Downregulation of a Dorsal Root Ganglion‐Specifically Enriched Long Noncoding RNA is Required for Neuropathic Pain by Negatively Regulating RALY‐Triggered Ehmt2 Expression

Abstract

Nerve injury-induced maladaptive changes of gene expression in dorsal root ganglion (DRG) neurons contribute to neuropathic pain. Long non-coding RNAs (lncRNAs) are emerging as key regulators of gene expression. Here, a conserved lncRNA is reported, named DRG-specifically enriched lncRNA (DS-lncRNA) for its high expression in DRG neurons. Peripheral nerve injury downregulates DS-lncRNA in injured DRG due, in part, to silencing of POU domain, class 4, transcription factor 3, a transcription factor that interacts with the DS-lncRNA gene promoter. Rescuing DS-lncRNA downregulation blocks nerve injury-induced increases in the transcriptional cofactor RALY-triggered DRG Ehmt2 mRNA and its encoding G9a protein, reverses the G9a-controlled downregulation of opioid receptors and Kcna2 in injured DRG, and attenuates nerve injury-induced pain hypersensitivities in male mice. Conversely, DS-lncRNA downregulation increases RALY-triggered Ehmt2/G9a expression and correspondingly decreases opioid receptor and Kcna2 expression in DRG, leading to neuropathic pain symptoms in male mice in the absence of nerve injury. Mechanistically, downregulated DS-lncRNA promotes more binding of increased RALY to RNA polymerase II and the Ehmt2 gene promoter and enhances Ehmt2 transcription in injured DRG. Thus, downregulation of DS-lncRNA likely contributes to neuropathic pain by negatively regulating the expression of RALY-triggered Ehmt2/G9a, a key neuropathic pain player, in DRG neurons.

DNA Methylation and Non-Coding RNAs during Tissue-Injury Associated Pain

“…Recently, Pan and colleagues have identified a DRG-specifically enriched lncRNA (DS-lncRNA), a lncRNA specifically and highly (>70%) expressed in DRG neuronal nuclei that gets downregulated following different models of peripheral nerve injury (CCI and SNL, [ 49 ]). Downregulation of DS-lncRNA, which seems to be mediated by silencing of the Pou4f3 gene (transcriptional activator POU domain, class 4, transcription factor 3), leads to alterations in the opiodergic signalling system and negatively regulates the expression of RALY-triggered Ehmt2/G9a ( Figure 3 A) [ 49 ].…”

A Compound Mitigates Cancer Pain and Chemotherapy-Induced Neuropathic Pain by Dually Targeting nNOS-PSD-95 Interaction and GABAA Receptor

“…Mechanical tests were performed as described previously [26,27]. In brief, each mouse was placed in a Plexiglas chamber on an elevated mesh screen.…”

“…Thermal tests were carried out following the protocol as reported previously [26,27]. Briefly, each mouse was placed in a Plexiglas chamber on a glass plate.…”

“…Cold tests were performed to the measurement of paw withdrawal latency to noxious cold (0 ℃) as described previously [26,27]. Briefly, each mouse was placed in a Plexiglas chamber on the cold aluminum plate with continuous temperature monitoring by a thermometer.…”

“…Locomotor functional tests including placing, grasping, and righting reflexes were carried out as described previously [26,27] before the mice were euthanized. For the placing reflex, the hind limbs were placed slightly lower than the forelimbs and the dorsal surfaces of the hind paws were brought into contact with the edge of a table.…”