Abstract Introduction Acute lung injury (ALI) results in endothelial dysfunction and increased vascular permeability, leading to systemic vascular leakage and heightened risk of secondary complications. Despite significant progress in understanding its pathogenesis, no targeted pharmacological therapy has been shown to improve clinical outcomes. The complement system is an innate immune defense system that eliminates pathogens by activating and forming the membrane attack complex (MAC), leading to cell lysis. Excessive complement activation, accompanied by endothelial injury and cell death, has been observed in patients with ALI. CD59 is abundantly expressed on vascular endothelial cells, where it is a key inhibitor of complement activation by blocking MAC formation on the cell surface. Extracellular vesicles (EVs) are naturally secreted by cells and serve as a “natural delivery system,” mediating intercellular and inter-organ communication. EVs could regulate inflammation and vascular homeostasis by transferring complement-regulatory proteins, such as CD59, that inhibits complement-mediated injury. However, the role of CD59 in maintaining endothelial integrity and attenuating vascular leakage during acute lung injury remains unclear. Methods This study used a Wild-type (WT) and Cd59 knockout (Cd59-/-) mouse model, and Klebsiella pneumoniae (K. pneu) was used to induce ALI. Hematoxylin and eosin staining and the lung wet-to-dry weight ratio were measured to assess the lung injury. Pulmonary vascular permeability following K. pneu infection was quantified using Evans Blue and fluorescein dye administered via tail-vein injection. Immunofluorescence and Western blot assays were employed to evaluate membrane attack complex expression under infected conditions. Results Our results demonstrate that both mRNA and protein levels of CD59 were significantly decreased in human and primary murine endothelial cells following K. pneu infection. Consistently, reduced CD59 expression was observed in CD31-positive endothelial cells within infected murine lung tissues. Moreover, Cd59-/- mice exhibited worsened outcomes, including decreased survival, greater body weight loss, enhanced pulmonary edema, and increased vascular leakage. To evaluate the therapeutic potential of CD59, PKH26-labeled engineered EVs overexpressing CD59 and LFA-1, which bind to endothelial ICAM-1/2, were injected in vivo. Engineered EVs efficiently targeted endothelial cells in the murine lung, and have significantly improved survival, body weight loss, pulmonary edema and vascular leakage after infection. Conclusion Our results demonstrate that Cd59-/- mice show worsened outcomes during bacteria-induced lung injury and endothelial barrier integrity. Delivering engineered EV carrying CD59 attenuated bacteria-induced pulmonary edema and vascular leakage. Thus, CD59 could be a potential target for treating ALI-induced vascular dysfunction. This abstract is funded by: National Institutes of Health and American Heart Association Postdoctoral Fellowship
Zhu et al. (Fri,) studied this question.