ACTA1 and idiopathic pulmonary arterial hypertension: We have reported that (1) TWIST1 overexpression increases the expression of PDGFB in human pulmonary arterial endothelial (HPAE) cells, (2) Twist1 knockdown suppresses hypoxia-induced upregulation of PDGFB expression and accumulation of αSMA–positive cells in the mouse lungs, and (3) IPAH patient-derived PAE cells stimulate accumulation of αSMA–positive cells through endothelial TWIST1-PDGFB signaling (11).