Spinal cord injury-derived exosomes exacerbate damage: miR-155-5p mediates inflammatory responses.

Spinal cord injury (SCI) is a critical event characterized by intricate pathogenic mechanisms. Although recent studies have highlighted tissue exosomes as key mediators of inflammatory responses in diverse organs and tissues, their role in SCI has yet to be determined. In this study, we investigated the role and mechanisms of spinal cord tissue exosomes in the inflammatory response following SCI. We found morphological, concentration, and functional differences between exosomes extracted from injured and normal spinal cord tissues, and identified proinflammatory effects associated with SCI-generated tissue exosomes (SCI-Exos) but not with exosomes derived from normal spinal cord tissue (Sham-Exos). Our in vivo and in vitro analyses showed that SCI-Exos promoted microglial M1 polarization and inflammatory cytokine expression, thereby exacerbating tissue and neuronal injury in the spinal cord. In addition, the combination of exosomal miRNA sequencing and experimental verification showed that the miR-155-5p level was higher in SCI-Exos than in Sham-Exos. We further found that SCI-Exos-derived miR-155-5p induced a significant inhibition of forkhead box O3a phosphorylation and activated the nuclear factorkappa B pathway, thereby promoting microglial M1 polarization and inflammatory cytokine expression. These findings suggest that injury-induced miR-155-5pcontaining exosomes exacerbate SCI via the promotion of microglial M1 polarization and inflammatory responses. Thus, targeting miR-155-5p expression or exosome secretion could be a novel strategy for attenuating inflammation and reducing secondary injury post-SCI.