BACKGROUND: Pulmonary vascular remodeling of pulmonary arterial hypertension (PAH) is characterized by an inappropriate increase of vascular cells. The receptor for advanced glycation end products (RAGE) is a type I single-pass transmembrane protein belonging to the immunoglobulin superfamily and is involved in a broad range of hyperproliferative diseases. RAGE is also implicated in the etiology of PAH and is overexpressed in pulmonary artery smooth muscle cells (PASMCs) in patients with PAH. We examined the role of RAGE in the inappropriate increase of PASMCs in patients with PAH. METHODS AND RESULTS: PASMCs were obtained from 12 patients with PAH including 9 patients with idiopathic PAH (IPAH) and 3 patients with heritable PAH (HPAH) (2 patients with BMPR2 mutation and one patient with SMAD9 mutation) who underwent lung transplantation. Western blot analysis and immunofluorescence staining revealed that RAGE and S100A8 and A9, ligands of RAGE, were overexpressed in IPAH and HPAH-PASMCs in the absence of any external growth stimulus. PDGF-BB (10 ng/mL) up-regulated the expression of RAGE in IPAH and HPAH-PASMCs. PAH-PASMCs are hyperplastic in the absence of any external growth stimulus as assessed by 3H-thymidine incorporation. This result indicates overgrowth characterized by continued growth under a condition of no growth stimulation in PAH-PASMCs. PDGF-BB stimulation caused a higher growth rate of PAH-PASMCs than that of non-PAH-PASMCs. AS-1, an inhibitor of TIR domain-mediated RAGE signaling, significantly inhibited overgrowth characterized by continued growth under a condition of no growth stimulation in IPAH and HPAH-PASMCs (P<0.0001). Furthermore, AS-1 significantly inhibited PDGF-stimulated proliferation of IPAH and HPAH-PASMCs (P<0.0001). CONCLUSIONS: RAGE plays a crucial role in the inappropriate increase of PAH-PASMCs. Inhibition of RAGE signaling may be a new therapeutic strategy for PAH.