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Maladaptive changes of nerve injury-associated genes in dorsal root ganglia (DRGs) are critical for neuropathic pain genesis. Emerging evidence supports the role of long noncoding RNAs (lncRNAs) in regulating gene transcription. Here we identified a conserved lncRNA, named nerve injury-specific lncRNA (NIS-lncRNA) for its upregulation in injured DRGs exclusively in response to nerve injury. This upregulation was triggered by nerve injury-induced increase in DRG ELF1, a transcription factor that bound to the NIS-lncRNA promoter. Blocking this upregulation attenuated nerve injury-induced CCL2 increase in injured DRGs and nociceptive hypersensitivity during the development and maintenance periods of neuropathic pain. Mimicking NIS-lncRNA upregulation elevated CCL2 expression, increased CCL2-mediated excitability in DRG neurons, and produced neuropathic pain symptoms. Mechanistically, NIS-lncRNA recruited more binding of the RNA-interacting protein FUS to the Ccl2 promoter and augmented Ccl2 transcription in injured DRGs. Thus, NIS-lncRNA participates in neuropathic pain likely by promoting FUS-triggered DRG Ccl2 expression and may be a potential target in neuropathic pain management., Introduction Peripheral neuropathic pain caused by primary damage or injury to the peripheral nervous system is a complex and debilitating major health problem. It impacts the quality of life of [...]

Nerve injury to peripheral somatosensory system causes refractory neuropathic pain. Maladaptive changes of gene expression in primary sensory neurons are considered molecular basis of this disorder. Long non-coding RNAs (lncRNAs) are key regulators of gene transcription; however, their significance in neuropathic pain remains largely elusive.Here, we reported a novel lncRNA, named sensory neuron-specific lncRNA (SS-lncRNA), for its expression exclusively in dorsal root ganglion (DRG) and trigeminal ganglion. SS-lncRNA was predominantly expressed in small DRG neurons and significantly downregulated due to a reduction of early B cell transcription factor 1 in injured DRG after nerve injury. Rescuing this downregulation reversed a decrease of the calcium-activated potassium channel subfamily N member 1 (KCNN1) in injured DRG and alleviated nerve injury-induced nociceptive hypersensitivity. Conversely, DRG downregulation of SS-lncRNA reduced the expression of KCNN1, decreased total potassium currents and afterhyperpolarization currents and increased excitability in DRG neurons and produced neuropathic pain symptoms.Mechanistically, downregulated SS-lncRNA resulted in the reductions of its binding to Kcnn1 promoter and heterogeneous nuclear ribonucleoprotein M (hnRNPM), consequent recruitment of less hnRNPM to the Kcnn1 promoter and silence of Kcnn1 gene transcription in injured DRG.These findings indicate that SS-lncRNA may relieve neuropathic pain through hnRNPM-mediated KCNN1 rescue in injured DRG and offer a novel therapeutic strategy specific for this disorder. [ABSTRACT FROM AUTHOR]

Dysregulation of pain-associated genes in the dorsal root ganglion (DRG) is considered to be a molecular basis of neuropathic pain genesis. Fused in sarcoma (FUS), a DNA/RNA-binding protein, is a critical regulator of gene expression. However, whether it contributes to neuropathic pain is unknown. This study showed that peripheral nerve injury caused by the fourth lumbar (L4) spinal nerve ligation (SNL) or chronic constriction injury (CCI) of the sciatic nerve produced a marked increase in the expression of FUS protein in injured DRG neurons. Blocking this increase through microinjection of the adeno-associated virus (AAV) 5-expressing Fus shRNA into the ipsilateral L4 DRG mitigated the SNL-induced nociceptive hypersensitivities in both male and female mice. This microinjection also alleviated the SNL-induced increases in the levels of phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) and glial fibrillary acidic protein (GFAP) in the ipsilateral L4 dorsal horn. Furthermore, mimicking this increase through microinjection of AAV5 expressing full-length Fus mRNA into unilateral L3/4 DRGs produced the elevations in the levels of p-ERK1/2 and GFAP in the dorsal horn, enhanced responses to mechanical, heat and cold stimuli, and induced the spontaneous pain on the ipsilateral side of both male and female mice in the absence of SNL. Mechanistically, the increased FUS activated the NF-jB signaling pathway by promoting the translocation of p65 into the nucleus and phosphorylation of p65 in the nucleus from injured DRG neurons. Our results indicate that DRG FUS contributes to neuropathic pain likely through the activation of NF-jB in primary sensory neurons. [ABSTRACT FROM AUTHOR]

