MiR-128 mediates negative regulation in Staphylococcus aureus induced inflammation by targeting MyD88.

Acute lung injury (ALI) is a common clinical syndrome of excessive uncontrolled inflammatory response in lung tissues with high mortality rates and limited therapeutic approaches. MicroRNAs (miRNAs) are a class of small non-coding RNAs which attach at 3'UTR of mRNA for further regulation of diverse proteins. MiRNAs are a current focus in regulating the inflammatory processes. The extent of pro-inflammatory gene activated against Staphylococcus aureus (S. aureus) is still unclear. Myeloid differentiation primary response 88 (MyD88) is involved in gram positive bacteria-induced lung inflammation by Toll-like receptors (TLRs). Then MyD88 activates NF-κB through IRAKs which are in charge of inflammation. Target prediction analyses revealed MyD88, a result of projections from multiple bio-websites, to be a putative target of miR-128. Here we probe the expression of the MyD88 and miRNA in mode of inflammation. We found up-regulated expression of MyD88 and down-regulation of miR-128 after S. aureus infection in mouse lung tissues and RAW264.7 cells via qPCR and western blotting (WB) analysis. Moreover, MyD88-miR-128 interaction was validated by luciferase assays. Then, we proved that miR-128 expression caused a reduction in IκBα and p65 phosphorylation and resulted in significant reduction in secretion of inflammatory cytokines, being consistent with the deletion of MyD88 in macrophages. It revealed that miR-128 specifically blocked the further development of inflammation through MyD88 down-regulation. Finally, we demonstrated a novel role of miR-128 that it mediates negative regulation in S. aureus induced inflammation by targeting MyD88.