Lung epithelial cell-derived IL-25 negatively regulates LPS-induced exosome release from macrophages

Background: Acute lung injury(ALI) is a major component of multiple organ dysfunction syndrome(MODS) following pulmonary and systemic infection. Alveolar macrophages(AMφ) are at the center of ALI pathogenesis. Emerging evidence has shown that cell-cell interactions in the lungs play an important regulatory role in the development of acute lung inflammation. However, the underneath mechanisms remain poorly addressed. In this study, we explore a novel function of lung epithelial cells(LEPCs) in regulating the release of exosomes from AMφ following LPS stimulation.Methods: For the in vivo experiments, C57 BL/6 wildtype(WT) mice were treated with lipopolysaccharide(LPS)(2 mg/kg) in 0.2 ml of saline via intratracheal aerosol administration. Bronchoalveolar lavage fluid was collected at 0–24 h after LPS treatment, and exosomes derived from AMφ were measured. For the in vitro studies, LEPCs and bone marrowderived Mφ(BMDM) were isolated from WT or TLR4-/-mice and were then cocultured in the Transwell? system. After coculture for 0–24 h, the BMDM and supernatant were harvested for the measurement of exosomes and cytokines.Results: We demonstrate that LPS induces macrophages(Mφ) to release exosomes, which are then internalized by neighboring Mφ to promote TNF-α expression. The secreted interleukin(IL)-25 from LEPCs downregulates Rab27 a and Rab27 b expression in Mφ, resulting in suppressed exosome release and thereby attenuating exosome-induced TNF-α expression and secretion.Conclusion: These findings reveal a previously unidentified crosstalk pathway between LEPCs and Mφ that negatively regulates the inflammatory responses of Mφ to LPS. Modulating IL-25 signaling and targeting exosome release may present a new therapeutic strategy for the treatment of ALI.