Metastatic bone pain and chemotherapy-induced peripheral neuropathic pain are the most common clinical symptoms in cancer patients. The current clinical management of these two disorders is ineffective and/or produces severe side effects. The present study employed a dual-target compound named as ZL006-05 and examined the effect of systemic administration of ZL006-05 on RM-1–induced bone cancer pain and paclitaxel-induced neuropathic pain. Intravenous injection of ZL006-05 dose-dependently alleviated RM-1–induced mechanical allodynia, heat hyperalgesia, cold hyperalgesia, and spontaneously ongoing nociceptive responses during both induction and maintenance periods, without analgesic tolerance, affecting basal/acute pain and locomotor function. Similar behavioral results were observed in paclitaxel-induced neuropathic pain. This injection also decreased neuronal and astrocyte hyperactivities in the lumbar dorsal horn after RM-1 tibial inoculation or paclitaxel intraperitoneal injection. Mechanistically, intravenous injection of ZL006-05 potentiated the GABAA receptor agonist–evoked currents in the neurons of the dorsal horn and anterior cingulate cortex and also blocked the paclitaxel-induced increase in postsynaptic density-95–neuronal nitric oxide synthase interaction in dorsal horn. Our findings strongly suggest that ZL006-05 may be a new candidate for the management of cancer pain and chemotherapy-induced peripheral neuropathic pain. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Expressional changes of pain-associated genes in primary sensory neurons of DRG are critical for neuropathic pain genesis. DNA methyltransferase (DNMT)-triggered DNA methylation silences gene expression. We show here that DNMT1, a canonical maintenance methyltransferase, acts as the de novo DNMT and is required for neuropathic pain genesis likely through repressing at least DRG Kcna2 gene expression in male mice. Peripheral nerve injury upregulated DNMT1 expression in the injured DRG through the transcription factor cAMP response element binding protein-triggered transcriptional activation of Dnmtl gene. Blocking this upregulation prevented nerve injury-induced DNA methylation within the promoter and 5'-untranslated region of Kcna2 gene, rescued Kcna2 expression and total Kv current, attenuated hyperexcitability in the injured DRG neurons, and alleviated nerve injury-induced pain hypersensitivities. Given that Kcna2 is a key player in neuropathic pain, our findings suggest that DRG DNMT 1 may be a potential target for neuropathic pain management. [ABSTRACT FROM AUTHOR]

Oral formulations of meloxicam, a preferential cyclooxygenase‑2 (COX‑2) inhibitor, have long been used to treat osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, as well as various pain syndromes of skeletomuscular origin (e.g., low back pain). However, these preparations are rarely indicated for the treatment of acute pain due to a poor dissolution rate and consequently a slow onset of action. The recent introduction of an intravenous (IV) NanoCrystal Colloidal Dispersion formulation opens up the possibility of using this drug during the perioperative period. The present review summarizes the pharmacologic properties of meloxicam, including its pharmacokinetics, adverse effects, and tolerability. In addition, we critically examined a number of recently completed clinical trials that evaluated the efficacy and safety of meloxicam IV in the treatment of post‑operative pain. Literature retrieval was performed through PubMed and Medline (through March 2018) using combinations of the terms meloxicam, acute pain, and pharmacology. In addition, bibliographical information, including contributory unpublished data, was requested from the company developing the drug. Clinical trials suggest that single IV doses of 30 mg meloxicam significantly reduce post‑operative pain as well as opioid requirements. We conclude that meloxicam IV is an effective and well‑tolerated analgesic agent for the management of moderate to severe post‑operative pain. [ABSTRACT FROM AUTHOR]

