MicroRNA-149 negatively regulates TLR-triggered inflammatory response in macrophages by targeting MyD88

MicroRNAs (miRNAs) have been shown to be important regulators of TLR signaling pathway at the post-transcriptional level. In this study, the potential role of miR-149 was explored in murine alveolar macrophage RAW264.7 cells. Our results demonstrated a dynamic change of the expressions of miR-149 expression and MyD88 in macrophage RAW264.7 upon Mycobacterium bovis Bacillus Calmette-Guerlin (BCG) infection or lipopolysaccharide (LPS) stimulation. The presence of BCG or LPS dynamically reduced the miR-149 expression, along with a substantially striking increase of MyD88 expression in these cells. More importantly, overexpression of miR-149 in RAW264.7 cells was associated with a significant decrease of MyD88 protein expression, as well as a reduced production of inflammatory mediator NF-κB 1, TNF-α and IL-6 in response to BCG infection or LPS stimulation. Further studies using immunoblotting assay against anti-MyD88 antibody and microRNA targeting luciferase reporter assay revealed that miR-149 was able to directly target the 3'-UTR of MyD88 mRNA and post-transcriptionally regulated MyD88 protein expression. These data suggested that miR-149 might be a key player of immune modulator for TLR/MyD88 signaling pathway in macrophages, which may through a mechanism of negatively regulating MyD88-dependent Toll-like receptors signaling pathway.