The ERK/MAPK pathway, as a target for the treatment of neuropathic pain

Involvement of HDAC2-mediated kcnq2/kcnq3 genes transcription repression activated by EREG/EGFR-ERK-Runx1 signaling in bone cancer pain

Bone cancer pain (BCP) represents a prevalent symptom among cancer patients with bone metastases, yet its underlying mechanisms remain elusive. This study investigated the transcriptional regulation mechanism of Kv7(KCNQ)/M potassium channels in DRG neurons and its involvement in the development of BCP in rats. We show that HDAC2-mediated transcriptional repression of kcnq2/kcnq3 genes, which encode Kv7(KCNQ)/M potassium channels in dorsal root ganglion (DRG), contributes to the sensitization of DRG neurons and the pathogenesis of BCP in rats. Also, HDAC2 requires the formation of a corepressor complex with MeCP2 and Sin3A to execute transcriptional regulation of kcnq2/kcnq3 genes. Moreover, EREG is identified as an upstream signal molecule for HDAC2-mediated kcnq2/kcnq3 genes transcription repression. Activation of EREG/EGFR-ERK-Runx1 signaling, followed by the induction of HDAC2-mediated transcriptional repression of kcnq2/kcnq3 genes in DRG neurons, leads to neuronal hyperexcitability and pain hypersensitivity in tumor-bearing rats. Consequently, the activation of EREG/EGFR-ERK-Runx1 signaling, along with the subsequent transcriptional repression of kcnq2/kcnq3 genes by HDAC2 in DRG neurons, underlies the sensitization of DRG neurons and the pathogenesis of BCP in rats. These findings uncover a potentially targetable mechanism contributing to bone metastasis-associated pain in cancer patients.

Study on analgesic effect of Shentong Zhuyu Decoction in neuropathic pain rats by network pharmacology and RNA-Seq

ETHNOPHARMACOLOGICAL RELEVANCE

Shentong Zhuyu Decoction (STZYD) is a traditional prescription for promoting the flow of Qi and Blood which is often used in the treatment of low back and leg pain clinicall with unclear mechanism. Neuropathic pain (NP) is caused by disease or injury affecting the somatosensory system. LncRNAs may play a key role in NP by regulating the expression of pain-related genes through binding mRNAs or miRNAs sponge mechanisms.

AIM OF THE STUDY

To investigate the effect and potential mechanism of STZYD on neuropathic pain.

METHODS

Chronic constriction injury (CCI) rats, a commonly used animal model, were used in this study. The target of STZYD in NP was analyzed by network pharmacology, and the analgesic effect of STZYD in different doses (H-STZYD, M-STZYD, L-STZYD) on CCI rats was evaluated by Mechanical withdrawal thresholds (MWT) and thermal withdrawal latency (TWL). Meanwhile, RNA-seq assay was used to detect the changed mRNAs and lncRNAs in CCI rats after STZYD intervention. GO analysis, KEGG pathway analysis, and IPA analysis were used to find key target genes and pathways, verified by qPCR and Western Blot. The regulatory effect of lncRNAs on target genes was predicted by co-expression analysis and ceRNA network construction.

RESULTS

We found that STZYD can improve hyperalgesia in CCI rats, and H-STZYD has the best analgesic effect. The results of network pharmacological analysis showed that STZYD could play an analgesic role in CCI rats through the MAPK/ERK/c-FOS pathway. By mRNA-seq and lncRNA-seq, we found that STZYD could regulate the expression of Cnr1, Cacng5, Gucy1a3, Kitlg, Npy2r, and Grm8, and inhibited the phosphorylation level of ERK in the spinal cord of CCI rats. A total of 27 lncRNAs were associated with the target genes and 30 lncRNAs, 83 miRNAs and 5 mRNAs participated in the ceRNA network.

CONCLUSION

STZYD has the effect of improving hyperalgesia in CCI rats through the MAPK/ERK/c-FOS pathway, which is related to the regulation of lncRNAs to Cnr1 and other key targets.

ephrin-B2 promotes nociceptive plasticity and hyperalgesic priming through EphB2-MNK-eIF4E signaling in both mice and humans

Ephrin-B-EphB signaling can promote pain through ligand-receptor interactions between peripheral cells, like immune cells expressing ephrin-Bs, and EphB receptors expressed by DRG neurons. Previous studies have shown increased ephrin-B2 expression in peripheral tissues like synovium of rheumatoid and osteoarthritis patients, indicating the clinical significance of this signaling. The primary goal of this study was to understand how ephrin-B2 acts on mouse and human DRG neurons, which express EphB receptors, to promote pain and nociceptor plasticity. We hypothesized that ephrin-B2 would promote nociceptor plasticity and hyperalgesic priming through MNK-eIF4E signaling, a critical mechanism for nociceptive plasticity induced by growth factors, cytokines and nerve injury. Both male and female mice developed dose-dependent mechanical hypersensitivity in response to ephrin-B2, and both sexes showed hyperalgesic priming when challenged with PGE2 injection either to the paw or the cranial dura. Acute nociceptive behaviors and hyperalgesic priming were blocked in mice lacking MNK1 (Mknk1 knockout mice) and by eFT508, a specific MNK inhibitor. Sensory neuron-specific knockout of EphB2 using Pirt-Cre demonstrated that ephrin-B2 actions require this receptor. In Ca2+-imaging experiments on cultured DRG neurons, ephrin-B2 treatment enhanced Ca2+ transients in response to PGE2 and these effects were absent in DRG neurons from MNK1-/- and EphB2-PirtCre mice. In experiments on human DRG neurons, ephrin-B2 increased eIF4E phosphorylation and enhanced Ca2+ responses to PGE2 treatment, both blocked by eFT508. We conclude that ephrin-B2 acts directly on mouse and human sensory neurons to induce nociceptor plasticity via MNK-eIF4E signaling, offering new insight into how ephrin-B signaling promotes pain.

Light-Inducible Activation of TrkA for Probing Chronic Pain in Mice

Chronic pain is a prevalent problem that plagues modern society, and better understanding its mechanisms is critical for developing effective therapeutics. Nerve growth factor (NGF) and its primary receptor, Tropomyosin receptor kinase A (TrkA), are known to be potent mediators of chronic pain, but there is a lack of established methods for precisely perturbing the NGF/TrkA signaling pathway in the study of pain and nociception. Optobiological tools that leverage light-induced protein-protein interactions allow for precise spatial and temporal control of receptor signaling. Previously, our lab reported a blue light-activated version of TrkA generated using light-induced dimerization of the intracellular TrkA domain, opto-iTrkA. In this work, we show that opto-iTrkA activation is able to activate endogenous ERK and Akt signaling pathways and causes the retrograde transduction of phospho-ERK signals in dorsal root ganglion (DRG) neurons. Opto-iTrkA activation also sensitizes the transient receptor potential vanilloid 1 (TRPV1) channel in cellular models, further corroborating the physiological relevance of the optobiological stimulus. Finally, we show that opto-iTrkA enables light-inducible potentiation of mechanical sensitization in mice. Light illumination enables nontraumatic and reversible (<2 days) sensitization of mechanical pain in mice transduced with opto-iTrkA, which provides a platform for dissecting TrkA pathways for nociception in vitro and in vivo.

The role of non-coding RNAs in neuropathic pain

Neuropathic pain (NPP) is a refractory pain syndrome, caused by damage or disease of the somatosensory nervous system and characterized by spontaneous pain, hyperalgesia, abnormal pain and sensory abnormality. Non-coding RNAs (ncRNAs), including microRNA (miRNA), long non-coding RNA (lncRNA), circular RNA (circRNA) and Piwi interacting RNA (piRNA), play a notable role in initiation and maintenance of NPP. In this review, we summarize the role of ncRNAs in NPP and their underlaying mechanism. Generally, ncRNAs are interacted with mRNA, protein or DNA to regulate the molecules and signals assciated with neuroinflammation, ion channels, neurotrophic factors and others, and then involved in the occurrence and development of NPP. Therefore, this review not only contributes to deepen our understanding of the pathophysiological mechanism of NPP, but also provides theoretical basis for the development of new therapy strategies for this disorder.

Gooderoside A from Anoectochilus elatus attenuates acute and chronic pains by inhibiting NO/cGMP and IRAK4/IRAK1/TAK1 signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Anoectochilus elatus Lindl. was traditionally used for pain treatment and Gooderoside A (GA) was regarded as its principal constituent.

AIM OF THE STUDY

To investigate whether GA can be responsible for the antinociceptive activity of A. elatus and explore its underlying mechanism.

MATERIALS AND METHODS

Acetic acid-induced abdominal writhing and tail flick tests were employed to evaluate the antinociceptive activity of ethanolic extract of A. elatus (EEA) and GA. Formalin test was used to ascertain the antinociceptive pattern of GA. Entobarbital sodium induced sleep test was adopted to exclude its hypnotic effect, while open-field test was performed to rule out its motor impairment effect. Chronic constriction injury (CCI)-induced neuropathic pain in rats was developed to evaluate its efficacy on neuropathic pain, and BV-2 cells were used to explore the underlying mechanism.

RESULTS

EEA and GA, significantly inhibited chemical and thermal nociception. GA suppressed nociception in formalin test in both phase I and II, whereas methylene blue and L-NAME partially reversed its efficacy. GA located inner and slightly blocked sodium channel current, and did not show any hypnotic effect or motor impairment effect. Crucially, GA markedly attenuated chronic neuropathic pain in rats, inhibited the phosphorylation of IRAK4, IRAK1 and TAK1, and suppressed MAPKs pathway in BV-2 cells.

CONCLUSION

GA relieved acute and chronic pains in vivo. The mechanism of action involves the blocking of NO/cGMP and IRAK4/IRAK1/TAK1 pathways. These results suggested GA may be a promising candidate for antinociceptive drug development.

