Conditioned medium from the stem cells of human exfoliated deciduous teeth ameliorates neuropathic pain in a partial sciatic nerve ligation model

Background: Although recent studies have revealed the powerful antinociceptive effect of human dental pulp stem cells in an animal model for diabetes and osteoarthritis, its analgesic mechanisms are still largely elusive. We have previously reported that conditioned medium (CM) from dental pulp stem cells of deciduous teeth (SHED-CM) or its components, monocyte chemoattractant protein-1 (MCP-1) and the secreted ectodomain of sialic acid-binding Ig-like lectin-9 (sSiglec-9), directly induces anti-inflammatory M2 macrophages, however the antinociceptive activity of induced M2 is unknown. In this study, we investigated the antinociceptive effect of SHED-CM, MCP-1, and sSiglec-9 or secretome from M2-induced by SHED-CM (M2-CM) against neuropathic pain (NP) using a partial sciatic nerve ligation (PSL) mouse model and analyzed the mechanical bases of their antinociceptive effects. Methods: PSL mice were treated using SHED-CM with or without mannosylated-Clodrosome, specifically depleting M2 macrophages, recombinant MCP-1 and sSiglec-9 protein, M2-CM, or fibroblast-CM. Human Schwann cells activated by TNF-α in vitro were treated with M2-CM. The expression of pro-inflammatory mediators, neuroprotective factors, the nociceptive receptor, and markers for M1, M2, and activated glial cells in injured sciatic nerve (SCN), dorsal root ganglion, or spinal cord were evaluated by RT-PCR and immunohistochemistry. Mechanical allodynia of PSL mice was analyzed via von Frey test. Results: In the behavioral test, intravenous administration of SHED-CM greatly improved the PSL-induced hypersensitivity. SHED-CM treatment recruited M2 macrophages in the injured SCN and ipsilateral L4/L5 dorsal root ganglion and suppressed microglial activation in the spinal cord. Specific depletion of the M2 by mannosylated-Clodrosome markedly reduced the antinociceptive effect of SHED-CM. Intravenous administration of both MCP-1/sSiglec-9 and M2-CM ameliorated the PSL-induced hypersensitivity. We found that M2-CM directly suppressed the expression of nociceptive receptors as well as proinflammatory mediators in Schwann cells. Conclusion: Taken together, our data suggest that SHED-CM ameliorates NP through the induction of the analgesic anti-inflammatory M2 macrophages. Thus, SHED-CM may present as a potential novel therapeutic candidate for NP.