Analysis of Differentially Expressed Proteins in Bovine Mammary Glands Infected with <i>Staphylococcus aureus</i>

Mastitis is among the most prevalent diseases in dairy cows, leading to substantial issues such as decreased milk yield and quality, reduced reproductive performance, early culling, and increased production costs. <i>Staphylococcus aureus</i>, a naturally occurring opportunistic pathogen, is majorly responsible for mastitis in dairy cows. Mammary tissues from healthy cows were used as a control group (M_C, <i>n</i> = 3), and mammary glands of Chinese Holstein cows infected with <i>S. aureus</i> (10⁵ colony-forming unit/mL) were used as experimental groups (M_S, <i>n</i> = 3). Histopathological examination and analysis of inflammatory factor expression confirmed the successful establishment of the mastitis model. Using label-free quantitative proteomics, we analyzed the protein expression profiles of normal healthy mammary tissues (M_C) and <i>S. aureus</i>-infected mammary tissues (M_S). The analysis identified 933 differentially expressed proteins in <i>S. aureus</i>-infected mammary tissues, with 608 upregulated and 325 downregulated proteins, compared with the healthy tissues. Gene ontology functional annotation indicated that these proteins are involved in biological processes such as oxidation-reduction, the extracellular region, and catalytic activity. The Kyoto Encyclopedia of Genes and Genomes enrichment unveiled that these proteins were associated with pathways including <i>S. aureus</i> infection, cell adhesion molecules, antigen processing, and presentation. According to the InterPro enrichment analysis, the immunoglobulin-like fold and pleckstrin homology domain were the most enriched structural domains. Integrated transcriptomic and proteomic analyses revealed that ETNK1 and VNN1 exhibited consistent expression trends at both the mRNA and protein levels, suggesting their potential roles as key regulators in the pathogenesis of mastitis. The results not only enhance our understanding of mastitis management at the protein level but also point the way to potential antimastitis targets.