Protease-activated receptor 2 sensitizes the capsaicin receptor transient receptor potential vanilloid receptor 1 to induce hyperalgesia

Inflammatory proteases (mast cell tryptase and trypsins) cleave protease-activated receptor 2 (PAR(2)) on spinal afferent neurons and cause persistent inflammation and hyperalgesia by unknown mechanisms. We determined whether transient receptor potential vanilloid receptor 1 (TRPV1), a cation channel activated by capsaicin, protons, and noxious heat, mediates PAR(2)-induced hyperalgesia. PAR(2) was coexpressed with TRPV1 in small- to medium-diameter neurons of the dorsal root ganglia (DRG), as determined by immunofluorescence. PAR(2) agonists increased intracellular [Ca2+] ([Ca2+](i)) in these neurons in culture, and PAR(2)-responsive neurons also responded to the TRPV1 agonist capsaicin, confirming coexpression of PAR(2) and TRPV1. PAR(2) agonists potentiated capsaicin-induced increases in [Ca2+](i) in TRPV1-transfected human embryonic kidney (HEK) cells and DRG neurons and potentiated capsaicin-induced currents in DRG neurons. Inhibitors of phospholipase C and protein kinase C (PKC) suppressed PAR(2)-induced sensitization of TRPV1-mediated changes in [Ca2+](i) and TRPV1 currents. Activation of PAR(2) or PKC induced phosphorylation of TRPV1 in HEK cells, suggesting a direct regulation of the channel. Intraplantar injection of a PAR(2) agonist caused persistent thermal hyperalgesia that was prevented by antagonism or deletion of TRPV1. Coinjection of nonhyperalgesic doses of PAR(2) agonist and capsaicin induced hyperalgesia that was inhibited by deletion of TRPV1 or antagonism of PKC. PAR(2) activation also potentiated capsaicin-induced release of substance P and calcitonin gene-related peptide from superfused segments of the dorsal horn of the spinal cord, where they mediate hyperalgesia. We have identified a novel mechanism by which proteases that activate PAR(2) sensitize TRPV1 through PKC. Antagonism of PAR(2), TRPV1, or PKC may abrogate protease-induced thermal hyperalgesia.