Opposite effects of ANP receptors in attenuation of LPS-induced endothelial permeability and lung injury

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.

Lipopolysaccharide Induces Alveolar Macrophage Necrosis via CD14 and the P2X7 Receptor Leading to Interleukin-1α Release

“…There is great interest in the mechanisms by which LPS disrupts the endothelial barrier to allow increased lung vascular permeability and alveolar edema. Multiple mechanisms have been postulated, including decreased intracellular cAMP concentrations (Schlegel et al, 2009), modulation of atrial natriuretic peptide receptors (Xing et al, 2012), induction of sphingosine-1-phosphatase (Zhao et al, 2011), and stimulation of RhoA-Rho kinase pathway (Han et al, 2013), among others. However, while experimental evidence indicates that LPS administered to the lung does not signal through toll-like receptor-4 (TLR4) on the endothelium but instead targets hematopoietic and epithelial cells (Andonegui et al, 2009), it remains uncertain as to which secondary mediators, such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and other cytokines released from macrophages and/or damaged epithelium, provide the necessary signals on the endothelium for vascular dysfunction and neutrophil influx (Salgado et al, 1994).…”

Role of microtubules in attenuation of PepG-induced vascular endothelial dysfunction by atrial natriuretic peptide

“…For example, introduction of ANP reduced mortality rate and had a beneficial effect in patients with ALI [48]. Transient elevation of ANP mRNA levels was observed in the lungs of LPS-challenged mice [25,49] and is consistent with the hypothesis of increased endogenous ANP levels as a compensatory mechanism to reduce the lung’s inflammatory response to bacterial agents.…”