title: 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.affiliation: Laboratory of Neuroimmunology and Developmental Origins of Disease, University Medical Center Utrecht, 3584 EA Utrecht, The Netherlands.
authors.forename: Niels
authors.initials: N
authors.lastname: Eijkelkamp
authors.forename: Huijing
authors.initials: H
authors.lastname: Wang
authors.forename: Anibal
authors.initials: A
authors.lastname: Garza-Carbajal
authors.forename: Hanneke L D M
authors.initials: HL
authors.lastname: Willemen
authors.forename: Fried J
authors.initials: FJ
authors.lastname: Zwartkruis
authors.forename: John N
authors.initials: JN
authors.lastname: Wood
authors.forename: Robert
authors.initials: R
authors.lastname: Dantzer
authors.forename: Keith W
authors.initials: KW
authors.lastname: Kelley
authors.forename: Cobi J
authors.initials: CJ
authors.lastname: Heijnen
authors.forename: Annemieke
authors.initials: A
authors.lastname: Kavelaars
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D015232:Dinoprostone / Q000378:metabolism / Q000494:pharmacology*; D015536:Down-Regulation; D005260:Female; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000235:genetics / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced / Q000378:metabolism*; D047468:Immunoprecipitation; D007249:Inflammation / Q000139:chemically induced / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D051744:Protein Kinase C-epsilon / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: C482601:Epac protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D000242:Cyclic AMP; D051744:Protein Kinase C-epsilon; C496568:GRK2 protein, mouse; D054769:G-Protein-Coupled Receptor Kinase 2; D020928:Mitogen-Activated Protein Kinases; D020827:rap1 GTP-Binding Proteins; D015232:Dinoprostone