Inflammation contributes to pain hypersensitivity through multiple mechanisms. Among the most well characterized of these is the sensitization of primary nociceptive neurons by arachidonic acid metabolites such as prostaglandins through G protein-coupled receptors. However, in light of the recent discovery that the nociceptor-specific ion channel transient receptor potential A1 (TRPA1) can be activated by exogenous electrophilic irritants through direct covalent modification, we reasoned that electrophilic carbon-containing A- and J- series prostaglandins, metabolites of prostaglandins (PG) E2 and D2, respectively, would excite nociceptive neurons through direct activation of TRPA1. Consistent with this prediction, the PGD2 metabolite 15-deoxy-Δ12,14-prostaglandin J2 (15dPGJ2) activated heterologously expressed human TRPA1 (hTRPA1-HEK), as well as a subset of chemosensitive mouse trigeminal neurons. The effects of 15dPGJ2 on neurons were blocked by both the nonselective TRP channel blocker ruthenium red and the TRPA1 inhibitor (HC-030031), but unaffected by the TRPV1 blocker iodo-resiniferatoxin. In whole-cell patch-clamp studies on hTRPA1-HEK cells, 15dPGJ2 evoked currents similar to equimolar allyl isothiocyanate (AITC) in the nominal absence of calcium, suggesting a direct mechanism of activation. Consistent with the hypothesis that TRPA1 activation required reactive electrophilic moieties, A- and J-series prostaglandins, and the isoprostane 8-iso-prostaglandin A 2-evoked calcium influx in hTRPA1-HEK cells with similar potency and efficacy. It is note-worthy that this effect was not mimicked by their nonelectrophilic precursors, PGE2 and PGD2, or PGB 2, which differs from PGA2 only in that its electrophilic carbon is rendered unreactive through steric hindrance. Taken together, these data suggest a novel mechanism through which reactive prostanoids may activate nociceptive neurons independent of prostaglandin receptors.
ASJC Scopus subject areas
- Molecular Medicine