Small extracellular vesicles mediated signaling and pain

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Abstract Chronic pain is the most prevalent, disabling, and expensive public health condition in the United States. The goal of this project is to elucidate how to harness body’s own analgesic mechanisms to provide pain relief. We propose to investigate 30-150 nm small extracellular vesicles (sEVs) that transport mRNAs, miRNAs, proteins, and lipid mediators to recipient cells via circulation. Uptake of sEVs induce gene expression changes in recipient cells and thus, sEVs play an important role in intercellular communication. We observed that sEVs from RAW 264.7 macrophage cells show therapeutic and prophylactic efficacy in a complete Freud adjuvant (CFA) mouse model of inflammatory pain. Our preliminary studies show that mouse serum derived sEVs also conferred prophylaxis when injected intrathecally in naïve recipient mice that, two weeks later, received a hind paw injection of CFA. Thus, mice that received sEVs can remember this stimulation for at least 2 weeks and show an attenuated response to CFA. How this long-term memory develop is unknown. Though chronic pain is prevalent, an immunization strategy has not yet been tested and our studies will provide the rationale and mechanistic basis for such a strategy. Here we propose to test the hypothesis that monocyte/macrophage-derived sEV subsets in serum are necessary and sufficient to attenuate inflammatory pain hypersensitivity and confer prophylaxis. We will also investigate if monocyte/macrophage sEVs recruit, or promote anti- inflammatory phenotype switching of immune cells in dorsal root ganglion and spinal cord by quantitative immunophenotyping in situ, before and after CFA treatment. Recent studies show that microglia, the resident macrophages of the central nervous system can enhance or suppress responses to a delayed secondary insult through epigenetic modifications. We hypothesize that monocyte/macrophage-derived sEVs impart epigenetic immune memory in spinal microglia of recipient mice, granting the capacity to attenuate pain from a future insult and contribute to the prophylactic effect of sEVs. The studies proposed will elucidate the role of sEVs in immune regulation and memory.