Differential Gene Expression in Pain-Related Genes are not Affected by the Presence of Dementia

BACKGROUND

Prior work has demonstrated differences in the transcriptome between those with and without chronic musculoskeletal pain.

AIMS

The aim of this study was to explore whether pain-related gene expression is similar between individuals with and without dementia.

DESIGN

This was a descriptive study using a one-time assessment.

SETTINGS

PARTICIPANTS/SUBJECTS: A total of 20 older adults living in a continuing care retirement community, 50% of whom had dementia were inlcuded in this study. All were female and the mean age of participants was 89 (SD = 6).

METHODS

Pain was evaluated based on the PROMIS Pain Intensity Short Form 3a. Whole blood was collected by venipuncture into Tempus vacutainer tubes (3 ml) and the RNA was extracted at the Translational Genomics Laboratory at the University of Maryland Baltimore. Analyses included a differential expression analysis, a weighted gene co-expression network analysis, and a pathway enrichment analysis.

RESULTS

Eighty-three genes were differentially expressed between individuals with and without pain (p <.05). After normalizing gene counts and removing the low expressed genes, 18,028 genes were left in the final analysis. There was no clustering of the samples related to study variables of pain or dementia.

CONCLUSION

The findings from this study provided some preliminary support that pain-related gene expression is similar between individuals with and without dementia.

Effects of Nutraceutical Compositions Containing Rhizoma Gastrodiae or Lipoic Acid in an In Vitro Induced Neuropathic Pain Model

BACKGROUND

Peripheral neuropathy is caused by a malfunction in the axons and myelin sheaths of peripheral nerves and motor and sensory neurons. In this context, nonpharmacological treatments with antioxidant potential have attracted much attention due to the issues that some conventional pharmaceutical therapy can generate. Most of these treatments contain lipoic acid, but issues have emerged regarding its use. Considering this, the present study evaluated the beneficial effects of nutraceuticals based on Gastrodiae elata dry extract 10:1 or lipoic acid in combination with other substances (such as citicholine, B vitamins, and acetyl L-carnitine).

METHOD

To assess the combination's absorption and biodistribution and exclude cytotoxicity, its bioavailability was first examined in a 3D intestinal barrier model that replicated oral ingestion. Subsequently, a 3D model of nerve tissue was constructed to investigate the impacts of the new combination on the significant pathways dysregulated in peripheral neuropathy.

RESULTS

Our findings show that the novel combination outperformed in initial pain relief response and in recovering the mechanism of nerve healing following Schwann cell injury by successfully crossing the gut barrier and reaching the target site.

CONCLUSION

This article describes a potential alternative nutraceutical approach supporting the effectiveness of combinations with Gastrodiae elata extract in decreasing neuropathy and regulating pain pathways.

Silencing of secreted phosphoprotein 1 attenuates sciatic nerve injury-induced neuropathic pain: Regulating extracellular signal-regulated kinase and neuroinflammatory signaling pathways

BACKGROUND

Neuropathic pain (NP) is a chronic pathological pain that affects the quality of life and is a huge medical burden for affected patients. In this study, we aimed to explore the effects of secreted phosphoprotein 1 (SPP1) on NP.

METHODS

We established a chronic constriction injury (CCI) rat model, knocked down SPP1 via an intrathecal injection, and/or activated the extracellular signal-regulated kinase (ERK) pathway with insulin-like growth factor 1 (IGF-1) treatment. Pain behaviors, including paw withdrawal threshold (PWT), paw withdrawal latency (PWL), lifting number, and frequency, were assessed. After sacrificing rats, the L4-L5 dorsal root ganglion was collected. Then, SPP1 levels were determined using quantitative polymerase chain reaction (qPCR) and western blot analysis. The levels of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6, IL-10, epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), and transforming growth factor (TGF)-β were determined using qPCR and enzyme-linked immunosorbent assay. The levels of ERK pathway factors were determined via western blot analysis.

RESULTS

We found that CCI decreased PWT and PWL, increased the lifting number and frequency, and upregulated SPP1 levels. The loss of SPP1 reversed these CCI-induced effects. Additionally, CCI upregulated IL-1β, TNF-α, IL-6, EGF, and VEGF levels, downregulated TGF-β levels, and activated the ERK pathway, while silencing of SPP1 abrogated these CCI-induced effects. Moreover, IGF-1 treatment reversed the effects of SPP1 loss.

CONCLUSIONS

The data indicate that silencing SPP1 attenuates NP via inactivation of the ERK pathway, suggesting that SPP1 may be a promising target for NP treatment.

Role of ERK in gender difference of fibromyalgia pain

This study investigated the ERK pathway of the peripheral nervous system and discovered a gender-specific pattern of ERK activation in the dorsal root ganglion of an acid-induced chronic widespread muscular pain model. We employed a twice acid-induced chronic musculoskeletal pain model in rats to evaluate mechanical pain behavior in both male and female groups. We further conducted protein analysis of dissected dorsal root ganglions from both genders. Both male and female rats exhibited a similar pain behavior trend, with females demonstrating a lower pain threshold. Protein analysis of the dorsal root ganglion (DRG) showed a significant increase in phosphorylated ERK after the second acid injection in all groups. However, phosphorylation of ERK was observed in the dorsal root ganglion, with higher levels in the male ipsilateral group compared to the female group. Moreover, there was a no difference between the left and right sides in males, whereas the significant difference was observed in females. In conclusions, the administration of acid injections induced painful behavior in rats, and concurrent with this, a significant upregulation of pERK was observed in the dorsal root ganglia, with a greater magnitude of increase in males than females, and in the contralateral side compared to the ipsilateral side. Our findings shed light on the peripheral mechanisms underlying chronic pain disorders and offer potential avenues for therapeutic intervention.

Advances in Neuropathic Pain Research: Selected Intracellular Factors as Potential Targets for Multidirectional Analgesics

Neuropathic pain is a complex and debilitating condition that affects millions of people worldwide. Unlike acute pain, which is short-term and starts suddenly in response to an injury, neuropathic pain arises from somatosensory nervous system damage or disease, is usually chronic, and makes every day functioning difficult, substantially reducing quality of life. The main reason for the lack of effective pharmacotherapies for neuropathic pain is its diverse etiology and the complex, still poorly understood, pathophysiological mechanism of its progression. Numerous experimental studies, including ours, conducted over the last several decades have shown that the development of neuropathic pain is based on disturbances in cell activity, imbalances in the production of pronociceptive factors, and changes in signaling pathways such as p38MAPK, ERK, JNK, NF-κB, PI3K, and NRF2, which could become important targets for pharmacotherapy in the future. Despite the availability of many different analgesics, relieving neuropathic pain is still extremely difficult and requires a multidirectional, individual approach. We would like to point out that an increasing amount of data indicates that nonselective compounds directed at more than one molecular target exert promising analgesic effects. In our review, we characterize four substances (minocycline, astaxanthin, fisetin, and peimine) with analgesic properties that result from a wide spectrum of actions, including the modulation of MAPKs and other factors. We would like to draw attention to these selected substances since, in preclinical studies, they show suitable analgesic properties in models of neuropathy of various etiologies, and, importantly, some are already used as dietary supplements; for example, astaxanthin and fisetin protect against oxidative stress and have anti-inflammatory properties. It is worth emphasizing that the results of behavioral tests also indicate their usefulness when combined with opioids, the effectiveness of which decreases when neuropathy develops. Moreover, these substances appear to have additional, beneficial properties for the treatment of diseases that frequently co-occur with neuropathic pain. Therefore, these substances provide hope for the development of modern pharmacological tools to not only treat symptoms but also restore the proper functioning of the human body.

BTD: A TRPC5 activator ameliorates mechanical allodynia in diabetic peripheral neuropathic rats by modulating TRPC5-CAMKII-ERK pathway

Mechanical allodynia is a serious complication of painful diabetic neuropathy (PDN) with limited treatment options. The transient receptor potential canonical 5 (TRPC5) channel is a promising target in pain; however, its role in painful diabetic neuropathy has not yet been elucidated. In this study, we have investigated the role of TRPC5 channels using BTD [N-{3-(adamantan-2-yloxy)-propyl}-3-(6-methyl-1,1-dioxo-2H-1λ6,2,4-benzothiadiazin-3-yl)-propanamide)],a potent TRPC5 activator and HC070, as TRPC5 channel inhibitor in rat model of PDN. In this study, streptozotocin was used to induce diabetes in male Sprague-Dawley rats. The alterations in mechanical and thermal pain thresholds, nerve functional deficits in diabetic animals were assessed by various behavioral and functional parameters.TRPC5 involvement was investigated by treating neuropathic rats with BTD, TRPC5 channel activator (1 and 3 mg/kg, i.p. for 14 days) and HC070, a TRPC5 channel inhibitor (1 and 3 mg/kg). BTD and HC070 effects in pain reduction were assessed by western blotting, estimating oxidative stress and inflammatory markers in the lumbar spinal cord. BTD treatment (3 mg/kg, i.p.) once daily for 14 days ameliorated mechanical allodynia but not thermal hyposensation or nerve functional deficit in diabetic neuropathic rats. BTD treatment down-regulated TRPC5 expression by increasing the activity of protein kinase C. It also subsequently down-regulated the downstream pain markers (CAMKII, ERK) in the spinal cord. Additionally, a decrease in inflammatory cytokines (TNF-α, IL-6) also demonstrated BTD's potent anti-inflammatory properties in reducing mechanical allodynia. On the other hand, HC070 did not exert any beneficial effects on behavioural and nerve functional parameters. The study concludes that BTD ameliorated mechanical allodynia in a rat model of painful diabetic neuropathy not only through modulation of the TRPC5-CAMKII-ERK pathway but also through its anti-inflammatory and anti-apoptotic properties. Overall, BTD is a promising therapeutic molecule in the treatment of mechanical allodynia in painful diabetic neuropathy.

