Spinal SGK1/GRASP-1/Rab4 is involved in complete Freund's adjuvant-induced inflammatory pain via regulating dorsal horn GluR1-containing AMPA receptor trafficking in rats

Pain. 2012 Dec;153(12):2380-2392. doi: 10.1016/j.pain.2012.08.004. Epub 2012 Sep 11.


The elusiveness of the mechanism underlying pain is a major impediment in developing effective clinical treatments. We examined whether the phosphorylation of spinal serum- and glucocorticoid-inducible kinase 1 (SGK1) and downstream glutamate receptor interacting protein (GRIP)-associated protein-1 (GRASP-1)/Rab4-dependent GluR1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) recycling play a role in inflammatory pain. After intraplantar injection of complete Freund's adjuvant (CFA), we assessed thermal hyperalgesia using the Hargreaves test and analyzed dorsal horn samples (L4-5) using Western blotting, coprecipitation, and immunofluorescence. CFA administration provoked behavioral hyperalgesia along with SGK1 phosphorylation, GluR1 trafficking from the cytosol to the membrane, and phosphorylated SGK1 (pSGK1)-GRASP-1, GRASP-1-Rab4, and Rab4-GluR1 coprecipitation in the ipsilateral dorsal horn. In the dorsal horns of hyperalgesic rats, CFA-enhanced pSGK1 was demonstrated to be colocalized with NeuN, GRASP-1, Rab4, and GluR1 by immunofluorescence. GSK-650394 (an SGK1 activation antagonist, 1, 10, and 30 μM, 10 μL/rat, intrathecally) dose-dependently prevented CFA-induced pain behavior and the associated SGK1 phosphorylation, GluR1 trafficking, and protein-protein interactions at 1 day after CFA administration. Intrathecal 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, an AMPAR antagonist, 1, 3, and 10 μM, 10 μL/rat) attenuated the hyperalgesia and GluR1 trafficking caused by CFA; however, it had no effect on SGK1 phosphorylation. Small interfering RNA targeting Rab4 hindered the CFA-induced hyperalgesia and the associated GluR1 trafficking and Rab4-GluR1 coprecipitation. Our results suggest that spinal SGK1 phosphorylation, which subsequently triggers the GRASP-1/Rab4 cascade, plays a pivotal role in CFA-induced inflammatory pain by regulating GluR1-containing AMPAR recycling in the dorsal horn.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adjuvants, Immunologic
  • Animals
  • Carrier Proteins / metabolism*
  • Freund's Adjuvant
  • Hyperalgesia / chemically induced
  • Hyperalgesia / metabolism*
  • Immediate-Early Proteins / metabolism*
  • Male
  • Membrane Proteins / metabolism*
  • Posterior Horn Cells / metabolism*
  • Protein Serine-Threonine Kinases / metabolism*
  • Protein Transport
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, AMPA / metabolism*
  • rab4 GTP-Binding Proteins / metabolism*


  • Adjuvants, Immunologic
  • Carrier Proteins
  • GRASP protein, rat
  • Immediate-Early Proteins
  • Membrane Proteins
  • Receptors, AMPA
  • Freund's Adjuvant
  • Protein Serine-Threonine Kinases
  • serum-glucocorticoid regulated kinase
  • rab4 GTP-Binding Proteins
  • glutamate receptor ionotropic, AMPA 1