However, another in vitro study showed that Ang-1 expression in lung tissue and cultured pulmonary smooth muscle cells did not differ between patients with iPAH and controls; instead, the Tie-2 receptor was overexpressed in pulmonary endothelial cells and mediated the pathological effects of Ang-1 by stimulating synthesis of endothelium-derived growth factors [38]. This evidence concerns the gene ANGPT1 and idiopathic pulmonary arterial hypertension.