Rap1 mediates protective effects of iloprost against ventilator-induced lung injury.

Prostaglandin I(2) (PGI(2)) has been shown to attenuate vascular constriction, hyperpermeability, inflammation, and acute lung injury. However, molecular mechanisms of PGI(2) protective effects on pulmonary endothelial cells (EC) are not well understood. We tested a role of cAMP-activated Epac-Rap1 pathway in the barrier protective effects of PGI(2) analog iloprost in the murine model of ventilator-induced lung injury. Mice were treated with iloprost (2 microg/kg) after onset of high tidal volume ventilation (30 ml/kg, 4 h). Bronchoalveolar lavage, histological analysis, and measurements of Evans blue accumulation were performed. In vitro, microvascular EC barrier function was assessed by morphological analysis of agonist-induced gap formation and monitoring of Rho pathway activation and EC permeability. Iloprost reduced bronchoalveolar lavage protein content, neutrophil accumulation, capillary filtration coefficient, and Evans blue albumin extravasation caused by high tidal volume ventilation. Small-interfering RNA-based Rap1 knockdown inhibited protective effects of iloprost. In vitro, iloprost increased barrier properties of lung microvascular endothelium and alleviated thrombin-induced EC barrier disruption. In line with in vivo results, Rap1 depletion attenuated protective effects of iloprost in the thrombin model of EC permeability. These data describe for the first time protective effects for Rap1-dependent signaling against ventilator-induced lung injury and pulmonary endothelial barrier dysfunction.