A74-04 Loss of Lung Endothelial Protectin/CD59 Leads to Complement-mediated Endothelial Dysfunction in Pulmonary Fibrosis

Rationale A major contributor to the poor prognosis of Idiopathic Pulmonary Fibrosis (IPF) is the lack of effective therapeutics. Our published studies suggest that targeting dysfunctional pulmonary endothelial cells (ECs) and associated signaling pathways holds promising therapeutic potential. Using multiomics and bioinformatics analyses in preclinical aged mouse models of progressive lung fibrosis, we identified the complement system as a previously unrecognized mediator of pulmonary EC dysfunction. Recent studies report upregulation of complement regulators, including the terminal complement complex (C5b-9, or Membrane Attack Complex, MAC), in bronchoalveolar lavage fluid and serum from IPF patients. Importantly, our preliminary data reveal a decrease in endothelial CD59 (also known as protectin), a key surface receptor that shields cells from C5b-9-mediated injury, in lung ECs isolated from aged mice with persistent lung fibrosis. Thus, we sought to investigate whether loss of CD59 impairs endothelial protection against complement-mediated injury, potentially contributing to vascular dysfunction during progressive fibrosis. Methods lung ECs were isolated from human lung tissue (healthy donors: Gift of Hope, IL; IPF patients: Loyola University Chicago Transplant Center) and from lungs of young mice with persistent lung fibrosis induced by repetitive bleomycin injury (single dose bleomycin used as control). CD59 transcript levels were assessed by qPCR. Primary human lung ECs (healthy- and IPF-derived) were exposed to 20% human serum containing active complement or to 20% heat-inactivated serum as a control. Additionally, IPF-lung ECs were exposed to 20% human serum and treated with soluble CD59 (2 μg/ml). Complement deposition on lung ECs was assessed by immunostaining for C5b-9 (MAC). Results CD59 transcript levels were significantly downregulated in lung ECs isolated from 1) the repetitive injury mouse model (vs single dose) and 2) from human IPF lungs (vs healthy lungs), confirming its downregulation in multiple mouse and human models of progressive lung fibrosis. Upon treatment with human serum containing complement, MAC deposition was increased in IPF-lung ECs vs healthy lung ECs, indicating that CD59 plays an important role in protecting the endothelium from complement-mediated injury. Addition of soluble CD59 protected IPF-lung ECs from MAC deposition. Conclusion collectively, our data demonstrate that CD59 downregulation in lung ECs from mouse and human lungs increases their susceptibility to complement-mediated injury, while soluble CD59 can rescue human IPF lung ECs from such damage. These findings provide a foundation for future efforts to develop therapeutic approaches to restore or mimic CD59 function and protect lung ECs during progressive fibrosis. This abstract is funded by: James Depauw Grant for Pilot Projects