New targets to control skeletal muscle inflammation: MicroRNAs regulated by adiponectin

Abstract

Background and aims: Low-grade pro-inflammatory state contributes to the metabolic syndrome (MS). Adiponectin (ApN), which is reduced in the MS, has emerged as a master regulator of inflammation/immunity. We wished to identify whether microRNAs (miRNAs) may mediate the antiinflammatory action of ApN on skeletal muscle. Materials and methods: miRNA expression profiling was performed in tibialis anterior muscles of ApN-knockout (ApN-KO) mice: one leg was electrotransferred with a plasmid coding for the ApN gene, while the contralateral leg received an empty plasmid and served as control. Mice were next challenged by lipopolysaccharide (LPS) to induce inflammation. Role of specific miRNAs was analyzed by gain-of or loss-of function approaches in C2C12 myotubes and in vivo by muscle electrotransfer. miRNA expression was also studied in human myotubes. Results: Expression of miR-711 was up-regulated by muscle electrotransfer of ApN, which concomitantly reduced inflammation (TNFα, IL-1β) and oxidative stress (peroxiredoxin-3) markers. Likewise, in C2C12 cells, ApN treatment upregulated miR-711 expression. Transfection of miR-711 mimic reproduced the anti-inflammatory effects of ApN, while miR-711 blockade attenuated its protective effects. We found that miR-711 repressed the expression of 4 genes belonging to the Toll-like receptor-4 (TLR4) pathway. This pathway is activated by LPS and ultimately leads to stimulation of NF-kB, a pro-inflammatory transcription factor. As expected, NF-kB activity, measured via a luciferase reporter plasmid, was reduced by the miR mimic and enhanced by miR silencing. This protection against inflammation was recapitulated in ApN-KO mice by in vivo muscle electrotransfer of a plasmid coding for miR-711. Eventually, miR-711 expression was also upregulated in human myotubes after ApN treatment. Conclusion: miR-711, which is up-regulated by ApN, represses TLR4 signaling and NF-kB, acting therefore as a major mediator of the antiinflammatory action of ApN on muscle. This novel miRNA may open new therapeutic perspectives for the MS or other inflamed muscle condition