RAGE deficiency improves alveolar fluid clearance in LPS-induced acute lung injury by preventing downregulation of Na-K-ATPase and ENaC

Abstract

Rationale: Receptor for advanced glycation end products (RAGE) is implicated in inflammatory responses in acute respiratory distress syndrome (ARDS) /acute lung injury (ALI), but its role in pulmonary edema formation remains unclear. Hence, we aim to explore potential mechanisms of RAGE signaling in ALI-related impaired alveolar fluid clearance (AFC). Methods: Serum and Bronchial Alveolar Lavage Fluid (BALF) samples were obtained from 11 ARDS patients and 10 healthy volunteers. Soluble RAGE (sRAGE) and albumin (ALB) levels were measured by ELISA, and the ratio of BALF and serum ALB (B/S) was defined as an indicator of pulmonary vascular permeability. ARDS mouse model was established by LPS intratracheal instillation in wide-type (WT) mice and RAGE knockout (KO) mice. AFC was determined by the change of FITC-labeled BSA instilled in the lung, and Na-K-ATPase and ENaC expressions were evaluated by Western-blot. Results: BALF sRAGE and B/S in ARDS patients was much higher than those in healthy volunteers (1004.74±1219.72vs.163.55±120.11 pg/ml; 5.60±7.73vs.0.40±0.31‰), and BALF sRAGE was positively related to B/S. In animal study, LPS markedly increased BALF sRAGE and B/S levels, whereas significantly decreased AFC; BALF sRAGE was negatively related to AFC but positively related to B/S. All the effects of LPS were alleviated in KO mice (AFC: 14.43±4.76vs.6.82±2.31%; B/S: 5.37±2.75vs.9.42±0.47‰). BALF sRAGE was undetectable in KO mice. Moreover, LPS-induced downregulation of Na-K-ATPase and ENaC was prevented by RAGE depletion. Conclusions: Our findings imply that RAGE is involved in impaired AFC by regulating Na-K-ATPase and ENaC expression in ALI/ARDS.