APLN and idiopathic pulmonary arterial hypertension: Our data showed both of these genes increased in IPAH ECs.APLN, a peptide that binds to apelin receptor (APLNR),25 promotes angiogenesis through activation of extracellular-signal-regulatedkinases, Akt, and p70S6kinase, and has vasodilator properties through induction ofnitric oxide release.26 Previous studies showed reduced APLN mRNA levels andAPLN expression in cultured ECs from IPAH compared to control lungs.24 Furthermore, administration of APLN was shown to reverse PAH in mice.