[Role and mechanism of lipopolysaccharide induced exosome in the pathogenesis of acute lung injury].

Objective: To explore the effect and mechanism of exosome derived from lipopolysaccharide (LPS)-induced mouse macrophage (RAW264.7) on acute lung injury. Methods: RAW264.7 were cultured in vitro and divided into 2 groups: control group and LPS-induced group. The exosomes were extracted from the two groups of cell supernatant by ultracentrifugation and classified into 2 groups: C-EXO group and LPS-EXO group. In vivo, random allocation was used to averagely divide the eighteen male C57BL/6 mice into 3 groups: control group, EXO-control group and EXO-LPS group. All mice were sacrificed after 12 h. The lung tissue was used for HE staining to assess the degree of acute lung injury as well as immunohistochemical staining for interleukin (IL) -1ß and tumor necrosis factor (TNF)-α. The tissue protein expression levels of IL-1ß, TNF-α, ß-catenin, E-cadhein, ZO-1 and Occludin were measured by Western blot. In vitro, alveolar type Ⅱ epithelial cells (MLE-12) were cultured and divided into 3 groups: C-control group, EXO-control-induced group and EXO-LPS-induced group. The tissue protein expression levels of IL-1ß, TNF-α, and Occludin were measured by Western blot after 12 h. Results: The two samples of C-EXO group and LPS-EXO group was proved to be exosomes. Under a light microscope, the lung tissue of EXO-LPS group showed inflammatory cell infiltration, hemorrhage, interstitial and alveolar edema, and the thickness of alveolar septum. The tissue protein levels of IL-1ß and TNF-α in EXO-LPS group were obviously higher than the control group, EXO-control group (1.331±0.203 and 0.274±0.018, 0.892±0.074; 0.800±0.096 and 0.596±0.025, 0.441±0.061; all P<0.05). While the tissue protein levels of Occludin showed the opposite phenomenon (0.251±0.021 and 0.862±0.029, 0.453±0.013; all P<0.05). In vitro, Compared with the C-control group and the EXO-control-induced group, the expression levels of IL-1ß and TNF-α increased significantly in the EXO-LPS-induced group (0.900±0.033 and 0.320±0.030, 0.661±0.028; 0.739±0.045 and 0.151±0.024, 0.360±0.037; all P<0.05). whereas the protein levels of Occludin expression were reversed in MLE-12 (0.585±0.082 and 0.941±0.090, 0.732±0.083; all P<0.05). Conclusion: Exosomes derived from LPS-induced RAW264.7 can induced the acute lung injury by affecting barrier function, which probably is related to the low degree of Occludin in alveolar type Ⅱ epithelial cells.