Abstract：Quercetin (QUE), an ingredient of traditional Chinese medicine, is a flavonoid compound with anti-inflammatory and antioxidant effects. This study aimed to investigate the protective mechanism of QUE against lipopolysaccharide (LPS)-induced inflammatory damage in mouse (Mus musculus) mammary epithelial cells (MMECs), and provide a theoretical basis for the treatment of clinical mastitis in dairy cows (Bos taurus). First, the optimal inflammatory concentration of LPS, the optimal dose of drug QUE and LPS+QUE were successfully screened by the Cell Counting Kit-8 (CCK-8) in an in vitro experiment. After that, LPS was used to induce inflammation, and MMECs were divided into control, model (10 μg/mL LPS), LPS+QUE high dose (125 μg/mL), LPS+QUE medium dose (62.5 μg/mL), and LPS+QUE low dose (31.25 μg/mL) groups. The growth status of MMECs was observed by morphology, MMECs were identified by immunofluorescence, and the relative expression of inflammatory-related factors were measured by qRT-PCR and Western blot. The results showed the existence of specific protein CK-18 in the cells which proved that the cells were MMECs; after 12 h of cell inflammation induced by 10 μg/mL LPS, the gene expression of inflammatory-related factors TNFα and IL6 were significantly higher than that of the blank control (P<0.01), proving successful induction of inflammation in MMECs; After QUE acted on MMECs, qRT-PCR and Western blot showed that inflammatory- related factors TNFα, IL6, NF-κB, and AKT gene and protein expression were down-regulated and appeared to be dosage dependent. Therefore, QUE might ameliorate LPS-induced mastitis in mice by inhibiting the PI3K-AKT/NF- κB signaling pathway, thereby reducing the expression of downstream inflammatory factors TNFα and IL6, and exerting anti-inflammatory effects. This study provides basic materials for the treatment of clinical mastitis in cows and the development of potential anti-inflammatory drugs.
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