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Blocking increased expression of nerve injury-specific long non-coding RNA (NIS-lncRNA) in injured dorsal root ganglia (DRG) through DRG microinjection of NIS-lncRNA small hairpin interfering RNA or generation of NIS-lncRNA knockdown mice mitigates neuropathic pain. However, these strategies are impractical in the clinic. This study employed a Food and Drug Administration (FDA)-approved antisense oligonucleotides strategy to examine the effect of NIS-lncRNA ASOs on neuropathic pain.Effects of intrathecal injection of NIS-lncRNA antisense oligonucleotides on day 7 or 14 after chronic constriction injury (CCI) of the sciatic nerve, fourth lumbar (L4) spinal nerve ligation, or intraperitoneal injection of paclitaxel or streptozotocin on the expression of DRG NIS-lncRNA and C-C chemokine ligand 2 (CCL2, an NIS-lncRNA downstream target) and nociceptive hypersensitivity were examined. We also assessed whether NIS-lncRNA antisense oligonucleotides produced cellular toxicity.Intrathecal NIS-lncRNA antisense oligonucleotides attenuated CCI-induced mechanical allodynia, heat hyperalgesia, cold hyperalgesia, and ongoing nociceptive responses, without changing basal or acute nociceptive responses and locomotor function. Intrathecal NIS-lncRNA antisense oligonucleotides also blocked CCI-induced increases in NIS-lncRNA and CCL2 in the ipsilateral L3 and L4 DRG and hyperactivities of neurones and astrocytes in the ipsilateral L3 and L4 spinal cord dorsal horn. Similar results were found in antisense oligonucleotides-treated mice after spinal nerve ligation or intraperitoneal injection of paclitaxel or streptozotocin. Normal morphologic structure and no cell loss were observed in the DRG and spinal cord of antisense oligonucleotides-treated mice.These findings further validate the role of NIS-lncRNA in trauma-, chemotherapy-, or diabetes-induced neuropathic pain and demonstrate potential clinical application of NIS-lncRNA antisense oligonucleotides for neuropathic pain management.

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-expressingFusshRNA 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-lengthFusmRNA 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-κB 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-κB in primary sensory neurons.SIGNIFICANCE STATEMENTIn the present study, we reported that fused in sarcoma (FUS), a DNA/RNA-binding protein, is upregulated in injured dorsal root ganglion (DRG) following peripheral nerve injury. This upregulation is responsible for nerve injury-induced translocation of p65 into the nucleus and phosphorylation of p65 in the nucleus from injured DRG neurons. Because blocking this upregulation alleviates nerve injury-induced nociceptive hypersensitivity, DRG FUS participates in neuropathic pain likely through the activation of NF-κB in primary sensory neurons. FUS may be a potential target for neuropathic pain management.

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.

Several intracellular signals are involved in the sexual dimorphism of chronic pain. Our previous studies demonstrated that the fat-mass and obesity-associated protein (FTO), a demethylase of RNA N6-methyladenosine, in the injured dorsal root ganglion (DRG) contributed to the development and maintenance of nerve injury-induced nociceptive hypersensitivity in male rats and male mice. However, whether these effects of DRG FTO are in a sex-dependent manner is still unknown. The present study sought to investigate the effect of intrathecal administration of a specific FTO inhibitor, meclofenamic acid (MA), on chronic constriction injury (CCI)-induced nociceptive hypersensitivity in female rats. Intrathecal injection of MA attenuated the CCI-induced mechanical allodynia, heat hyperalgesia, and cold hyperalgesia in both the induction and maintenance periods, without changing acute/basal pain and locomotor function, in female rats. Intrathecal MA also blocked the CCI-induced hyperactivations of neurons and astrocytes in the ipsilateral L4 and L5 dorsal horns of female rats. Mechanistically, intrathecal MA prevented the CCI-induced increase in the histone methyltransferase G9a expression and reversed the G9a-controlled downregulation of mu-opioid receptor and Kv1.2 proteins in the ipsilateral L4 and L5 DRGs of female rats. These findings indicate that the effects of the FTO inhibitor on nerve injury-induced nociceptive hypersensitivity in female rats are similar to those in male rats reported previously. Our data also further confirm the role of DRG FTO in neuropathic pain and suggest potential clinical application of the FTO inhibitors for the prevention and treatment of this disorder in both men and women.

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 GABA(A) 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. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13311-021-01158-8.

Group I metabotropic glutamate receptors (group I mGluRs) have been implicated in several central nervous system diseases including chronic pain. It is known that activation of group I mGluRs results in the production of inositol triphosphate (IP3) and diacylglycerol that leads to activation of extracellular signal-regulated kinases (ERKs) and an increase in neuronal excitability, but how group I mGluRs mediate this process remains unclear. We previously reported that Orai1 is responsible for store-operated calcium entry and plays a key role in central sensitization. However, how Orai1 is activated under physiological conditions is unknown. Here, we tested the hypothesis that group I mGluRs recruit Orai1 as part of its downstream signaling pathway in dorsal horn neurons. We demonstrate that neurotransmitter glutamate induces STIM1 puncta formation, which is not mediated by N-Methyl-D-aspartate (NMDA) or α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Glutamate-induced Ca2+ entry in the presence of NMDA or AMPA receptor antagonists is eliminated in Orai1-deficient neurons. Dihydroxyphenylglycine (DHPG) (an agonist of group I mGluRs)-induced Ca2+ entry is abolished by Orai1 deficiency, but not affected by knocking down of transient receptor potential cation channel 1 (TRPC1) or TRPC3. Dihydroxyphenylglycine-induced activation of ERKs and modulation of neuronal excitability are abolished in cultured Orai1-deficient neurons. Moreover, DHPG-induced nociceptive behavior is markedly reduced in Orai1-deficient mice. Our findings reveal previously unknown functional coupling between Orai1 and group I mGluRs and shed light on the mechanism underlying group I mGluRs-mediated neuronal plasticity.

