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.
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.
Chiechio
Santina
S
Washington University Pain Center and Department of Anesthesiology, Washington University School of Medicine, St Louis, MO, USA. gereaur@wustl.edu
Copani
Agata
A
De Petris
Laura
L
Morales
Maria Elena P
ME
Nicoletti
Ferdinando
F
Gereau
Robert W
RW
D000108:Acetylcarnitine / Q000378:metabolism / Q000494:pharmacology*; D000700:Analgesics / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002109:Caffeic Acids / Q000494:pharmacology; D002478:Cells, Cultured; D005727:Ganglia, Spinal / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008813:Mice, Inbred ICR; D016328:NF-kappa B / Q000378:metabolism*; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D010626:Phenylethyl Alcohol / Q000031:analogs & derivatives / Q000494:pharmacology; D020569:Proto-Oncogene Proteins c-rel / Q000235:genetics; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D018094:Receptors, Metabotropic Glutamate / Q000096:biosynthesis / Q000235:genetics*; D051996:Transcription Factor RelA / Q000235:genetics; D015533:Transcriptional Activation / Q000187:drug effects / Q000235:genetics*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D000700:Analgesics; D002109:Caffeic Acids; D016328:NF-kappa B; D020569:Proto-Oncogene Proteins c-rel; D012333:RNA, Messenger; D018094:Receptors, Metabotropic Glutamate; D051996:Transcription Factor RelA; C108822:metabotropic glutamate receptor 2; C102718:metabotropic glutamate receptor 3; D000108:Acetylcarnitine; C055494:caffeic acid phenethyl ester; D010626:Phenylethyl Alcohol