APLN and pulmonary arterial hypertension: Daily injection of apelin (Falcão-Pires et al., 2009; Alastalo et al., 2011), agents that stimulate apelin expression (Spiekerkoetter et al., 2013; Bertero et al., 2014; Nickel et al., 2015), or downstream mediators of the apelin pathway (Kim et al., 2013) attenuate the development of PAH in these models.