Brain nuclei and neural circuits in neuropathic pain and brain modulation mechanisms of acupuncture: a review on animal-based experimental research

Neuropathic pain (NP) is known to be associated with abnormal changes in specific brain regions, but the complex neural network behind it is vast and complex and lacks a systematic summary. With the help of various animal models of NP, a literature search on NP brain regions and circuits revealed that the related brain nuclei included the periaqueductal gray (PAG), lateral habenula (LHb), medial prefrontal cortex (mPFC), and anterior cingulate cortex (ACC); the related brain circuits included the PAG-LHb and mPFC-ACC. Moreover, acupuncture and injurious information can affect different brain regions and influence brain functions via multiple aspects to play an analgesic role and improve synaptic plasticity by regulating the morphology and structure of brain synapses and the expression of synapse-related proteins; maintain the balance of excitatory and inhibitory neurons by regulating the secretion of glutamate, γ-aminobutyric acid, 5-hydroxytryptamine, and other neurotransmitters and receptors in the brain tissues; inhibit the overactivation of glial cells and reduce the release of pro-inflammatory mediators such as interleukins to reduce neuroinflammation in brain regions; maintain homeostasis of glucose metabolism and regulate the metabolic connections in the brain; and play a role in analgesia through the mediation of signaling pathways and signal transduction molecules. These factors help to deepen the understanding of NP brain circuits and the brain mechanisms of acupuncture analgesia.

Magnolin Inhibits Paclitaxel-Induced Cold Allodynia and ERK1/2 Activation in Mice

Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of anti-cancer drugs. The main symptoms often include sensory disturbances and neuropathic pain, and currently there is no effective treatment for this condition. This study aimed to investigate the suppressive effects of magnolin, an extracellular signal-regulated kinase (ERK) inhibitor substance derived from a 95% EtOH extract of the seeds of Magnolia denudata, on the symptoms of CIPN. A taxol-based anti-cancer drug paclitaxel (PTX) was repeatedly injected (2 mg/kg/day, total 8 mg/kg) into mice to induce CIPN. A neuropathic pain symptom was assessed using a cold allodynia test that scores behaviors of licking and shaking paw after plantar administration of acetone drop. Magnolin was administered intraperitoneally (0.1, 1, or 10 mg/kg) and behavioral changes to acetone drop were measured. The effect of magnolin administration on ERK expression in the dorsal root ganglion (DRG) was investigated using western blot analysis. The results showed that the repeated injections of PTX induced cold allodynia in mice. Magnolin administration exerted an analgesic effect on the PTX-induced cold allodynia and inhibited the ERK phosphorylation in the DRG. These results suggest that magnolin could be developed as an alternative treatment to suppress paclitaxel-induced neuropathic pain symptoms.

Analgesic Effects of Fisetin, Peimine, Astaxanthin, Artemisinin, Bardoxolone Methyl and 740 Y-P and Their Influence on Opioid Analgesia in a Mouse Model of Neuropathic Pain

Treatment of neuropathic pain remains a challenge for modern medicine due to the insufficiently understood molecular mechanisms of its development and maintenance. One of the most important cascades that modulate the nociceptive response is the family of mitogen-activated protein (MAP) kinases and phosphatidylinositol-3-kinase (PI3K), as well as nuclear factor erythroid 2-related factor 2 (Nrf2). The aim of this study was to determine the effect of nonselective modulators of MAP kinases-fisetin (ERK1/2 and NFκB inhibitor, PI3K activator), peimine (MAPK inhibitor), astaxanthin (MAPK inhibitor, Nrf2 activator) and artemisinin (MAPK inhibitor, NFκB activator), as well as bardoxolone methyl (selective activator of Nrf2) and 740 Y-P (selective activator of PI3K)-in mice with peripheral neuropathy and to compare their antinociceptive potency and examine their effect on analgesia induced by opioids. The study was performed using albino Swiss male mice that were exposed to chronic constriction injury of the sciatic nerve (CCI model). Tactile and thermal hypersensitivity was measured using von Frey and cold plate tests, respectively. Single doses of substances were administered intrathecally on day 7 after CCI. Among the tested substances, fisetin, peimine, and astaxanthin effectively diminished tactile and thermal hypersensitivity in mice after CCI, while artemisinin did not exhibit analgesic potency in this model of neuropathic pain. Additionally, both of the activators tested, bardoxolone methyl and 740 Y-P, also showed analgesic effects after intrathecal administration in mice exposed to CCI. In the case of astaxanthin and bardoxolone methyl, an increase in analgesia after combined administration with morphine, buprenorphine, and/or oxycodone was observed. Fisetin and peimine induced a similar effect on tactile hypersensitivity, where analgesia was enhanced after administration of morphine or oxycodone. In the case of 740 Y-P, the effects of combined administration with each opioid were observed only in the case of thermal hypersensitivity. The results of our research clearly indicate that substances that inhibit all three MAPKs provide pain relief and improve opioid effectiveness, especially if they additionally block NF-κB, such as peimine, inhibit NF-κB and activate PI3K, such as fisetin, or activate Nrf2, such as astaxanthin. In light of our research, Nrf2 activation appears to be particularly beneficial. The abovementioned substances bring promising results, and further research on them will broaden our knowledge regarding the mechanisms of neuropathy and perhaps contribute to the development of more effective therapy in the future.

Insular cortex stimulation alleviates neuropathic pain via ERK phosphorylation in neurons

AIMS

The clinical use of brain stimulation is attractive for patients who have side effects or tolerance. However, studies on insular cortex (IC) stimulation are lacking in neuropathic pain. The present study aimed to investigate the effects of IC stimulation (ICS) on neuropathic pain and to determine how ICS modulates pain.

METHODS

Changes in pain behaviors were observed following ICS with various parameters in neuropathic rats. Western blotting was performed to assess molecular changes in the expression levels of phosphorylated extracellular signal-regulated kinase (pERK), neurons, astrocytes, and microglia between experimental groups. Immunohistochemistry was performed to investigate the colocalization of pERK with different cell types.

RESULTS

The most effective pain-relieving effect was induced at 50 Hz-120 μA in single trial of ICS and it maintained 4 days longer after the termination of repetitive ICS. The expression levels of pERK, astrocytes, and microglia were increased in neuropathic rats. However, after ICS, the expression levels of pERK were decreased, and colocalization of pERK and neurons was reduced in layers 2-3 of the IC.

CONCLUSION

These results indicated that ICS attenuated neuropathic pain by the regulation of pERK in neurons located in layers 2-3 of the IC. This preclinical study may enhance the potential use of ICS and identify the therapeutic mechanisms of ICS in neuropathic pain.

The neuroprotective effect of pterostilbene on oxaliplatin-induced peripheral neuropathy via its anti-inflammatory, anti-oxidative and anti-apoptotic effects: Comparative study with celecoxib

BACKGROUND

Oxaliplatin is one of the first-line drugs in solid tumors treatment. However, neuropathy is a devastating side effect leading to poor compliance and treatment cessation.

AIM

The current study explored pterostilbene plausible neuroprotective effects aiming to ascertain the potential mechanisms involved in relieving oxaliplatin-induced peripheral neuropathy (OIPN) and investigating whether pterostilbene and celecoxib combination could show better relief.

MAIN METHODS

Rats were divided into six groups; control, pterostilbene (40 mg/kg/day, p.o. for 5 weeks), oxaliplatin (4 mg/kg, i.p. twice per week for 4.5 weeks), celecoxib (30 mg/kg/day, p.o. for 5 weeks) and combination of pterostilbene and celecoxib. Behavioral tests and histopathological analysis of sciatic nerves were done. MAPKs, cytokines, COX-2, and PGE₂ gene and protein expressions were estimated using qRT-PCR, western, and ELISA techniques. Malondialdehyde (MDA) and total antioxidant capacity (TAC) were assessed by colorimetric assay while apoptotic markers by immunohistochemical analysis and qRT-PCR.

KEY FINDINGS

The study revealed that pterostilbene and celecoxib averted oxaliplatin-induced behavioral and motor impairments along with restoration of histopathological changes. Moreover, pterostilbene and celecoxib have significantly attenuated sciatic nerve: p38 MAPK, JNK, ERK1/2, NF-κB, COX-2, PGE₂, TNF-α, and interleukins levels. Pterostilbene and celecoxib have reduced caspase-3, Bax, and MDA while increasing Bcl-2 level and TAC.

SIGNIFICANCE

Altogether, Pterostilbene mitigates OIPN by interrupting the vicious cycle of inflammation, oxidation, and apoptosis. Furthermore, pterostilbene and celecoxib show comparable attenuation on MAPKs cascades, inflammatory cytokines, oxidative and apoptotic markers. Likewise, co-administration of pterostilbene and celecoxib shows further relief of neuropathic pain.

Recent applications of computational methods to allosteric drug discovery

Interest in exploiting allosteric sites for the development of new therapeutics has grown considerably over the last two decades. The chief driving force behind the interest in allostery for drug discovery stems from the fact that in comparison to orthosteric sites, allosteric sites are less conserved across a protein family, thereby offering greater opportunity for selectivity and ultimately tolerability. While there is significant overlap between structure-based drug design for orthosteric and allosteric sites, allosteric sites offer additional challenges mostly involving the need to better understand protein flexibility and its relationship to protein function. Here we examine the extent to which structure-based drug design is impacting allosteric drug design by highlighting several targets across a variety of target classes.

