Lycium barbarum Polysaccharide Inhibits E. coli-Induced Inflammation and Oxidative Stress in Mammary Epithelial Cells of Dairy Cows via SOCS3 Activation and MAPK Suppression

Abstract

Escherichia coli (E. coli) is one of the main causative agents of mastitis in dairy cows. Lycium barbarum polysaccharide (LBP) has a variety of physiological effects as it has antioxidants, it is hypoglycemic, it has anti-aging properties, it is neuroprotective, immune boosting, and it has anti-inflammatory effects in vivo and in vitro. In this study, we examined whether LBP affects the expression of pro-inflammatory factors, and the mitogen-activated protein kinase (MAPK) signaling pathway via activation of the suppressor of cytokine signaling-3 (SOCS3) in E. coli-induced primary bovine mammary epithelial cell (pbMEC) inflammatory responses. The experiment was designed with the control group (NC), cells were treated with E. coli for 6 h as the E. coli group (E. coli), and cells were pretreated with 100 μg/mL or 300 μg/mL of LBP for 24 h, followed by the addition of E. coli for 6 h as the E. coli + low level (E + LL) or E. coli + high level (E + HL) groups. The addition of LBP did not alter the cell viability of pbMEC in a dose-dependent assay. Pretreatment with LBP significantly decreased the expression of pro-inflammatory genes (IL1B, MAPK14, COX-2, iNOS) and proteins (COX-2, IL-1β, TNF-α) in the cells challenged by E. coli as compared with the control group (p < 0.05). E. coli stimulation significantly increased the production of reactive oxygen species (ROS) and malondialdehyde (MDA) in pbMEC, and decreased the antioxidants’ capacity with regard to decreased superoxide dismutase (SOD) and total antioxidant capacity (T-AOC); however, pretreatment with LBP reversed the oxidative stress and inhibition of antioxidants in cells challenged by E. coli. Moreover, LBP reversed the upregulated expression of the components of the MAPK pathway (increased phosphorylation level of p38, JNK, and ERK), followed by E. coli stimulation. Consistently, cells exposed to E. coli strengthened the staining of p38, whereas pretreatment of LBP weakened the staining of p38 in cells challenged by E. coli. Notably, the expression of SOCS3 was increased by LBP added to the cells in a dose-dependent manner. Additionally, the level of decreased expression of proinflammatory factors (IL-1β, TNF-α, and COX-2) was higher in the E + LL group than in the E + HL group. These results indicate that LBP pretreatment is effective in the alleviation of E. coli-induced inflammatory and oxidative responses in pbMEC through activation of SOCS3 and depression of MAPK signaling. As such, this might help us to develop molecular strategies for mitigating the detrimental effects of clinical bovine mastitis.