In S/H animals treated with etanercept, the reversal of PAH progression was associated with restored BMPR-II, phospho-Smad1/5 and Notch3 expression (Fig. 6d,e,g) and a reduction of the pathological increases in Acvr2a, Alk2, Bmp6, Tnf, Notch2, Hey1, Hey2, cleaved caspase-3 and alpha-smooth muscle actin (Fig. 6d-f and Supplementary Fig. 17 c,d,f). Here, SMAD1 is linked to pulmonary arterial hypertension.