STEAP4 and pulmonary arterial hypertension: In line with this observation, exposure to chronic hypoxia (10% O2 for 3 weeks) also moderately augmented PAH in Stamp2−/− mice, as indicated by a significantly higher increase of the right ventricular systolic pressure (RVSP) to 33.2 ± 0.6 mmHg (p < 0.001) as compared to Stamp2+/+ mice (30.4 ± 1.1 mmHg; p < 0.05) (Fig. 2c).