Lactoferrin (LF), a member of the transferrin family, is widely present in mammalian milk and other secretions, exhibiting anti-inflammatory, antibacterial, and anti-infective properties. Although the biological functions of LF have been extensively studied, there are few reports on its effects and molecular mechanisms concerning bovine mastitis caused by bacterial infection. This study used bovine mammary epithelial cells (BMECs) cultured in vitro as the research model. An inflammatory injury model was established by stimulating BMECs with LPS to investigate whether LF at different concentrations (10, 50, 100, and 200 μg·mL⁻¹) could inhibit the inflammatory response before and after the onset of inflammation. The expression of inflammatory cytokines IL-1β, IL-6, IL-8, and TNF-α at both the gene and protein levels was detected using RT-qPCR and ELISA. Western blotting was employed to evaluate the phosphorylation levels in the inflammatory signaling pathways MAPK/P38/ERK and NF-κB/P65, while RT-qPCR was used to examine the impact on TLR4 receptor gene expression. The results display that pretreatment with LF prior to LPS-induced inflammation in BMECs reduced the expression of inflammatory cytokines IL-1β, IL-6, IL-8, and TNF-α at both the gene and protein levels (p < 0.05). LF also inhibited the phosphorylation of NF-κB/P65 and MAPK/P38/ERK signaling pathways and downregulated TLR4 receptor gene expression (p < 0.05). However, when LF was added after the onset of LPS-induced inflammation, inflammatory cytokine expression and phosphorylation levels in the NF-κB/P65 and MAPK/P38/ERK pathways remained elevated, along with high expression of the TLR4 receptor gene (p < 0.05). These findings show that LF can antagonize LPS-induced inflammatory responses in BMECs and reduce cytokine expression, exhibiting anti-inflammatory effects when administered before inflammation. Conversely, when LF is added post-inflammation, it appears to enhance cytokine expression, potentially promoting the recruitment of more cells or factors to resolve inflammation rapidly. Both effects are mediated through the TLR4 receptor and the NF-κB/P65 and MAPK/P38/ERK signaling pathways.

The aim of this study is to explore the mechanism of IL-17A infection in the development of bacterial mastitis in dairy cows. In this study, RT-qPCR and ELISA were used to measure the promoting effect of IL-17A on the generation of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) and chemokine (IL-8). In addition, Western blot (WB) was applied to measure the influences of IL-17A on the inflammation-related ERK and p38 proteins in the MAPK pathways. The results show that under the stimulation of LPS on cow mammary epithelial cells (CMECs), cytokines IL-1β, IL-6, IL-8, TNF-α, and IL-17A will exhibit significantly increased expression levels (p < 0.05). With inhibited endogenous expression of IL-17A, cytokines IL-1β, IL-6, IL-8, and TNF-α will present reduced genetic expression (p < 0.01), with reduced phosphorylation levels of ERK and p38 proteins in the MAPK signaling pathways (p < 0.001). Upon the exogenous addition of the IL-17A cytokine, the genetic expression of cytokines IL-1β, IL-6, IL-8, and TNF-α will increase (p < 0.05), with increased phosphorylation levels of the ERK and p38 proteins in the MAPK signaling pathways (p < 0.001). These results indicate that under the stimulation of CMECs with LPS, IL-17A can be expressed together with relevant inflammatory cytokines. Meanwhile, the inflammatory responses of mammary epithelial cells are directly proportional to the expression levels of IL-17A inhibited alone or exogenously added. In summary, this study shows that IL-17A could be used as an important indicator for assessing the bacterial infections of mammary glands, indicating that IL-17A could be regarded as one potential therapeutic target for mastitis.

Bovine mastitis is one of the most prevalent and economically significant diseases affecting dairy cows worldwide, with Escherichia coli (E. coli) recognized as one of the principal pathogens causing acute mastitis. The innate immune system plays a crucial role in the defense of the bovine mammary gland, serving as the first line of defense against pathogen invasion. This study elucidated the pathological mechanisms and immune response-related molecular regulatory networks involved in E. coli-induced bovine mastitis. Histopathological and apoptosis analyses of mammary tissues were performed using hematoxylin-eosin (HE) staining and TUNEL staining, respectively, while RNA sequencing (RNA-seq) was conducted to identify differentially expressed genes (DEGs) and their associated signaling pathways. HE staining revealed typical inflammatory lesions in the mammary glands of mastitis cows. TUNEL staining further confirmed that the level of apoptosis in the mastitis group was significantly higher than in the healthy control group (p < 0.0001). RNA-seq analysis identified 2717 DEGs, with 2238 upregulated and 479 downregulated genes. The top 20 significantly upregulated genes (e.g., S100A12, IL1RN, IL1R2, CXCL8, SAA3, S100A8, S100A9, TREML2, TREM1, M-SAA3.2, PTX3, MMP9) were predominantly involved in inflammatory immune regulation, acute phase responses (e.g., HP, SAA3), and cellular signal transduction (e.g., PLEK, LPAR3). Gene Ontology (GO) enrichment analysis revealed that these DEGs were mainly associated with biological processes, such as signal transduction, immune response, inflammatory response, and transcriptional regulation. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that these DEGs were significantly enriched in key inflammatory and immune regulatory pathways, including the TNF signaling pathway, C-type lectin receptor signaling pathway, Chemokine signaling pathway, NOD-like receptor signaling pathway, NF-κ B signaling pathway, and IL-17 signaling pathway, suggesting that these pathways play central roles in the mammary immune defense against E. coli infection. In conclusion, this study demonstrated at the histopathological, cellular apoptosis, and transcriptomic levels that E. coli infection induces mammary tissue damage and apoptosis by activating immune and inflammation-related genes (S100A12, IL1RN, IL1R2, CXCL8, SAA3, S100A8, S100A9, TREML2, TREM1, M-SAA3.2, PTX3, MMP9) and key signaling pathways (TNF signaling pathway, C-type lectin receptor signaling pathway, Chemokine signaling pathway, NOD-like receptor signaling pathway, NF-κ B signaling pathway, IL-17 signaling pathway). The findings of this study provide a theoretical basis for probing into the pathogenesis of bovine mastitis and the development of targeted interventions.

