Macrophage-derived exosomes induce M2 microglial polarization to alleviate bone cancer pain

Bone cancer pain (BCP) is a frequent and debilitating complication in patients with malignant tumors, arising from a multifactorial interplay of bone destruction, neural injury, and inflammatory responses. Microglia can polarize into either an M1 phenotype, which aggravates nociception, or an M2 phenotype, which facilitates pain resolution. Activation of the TLR4/NF-κB signaling cascade is known to drive M1 polarization, thereby amplifying inflammation and neuronal damage. This study aimed to investigate whether macrophage-derived exosomes could mitigate BCP by modulating the TLR4/NF-κB pathway, suppressing M1 polarization, and enhancing M2 microglial polarization. In vitro, RAW264.7 macrophages were polarized to the M2 phenotype via IL-4 stimulation, and exosomes were subsequently isolated and applied to LPS-challenged BV2 microglial cultures. Polarization profiles were analyzed using flow cytometry, immunofluorescence, qRT-PCR, and Western blotting. In vivo, a rat BCP model was established, and exosome treatments were administered. Behavioral assays were performed to assess pain responses, followed by evaluation of microglial polarization and TLR4/NF-κB pathway activity in spinal cord tissue. Results demonstrated that IL-4 treatment effectively induced M2 polarization in RAW264.7 cells, and the isolated exosomes displayed characteristic morphology and marker expression. BV2 microglia internalized these vesicles, leading to pronounced inhibition of LPS-induced M1 polarization, promotion of M2 polarization, suppression of pro-inflammatory cytokine release, and downregulation of TLR4/NF-κB activation. In vivo, exosome administration elevated the mechanical pain threshold and attenuated pain-related behaviors, while spinal cord analyses revealed reduced expression of M1 markers, increased M2 markers, and marked suppression of TLR4/NF-κB signaling. Collectively, these findings indicate that macrophage-derived exosomes alleviate BCP through coordinated regulation of TLR4/NF-κB signaling and microglial polarization, suggesting their potential as a novel therapeutic option for managing bone cancer pain.