JAK-STAT3 pathway regulates spinal astrocyte proliferation and neuropathic pain maintenance in rats

Gabapentinoids Suppress Lipopolysaccharide-Induced Interleukin-6 Production in Primary Cell Cultures of the Rat Spinal Dorsal Horn

INTRODUCTION

Gabapentin and pregabalin are drugs to treat neuropathic pain. Several studies highlighted effects on presynaptic terminals of nociceptors. Via binding to α2δ subunits of voltage-gated calcium channels, gabapentinoids modulate the synaptic transmission of nociceptive information. However, recent studies revealed further properties of these substances. Treatment with gabapentin or pregabalin in animal models of neuropathic pain resulted not only in reduced symptoms of hyperalgesia but also in an attenuated activation of glial cells and decreased production of pro-inflammatory mediators in the spinal dorsal horn.

METHODS

In the present study, we aimed to investigate the impact of gabapentinoids on the inflammatory response of spinal dorsal horn cells, applying the established model of neuro-glial primary cell cultures of the superficial dorsal horn (SDH). We studied effects of gabapentin and pregabalin on lipopolysaccharide (LPS)-induced cytokine release (bioassays), expression of inflammatory marker genes (RT-qPCR), activation of transcription factors (immunocytochemistry), and Ca2+ responses of SDH neurons to stimulation with substance P and glutamate (Ca2+-imaging).

RESULTS

We detected an attenuated LPS-induced expression and release of interleukin-6 by SDH cultures in the presence of gabapentinoids. In addition, a significant main effect of drug treatment was observed for mRNA expression of microsomal prostaglandin E synthase 1 and the inhibitor of nuclear factor kappa B. Nuclear translocation of inflammatory transcription factors in glial cells was not significantly affected by gabapentinoid treatment. Moreover, both substances did not modulate neuronal responses upon stimulation with substance P or glutamate.

CONCLUSION

Our results provide evidence for anti-inflammatory capacities of gabapentinoids on the acute inflammatory response of SDH primary cultures upon LPS stimulation. Such effects may contribute to the pain-relieving effects of gabapentinoids.

Selective Involvement of a Subset of Spinal Dorsal Horn Neurons Operated by a Prodynorphin Promoter in Aβ Fiber-Mediated Neuropathic Allodynia-Like Behavioral Responses in Rats

Mechanical allodynia (pain produced by innocuous stimuli such as touch) is the main symptom of neuropathic pain. Its underlying mechanism remains to be elucidated, but peripheral nerve injury (PNI)-induced malfunction of neuronal circuits in the central nervous system, including the spinal dorsal horn (SDH), is thought to be involved in touch-pain conversion. Here, we found that intra-SDH injection of adeno-associated viral vectors including a prodynorphin promoter (AAV-PdynP) captured a subset of neurons that were mainly located in the superficial laminae, including lamina I, and exhibited mostly inhibitory characteristics. Using transgenic rats that enable optogenetic stimulation of touch-sensing Aβ fibers, we found that the light-evoked paw withdrawal behavior and aversive responses after PNI were attenuated by selective ablation of AAV-PdynP-captured SDH neurons. Notably, the ablation had no effect on withdrawal behavior from von Frey filaments. Furthermore, Aβ fiber stimulation did not excite AAV-PdynP⁺ SDH neurons under normal conditions, but after PNI, this induced excitation, possibly due to enhanced Aβ fiber-evoked excitatory synaptic inputs and elevated resting membrane potentials of these neurons. Moreover, the chemogenetic silencing of AAV-PdynP⁺ neurons of PNI rats attenuated the Aβ fiber-evoked paw withdrawal behavior and c-FOS expression in superficial SDH neurons. Our findings suggest that PNI renders AAV-PdynP-captured neurons excitable to Aβ fiber stimulation, which selectively contributes to the conversion of Aβ fiber-mediated touch signal to nociceptive. Thus, reducing the excitability of AAV-PdynP-captured neurons may be a new option for the treatment of neuropathic allodynia.

Reactive astrocytes in pain neural circuit pathogenesis

Reactive astrocytes are commonly activated in the spinal dorsal horn (SDH) of various animal models of pathological pain. Previous investigations suggest an association between astrogliosis and pain pathogenesis. However, our understanding of the mechanisms underlying astrogliosis activation and the contributions of reactive astrocytes to pain neural circuit malfunction is rudimentary. This short review highlights recent advances in these areas.

