Staphylococcus aureus induces TGF-β1 and bFGF expression through the activation of AP-1 and NF-κB transcription factors in bovine mammary gland fibroblasts

• S. aureus upregulated TGF-β1 and bFGF mRNA expression and secretion.
• S.aureus increased the mRNA and protein expression of TLR2 and TLR4.
• S. aureus increased the protein expression of p-NF-κB and p-c-jun.
• The increase in TGF-β1 and bFGF expression was shown to be inhibited by AP-1- and NF-κB-specific inhibitors.

Staphylococcus aureus is a common Gram-positive pathogen that causes bovine mastitis, a persistent infection of the bovine mammary gland. To better understand the importance of bovine mammary fibroblasts (BMFBs) and the roles of the TLR–NF-κB and TLR–AP-1 signaling pathways in the regulation of S. aureus-associated mastitis and mammary fibosis, BMFBs cultured in vitro were stimulated with different concentrations of heat-inactivated S. aureus to analyze the gene and protein expression of toll-like receptor 2 (TLR2), toll-like receptor 4 (TLR4), transforming growth factor beta 1 (TGF-β1), basic fibroblast growth factor (bFGF) as well as the protein expression of nuclear factor-kappa B (NF-κB) and activation protein-1 (AP-1) by means of quantitative polymerase chain reaction (qPCR) and western blotting, respectively. Specific NF-κB and AP-1 inhibitors were also used to investigate their effects on the regulation of TGF-β1 and bFGF expression. The results indicated that, in addition to increasing mRNA and protein expression of TLR2 and TLR4, S. aureus could also upregulate TGF-β1 and bFGF mRNA expression and secretion through the activation of NF-κB and AP-1. The increase in TGF-β1 and bFGF expression was shown to be inhibited by AP-1- and NF-κB-specific inhibitors. Taken together, S. aureus induces TGF-β1 and bFGF expression through the activation of AP-1 and NF-κB in BMFBs. This information offers new potential targets for the treatment of bovine mammary fibrosis.