A study on the inflammatory responses of alveolar epithelial cells induced by lipopolysaccharide and the underlying mechanisms

Objective Lipopolysaccharide(LPS)can activate alveolar epithelial cells(AECs)and induce inflammatory injury. Toll-like receptor-4(TLR-4)is integrally involved in LPS signaling and plays a requisite role in the activation of NF-κB. NF-κB is a key intercellular signaling event that mediates cell inflammatory responses. The aim of the study was to investigate in an in vitro model the inflammatory responses of AECs induced by LPS and the underlying mechanisms. Methods The study was performed on A549 cells(Human lung adenocarcinoma cell line). A549 cells were divided into 2 groups: a control group and a LPS stimulation group. Proinflammatory cytokines ICAM-1, TNF-α and IL-8 were detected by ELISA or radioimmunological methods. The expression of TLR-4 mRNA was detected by real time PCR. The activation of NF-κB was detected by Western blot(proteins of I-κBα and NF-κB p65). Results Compared with the control group, the ICAM-1 and TNF-α levels of the LPS-stimulated group were significantly higher, peaked after 2 h, and then gradually decreased at 6 and 12 h. IL-8 was also significantly increased after 2 h, which continued up to 12 h. The expression of TLR-4 mRNA in the LPS group was significantly higher, peaked after 2 h and gradually decreased at 6 and 12 h. NF-κB was activated after 0.5, 2, 6 and 12 h, indicated by the significant degradation of IκB-α and the significant release of NF-κB P65 and its subsequent translocation into the nucleus approximately synchronized. Conclusion The results demonstrate that LPS induced inflammatory injury in AECs via activating TLR-4 and subsequently NF-κB. Key words: Lipopolysaccharide; Toll-like receptor 4; Nuclear factor-κB; Alveolar epithelia cells