Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle.
Level 3 - non-randomized controlled study
Controlled non-randomized comparative physiological cohort study comparing young and older men.
PubMed 15596483 · doi:10.1096/fj.04-2640fje
What was done
Researchers measured myofibrillar and sarcoplasmic muscle protein synthesis (MPS) rates in 44 healthy young and older men of similar body build after the ingestion of varying quantities of essential amino acids (EAA). Plasma insulin was clamped at basal concentrations to isolate amino acid effects. Muscle tissue was analyzed for expression and phosphorylation of signaling proteins (mTOR, p70S6k, eIF4BP-1, eIF2B) and NF-κB.
What was found
Basal MPS rates were indistinguishable between young and older men. Older men exhibited reduced sensitivity and responsiveness of MPS following EAA ingestion. This reduction coincided with decreased intramuscular expression and activation of mTOR, p70S6k, eIF4BP-1, and eIF2B, alongside marked increases in NF-κB. The abstract reports no numerical values, effect sizes, or variance estimates.
Why it matters
This study shows that age-related muscle wasting is characterized by blunted postprandial signaling and protein synthesis responses to amino acids rather than a basal synthesis deficit, highlighting potential signaling targets for nutritional countermeasures.
Limits
The abstract omits exact numerical values, statistical test statistics, and variance measurements. The sample was limited to healthy men, excluding women and clinically frail populations, and acute physiological signaling was evaluated without measuring long-term muscle mass changes or functional outcomes.
Cited by
- supports Aging reduces the sensitivity of the mTOR translation initiation signaling pathway and decreases the abundance of cellular machinery associated with muscle protein synthesis.