Critical Role of the Small GTPase RhoA in the Development of Pulmonary Edema Induced by Pseudomonas aeruginosa in Mice

Background: Pseudomonas aeruginosa is an opportunistic pathogen that can cause severe pneumonia in critically ill patients. We have reported previously that P. aeruginosa exotoxins S and T mediate in vitro the increase in protein permeability across lung endothelial cell monolayers via a RhoA-dependent mechanism. However, whether inhibition of RhoA would significantly attenuate P. aeruginosa-mediated lung injury in mice is unknown. Methods: P. aeruginosa-induced paracellular protein permeability was measured across bovine lung endothelial and rat alveolar epithelial type II cell monolayers with 125 I-albumin. Some cell monolayers were pretreated with RhoA inhibitor CGX0287 1 h before P. aeruginosa exposure. At 4 h after exposure, lung endothelial and epithelial permeability, bacterial counts, bronchoalveolar lavage fluid levels of keratinocyte-derived chemokine, myeloperoxidase activity, and alveolar fluid clearance were measured. Some mice were treated intraperitoneally with CGX0287 1 h before or after airspace instillation of P. aeruginosa. Results: RhoA inhibition attenuated in vitro P. aeruginosa— mediated increase in lung endothelial and epithelial permeability to protein and in vivo the development of pulmonary edema and inhibition of alveolar fluid clearance associated with P. aeruginosa pneumonia. Furthermore, RhoA inhibition decreased the systemic dissemination of P. aeruginosa and neutrophil activity in the lung tissue observed after airspace instillation of these bacteria. Conclusions: The small GTPase RhoA plays a critical role in mediating lung injury associated with P. aeruginosa pneumonia in mice. Thus, transient blockade of RhoA could attenuate lung damage caused by P. aeruginosa in critically ill patients.