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Immune regulation by macrophage-derived small extracellular vesicles in attenuating inflammatory pain
Dissertation

Immune regulation by macrophage-derived small extracellular vesicles in attenuating inflammatory pain

Xuan Luo
Doctor of Philosophy (Ph.D.), Drexel University
May 2024
DOI:
https://doi.org/10.17918/00010442
pdf
Luo_Xuan_20247.78 MB
PDF Embargoed Access, Embargo ends: 30 Jun 2026

Abstract

Chronic inflammatory pain Exosomes Innate immunity Microglia Small extracellular vesicles Pain
Chronic pain affects millions in the United States, and its development is associated with aberrant neuroimmune signaling. Small extracellular vesicles (sEVs) that transport RNAs, proteins, and lipids play a role in intercellular communication and can exert immunomodulatory effects in recipient cells. We showed that a single prophylactic injection of sEVs from RAW 264.7 macrophages two weeks prior attenuated inflammatory pain induced by complete Freund's adjuvant (CFA). How this long-term memory develops, and how sEVs regulate immune responses are unknown. Recent studies show that microglia that were primed with inflammatory stimuli can enhance or suppress responses to a delayed secondary insult via epigenetic modifications. We hypothesized that prophylactic macrophage-derived sEVs, when administered intrathecally, confer accelerated resolution of inflammatory pain by reprogramming epigenetic immune memory in spinal microglia and by promoting anti-inflammatory immune responses in recipient CFA model mice. To study immune cell dynamics, we used ChipCytometry, a high-plex spatial assay, and observed a decrease in natural killer cells in spinal cord and an increase in the percentage of CD206+ anti-inflammatory macrophages out of all macrophages detected in dorsal root ganglion in sEV-treated CFA model compared to control model mice. To determine whether prophylactic sEVs could attenuate pain in the absence of microglia, we ablated spinal microglia using a CSF1R inhibitor PLX5622. sEV-induced pain prophylaxis was completely abolished in PLX5622-fed mice, indicating that microglia are necessary for sEVs to confer pain protection. ChIP-seq analysis revealed an increased number of gene loci enriched for H3K4me1, a hallmark of innate immune memory, in spinal microglia 14 days after sEV administration. Furthermore, inhibiting the H3K4 methyltransferase SETD7 to prevent H3K4me1 deposition abolished sEV-induced pain attenuation. Overall, our findings shed light on the mechanisms underlying pain prophylaxis, providing novel insights for the development of non-addictive preventive analgesia.

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