Propofol is a short-acting intravenous anesthetic agent suitable for induction and maintenance of general anesthesia as well as for procedural and intensive care unit sedation. As such it has become an unparalleled anesthetic agent of choice in many institutional and office practices. However, in addition to its idealistic properties as an anesthetic agent, there is accumulating evidence suggesting its potential for abuse. Clinical and experimental evidence has revealed that not only does propofol have the potential to be abused, but also that addiction to propofol shows a high mortality rate. Based on this evidence, different researchers have shown interest in determining the probability of propofol to be an addictive agent by comparing it with other drugs of abuse and depicting a functional similitude that involves the mesocorticolimbic pathway of addiction. In light of this, the Drug Enforcement Agency and the American Society of Anesthesiologists have put forth certain safety recommendations for the use of propofol. Despite this, the abuse potential of propofol has been challenged at different levels and therefore the preeminent focus will be to further validate the linkage from medicinal and occasional use of propofol to its addiction, as well as to explore the cellular and molecular targets involved in establishing this linkage, so as to curb the harm arising out of it. This review incorporates the clinical and biomolecular evidence supporting the abuse potential of propofol and brings forth the promising targets and the foreseeable mechanism causing the propofol addiction phenotypes, which can be called upon for future developments in this field. [ABSTRACT FROM AUTHOR]

Peripheral nerve injury-caused hyperexcitability and abnormal ectopic discharges in the primary sensory neurons of dorsal root ganglion (DRG) play a key role in neuropathic pain development and maintenance. The two-pore domain background potassium (K2P) channels have been identified as key determinants of the resting membrane potential and neuronal excitability. However, whether K2P channels contribute to neuropathic pain is still elusive. We reported here that K2P1.1, the first identified mammalian K2P channel, was highly expressed in mouse DRG and distributed in small-, medium-, and large-sized DRG neurons. Unilateral lumbar (L) 4 spinal nerve ligation led to a significant and time-dependent reduction of K2P1.1 mRNA and protein in the ipsilateral L4 DRG, but not in the contralateral L4 or ipsilateral L3 DRG. Rescuing this reduction through microinjection of adeno-associated virus-DJ expressing full-length K2P1.1 mRNA into the ipsilateral L4 DRG blocked spinal nerve ligation-induced mechanical, thermal, and cold pain hypersensitivities during the development and maintenance periods. This DRG viral microinjection did not affect acute pain and locomotor function. Our findings suggest that K2P1.1 participates in neuropathic pain development and maintenance and may be a potential target in the management of this disorder. [ABSTRACT FROM AUTHOR]

Background: Development of new strategies that can effectively prevent and/or treat alcohol use disorders is of paramount importance, because the currently available treatments are inadequate. Increasing evidence indicates that the lateral habenula (LHb) plays an important role in aversion, drug abuse, and depression. In light of the success of high-frequency stimulation (HFS) of the LHb in improving helplessness behavior in rodents, we assessed the effects of LHb HFS on ethanoldrinking behavior in rats. Methods: We trained rats to drink ethanol under an intermittent access two-bottle choice procedure. We used c-Fos immunohistochemistry and electrophysiological approaches to examine LHb activity. We applied a HFS protocol that has proven effective for reducing helplessness behavior in rats via a bipolar electrode implanted into the LHb. Results: c-Fos protein expression and the frequency of both spontaneous action potential firings and spontaneous excitatory postsynaptic currents were higher in LHb neurons of ethanol-withdrawn rats compared to their ethanol-naïve counterparts. HFS to the LHb produced long-term reduction of intake and preference for ethanol, without altering locomotor activity. Conversely, low-frequency electrical stimulation to the LHb or HFS applied to the nearby nucleus did not affect drinking behavior. Conclusions: Our results suggest that withdrawal from chronic ethanol exposure increases glutamate release and the activity of LHb neurons, and that functional inhibition of the LHb via HFS reduces ethanol consumption. Thus, LHb HFS could be a potential new therapeutic option for alcoholics. [ABSTRACT FROM AUTHOR]

