mastitis. Now antibiotic therapy is still the preferred approach of treating mastitis. However, antibiotic usage is easy to lead to antibiotic resistance. There is an urgent need for developing efficacious alternative antimicrobials. Pheromonicin-NM (PMC-NM) is a new engineered bactericidal peptide consisting of colicin Ia and an anti-porin A antibody mimetic. It can lead to the dissipation of cellular energy and therefore kill the bacteria rapidly. The aim of the present study was to investigate the comparative effects of PMC-NM and antibiotic ceftiofur on antibacterial and innate immune responses of bovine mammary epithelial cells (BMEC) to E. coli infection. We found that E. coli growth was inhibited by PMC-NM from 0.5 h after treatment and was completely inhibited at 3 h, indicating a rapid antibacterial activity for PMC-NM. The mRNA expression of TLR2, IL-1β, IL-8, lactoferrin, LAP, TAP and DEFB1 was increased by PMC-NM treatment at 2 h after E. coli infection, suggesting the enhanced inflammatory responses induced by PMC-NM contribute to pathogens clearance at early phase. By contrast, in E. coli-infected BMECs, ceftiofur treatment upregulated TLR2 and NOD2 levels at 12 h, and extremely elevated transcription levels of TNF-α, IL-1β, IL-8, lactoferrin, LAP, TAP, BNBD5, DEFB1 at 6 h. The excessive expression of these genes at later phase can induce uncontrolled inflammatory responses and finally cause damage. Taken together, PMC-NM might be used as an ideal antibacterial agent against E. coli mastitis.

Short communication: Recombinant mammary serum amyloid A3 as a potential strategy for preventing intramammary infections in dairy cows at dryoff

Mammary serum amyloid A3 (M-SAA3) has shown potential in stimulating innate immunity during intramammary infections, at calving and at dryoff. In this study, we produced recombinant caprine M-SAA3 to test its ability to reduce intramammary infections with Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae, and Escherichia coli, which are all common mastitis-producing pathogens. Recombinant production of M-SAA3 (followed by lipopolysaccharide removal to avoid lipopolysaccharide-nonspecific stimulation of the immune system) was successfully achieved. Mammary serum amyloid A3 stimulated the expression of IL-8 in a dose-dependent manner in primary mammary cultures. Although a direct killing effect on Staph. aureus by M-SAA3 was not detected, this acute phase protein was able to reduce Staph. aureus, Strep. uberis, and Strep. dysgalactiae infections by up to 50% and induced a reduction in E. coli counts of 67%. In general, the best concentration of caprine M-SAA3 for inhibiting infections was the lowest concentration tested (10 μg/mL), although higher concentrations (up to 160 μg/mL) increased its antimicrobial potential against some pathogens.

Activation of a Bovine Mammary Epithelial Cell Line by Ruminant-Associated Staphylococcus aureus is Lineage Dependent

Bovine mastitis is a costly disease to the dairy industry and intramammary infections (IMI) with Staphylococcus aureus are a major cause of mastitis. Staphylococcus aureus strains responsible for mastitis in cattle predominantly belong to ruminant-associated clonal complexes (CCs). Recognition of pathogens by bovine mammary epithelial cells (bMEC) plays a key role in activation of immune responsiveness during IMI. However, it is still largely unknown to what extent the bMEC response differs according to S. aureus CC. The aim of this study was to determine whether ruminant-associated S. aureus CCs differentially activate bMEC. For this purpose, the immortalized bMEC line PS was stimulated with S. aureus mastitis isolates belonging to four different clonal complexes (CCs; CC133, CC479, CC151 and CC425) and interleukin 8 (IL-8) release was measured as indicator of activation. To validate our bMEC model, we first stimulated PS cells with genetically modified S. aureus strains lacking (protein A, wall teichoic acid (WTA) synthesis) or expressing (capsular polysaccharide (CP) type 5 or type 8) factors expected to affect S. aureus recognition by bMEC. The absence of functional WTA synthesis increased IL-8 release by bMEC in response to bacterial stimulation compared to wildtype. In addition, bMEC released more IL-8 after stimulation with S. aureus expressing CP type 5 compared to CP type 8 or a strain lacking CP expression. Among the S. aureus lineages, isolates belonging to CC133 induced a significantly stronger IL-8 release from bMEC than isolates from the other CCs, and the IL-8 response to CC479 was higher compared to CC151 and CC425. Transcription levels of IL-8, tumor necrosis factor alpha (TNFα), serum amyloid A3 (SAA3), Toll-like receptor (TLR)-2 and nuclear factor κB (NF-κB) in bMEC after bacterial stimulation tended to follow a similar pattern as IL-8 release, but there were no significant differences between the CCs. This study demonstrates a differential activation of bMEC by ruminant-associated CCs of S. aureus, which may have implications for the severity of mastitis during IMI by S. aureus belonging to these lineages.

