TGFB1 and pulmonary arterial hypertension: Most of these changes are due to the growth factors that are overexpressed in patients with PAH, such as platelet-derived growth factor (PDGF), endothelin (ET), serotonin (5-HT), transforming growth factor-β (TGF-β), epidermal growth factor (EGF), fibroblast growth factor (FGF) [8].