Background and Purpose: Hemorrhage-caused gene changes in the thalamus likely contribute to thalamic pain genesis. RNA N 6 -methyladenosine modification is an additional layer of gene regulation. Whether FTO (fat-mass and obesity-associated protein), an N 6 -methyladenosine demethylase, participates in hemorrhage-induced thalamic pain is unknown. Methods: Expression of Fto mRNA and protein was assessed in mouse thalamus after hemorrhage caused by microinjection of Coll IV (type IV collagenase) into unilateral thalamus. Effect of intraperitoneal administration of meclofenamic acid (a FTO inhibitor) or microinjection of adeno-associated virus 5 (AAV5) expressing Cre into the thalamus of Fto fl/fl mice on the Coll IV microinjection–induced TLR4 (Toll-like receptor 4) upregulation and nociceptive hypersensitivity was examined. Effect of thalamic microinjection of AAV5 expressing Fto (AAV5- Fto ) on basal thalamic TLR4 expression and nociceptive thresholds was also analyzed. Additionally, level of N 6 -methyladenosine in Tlr4 mRNA and its binding to FTO or YTHDF2 (YTH N 6 -methyladenosine RNA binding protein 2) were observed. Results: FTO was detected in neuronal nuclei of thalamus. Level of FTO protein, but not mRNA, was time-dependently increased in the ipsilateral thalamus on days 1 to 14 after Coll IV microinjection. Intraperitoneal injection of meclofenamic acid or adeno-associated virus-5 expressing Cre microinjection into Fto fl/fl mouse thalamus attenuated the Coll IV microinjection–induced TLR4 upregulation and tissue damage in the ipsilateral thalamus and development and maintenance of nociceptive hypersensitivities on the contralateral side. Thalamic microinjection of AAV5- Fto increased TLR4 expression and elicited hypersensitivities to mechanical, heat and cold stimuli. Mechanistically, Coll IV microinjection produced an increase in FTO binding to Tlr4 mRNA, an FTO-dependent loss of N 6 -methyladenosine sites in Tlr4 mRNA and a reduction in the binding of YTHDF2 to Tlr4 mRNA in the ipsilateral thalamus. Conclusions: Our findings suggest that FTO participates in hemorrhage-induced thalamic pain by stabilizing TLR4 upregulation in thalamic neurons. FTO may be a potential target for the treatment of this disorder.

The management of persistent postsurgical pain and neuropathic pain remains a challenge in the clinic. Local anesthetics have been widely used as simple and effective treatment for these two disorders, but the duration of their analgesic effect is short. We here reported a new poly lactic-co-glycolic acid (PLGA)-coated ropivacaine that was continuously released in vitro for at least 6 days. Peri-sciatic nerve injection of the PLGA-coated ropivacaine attenuated paw incision-induced mechanical allodynia and heat hyperalgesia during the incisional pain period, and spared nerve injury-induced mechanical and cold allodynia for at least 7 days post-injection. This effect was dose-dependent. Peri-sciatic nerve injection of the PLGA-coated ropivacaine did not produce detectable inflammation, tissue irritation, or damage in the sciatic nerve and surrounding muscles at the injected site, dorsal root ganglion, spinal cord or brain cortex, although the scores for grasping reflex were mildly and transiently reduced in the higher dosage-treated groups. PERSPECTIVE: Given that PLGA is an FDA-approved medical material, and that ropivacaine is used currently in clinical practice, the injectable PLGA-coated ropivacaine represents a new and highly promising avenue in the management of postsurgical pain and neuropathic pain.

NrCAM, a neuronal cell adhesion molecule in the L1 family of the immunoglobulin superfamily, is subjected to extensively alternative splicing and involved in neural development and some disorders. The aim of this study was to explore the role of Nrcam mRNA alternative splicing in neuropathic pain. A next generation RNA sequencing analysis of dorsal root ganglions (DRGs) showed the differential expression of two splicing variants of Nrcam, Nrcam+10 and Nrcam-10, in the injured DRG after the fourth lumbar spinal nerve ligation (SNL) in mice. SNL increased the exon 10 insertion, resulting in an increase in the amount of Nrcam+10 and a corresponding decrease in the level of Nrcam-10 in the injured DRG. An antisense oligonucleotide (ASO) that specifically targeted exon 10 of Nrcam gene (Nrcam ASO) repressed RNA expression of Nrcam+10 and increased RNA expression of Nrcam-10 in in vitro DRG cell culture. Either DRG microinjection or intrathecal injection of Nrcam ASO attenuated SNL-induced the development of mechanical allodynia, thermal hyperalgesia, or cold allodynia. Nrcam ASO also relieved SNL- or chronic compression of DRG (CCD)-induced the maintenance of pain hypersensitivities in male and female mice. PERSPECTIVE: We conclude that the relative levels of alternatively spliced Nrcam variants are critical for neuropathic pain genesis. Targeting Nrcam alternative splicing via the antisense oligonucleotides may be a new potential avenue in neuropathic pain management.

