Quercetin attenuates LTA-induced tight junction disruption in mammary epithelial cells by modulating autophagy via the AMPK/mTOR pathway.

Mastitis in dairy cows impairs lactation and limits the development of the dairy industry. Lipoteichoic acid (LTA), a virulence factor of Staphylococcus aureus, disrupts the blood-milk barrier in the mammary gland. Quercetin, known for its anti-inflammatory and antibacterial properties, was evaluated for its protective effects against LTA-induced tight junction (TJ) injury. We established a TJ injury model using LTA-treated MAC-T cells (a mammary epithelial cell line) and mouse mammary tissue. Results demonstrated that LTA compromised TJ integrity and induced dysregulated autophagy in MAC-T cells. Notably, quercetin treatment was associated with the inhibition of this autophagic dysregulation and attenuated the LTA-induced disruption of TJ protein expression. Further mechanistic studies revealed that both quercetin and Compound C (CC, an AMPK inhibitor) reduced autophagy levels and mitigated the LTA-induced decline in key TJ proteins, suggesting that quercetin is associated with the attenuation of LTA-induced TJ integrity disruption under inflammatory stress, which correlates with modulated changes in AMPK phosphorylation and the mTOR signaling pathway. In vivo mouse experiments confirmed that quercetin acts as a dual-action modulator that regulates baseline signaling while attenuating LTA-induced TJ protein damage. This protective process is mediated through the modulation of AMPK/mTOR-dependent autophagy, thereby suppressing LTA-induced autophagic dysregulation. These findings provide a theoretical basis for further research into alternative, non-antibiotic strategies for mastitis control.