The apelin system is a therapeutic target in diseases (Read et al., 2019), such as diabetes (Castan-Laurell et al., 2012), fibrosis (Huang et al., 2016), heart failure (Berry et al., 2004; Jia et al., 2006; Atluri et al., 2007; Koguchi et al., 2012; Pang et al., 2014) and pulmonary arterial hypertension (PAH) (Falcão-Pires et al., 2009; Yang et al., 2015). Here, APLN is linked to pulmonary arterial hypertension.