GSI Treatment Preserves Protein Synthesis in C2C12 Myotubes

It has been demonstrated that inhibiting Notch signaling through gamma-secretase inhibitor (GSI) treatment increases myogenesis, AKT/mTOR signaling, and muscle protein synthesis (MPS) in C2C12 myotubes. The purpose of this study was to determine if GSI-mediated effects on myogenesis and MPS are dependent on AKT/mTOR signaling. C2C12 cells were assessed for indices of myotube formation, anabolic signaling, and MPS following GSI treatment in combination with rapamycin and API-1, inhibitors of mTOR and AKT, respectively. GSI treatment increased several indices of myotube fusion and MPS in C2C12 myotubes. GSI-mediated effects on myotube formation and fusion were completely negated by treatment with rapamycin and API-1. Meanwhile, GSI treatment was able to rescue MPS in C2C12 myotubes exposed to rapamycin or rapamycin combined with API-1. Examination of protein expression revealed that GSI treatment was able to rescue pGSK3 beta Ser9 despite AKT inhibition by API-1. These findings demonstrate that GSI treatment is able to rescue MPS independent of AKT/mTOR signaling, possibly via GSK3 beta modulation.

Automated summary

The study showed that inhibiting Notch signaling with GSI treatment promoted myogenesis and MPS in C2C12 myotubes, independent of AKT/mTOR signaling. However, the effects of GSI on myotube formation were completely reversed by rapamycin and API-1, while GSI treatment was able to rescue MPS in C2C12 myotubes exposed to these inhibitors. These results suggest that GSI treatment can rescue MPS via GSK3 beta modulation, regardless of AKT/mTOR signaling.