Context-specific angiogenic signaling in the pulmonary vasculature

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This project describes a research program to ascertain the functions of the BMP9-BMPR2-ALK1 signaling axis in pulmonary vascular biology, and to determine its contribution to pulmonary arterial hypertension (PAH). Loss-of-function mutations in genes encoding the BMP9 signaling complex in endothelial cells—BMPR2, ALK1, co-receptor ENG, GDF2, and downstream effector SMAD9—have been implicated in heritable PAH, while the acquired deficiency of these factors and of downstream SMAD1/5/9 signaling have been hallmarks of non-genetic forms (PH). The mechanisms by which BMPR2/ALK1 signaling regulates homeostasis of the pulmonary vasculature are not known, and the manner in which dysregulated BMP9 signaling may predisposes to PAH remains incompletely understood. In support of a protective role of BMP9 signaling, treatment with recombinant BMP9 ligand attenuates PH and pulmonary vascular remodeling in several models of PH, while deficiency of circulating BMP9 is associated with portopulmonary hypertension. Paradoxically, treatment with ALK1-Fc, a BMP9 ligand trap, also ameliorates experimental PH, suggesting Janus-like, context-sensitive effects of BMP9 signaling in PAH. Aim 1 of this program includes detailed mechanistic studies to discern how distinct co-receptors and effectors recruited by BMP9 signaling may elicit disparate functions in pulmonary vascular cells. Aim 2 investigates the physiologic effects of these signals using in vitro and in vivo models of pulmonary vascular barrier function. Aim 3 examines how selective engagement of various components of the BMP9 receptor complex may impact experimental PH and pulmonary vascular remodeling. These studies leverage the extensive experience in selective modulation and targeting of the BMP/TGFb signaling pathway, and novel pharmacologic probes designed to engage various components of the signaling pathway in a highly selective and translatable fashion. This program is supported by proof-of-concept studies using human cells, and state-of-the-art models. This project builds upon the demonstrated therapeutic potential of modulating BMP/TGFb family signaling for the treatment of pulmonary vascular disease and may generate novel strategies that would overcome the limitations of current approved and investigational therapies.