Neuronal exosomal miR-25-3p attenuates M1 microglial activation and neurotoxicity by targeting TLR4 to regulate the NF-κB signaling pathway.

Background: Perioperative neurocognitive disorders (PND) are severe postoperative complications in the elderly, with neuroinflammation driven by pro-inflammatory M1 microglia being a core pathological mechanism. This study aimed to investigate the role of neuron-derived exosomes in regulating microglial polarization and its underlying molecular mechanism. Methods: We utilized a neuron-microglia transwell co-culture system. By modulating microRNA-25-3p (miR-25-3p) in neurons or Toll-like receptor 4 (TLR4) in microglia, we assessed microglial M1/M2 polarization, TLR4/NF-κB pathway activation, and subsequent neurotoxicity using qRT-PCR, Western Blot, flow cytometry, and dual-luciferase reporter assays. Results: Neuronal exosomes were effectively internalized by microglia. Exosomal miR-25-3p suppressed the activation of the TLR4/MyD88/NF-κB signaling pathway by directly targeting the 3'-UTR of TLR4. This significantly inhibited microglial polarization towards the pro-inflammatory M1 phenotype and reduced the release of pro-inflammatory cytokines. Functionally, this process attenuated M1 microglia-mediated neuronal apoptosis, oxidative stress, and functional impairment. Direct manipulation of TLR4 expression in microglia confirmed its pivotal role in this regulatory axis. Conclusion: Our findings systematically demonstrate that neurons can release exosomes carrying miR-25-3p to target and suppress the microglial TLR4/NF-κB signaling pathway, thereby inhibiting M1 polarization and alleviating neurotoxicity. This discovery deepens the understanding of PND pathophysiology and provides a theoretical basis and potential therapeutic targets for novel PND treatment strategies targeting neuron-glia communication.