These data also demonstrate growth-inhibitory effects for anti-Activin A and anti-TGF-β, but not Gremlin 1 antibody, on human PAH PAVSMC, and indicate that PDGF-BB counteracts with such inhibition, suggestive of parallel activation of pro-proliferative pathways by PDGF-BB and TGF-β. Here, GREM1 is linked to pulmonary arterial hypertension.