Vascular smooth muscle cell-derived osteoprotegerin drives pulmonary arterial hypertension via AKT activation and is attenuated by monoclonal antibody therapy.

AIM: Pulmonary arterial hypertension (PAH) is driven by sustained vasoconstriction and structural remodelling of distal pulmonary arteries. We have previously demonstrated that osteoprotegerin (OPG, tnfrsf11b) is upregulated in PAH animal models and patient tissues, with circulating levels being prognostic. OPG knockout mice exhibit an attenuated PAH phenotype, and therapeutic inhibition using a human monoclonal anti-OPG antibody reduces disease severity in multiple rodent models. However, the key cellular source of pathogenic OPG and the mechanism underlying therapeutic blockade remain unknown. METHODS AND RESULTS: To define the main cellular source of OPG, conditional Tnfrsf11b deletion was generated by crossing OPGfl/fl mice with PGKcretg/+ (global), LysMcretg/+ (myeloid), Myl2cretg/+ (cardiac myocytes), Cdh5cretg/+ (endothelial cells, ECs), smMHCcretg/+ (VSMCs), Col1a2cretg/+ (fibroblasts, FBs). Knockouts were induced by tamoxifen injection, and PAH established using Sugen5416/hypoxia (SuHx) model. Cardiopulmonary phenotyping included echocardiography, cardiac catheterisation, and histological analysis. Mechanistic studies were performed in VSMCs using peptide-based kinase activity profiling (PamStation).PGKcretg/+/OPGfl/fl mice phenocopied the previous results obtained with global OPG knockout (OPG-/-). Only VSMC-specific deletion (smMHCcretg/0/OPGfl/fl) resulted in significantly improved haemodynamic parameters, evidenced by reduced RVSP and pulmonary vascular resistance (PVR), and reduced pulmonary vascular remodelling demonstrating that VSMC-derived OPG is the primary driver of PAH pathogenesis.Kinome profiling of control and IPAH-PASMCs treated with OPG +/- anti-OPG antibody revealed IPAH specific regulation of PI3K-Akt and enrichment of pathways involving autophagy, and longevity regulation linked to cellular stress resistance and growth. Anti-OPG antibody treatment reduced AKT phosphorylation in IPAH PASMCs. Knock-down of AKT1 by siRNA reduced OPG-induced proliferation and migration of human PASMC. These results align with emerging data implicating OPG in cellular senescence and vascular aging. CONCLUSION: Together, these findings highlight VSMC-derived OPG as a critical mediator of pulmonary vascular remodelling in PAH pathogenesis and suggest that targeting OPG via a therapeutic antibody is mediated through PI3K-Akt signalling.