APLN and pulmonary arterial hypertension: As PAH is a complex disease with multiple etiologies, miRNAs may be key candidates for more effective treatment, due to their capacity to coordinately regulate various signaling pathways associated with PAH such as bone morphogenetic protein (BMP) signaling, apelin (APLN) and apelin receptor (APLNR) signaling and hypoxia-related signaling, via the targeting of multiple mRNAs.1, 44, 45, 46 Thus, the abnormal expression and dysregulation of miRNAs contributes to the pathogenesis of PAH.