SMAD2 and pulmonary arterial hypertension: Recently, Yung and colleagues [49]found that the activin and growth and differentiation factor (GDF) ligandsactivin A, GDF8 and GDF11 were upregulated in the lungs of PAH subjects andactivated a SMAD2/3-mediated proproliferative, antiapoptotic phenotype in PAECsand PASMCs.