The bovine mammary gland, the exclusive site of milk synthesis, is a structurally specialized tissue that houses distinct cellular subsets, yet it remains highly susceptible to major mastitis pathogens, including Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli. Infection disrupts redox homeostasis, leading to excessive accumulation of reactive oxygen species (ROS) and rapid activation of antioxidant pathways. In this study, we integrated 16S DNA sequencing, histopathology (hematoxylin and eosin), and immunohistochemistry to map the mastitis-associated microbiota and visualize oxidative-damage foci in mammary tissues challenged by Staphylococcus aureus, Streptococcus agalactiae, or Escherichia coli. Quantitative reverse transcription polymerase chain reaction and Western blot analyses were subsequently performed on the same samples to measure the kinetic response of six oxidative-stress-related signalling nodes: adenosine 5′-monophosphate-activated protein kinase, cytochrome P450 1A1, heme oxygenase 1, nitric oxide synthase, mammalian target of rapamycin, and superoxide dismutase. By correlating the temporal expression patterns of these genes/proteins with ROS accumulation and histological severity, this study delineates the molecular cascade linking oxidative imbalance to mastitis pathology, providing data-driven targets for future preventive and therapeutic strategies.

Bovine mastitis is a condition typically induced by various pathogens, with Escherichia coli (E. coli) being a common causative agent known for its propensity to cause persistent infections. In experimental models of bovine mastitis, lipopolysaccharide (LPS), a key component of the E. coli cell wall, is frequently employed as an inducer. The extracellular matrix (ECM) is regulated by MMPs, TIMPs, and the uPA system. They collectively participate in ECM degradation and remodeling and have been identified as promising targets for mastitis treatment. However, investigations into the precise mechanisms underlying E. coli and LPS-induced mastitis, as well as the relationship between bovine mastitis and the MAPK signaling pathway, remain limited. In this study, bovine mammary epithelial cells (BMECs) were treated in vitro with 10⁶ CFU/mL heat-inactivated E. coli, 7.5 µg/mL LPS, or a combination of both. The treatments resulted in varying degrees of activation of the MAPK signaling pathway, specifically ERK1/2, JNK, and P38. BMECs were exposed to MAPK inhibitors (the JNK inhibitor SP600125, the ERK inhibitor PD98059, and the P38 inhibitor SB203580) after treatments with heat-inactivated E. coli (10⁶ CFU/mL), LPS (7.5 µg/mL), or a combination of the two for 6, 12, 24, and 48 h. The mRNA and protein levels of MMP-1, MMP-2, MMP-3, MMP-9, MMP-13, TIMP-1, TIMP-2, uPA, uPAR, and PAI-1 were assessed using RT-qPCR and Western blot analysis. The findings indicated that heat-inactivated E. coli and LPS stimulated the expression of MAPK mRNAs (ERK1/2, P38, and JNK) in BMECs, along with corresponding increases in the phosphorylated proteins. Furthermore, MAPK inhibitors substantially upregulated the expression of TIMP-1, TIMP-2, and PAI-1. However, no significant changes were observed in the mRNA and protein levels of MMP-1, MMP-2, MMP-3, MMP-9, MMP-13, uPA, or uPAR. In conclusion, heat-inactivated E. coli and LPS can activate the MAPK signaling pathway in BMECs. Inhibiting this signaling pathway can modulate the expression of TIMP-1, TIMP -2, and PAI-1 at both mRNA and protein levels.

Bovine mastitis is a multifactorial inflammatory disease primarily characterized by inflammatory cell infiltration and the destruction of mammary alveoli. It is a major cause of reduced milk yield and quality. The imbalance between antioxidant defenses and the generation of reactive oxygen species (ROS), which occurs due to the high metabolic activity of the mammary gland during the periparturient period, increases the incidence of mastitis. During early lactation, especially in high-yielding dairy cows, the massive synthesis and secretion of milk increase the energy demand of mammary tissue, leading to excessive ROS accumulation. This results in cell membrane disruption and, ultimately, antioxidant dysfunction in the mammary tissue. This study established an in vitro oxidative stress model by treating bovine mammary epithelial cells (BMECs) with 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH). The optimal concentration of 1000 μmol/L AAPH was determined using the CCK-8 assay. Model validation showed that, compared to the control group, ROS levels were significantly elevated (p < 0.001) and mitochondrial membrane potential was significantly decreased (p < 0.001) in the AAPH-treated group. Transmission electron microscopy (TEM) analysis revealed that AAPH treatment caused ultrastructural damage, including reduced microvilli, mitochondrial swelling, disappearance of cristae, and vacuolization. Mechanistic studies demonstrated that AAPH treatment significantly upregulated the mRNA and protein expression of AMPK, HMOX-1, mTOR, NOS, and SOD (p < 0.001), while significantly downregulating CYP1A1 expression (p < 0.001). Pretreatment with N-acetylcysteine (NAC) effectively alleviated the oxidative stress damage caused by AAPH. This study successfully established an in vitro AAPH-induced oxidative stress model in BMECs and revealed its molecular mechanism of cellular damage. The damage occurs through modulation of the AMPK/mTOR signaling pathway and the regulation of antioxidant-related gene expression.