SMAD2 and chronic obstructive pulmonary disease: Our data show that transfection of this miRNA into muscle cells causes SMAD2/3 phosphorylation and activation of the SMAD signalling system in the absence of exogenous ligand.19 Quadriceps expression of miR‐542‐5p is positively associated with disease severity in both patients with COPD in whom it is inversely proportional to lung function (measured as TLCO% predicted and FEV1% predicted) and in patients with reduced cardiac function, in whom it is inversely proportional to left ventricular ejection fraction.