Toll like receptor 7 (TLR7) is expressed in neurons of the dorsal root ganglion (DRG), but whether it contributes to neuropathic pain is elusive. We found that peripheral nerve injury caused by ligation of the fourth lumbar (L(4)) spinal nerve (SNL) or chronic constriction injury of sciatic nerve led to a significant increase in the expression of TLR7 at mRNA and/or protein levels in mouse injured DRG. Blocking this increase through microinjection of the adeno-associated virus (AAV) 5 expressing TLR7 shRNA into the ipsilateral L(4) DRG alleviated the SNL-induced mechanical, thermal and cold pain hypersensitivities in both male and female mice. This microinjection also attenuated the SNL-induced increases in the levels of phosphorylated extracellular signal-regulated kinase ½ (p-ERK1/2) and glial fibrillary acidic protein (GFAP) in L(4) dorsal horn on the ipsilateral side during both development and maintenance periods. Conversely, mimicking this increase through microinjection of AAV5 expressing full-length TLR7 into unilateral L(3/4) DRGs led to elevations in the amounts of p-ERK1/2 and GFAP in the dorsal horn, augmented responses to mechanical, thermal and cold stimuli, and induced the spontaneous pain on the ipsilateral side in the absence of SNL. Mechanistically, the increased TLR7 activated the NF-κB signaling pathway through promoting the translocation of p65 into the nucleus and phosphorylation of p65 in the nucleus from the injured DRG neurons. Our findings suggest that DRG TLR7 contributes to neuropathic pain by activating NF-κB in primary sensory neurons. TLR7 may be a potential target for therapeutic treatment of this disorder.

Toll-like receptor 4 (TLR4) has been implicated in pathological conditions including chronic pain. Activation of astrocytic TLRs leads to the synthesis of pro-inflammatory cytokines like interleukin 6 (IL-6) and tumor necrosis factor-ɑ (TNF-α), which can cause pathological inflammation and tissue damage in the central nervous system. However, the mechanisms of TLR4-mediated cytokine releases from astrocytes are incomplete understood. Our previous study has shown that Orai1, a key component of calcium release activated calcium channels (CRACs), mediates Ca(2+) entry in astrocytes. How Orai1 contributes to TLR4 signaling remains unclear. Here we show that Orai1 deficiency drastically attenuated lipopolysaccharides (LPS)-induced TNF-α and IL-6 production in astrocytes. Acute LPS treatment did not induce Ca(2+) response and had no effect on thapsigargin (Ca(2+)-ATPase inhibitor)-induced store-dependent Ca(2+) entry. Inhibition or knockdown of Orai1 showed no reduction in LPS-induced p-ERK1/2, p-c-Jun N-terminal kinase, or p-p38 MAPK activation. Interestingly, Orai1 protein level was significantly increased after LPS exposure, which was blocked by inhibition of NF-κB activity. LPS significantly increased basal Ca(2+) level and SOCE after exposure to astrocytes. Moreover, elevating extracellular Ca(2+) concentration increased cytosolic Ca(2+) level, which was almost eliminated in Orai1 KO astrocytes. Our study reports novel findings that Orai1 acts as a Ca(2+) leak channel regulating the basal Ca(2+) level and enhancing cytokine production in astrocytes under the inflammatory condition. These findings highlight an important role of Orai1 in astrocytic TRL4 function and may suggest that Orai1 could be a potential therapeutic target for neuroinflammatory disorders including chronic pain.

Nerve trauma-induced toll-like receptor 7 (TLR7) expression level increase in primary sensory neurons in the damaged dorsal root ganglion (DRG) avails to neuropathic pain, but the reason is still unknown. In the current study, we showed that unilateral lumbar 4 (L4) spinal nerve ligation (SNL) upregulated CCAAT/enhancer-binding protein-β (C/EBPβ) expression in ipsilateral L4 DRG. Preventing this elevation attenuated the SNL-induced upregulation of TLR7 in the ipsilateral L4 DRG and inhibited cold/thermal hyperalgesia and mechanical allodynia. Mimicking nerve trauma-induced C/EBPβ upregulation generated an elevated level of TLR7 in injected DRG, augmented responses to cold/thermal/mechanical stimuli while causing ipsilateral spontaneous pain with no SNL. Mechanistically, SNL upregulated binding of increased C/EBPβ to Tlr7 promoter in ipsilateral L4 DRG. Accorded that C/EBPβ could trigger the activation of Tlr7 promoter and co-expressed with Tlr7 mRNA in individual DRG neurons, our findings strongly suggest the role of C/EBPβ in nerve trauma-mediated TLR7 upregulation in damaged primary sensory neurons.