8-Methoxypsoralen protects bovine mammary epithelial cells against lipopolysaccharide-induced inflammatory injury via suppressing JAK/STAT and NF-κB pathway

Bovine mastitis is the most common disease in dairy cattle. Bacterial infections are the main cause of mastitis. Lipopolysaccharide (LPS), a major structural component of the cell wall of Escherichia coli, is a good inducer used to replicate inflammation models. 8-Methoxypsoralen (8-MOP), a formerly considered photosensitizing agent, has been used in immunotherapy. This study investigated the protective effects of 8-MOP on LPS-induced inflammatory injury in bovine mammary epithelial cells (BMECs). LPS treatment (50 μg/mL for 12 hr) caused a decrease in cell viability, morphological damage, and cell apoptosis. Pretreatment with 8-MOP at concentrations of 25 and 50 μg/ml significantly attenuated LPS-induced inflammation in BMECs. qRT-PCR analysis revealed that the messenger RNA expression of inflammatory cytokines and chemokine (interleukin-1β [IL-1β], IL-6, tumor necrosis factor-α, and IL-8) was suppressed by 8-MOP in LPS-stimulated BMECs. Western blot analysis showed that 8-MOP could also reduce the protein levels of cyclooxygenase-2 and promote the translocation of high-mobility group box 1 from the nucleus to cytoplasm. Furthermore, the anti-inflammatory property of 8-MOP was mediated by inhibiting nuclear factor kappa-light-chain-enhancer of activated B cells activation and STAT1 phosphorylation. Taken together, 8-MOP could protect cells from inflammatory injury induced by LPS, and may be a potential agent against bovine mastitis.

Effect of bovine leukemia virus on bovine mammary epithelial cells

Bovine leukemia virus (BLV) is a retrovirus that infects cattle and is associated with an increase in secondary infections. The objective of this study was to analyze the effect of BLV infection on cell viability, apoptosis and morphology of a bovine mammary epithelial cell line (MAC-T), as well as Toll like receptors (TLR) and cytokine mRNA expression. Our findings show that BLV infection causes late syncytium formation, a decrease in cell viability, downregulation of the anti-apoptotic gene Bcl-2, and an increase in TLR9 mRNA expression. Moreover, we analyzed how this stably infected cell line respond to the exposure to Staphylococcus aureus (S. aureus), a pathogen known to cause chronic mastitis. In the presence of S. aureus, MAC-T BLV cells had decreased viability and decreased Bcl-2 and TLR2 mRNA expression. The results suggest that mammary epithelial cells infected with BLV have altered the apoptotic and immune pathways, probably affecting their response to bacteria and favoring the development of mastitis.

