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Group II mGluRs suppress hyperexcitability in mouse and human nociceptors.

ABSTRACT: We introduce a strategy for preclinical research wherein promising targets for analgesia are tested in rodent and subsequently validated in human sensory neurons. We evaluate group II metabotropic glutamate receptors, the activation of which is efficacious in rodent models of pain. Immunohistochemical analysis showed positive immunoreactivity for mGlu2 in rodent dorsal root ganglia (DRG), peripheral fibers in skin, and central labeling in the spinal dorsal horn. We also found mGlu2-positive immunoreactivity in human neonatal and adult DRG. RNA-seq analysis of mouse and human DRG revealed a comparative expression profile between species for group II mGluRs and for opioid receptors. In rodent sensory neurons under basal conditions, activation of group II mGluRs with a selective group II agonist produced no changes to membrane excitability. However, membrane hyperexcitability in sensory neurons exposed to the inflammatory mediator prostaglandin E2 (PGE2) was prevented by (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (APDC). In human sensory neurons from donors without a history of chronic pain, we show that PGE2 produced hyperexcitability that was similarly blocked by group II mGluR activation. These results reveal a mechanism for peripheral analgesia likely shared by mice and humans and demonstrate a translational research strategy to improve preclinical validation of novel analgesics using cultured human sensory neurons.

SUBMITTER: Davidson S

PROVIDER: S-EPMC4988887 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Group II mGluRs suppress hyperexcitability in mouse and human nociceptors.

Davidson Steve S Golden Judith P JP Copits Bryan A BA Ray Pradipta R PR Vogt Sherri K SK Valtcheva Manouela V MV Schmidt Robert E RE Ghetti Andrea A Price Theodore J TJ Gereau Robert W RW

Pain 20160901 9

We introduce a strategy for preclinical research wherein promising targets for analgesia are tested in rodent and subsequently validated in human sensory neurons. We evaluate group II metabotropic glutamate receptors, the activation of which is efficacious in rodent models of pain. Immunohistochemical analysis showed positive immunoreactivity for mGlu2 in rodent dorsal root ganglia (DRG), peripheral fibers in skin, and central labeling in the spinal dorsal horn. We also found mGlu2-positive immu ...[more]

PMID: 27218869

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Project description:The amygdala plays a critical role in emotional-affective aspects of behaviors and pain modulation. The central nucleus of amygdala (CeA) serves major output functions, and neuroplasticity in the CeA is linked to pain-related behaviors in different models. Activation of Gi/o-coupled group II metabotropic glutamate receptors (mGluRs), which consist of mGluR2 and mGluR3, can decrease neurotransmitter release and regulate synaptic plasticity. Group II mGluRs have emerged as targets for neuropsychiatric disorders and can inhibit pain-related processing and behaviors. Surprisingly, site and mechanism of antinociceptive actions of systemically applied group II mGluR agonists are not clear. Our previous work showed that group II mGluR activation in the amygdala inhibits pain-related CeA activity, but behavioral and spinal consequences remain to be determined. Here we studied the contribution of group II mGluRs in the amygdala to the antinociceptive effects of a systemically applied group II mGluR agonist (LY379268) on behavior and spinal dorsal horn neuronal activity, using the kaolin/carrageenan-induced knee joint arthritis pain model. Audible and ultrasonic vocalizations (emotional responses) and mechanical reflex thresholds were measured in adult rats with and without arthritis (5-6 h postinduction). Extracellular single-unit recordings were made from spinal dorsal horn wide dynamic range neurons of anesthetized (isoflurane) rats with and without arthritis (5-6 h postinduction). Systemic (intraperitoneal) application of a group II mGluR agonist (LY379268) decreased behaviors and activity of spinal neurons in the arthritis pain model but not under normal conditions. Stereotaxic administration of LY379268 into the CeA mimicked the effects of systemic application. Conversely, stereotaxic administration of a group II mGluR antagonist (LY341495) into the CeA reversed the effects of systemic application of LY379268 on behaviors and dorsal horn neuronal activity in arthritic rats. The data show for the first time that the amygdala is the critical site of action for the antinociceptive behavioral and spinal neuronal effects of systemically applied group II mGluR agonists.

Project description:Mobile bacterial group II introns are evolutionary ancestors of spliceosomal introns and retroelements in eukaryotes. They consist of an autocatalytic intron RNA (a "ribozyme") and an intron-encoded reverse transcriptase, which function together to promote intron integration into new DNA sites by a mechanism termed "retrohoming". Although mobile group II introns splice and retrohome efficiently in bacteria, all examined thus far function inefficiently in eukaryotes, where their ribozyme activity is limited by low Mg2+ concentrations, and intron-containing transcripts are subject to nonsense-mediated decay (NMD) and translational repression. Here, by using RNA polymerase II to express a humanized group II intron reverse transcriptase and T7 RNA polymerase to express intron transcripts resistant to NMD, we find that simply supplementing culture medium with Mg2+ induces the Lactococcus lactis Ll.LtrB intron to retrohome into plasmid and chromosomal sites, the latter at frequencies up to ~0.1%, in viable HEK-293 cells. Surprisingly, under these conditions, the Ll.LtrB intron reverse transcriptase is required for retrohoming but not for RNA splicing as in bacteria. By using a genetic assay for in vivo selections combined with deep sequencing, we identified intron RNA mutations that enhance retrohoming in human cells, but <4-fold and not without added Mg2+. Further, the selected mutations lie outside the ribozyme catalytic core, which appears not readily modified to function efficiently at low Mg2+ concentrations. Our results reveal differences between group II intron retrohoming in human cells and bacteria and suggest constraints on critical nucleotide residues of the ribozyme core that limit how much group II intron retrohoming in eukaryotes can be enhanced. These findings have implications for group II intron use for gene targeting in eukaryotes and suggest how differences in intracellular Mg2+ concentrations between bacteria and eukarya may have impacted the evolution of introns and gene expression mechanisms.

Dataset Information

Group II mGluRs suppress hyperexcitability in mouse and human nociceptors.

Publications

Group II mGluRs suppress hyperexcitability in mouse and human nociceptors.

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