miR-122 regulates the JAK-STAT signalling pathway by down-regulating EPO in the mammary gland during Streptococcus agalactiae-induced mastitis

MicroRNA (miRNA) are single-stranded non-coding RNA of approximately 22 nucleotides estimated to regulate 60% of human and animal genes some of which are associated with cell differentiation, signal transduction and immune processes. Streptococcus agalactiae (S. agalactiae)-induced bovine mastitis is associated with up-regulation of miR-122 and down-regulation of erythropoietin (EPO) abundance in mammary gland tissue. TargetScan analysis revealed that EPO is a predicted target gene of miR-122 and this regulatory relationship was verified by dual-luciferase reporter assay. Overexpression of miR-122 in primary bovine mammary cells led to down-regulation of EPO and also the JAK-STAT signalling pathway genes EPOR, JAK2, STAT5A and STAT5B. Accordingly, the mRNA abundance of BCL-2, a downstream gene in the JAK-STAT signalling pathway was significantly down-regulated. Under conditions of miR-122 inhibition, EPO, EPOR, JAK2, STAT5A and STAT5B were up-regulated. These results demonstrated that, through its action on EPO, miR-122 may play an important role in S. agalactiae-induced mastitis by regulating the JAK-STAT signalling pathway.Highlights Understanding the relationship among miR-122, EPO and the JAK-STAT pathway would be helpful in developing new strategies for controlling mastitis.