Segmental Upregulation of ASIC1 Channels in the Formalin Acute Pain Mouse Model

BACKGROUND

Hindpaw injection of formalin in rodents is used to assess acute persistent pain. The response to formalin is biphasic. The initial response (first minutes) is thought to be linked to inflammatory, peripheral mechanisms, while the latter (around 30 min after the injection), is linked to central mechanisms. This model is useful to analyze the effect of drugs at one or both phases, and the involvement of ion channels in the response. Acid-sensing ion channels (ASICs) regulate synaptic activities and play important roles in pain conditions. Recently, psalmotoxin-1 (Pctx-1), a toxin that inhibits ASIC1a-constituted channels, and antisense ASIC1a-RNA, intrathecal administered in mice were shown to affect both phases of the test.

METHODS

The mouse formalin test was performed on C57/BL6 7- to 9-week-old mice. Behavioral tests were conducted and tissue was extracted to detect proteins (ASIC1 and pERK) and ASIC1-mRNA and mir485-5p levels.

RESULTS

The injection of formalin was accompanied by an increase in ASIC1 levels. This was detected at the contralateral anterior cingulate cortex (ACC) compared to the ipsilateral side, and both sides of the ACC of vehicle-injected animals. At the spinal cord and dorsal root ganglia, ASIC1 levels followed a gradient stronger at lumbar (L) 3 and decreased towards L5. Gender differences were detected at the ACC; with female mice showing higher ASIC1a levels at the ACC. No significant changes in ASIC1-mRNA levels were detected. Evidence suggests ASIC1 upregulation depends on regulatory microRNAs.

CONCLUSION

This work highlights the important role of ASIC1 in pain and the potential role of pharmacological therapies aimed at this channel.

Analgesic Effectiveness and Dorsal Root Ganglia Protein Modulation of a Peripheral Adenosine Monophosphate Kinase Alpha Activator (O304) Following Lumbar Disk Puncture in the Mouse

BACKGROUND

Disk herniation is a primary cause of radicular back pain. The purpose of this study was to evaluate the antiallodynic effective dose in 50% of the sample (ED 50 ) and dorsal root ganglion (DRG) protein modulation of a peripheral direct adenosine monophosphate kinase alpha (AMPKα) activator (O304) in a murine model of lumbar disk puncture.

METHODS

Male (n = 28) and female (n = 28) mice (C57BL6/J) were assessed for hind paw withdrawal threshold (PWT) and burrowing. Abdominal surgery was performed on all mice, and 48 received a lumbar disk puncture (27-G needle), with 8 serving as nondisk puncture controls. Assessments were repeated at day 7, and mice were then randomized into 5 groups of equal numbers of males and females: O304 at 100 mg/kg (n = 10), 150 mg/kg (n = 10), 200 mg/kg (n = 10), and 250 mg/kg (n = 10) or drug vehicle (n = 8). Starting on day 7, mice received daily gavages of O304 or vehicle for 7 days. On days 14 and 21 PWT and on day 14 burrowing were assessed. The area under the PWT by time curve (AUC) from day 7 to 21 was determined by trapezoidal integration. DRG protein modulation was evaluated in male (n = 10) and female (n = 10) mice (C57BL6/J). Following disk puncture, mice were randomized to receive O304 200 mg/kg or vehicle for 7 days starting on day 7. On day 14, mice were euthanized; the DRG harvested and immunoblot performed for mammalian target of rapamycin (mTOR), transient receptor potential ankyrin 1 (TRPA1), phosphorylated adenosine monophosphate kinase (p-AMPK), phosphorylated extracellular signal-regulated kinase (p-ERK), phosphorylated eukaryotic translation initiation factor 2 subunit 1 (p-EIF2S1), phosphorylated eukaryotic translation initiation factor 4e (p-EIF4E), and glyceraldehyde 3-phosphate dehydrogenase (GADPH).

RESULTS

Disk puncture decreased PWT greater in female mice compared with male mice and decreased burrowing at 7 days. PWTs were increased with increasing doses of O304 from 150 to 250 mg/g on day 14 and sustained through day 21. The ED 50 (95% confidence interval [CI]) for reducing mechanical allodynia was 140 (118-164) mg/kg. Burrowing was not increased at day 14 compared to day 7 by O304 administration. Compared to vehicle-treated animals, O304 increased (95% CI) the p-AMPK/GADPH ratio, difference 0.27 (0.08-0.45; P = . 004) and decreased (95% CI) the ratios of p-TRPA1, p-ERK1/2, pEIF4E, and p-EIF2S1 to GADPH by -0.49 (-0.61 to -0.37; P < . 001), -0.53 (-0.76 to -0.29; P < . 001), -0.27 (-0.42 to 0.11; P = . 001), and -0.21 (-0.32 to -0.08; P = . 003) in the DRG, respectively.

CONCLUSIONS

The direct peripheral AMPK activator O304 reduced allodynia in a dose-dependent manner, and immunoblot studies of the DRG showed that O304 increased p-AMPK and decreased TRPA1, p-ERK1/2, as well as translation factors involved in neuroplasticity. Our findings confirm the role of peripheral AMPKα activation in modulating nociceptive pain.

Chronic constriction injury-induced changes in circular RNA expression profiling of the dorsal root ganglion in a rat model of neuropathic pain

Background

The pathogenesis of neuropathic pain (NP) has not been fully elucidated. Gene changes in dorsal root ganglia (DRG) may contribute to the development of NP. Circular RNAs (circRNAs) are a class of endogenous noncoding RNAs that form covalently closed loop structures and are crucial for genetic and epigenetic regulation. However, little is known about circRNA changes in DRG neurons after peripheral nerve injury.

Methods

A sciatic nerve chronic constriction injury (CCI) model was established to induce neuropathic pain. We performed genome-wide circRNA analysis of four paired dorsal root ganglion (DRG) samples (L4–L5) from CCI and negative control (NC) rats using next-generation sequencing technology. The differentially expressed circRNAs (DEcircRNAs) were identified by differential expression analysis, and the expression profile of circRNAs was validated by quantitative PCR. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses were performed to predict the function of DEcircRNAs.

Results

A total of 374 DEcircRNAs were identified between CCI and NC rats using circRNA high-throughput sequencing. Among them, 290 were upregulated and 84 were downregulated in the CCI group. The expression levels of nine DEcircRNAs were validated by qPCR. Functional annotation analysis showed that the DEcircRNAs were mainly enriched in pathways and functions, including ‘dopaminergic synapse,’ ‘renin secretion,’ ‘mitogen-activated protein kinase signaling pathway,’ and ‘neurogenesis.’ Competing endogenous RNA analysis showed that the top 50 circRNAs exhibited interactions with four pain-related microRNAs (miRNAs). Circ:chr2:33950934–33955969 was the largest node in the circRNA–miRNA interaction network.

Conclusions

Peripheral nerve injury-induced neuropathic pain led to changes in the comprehensive expression profile of circRNAs in the DRG of rats. DEcircRNAs may advance our understanding of the molecular mechanisms underlying neuropathic pain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-022-00745-5.

Unleashing Intrinsic Growth Pathways in Regenerating Peripheral Neurons

Common mechanisms of peripheral axon regeneration are recruited following diverse forms of damage to peripheral nerve axons. Whether the injury is traumatic or disease related neuropathy, reconnection of axons to their targets is required to restore function. Supporting peripheral axon regrowth, while not yet available in clinics, might be accomplished from several directions focusing on one or more of the complex stages of regrowth. Direct axon support, with follow on participation of supporting Schwann cells is one approach, emphasized in this review. However alternative approaches might include direct support of Schwann cells that instruct axons to regrow, manipulation of the inflammatory milieu to prevent ongoing bystander axon damage, or use of inflammatory cytokines as growth factors. Axons may be supported by a growing list of growth factors, extending well beyond the classical neurotrophin family. The understanding of growth factor roles continues to expand but their impact experimentally and in humans has faced serious limitations. The downstream signaling pathways that impact neuron growth have been exploited less frequently in regeneration models and rarely in human work, despite their promise and potency. Here we review the major regenerative signaling cascades that are known to influence adult peripheral axon regeneration. Within these pathways there are major checkpoints or roadblocks that normally check unwanted growth, but are an impediment to robust growth after injury. Several molecular roadblocks, overlapping with tumour suppressor systems in oncology, operate at the level of the perikarya. They have impacts on overall neuron plasticity and growth. A second approach targets proteins that largely operate at growth cones. Addressing both sites might offer synergistic benefits to regrowing neurons. This review emphasizes intrinsic aspects of adult peripheral axon regeneration, emphasizing several molecular barriers to regrowth that have been studied in our laboratory.

Antimicrobial Peptides and Biomarkers Induced by Ultraviolet Irradiation Have the Potential to Reduce Endodontic Inflammation and Facilitate Tissue Healing

Background: Ultraviolet (UV) irradiation can modulate host immune responses and this approach is a novel application for treating endodontic infections and inflammation in root canals. Methods: A dataset of UV-induced molecules was compiled from a literature search. A subset of this dataset was used to calculate expression log2 ratios of endodontic tissue molecules from HEPM cells and gingival fibroblasts after 255, 405, and 255/405 nm UV irradiation. Both datasets were analyzed using ingenuity pathway analysis (IPA, Qiagen, Germantown, MD, USA). Statistical significance was calculated using Fisher’s exact test and z-scores were calculated for IPA comparison analysis. Results: The dataset of 32 UV-induced molecules contained 9 antimicrobial peptides, 10 cytokines, 6 growth factors, 3 enzymes, 2 transmembrane receptors, and 2 transcription regulators. These molecules were in the IPA canonical pathway annotations for the wound healing signaling pathway (9/32, p = 3.22 × 10⁻¹¹) and communication between immune cells (6/32, p = 8.74 × 10⁻¹¹). In the IPA disease and function annotations, the 32 molecules were associated with an antimicrobial response, cell-to-cell signaling and interaction, cellular movement, hematological system development and function, immune cell trafficking, and inflammatory response. In IPA comparison analysis of the 13 molecules, the predicted activation or inhibition of pathways depended upon the cell type exposed, the wavelength of the UV irradiation used, and the time after exposure. Conclusions: UV irradiation activates and inhibits cellular pathways and immune functions. These results suggested that UV irradiation can activate innate and adaptive immune responses, which may supplement endodontic procedures to reduce infection, inflammation, and pain and assist tissues to heal.

