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

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.

• Authors: Niels Eijkelkamp, Huijing Wang, Anibal Garza-Carbajal, Hanneke L D M Willemen, Fried J Zwartkruis, John N Wood, Robert Dantzer, Keith W Kelley, Cobi J Heijnen, Annemieke Kavelaars
• Journal: The Journal of neuroscience : the official journal of the Society for Neuroscience (J Neurosci) Vol. 30 Issue 38 Pg. 12806-15 (Sep 22 2010) ISSN: 1529-2401 [Electronic] United States
• PMID: 20861385 (Publication Type: Journal Article)

Chemical References

• 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

Topics

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