Effects of Neutrophil Extracellular Traps on Bovine Mammary Epithelial Cells in vitro

Bovine mastitis is a common infectious disease which causes huge economic losses in dairy cattle. Bovine mammary epithelial cell (BMEC) damage usually directly causes the decrease of milk production, which is one of the most important causes of economic loss. NETs, novel effector mechanisms, are reported to exacerbate the pathogenesis of several inflammatory diseases. NETs formation has also been observed in the milk and mammary glands of sheep. However, the effects and detailed mechanisms of NETs on BMEC damage remain unclear. Thus, we aim to examine the effects of NETs on BMECs in vitro, and further to investigate the detail mechanism. In this study, the cytotoxicity of NETs on BMECs was determined using lactic dehydrogenase (LDH) levels in culture supernatants. Histone-induced BMEC damage was examined by flow cytometry and immunofluorescence analysis. The activities of caspase 1, caspase 3, caspase 11, and NLRP3 was detected using western blotting and immunohistochemical analysis. The results showed that NETs and their component histone significantly increased cytotoxicity to BMECs, suggesting the critical role of NETs, and their component histone in BMEC damage. In addition, histone could also induce necrosis, pyroptosis, and apoptosis of BMECs, and the mechanisms by which histone leads to BMEC damage occurred via activating caspase 1, caspase 3, and NLRP3. Altogether, NETs formation regulates inflammation and BMEC damage in mastitis. Inhibiting excess NETs formation may be useful to ameliorate mammary gland damage associated with mastitis.

The in vitro host cell immune response to bovine-adapted Staphylococcus aureus varies according to bacterial lineage

Mastitis is the most economically important disease affecting dairy cattle worldwide. Staphylococcus aureus is a highly prevalent cause of mastitis, causing infections ranging from sub-clinical to gangrenous. However, the interaction between the genotype of the infecting strain of S. aureus and the host response remains largely uncharacterised. To better understand the variation in presentation and outcomes of S. aureus-mediated bovine mastitis, we studied the interaction of a panel of mastitis isolates from several prominent bovine-associated lineages with bovine mammary epithelial cells (bMEC) and neutrophils. Significant differences in immune gene expression by infected primary or immortalised bMEC, or their elaboration of neutrophil chemoattractants, were observed and were dependent on the lineage of the infecting strain. Differences were also apparent in the invasiveness of S. aureus strains and their ability to survive killing by neutrophils. Our results demonstrate that a range of immune responses occur, suggesting the importance of S. aureus strain in dictating mastitis disease course. S. aureus lineages may therefore have adopted differing strategies for exploitation of the intramammary niche. Consequently, improved diagnosis of infecting lineage may enable better prognosis for S. aureus mastitis and reduce morbidity and economic loss.

In vitro characteristics of an airway barrier-disrupting factor secreted by Staphylococcus aureus

BACKGROUND

Staphylococcus aureus is a major contributor to the pathophysiology of chronic rhinosinusitis (CRS). Previous research has shown that S. aureus-secreted products disrupt the airway barrier.

METHODS

S. aureus ATCC 13565 and 25923 strains were grown at exponential, postexponential, and stationary phases. Microbial conditioned media (CM) was collected from the cultures and ultrafiltered (UF). Liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) was performed on the UF-CM. UF-CM was subjected to heat and protease treatment, size fractionation, and ultracentrifugation (UC) separation. Human nasal epithelial cells grown at air-liquid interface (HNEC-ALI) cultures were exposed to purified alpha hemolysin (Hla), staphylococcal enterotoxin A (SEA), lipoteichoic acid (LTA), and UF-CM. Barrier function outcomes were measured by transepithelial electrical resistance (TEER) and apparent permeability (Papp). UC fraction exposed cultures were subjected to immunofluorescence microscopy for tight junction (TJ) protein zonula occludens-1 (ZO-1).

RESULTS

LC-ESI-MS/MS identified 107 proteins, with Hla being most abundant. Hla, SEA, and LTA did not alter the HNEC-ALI barrier as measured by TEER or Papp. Barrier disruption caused by UF-CM peaked in the postexponential phase, was sensitive to heat and protease treatment, >30-kDa in size, and enriched in the UC fraction. HNEC-ALI exposed to UF-CM and UC demonstrated loss of ZO-1 localization.

CONCLUSION

These results suggest that the S. aureus factor responsible for TJ disruption in HNEC-ALI cultures is either a protein-macromolecule or a combination of secreted factors. The product is enriched in the UC fraction, suggesting it is associated with large structures such as membrane components or vesicles.

