Investigating the impact of endothelial BMPR2 loss on the proliferative response to bone morphogenetic protein 9 in pulmonary arterial hypertension
Objective: Pulmonary arterial hypertension (PAH) is a disease of proliferative vascular occlusion that is strongly linked to heterozygous mutations in BMPR2, the gene encoding the bone morphogenetic protein (BMP) type II receptor (BMPR-II). The endothelial-selective BMPR-II ligand, BMP9, has been shown to reverse disease in animal models of PAH and suppress the proliferation of healthy endothelial cells. However, the impact of BMPR2 loss on the antiproliferative actions of BMP9 has yet to be assessed in endothelial cells from PAH patients. Approach: BMP9 responses were assessed in blood outgrowth endothelial cells (BOECs) from PAH patients and controls, as well as human pulmonary artery endothelial cells (HPAECs) with or without BMPR2 silencing. Mouse pulmonary endothelial cells (MPECs), bearing a wildtype genome or a heterozygous or homozygous deletion of Bmpr2, were isolated from endothelial-conditional knockout mice (Bmpr2EC+/+, Bmpr2EC+/- or Bmpr2EC-/-). These mice were also assessed in vivo for altered retinal and lung angiogenesis following post-natal BMP9 administration. Results: BMP9 suppressed proliferation in control endothelial cells, but increased proliferation in PAH patient BOECs, BMPR2 silenced HPAECs and Bmpr2-/- MPECs. This proliferative shift was not linked to altered metabolic activity or interactions with canonical TGFβ signaling, but was associated with the prolonged induction of the canonical BMP targets, the inhibitor of DNA-binding/differentiation genes, ID1 and ID2. In vivo, BMP9 administration reduced neonatal retinal and pulmonary vascular density in controls, but enhanced both measures in Bmpr2EC-/- mice. Conclusion: Loss of BMPR2 results in a shift of the endothelial BMP9 response towards enhanced proliferation. This finding has potential implications for the clinical translation of BMP9 for the treatment of PAH.