The Effect of Yiqi Huoxue Tongluo Decoction on Spinal Cord Microglia Activation and ASK1-MKK3-p38 Signal Pathway in Rats with Diabetic Neuropathic Pain

Diabetic neuropathic pain (DNP) is one of the most common chronic peripheral neuropathies in diabetes mellitus (DM). Objective. To observe the underlying mechanism of the effects of Yiqi Huoxue Tongluo Decoction (YQHX) on DNP rats. Methods. SD rats were intraperitoneally injected with 35 mg/kg streptozotocin (STZ) to prepare DNP models and were treated with YQHX for 8 weeks. Results. Studies have shown that the drug restores some levels of MWT, TWL, and MNCV, downregulates the levels of inflammatory factors IL-6, IL-1β, and TNF-α, downregulates the levels of ASK1-MKK3-p38, and weakens the level of OX42 activation. Conclusion. Yiqi Huoxue Tongluo Decoction can relieve DNP by affecting the activity of spinal cord microglia and the ASK1-MKK3-p38 signaling pathway, thereby reducing the central sensitization caused by the inflammatory response of DNP rats.

Transient astrocytic mGluR5 expression drives synaptic plasticity and subsequent chronic pain in mice

Activation of astrocytes has a profound effect on brain plasticity and is critical for the pathophysiology of several neurological disorders including neuropathic pain. Here, we show that metabotropic glutamate receptor 5 (mGluR5), which reemerges in astrocytes in a restricted time frame, is essential for these functions. Although mGluR5 is absent in healthy adult astrocytes, it transiently reemerges in astrocytes of the somatosensory cortex (S1). During a limited spatiotemporal time frame, astrocytic mGluR5 drives Ca²⁺ signals; upregulates multiple synaptogenic molecules such as Thrombospondin-1, Glypican-4, and Hevin; causes excess excitatory synaptogenesis; and produces persistent alteration of S1 neuronal activity, leading to mechanical allodynia. All of these events were abolished by the astrocyte-specific deletion of mGluR5. Astrocytes dynamically control synaptic plasticity by turning on and off a single molecule, mGluR5, which defines subsequent persistent brain functions, especially under pathological conditions.

Astrocyte-microglia interaction through C3/C3aR pathway modulates neuropathic pain in rats model of chronic constriction injury

Neuropathic pain (NP) is the cardinal symptom of neural injury, and its underlying molecular mechanism needs further investigation. Complements, especially complement 3 (C3), are involved in the pathophysiology of many neurological disorders, while the specific role of C3 in NP is still obscure. In this study, we found that both C3 and its receptor C3aR were upregulated in the spinal dorsal horn in a rat chronic constriction injury (CCI) model. In addition, C3 was mainly detected in astrocytes, while C3aR was expressed in microglia and neuron. Intrathecal injection of C3 antibody and C3aR antagonist alleviated NP in CCI model together with reduced M1 polarization of microglia. Our finding suggested that blockade of the C3/C3aR pathway might be a novel strategy for NP.

A Dual-Modal Magnetic Resonance/Photoacoustic Imaging Tracer for Long-Term High-Precision Tracking and Facilitating Repair of Peripheral Nerve Injuries

Neuroanatomical tracing is considered a crucial technique to assess the axonal regeneration level after injury, but traditional tracers do not meet the needs of in vivo neural tracing in deep tissues. Magnetic resonance (MR) and photoacoustic (PA) imaging have high spatial resolution, great penetration depth, and rich contrast. Fe₃ O₄ nanoparticles may work well as a dual-modal diagnosis probe for neural tracers, with the potential to improve nerve regeneration. The present study combines antegrade neural tracing imaging therapy for the peripheral nervous system. Fe₃ O₄ @COOH nanoparticles are successfully conjugated with biotinylated dextran amine (BDA) to produce antegrade nano-neural tracers, which are encapsulated by microfluidic droplets to control leakage and allow sustained, slow release. They have many notable advantages over traditional tracers, including dual-modal real-time MR/PA imaging in vivo, long-duration release effect, and limitation of uncontrolled leakage. These multifunctional anterograde neural tracers have potential neurotherapeutic function, are reliable and may be used as a new platform for peripheral nerve injury imaging and treatment integration.

Sphingosine-1 phosphate receptor 1 contributes to central sensitization in recurrent nitroglycerin-induced chronic migraine model

BACKGROUND

Central sensitization is an important pathophysiological mechanism of chronic migraine (CM), and microglia activation in trigeminocervical complex (TCC) contributes to the development of central sensitization. Emerging evidence implicates that blocking sphingosine-1-phosphate receptor 1 (S1PR1) can relieve the development of chronic pain and inhibit the activation of microglia. However, it is unclear whether S1PR1 is involved in the central sensitization of CM. Therefore, the purpose of this study is to explore the role of S1PR1 and its downstream signal transducers and activators of transcription 3 (STAT3) signaling pathway in the CM, mainly in inflammation.