LncRNA XIST mediates bovine mammary epithelial cell inflammatory response via NF-κB/NLRP3 inflammasome pathway

Objectives

The correlations between long non‐coding RNAs (lncRNAs) and diverse mammal diseases have been clarified by many researches, but the cognition about bovine mastitis‐related lncRNAs remains limited. This study aimed to investigate the potential role of lncRNA X‐inactive specific transcript (XIST) in the inflammatory response of bovine mammary epithelial cells.

Materials and methods

Two inflammatory bovine mammary alveolar cell‐T (MAC‐T) models were established by infecting the cells with Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The expressions of pro‐inflammatory cytokines were measured, and the proliferation, viability and apoptosis of the inflammatory cells were evaluated after XIST was knocked down by an siRNA. The relationship among XIST, NF‐κB pathway and NOD‐like receptor protein 3 (NLRP3) inflammasome was investigated using an inhibitor of NF‐κB signal pathway.

Results

The expression of XIST was abnormally increased in bovine mastitic tissues and inflammatory MAC‐T cells. Silencing of XIST significantly increased the expression of E. coli or S. aureus‐induced pro‐inflammatory cytokines. Additionally, knockdown of XIST could inhibit cell proliferation, suppress cell viability and promote cell apoptosis under inflammatory conditions. Furthermore, XIST inhibited E. coli or S. aureus‐induced NF‐κB phosphorylation and the production of NLRP3 inflammasome.

Conclusions

The expression of XIST was promoted by activated NF‐κB pathway and, in turn, XIST generated a negative feedback loop to regulate NF‐κB/NLRP3 inflammasome pathway for mediating the process of inflammation.

Innate immune response of bovine mammary epithelial cells to Mycoplasma bovis

Mycoplasma spp. are contagious bacteria, and mycoplasmal mastitis is a serious productivity problem on dairy farms. Bovine mammary epithelial cells (bMECs) have an important role in the elimination of pathogens, but the effect of Mycoplasma bovis on bMECs has not been fully described. To elucidate the immune response against intramammary infection by M. bovis, we undertook microarray analysis to examine and profile mRNA expression in bMECs after stimulation with M. bovis. We also compared the effects of M. bovis, Staphylococcus aureus, and Escherichia coli on immune-related mRNA expression in bMECs. Transcriptome analysis indicated a significant decrease in the level of mRNA-encoding lysine-specific demethylase 4D, suggesting that the immune response is suppressed by a decrease in histone demethylase activity. Interleukin (IL)-1β, IL-6, tumor necrosis factor alpha, toll-like receptor (TLR) 2, and TLR4 mRNA expression levels were significantly increased in bMECs stimulated with heat-killed M. bovis, but the expression levels were lower than those following stimulation by heat-killed S. aureus or E. coli. Our results suggest that M. bovis weakly affects mRNA expression in bMECs compared to the effects of E. coli or S. aureus. Moreover, live M. bovis may induce suppression of the immune response in bMECs.

Stable infection of a bovine mammary epithelial cell line (MAC-T) with bovine leukemia virus (BLV)

Bovine leukemia virus (BLV) is a retrovirus that affects cattle causing a lymphoproliferative disease. BLV infection has been associated with misbalance of the immune response causing a higher incidence of other infections. Mastitis is one of the most important conditions that affect milk production in cattle. The aim of this study was to stably infect a bovine mammary epithelial cell line (MAC-T). MAC-T cell line was successfully infected with BLV and the infection was confirmed by nested PCR, qPCR, immunocytochemistry, western blot and transmission electron microscopy. This is the first report of a bovine mammary epithelial cell line stably infected with BLV. This new cell line could be used as an in vitro model to study the effect of BLV on the immune response in the mammary gland and the relationship with other agents causing mastitis.

