GSE176530
Downregulation of let-7 by electrical acupuncture increases protein synthesis in mice
Our previous study found that acupuncture with low frequency electrical stimulation (Acu/LFES) prevents muscle atrophy by attenuation of protein degradation in mice.  The current study examines the impact of Acu/LFES on protein synthesis.  C57/BL6 mice received Acu/LFES treatment on hindlimb for 30 minutes once.  Acupuncture points were selected by WHO Standard Acupuncture Nomenclature and electric stimulation applied using an SDZ-II Electronic acupuncture instrument.  Muscle protein synthesis was measured by the surface-sensing of translation (SUnSET) assay.  Exosomes were isolated using serial centrifugation and concentration and size of the collected exosomes were measured using a NanoSight instrument.  The mature microRNA library in serum exosomes was validated using a High Sensitivity DNA chip.  Protein synthesis was enhanced in the both hindlimb and forelimb muscles.  Blocking exosome secretion with GW4869 decreased the Acu/LFES-induced increases in protein synthesis.  MicroRNA-deep sequencing demonstrated that four members of the Let-7 miRNA family were significantly decreased in serum exosomes.  Real time qPCR further verified Acu/LFES-mediated decreases of let-7c-5p in serum exosomes and skeletal muscles.  In cultured C2C12 myotubes, inhibition of let-7c not only increased protein synthesis, but also enhanced protein abundance of Igf1, Igf1 receptor.  Using a luciferase reporter assay, we demonstrated that let-7 directly inhibits Igf1.  Conclusion: Acu/LFES on hindlimb decreases let-7-5p leading to upregulation of the Igf1 signaling and increasing protein synthesis in skeletal muscles. This provides a new understanding of how the electrical acupuncture treatment can positively influence muscle health. Overall design: Three C57/BL6 mice received Acu/LFES treatment on hindlimb for 30 minutes once.  Acupuncture points were selected by WHO Standard Acupuncture Nomenclature and electric stimulation applied using an SDZ-II Electronic acupuncture instrument.  Three control mice had acupuncture needles inserted in close proximity to the ACU/LFES insertion position, needles were connected to the LFES device, but electrical stimulation was not applied. Muscle protein synthesis was measured by the surface-sensing of translation (SUnSET) assay.  Exosomes were isolated using serial centrifugation and concentration and size of the collected exosomes were measured using a NanoSight instrument.  The mature microRNA library in serum exosomes was validated using a High Sensitivity DNA chip.