Small extracellular vesicles derived from Nrf2-overexpressing human amniotic mesenchymal stem cells protect against lipopolysaccharide-induced acute lung injury by inhibiting NLRP3

Abstract Background Acute lung injury (ALI) is a major cause of respiratory failure in critically ill patients that results in significant morbidity and mortality. Recent studies indicate that cell-based therapies may be beneficial in the treatment of ALI. We recently demonstrated that Nrf2-overexpressing human amniotic mesenchymal stem cells (hAMSCs) reduce lung injury, fibrosis and inflammation in lipopolysaccharide (LPS)-challenged mice. Here we tested whether small extracellular vesicles (sEVs) derived from Nrf2-overexpressing hAMSCs (Nrf2-sEVs) could protect against ALI. sEVs were isolated from hAMSCs that overexpressed (Nrf2-sEVs) or silenced (siNrf2-sEVs) Nrf2. We examined the effects of sEVs treatment on lung inflammation in a mouse model of ALI, where LPS was administered intratracheally to mice, and lung tissues and bronchoalveolar lavage fluid (BALF) were analyzed 24 h later. Methods Histological analysis, immunofluorescence microscopy, western blotting, RT-PCR and ELISA were used to measure the inflammatory response in the lungs and BALF. Results We found that sEVs from hAMSCs are protective in ALI and that Nrf2 overexpression promotes protection against lung disease. Nrf2-sEVs significantly reduced lung injury in LPS-challenged mice, which was associated with decreased apoptosis, reduced infiltration of neutrophils and macrophages, and inhibition of pro-inflammatory cytokine expression. We further show that Nrf2-sEVs act by inhibiting the activation of the NLRP3 inflammasome and promoting the polarization of M2 macrophages. Conclusion Our data show that overexpression of Nrf2 protects against LPS-induced lung injury, and indicate that a novel therapeutic strategy using Nrf2-sEVs may be beneficial against ALI.