Analgesic tolerance and hyperalgesia hinder the long-term utility of opioids. We examined whether spinal high mobility group box 1 (HMGB1) is involved in morphine tolerance and its underlying mechanisms by using a model of repeated intrathecal (i.t.) injections of morphine. The results showed that chronic i.t. morphine exposure led to increased expression of HMGB1, Toll-like receptor 4 (TLR4), and receptor for advanced glycation end products (RAGE) and their mRNAs in the dorsal horn. Morphine challenge also promoted HMGB1 expression and release in cultured spinal neurons, but these effects were inhibited by TAK-242, naloxone (antagonists of TLR4), and TLR4 siRNA. Intrathecal coadministration of morphine with TAK-242 or PDTC (inhibitor of NF-κB activation) also reduced HMGB1 expression in the spinal cord. Repeated i.t. coinjections of morphine with glycyrrhizin (GL, an HMGB1 inhibitor) or HMGB1 siRNA prevented reduction of the maximal possible analgesic effect (MPAE) of morphine and alleviated morphine withdrawal-induced hyperalgesia. The established morphine tolerance and hyperalgesia were partially reversed when i.t. injections of GL or HMGB1 antibody started at day 7 of morphine injection. Repeated i.t. injections of morphine with HMGB1 siRNA inhibited the activation of NF-κB, but not that of JNK and p38. A single i.t. injection of HMGB1 in naïve rats caused pain-related hypersensitivity and reduction in MPAE. Moreover, phosphorylated NF-κB p65, TNF-α, and IL-1β levels in the dorsal horn were upregulated following this treatment, but this upregulation was prevented by coinjection with TAK-242. Together, these results suggest that morphine-mediated upregulation of spinal HMGB1 contributes to analgesic tolerance and hyperalgesia via activation of TLR4/NF-κB signaling, and the HMGB1 inhibitor might be a promising adjuvant to morphine in the treatment of intractable pain in the clinic. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13311-019-00800-w) contains supplementary material, which is available to authorized users.

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 Dnmt1 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 DNMT1 may be a potential target for neuropathic pain management.SIGNIFICANCE STATEMENT In the present study, we reported that DNMT1, a canonical DNA maintenance methyltransferase, is upregulated via the activation of the transcription factor CREB in the injured DRG after peripheral nerve injury. This upregulation was responsible for nerve injury-induced de novo DNA methylation within the promoter and 5'-untranslated region of the Kcna2 gene, reductions in Kcna2 expression and Kv current and increases in neuronal excitability in the injured DRG. Since pharmacological inhibition or genetic knockdown of DRG DNMT1 alleviated nerve injury-induced pain hypersensitivities, DRG DNMT1 contributes to neuropathic pain genesis partially through repression of DRG Kcna2 gene expression.

Fibroblast growth factor-inducible-14 (Fn14), a receptor for tumor necrosis-like weak inducer of apoptosis, is expressed in the neurons of dorsal root ganglion (DRG). Its mRNA is increased in the injured DRG following peripheral nerve injury. Whether this increase contributes to neuropathic pain is unknown. We reported here that peripheral nerve injury caused by spinal nerve ligation (SNL) increased the expression of Fn14 at both protein and mRNA levels in the injured DRG. Blocking this increase attenuated the development of SNL-induced mechanical, thermal, and cold pain hypersensitivities. Conversely, mimicking this increase produced the increases in the levels of phosphorylated extracellular signal-regulated kinase ½ and glial fibrillary acidic protein in ipsilateral dorsal horn and the enhanced responses to mechanical, thermal, and cold stimuli in the absence of SNL. Mechanistically, the increased Fn14 activated the NF-κB pathway through promoting the translocation of p65 into the nucleus of the injured DRG neurons. Our findings suggest that Fn14 may be a potential target for the therapeutic treatment of peripheral neuropathic pain.

Purpose The aim of the present study was to further elucidate the role of JAK2/STAT3-CAV-1-NR2B on painful diabetic neuropathy. Methods In vivo, the mechanical withdrawal threshold and thermal withdrawal latency were measured to evaluate neuropathic pain behaviors (n= 8), while western blot (n= 5) and an immunofluorescence double staining experiment (n= 6) were performed to understand the molecular mechanism. In vitro, the individual culture of BV2 mouse microglia cell lines, the co-culture of BV2 mouse microglia cell lines and PC12 rat neuron cell lines, and western blot analysis were performed to understand the molecular mechanism between microglia and neurons. Results The expression of p-JAK2, p-STAT3, t-CAV-1, and p-NR2B was upregulated in the dorsal horn of DNP rats throughout the experiment. Through the immunofluorescence double staining experiment, it was found that p-STAT3 was mainly expressed in activated microglia, and this condition can be stably maintained for approximately 2 weeks after the establishment of the DNP model. The intrathecal injection of JAK2 inhibitor AG490 can relieve the abnormal expression of p-JAK2, p-STAT3, t-CAV-1, and p-NR2B, and relieve pain. The remission of AG490 began on the third day, and it could be stably sustained for 14 days. In vitro high-glucose induced the activation of p-STAT3 in microglia, thereby upregulating the expression of p-CAV-1 and p-NR2B in neurons in the co-culture system. JAK2 inhibitor AG490 can alleviate the abnormal expression of these proteins in the JAK2/STAT3-CAV-1-NR2B signaling pathway in vitro. Conclusions Microglial JAK2/STAT3 signaling probably contributes to neuropathic pain by activating the CAV-1-NR2B pathway.

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.

The methyltransferase-like 3 (Mettl3) is a key component of the large N6-adenosine-methyltransferase complex in mammalian responsible for RNA N6-methyladenosine (m6A) modification, which plays an important role in gene post-transcription modulation. Although RNA m6A is enriched in mammalian neurons, its regulatory function in nociceptive information processing remains elusive. Here, we reported that Complete Freund's Adjuvant (CFA)-induced inflammatory pain significantly decreased global m6A level and m6A writer Mettl3 in the spinal cord. Mimicking this decease by knocking down or conditionally deleting spinal Mettl3 elevated the levels of m6A in ten-eleven translocation methylcytosine dioxygenases 1 (Tet1) mRNA and TET1 protein in the spinal cord, leading to production of pain hypersensitivity. By contrast, overexpressing Mettl3 reversed a loss of m6A in Tet1 mRNA and blocked the CFA-induced increase of TET1 in the spinal cord, resulting in the attenuation of pain behavior. Furthermore, the decreased level of spinal YT521-B homology domain family protein 2 (YTHDF2), an RNA m6A reader, stabilized upregulation of spinal TET1 because of the reduction of Tet1 mRNA decay by the binding to m6A in Tet1 mRNA in the spinal cord after CFA. This study reveals a novel mechanism for downregulated spinal cord METTL3 coordinating with YTHDF2 contributes to the modulation of inflammatory pain through stabilizing upregulation of TET1 in spinal neurons.