Lactobacillus casei BL23 modulates the innate immune response in Staphylococcus aureus-stimulated bovine mammary epithelial cells

Probiotics have been adopted to treat and prevent various diseases in humans and animals. They were notably shown to be a promising alternative to prevent mastitis in dairy cattle. This inflammation of the mammary gland is generally of infectious origin and generates extensive economic losses worldwide. In a previous study, we found that Lactobacillus casei BL23 was able to inhibit the internalisation of Staphylococcus aureus, one of the major pathogens involved in mastitis, into bovine mammary epithelial cells (bMEC). In this study, we further explored the capacity of this strain to modulate the innate immune response of bovine mammary epithelial cells during S. aureus infection. L. casei BL23 was able to decrease the expression of several pro-inflammatory cytokines, including interleukins 6, 8, 1α and 1β and tumour necrosis factor alpha, in S. aureus-stimulated bMEC, 8 h post-infection. On the other hand, L. casei did not impair the induction of defensins, such as lingual antimicrobial peptide and defensin β1 in the presence of S. aureus, and even slightly increased the induction of tracheal antimicrobial peptide during S. aureus infection. Finally, this strain did not alter the expression of the pattern recognition receptor nucleotide-binding oligomerisation domain proteins (NOD2). This study demonstrates that L. casei BL23 displayed anti-inflammatory properties on S. aureus-stimulated bMEC. These results open the way to further characterisation of the BL23 probiotic potential in a bovine mammary gland context and to a better understanding of how all these beneficial properties combine in vivo to combat mastitis pathogens.

Genome-Wide Association Study for Susceptibility to and Recoverability From Mastitis in Danish Holstein Cows

Because mastitis is very frequent and unavoidable, adding recovery information into the analysis for genetic evaluation of mastitis is of great interest from economical and animal welfare point of view. Here we have performed genome-wide association studies (GWAS) to identify associated single nucleotide polymorphisms (SNPs) and investigate the genetic background not only for susceptibility to – but also for recoverability from mastitis. Somatic cell count records from 993 Danish Holstein cows genotyped for a total of 39378 autosomal SNP markers were used for the association analysis. Single SNP regression analysis was performed using the statistical software package DMU. Substitution effect of each SNP was tested with a t-test and a genome-wide significance level of P-value < 10^-4 was used to declare significant SNP-trait association. A number of significant SNP variants were identified for both traits. Many of the SNP variants associated either with susceptibility to – or recoverability from mastitis were located in or very near to genes that have been reported for their role in the immune system. Genes involved in lymphocyte developments (e.g., MAST3 and STAB2) and genes involved in macrophage recruitment and regulation of inflammations (PDGFD and PTX3) were suggested as possible causal genes for susceptibility to – and recoverability from mastitis, respectively. However, this is the first GWAS study for recoverability from mastitis and our results need to be validated. The findings in the current study are, therefore, a starting point for further investigations in identifying causal genetic variants or chromosomal regions for both susceptibility to – and recoverability from mastitis.

Mechanism of pattern recognition receptors (PRRs) and host pathogen interplay in bovine mastitis

Bacterial infection in the mammary gland parenchyma induces local and subsequently systemic inflammation that results in a complex disease. Mastitis in bovine is the result of various factors which function together. This review is aimed to analyze the factors involved in the pathogenesis of common bacterial species for bovine mastitis. The bacterial growth patterns, signaling pathway and the pathogen-associated molecular patterns (PAMPs) which activate immune responses is discussed. Clear differences in bacterial infection pattern are shown between bacterial species and illustrated TLRs, NLRs and RLGs molecular mechanism for the initiation of intramammary infection. The underlying reasons for the differences and the resulting host response are analyzed. Understandings of the mechanisms that activate and regulate these responses are central to the development of efficient anticipatory and treatment management. The knowledge of bovine mammary gland to common mastitis causing pathogens with possible immune mechanism could be a new conceptual understanding for the prospect of mastitis control program.

