Although Fis1 is found to be upregulated in PASMC in human PAH patients (Marsboom et al., 2012; Ryan et al., 2013), knockdown of Fis1 using a small interfering RNA (siRNA) does not inhibit mitochondrial fission nor reduce proliferation in PASMC in human PAH patients (Chen et al., 2018). Here, FIS1 is linked to pulmonary arterial hypertension.