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To explore the effect of double-stranded RNA-dependent kinase (PKR) in acute lung injury (ALI) and resultant acute respiratory distress syndrome (ARDS). A mouse model of lipopolysaccharide (LPS)-induced ALI was used to evaluate the levels of phosphorylated (p)-PKR and NLRP3 in lung tissue, and the protective effects of a PKR inhibitor on lung injury. And in vitro, macrophages were incubated with LPS, with or without PKR inhibitor pre-treatment. It was observed that the levels of p-PKR protein and NLRP3 protein were significantly increased compared with those in control tissues after LPS administration. Meanwhile, treatment with PKR inhibitor decreased inflammation, injury score, wet/dry weight ratio, bronchoalveolar lavage fluid (BALF) protein levels, neutrophil count in BALF, myeloperoxidase activity and expression of high-mobility group box1(HMGB1) and interleukin(IL)-1β in the lungs of LPS-challenged mice. In vitro, we demonstrated that the levels of p-PKR and NLRP3, and cell mortality rate were increased in macrophages which were incubated with LPS compared with those without LPS administration, and PKR inhibitor significantly suppressed the level of NLRP3, caspase-1, HMGB1 and IL-1β. These results indicate that PKR plays a key role in ALI through NLRP3-pyrotosis pathway and pharmacological inhibition of PKR may have potential therapeutic effects in the treatment of patients with ALI and ARDS. • The role of PKR in the pathogenesis of ALI/ARDS was explored. • Inhibition of PKR protects against LPS-induced ALI by suppressing NLRP3-pyrotosis pathway. • Pharmacological inhibition of PKR may have potential therapeutic effects in the treatment of patients with ALI and ARDS. [ABSTRACT FROM AUTHOR]

Neutrophils activated during acute lung injury (ALI) form neutrophil extracellular traps (NETs) to capture pathogens. However, excessive NETs can cause severe inflammatory reactions. Macrophages are classified as M1 macrophages with proinflammatory effects or M2 macrophages with anti-inflammatory effects. During ALI, alveolar macrophages (AMs) polarize to the M1 phenotype. This study tested the hypothesis that NETs may aggravate ALI or acute respiratory distress syndrome (ARDS) inflammation by promoting alveolar macrophage polarization to the M1 type. Our research was carried out in three aspects: clinical research, animal experiments and in vitro experiments. We determined that NET levels in ARDS patients were positively correlated with M1-like macrophage polarization. NET formation was detected in murine ALI tissue and associated with increased M1 markers and decreased M2 markers in BALF and lung tissue. Treatment with NET inhibitors significantly inhibitor NETs generation, downregulated M1 markers and upregulated M2 markers. Regardless of LPS pre-stimulation, significant secretion of proinflammatory cytokines and upregulated M1 markers were detected from bone marrow-derived macrophages (M0 and M2) cocultured with high concentrations of NETs; conversely, M2 markers were downregulated. In conclusion, NETs promote ARDS inflammation during the acute phase by promoting macrophage polarization to the M1 phenotype. We propose that NETs play an important role in the interaction between neutrophils and macrophages during the early acute phase of ALI. [ABSTRACT FROM AUTHOR]