Exosomes derived from TGF-β1-modified mesenchymal stem cells protect septic mice by inducing macrophage M2 polarization

Exosomes derived from mesenchymal stem cells (MSCs) have been reported to improve the prognosis in septic mice. Additionally, we have confirmed that TGF-β1 plays a critical role in MSC-mediated protection against sepsis. In this study, we aimed to investigate whether exosomes derived from TGF-β1-overexpressing MSCs (TGF-β1-Exo) offer protective effects in sepsis. MSCs were collected from mouse MSCs stably transfected with TGF-β1 using a lentiviral vector. Exosomes were isolated and purified from MSCs (Exo), GFP-MSCs (GFP-Exo), and TGF-β1-MSCs (TGF-β1-Exo). A sepsis model was induced in mice via cecal ligation and perforation (CLP). After 6 h, exosomes from different sources were intravenously administered into septic mice. Mice were euthanised 24 h later, and histopathological changes were assessed using hematoxylin and eosin (H&E) staining. Inflammatory cytokine levels were measured using ELISA and RT-PCR. Flow cytometry was employed to evaluate macrophage phenotypes in lung tissues and in vitro macrophages. Additionally, we co-cultured fluorescently labeled exosomes with macrophages in vitro. TGF-β1-Exo significantly ameliorated histopathological damage and improved survival rates in septic mice. ELISA and RT-PCR analyses revealed that several pro-inflammatory cytokines were notably suppressed in the TGF-β1-Exo group. Furthermore, TGF-β1-Exo promoted the polarization of M1 macrophages to M2 macrophages both in vivo. In vitro, TGF-β1-Exo were internalized by LPS-pretreated macrophages, promoting the shift from the M1 to M2 phenotype, reducing the expression of pro-inflammatory cytokines, and enhancing the production of anti-inflammatory factors. Our findings suggest that TGF-β1-Exo exert therapeutic effects in septic mice by modulating macrophage polarization and inhibiting macrophage-mediated inflammation.