Transcriptional Regulation of Metabotropic Glutamate Receptor 2/3 Expression by the NF-κB Pathway in Primary Dorsal Root Ganglia Neurons: A Possible Mechanism for the Analgesic Effect of L-Acetylcarnitine

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-κB). A single application of LAC (250 μM) 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-κB binding to DNA by caffeic acid phenethyl ester (CAPE) (2.5 μg/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-κB 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-κB 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-κB transcriptional machinery, and that agents that increase acetylation and activation of NF-κB transcription factors might induce analgesia via upregulation of mGlu2 in DRG neurons.

Prevention of paclitaxel-evoked painful peripheral neuropathy by acetyl-l-carnitine: Effects on axonal mitochondria, sensory nerve fiber terminal arbors, and cutaneous Langerhans cells

“…Our results are in contrast to studies that demonstrate neuroprotective and pro-regenerative ALCAR effects in other nerve injury models (Fernandez et al, 1991;Pacifici et al, 1992;Lowitt et al, 1995;Sima et al, 1996Sima et al, , 2005Hart et al, 2002Hart et al, , 2004aHart et al, , 2004bDeGrandis and Minardi, 2002;Wilson et al, 2003Wilson et al, , 2007Chiechio et al, 2006;Youle et al, 2007). Pisano et al (2003) showed that a prophylactic ALCAR treatment protocol prevented the decrease in the sensory nerve conduction velocity (SNCV) seen after paclitaxel and cisplatin.…”

“…2006;Chiechio et al, 2006). It seems unlikely that such mechanisms could account for ALCAR's ability to completely prevent paclitaxel-evoked neuropathic pain.…”

“…Paclitaxel also causes degeneration of the sensory neurons' intraepidermal terminal arbors, without degeneration of the parent axons in the peripheral nerve, and it activates cutaneous Langerhans cells . ALCAR has been shown to have neuroprotective and pro-regenerative effects following primary afferent neuron axotomy (Fernandez et al, 1991;Chiechio et al, 2006;Hart et al, 2002Hart et al, , 2004aWilson et al, 2003Wilson et al, , 2007, in the peripheral neuropathy produced by antiretroviral chemotherapy (Hart et al, 2004b;Youle et al, 2007), and in diabetic peripheral neuropathy (Lowitt et al, 1995;Pacifici et al, 1992;Sima et al, 1996Sima et al, , 2005DeGrandis and Minardi, 2002).…”

Muscle IL1 Drives Ischemic Myalgia via ASIC3-Mediated Sensory Neuron Sensitization

“…To confirm more specifically that our effects were not due to other potential signaling pathways linked to IL1␤/IL1r1, we also performed control experiments to assess whether IL1␤ may be mediating its effects on ASIC3 expression via the NFB pathway (O'Neill and Greene, 1998). To this end, we treated afferents retrogradely labeled by FG from the muscles with IL1␤ and the NFB inhibitor CAPE (Chiechio et al, 2006) and found that CAPE treatment had no effect on IL1␤-mediated ASIC3 upregulation (IL1␤ ϩ CAPE: 73.03 Ϯ 4.92 fold, p ϭ 0.343 vs untreated; CAPE only: 23.77 Ϯ 4.85, p ϭ 0.041). Using MatInspector software (Genomatix), we determined that JNKmediated ASIC3 expression is likely due to the fact that ASIC3 has multiple AP1/Jun transcription factor-binding sites in its upstream promoter region (Fig.…”

L -acetylcarnitine causes rapid antidepressant effects through the epigenetic induction of mGlu2 receptors

“…Recent evidence suggests that the acetylating agent L-acetylcarnitine (LAC), a drug marketed for the treatment of neuropathic pain (9), causes analgesia increasing type 2 metabotropic glutamate (mGlu2) expression via an epigenetic mechanism shared by HDAC inhibitors (10)(11)(12). mGlu2 and its cognate receptor, mGlu3, are coupled to Gi/Go proteins and are preferentially (albeit not exclusively) localized in the preterminal region of axons, where they negatively modulate neurotransmitter release (13).…”