Restoration of Endothelial BMP9 Signaling During Ex Vivo Lung Perfusion Improves Marginal Donor Lung Recovery

Background: The limited availability of transplantable donor lungs remains a major barrier in lung transplantation, driving increasing reliance on marginal and extended-criteria donor organs. Ex vivo lung perfusion (EVLP) has emerged as a clinically important platform to assess, preserve, and recondition donor lungs that might otherwise be declined. However, effective biologic strategies to actively improve donor lung quality during EVLP remain limited. Bone morphogenetic protein 9 (BMP9) is a circulating endothelial homeostatic ligand that maintains vascular quiescence through ALK1/BMPR2 signaling, but its potential as a graft-directed therapeutic during EVLP is unknown.
Methods: Public human EVLP transcriptomic datasets were analyzed to define BMP9 pathway dysregulation during clinical lung perfusion. Mechanistic studies were then performed in pulmonary microvascular endothelial cells exposed to simulated cold-storage ischemia-reperfusion injury, where canonical BMP signaling and downstream target gene induction were assessed following recombinant BMP9 treatment. A modified alveolus-on-a-chip model incorporating cold storage, STEEN perfusion, and reperfusion was used to recapitulate EVLP-associated donor lung injury in a multicellular epithelial-endothelial system. Recombinant BMP9 was subsequently evaluated in a porcine donation-after-circulatory-death EVLP model, with assessment of lung physiology, edema, vascular barrier preservation, and metabolic stress. Transcriptomic, proteomic, and graph-based network analyses were integrated to identify molecular programs modulated by BMP9 therapy.
Results: Human EVLP datasets demonstrated coordinated suppression of BMP9 pathway components, including BMPR2, ACVRL1, ENG, ID1, ID3, TMEM100, and GADD45B. This phenotype was recapitulated in the lung-chip model. In pulmonary microvascular endothelial cells, exogenous BMP9 restored SMAD1/5/9 phosphorylation after cold-storage injury and induced ID1 and TMEM100 through ALK-dependent signaling. In the lung-chip system, vascular BMP9 selectively reprogrammed endothelial transcriptional responses with minimal epithelial effects. In porcine DCD EVLP, BMP9 improved physiologic performance, reduced edema, preserved vascular barrier proteins, and attenuated metabolic stress. Multi-omic profiling identified broad molecular remodeling and highly interconnected injury-network cores preferentially modulated by BMP9.
Conclusions: BMP9 signaling is suppressed in donor lungs during EVLP. Restoration of endothelial BMP9 signaling improves donor lung recovery and modulates central molecular injury networks, supporting BMP9 as a promising graft-directed reconditioning strategy for marginal donor lungs.