Objective(s). Examine the effect of preoperative dose of IV ibuprofen on stress response and postoperative recovery in laparoscopic cholecystectomy patients. Design. Prospective, randomized, controlled, double-blind, multicenter trial. Setting. Three university-based, tertiary care hospitals. Subjects. Fifty-five adults, ASA 1, 2, or 3 scheduled for laparoscopic cholecystectomy were given a single preoperative dose of placebo or IV ibuprofen 800 mg. Methods. Neurobehavioral assessments were evaluated preoperatively, in PACU, POD 1, and POD 3, using the 40-item Quality of Recovery questionnaire (QoR40), 9-item Modified Fatigue Severity Scale (MFSS), and 15-item Geriatric Depression scale (GDS). Blood samples were taken for cytokines (TNF-alpha, IL-1β, IL-2, IL-6, IL-10, IFNγ), cortisol, CRP, epinephrine, and norepinephrine prior to the administration of study drug/placebo, intraoperatively, and after surgery. Results. Global QoR40 scores remained at baseline for ibuprofen patients but significantly decreased in the placebo group. Severity of fatigue increased in patients receiving placebo but had no change with ibuprofen. The placebo group had lower GDS scores on POD 3. Epinephrine and norepinephrine were significantly lower intraoperatively for the ibuprofen group. Cortisol decreased postoperatively in the ibuprofen group. There was an impact of drug treatment on the immune response, as seen by an increase in TNFαand an increase in IL-10 when compared with placebo. Conclusions. Our results suggest the addition of NSAIDs may improve the overall quality of recovery, postsurgical fatigue, and early postoperative outcomes. Preoperative administration of IV ibuprofen modulates the stress and inflammatory response, as demonstrated by a decrease in the level of cat-echolamines, cortisol, and cytokines. [ABSTRACT FROM AUTHOR]

In the past twenty years, evidence of neurotoxicity in the developing brain in animal studies from exposure to several general anesthetics has been accumulating. Propofol, a commonly used general anesthetic medication, administered during synaptogenesis, may trigger widespread apoptotic neurodegeneration in the developing brain and long-term neurobehavioral disturbances in both rodents and non-human primates. Despite the growing evidence of the potential neurotoxicity of different anesthetic agents in animal studies, there is no concrete evidence that humans may be similarly affected. However, given the growing evidence of the neurotoxic effects of anesthetics in laboratory studies, it is prudent to further investigate the mechanisms causing these effects and potential ways to mitigate them. Here, we review multiple studies that investigate the effects of in utero propofol exposure and the developmental agents that may modify these deleterious effects. [ABSTRACT FROM AUTHOR]

Neuropathic pain, a distressing and debilitating disorder, is still poorly managed in clinic. Opioids, like morphine, remain the mainstay of prescribed medications in the treatment of this disorder, but their analgesic effects are highly unsatisfactory in part due to nerve injury-induced reduction of opioid receptors in the first-order sensory neurons of dorsal root ganglia. G9a is a repressor of gene expression. We found that nerve injury-induced increases in G9a and its catalyzed repressive marker H3K9m2 are responsible for epigenetic silencing of Oprm1, Oprk1, and Oprd1 genes in the injured dorsal root ganglia. Blocking these increases rescued dorsal root ganglia Oprm1, Oprk1, and Oprd1 gene expression and morphine or loperamide analgesia and prevented the development of morphine or loperamide-induced analgesic tolerance under neuropathic pain conditions. Conversely, mimicking these increases reduced the expression of three opioid receptors and promoted the mu opioid receptor-gated release of primary afferent neurotransmitters. Mechanistically, nerve injury-induced increases in the binding activity of G9a and H3K9me2 to the Oprm1 gene were associated with the reduced binding of cyclic AMP response element binding protein to the Oprm1 gene. These findings suggest that G9a participates in the nerve injury-induced reduction of the Oprm1 gene likely through G9a-triggered blockage in the access of cyclic AMP response element binding protein to this gene. [ABSTRACT FROM AUTHOR]