Resolvin D1 alleviates mechanical allodynia via ALX/FPR2 receptor targeted NLRP3/ERK signaling in a neuropathic pain model

The current study aimed to investigate the role and underlying mechanism of Resolvin D1 (RvD1) alleviating spinal nerve ligation (SNL)-induced neuropathic pain (NP) and its interplay with regulatory cascades of NLRP3 inflammasome. Sprague-Dawley male rat model of SNL-stimulated NP was established, which were pre-treated with different doses of RvD1, WRW4 (ALX/FPR2 inhibitor) or U0126 (ERK inhibitor) for three successive days following the operation. Pain behavior was assessed by measuring changes in the mechanical sensitivity of the hind paws during an observation period of 7 consecutive days. The spinal cord (SC) and dorsal root ganglions (DRGs) tissues were collected on postoperative day 7. Immunohistochemistry (IHC) and western blot were performed to determine the expression levels of NLRP3 inflammasome complex, ALX/FPR2 receptor and extracellular signal-related kinase (ERK). The pro-inflammatory mediators (IL-1β and IL-18) were measured by enzyme-linked immunosorbent assay (ELISA). The results showed that RvD1 could alleviate mechanical allodynia significantly in the SNL-induced NP rat model. Also, RvD1 inhibited the expression of p-ERK, the NLRP3 inflammasomes complex and its corresponding downstream pro-inflammatory mediators which were significantly enhanced in the SC and DRGs of the rat of SNL model. While these changes were partially reversed by pre-administration of WRW4 and further strengthened by co-treated with U0126. Our results suggest that RvD1 dependent on ALX/FPR2 may have an analgesic and anti-inflammatory influence on SNL-induced NP driven by inhibiting NLRP3 inflammasome via ERK signaling pathway. These data also provide strong support for the recent modulation of neuro-inflammatory priming and highlight the potential for specialized pro-resolving mediators (SPMs) as novel therapeutic avenues for NP.

The Role of Transient Receptor Potential A1 and G Protein-Coupled Receptor 39 in Zinc-Mediated Acute and Chronic Itch in Mice

Itching is a common symptom of many skin or systemic diseases and has a negative impact on the quality of life. Zinc, one of the most important trace elements in an organism, plays an important role in the regulation of pain. Whether and how zinc regulates itching is largely unclear. Herein, we explored the role of Zn²⁺ in the regulation of acute and chronic itch in mice. It is found that intradermal injection (i.d.) of Zn²⁺ dose-dependently induced acute itch and transient receptor potential A1 (TRPA1) participated in Zn²⁺-induced acute itch in mice. Moreover, the pharmacological analysis showed the involvement of histamine, mast cells, opioid receptors, and capsaicin-sensitive C-fibers in Zn²⁺-induced acute itch in mice. Systemic administration of Zn²⁺ chelators, such as N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), pyrithione, and clioquinol were able to attenuate both acute itch and dry skin-induced chronic itch in mice. Quantitative polymerase chain reaction (Q-PCR) analysis showed that the messenger RNA (mRNA) expression levels of zinc transporters (ZIPs and ZnTs) significantly changed in the dorsal root ganglia (DRG) under dry skin-induced chronic itch condition in mice. Activation of extracellular signal-regulated kinase (ERK) pathway was induced in the DRG and skin by the administration of zinc or under dry skin condition, which was inhibited by systemic administration of Zn²⁺ chelators. Finally, we found that the expression of GPR39 (a zinc-sensing GPCR) was significantly upregulated in the dry skin mice model and involved in the pathogenesis of chronic itch. Together, these results indicated that the TRPA1/GPR39/ERK axis mediated the zinc-induced itch and, thus, targeting zinc signaling may be a promising strategy for anti-itch therapy.

Modulation of the Extracellular Signal-Regulated Protein Kinase and Tissue Inhibitors of Matrix Metalloproteases-1 Gene in Chronic Neuropathic Pain

Objectives:

The aim of this study is to study the modulation of extracellular signal-regulated protein kinase (ERK) and tissue inhibitors of matrix metalloproteases 1 (TIMP 1) gene in patients with neuropathic pain (NP).

Materials and Methods:

In the present, cross-sectional, observational study, 2 ml of venous baseline sample was withdrawn from all the patients with neuropathic (NP) or non NP (NNP) soon after their diagnosis or on their first visit to the pain clinic. A real-time quantitative polymerase chain reaction experiment was conducted to measure the mRNA expression of TIMP1 and ERK genes in blood samples. The Delta Ct, Delta Ct, and fold change analysis of both the genes were conducted between patients with NP and NNP.

Results:

A total of 285 patients with chronic pain were assessed, out of which, 153 patients had NP and 132 had NNP. The average duration of chronic pain was 11 months for 285 patients. The mRNA expression of TIMP1 gene is significantly down regulated (2.65-fold) (P (-f. 01), and the mRNA expression level of ERK is significantly up regulated (2.03-fold) (P (-f. 01) in NP patients when compared with NNP.

Conclusion:

The mRNA expression of TIMP1 gene is significantly down regulated, and ERK is significantly up regulated in patients with NP. Further, multicentric trials with larger sample size are recommended to confirm this finding.

ZEB1 Induces Ddr1 Promoter Hypermethylation and Contributes to the Chronic Pain in Spinal Cord in Rats Following Oxaliplatin Treatment

Application of chemotherapeutic oxaliplatin represses gene transcription through induction of DNA methylation, which may contribute to oxaliplatin-induced chronic pain. Here, Ddr1, which showed an increased methylation in the promoter, was screened from the SRA methylation database (PRJNA587622) after oxaliplatin treatment. qPCR and MeDIP assays verified that oxaliplatin treatment increased the methylation in Ddr1 promoter region and decreased the expression of DDR1 in the neurons of spinal dorsal horn. In addition, overexpression of DDR1 by intraspinal injection of AAV-hSyn-Ddr1 significantly alleviated the mechanical allodynia induced by oxaliplatin. Furthermore, we found that oxaliplatin treatment increased the expression of DNMT3b and ZEB1 in dorsal horn neurons, and promoted the interaction between DNMT3b and ZEB1. Intrathecal injection of ZEB1 siRNA inhibited the enhanced recruitment of DNMT3b and the hypermethylation in Ddr1 promoter induced by oxaliplatin. Finally, ZEB1 siRNA rescued the DDR1 downregulation and mechanical allodynia induced by oxaliplatin. In conclusion, these results suggested that the ZEB1 recruited DNMT3b to the Ddr1 promoter, which induced the DDR1 downregulation and contributed to the oxaliplatin-induced chronic pain.

CNTs-CaP/chitosan-coated AZ91D magnesium alloy extract promoted rat dorsal root ganglia neuron growth via activating ERK signalling pathway

Increasing attention has been paid on the application of biodegradable materials such as magnesium and its alloys in neuron repair. AZ91D magnesium alloy coated with carbon nanotubes (CNTs) and/or calcium phosphate (CaP)/chitosan (CS) was fabricated in this study. To evaluate the bioactivity of these AZ91D-based composites, the extracts were prepared by immersing samples in modified simulated body fluid (m-SBF) for 0, 2, 8, 16, 24, 34, 44, 60, or 90 days. Immunofluorescence staining for neuronal class III β-tubulin (TUJ1) revealed that both CNTs-CaP/CS-AZ91D and CaP/CS-AZ91D extracts promoted axon outgrowth of dorsal root ganglia (DRG) neurons, accompanied with increased expression of phosphorylated focal adhesion kinase (p-FAK) and growth associated protein-43 (GAP-43). Besides, the extracts increased the expression and the release of neurotrophic factors including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). ERK signalling was activated in DRG neurons after treating with either CNTs-CaP/CS-AZ91D or CaP/CS-AZ91D extracts, and its inhibition with U0126 counteracted the beneficial effects of these extracts on DRG neuron. Overall, the extracts from these AZ91D-based composites might promote DRG neuron growth via activating ERK signalling pathway. Notably, CNTs-CaP/CS-AZ91D extracts showed a better promoting effect on neuron growth than CaP/CS-AZ91D. Assessment of ion elements showed that the addition of CNTs coating enhanced magnesium corrosion resistance and reduced the deposition of calcium and phosphorus on the surface of CaP/CS-AZ91D alloy. These findings demonstrate that CNTs-CaP/CS-AZ91D likely provide a more suitable environment for neuron growth, which suggests a potential implantable biomaterial for the treatment of nerve injury. SIGNIFICANCE: AZ91D magnesium alloy coated with carbon nanotubes (CNTs) and/or calcium phosphate (CaP)/chitosan (CS) was fabricated and their immersion extracts were prepared using modified simulated body fluid in this study. Both extracts from CNTs-CaP/CS and CaP/CS-coated AZ91D magnesium alloy promotes rat dorsal root ganglia (DRG) neuron growth via activating ERK signalling pathway. Notably, the addition of CNTs improves the performance of CaP/CS-AZ91D. For the first time, our research demonstrates that CNTs-CaP/CS-AZ91D likely provide a suitable environment for neuron growth, suggesting these AZ91D-based composites as potential implantable biomaterials for the treatment of nerve injury.

