title: Netrin-1 promotes epithelial sodium channel-mediated alveolar fluid clearance via activation of the adenosine 2B receptor in lipopolysaccharide-induced acute lung injury.
abstract: BACKGROUND
  The epithelial sodium channel (ENaC) is the driving force for pulmonary edema absorption in acute lung injury (ALI). Netrin-1 is a newly found anti-inflammatory factor that works by activating the adenosine 2B receptor (A2BAR). Meanwhile, activated A2BAR has the potential to enhance ENaC-dependent alveolar fluid clearance (AFC). However, whether netrin-1 can increase ENaC-mediated AFC by activating A2BAR remains unclear.
  
  
  OBJECTIVE
  To investigate the effect of netrin-1 on AFC in ALI and clarify the pathway via which netrin-1 regulates the expression of ENaC in vivo and in vitro.
  
  
  METHODS
  An ALI model was established by intratracheal instillation of lipopolysaccharide (LPS; 5 mg/kg) in C57BL/J mice, followed by netrin-1 with or without pretreatment with PSB1115, via the caudal vein. Twenty-four hours later, the lungs were isolated for determination of the bronchoalveolar lavage fluid, the lung wet/dry weight (W/D) ratio, AFC, the expressions of α-, β-, and γ-ENaC, and cyclic adenosine monophosphate (cAMP) levels. LPS-stimulated MLE-12 cells were incubated with netrin-1 with or without preincubation with PSB1115. Twenty-four hours later, the expressions of α-, β-, and γ-ENaC were detected.
  
  
  RESULTS
  In vivo, netrin-1 expression was significantly decreased during ALI. Substituted netrin-1 significantly dampened the lung injury, decreased the W/D ratio, and enhanced AFC, the expressions of α-, β-, and γ-ENaC, and cAMP levels in ALI, which were abolished by specific A2BAR inhibitor PSB1115. In vitro, netrin-1 increased the expressions of α-, β-, and γ-ENaC, which were prevented by PSB1115.
  
  
  CONCLUSIONS
  These results indicate that netrin-1 dampens pulmonary inflammation and increases ENaC-mediated AFC to alleviate pulmonary edema in LPS-induced ALI by enhancing cAMP levels through the activation of A2BAR.
authors.affiliation: Respiratory Medicine, Second Afﬁliated Hospital of Chongqing Medical University, Chongqing, China.
authors.forename: Jing
authors.initials: J
authors.lastname: He
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Wang
authors.initials: W
authors.lastname: Deng
authors.forename: Dao-xin
authors.initials: DX
authors.lastname: Wang
mesh_terms: D055371:Acute Lung Injury / Q000139:chemically induced / Q000378:metabolism*; D058917:Adenosine A2 Receptor Antagonists; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D004195:Disease Models, Animal; D053503:Epithelial Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000633:toxicity; D008168:Lung / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009414:Nerve Growth Factors / Q000378:metabolism* / Q000494:pharmacology; D000075388:Netrin-1; D011654:Pulmonary Edema / Q000139:chemically induced / Q000378:metabolism*; D043704:Receptor, Adenosine A2B / Q000187:drug effects / Q000378:metabolism*; D065589:Respiratory Tract Absorption / Q000187:drug effects; D025521:Tumor Suppressor Proteins / Q000378:metabolism* / Q000494:pharmacology; D014970:Xanthines
chemical_list: C518874:1-propyl-8-(4-sulfophenyl)xanthine; D058917:Adenosine A2 Receptor Antagonists; D053503:Epithelial Sodium Channels; D008070:Lipopolysaccharides; D009414:Nerve Growth Factors; C000617353:Ntn1 protein, mouse; D043704:Receptor, Adenosine A2B; C507047:Scnn1a protein, mouse; C507049:Scnn1b protein, mouse; C507053:Scnn1g protein, mouse; D025521:Tumor Suppressor Proteins; D014970:Xanthines; D000075388:Netrin-1; D000242:Cyclic AMP