Transcriptional regulation of metabotropic glutamate receptor 2/3 expression by the NF-kappaB pathway in primary dorsal root ganglia neurons: a possible mechanism for the analgesic effect of L-acetylcarnitine

Mol Pain. 2006 Jun 9;2:20. doi: 10.1186/1744-8069-2-20.

Abstract

L-acetylcarnitine (LAC), a drug utilized for the treatment of neuropathic pain in humans, has been shown to induce analgesia in rodents by up-regulating the expression of metabotropic glutamate receptor 2 (mGlu2) in dorsal root ganglia (DRG). We now report that LAC-induced upregulation of mGlu2 expression in DRG cultures involves transcriptional activation mediated by nuclear factor-kappaB (NF-kappaB). A single application of LAC (250 muM) to DRG cultures induced a transient increase in mGlu2 mRNA, which was observable after 1 hour and was no longer detectable after 1 to 4 days. In contrast, LAC treatment had no effect on mGlu3 mRNA expression. Pharmacological inhibition of NF-kappaB binding to DNA by caffeic acid phenethyl ester (CAPE) (2.5 microg/ml for 30 minutes) reduced the constitutive expression of mGlu2 and mGlu3 mRNA after 1-4 days and reduced the constitutive expression of mGlu2/3 protein at 4 days. This evidence combined with the expression of p65/RelA and c-Rel in DRG neurons indicated that expression of mGlu2 and mGlu3 is endogenously regulated by the NF-kappaB family of transcription factors. Consistent with this idea, the transient increase in mGlu2 mRNA induced by LAC after 1 hour was completely suppressed by CAPE. Furthermore, LAC induced an increase in the acetylation of p65/RelA, a process that enhances the transcriptional activity of p65/RelA. These results are consistent with the hypothesis that LAC selectively induces the expression of mGlu2 by acting as a donor of acetyl groups, thus enhancing the activity of the NF-kappaB family of transcription factors. Accordingly, we show that carnitine, which has no effect on pain thresholds, had no effect on p65/RelA acetylation and did not enhance mGlu2 expression. Taken together, these results demonstrate that expression of mGlu2 and mGlu3 mRNA is regulated by the NF-kappaB transcriptional machinery, and that agents that increase acetylation and activation of NF-kappaB transcription factors might induce analgesia via upregulation of mGlu2 in DRG neurons.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcarnitine / metabolism
  • Acetylcarnitine / pharmacology*
  • Analgesics / metabolism
  • Analgesics / pharmacology*
  • Animals
  • Caffeic Acids / pharmacology
  • Cells, Cultured
  • Ganglia, Spinal / drug effects
  • Ganglia, Spinal / metabolism*
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / physiology
  • Mice
  • Mice, Inbred ICR
  • NF-kappa B / metabolism*
  • Neurons, Afferent / drug effects
  • Neurons, Afferent / metabolism*
  • Phenylethyl Alcohol / analogs & derivatives
  • Phenylethyl Alcohol / pharmacology
  • Proto-Oncogene Proteins c-rel / genetics
  • RNA, Messenger / drug effects
  • RNA, Messenger / metabolism
  • Receptors, Metabotropic Glutamate / biosynthesis
  • Receptors, Metabotropic Glutamate / genetics*
  • Transcription Factor RelA / genetics
  • Transcriptional Activation / drug effects
  • Transcriptional Activation / genetics*
  • Up-Regulation / drug effects
  • Up-Regulation / physiology

Substances

  • Analgesics
  • Caffeic Acids
  • NF-kappa B
  • Proto-Oncogene Proteins c-rel
  • RNA, Messenger
  • Receptors, Metabotropic Glutamate
  • Transcription Factor RelA
  • metabotropic glutamate receptor 2
  • metabotropic glutamate receptor 3
  • Acetylcarnitine
  • caffeic acid phenethyl ester
  • Phenylethyl Alcohol