Among these differently regulated proteins, we found some known PAH-associated proteins, such as resistin-like alpha (Retnla) [18], arginase-1 (Arg1) [19], Chymase 1 (Cma1) [20] and haptoglobin (HP) [21]; their relative abundances are shown in Figure 3a–d. Here, HP is linked to pulmonary arterial hypertension.