Pulmonary arterial hypertension (PAH) is characterized by vascular remodeling associated with obliteration of pulmonary arterioles and formation of plexiform lesions composed of hyperproliferative endothelial and vascular smooth-muscle cells. Here we describe a microRNA (miRNA)-dependent association between apelin (APLN) and fibroblast growth factor 2 (FGF2) signaling in pulmonary artery endothelial cells (PAECs). APLN deficiency in these cells led to increased expression of FGF2 and its receptor FGFR1 as a consequence of decreased expression of miR-424 and miR-503, which directly target FGF2 and FGFR1. miR-424 and miR-503 were downregulated in PAH, exerted antiproliferative effects in PAECs and inhibited the capacity of PAEC-conditioned medium to induce the proliferation of pulmonary artery smooth-muscle cells. Reconstitution of miR-424 and miR-503 in vivo ameliorated pulmonary hypertension in experimental models. These studies identify an APLN-dependent miRNA-FGF signaling axis needed for the maintenance of pulmonary vascular homeostasis.