RAGE inhibition alleviates LPS-induced lung injury via directly suppressing autophagic apoptosis of alveolar epithelial cells

Abstract Background: Advanced glycation end product receptor (RAGE) acts as the receptor of pro-inflammatory ligands and highly expressed in alveolar epithelial cells (AECs). Autophagy in AECs has received much attention nowadays. However, the role between autophagy and RAGE in the pathogenesis of acute lung injury remains unclear. Therefore, the aim of this study is to explore whether RAGE activation signals take part in disfunction of alveolar epithelial barrier through autophagic death.Methods: We established the acute lung injury animal model using C57BL/6 and ager genes knockout (ager -/- mice) mice. A549 cells were treated with siRNA to reduce ager gene expression. Autophagy was inhibited by 3-methyladenine. Lung injury was assessed by histopathological examination. Cell viability was estimated by cell counting kit-8. The serum and bronchoalveolar lavage fluid (BALF) of IL-6, IL-8 and soluble RAGE (sRAGE) evaluated by ELISA, further studied the involvement of RAGE signals, autophagy and apoptosis by western blots, immunohistochemistry, immunofluorescence, transmission electron microscopy and TUNEL test.Results: The expression of RAGE was promoted by LPS, which was associated with activation of autophagy both in mice lungs and A549 cells. sRAGE in the BALF presented a positive correlation with inflammatory factors, inflammation and apoptosis in lungs were alleviated in ager-/- mice than wild-type controls. Persistently activated autophagy contributed to cells apoptosis, while blocking autophagy by 3-MA protects from lung damage, ager knockdown inhibited LPS-induced autophagy and attenuated lung injury. RAGE knockdown by siRNA in A549 cells significantly suppressed LPS-induced autophagy activation and apoptosis. The expression of RAGE activates the downstream STAT3 signaling pathway. Conclusion: RAGE plays an essential role in the pathogenesis of AECs injury, RAGE inhibition alleviates LPS-induced lung injury via directly suppressing autophagic apoptosis of alveolar epithelial cells.