Beta‐hydroxy‐beta‐methylbutyrate (HMB) augments muscle contraction‐induced protein synthesis via mTORC1 signaling in cultured L6 myotubes

Introduction Beta‐hydroxy‐beta‐methylbutyrate (HMB), a metabolite of L‐leucine, has been shown to enhance resistance exercise‐induced protein synthesis in human and animal studies. Since there is no suitable contraction model using skeletal muscle cell line for analyzing protein synthesis level, the combined effects of HMB and muscle contraction on the protein synthesis is still unknown. Objective The present study aimed to establish a new muscle contraction model in L6 myotubes for analyzing protein synthesis. Using this model, we investigated the effects of HMB on the contraction‐induced protein synthesis via the mammalian target of rapamycin complex 1 (mTORC1) pathway. Methods L6 myotubes seeded into 4‐well rectangular plates were placed in contraction system equipped with carbon electrode at each end. The myotubes were stimulated with electric pulses of 50 V at 100 Hz for 10 min followed by the HMB treatment. Cells were collected at 3 hours poststimulation and evaluated mTORC1 signaling pathway activation by Western blot analysis. Results The phosphorylation level of Akt which is upstream components of mTORC1 pathway and the phosphorylation of 70‐kDa ribosomal protein S6 kinase (p70S6K) which is downstream components of this pathway were significantly increased 3 hours after electric stimulation ( p <0.05). Furthermore, the phosphorylation level of p70S6K in contraction cells combined with HMB was significantly increased compared with that in contraction‐only cells ( p <0.05). Conclusion We established a new muscle contraction model for analyzing protein synthesis in cultured L6 myotubes. Additionally, we found that HMB enhances muscle contraction‐activated mTORC1 signaling pathway using this model. Support or Funding Information This work was funded by Lion Corporation. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .