Protease-activated receptor 2 activation is sufficient to induce the transition to a chronic pain state

Pain. 2015 May;156(5):859-867. doi: 10.1097/j.pain.0000000000000125.

Abstract

Protease-activated receptor type 2 (PAR2) is known to play an important role in inflammatory, visceral, and cancer-evoked pain based on studies using PAR2 knockout (PAR2(-/-)) mice. We have tested the hypothesis that specific activation of PAR2 is sufficient to induce a chronic pain state through extracellular signal-regulated kinase (ERK) signaling to protein synthesis machinery. We have further tested whether the maintenance of this chronic pain state involves a brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (trkB)/atypical protein kinase C (aPKC) signaling axis. We observed that intraplantar injection of the novel highly specific PAR2 agonist, 2-aminothiazol-4-yl-LIGRL-NH2 (2-at), evokes a long-lasting acute mechanical hypersensitivity (median effective dose ∼12 pmoles), facial grimacing, and causes robust hyperalgesic priming as revealed by a subsequent mechanical hypersensitivity and facial grimacing to prostaglandin E2 (PGE2) injection. The promechanical hypersensitivity effect of 2-at is completely absent in PAR2(-/-) mice as is hyperalgesic priming. Intraplantar injection of the upstream ERK inhibitor, U0126, and the eukaryotic initiation factor (eIF) 4F complex inhibitor, 4EGI-1, prevented the development of acute mechanical hypersensitivity and hyperalgesic priming after 2-at injection. Systemic injection of the trkB antagonist ANA-12 similarly inhibited PAR2-mediated mechanical hypersensitivity, grimacing, and hyperalgesic priming. Inhibition of aPKC (intrathecal delivery of ZIP) or trkB (systemic administration of ANA-12) after the resolution of 2-at-induced mechanical hypersensitivity reversed the maintenance of hyperalgesic priming. Hence, PAR2 activation is sufficient to induce neuronal plasticity leading to a chronic pain state, the maintenance of which is dependent on a BDNF/trkB/aPKC signaling axis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Azepines / pharmacology
  • Behavior, Animal / drug effects
  • Benzamides / pharmacology
  • Brain-Derived Neurotrophic Factor / antagonists & inhibitors
  • Brain-Derived Neurotrophic Factor / metabolism
  • Butadienes / pharmacology
  • Chronic Pain / chemically induced
  • Chronic Pain / drug therapy
  • Chronic Pain / metabolism*
  • Chronic Pain / psychology
  • Dinoprostone / pharmacology
  • Disease Models, Animal
  • Facial Expression
  • Hydrazones / pharmacology
  • Hyperalgesia / chemically induced
  • Hyperalgesia / drug therapy
  • Hyperalgesia / metabolism*
  • Hyperalgesia / psychology
  • MAP Kinase Signaling System / drug effects
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Inbred ICR
  • Mice, Knockout
  • Nitriles / pharmacology
  • Protein Kinase C / antagonists & inhibitors
  • Receptor, PAR-2 / agonists*
  • Receptor, PAR-2 / antagonists & inhibitors*
  • Receptor, PAR-2 / deficiency
  • Receptor, PAR-2 / metabolism*
  • Receptor, trkB / antagonists & inhibitors
  • Signal Transduction / drug effects*
  • Thiazoles / pharmacology

Substances

  • 4EGI-1 compound
  • ANA 12 compound
  • Azepines
  • Benzamides
  • Brain-Derived Neurotrophic Factor
  • Butadienes
  • Hydrazones
  • Nitriles
  • Receptor, PAR-2
  • Thiazoles
  • U 0126
  • Receptor, trkB
  • PKC-3 protein
  • Protein Kinase C
  • Dinoprostone