Background: Peripheral nerve injury leads to changes in gene expression in primary sensory neurons of the injured dorsal root ganglia. These changes are believed to be involved in neuropathic pain genesis. Previously, these changes have been identified using gene microarrays or next generation RNA sequencing with poly-A tail selection, but these approaches cannot provide a more thorough analysis of gene expression alterations after nerve injury. Methods: The present study chose to eliminate mRNA poly-A tail selection and perform strand-specific next generation RNA sequencing to analyze whole transcriptomes in the injured dorsal root ganglia following spinal nerve ligation. Quantitative real-time reverse transcriptase polymerase chain reaction assay was carried out to verify the changes of some differentially expressed RNAs in the injured dorsal root ganglia after spinal nerve ligation. Results: Our results showed that more than 50 million (M) paired mapped sequences with strand information were yielded in each group (51.87 M-56.12M in sham vs. 51.08 M-57.99M in spinal nerve ligation). Six days after spinal nerve ligation, expression levels of 11,163 out of a total of 27,463 identified genes in the injured dorsal root ganglia significantly changed, of which 52.14% were upregulated and 47.86% downregulated. The largest transcriptional changes were observed in proteincoding genes (91.5%) followed by noncoding RNAs. Within 944 differentially expressed noncoding RNAs, the most significant changes were seen in long interspersed noncoding RNAs followed by antisense RNAs, processed transcripts, and pseudogenes.We observed a notable proportion of reads aligning to intronic regions in both groups (44.0% in sham vs. 49.6% in spinal nerve ligation). Using quantitative real-time polymerase chain reaction, we confirmed consistent differential expression of selected genes including Kcna2, Oprm1 as well as lncRNAs Gm21781 and 4732491K20Rik following spinal nerve ligation. Conclusion: Our findings suggest that next generation RNA sequencing can be used as a promising approach to analyze the changes of whole transcriptomes in dorsal root ganglia following nerve injury and to possibly identify new targets for prevention and treatment of neuropathic pain. [ABSTRACT FROM AUTHOR]

Background: Chronic stress has been reported to increase basal pain sensitivity and/or exacerbate existing persistent pain. However, most surgical patients have normal physiological and psychological health status such as normal pain perception before surgery although they do experience short-term stress during pre- and post-operative periods. Whether or not this short-term stress affects persistent postsurgical pain is unclear. Results: In this study, we showed that pre- or post-surgical exposure to immobilization 6 h daily for three consecutive days did not change basal responses to mechanical, thermal, or cold stimuli or peak levels of incision-induced hypersensitivity to these stimuli; however, immobilization did prolong the duration of incision-induced hypersensitivity in both male and female rats. These phenomena were also observed in post-surgical exposure to forced swimming 25 min daily for 3 consecutive days. Short-term stress induced by immobilization was demonstrated by an elevation in the level of serum corticosterone, an increase in swim immobility, and a decrease in sucrose consumption. Blocking this short-term stress via intrathecal administration of a selective glucocorticoid receptor antagonist, RU38486, or bilateral adrenalectomy significantly attenuated the prolongation of incision-induced hypersensitivity to mechanical, thermal, and cold stimuli. Conclusion: Our results indicate that short-term stress during the pre- or post-operative period delays postoperative pain recovery although it does not affect basal pain perception. Prevention of short-term stress may facilitate patients' recovery from postoperative pain. [ABSTRACT FROM AUTHOR]

Chronic pain is a major public health problem with limited treatment options. Opioids remain a routine treatment for chronic pain, but extended exposure to opioid therapy can produce opioid tolerance and hyperalgesia. Although the mechanisms underlying chronic pain, opioid-induced tolerance, and opioid-induced hyperalgesia remain to be uncovered, mammalian target of rapamycin (mTOR) is involved in these disorders. The mTOR complex 1 and its triggered protein translation are required for the initiation and maintenance of chronic pain (including cancer pain) and opioid-induced tolerance/hyperalgesia. Given that mTOR inhibitors are FDA-approved drugs and an mTOR inhibitor is approved for the treatment of several cancers, these findings suggest that mTOR inhibitors will likely have multiple clinical benefits, including anticancer, antinociception/anti-cancer pain, and antitolerance/hyperalgesia. This paper compares the role of mTOR complex 1 in chronic pain, opioid-induced tolerance, and opioid-induced hyperalgesia. [ABSTRACT FROM AUTHOR]

