Abstract
Atrial natriuretic peptide (ANP) has been recently identified as a modulator of acute lung injury (ALI) induced by pro-inflammatory agonists. While previous studies tested effects of exogenous ANP administration, the role of endogenous ANP in the course of ALI remains unexplored. This study examined regulation of ANP and its receptors NPR-A, NPR-B and NPR-C by LPS and involvement of ANP receptors in the modulation of LPS-induced lung injury. Primary cultures of human pulmonary endothelial cells (EC) were used in the in vitro tests. Expression of ANP and its receptors was determined by quantitative RT-PCR analysis. Agonist-induced cytoskeletal remodeling was evaluated by immunofluorescence staining, and EC barrier function was characterized by measurements of transendothelial electrical resistance. In the murine model of ALI, LPS-induced lung injury was assessed by measurements of protein concentration and cell count in bronchoalveolar lavage fluid (BAL). LPS stimulation significantly increased mRNA expression levels of ANP and NPR-A in pulmonary EC. Pharmacological inhibition of NPR-A augmented LPS-induced EC permeability and blocked barrier protective effects of exogenous ANP on LPS-induced intercellular gap formation. In contrast, pharmacological inhibition of ANP clearance receptor NPR-C significantly attenuated LPS-induced barrier disruptive effects. Administration of NPR-A inhibitor in vivo exacerbated LPS-induced lung injury, whereas inhibition of NPR-C suppressed LPS-induced increases in BAL cell count and protein content. These results demonstrate for the first time opposite effects of NPR-A and NPR-C in the modulation of ALI and suggest a compensatory protective mechanism of endogenous ANP in the maintenance of lung vascular permeability in ALI.