GREM1 and pulmonary arterial hypertension: Here, we report that proliferative distal PAVSMC derived from lungs of patients with PAH have increased secretion of TGF-β1 and, to a lesser extent, Activin A, but not Gremlin 1; factors, secreted by PAH PAVSMC are able to promote proliferation and up-regulate multiple signaling pathways in non-diseased PAVSMC.