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., This work reports that nerve trauma‐induced the downregulation of a dorsal root ganglion‐specifically enriched long noncoding RNA (DS‐lncRNA) promotes the binding of the transcription co‐factor RALY to RNA polymerase II (RNP II) and the Ehmt2 gene promoter, increases the expression of Ehmt2 mRNA and G9a protein, downregulates many pain‐associated genes including Oprm1 mRNA and mu opioid receptor (MOR), and causes neuropathic pain.

Nerve injury–induced changes of gene expression in dorsal root ganglion (DRG) are critical for neuropathic pain genesis. However, how these changes occur remains elusive. Here we report the down-regulation of zinc finger protein 382 (ZNF382) in injured DRG neurons after nerve injury. Rescuing this down-regulation attenuates nociceptive hypersensitivity. Conversely, mimicking this down-regulation produces neuropathic pain symptoms, which are alleviated by C-X-C motif chemokine 13 (CXCL13) knockdown or its receptor CXCR5 knockout. Mechanistically, an identified cis-acting silencer at distal upstream of the Cxcl13 promoter suppresses Cxcl13 transcription via binding to ZNF382. Blocking this binding or genetically deleting this silencer abolishes the ZNF382 suppression on Cxcl13 transcription and impairs ZNF382-induced antinociception. Moreover, ZNF382 down-regulation disrupts the repressive epigenetic complex containing histone deacetylase 1 and SET domain bifurcated 1 at the silencer-promoter loop, resulting in Cxcl13 transcriptional activation. Thus, ZNF382 down-regulation is required for neuropathic pain likely through silencer-based epigenetic disinhibition of CXCL13, a key neuropathic pain player, in DRG neurons.

Genetic knockout or knockdown of fat-mass and obesity-associated protein (FTO), a demethylase that participates in RNA N(6)-methyladenosine modification in injured dorsal root ganglion (DRG), has been demonstrated to alleviate nerve trauma-induced nociceptive hypersensitivities. However, these genetic strategies are still impractical in clinical neuropathic pain management. The present study sought to examine the effect of intrathecal administration of two specific FTO inhibitors, meclofenamic acid (MA) and N-CDPCB, on the development and maintenance of nociceptive hypersensitivities caused by unilateral L5 spinal nerve ligation (SNL) in rats. Intrathecal injection of either MA or N-CDPCB diminished dose-dependently the SNL-induced mechanical allodynia, heat hyperalgesia, cold hyperalgesia, and spontaneous ongoing nociceptive responses in both development and maintenance periods, without altering acute/basal pain and locomotor function. Intrathecal MA also reduced the SNL-induced neuronal and astrocyte hyperactivities in the ipsilateral L5 dorsal horn. Mechanistically, intrathecal injection of these two inhibitors blocked the SNL-induced increase in the histone methyltransferase G9a expression and rescued the G9a-controlled downregulation of mu opioid receptor and Kv1.2 proteins in the ipsilateral L5 DRG. These findings further indicate the role of DRG FTO in neuropathic pain and suggest potential clinical application of the FTO inhibitors for management of this disorder. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13311-021-01053-2.

Chemotherapy-induced peripheral neuropathic pain (CIPNP) often occurs in cancer patients treated with antineoplastic drugs. Therapeutic management of CIPNP is very limited, at least in part due to the largely unknown mechanisms that underlie CIPNP genesis. Here, we showed that systemic administration of the chemotherapeutic drug paclitaxel significantly and time-dependently increased the levels of cyclic AMP response element-binding protein (CREB) in dorsal root ganglion (DRG) neurons. Blocking this increase through DRG microinjection of Creb siRNA attenuated paclitaxel-induced mechanical, heat, and cold nociceptive hypersensitivities. Mimicking this increase through DRG microinjection of the adeno-associated virus 5 expressing full-length Creb mRNA led to enhanced responses to basal mechanical, heat, and cold stimuli in mice in absence of paclitaxel treatment. Mechanically, paclitaxel-induced increase of DRG CREB protein augmented Dnmt3a promoter activity and participated in the paclitaxel-induced upregulation of DNMT3a protein in the DRG. CREB overexpression also elevated the expression of DNMT3a in in vivo and in vitro DRG neurons of naïve mice. Given that DNMT3a is an endogenous instigator of CIPNP and that CREB co-expresses with DNMT3a in DRG neurons, CREB may be a key player in CIPNP through transcriptional activation of the Dnmt3a gene in primary sensory neurons. CREB is thus a likely potential target for the therapeutic management of this disorder. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13311-020-00931-5) contains supplementary material, which is available to authorized users.