Comparison of microRNA Profiles between Bovine Mammary Glands Infected with Staphylococcus aureus and Escherichia coli

MicroRNAs (miRNAs) play crucial roles in regulating innate and adaptive immunity in humans and animals. Infection with E. coli or S. aureus can cause inflammation of the mammary glands, which results in significant economic losses in dairy cattle. However, the regulatory mechanisms of miRNAs in response to E. coli or S. aureus infection in bovine mammary glands have not been thoroughly explored. To discover the differential expression of miRNA in bovine mammary gland challenged with E. coli or S. aureus, we performed miRNA sequencing on tissue samples. A total of 1838 miRNAs were identified, including 580 known-miRNAs (included in the miRbase database) and 1258 predicted novel miRNAs. The miRNA expression patterns indicated that, compared with control samples, 279 miRNAs and 305 miRNAs were differentially expressed miRNAs (DIE-miRNA) in S. aureus and E. coli infected tissues, respectively. Moreover, the results of comparison the DIE-miRNAs between the E. coli and S. aureus infected groups showed that 197 DIE-miRNAs are identical, 108 DIE-miRNAs are specific to the E. coli group, and 82 DIE-miRNAs are specific to the S. aureus group. Many DIE-miRNAs, such as bta-miR-144, bta-miR-451 and bta-miR-7863, might be the useful biomarkers of mastitis caused by E. coli and S. aureus. In addition, target genes of the DIE-miRNAs were predicted. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis indicated that these DIE-miRNAs are likely involved in many immune signaling pathways, including the Toll-like receptor signaling pathways, MAPK signaling pathway, cell adhesion molecules, TGF-β signaling pathway, leukocyte trans endothelial migration, cytokine-cytokine receptor interaction, and chemokine signaling pathways. This study has provided supportive evidence that miRNAs may serve as diagnostic biomarkers of mastitis in dairy cows, and suggests potentially of effective strategies to combat mastitis.

Preconditioning with Lipopolysaccharide or Lipoteichoic Acid Protects against Staphylococcus aureus Mammary Infection in Mice

Staphylococcus aureus is one of the most causative agents of mastitis and is associated with chronic udder infections. The persistency of the pathogen is believed to be the result of an insufficient triggering of local inflammatory signaling. In this study, the preclinical mastitis model was used, aiming to evaluate if lipopolysaccharide (LPS) or lipoteichoic acid (LTA) preconditioning could aid the host in more effectively clearing or at least limiting a subsequent S. aureus infection. A prototypic Gram-negative virulence factor, i.e., LPS and Gram-positive virulence factor, i.e., LTA were screened whether they were able to boost the local immune compartment. Compared to S. aureus-induced inflammation, both toxins had a remarkable high potency to efficiently induce two novel selected innate immunity biomarkers i.e., lipocalin 2 (LCN2) and chitinase 3-like 1 (CHI3L1). When combining mammary inoculation of LPS or LTA prior to a local S. aureus infection, we were able to modulate the innate immune response, reduce local bacterial loads, and induce either LCN2 or CHI3L1 at 24 h post-infection. Clodronate depletion of mammary macrophages also identified that macrophages contribute only to a limited extend to the LPS/LTA-induced immunomodulation upon S. aureus infection. Based on histological neutrophil influx evaluation, concomitant local cytokine profiles and LCN2/CHI3L1 patterns, the macrophage-independent signaling plays a major role in the LPS- or LTA-pretreated S. aureus-infected mouse mammary gland. Our results highlight the importance of a vigilant microenvironment during the innate immune response of the mammary gland and offer novel insights for new approaches concerning effective immunomodulation against a local bacterial infection.

Bovine miR-146a regulates inflammatory cytokines of bovine mammary epithelial cells via targeting the TRAF6 gene

