Selenomethionine Suppressed TLR4/NF-κB Pathway by Activating Selenoprotein S to Alleviate ESBL Escherichia coli-Induced Inflammation in Bovine Mammary Epithelial Cells and Macrophages

Inflammation is the hallmark of extended-spectrum beta-lactamase (ESBL)-producingEscherichia coli-induced bovine mastitis. Organic selenium can activate pivotal proteins in immune responses and regulate the immune system. The present study aimed to investigate whether selenomethionine (SeMet) attenuates ESBLE. coli-induced inflammation in bovine mammary epithelial cells (bMECs) and macrophages. Cells were treated with 0, 5/10, 10/20, 20/40, or 40/60 mu M SeMet for 12 h and/or inoculated with ESBL-E. coli[multiplicity of infection (MOI) = 5] for 4/6 h, respectively. We assessed inflammatory responses, including selenoprotein S (SeS), Toll-like receptor 4 (TLR4), Ikappa-B (I kappa B), phospho-NF-kappa B p65 (Ser536), interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), and lactate dehydrogenase (LDH) activities. Treatment with 40/60 mu M SeMet promoted cell viability and inhibited LDH activities in both bMECs and macrophages. Inoculation with ESBL-E. colireduced cell viability, which was attenuated by SeMet treatment in bMECs and macrophages. SeMet increased ESBLE. coli-induced downregulation of SeS and decreased LDH activities, TLR4, I kappa B, phospho-NF-kappa B p65 (Ser536), IL-1 beta, and TNF-alpha protein expressions in bMECs and macrophages. In addition, knockdown of SeS promoted protein expression of TLR4-mediated nuclear factor-kappa (NF-kappa B) pathway and BAY 11-708 inhibited TNF-alpha and IL-1 beta protein levels in bMECs and macrophages after ESBL-E. colitreatment. Moreover, ESBL-E. coliinoculation increased monocyte chemoattractant protein 1 (MCP-1), C-C motif ligand 3 (CCL-3), and CCL-5 mRNA expressions in bMECs. In conclusion, ESBL-E. coliinduced expression of MCP-1, CCL-3, and CCL-5 in bMECs and then recruited and activated macrophages, whereas SeMet attenuated ESBLE. coli-induced inflammation through activated SeS-mediated TLR4/NF-kappa B signaling pathway in bMECs and macrophages.