Previous studies of rat PAH models have shown that a reduction in BMP/Smad1/5 signaling is accompanied by an increase in TGF-β1/Smad2/3 signaling, and the TGF-β signaling inhibitor ALK5 attenuates these changes, effectively preventing the progression of PAH [33]. This evidence concerns the gene TGFBR1 and pulmonary arterial hypertension.