Distinct anabolic signalling responses to amino acids in C2C12 skeletal muscle cells.
Level 5 - mechanism / opinion, no new human data
Bench research in cell culture with no human data
PubMed 19882215 · doi:10.1007/s00726-009-0377-x
What was done
C2C12 mouse myotubes were serum-starved for 4 hours and amino acid-starved for 1 hour, then stimulated individually with 2 mM of each essential amino acid (EAA). Immunoblotting was used to measure the phosphorylation of Akt/mTORC1 pathway signaling proteins: Akt, mTOR, 4EBP1, p70S6K1, RPS6, eIF2alpha, and eEF2.
What was found
Akt, eIF2alpha, and eEF2 phosphorylation remained unchanged across all EAAs. Leucine was the only EAA that increased phosphorylation of mTOR (1.67 ± 0.1-fold) and 4EBP1 (2.5 ± 0.1-fold). Phosphorylation of p70S6K1 increased with all EAAs except isoleucine and valine, with leucine inducing a 5.9 ± 0.3-fold increase versus 1.6–2.0-fold for non-BCAA EAAs. RPS6 phosphorylation showed an identical pattern, with leucine producing a 3.8 ± 0.3-fold increase versus 1.5–2.0-fold for non-BCAA EAAs.
Why it matters
This study provides a systematic comparison of individual essential amino acids on skeletal muscle anabolic signaling, demonstrating that leucine is uniquely potent in activating mTOR, 4EBP1, and downstream ribosomal signaling.
Limits
The study was conducted entirely in vitro using mouse C2C12 cell lines, which may not reflect human in vivo physiology. Replicate counts (n) are not reported in the abstract, single fixed concentrations (2 mM) were used, and muscle protein synthesis rates were not directly measured.
Cited by
- supports Leucine activates mTOR more strongly than other amino acids.