ANGIOPOIETIN/TIE2 PATHWAY INFLUENCES SMOOTH MUSCLE HYPERPLASIA IN IDIOPATHIC PULMONARY HYPERTENSION Dewachter L: Ang1/Tie2 in Pulmonary Hypertension

Rationale: Angiopoietins are involved in blood-vessel maturation and remodeling. Objectives: One consequence of endothelial-specific receptor Tie2 activation by angiopoietin-1 (Ang1) is the release of endothelial-derived growth factors that recruit vascular wall cells. We investigated this process in idiopathic pulmonary arterial hypertension (iPAH). Methods: Ang1, Ang2, total and phosphorylated Tie2 expressions (mRNA and protein) were evaluated in human lung specimens and in cultured pulmonary smooth muscle (PA-SMCs) and endothelial cells (P-ECs) isolated from iPAH patients and controls. Media collected from Ang1-treated P-ECs were assessed for their PA-SMC growth promoting effect. Measurements and Main Results: Tie2 receptor was 4-fold higher in lungs and P-ECs from iPAH patients than in those from controls, with a parallel increase in phosphorylated lung Tie2 receptor. In contrast, Ang1 and Ang2 expression in lungs, P-ECs and PA-SMCs didn’t differ. Incubation of PA-SMCs with medium collected from P-EC cultures induced marked proliferation, and this effect was stronger using P-ECs from patients with iPAH than from controls. Ang1 pretreatment of P-ECs from either patients or controls induced a further increase in PA-SMC proliferation. Fluoxetine, an inhibitor of mitogenic action of serotonin, reduced growth-promoting effect of P-EC media. Ang1 added to P-ECs from iPAH patients increased the production of endothelin-1 (ET-1) and serotonin, but not of PDGF-BB or EGF, and increased the amount of mRNA encoding tryptophan-hydroxylase1 (TPH1, the ratelimiting enzyme of serotonin synthesis), preproET-1, and ET-1 converting enzyme. Conclusions: Ang1/Tie2 pathway is potentiated in iPAH, contributing to PA-SMC hyperplasia via increased stimulation of endothelium-derived growth factors synthesis by PECs. Abstract Word Count: 250