Type I interferons enhance human dorsal root ganglion nociceptor excitability and induce TRPV1 sensitization
Type I interferons (IFNs) are critical cytokines for antiviral defense and are linked to painful inflammatory diseases like rheumatoid arthritis and neuropathic pain in humans. Studies in rodent models demonstrate a direct action on sensory neurons in the dorsal root ganglion (DRG) to promote hyperexcitability but rodent behavioral results are conflicting with some reports of pro-nociceptive actions and others of anti-nociception. Given the role of type I IFNs in human disease, we sought to clarify the action of action of IFN- and IFN-{beta} on human DRG (hDRG) nociceptors. We found that IFN receptor subunits IFNAR1 and IFNAR2 are functionally expressed by these neurons and their engagement induces canonical STAT1 signaling and non-canonical MAPK activation as measured by increased phosphorylation of the cap-binding protein eIF4E by MNK1/2 kinases. Using patch clamp electrophysiology, Ca2+-imaging, and multi-electrode arrays we demonstrate that IFN- and -{beta} increase the excitability of hDRG neurons with short (30 min) and long-term (24-48 h) exposure and prolong the duration of capsaicin responses, an effect that is blocked by inhibition of MNK1/2 with eFT508, a specific inhibitor of these kinases. Our studies support the conclusion that type I IFNs are pronociceptive when they interact with hDRG nociceptors in the periphery.