The Role Of PKR In Lipopolysaccharide Induced Acute Lung Injury In Mice And Its Mechanism

Background: Acute lung injury(ALI)/ acute respiratory distress syndrome(ARDS)is characterized by increased pulmonary capillary permeability,diffuse infiltration of inflammatory cells and progressive hypoxemia with poor prognosis,which can rapidly progress to multi-organ function failure.Patients with ALI/ARDS are usually critically ill and refractory,and also show a high mortality.Although many basic and clinical researches have been done,the pathology and pathogenesis have not yet been fully elucidated.And few drugs but only protective mechanical ventilation have been demonstrated to decrease the mortality.Protein kinase R(PKR),a double stranded RNA dependent protein kinase,was initially characterized to sense viral dsRNA and inhibit general protein synthesis.PKR was recently suggested as a danger-sensing molecule implicated in multiple pathophysiological processes such as inflammation,antitumor and immunomodulatory.However,whether PKR plays roles in lipopolysaccharide(LPS)-induced acute lung injury remains unclear.Objective: This study was aimed to reveal whether PKR was involved in LPS-induced ALI pathology and the potential mechanism.Methods: Acute lung injury was induced by a single intratracheal injection of LPS(1 mg/kg body weight,total volume of 50 ul).PKR phosphorylation was inhibited by intraperitoneal injection of different doses of C16(100 ug/kg and 500 ug/kg)1 h before LPS challenge.At 3 h,6 h,12 h after LPS challenge,lung phosphorylated PKR was detected.At 6h,lung tissues and bronchoalveolar lavage fluid were collected to evaluate lung injury.BCA,ELISA,Western Blot and immunohistochemistry wereused to detected inflammatory cytokines such as IL-1?,IL-6,TNF? in bronchoalveolar lavage fluid and the expression of caspase3,IKK,I?B?,NF-?B in lung.Results:1.Lung phosphor-PKR was increased after LPS challenge and peaked at 6h.2.Lung PKR phosphorylation was inhibited by intraperitoneal injection of C16.3.The level of protein in bronchoalveolar lavage fluid was significantly decreased by C16(P < 0.05).4.The expression of pro-inflammatory cytokines were significantly reduced by C16: TNF-?(P < 0.05),IL-1?(P < 0.05),IL-6(P < 0.05).5.C16 improved lung injury including neutrophil infiltration,pulmonary interstitial edema and alveolar destruction.6.There was no significant difference in the severity of pulmonary edema.7.C16 reduced the number of apoptotic cells in lung?8.C16 reduced the expression of Caspase3,p-IKK,p-IkB and p-NF-kB.Conclusion:These findings suggested that PKR inhibitor C16 ameliorated LPS-induced lung injury in mice by suppressing caspase3 and NF-?B signaling pathway.