Macrophage-derived exosomal HMGB3 regulates silica-induced pulmonary inflammation by promoting M1 macrophage polarization and recruitment

Background: Chronic inflammation and fibrosis are characteristics of silicosis, and the inflammatory mediators involved in silicosis have not been fully elucidated. Recently, macrophage-derived exosomes have been reported as inflammatory modulators, but their role in silicosis remains largely unexplored. The purpose of the present study was to investigate the role of macrophage-derived exosomal HMGB3 in silicosis. Methods: First, HMGB3 expression in macrophages (with or without silica (SiO2) exposure) and exosomes derived from these cells was measured by western blot analysis. Second, the role of exosomal HMGB3 in the inflammatory activation and migration of macrophages was evaluated by immunofluorescence, flow cytometry and transwell assays. The expression of IL-1β, IL-6 and TNF-α was detected by RT-PCR and ELISA, and the involved signal transduction pathways were studied by western blot analysis. Results: HMGB3 expression in SiO2-exposed macrophages and exosomes derived from these cells was significantly upregulated. In silicosis mouse model, upregulated HMGB3 was mainly colocalized with infiltrating macrophages. In vitro experiments demonstrated that exosomes derived from SiO2-exposed macrophages (SiO2-Exos) significantly upregulated the expression of TNF-α, IL-6, IL-1β, iNOS and CCR2 in monocytes or M0 macrophages, promoting M1 polarization and migration of these cells. An in vivo study demonstrated that SiO2-Exos promoted the infiltration of pulmonary macrophages and increased the proportion of iNOS+/F4/80+ macrophages. Knockdown of exosomal HMGB3 partially reversed this phenotype, while overexpression of exosomal HMGB3 promoted this phenotype. The proinflammatory effect of exosomal HMGB3 may be mediated through the activation of the STAT3/MAPK (ERK1/2 and P38)/NF-κB pathways. Conclusions: Exosomal HMGB3 is a potential inflammatory modulator in silicosis that induces inflammatory activation and recruitment of monocytes/macrophages by regulating the activation of the STAT3/MAPK/NF-κB/CCR2 pathways.