Glioblastoma- derived exosomes (GBM-Exo) regulate microglial M2 polarization via the RAC1/AKT/NRF2 pathway

The impact of exosome-mediated communication between glioblastoma and microglia on the formation of an immunosuppressive microenvironment remains to be explored. Tumor-associated macrophages are more likely to adopt an M2-like phenotype within the immunosuppressive environment. Here, we investigate the molecular mechanisms by which glioblastoma-derived exosomes promote microglial M2 polarization through RAC1.

The expression of RAC1 in GBM was collected from public databases. A C57BL/6 mouse glioma xenograft model was established using intracranial stereotactic injection. RAC1 expression was validated by qRT-PCR, Western blotting, and immunohistochemistry. Glioblastoma-derived exosomes were isolated by ultracentrifugation and characterized by Nanoparticle Tracking Analysis (NTA), transmission electron microscopy, and Western blotting for exosome markers, with the content of RAC1 being profiled. RAC1 and AKT inhibitors were used to co-treat microglia with exosomes. Microglial polarization under different treatment conditions was assessed by Western blotting and immunofluorescence.

Our study reveals that RAC1 is aberrantly expressed in glioblastoma and is associated with macrophage immune infiltration. GBM-derived exosomes, carrying RAC1, promote the M2 polarization of microglia. In microglia treated with GBM-derived exosomes, inhibition of RAC1 activity suppressed AKT phosphorylation and NRF2 nuclear translocation, while reducing the expression of M2 phenotype markers. Notably, following AKT inhibition, the exosome-induced NRF2 nuclear translocation was also significantly suppressed, highlighting the critical role of RAC1-mediated AKT activation in NRF2 translocation and microglial M2 polarization.

Our study demonstrates that RAC1-carrying GBM-exosomes promote M2 polarization of microglia, a process mediated through the RAC1/AKT/NRF2 pathway.