Role of Quercetin in Modulating Inflammation and Epigenetic Regulation of <i>Staphylococcus aureus</i>-Induced Bovine Mastitis

Mastitis is a prevalent inflammatory disease in dairy herds and presents substantial economic and welfare challenges. Although antibiotics are the most widely used and effective treatment for mastitis, research into alternative antibiotics with plant-derived compounds has gained increasing attention due to the high side effects of antibiotics. Quercetin is known to play a crucial role in regulating inflammation, yet its role in preventing and treating mastitis requires further investigation. To fill this gap, we construct a bovine mastitis model using <i>Staphylococcus aureus</i> (<i>S. aureus</i>) as the pathogen and bovine mammary epithelial cells (BMECs) as the cell model. Based on this, our study further investigated the therapeutic potential of quercetin by using <i>in vitro</i> assays and murine models. Our results demonstrated that quercetin inhibited the inflammatory response and reduced morphological damage in <i>S. aureus</i>-induced BMECs by disrupting cell adhesion. Direct RNA sequencing revealed that multiple genes enriched in the TNF/IL-17 pathway were pivotal in the ability of quercetin to mitigate inflammation, which was influenced by N6-methyladenosine (m6A) methylation. Quercetin effectively modulated CCL5 expression, a key chemokine in inflammatory responses in <i>S. aureus</i>-induced BMECs, through m6A methylation mediated by YTHDF2, revealing a novel epigenetic mechanism in mastitis. RNA-seq analysis showed that quercetin significantly altered genes related to inflammation, extracellular matrix regulation, and matrix metalloproteinase activity, including MMP3, MMP1, MMP1A, and IGFBP3, indicating its impact on tissue remodeling and inflammation. Additionally, quercetin disrupted <i>S. aureus</i> adhesion to BMECs, inhibited biofilm formation, and reduced the severity of infection. The <i>in vivo</i> assay supported the notion that quercetin regulates CCL5 activity to alleviate the inflammatory response in an m6A-YTHDF2-dependent manner. This study demonstrated the dual role of quercetin in inflammation suppression and epigenetic modulation via m6A, positioning quercetin as a promising therapeutic for bovine mastitis and suggesting new treatment strategies targeting CCL5- and m6A-related pathways.