Thalamic pain, a type of central poststroke pain, frequently occurs following ischemia/hemorrhage in the thalamus. Current treatment of this disorder is often ineffective, at least in part due to largely unknown mechanisms that underlie thalamic pain genesis. Here, we report that hemorrhage caused by microinjection of type IV collagenase or autologous whole blood into unilateral ventral posterior lateral nucleus and ventral posterior medial nucleus of the thalamus increased the expression of Fgr, a member of the Src family nonreceptor tyrosine kinases, at both mRNA and protein levels in thalamic microglia. Pharmacological inhibition or genetic knockdown of thalamic Fgr attenuated the hemorrhage-induced thalamic injury on the ipsilateral side and the development and maintenance of mechanical, heat, and cold pain hypersensitivities on the contralateral side. Mechanistically, the increased Fgr participated in hemorrhage-induced microglial activation and subsequent production of TNF-α likely through activation of both NF-κB and ERK1/2 pathways in thalamic microglia. Our findings suggest that Fgr is a key player in thalamic pain and a potential target for the therapeutic management of this disorder., Fgr, a member of the Src-family nonreceptor tyrosine kinases, promotes hemorrhage-induced thalamic pain through both NF-κB and ERK1/2-triggered TNF-α production in thamalic microglia.

BACKGROUND: Nerve injury-induced changes in gene expression in the dorsal root ganglion (DRG) contribute to neuropathic pain genesis. Eukaryotic initiation factor 4 gamma 2 (eIF4G2) is a general repressor of cap-dependent mRNA translation. Whether DRG eIF4G2 participates in nerve injury-induced alternations in gene expression and nociceptive hypersensitivity is unknown. METHODS: The expression and distribution of eIF4G2 mRNA and protein in mouse DRG after spinal nerve ligation (SNL) were assessed. Effects of eIF4G2 siRNA microinjected through a glass micropipette into the injured DRG on the SNL-induced DRG mu opioid receptor (MOR) and Kv1.2 downregulation and nociceptive hypersensitivity were examined. In addition, effects of DRG microinjection of adeno-associated virus 5-expressing eIF4G2 (AAV5-eIF4G2) on basal DRG MOR and Kv1.2 expression and nociceptive thresholds were analysed. RESULTS: eIF4G2 protein co-expressed with Kv1.2 and MOR in DRG neurones. Levels of eIF4G2 mRNA (1.7 [0.24] to 2.3 [0.14]-fold of sham, P

Antineoplastic drugs induce dramatic transcriptional changes in dorsal root ganglion (DRG) neurons, which may contribute to chemotherapy-induced neuropathic pain. K2p 1.1 controls neuronal excitability by setting the resting membrane potential. Here, we report that systemic injection of the chemotherapy agent paclitaxel time-dependently downregulates the expression of K 2p 1.1 mRNA and its coding K2p 1.1 protein in the DRG neurons. Rescuing this downregulation mitigates the development and maintenance of paclitaxel-induced mechanical allodynia and heat hyperalgesia. Conversely, in the absence of paclitaxel administration, mimicking this downregulation decreases outward potassium current and increases excitability in the DRG neurons, leading to the enhanced responses to mechanical and heat stimuli. Mechanically, the downregulation of DRG K 2p 1.1 mRNA is attributed to paclitaxel-induced increase in DRG DNMT3a, as blocking this increase reverses the paclitaxel-induced the decrease of DRG K2p 1.1 and mimicking this increase reduces DRG K2p 1.1 expression. In addition, paclitaxel injection increases the binding of DNMT3a to the K 2p 1.1 gene promoter region and elevates the level of DNA methylation within this region in the DRG. These findings suggest that DNMT3a-triggered downregulation of DRG K2p 1.1 may contribute to chemotherapy-induced neuropathic pain.

Earlier studies on genetically modified mice indicated that plasma membrane calcium ATPase 2 (PMCA2), a calcium extrusion pump, plays a novel and sex-dependent role in mechanical pain responses: female, but not male, PMCA2+/− mice manifest increased mechanical pain compared to female PMCA2+/+ mice. The goal of the present studies was to determine the contribution of ovarian steroids to the genotype- and sex-dependent manifestation of mechanical pain in PMCA2+/+ versus PMCA2+/− mice. Ovariectomy increased mechanical pain sensitivity and 17β-estradiol (E2) replacement restored it to basal levels in PMCA2+/+ mice, but not in PMCA2+/− littermates. Intrathecal administration of an estrogen receptor alpha (ERα) agonist induced ERα signaling in the dorsal horn (DH) of female PMCA2+/+ mice, but was ineffective in PMCA2+/− mice. In male PMCA2+/+ and PMCA2+/− mice, E2 treatment following orchidectomy did not recapitulate the genotype-dependent differential pain responses observed in females and the agonist did not elicit ERα signaling. These findings establish a novel, female-specific link between PMCA2, ERα and mechanical pain. It is postulated that PMCA2 is essential for adequate ERα signaling in the female DH and that impaired ERα signaling in the female PMCA2+/− mice hinders the analgesic effects of E2 leading to increased sensitivity to mechanical stimuli.