Novel Non-Opioid Based Therapeutics for Chronic Neuropathic Pain

Chronic neuropathic pain is currently a major health issue in U.S. complicated by the lack of non-opioid analgesic alternatives. Our investigations led to the discovery of major signaling pathways involved in the transition of acute to chronic neuropathic pain and the identification of several targets for therapeutic intervention. Our translational approach has facilitated the advancement of novel medicines for chronic neuropathic pain that are in advanced clinical development and clinical trials.

The role of cyclin-dependent kinase 5 in neuropathic pain

The chronification of pain can be attributed to changes in membrane receptors and channels underlying neuronal plasticity and signal transduction largely within nociceptive neurons that initiate and maintain pathological pain states. These proteins are subject to dynamic modification by posttranslational modifications, creating a code that controls protein function in time and space. Phosphorylation is an important posttranslational modification that affects ∼30% of proteins in vivo. Increased phosphorylation of various nociceptive ion channels and of their modulators underlies sensitization of different pain states. Cyclin-dependent kinases are proline-directed serine/threonine kinases that impact various biological and cellular systems. Cyclin-dependent kinase 5 (Cdk5), one member of this kinase family, and its activators p35 and p39 are expressed in spinal nerves, dorsal root ganglia, and the dorsal horn of the spinal cord. In neuropathic pain conditions, expression and/or activity of Cdk5 is increased, implicating Cdk5 in nociception. Experimental evidence suggests that Cdk5 is regulated through its own phosphorylation, through increasing p35's interaction with Cdk5, and through cleavage of p35 into p25. This narrative review discusses the molecular mechanisms of Cdk5-mediated regulation of target proteins involved in neuropathic pain. We focus on Cdk5 substrates that have been linked to nociceptive pathways, including channels (eg, transient receptor potential cation channel and voltage-gated calcium channel), proteins involved in neurotransmitter release (eg, synaptophysin and collapsin response mediator protein 2), and receptors (eg, glutamate, purinergic, and opioid). By altering the phosphoregulatory "set point" of proteins involved in pain signaling, Cdk5 thus appears to be an attractive target for treating neuropathic pain conditions.

The changes of nociception and the signal molecules expression in the dorsal root ganglia and the spinal cord after cold water swimming stress in mice

Several studies have previously reported that exposure to stress provokes behavioral changes, including antinociception, in rodents. In the present study, we studied the effect of acute cold-water (4°C) swimming stress (CWSS) on nociception and the possible changes in several signal molecules in male ICR mice. Here, we show that 3 min of CWSS was sufficient to produce antinociception in tail-flick, hot-plate, von-Frey, writhing, and formalin-induced pain models. Significantly, CWSS strongly reduced nociceptive behavior in the first phase, but not in the second phase, of the formalin-induced pain model. We further examined some signal molecules' expressions in the dorsal root ganglia (DRG) and spinal cord to delineate the possible molecular mechanism involved in the antinociceptive effect under CWSS. CWSS reduced p-ERK, p-AMPKα1, p-AMPKα2, p-Tyk2, and p-STAT3 expression both in the spinal cord and DRG. However, the phosphorylation of mTOR was activated after CWSS in the spinal cord and DRG. Moreover, p-JNK and p-CREB activation were significantly increased by CWSS in the spinal cord, whereas CWSS alleviated JNK and CREB phosphorylation levels in DRG. Our results suggest that the antinociception induced by CWSS may be mediated by several molecules, such as ERK, JNK, CREB, AMPKα1, AMPKα2, mTOR, Tyk2, and STAT3 located in the spinal cord and DRG.

LIFU Alleviates Neuropathic Pain by Improving the KCC2 Expression and Inhibiting the CaMKIV-KCC2 Pathway in the L4-L5 Section of the Spinal Cord

Effective treatment remains lacking for neuropathic pain (NP), a type of intractable pain. Low-intensity focused ultrasound (LIFU), a noninvasive, cutting-edge neuromodulation technique, can effectively enhance inhibition of the central nervous system (CNS) and reduce neuronal excitability. We investigated the effect of LIFU on NP and on the expression of potassium chloride cotransporter 2 (KCC2) in the spinal cords of rats with peripheral nerve injury (PNI) in the lumbar 4-lumbar 5 (L4-L5) section. In this study, rats received PNI surgery on their right lower legs followed by LIFU stimulation of the L4-L5 section of the spinal cord for 4 weeks, starting 3 days after surgery. We used the 50% paw withdraw threshold (PWT50) to evaluate mechanical allodynia. Western blotting (WB) and immunofluorescence (IF) were used to calculate the expression of phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), calcium/calmodulin-dependent protein kinase type IV (CaMKIV), phosphorylated cyclic adenosine monophosphate response element-binding protein (p-CREB), and KCC2 in the L4-L5 portion of the spinal cord after the last behavioral tests. We found that PWT50 decreased (P < 0.05) 3 days post-PNI surgery in the LIFU- and LIFU+ groups and increased (P < 0.05) after 4 weeks of LIFU stimulation. The expression of p-CREB and CaMKIV decreased (P < 0.05) and that of KCC2 increased (P < 0.05) after 4 weeks of LIFU stimulation, but that of p-ERK1/2 (P > 0.05) was unaffected. Our study showed that LIFU could effectively alleviate NP behavior in rats with PNI by increasing the expression of KCC2 on spinal dorsal corner neurons. A possible explanation is that LIFU could inhibit the activation of the CaMKIV-KCC2 pathway.

Inhibition of lncRNA DILC attenuates neuropathic pain via the SOCS3/JAK2/STAT3 pathway

Long noncoding RNAs (lncRNAs) have been involved in the development of multiple pathological processes including neuropathic pain. The aim of the present study is to investigate the role of lncRNA down-regulated in liver cancer stem cells (DILC) in the progression of neuropathic pain and its underlying mechanism. Neuropathic pain rat model was established with the bilateral chronic constriction injury (bCCI) method. The results from quantitative PCR analysis in the spinal cord showed that DILC was significantly up-regulated in rats with bCCI compared with the sham group. DILC down-regulation mediated by intrathecal administration of DILC siRNA significantly increased the mechanical shrinkage threshold (MWT) and paw withdrawal threshold latency (PWTL), decreased the positive frequency for nerve sensitivity to cold and suppressed the expression of inflammatory genes in bCCI rats. Down-regulation of DILC induced suppressor of cytokine signaling (SOCS3) expression and inhibited the phosphorylation of signal transducer and activator of transcription 3 (p-STAT3) in spinal cord tissues. Western blotting showed that down-regulation of DILC by DILC siRNA transfection induced SOCS3 expression and inhibited the expression of p-Janus kinase 2 (p-JAK2) and p-STAT3 and their downstream genes in primary microglia. Furthermore, down-regulation of DILC increased the viability of primary microglia, suppressed apoptosis, and inhibited the production of interleukin (IL)-6 and IL-1β in microglia. In contrast, overexpression of DILC showed the opposite functions to those of DILC knockdown. In conclusion, silence of lncRNA DILC attenuates neuropathic pain via SOCS3-induced suppression of the JAK2/STAT3 pathway.

N-Acetylcysteine causes analgesia in a mouse model of painful diabetic neuropathy

N-Acetylcysteine, one of the most prescribed antioxidant drugs, enhances pain threshold in rodents and humans by activating mGlu2 metabotropic glutamate receptors. Here, we assessed the analgesic activity of N-acetylcysteine in the streptozotocin model of painful diabetic neuropathy and examined the effect of N-acetylcysteine on proteins that are involved in mechanisms of nociceptive sensitization. Mice with blood glucose levels ≥250 mg/dl in response to a single intraperitoneal (i.p.) injection of streptozotocin (200 mg/kg) were used for the assessment of mechanical pain thresholds. Systemic treatment with N-acetylcysteine (100 mg/kg, i.p., either single injection or daily injections for seven days) caused analgesia in diabetic mice. N-acetylcysteine-induced analgesia was abrogated by the Sxc− inhibitors, sulfasalazine (8 mg/kg, i.p.), erastin (30 mg/kg, i.p.), and sorafenib (10 mg/kg, i.p.), or by the mGlu2/3 receptor antagonist, LY341495 (1 mg/kg, i.p.). Repeated administrations of N-acetylcysteine in diabetic mice reduced ERK1/2 phosphorylation in the dorsal region of the lumbar spinal cord. The analgesic activity of N-acetylcysteine was occluded by the MEK inhibitor, PD0325901 (25 mg/kg, i.p.), the TRPV1 channel blocker, capsazepine (40 mg/kg, i.p.), or by a cocktail of NMDA and mGlu5 metabotropic glutamate receptor antagonists (memantine, 25 mg/kg, plus MTEP, 5 mg/kg, both i.p.). These findings offer the first demonstration that N-acetylcysteine relieves pain associated with diabetic neuropathy and holds promise for the use of N-acetylcysteine as an add-on drug in diabetic patients.

In Vivo Gene Delivery of STC2 Promotes Axon Regeneration in Sciatic Nerves

Neurons are vulnerable to injury, and failure to activate self-protective systems after injury leads to neuronal death. However, sensory neurons in dorsal root ganglions (DRGs) mostly survive and regenerate their axons. To understand the mechanisms of the neuronal injury response, we analyzed the injury-responsive transcriptome and found that Stc2 is immediately upregulated after axotomy. Stc2 is required for axon regeneration in vivo and in vitro, indicating that Stc2 is a neuronal factor regulating axonal injury response. The application of the secreted stanniocalcin 2 to injured DRG neurons promotes regeneration. Stc2 thus represents a potential secretory protein with a feedback function regulating regeneration. Finally, the in vivo gene delivery of STC2 increases regenerative growth after injury in peripheral nerves in mice. These results suggest that Stc2 is an injury-responsive gene required for axon regeneration and a potential target for developing therapeutic applications.