METHODS

Chronic intermittent intraperitoneal injection of nitroglycerin (NTG) established a mouse model of CM. First, we observed the changes and subcellular localization of S1PR1 in the trigeminocervical complex (TCC). Then, W146, a S1PR1 antagonist; SEW2871, a S1PR1 agonist; AG490, a STAT3 inhibitor were applied by intraperitoneal injection to investigate the related molecular mechanism. The changes in the number of microglia and the expression of calcitonin gene-related peptide (CGRP) and c-fos in the TCC site were explored by immunofluorescence. In addition, we studied the effect of S1PR1 inhibitors on STAT3 in lipopolysaccharide-treated BV-2 microglia.

RESULTS

Our results showed that the expression of S1PR1 was increased after NTG injection and S1PR1 was colocalized with in neurons and glial cells in the TCC. The S1PR1 antagonist W146 alleviated NTG-induced hyperalgesia and suppressed the upregulation of CGRP, c-fos and pSTAT3 in the TCC. Importantly, blocking S1PR1 reduced activation of microglia. In addition, we found that inhibiting STAT3 signal also attenuated NTG-induced basal mechanical and thermal hyperalgesia.

CONCLUSIONS

Our results indicate that inhibiting S1PR1 signal could alleviate central sensitization and inhibit microglia activity caused by chronic NTG administration via STAT3 signal pathway, which provide a new clue for the clinical treatment of CM.

IL-33 induces orofacial neuropathic pain through Fyn-dependent phosphorylation of GluN2B in the trigeminal spinal subnucleus caudalis

Orofacial neuropathic pain can cause considerable disruptions in patients' daily lives, especially because of a lack of effective medications as its underlying causative mechanisms are not fully understood. Here, we found neuron-specific expression of the interleukin (IL)-33 receptor in the trigeminal spinal subnucleus caudalis (Vc), distinct from the spinal dorsal horn. Reduction in head withdrawal threshold in response to von Frey filament stimulation of the whisker pad skin was inversely correlated with the upregulation of IL-33 in the Vc after infraorbital nerve injury (IONI). Neutralization of IL-33 in the Vc alleviated mechanical allodynia in the whisker pad skin after IONI; conversely, intracisternal administration of IL-33 elicited mechanical allodynia in the whisker pad skin, which was relieved by GluN2B antagonism. Moreover, IL-33 triggered the potentiation of GluN2B-containing N-methyl-D-aspartate receptor-mediated synaptic currents and phosphorylation of synaptosomal GluN2B in the Vc, whereas IONI-induced GluN2B phosphorylation was inhibited by neutralization of IL-33 in the Vc. IL-33-induced GluN2B phosphorylation was mediated by phosphorylation of Fyn kinase, and inhibition of the Fyn kinase pathway prevented the development of IL-33-induced mechanical allodynia. Our findings provide insights into a new mechanism by which IL-33 directly regulates synaptic transmission and suggest that IL-33 signaling could be a candidate target for therapeutic interventions for orofacial neuropathic pain.

The protective effects of hesperidin against paclitaxel-induced peripheral neuropathy in rats

Paclitaxel (PTX), which is widely used in the treatment of solid tumors, leads to dose limitation because it causes peripheral neuropathy. This study was conducted to evaluate the potential effects of hesperidin (HES), which has various biological and pharmacological properties, against PTX-induced sciatic nerve damage. For this purpose, Sprague Dawley rats were given PTX 2 mg/kg/b.w for 5 days, then 100 or 200 mg/kg/b.w HES for 10 days, and behavioral tests were conducted at the end of the experiment. The data obtained show that PTX-induced MDA, NF-κB, IL-1β, TNF-α, COX-2, nNOS, JAK2, STAT3, and GFAP levels decreased with HES administration. Moreover, it was observed that SOD, CAT, and GPx activities inhibited by PTX increased with HES administration. It was determined that PTX caused apoptosis in the sciatic nerve by increasing Caspase-3 and Bax levels and suppressing Bcl-2 levels. HES, on the other hand, showed an anti-apoptotic effect, increasing Bcl-2 levels and decreasing Caspase-3 and Bax levels. Also, it was observed that PTX could cause endoplasmic reticulum stress (ERS) by increasing PERK, IRE1, ATF-6, GRP78 and CHOP mRNA transcript levels, while HES could alleviate ERS by suppressing them. The results indicate that neuropathic pain associated with PTX-induced peripheral neuropathy can be alleviated by HES administration and that it is a promising compound for cancer patients. In addition, it is thought that the results of the present study contain information that will shed light for researchers regarding further studies to be conducted with HES.

