AMP-activated Protein Kinase Activation Suppresses Protein Synthesis and mTORC1 Signaling in Chick Myotube Cultures

Protein synthesis in skeletal muscle is considered one of the most energy-consuming cellular processes. AMP-activated protein kinase (AMPK) is a metabolic master switch that regulates glucose and lipid metabolism, and it is implicated in protein synthesis control in skeletal muscles. The mechanistic target of rapamycin complex 1 (mTORC1) is a central regulator of protein metabolism in cells. However, the effect of AMPK activation on protein synthesis and mTORC1 signaling in chicken skeletal muscle remains unclear. Therefore, in this study, we aimed to investigate the effect of 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR), an AMPK activator, on protein synthesis and mTORC1 signaling in chick myotube cultures. The incubation of chick myotubes with AICAR (1 mM) for 3 h led to a significant increase in AMPK (Thr172) phosphorylation. Nonetheless, protein synthesis, measured using the surface sensing of translation method, was significantly decreased by AICAR. In addition, the phosphorylation of p70 ribosomal S6 kinase 1 (S6K1, Thr389), S6 ribosomal protein (Ser240/244), and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1, Thr37/46) was significantly reduced by AICAR. These results suggest that AMPK activation suppresses protein synthesis and mTORC1 signaling (through the phosphorylation of S6K1, S6 ribosomal protein, and 4E-BP1) in chick myotubes.