Mir-122 Regulates The Jak-Stat Signalling Pathway By Down-Regulatingepoin The Mammary Gland Duringstreptococcus 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 thatEPOis 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 ofEPOand also the JAK-STAT signalling pathway genesEPOR,JAK2,STAT5AandSTAT5B. Accordingly, the mRNA abundance ofBCL-2, a downstream gene in the JAK-STAT signalling pathway was significantly down-regulated. Under conditions of miR-122 inhibition,EPO,EPOR,JAK2,STAT5AandSTAT5Bwere up-regulated. These results demonstrated that, through its action onEPO, miR-122 may play an important role inS. agalactiae-induced mastitis by regulating the JAK-STAT signalling pathway.