Protective Roles of Folic Acid in the Responses of Bovine Mammary Epithelial Cells to Different Virulent Staphylococcus aureus Strains

Simple Summary: Mastitis caused by zoonotic Staphylococcus aureus (S. aureus) is hard to cure. The cross-talk between host, pathogen, and environment influences bovine resistance to S. aureus infection. Our previous study observed that the inflammation of bovine mammary gland could be reduced by folic acid, i.e., a kind of beneficial micronutrient. However, the heterogeneity of inflammatory responses in bovine mammary epithelial cells challenged with different virulent S. aureus strains and the protective effects of folic acid on improving host defense against S. aureus infection are still unclear. RNA-seq was performed to investigate the effects of different S. aureus lineages and folic acid on the global transcriptome of bovine mammary epithelial cells (Mac-T cell line). Functional enrichment analysis indicated different S. aureus strains share few differentially expressed and spliced genes and activate host differentially inflammatory responses, and folic acid plays the protective role in host defense against the S. aureus challenge partially through activating cytoplasmic DNA sensing and tight junction pathway. This study provides novel insights into the improvement of S. aureus mastitis defense. Mastitis caused by Staphylococcus aureus (S. aureus) infection is one of the most difficult diseases to treat in dairy cattle. Exploring the biological progression of S. aureus mastitis via the interaction between host, pathogen, and environment is the key to an effective and sustainable improvement of animal health. Here, two strains of S. aureus and a strain of MRSA (Methicillin-resistant Staphylococcus aureus) isolated from cows with different inflammation phenotypes were used to challenge Mac-T cells and to investigate their effects on the global transcriptome of the cells, then to explore the potential regulatory mechanisms of folic acid on S. aureus mastitis prevention. Differential gene expression or splicing analysis showed that different strains of S. aureus led to distinct transcriptional responses from the host immune system. Folic acid could protect host defense against the challenge of S. aureus and MRSA partially through activating cytoplasmic DNA sensing and tight junction pathway. ZBP1 at the upstream of cytoplasmic DNA sensing pathway was verified and related to anti-pathogen through RNA interference. Further enrichment analysis using these transcriptome data with cattle large-scale genome-wide association study (GWAS) data confirmed that ZBP1 gene is highly associated with bovine somatic cell score (SCS) trait. Our data shed light on the potential effect of FA through regulating key gene and then protect host cells' defense against S. aureus and MRSA.