AKT1 and pulmonary arterial hypertension: We found that anti-Gremlin 1, but not anti-Activin A or anti-TGF-β antibodies reduced Akt phosphorylation, as seen in Figure 5A. Both anti-Gremlin 1 and anti-TGF-β, but not anti-Activin A, significantly decreased ERK1/2 phosphorylation in PAH PAVSMC, which was not affected by PDGF-BB treatment, as seen in Figure 5B. Interestingly, none of tested antibody modulated p38 MAPK phosphorylation rates, as shown in Figure 5C. Collectively, these data suggest that one of potential mechanisms by which anti-TGF-β antibody decrease PAH PAVSMC proliferation is via inhibition of ERK1/2 signaling pathway.