M2 microglial exosomal miR-1949 ameliorates sepsis-associated encephalopathy through DKK1/Wnt/β-catenin-mediated microglial repolarization.

Sepsis-associated encephalopathy (SAE), the most common neurological complication of sepsis with high mortality, lacks effective treatments. Although microglia play a significant role in SAE pathogenesis, the mechanisms of M2 microglial exosomes (M2-EXOs) and their microRNAs (miRNAs) remain unclear. The present study demonstrated that both M2 microglial conditioned media (M2-CM) and M2-EXO promote the phenotypic transformation of M1 microglia toward the M2 phenotype. In M2-EXO, among the differentially expressed miRNAs, miR-1949 exhibited the most significant difference. The dual-luciferase assay showed that miR-1949 could bind to the 3'UTR of Dickkopf-related protein 1 (DKK1). Further experiments confirmed that M2-EXO-miR-1949 mimic mediated microglial phenotypic transformation by inhibiting DKK1 and activating the Wnt/β-catenin pathway. Notably, a single injection of M2-EXO (10 μg/mouse, i.c.v.) or M2-EXO-miR-1949 mimic (0.1 nmol/mouse, i.c.v.) significantly reduced the mouse sepsis score (MSS), decreased cortical neural cell damage in SAE mice induced by lipopolysaccharide (LPS), inhibiting abnormal microglial activation and alleviating neuroinflammation. Meanwhile, M2-EXO-miR-1949 mimic markedly inhibited DKK1 and activated the Wnt/β-catenin pathway in vivo. What's more, the effects of M2-EXO-miR-1949 mimic were reversed by the Wnt/β-catenin pathway inhibitor XAV939. In contrast, the effect of M2-EXO-miR-1949 inhibitor (0.1 nmol/mouse, i.c.v.) was opposite to that of M2-EXO-miR-1949 mimic. Furthermore, co-transfection of the M2-EXO-miR-1949 mimic and inhibitor mutually neutralized their opposing effects, resulting in no significant changes in the expression of inflammatory and pathway-related markers, thereby confirming the functional specificity of exosomal miR-1949. In summary, the present study indicates that M2-EXO, especially its contained miR-1949, ameliorates LPS-induced SAE in mice through inhibiting DKK1 to activate the Wnt/β-catenin pathway, thereby leading to microglial phenotypic transformation and neuroinflammation inhibition. This study reveals a novel mechanism by which M2-EXO and miRNA ameliorate SAE, providing a theoretical basis for further studies.