Low nociceptor GRK2 prolongs prostaglandin E2 hyperalgesia via biased cAMP signaling to Epac/Rap1, protein kinase Cepsilon, and MEK/ERK

J Neurosci. 2010 Sep 22;30(38):12806-15. doi: 10.1523/JNEUROSCI.3142-10.2010.

Abstract

Hyperexcitability of peripheral nociceptive pathways is often associated with inflammation and is an important mechanism underlying inflammatory pain. Here we describe a completely novel mechanism via which nociceptor G-protein-coupled receptor kinase 2 (GRK2) contributes to regulation of inflammatory hyperalgesia. We show that nociceptor GRK2 is downregulated during inflammation. In addition, we show for the first time that prostaglandin E2 (PGE2)-induced hyperalgesia is prolonged from <6 h in wild-type (WT) mice to 3 d in mice with low GRK2 in Nav1.8+ nociceptors (SNS-GRK2+/- mice). This prolongation of PGE2 hyperalgesia in SNS-GRK2+/- mice does not depend on changes in the sensitivity of the prostaglandin receptors because prolonged hyperalgesia also developed in response to 8-Br-cAMP. PGE2 or cAMP-induced hyperalgesia in WT mice is PKA dependent. However, PKA activity is not required for hyperalgesia in SNS-GRK2+/- mice. SNS-GRK2+/- mice developed prolonged hyperalgesia in response to the Exchange proteins directly activated by cAMP (Epac) activator 8-pCPT-2'-O-Me-cAMP (8-pCPT). Coimmunoprecipitation experiments showed that GRK2 binds to Epac1. In vitro, GRK2 deficiency increased 8-pCPT-induced activation of the downstream effector of Epac, Rap1, and extracellular signal-regulated kinase (ERK). In vivo, inhibition of MEK1 or PKCε prevented prolonged PGE2, 8-Br-cAMP, and 8-pCPT hyperalgesia in SNS-GRK2+/- mice. In conclusion, we discovered GRK2 as a novel Epac1-interacting protein. A reduction in the cellular level of GRK2 enhances activation of the Epac-Rap1 pathway. In vivo, low nociceptor GRK2 leads to prolonged inflammatory hyperalgesia via biased cAMP signaling from PKA to Epac-Rap1, ERK/PKCε pathways.

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Line
  • Cells, Cultured
  • Cyclic AMP / metabolism*
  • Dinoprostone / metabolism
  • Dinoprostone / pharmacology*
  • Down-Regulation
  • Female
  • G-Protein-Coupled Receptor Kinase 2 / genetics
  • G-Protein-Coupled Receptor Kinase 2 / metabolism*
  • Ganglia, Spinal / cytology
  • Ganglia, Spinal / metabolism
  • Guanine Nucleotide Exchange Factors / metabolism*
  • Humans
  • Hyperalgesia / chemically induced
  • Hyperalgesia / metabolism*
  • Immunoprecipitation
  • Inflammation / chemically induced
  • Inflammation / metabolism*
  • Mice
  • Mice, Transgenic
  • Mitogen-Activated Protein Kinases / metabolism
  • Protein Kinase C-epsilon / metabolism*
  • Signal Transduction / physiology
  • rap1 GTP-Binding Proteins / metabolism*

Substances

  • Epac protein, mouse
  • Guanine Nucleotide Exchange Factors
  • Cyclic AMP
  • Protein Kinase C-epsilon
  • GRK2 protein, mouse
  • G-Protein-Coupled Receptor Kinase 2
  • Mitogen-Activated Protein Kinases
  • rap1 GTP-Binding Proteins
  • Dinoprostone