Protease-activated receptor 2 sensitizes TRPV1 by protein kinase Ce- and A-dependent mechanisms in rats and mice

摘要

Proteases that are released during inflammation and injury cleave protease-activated receptor 2 (PAR_2) on primary afferent neurons to cause neurogenic inflammation and hyper algesia. PAR_2-induced thermal hyperalgesia depends on sensitization of transient receptor potential vanilloid receptor 1 (TRPV1), which is gated by capsaicin, protons and noxious heat. However, the signalling mechanisms by which PAR_2 sensitizes TRPV1 are not fully characterized. Using immunofluorescence and confocal microscopy, we observed that PAR_2 was colocalized with protein kinase (PK) Ce and PKA in a subset of dorsal root ganglia neurons in rats, and that PAR_2 agonists promoted translocation of PKCe and PKA catalytic subunits from the cytosol to the plasma membrane of cultured neurons and HEK 293 cells. Subcellular fractionation and Western blotting confirmed this redistribution of kinases, which is indicative of activation. Although PAR_2 couples to phospholipase Cbeta, leading to stimulation of PKC, we also observed that PAR_2 agonists increased cAMP generation in neurons and HEK 293 cells, which would activate PKA. PAR_2 agonists enhanced capsaicin-stimulated increases in [Ca~(2+)]_i and whole-cell currents in HEK 293 cells, indicating TRPV1 sensitization. The combined intraplantar injection of non-algesic doses of PAR_2 agonist and capsaicin decreased the latency of paw withdrawal to radiant heat in mice, indicative of thermal hyperalgesia. Antagonists of PKCe and PKA prevented sensitization of TRPV1 Ca~(2+) signals and currents in HEK 293 cells, and suppressed thermal hyperalgesia in mice. Thus, PAR_2 activates PKCe and PKA in sensory neurons, and thereby sensitizes TRPV1 to cause thermal hyperalgesia. These mechanisms may underlie inflammatory pain, where multiple proteases are generated and released.