SMAD3 and sarcopenia: Mechanistically, differentiated C2C12 myotubes were treated with recombinant GDF11 (rGDF11), followed by assessment of canonical SMAD signaling and muscle atrophy-related markers, including phosphorylated SMAD3 (immunoblotting) and the E3 ubiquitin ligases Atrogin-1 and MuRF1 at both protein (immunoblotting) and transcript (RT-qPCR) levels.<h4>Results</h4>Circulating GDF11 concentrations were significantly higher in older adults than in younger individuals and were further elevated in participants with sarcopenia, both before and after PSM.