Exosomes Derived from Human Umbilical Cord Mesenchymal Stem Cells Regulate Macrophage Polarization to Attenuate Systemic Lupus Erythematosus-Associated Diffuse Alveolar Hemorrhage in Mice

BACKGROUND AND OBJECTIVES: To investigate the effect and the underlying mechanism of exosomes secreted by human umbilical cord mesenchymal stem cells (hUCMSCs) on diffuse alveolar hemorrhage (DAH) in murine lupus. METHODS AND RESULTS: Exosomes were extracted from cultured hUCMSCs by ultracentrifugation. The expressions of exosome markers (Alix, CD63 and TSG101) were measured for identification of hUCMSC-derived exosomes (hUCMSC-exosomes). The alveolar hemorrhage of DAH mice was revealed by H&E staining. The primary alveolar macrophages were isolated from bronchoalveolar lavage fluid (BALF) of DAH mice. The expressions of M1 macrophage markers (iNOS, IL-6, TNF-α and IL-1β) and M2 macrophage markers (Arg1, IL-10, TGF-β and chi3l3) were detected. Flow cytometry measured the ratio of M1/M2 macrophages. ELISA measured the secretion of pro-inflammatory cytokines (IL-6 and TNF-α) and anti-inflammatory cytokines (IL-10 and TGF-β). DAH mice had hemorrhage and small-vessel vasculitis in the lung, with neutrophil and monocyte infiltration observed around the capillary and small artery. Furthermore, increases of IL-6 and TNF-α, and decreases of IL-10 and TGF-β were detected in the BALF of DAH mice. M1 makers were overexpressed in alveolar macrophages of DAH mice while M2 makers were lowly expressed. DAH mice had a higher proportion of M1 macrophages than M2 macrophages. After hUCMSC-exosome or methylprednisolone treatment in DAH mice, the alveolar injuries and inflammatory responses were attenuated, and the proportion of M2 macrophages was increased. CONCLUSIONS: hUCMSC-exosomes attenuate DAH-induced inflammatory responses and alveolar hemorrhage by regulating macrophage polarization.