Background: Loss of function mutations in the bone morphogenetic protein (BMP) pathway are known to be causative for pulmonary arterial hypertension (PAH). BMP9-based therapy is being investigated in PAH, as it inhibits endothelial cell permeability and reverses vascular remodeling in preclinical models. However, the exact mechanism by which BMP9 regulates vessel stability is unknown.

Aim: To investigate the functional consequence of semaphorin 3G (Sema3G) expression induced by BMP9 in pulmonary microvascular endothelial cells (PMECs). Semaphorins have been implicated in vascular endothelial growth factor (VEGF) antagonism. Therefore, we hypothesized that endothelial Sema3G promotes vessel stability.

Methods: We examined the ability of both BMP9 and Sema3G to antagonize the pro-angiogenic, pro-migratory effects of VEGF stimulation with functional in vitro assays in primary PMECs. We also used preclinical models of PAH to study changes in SEMA3G expression in disease.

Results: BMP9 treatment of PMECs increased SEMA3G expression 5-10-fold via the canonical Smad signalling pathway. Interestingly, VEGF treatment inhibited the BMP9-mediated increase of SEMA3G expression. Additionally, SEMA3G mRNA expression was reduced in animal models of PAH. BMP9 and Sema3G inhibited VEGF-induced PMEC migration. Angiogenesis assays confirmed that BMP9 treatment significantly reduced VEGF-induced PMEC sprouting.

Conclusion: These findings, along with those previously published on class 3 semaphorins, suggest that Sema3G might play an important role in balancing pro-angiogenic VEGF and anti-angiogenic BMP9 signaling, further elucidating the mechanism by which BMP9 treatment may reverse pathologic remodeling and promote vessel stability in PAH.