Analysis of pain markers and epidural fibrosis caused by repeated spinal surgery in Sprague-Dawley rats

Background

Epidural fibrosis is one of the aetiologies of pain following a spinal revision surgery. It is reported that the specific members of the mitogen – activated protein kinases (MAPK) family might mediate neuropathic pain. However, roles of epidural fibrosis caused by repeated spinal surgeries and pain-related proteins in causing the post spinal surgery syndrome remain unknown. Using a rat spinal surgery epidural fibrosis and adhesion model, in this study, we evaluated and investigated the relationship between pain markers and epidural fibrosis.

Methods

Sprague–Dawley rats that underwent the spinal surgery were divided into three groups: group A (single laminectomy), group B (two repeated surgeries) and group C (three repeated surgeries). Dural thickness was measured in each experimental group, and immunohistochemical analysis and western blotting of mitogen-activated protein kinases were performed (ERK, p38 and JNK) using the spine cord.

Results

Dural thickness was 6.363 ± 1.911 μm in group A, 13.238 ± 2.123 μm in group B and 19.4 ± 2.115 μm in group C, respectively. In the western blotting, phosphorylated ERK expression gradually increased with the number of repeated surgeries, and expression in groups B (1.77-fold) and C (2.42-fold) increased as compared to expression in group A. Phosphorylated p38 showed an increasing trend with the number of repeated surgeries, and groups B (1.17-fold) and C (1.33-fold) expression increased compared with group A. However, phosphorylated JNK expression did not gradually increase with the number of repeated surgeries, and groups B (1.62-fold) and C (1.43-fold) expression increased compared with group A. Excluding phosphorylated JNK, immunohistochemical analysis revealed that phosphorylated ERK and p38 expression gradually increased with the number of repeated surgeries in the spine dorsal horn, as evidenced by western blotting.

Conclusions

Repeated spinal surgeries may increase dural thickness and expression of phosphorylated ERK and p38 in the spinal dorsal horn, and it suggests that the neuropathic pain is likely induced by epidural fibrosis and that the pain increases with the number of repeated surgeries.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-020-03920-z.

Gabapentin and Duloxetine Prevent Oxaliplatin- and Paclitaxel-Induced Peripheral Neuropathy by Inhibiting Extracellular Signal-Regulated Kinase 1/2 (ERK1/2) Phosphorylation in Spinal Cords of Mice

Chemotherapy-induced peripheral neuropathy is a common factor in limiting therapy which can result in therapy cessation or dose reduction. Gabapentin, a calcium channel inhibitor, and duloxetine, a serotonin noradrenaline reuptake inhibitor, are used to treat a variety of pain conditions such as chronic low back pain, postherpetic neuralgia, and diabetic neuropathy. It has been reported that administration of gabapentin suppressed oxaliplatin- and paclitaxel-induced mechanical hyperalgesia in rats. Moreover, duloxetine has been shown to suppress oxaliplatin-induced cold allodynia in rats. However, the mechanisms by which these drugs prevent oxaliplatin- and paclitaxel-induced neuropathy remain unknown. Behavioral assays were performed using cold plate and the von Frey test. The expression levels of proteins were examined using western blot analysis. In this study, we investigated the mechanisms by which gabapentin and duloxetine prevent oxaliplatin- and paclitaxel-induced neuropathy in mice. We found that gabapentin and duloxetine prevented the development of oxaliplatin- and paclitaxel-induced cold and mechanical allodynia. In addition, our results revealed that gabapentin and duloxetine suppressed extracellular signal-regulated protein kinase 1/2 (ERK1/2) phosphorylation in the spinal cord of mice. Moreover, PD0325901 prevented the development of oxaliplatin- and paclitaxel-induced neuropathic-like pain behavior by inhibiting ERK1/2 activation in the spinal cord of mice. In summary, our findings suggest that gabapentin, duloxetine, and PD0325901 prevent the development of oxaliplatin- and paclitaxel-induced neuropathic-like pain behavior by inhibiting ERK1/2 phosphorylation in mice. Therefore, inhibiting ERK1/2 phosphorylation could be an effective preventive strategy against oxaliplatin- and paclitaxel-induced neuropathy.

Fcγ Receptor I-Coupled Signaling in Peripheral Nociceptors Mediates Joint Pain in a Rat Model of Rheumatoid Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is often accompanied by joint pain and inflammation. Previous studies have demonstrated that functional Fcγ receptor I (FcγRI) is expressed in dorsal root ganglion (DRG) neurons and might contribute to pain in rodent models of antigen-induced arthritis (AIA). This study was undertaken to elucidate the roles of nociceptive neuronal FcγRI-coupled signaling in the development of joint pain in AIA.

METHODS

RNA sequencing was used to investigate the transcriptome profile changes in the DRG in a rat model of AIA. A primary sensory neuron-specific Fcgr1a conditional-knockout (CKO) rat was established by crossing rats carrying a loxP-flanked Fcgr1a with a Pirt-specific Cre line. Behavioral, morphologic, and molecular studies were conducted to evaluate the differences between wild-type (WT) and CKO rats after AIA.

RESULTS

We first showed that AIA induced a transcriptome profile change in the DRG, involving a number of key proteins downstream of the FcγRI-related signaling pathway. Compared to the WT rats, both the IgG immune complex-induced acute pain and AIA-induced pain were alleviated in CKO rats. Moreover, the AIA-induced activation of FcγRI-related signaling in DRGs was significantly reduced in CKO rats. In addition, CKO rats showed attenuated joint swelling after AIA.

CONCLUSION

These results indicate that activation of FcγRI-coupled signaling in DRG neurons plays an important role in the development of joint pain in AIA. Our findings may provide novel insights into the interactions between the peripheral nervous system and the immune system in pathologic conditions and might suggest potential biotargets for the treatment of pain in RA.

How oncogenic mutations activate human MAP kinase 1 (MEK1): a molecular dynamics simulation study

Approximately 30% of all types of human cancers possess a constitutively activated the mitogen-activated protein kinase (MAPK) signaling pathway while MAP kinase 1 (MEK1) is a critical component of this pathway. It has been reported mutations could improve the activity of MEK1 to result in cell proliferation and transformation, which is a known oncogenic event in various cancer types. In this study, eight molecular dynamics simulations, molecular mechanics Poisson-Boltzmann surface area (MM-PBSA), combined with protein structure network were performed to explore the mechanism that mutations activate MEK1. Protein structure networks and hydrogen bonds analysis demonstrated that active mutations broke the interaction between activation segments (residues 216-222) and C-helix (residues 105-121) in MEK1, leading to it transform inactive form to active form. Moreover, hydrogen bond analysis and MM-PBSA calculation indicated that activating mutations decrease the binding affinity between MEK1 and inhibitor to reduce the inhibitory effect of inhibitors. In addition, some active mutations cause structural changes in the Pro-rich loop (residues 261-268) of MEK1. These changes may stabilize the interaction between the MEK1 mutants and the ligands by increasing the number of exposed hydrophobic residues in the active site of MEK1. Our results may provide useful theoretical evidences for the mechanism underlying the role of human MEK1 in human cancers.Communicated by Ramaswamy H. Sarma.

β-Arrestin 2 and ERK1/2 Are Important Mediators Engaged in Close Cooperation between TRPV1 and µ-Opioid Receptors in the Plasma Membrane

The interactions between TRPV1 and µ-opioid receptors (MOR) have recently attracted much attention because these two receptors play important roles in pain pathways and can apparently modulate each other’s functioning. However, the knowledge about signaling interactions and crosstalk between these two receptors is still limited. In this study, we investigated the mutual interactions between MOR and TRPV1 shortly after their activation in HEK293 cells expressing these two receptors. After activation of one receptor we observed significant changes in the other receptor’s lateral mobility and vice versa. However, the changes in receptor movement within the plasma membrane were not connected with activation of the other receptor. We also observed that plasma membrane β-arrestin 2 levels were altered after treatment with agonists of both these receptors. Knockdown of β-arrestin 2 blocked all changes in the lateral mobility of both receptors. Furthermore, we found that β-arrestin 2 can play an important role in modulating the effectiveness of ERK1/2 phosphorylation after activation of MOR in the presence of TRPV1. These data suggest that β-arrestin 2 and ERK1/2 are important mediators between these two receptors and their signaling pathways. Collectively, MOR and TRPV1 can mutually affect each other’s behavior and β-arrestin 2 apparently plays a key role in the bidirectional crosstalk between these two receptors in the plasma membrane.

Extracellular signal-regulated kinases (ERK) 1 and 2 as a key molecule in pain research

Pain can be divided into nociceptive, inflammatory, and neuropathic pain. It is important to understanding the molecular mechanism of pain signaling in the development of pain relief therapies. Twenty years ago, extracellular signal-regulated kinases (ERK) 1 and 2, which are members of the mitogen-activated protein kinase superfamily, were identified as molecules activated in neurons by the exposure of peripheral tissues to noxious stimuli. Further studies have revealed that peripheral nerve injury induces ERK activation in glial cells, sensory neurons, and second-order neurons, albeit at different time points. Moreover, inhibition of ERK suppresses pathological pain in animals with peripheral nerve injury. Therefore, ERK is currently recognized as an important molecule in pain signaling and a potential novel target for pain treatment. This review introduces recent advances in revealing the regulation of ERK in pain research.

