The Interplay Between IL-6, Hepcidin, and BMPR2 Signalling in Pulmonary Arterial Hypertension: Mechanistic Insights Into Vascular Remodelling.

Pulmonary arterial hypertension (PAH) is characterized by excessive pulmonary vasoconstriction and vascular remodelling, with mutations in bone morphogenetic protein receptor type 2 (BMPR2) being the most common genetic alteration associated with the disease. While inflammatory mediators like interleukin-6 (IL-6) and the iron-regulatory hormone hepcidin have been implicated in vascular remodelling, their interaction with BMPR2 signalling remains poorly understood. This study investigated how IL-6 and hepcidin influence BMPR2 expression and downstream signalling in human pulmonary arterial endothelial cells (hPAECs). Using qPCR and Western blot analyses, we demonstrated that both IL-6 and hepcidin significantly reduced BMPR2 mRNA and protein levels in hPAECs. Intriguingly, despite this reduction, SMAD1/5 phosphorylation remained active, suggesting compensatory signalling through alternative receptor complexes. Treatment with IL-6 and hepcidin upregulated inhibitors of differentiation (ID) protein expression, mimicking the effects observed with BMPR2 knockdown. These findings reveal a novel regulatory axis involving IL-6, hepcidin, and BMPR2 in PAH pathogenesis, where IL-6 and hepcidin promote vascular remodelling through both BMPR2-dependent and independent mechanisms. These results suggest that therapeutic strategies targeting this axis, particularly those aimed at rebalancing BMP/TGF-β signalling, may hold promise for treating PAH.