The complexity of chronic pain and the challenges of pharmacotherapy highlight the importance of development of new approaches to pain management. Gene therapy approaches may be complementary to pharmacotherapy for several advantages. Gene therapy strategies may target specific chronic pain mechanisms in a tissue-specific manner. The present collection of articles features distinct gene therapy approaches targeting specific mechanisms identified as important in the specific pain conditions. Dr. Fairbanks group describes commonly used gene therapeutics (herpes simplex viral vector (HSV) and adeno-associated viral vector (AAV)), and addresses biodistribution and potential neurotoxicity in pre-clinical models of vector delivery. Dr. Tao group addresses that downregulation of a voltage-gated potassium channel (Kv1.2) contributes to the maintenance of neuropathic pain. Alleviation of chronic pain through restoring Kv1.2 expression in sensory neurons is presented in this review. Drs Goins and Kinchington group describes a strategy to use the replication defective HSV vector to deliver two different gene products (enkephalin and TNF soluble receptor) for the treatment of post-herpetic neuralgia. Dr. Hao group addresses the observation that the pro-inflammatory cytokines are an important shared mechanism underlying both neuropathic pain and the development of opioid analgesic tolerance and withdrawal. The use of gene therapy strategies to enhance expression of the anti-pro-inflammatory cytokines is summarized. Development of multiple gene therapy strategies may have the benefit of targeting specific pathologies associated with distinct chronic pain conditions (by Guest Editors, Drs. C. Fairbanks and S. Hao). [ABSTRACT FROM AUTHOR]

Most opioid analgesics used clinically, including morphine and fentanyl, as well as the recreational drug heroin, act primarily through the mu opioid receptor, a class A Rhodopsin-like G protein-coupled receptor (GPCR). The single-copy mu opioid receptor gene, OPRM1, undergoes extensive alternative splicing, creating multiple splice variants or isoforms via a variety of alternative splicing events. These OPRM1 splice variants can be categorized into three major types based on the receptor structure: (1) full-length 7 transmembrane (TM) C-terminal variants; (2) truncated 6TM variants; and (3) single TM variants. Increasing evidence suggests that these OPRM1 splice variants are pharmacologically important in mediating the distinct actions of various mu opioids. More importantly, the OPRM1 variants can be targeted for development of novel opioid analgesics that are potent against multiple types of pain, but devoid of many side-effects associated with traditional opiates. In this review, we provide an overview of OPRM1 alternative splicing and its functional relevance in opioid pharmacology. [ABSTRACT FROM AUTHOR]

Nerve injury-induced downregulation of voltage-gated potassium channel subunit Kcna2 in the dorsal root ganglion (DRG) is critical for DRG neuronal excitability and neuropathic pain genesis. However, how nerve injury causes this downregulation is still elusive. Euchromatic histone-lysine N-methyltransferase 2, also known as G9a, methylates histone H3 on lysine residue 9 to predominantly produce a dynamic histone dimethylation, resulting in condensed chromatin and gene transcriptional repression. We showed here that blocking nerve injury-induced increase in G9a rescued Kcna2 mRNA and protein expression in the axotomized DRG and attenuated the development of nerve injury-induced pain hypersensitivity. Mimicking this increase decreased Kcna2 mRNA and protein expression, reduced Kv current, and increased excitability in the DRG neurons and led to spinal cord central sensitization and neuropathic pain-like symptoms. G9a mRNA is co-localized with Kcna2 mRNA in the DRG neurons. These findings indicate that G9a contributes to neuropathic pain development through epigenetic silencing of Kcna2 in the axotomized DRG. [ABSTRACT FROM AUTHOR]

