Mycoplasma gallisepticum (MG) can target host cells and cause chronic respiratory disease (CRD) in chickens that is characterized by pMGA and concomitant. Although microRNAs (miRNAs) have been manifested are crucial regulatory noncoding RNAs with important effects on microbial pathogenesis and inflammatory response, how miRNAs regulate MG-induced inflammation remains to be discovered. The results showed that gga-miR-21 was up-regulated in MG-infected chicken embryonic lungs and MG infection of chicken embryo fibroblast cells (DF-1) compared with the control group. Overexpression of gga-miR-21 increased the inflammatory cytokines production, including tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and interleukin-8 (IL-8) after MG infection, knockdown of gga-miR-21 had thoroughly inverse effects. Gene expression data combined with bioinformatics analysis and luciferase reporter assays demonstrated that mitogen-activated protein kinase kinase kinase 1(MAP3K1) was a novel target of gga-miR-21. The inhibition of MAP3K1 by gga-miR-21 resulted in the accumulation of NF-κB in the nucleus, which in turn generate higher inflammatory cytokines. Furthermore, upregulation of gga-miR-21 significantly inhibited MG propagation and promoted MG-infected DF-1 cells proliferation by increasing the cell cycle progression and suppressing cell apoptosis. Our study provides evidence for proinflammatory effects of gga-miR-21 which is mediated at least in part by targeting MAP3K1 in the MG-infected DF-1 cells. gga-miR-21 activates MAPKs and NF-κB signaling pathways via targeting MAP3K1, and then promotes the production of inflammatory cytokines and cell proliferation by increasing the cell cycle progression and suppressing cell apoptosis to defend against MG infection.
Keywords: Inflammatory cytokines; MAP3K1; Mycoplasma gallisepticum (HS strain); NF-κB signaling pathway; gga-miR-21.
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