It has been reported previously that bovine miR-146a (bta-miR-146a) is significantly differentially expressed in mammary glands infected with mastitis, compared with healthy udders. This suggests that bta-miR-146a plays an important role in the regulation of mammary inflammation. However, the specifics of this function have yet to be elucidated. Bovine mammary epithelial cells (bMEC) represent the first line of defense against pathogens and have important roles in initiating and regulating inflammatory responses and innate immunity during infection. In this study, a double luciferase reporter assay was used to confirm that bta-miR-146a directly targets the 3' UTR of the tumor-necrosis factor receptor-associated factor 6 (TRAF6) gene. To elucidate the role of bta-miR-146a in innate immune responses, either a mimic or inhibitor of bta-miR-146a was transfected into bMEC stimulated with lipopolysaccharide, which activates the innate immune response through the toll-like receptor (TLR) 4/nuclear factor (NF)-κB signaling pathway. Forty-eight hours posttransfection, quantitative real-time PCR and Western blots were used to detect the expressions of the related genes and proteins, respectively. An ELISA was used to measure the quantity of inflammatory factors in culture supernatants. The results showed that bta-miR-146a significantly inhibits both mRNA and protein expression levels of bovine TRAF6, and ultimately suppresses downstream expression of NF-κB mRNA and protein. As a result, production of NF-κB-dependent inflammatory mediators such as tumor necrosis factor α, IL-6, and IL-8 are suppressed following lipopolysaccharide stimulation of bMEC. Thus, we concluded that bta-miR-146a acts as a negative feedback regulator of bovine inflammation and innate immunity through downregulation of the TLR4/TRAF6/NF-κB pathway. This study presents a potential regulatory mechanism of bta-miR-146a on immune responses in bovine mammary infection and may provide a potential therapeutic target for mastitis.

Sodium acetate inhibits Staphylococcus aureus internalization into bovine mammary epithelial cells by inhibiting NF-κB activation

Bovine mastitis is one of the most costly and prevalent disease affecting dairy cows worldwide. It was reported that Staphylococcus aureus could internalize into bovine mammary epithelial cells (bMEC) and induce mastitis. Some short chain fatty acids (SCFA) have shown to suppress S. aureus invasion into bMEC and regulate antimicrobial peptides expression. But it has not been evaluated that sodium acetate has the similar effect. The aim of this study was to investigate the effect of sodium acetate on the invasion of bovine mammary epithelial cells (bMEC) by S. aureus. Gentamicin protection assay showed that the invasion of S. aureus into bMEC was inhibited by sodium acetate in a dose-dependent manner. Sodium acetate (0.25-5 mM) did not affect S. aureus growth and bMEC viability. The TAP gene level was decreased, while the BNBD5 mRNA level was enhanced in sodium acetate treated bMEC. In sodium acetate treated and S. aureus challenged bMEC, the TAP gene expression was increased and BNBD5 gene expression was not modified at low concentrations, but decreased at high concentrations. The Nitric oxide (NO) production of bMEC after S. aureus stimulation was decreased by sodium acetate treatment. Furthermore, sodium acetate treatment suppressed S. aureus-induced NF-κB activation in bMEC in a dose manner. In conclusion, our results suggested that sodium acetate exerts an inhibitory property on S. aureus internalization and modulates antimicrobial peptides gene expression.

Sodium houttuyfonate inhibits LPS-induced inflammatory response via suppressing TLR4/NF-ĸB signaling pathway in bovine mammary epithelial cells

Mastitis is an inflammatory reaction caused by microorganisms in the mammary gland which usually leads to the decrease of the dairy production. It vastly makes bad effect on the cattle industry all over the world. Nowadays, an increasing number of scientists keep a watchful eye on natural compounds to prevent mastitis. Sodium houttuyfonate (SH) has been reported to have antibacterial and anti-inflammatory effects. This experiment aimed to investigate the anti-inflammatory properties of SH on LPS-stimulated primary bovine mammary epithelial cells (bMEC). The effects of SH on TNF-α, IL-1β, and IL-6 production were detected by qRT-PCR. Western blot analysis was used for detecting the effects of SH on TLR4/NF-κB signal pathways. The results showed that SH significantly inhibited LPS-stimulated TNF-α, IL-1β and IL-6 production. Furthermore, SH significantly inhibited LPS-induced TLR4 expression and NF-ĸB activation. In summary, these results suggested that SH inhibited LPS-induced inflammatory response by inhibiting TLR4/NF-ĸB signaling pathway. SH is a potential agent for the treatment of mastitis.