Computational Study on the Effect of Inactivating/Activating Mutations on the Inhibition of MEK1 by Trametinib

Activation of the mitogen-activated protein kinase (MAPK) signaling pathway regulated by human MAP kinase 1 (MEK1) is associated with the carcinogenesis and progression of numerous cancers. In addition, two active mutations (P124S and E203K) have been reported to enhance the activity of MEK1, thereby eventually leading to the tumorigenesis of cancer. Trametinib is an MEK1 inhibitor for treating EML4-ALK-positive, EGFR-activated, and KRAS-mutant lung cancers. Therefore, in this study, molecular docking and molecular dynamic (MD) simulations were performed to explore the effects of inactive/active mutations (A52V/P124S and E203K) on the conformational changes of MEK1 and the changes in the interaction of MEK1 with trametinib. Moreover, steered molecular dynamic (SMD) simulations were further utilized to compare the dissociation processes of trametinib from the wild-type (WT) MEK1 and two active mutants (P124S and E203K). As a result, trametinib had stronger interactions with the non-active MEK1 (WT and A52V mutant) than the two active mutants (P124S and E203K). Moreover, two active mutants may make the allosteric channel of MEK1 wider and shorter than that of the non-active types (WT and A52V mutant). Hence, trametinib could dissociate from the active mutants (P124S and E203K) more easily compared with the WT MEK1. In summary, our theoretical results demonstrated that the active mutations may attenuate the inhibitory effects of MEK inhibitor (trametinib) on MEK1, which could be crucial clues for future anti-cancer treatment.

Systems biology-based approaches to summarize and identify novel genes and pathways associated with acute and chronic postsurgical pain

STUDY OBJECTIVE

To employ systems biology-based machine learning to identify biologic processes over-represented with genetic variants (gene enrichment) implicated in post-surgical pain.

DESIGN

Informed systems biology based integrative computational analyses.

SETTING

Pediatric research and teaching institution.

INTERVENTIONS

Pubmed search (01/01/2001-10/31/2017) was performed to identify "training" genes associated with postoperative pain in humans. Candidate genes were identified and prioritized using Toppgene suite, based on functional enrichment using several gene ontology annotations, and curated gene sets associated with mouse phenotype-knockout studies.

MEASUREMENTS

Computationally top-ranked candidate genes and literature-curated genes were included in pathway enrichment analyses. Hierarchical clustering was used to visualize select functional enrichment results between the two phenotypes.

MAIN RESULTS

Literature review identified 38 training genes associated with postoperative pain and 31 with CPSP. We identified 2610 prioritized novel candidate genes likely associated with acute and chronic postsurgical pain, the top 10th percentile jointly enriched (p 0.05; Benjamini-Hochberg correction) several pathways, topmost being cAMP response element-binding protein and ion channel pathways. Heat maps demonstrated enrichment of inflammatory/drug metabolism processes in acute postoperative pain and immune mechanisms in CPSP.

CONCLUSION

High interindividual variability in pain responses immediately after surgery and risk for CPSP suggests genetic susceptibility. Lack of large homogenous sample sizes have led to underpowered genetic association studies. Systems biology can be leveraged to integrate genetic-level data with biologic processes to generate prioritized candidate gene lists and understand novel biological pathways involved in acute postoperative pain and CPSP. Such data would be key to informing future polygenic studies with targeted genome wide profiling. This study demonstrates the utility of functional annotation - based prioritization and enrichment approaches and identifies novel genes and unique/shared biological processes involved in acute and chronic postoperative pain. Results provide framework for future targeted genetic profiling of CPSP risk, to enable preventive and therapeutic approaches.

A Review on Chronic Pain in Rheumatoid Arthritis: A Focus on Activation of NR2B Subunit of N-Methyl-D-Aspartate Receptors

Chronic pain is a debilitating condition that occurs after tissue damage, which substantially affects the patient's emotional state and physical activity. The chronic pain in rheumatoid arthritis (RA) is the result of various autoimmune-induced inflammatory reactions in the joints. Both types of peripheral and central pain processing can lead to sensitisation. Non-steroidal anti-inflammatory drugs (NSAIDs) and disease-modifying anti-rheumatic drugs (DMARDs) can result in potent anti-inflammatory effect. However, these drugs are not able to suppress the pain from RA for a prolonged period. For years, researchers have examined the role of the N-methyl-D-aspartic acid receptor 2B (NR2B) subunit of N-methyl-D-aspartate receptors (NMDAR) in chronic and neuropathic pain models. This NMDAR subtype can be found in at the peripheral and central nervous system and it represents an effective therapy for RA pain management. This review focuses on the NR2B subunit of NMDAR and the different pathways leading to its activation. Furthermore, specific attention is given to the possible involvement of NR2B subunit in the peripheral and central pathogenesis of RA.

Electroacupuncture reduces fibromyalgia pain by downregulating the TRPV1-pERK signalling pathway in the mouse brain

BACKGROUND

Acupuncture has been clinically recommended as a method of pain relief by the World Health Organization and is widely used by medical doctors. Fibromyalgia (FM) pain has a complex physiological and psychological origin and can be pharmacologically treated with duloxetine, milnacipran and pregabalin. However, these drugs produce undesirable side effects, such as headaches, nausea and diarrhoea. Acupuncture may serve as an effective alternative treatment for pain relief with few side effects.

AIMS

We hypothesised that acupuncture would reduce FM pain by influencing transient receptor potential cation channel subfamily V member 1 (TRPV1) and the downstream phosphorylated extracellular signal-regulated kinases (pERK), which are located in the central thalamus, amygdala and cortex.

METHODS

A FM mouse model was established by injecting two doses of acid saline into 32 female C57/B6 mice. The mice were then assigned to different subgroups (n=8 each) and treated with electroacupuncture (EA) or EA sham control. TRPV1 and pERK expression levels were measured using Western blotting and immunohistochemistry.

RESULTS

Our results demonstrated that the expression of TRPV1 and pERK in the thalamus, amygdala and somatosensory cortex was normal in the control mice, but significantly increased in FM mice; these FM-induced changes in expression were attenuated by EA.

CONCLUSION

Our data suggest that EA can reverse the central sensitisation of the TRPV1-ERK signalling pathway in the mouse brain. Thus, our findings provide mechanistic evidence supporting the potential therapeutic efficacy of EA for treating FM pain.

Differential methylation and expression of genes in the hypoxia-inducible factor 1 signaling pathway are associated with paclitaxel-induced peripheral neuropathy in breast cancer survivors and with preclinical models of chemotherapy-induced neuropathic pain

BACKGROUND

Paclitaxel is an important chemotherapeutic agent for the treatment of breast cancer. Paclitaxel-induced peripheral neuropathy (PIPN) is a major dose-limiting toxicity that can persist into survivorship. While not all survivors develop PIPN, for those who do, it has a substantial negative impact on their functional status and quality of life. No interventions are available to treat PIPN. In our previous studies, we identified that the HIF-1 signaling pathway (H1SP) was perturbed between breast cancer survivors with and without PIPN. Preclinical studies suggest that the H1SP is involved in the development of bortezomib-induced and diabetic peripheral neuropathy, and sciatic nerve injury. The purpose of this study was to identify H1SP genes that have both differential methylation and differential gene expression between breast cancer survivors with and without PIPN.

METHODS

A multi-staged integrated analysis was performed. In peripheral blood, methylation was assayed using microarray and gene expression was assayed using RNA-seq. Candidate genes in the H1SP having both differentially methylation and differential expression were identified between survivors who received paclitaxel and did (n = 25) and did not (n = 25) develop PIPN. Then, candidate genes were evaluated for differential methylation and differential expression in public data sets of preclinical models of PIPN and sciatic nerve injury.

RESULTS

Eight candidate genes were identified as both differential methylation and differential expression in survivors. Of the eight homologs identified, one was found to be differential expression in both PIPN and "normal" mice dorsal root ganglia; three were differential methylation in sciatic nerve injury versus sham rats in both pre-frontal cortex and T-cells; and two were differential methylation in sciatic nerve injury versus sham rats in the pre-frontal cortex.

CONCLUSIONS

This study is the first to evaluate for methylation in cancer survivors with chronic PIPN. The findings provide evidence that the expression of H1SP genes associated with chronic PIPN in cancer survivors may be regulated by epigenetic mechanisms and suggests genes for validation as potential therapeutic targets.

Cholecystokinin type B receptor-mediated inhibition of A-type K+ channels enhances sensory neuronal excitability through the phosphatidylinositol 3-kinase and c-Src-dependent JNK pathway

Background

Cholecystokinin (CCK) is implicated in the regulation of nociceptive sensitivity of primary afferent neurons. Nevertheless, the underlying cellular and molecular mechanisms remain unknown.

Methods

Using patch clamp recording, western blot analysis, immunofluorescent labelling, enzyme-linked immunosorbent assays, adenovirus-mediated shRNA knockdown and animal behaviour tests, we studied the effects of CCK-8 on the sensory neuronal excitability and peripheral pain sensitivity mediated by A-type K⁺ channels.

Results

CCK-8 reversibly and concentration-dependently decreased A-type K⁺ channel (I_A) in small-sized dorsal root ganglion (DRG) neurons through the activation of CCK type B receptor (CCK-BR), while the sustained delayed rectifier K⁺ current was unaffected. The intracellular subunit of CCK-BR coimmunoprecipitated with Gα_o. Blocking G-protein signaling with pertussis toxin or by the intracellular application of anti-G_β antibody reversed the inhibitory effects of CCK-8. Antagonism of phosphatidylinositol 3-kinase (PI3K) but not of its common downstream target Akts abolished the CCK-BR-mediated I_A response. CCK-8 application significantly activated JNK mitogen-activated protein kinase. Antagonism of either JNK or c-Src prevented the CCK-BR-mediated I_A decrease, whereas c-Src inhibition attenuated the CCK-8-induced p-JNK activation. Application of CCK-8 enhanced the action potential firing rate of DRG neurons and elicited mechanical and thermal pain hypersensitivity in mice. These effects were mediated by CCK-BR and were occluded by I_A blockade.

Conclusion

Our findings indicate that CCK-8 attenuated I_A through CCK-BR that is coupled to the G_βγ-dependent PI3K and c-Src-mediated JNK pathways, thereby enhancing the sensory neuronal excitability in DRG neurons and peripheral pain sensitivity in mice.