Bio-alchemy: Can muscle convert glucose to protein?

Introduction: Nearly 100 years ago, Otto Warburg discovered that growing tissues (esp. tumors) take up more glucose than tissues that do not grow. Recent research has shown that some of this glucose is used for biosynthesis among other via a glucose => glycolytic intermediates => non-essential amino acids => protein reaction. The aim of this study was to investigate whether C2C12 myotubes can also incorporate carbon from glucose into protein and whether the rate of incorporation is increased by the hypertrophy stimulator IGF-1. Methods: We incubated C2C12 myotubes with 14C- or 13C-labelled glucose, treated the myotubes with vehicle or 100 ng/mL IGF-1, extracted protein, and measured 14C-incorporation into protein with a scintillation counter or 13C-incorporation into amino acids and protein with a mass spectrometer, respectively. Results: Both methods reveal that C2C12 myotubes incorporate carbon from glucose into protein and that 100 ng/mL IGF-1 increases the rate of carbon incorporation into protein. Specifically, we detected radioactivity from 14C-radiolabeled glucose (1 μL/mL of 0.1 mCi/mL; all per 10 cm diameter dish) in C2C12 myotube protein (7581 ± 1586 counts per minute) and RNA (251 ± 50.08 counts per minute) after 48 h of incubation. IGF-1 increased incorporation of 14C from glucose into protein by 70% (12924 ± 2113 counts per minute). Discussion: C2C12 myotubes synthesize non-essential amino acids and protein partially from glucose (nitrogen-donating metabolites are additionally needed). This shows that muscle cells not only use glucose for glycogen synthesis or ATP resynthesis but also for the production of biomass. Several studies suggest that hypertrophying muscles take up more glucose and this could explain why muscle hypertrophy is anti-diabetic and associated with leanness.     «

Introduction: Nearly 100 years ago, Otto Warburg discovered that growing tissues (esp. tumors) take up more glucose than tissues that do not grow. Recent research has shown that some of this glucose is used for biosynthesis among other via a glucose => glycolytic intermediates => non-essential amino acids => protein reaction. The aim of this study was to investigate whether C2C12 myotubes can also incorporate carbon from glucose into protein and whether the rate of incorporation is increased by...     »