Since both endothelial21 and mesenchymal22 progenitors have been implicated in PAH, and are present in remodelled arteries we investigated the expression of OPG in PASMCs (SMC), pulmonary artery fibroblasts (PA-Fib) and fibrocytes isolated from the hypoxic neonatal calf model of PAH23 and blood outgrowth endothelial cells (BOEC)24. Here, TNFRSF11B is linked to pulmonary arterial hypertension.