Small extracellular vesicles mediated signaling and pain

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.

Grant Number: 5R01NS129191-04
NIH Institute/Center: NIH
Principal Investigator: Seena Ajit