In control PAECs and control and PAH pulmonary artery smooth muscle cells, apelin and ELA-32 increased levels of ERK1/2 phosphorylation, and in PAECs there was also a significant increase in phosphorylation of endothelial nitric oxide synthase (online-only Data Supplement Figure IIA through IID). The gene discussed is NOS3; the disease is pulmonary arterial hypertension.