IL-1β induces increased tight junction permeability in bovine mammary epithelial cells via the IL-1β-ERK1/2-MLCK axis upon blood-milk barrier damage.

Bovine mastitis occurs frequently in dairy cows and is often caused by various aetiological organisms, for example, Escherichia coli. Lipopolysaccharide (LPS) is a key virulence factor of E. coli. In this study, we stimulated bovine mammary epithelial cells (BMECs) with LPS to investigate the global transcriptional response and identify specific proinflammatory factors that play important roles in blood-milk barrier damage during mastitis caused by E. coli. By performing RNA-seq, we identified a large number of significantly differentially expressed genes (DEGs) between the LPS-treated BMECs and the control cells. Among the DEGs, interleukin-1β (IL-1β) was selected because its messenger RNA expression was induced by LPS and its enrichment is involved in multiple inflammatory signal pathways, and its roles in blood-milk barrier damage during the process of mastitis were investigated. Exogenous IL-1β treatment damaged the integrity of the blood-milk barrier, as indicated by the increased BMEC tight junction (TJ) permeability and confirmed by in vitro and in vivo experiments. Furthermore, the IL-1β-induced increase in the BMEC TJ permeability was mediated by the IL-1β-ERK1/2-MLCK axis pathway. Our data provide insights into the functions of IL-1β in blood-milk barrier damage caused by mastitis in dairy cows.