Neuropathic pain, a distressing and debilitating disorder, is still poorly managed in clinic. Opioids, like morphine, remain the mainstay of prescribed medications in the treatment of this disorder, but their analgesic effects are highly unsatisfactory in part due to nerve injury-induced reduction of opioid receptors in the first-order sensory neurons of dorsal root ganglia. G9a is a repressor of gene expression. We found that nerve injury-induced increases in G9a and its catalyzed repressive marker H3K9m2 are responsible for epigenetic silencing of Oprm1, Oprk1, and Oprd1 genes in the injured dorsal root ganglia. Blocking these increases rescued dorsal root ganglia Oprm1, Oprk1, and Oprd1 gene expression and morphine or loperamide analgesia and prevented the development of morphine or loperamide-induced analgesic tolerance under neuropathic pain conditions. Conversely, mimicking these increases reduced the expression of three opioid receptors and promoted the mu opioid receptor-gated release of primary afferent neurotransmitters. Mechanistically, nerve injury-induced increases in the binding activity of G9a and H3K9me2 to the Oprm1 gene were associated with the reduced binding of cyclic AMP response element binding protein to the Oprm1 gene. These findings suggest that G9a participates in the nerve injury-induced reduction of the Oprm1 gene likely through G9a-triggered blockage in the access of cyclic AMP response element binding protein to this gene. [ABSTRACT FROM AUTHOR]

Background: Peripheral nerve injury leads to changes in gene expression in primary sensory neurons of the injured dorsal root ganglia. These changes are believed to be involved in neuropathic pain genesis. Previously, these changes have been identified using gene microarrays or next generation RNA sequencing with poly-A tail selection, but these approaches cannot provide a more thorough analysis of gene expression alterations after nerve injury. Methods: The present study chose to eliminate mRNA poly-A tail selection and perform strand-specific next generation RNA sequencing to analyze whole transcriptomes in the injured dorsal root ganglia following spinal nerve ligation. Quantitative real-time reverse transcriptase polymerase chain reaction assay was carried out to verify the changes of some differentially expressed RNAs in the injured dorsal root ganglia after spinal nerve ligation. Results: Our results showed that more than 50 million (M) paired mapped sequences with strand information were yielded in each group (51.87 M–56.12 M in sham vs. 51.08 M–57.99 M in spinal nerve ligation). Six days after spinal nerve ligation, expression levels of 11,163 out of a total of 27,463 identified genes in the injured dorsal root ganglia significantly changed, of which 52.14% were upregulated and 47.86% downregulated. The largest transcriptional changes were observed in protein-coding genes (91.5%) followed by noncoding RNAs. Within 944 differentially expressed noncoding RNAs, the most significant changes were seen in long interspersed noncoding RNAs followed by antisense RNAs, processed transcripts, and pseudogenes. We observed a notable proportion of reads aligning to intronic regions in both groups (44.0% in sham vs. 49.6% in spinal nerve ligation). Using quantitative real-time polymerase chain reaction, we confirmed consistent differential expression of selected genes including Kcna2, Oprm1 as well as lncRNAs Gm21781 and 4732491K20Rik following spinal nerve ligation. Conclusion: Our findings suggest that next generation RNA sequencing can be used as a promising approach to analyze the changes of whole transcriptomes in dorsal root ganglia following nerve injury and to possibly identify new targets for prevention and treatment of neuropathic pain. [ABSTRACT FROM AUTHOR]

Maladaptive changes of nerve injury-associated genes in dorsal root ganglia (DRGs) are critical for neuropathic pain genesis. Emerging evidence supports the role of long noncoding RNAs (lncRNAs) in regulating gene transcription. Here we identified a conserved lncRNA, named nerve injury-specific lncRNA (NIS-lncRNA) for its upregulation in injured DRGs exclusively in response to nerve injury. This upregulation was triggered by nerve injury-induced increase in DRG ELF1, a transcription factor that bound to the NIS-lncRNA promoter. Blocking this upregulation attenuated nerve injury-induced CCL2 increase in injured DRGs and nociceptive hypersensitivity during the development and maintenance periods of neuropathic pain. Mimicking NIS-lncRNA upregulation elevated CCL2 expression, increased CCL2-mediated excitability in DRG neurons, and produced neuropathic pain symptoms. Mechanistically, NIS-lncRNA recruited more binding of the RNA-interacting protein FUS to the Ccl2 promoter and augmented Ccl2 transcription in injured DRGs. Thus, NIS-lncRNA participates in neuropathic pain likely by promoting FUS-triggered DRG Ccl2 expression and may be a potential target in neuropathic pain management. [ABSTRACT FROM AUTHOR]