GREM1 and pulmonary arterial hypertension: Here we report that hyper-proliferative human PAH PAVSMC have elevated secretion of TGF-β1 and, to a lesser extent, Activin A, but not Gremlin 1, and significantly reduced Ser465/467-Smad2 and Ser423/425-Smad3 phosphorylation compared to controls.