The transmission of normal sensory and/or acute noxious information requires intact expression of pain-associated genes within the pain pathways of nervous system. Expressional changes of these genes after peripheral nerve injury are also critical for neuropathic pain induction and maintenance. Methyl-CpG-binding domain protein 1 (MBD1), an epigenetic repressor, regulates gene transcriptional activity. We report here that MBD1 in the primary sensory neurons of DRG is critical for the genesis of acute pain and neuropathic pain as DRG MBD1-deficient mice exhibit the reduced responses to acute mechanical, heat, cold, and capsaicin stimuli and the blunted nerve injury-induced pain hypersensitivities. Furthermore, DRG overexpression of MBD1 leads to spontaneous pain and evoked pain hypersensitivities in the WT mice and restores acute pain sensitivities in the MBD1-deficient mice. Mechanistically, MDB1 repressesOprm1andKcna2gene expression by recruiting DNA methyltransferase DNMT3a into these two gene promoters in the DRG neurons. DRG MBD1 is likely a key player under the conditions of acute pain and neuropathic pain.SIGNIFICANCE STATEMENTIn the present study, we revealed that the mice with deficiency of methyl-CpG-binding domain protein 1 (MBD1), an epigenetic repressor, in the DRG displayed the reduced responses to acute noxious stimuli and the blunted neuropathic pain. We also showed that DRG overexpression of MBD1 produced the hypersensitivities to noxious stimuli in the WT mice and rescued acute pain sensitivities in the MBD1-deficient mice. We have also provided the evidence that MDB1 repressesOprm1andKcna2gene expression by recruiting DNA methyltransferase DNMT3a into these two gene promoters in the DRG neurons. DRG MBD1 may participate in the genesis of acute pain and neuropathic pain likely through regulating DNMT3a-controlledOprm1andKcna2gene expression in the DRG neurons.

Background Accumulated evidence suggests that spinal cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2) may be implicated in the development of opioid-induced hyperalgesia. Methods Rats received subcutaneous fentanyl injections at different doses (20–80 μg kg −1 ), four separate times at 15-min intervals. Some rats only received fentanyl (60 μg kg −1 × 4 doses) with or without surgical incision. Fentanyl-induced hyperalgesia was evaluated via a tail-pressure or paw-withdrawal test. The concentrations of spinal COX-2, EP-1 receptor (EP-1R) mRNA, and PGE2 were measured. The effects of the COX-2 inhibitor, parecoxib (intraperitoneal 10 mg kg −1 ), or the EP-1R antagonist, SC51089 (intraperitoneal 100 μg kg −1 ), on hyperalgesia and spinal PGE2 were examined. Results Acute repeated injections of fentanyl dose-dependently induced mechanical hyperalgesia, which reached a peak at the 1 st day and persisted for 1–4 days postinjection. This hyperalgesia could be partly or totally prevented by the pretreatment of either parecoxib or SC51089. Consistently, the levels of spinal COX-2 mRNA and PGE2 were also dose-dependently increased, reaching a peak at the first day and persisting for 2 days postinjection. Pretreatment with parecoxib could block the increase in spinal PGE2 and had no effects on spinal COX-2 and EP-1R mRNA. Fentanyl injection enhanced incision-induced mechanical and thermal hyperalgesia. Conclusions Acute repeated fentanyl administration dose-dependently produced mechanical hyperalgesia and augmented surgery induced postoperative hyperalgesia. This behavioural change was paralleled with an increase in spinal COX-2 mRNA and PGE2 after fentanyl administration. Inhibition of COX-2 or blockade of EP-1R can partly or totally prevent hyperalgesia.

BACKGROUND: Perioperative fentanyl has been reported to induce hyperalgesia and increase postoperative pain. In this study, we tried to investigate behavioral hyperalgesia, the expression of proinflammatory cytokines, such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), and the activation of microglia in the spinal cord and dorsal root ganglion (DRG) in a rat model of surgical plantar incision with or without perioperative fentanyl. METHODS: Four groups of rats (n = 32 for each group) were subcutaneously injected with fentanyl at 60 μg/kg or normal saline for 4 times with 15-minute intervals. Plantar incisions were made to rats in 2 groups after the second drug injection. Mechanical and thermal nociceptive thresholds were assessed by the tail pressure test and paw withdrawal test on the day before, at 1, 2, 3, 4 hours, and on the days 1–7 after drug injection. The lumbar spinal cord, bilateral DRG, and cerebrospinal fluid of 4 rats in each group were collected to measure IL-1β, IL-6, and TNF-α on the day before, at the fourth hour, and on the days 1, 3, 5, and 7 after drug injection. The lumbar spinal cord and bilateral DRG were removed to detect the ionized calcium-binding adapter molecule 1 on the day before and on the days 1 and 7 after drug injection. RESULTS: Rats injected with normal saline only demonstrated no significant mechanical or thermal hyperalgesia or any increases of IL-1β, IL-6, and TNF-α in the spinal cord or DRG. However, injection of fentanyl induced analgesia within as early as 4 hours and a significant delayed tail mechanical and bilateral plantar thermal hyperalgesia after injections lasting for 2 days, while surgical plantar incision induced a significant mechanical and thermal hyperalgesia lasting for 1–4 days. The combination of fentanyl and incision further aggravated the hyperalgesia and prolonged the duration of hyperalgesia. The fentanyl or surgical incision upregulated the expression of IL-1β, IL-6, and TNF-α in the spinal cord and bilateral DRG for more than 7 days and increase of ionized calcium-binding adapter molecule 1 in the spinal cord. The combination of fentanyl and incision resulted in higher increase of IL-1β, IL-6, and TNF-α in the spinal cord and bilateral DRG. CONCLUSIONS: The surgical plantar incision with or without perioperative fentanyl induced significant mechanical and thermal hyperalgesia, an increased expression of IL-1β, IL-6, TNF-α in the spinal cord and DRG, and activation of microglia in the spinal cord.

