Enhanced itaconic acid secretion from macrophages mediates the protection of mesenchymal stem cell-derived exosomes on lipopolysaccharide-induced acute lung injury mice.

Background: Alveolar macrophages (AMs) is critical to exacerbate acute lung injury (ALI) induced by lipopolysaccharide (LPS) via inhibiting inflammation, which could by shifted by mesenchymal stem cell-derived exosomes (MSC-exos). But the underlying rationale is not fully clarified. Our study aimed to analyze the significance of itaconic acid (ITA) in mediating the protective effects of MSC-exos on LPS-induced ALI.

Methods: MSC-exos were used to treat pulmonary microvascular endothelial cells (PMVECs) co-cultured with AMs under LPS stimulation. si-IRG1 was transfected to AMs. PMVEC permeability, apoptosis rates, and inflammatory cytokine levels were assessed. In vivo, C57BL/6 wild-type (WT) and Irg1-/- mice were employed to explore the protection of MSC-exos against LPS-induced ALI. The lung injury was determined by histological and biochemical assays. ITA levels were measured using gas chromatography-mass spectrometry. Western blot and flow cytometry analyses were performed to assess M1/M2 polarization.

Results: Co-culture with AMs significantly increased PMVEC permeability, apoptosis rates, IL-6, TNF-α levels and Claudin-5 and ZO-1 expression induced by LPS treatment, which were attenuated by MSC-exos accompanied by enhanced ITA level. After si-IRG1 transfection, MSC-exos' protective efficacy was reversed, with suppressed M2 polarization. In vivo, MSC-exos alleviated alveolar structure disruption, pulmonary edema, inflammation and increased ITA concentration in WT mice but had reduced effects in Irg1-/- mice, with neglected M2 polarization.

Conclusions: ITA secretion facilitated the MSC-exos' protective benefits on LPS-induced PMVEC damage and ALI in mice by promoting AM M2 polarization, highlighting a potential therapeutic strategy for ALI and related inflammatory lung diseases.