Immune regulation by macrophage-derived small extracellular vesicles in attenuating inflammatory pain
Year: 2024
Type: dissertation
Abstract: 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.
DOI: 10.17918/00010442
Authors: Xuan Luo, Seena Ajit
Language: English
Subfield: Physiology
Field: Medicine
Domain: Health Sciences
Open Access status: gold
OpenAlex ID: W4401639102