Opioids are the gold standard for pharmacological treatment of neuropathic pain, but their analgesic effects are unsatisfactory in part due to nerve injury-induced downregulation of opioid receptors in dorsal root ganglia (DRG) neurons. How nerve injury drives such downregulation remains elusive. DNA methyltransferase-(DNMT-) triggered DNA methylation represses gene expression. We show here that blocking the nerve injury-induced increase in DRG DNMT3a (a de novo DNMT) rescued the expression of Oprm1 and Oprk1 mRNAs and their respective encoding mu opioid receptor (MOR) and kappa opioid receptor (KOR) proteins in the injured DRG. Blocking this increase also prevented the nerve injury-induced increase in DNA methylation in the promoter and 5′-untranslated region of the Oprm1 gene in the injured DRG, restored morphine or loperamide (a peripheral acting MOR preferring agonist) analgesic effects, and attenuated the development of their analgesic tolerance under neuropathic pain conditions. Mimicking this increase reduced the expression of Oprm1 and Oprk1 mRNAs and their coding MOR and KOR in DRG and augmented MOR-gated neurotransmitter release from the primary afferents. Mechanistically, DNMT3a regulation of Oprm1 gene expression required the methyl-CpG-binding protein 1, MBD1, as MBD1 knockout resulted in the decreased binding of DNMT3a to the Oprm1 gene promoter and blocked the DNMT3a-triggered repression of Oprm1 gene expression in DRG neurons. These data suggest that DNMT3a is required for nerve injury-induced and MBD1-mediated epigenetic silencing of the MOR and KOR in the injured DRG. DNMT3a inhibition may serve as a promising adjuvant therapy for opioid use in neuropathic pain management.

Nerve injury induces changes in gene transcription in dorsal root ganglion (DRG) neurons, which may contribute to nerve injury-induced neuropathic pain. DNA methylation represses gene expression. Here, we report that peripheral nerve injury increases expression of the DNA methyltransferase DNMT3a in the injured DRG neurons via the activation of the transcription factor octamer transcription factor 1. Blocking this increase prevents nerve injury-induced methylation of the voltage-dependent potassium (Kv) channel subunit Kcna2 promoter region and rescues Kcna2 expression in the injured DRG and attenuates neuropathic pain. Conversely, in the absence of nerve injury, mimicking this increase reduces the Kcna2 promoter activity, diminishes Kcna2 expression, decreases Kv current, increases excitability in DRG neurons and leads to spinal cord central sensitization and neuropathic pain symptoms. These findings suggest that DNMT3a may contribute to neuropathic pain by repressing Kcna2 expression in the DRG.

Objective: Diabetic neuropathic pain (DNP) is one of the common complications in type 2 Diabetes Mellitus (DM) patients. However, molecular mechanisms in underlying diabetic neuropathic pain are still poorly understood. Kalirin-7, a multifunctional Rho GDP/GTP exchange factor, located at the excitatory synapses, was reported to modulate the neuronal cytoskeleton. Therefore, in this study, we explored the effects of Kalirin-7 on type 2 diabetic neuropathic pain and the mechanisms in spinal cord in rats. Methods: The type 2 diabetic neuropathic pain model was established in rats by feeding them with a high-sugar and high-fat diet for 8 weeks, and then fasting them for 12 hours, followed by a single intraperitoneal injection of STZ. Kalirin-7 was knocked down in the spinal cord by an intrathecal administration of Kalirin-7 siRNA. Results: The levels of Kalirin-7, p-NR2B and PSD-95 as well as the PSD-95-NR2B coupling were significantly increased in the spinal cord of type 2 DM rats. The knockdown of Kalirin-7 expression in the spinal cord by the intrathecal administration of Kalirin-7 siRNA not only reduced the levels of p-NR2B and the PSD-95-NR2B coupling in the spinal cord, but also relieved mechanical allodynia and thermal hyperalgesia in type 2 DM rats. Conclusions: Our findings suggest that spinally expressed Kalirin-7 likely contributes to type 2 diabetic neuropathic pain through regulating the PSD-95/NR2B interaction-dependent NR2B phosphorylation in the spinal cord.

The mechanisms underlying type-2 diabetic neuropathic pain (DNP) are unclear. This study investigates the coupling of postsynaptic density-95 (PSD-95) to N-methyl-D-aspartate receptor subunit 2B (GluN2B), and the subsequent phosphorylation of GluN2B (Tyr1472-GluN2B) in the spinal cord in a rat model of type-2 DNP. Expression levels of PSD-95, Tyr1472-GluN2B, Ca2+/calmodulin-dependent protein kinase II (CaMKII) and its phosphorylated counterpart (Thr286-CaMKII), and α-amino-3-hydroxy-5-methyl-4-soxazole propionic acid receptor subtype 1 (GluR1) and its phosphorylated counterpart (Ser831-GluR1) were significantly increased versus controls in the spinal cord of type-2 DNP rats whereas the expression of total spinal GluN2B did not change. The intrathecal injection of Ro25-6981 (a specific antagonist of GluN2B) or Tat-NR2B9c (a mimetic peptide disrupting the interaction between PSD-95 and GluN2B) induced an antihyperalgesic effect and blocked the increased expression of Tyr1472-GluN2B, CaMKII, GluR1, Thr286-CaMKII, and Ser831-GluR1 in the spinal cords; the increase in spinal cord PSD-95 was not affected. These findings indicate that the PSD-95-GluN2B interaction may increase phosphorylation of GluN2B, and subsequently induce the expression of phosphorylation of CaMKII and GluR1 in the spinal cord of type-2 DNP rats. Targeting the interaction of PSD-95 with GluN2B may provide a new therapeutic strategy for type-2 DNP.