MSTN and Atrophy: For example, miR-1, miR-133a, miR-181a and miR-499 interacted with TFG-β signalling pathways in several cell lines.15–17 TGF-β signalling via small mothers against decapentaplegic (SMAD) protein phosphorylation is an essential pathway in muscle atrophy that can be stimulated by various ligands, including myostatin (GDF-8) and TGF-β1.18 In this observational study, we hypothesised that GDF-15, both muscle and from the circulation, mediates ICUAW-associated muscle atrophy through regulation of microRNA expression.