Angiopoietin ligands Ang1 and Ang2 and the Tie2 receptor tyrosine kinases form an endothelial signaling pathway regulating vascular homeostasis and controlling vessel permeability, inflammation and angiogenic responses. Whereas Ang1-mediated Tie2 activation reduces inflammation and endothelial permeability, its antagonist, Ang2 increases it. Increased plasma Ang2 levels are associated with poor outcomes in patients with acute lung injury (ALI), as well as in acute respiratory distress syndrome (ARDS). In the study presented here we tested the effect of a novel synthetic, nucleoside-modified mRNA-76 encoding for a hyperactive Ang1 derived fusion protein (COMP-Ang1) on attenuating post-inflammation vascular leakage. COMP-Ang1 mRNA was formulated into a cationic lipid nanoparticle (cLNP) using an optimized mixture of three different lipids and a microfluidic mixing technology. After intravenous injection, the respective mRNA-loaded LNPs were found to be delivered predominantly to the endothelial cells of the lung, while sparing other vascular beds. Also, the specific multimeric folding of the COMP-Ang1 protein complex appeared to be pivotal for its activity in preventing vascular leakage and in restoring the alveolar-endothelial barrier function in the inflamed and injured pulmonary vasculature. The mode of action of mRNA-76, such as its activation of the Tie2 signal transduction pathway, was tested by pharmacological studies in vitro and in vivo by systemic administration in respective mouse models. mRNA-76 was found to prevent lung vascular leakage/lung edema as well as neutrophil infiltration in an LPS-challenging model.