BONE MORPHOGENETIC PROTEIN SIGNALING IN HERITABLE VERSUS IDIOPATHIC PULMONARY HYPERTENSION BMP signaling in Pulmonary Hypertension

Mutations in gene encoding for bone morphogenetic protein type 2 receptor (BMPR-2) have been reported in pulmonary arterial hypertension (PAH), but their functional relevance remains incompletely understood. BMP receptors expression was evaluated in human lungs and in cultured pulmonary artery smooth muscle cells (PASMCs) isolated from 19 idiopathic PAH patients and 9 heritable PAH patients with demonstrated BMPR-2 mutations. BMP4-treated PASMCs were assessed for Smad and p38MAPK signaling associated to mitosis and apoptosis. Lung tissue and PASMCs from heritable PAH patients presented with decreased BMPR-2 expression and variable increases in BMPR-1A and BMPR-1B expressions, while a less important decreased BMPR-2 expression was observed in PASMCs from idiopathic PAH patients. Heritable PAH PASMCs showed no increased phosphorylation of Smad1/5/8 in the presence of BMP4, which actually activated the p38MAPK pathway. Individual responses varied from one mutation to another. PASMCs from PAH patients presented with an in vitro proliferative pattern, which could be inhibited by BMP4 in idiopathic PAH, not in heritable PAH. PASMCs from idiopathic PAH and more so from heritable presented an inhibition of BMP4-induced apoptosis. Most heterogenous BMPR-2 mutations are associated with defective Smad signaling compensed for by an activation of p38MAPK signaling, accounting for PASMC proliferation and deficient apoptosis. Abstract Word Count: 200Word Count: 200