IRF1α/XBP-1 Promoted β-catenin Signaling Activation Of Airway Epithelium In Lipopolysaccharide-induced Acute Lung Injury

Background:Acute lung injury(ALI)/acute respiratory distress syndrome(ARDS)is a major cause of respiratory failure in critically ill patients,with high morbidity and mortality.Previous study of ours have reported airway epithelium barrier dysfunction in LPS-induced ALI models of mice,which suggests epithelial injury as a major cause of ALI.β-catenin not only plays a vital role in maintaining the integrity of intercellular connections,but also involves in classical Wnt signal activation participating in inflammation.Compared with all other pulmonary cell types,airway epithelial-cells expressed the higher abundant β-catenin.However,it remains unclear about the activation pathway of β-catenin in airway epithelium under ALI.Inositol-requiring protein 1α(IRE1α)/X box protein-1(XBP1)pathway was proved to regulate inflammation in lipopolysaccharide(LPS)-induced lung injury.XBP-lu(unspliced X box protein-1)directly binds to β-catenin and promotes its ubiquitin-mediated degradation.Yet,the role of IRE1α/XBP-1 on epithelia β-catenin in LPS-induced ALI remains to be elucidated.Our study clarified whether IRE1α/XBP-1 signaling mediates the activation of epithelia β-catenin in LPS-induced ALI.Methods:In vitro and in vivo ALI models were induced with LPS in Beas-2B cells(200μg/mL)and mice(5mg/kg).Four groups were divided randomly:(1)control;(2)LPS;(3)LPS+4μ8c;(4)LPS+STF-083010,where 4μ8c and STF-083010 are targeted antagonists of IRE1α.Methods,including immunohistochemical staining,immunofluorescence,western blot,ELISA and qPCR,were exploited to measure pathologic features and the gene expression,which would reveal the possible effect of IRE1α/XBP-1 signaling on β-catenin pathway in LPS-induced ALI airway epithelia.Results:In mice and cell models,up-regulated expression of IRE1α/XBP1 markers,immunoglobulin-binding protein(BIP)and XBP-1s(spliced X box protein-1),was detected after LPS exposure,along with the increased expression of p-Akt(Ser473)and p-GSK 3β(Ser9).Besides,LPS also led to a down-regulation of total β-catenin in the lungs of mice and Beas-2B cells,featuring decreased membranous distribution and increased cytoplasmic and nuclear accumulation,paralleled by extensively up-regulated downstream targets of the Wnt/β-catenin signaling(MMP3、MMP7、MMP9).Treatment with either 4μ8c or STF-083010 reversed the afore-mentioned processes(except for MMP3 and MMP7),as well as significantly attenuating LPS-induced neutrophilic airway inflammation and lung injury,down-regulating the level of inflammatory factors in BALF(IL-6、TNF-α),improving capillary permeability and pulmonary edema,and reducing the exudation of proteins in the alveolar lumen.Conclusion:Blockade of IRE1α/XBP1 pathway alleviated LPS-induced ALI and inhibited the activation of airway epithelial β-catenin signaling.