P2X receptors‐mediated cytosolic phospholipase A₂ activation in primary afferent sensory neurons contributes to neuropathic pain

Abstract

Activation of P2X 3 and P2X 2/3 receptors (P2X 3 R/P2X 2/3 R), ionotropic ATP receptor subtypes, in primary sensory neurons is involved in neuropathic pain, a debilitating chronic pain that occurs after peripheral nerve injury. However, the underlying mechanisms remain unknown. We investigated the role of cytosolic phospholipase A 2 (cPLA 2 ) as a downstream molecule that mediates the P2X 3 R/P2X 2/3 R-dependent neuropathic pain. We found that applying ATP to cultured dorsal root ganglion (DRG) neurons increased the level of Ser505-phosphorylated cPLA 2 and caused translocation of Ser505-phosphorylated cPLA 2 to the plasma membrane. The ATP-induced cPLA 2 activation was inhibited by a selective antagonist of P2X 3 R/P2X 2/3 R and by a selective inhibitor of cPLA 2 . In the DRG in vivo, the number of cPLA 2 -activated neurons was strikingly increased after peripheral nerve injury but not after peripheral inflammation produced by complete Freund's adjuvant. Pharmacological blockade of P2X 3 R/P2X 2/3 R reversed the nerve injury-induced cPLA 2 activation in DRG neurons. Moreover, administering the cPLA 2 inhibitor near the DRG suppressed nerve injury-induced tactile allodynia, a hallmark of neuropathic pain. Our results suggest that P2X 3 R/P2X 2/3 R-dependent cPLA 2 activity in primary sensory neurons is a key event in neuropathic pain and that cPLA 2 might be a potential target for treating neuropathic pain.

Local Application of Nucleus Pulposus Induces Expression of P2x3 in Rat Dorsal Root Ganglion Cells

“…spinal nerve ligation, sciatic nerve ligation, Freund's adjuvant or carrageenan injection) using a selective P2X 3 /P2X 2/3 receptor antagonist 18) . In addition, P2X 3 /P2X 2/3 receptors dependent cytosolic phospholipase A2 activity in primary sensory neurons is a ley event in neuropathic pain 19) . In this study, incision of annulus fibrosis induced a significant increase the P2X 3 receptor expression in the DRG adjacent to the disc incision.…”

Platelet-Activating Factor and Pain

“…31) Contrastingly, neither the level of the phosphorylated cPLA 2 nor its localization was altered in DRG neurons after intraplantar injection of complete Freund's adjuvant in an animal model of chronic inflammatory pain. Thus, it is likely that cPLA 2 activation in DRG neurons is specifically associated with nerve injury.…”

“…Intrathecal administration of an inhibitor of cPLA 2 suppresses nerve injury-induced tactile allodynia. 31) Furthermore, nerve injury increased phosphorylation of serine at amino acid position 505 of cPLA 2 in injured DRG neurons and translocation of phosphorylated cPLA 2 at the plasma membrane of injured DRG neurons. Phosphorylation and translocation are required for full activation of cPLA 2 .…”

“…42,43) Among the seven subtypes, pharmacological blockade of P2X3R and P2X2/3R by the selective antagonist A-317491 inhibits cPLA 2 activation in DRG neurons after nerve injury. 31) Applying ATP to cultured DRG neurons phosphorylates CaMKII and cPLA 2 and translocates these two proteins to the plasma membrane. Phosphorylation and translocation of CaMKII and cPLA 2 was abolished by A-317491 and by EGTA or a nonselective voltage-dependent Ca 2ϩ channel blocker.…”

“…We demonstrated an involvement of purinergic P2XRs. 31) P2XRs are a family of ligand-gated cation channels activated by extracellular ATP. 40,41) Molecular cloning has so far identified seven genes encoding P2XRs (P2X1R-P2X7R).…”