Antinociceptive and Antipruritic Effects of HSK21542, a Peripherally-Restricted Kappa Opioid Receptor Agonist, in Animal Models of Pain and Itch

Kappa opioid receptor (KOR) agonists have been promising therapeutic candidates, owing to their potential for relieving pain and treating intractable pruritus. Although lacking morphine-like central nervous system (CNS) effects, KOR agonists do elicit sedation, dysphoria and diuresis which seriously impede their development. Peripherally-restricted KOR agonists have a poor ability to penetrate into the CNS system, so that CNS-related adverse effects can be ameliorated or even abolished. However, the only approved peripherally-restricted KOR agonist CR845 remains some frequent CNS adverse events. In the present study, we aim to address pharmacological profiles of HSK21542, with an expectation to provide a safe and effective alternative for patients who are suffering from pain and pruritus. The in vitro experimental results showed that HSK21542 was a selective and potent KOR agonist with higher potency than CR845, and had a brain/plasma concentration ratio of 0.001, indicating its peripheral selectivity. In animal models of pain, HSK21542 significantly inhibited acetic acid-, hindpaw incision- or chronic constriction injury-induced pain-related behaviors, and the efficacy was comparable to CR845 at 15 min post-dosing. HSK21542 had a long-lasting analgesic potency with a median effective dose of 1.48 mg/kg at 24 h post-drug in writhing test. Meanwhile, the antinociceptive activity of HSK21542 was effectively reversed by a KOR antagonist nor-binaltorphimine. In addition, HSK21542 had powerful antipruritic activities in compound 48/80-induced itch model. On the other hand, HSK21542 had a weak ability to produce central antinociceptive effects in a hot-plate test and fewer effects on the locomotor activity of mice. HSK21542 didn't affect the respiratory rate of mice. Therefore, HSK21542 might be a safe and effective KOR agonist and promising candidate for treating pain and pruritus.

Photobiomodulation Therapy Partially Restores Cartilage Integrity and Reduces Chronic Pain Behavior in a Rat Model of Osteoarthritis: Involvement of Spinal Glial Modulation

OBJECTIVE

Chronic pain associated with osteoarthritis (OA) often leads to reduced function and engagement in activities of daily living. Current pharmacological treatments remain relatively ineffective. This study investigated the efficacy of photobiomodulation therapy (PBMT) on cartilage integrity and central pain biomarkers in adult male Wistar rats.

DESIGN

We evaluated the cartilage degradation and spinal cord sensitization using the monoiodoacetate (MIA) model of OA following 2 weeks of delayed PBMT treatment (i.e., 15 days post-MIA). Multiple behavioral tests and knee joint histology were used to assess deficits related to OA. Immunohistochemistry was performed to assess chronic pain sensitization in spinal cord dorsal horn regions. Furthermore, we analyzed the principal components related to pain-like behavior and cartilage integrity.

RESULTS

MIA induced chronic pain-like behavior with respective cartilage degradation. PBMT had no effects on overall locomotor activity, but positive effects on weight support (P = 0.001; effect size [ES] = 1.01) and mechanical allodynia (P = 0.032; ES = 0.51). Greater optical densitometry of PBMT-treated cartilage was evident in superficial layers (P = 0.020; ES = 1.34), likely reflecting the increase of proteoglycan and chondrocyte contents. In addition, PBMT effects were associated to decreased contribution of spinal glial cells to pain-like behavior (P = 0.001; ES = 0.38).

CONCLUSION

PBMT during the chronic phase of MIA-induced OA promoted cartilage recovery and reduced the progression or maintenance of spinal cord sensitization. Our data suggest a potential role of PBMT in reducing cartilage degradation and long-term central sensitization associated with chronic OA.

hsa-MiR-19a-3p and hsa-MiR-19b-3p Are Associated with Spinal Cord Injury-Induced Neuropathic Pain: Findings from a Genome-Wide MicroRNA Expression Profiling Screen

Neuropathic pain in spinal cord injury (SCI) is associated with inflammation in both the peripheral and central nervous system (CNS), which may contribute to the initiation and maintenance of persistent pain. An understanding of factors contributing to neuroinflammation may lead to new therapeutic targets for neuropathic pain. Moreover, novel circulating biomarkers of neuropathic pain may facilitate earlier and more effective treatment. MicroRNAs (miRNAs) are short, non-coding single-stranded RNA that have emerged as important biomarkers and molecular mediators in physiological and pathological conditions. Using a genome-wide miRNA screening approach, we studied differential miRNA expression in plasma from 68 healthy, community-dwelling adults with and without SCI enrolled in ongoing clinical studies. We detected 2367 distinct miRNAs. Of these, 383 miRNAs were differentially expressed in acute SCI or chronic SCI versus no SCI and 71 were differentially expressed in chronic neuropathic pain versus no neuropathic pain. We selected homo sapiens (hsa)-miR-19a-3p and hsa-miR-19b-3p for additional analysis based on p-value, fold change, and their known role as regulators of neuropathic pain and neuroinflammation. Both hsa-miR-19a-3p and hsa-miR-19b-3p levels were significantly higher in those with chronic SCI and severe neuropathic pain versus those with chronic SCI and no neuropathic pain. In confirmatory studies, both hsa-miR-19a-3p and hsa-miR-19b-3p have moderate to strong discriminative ability to distinguish between those with and without pain. After adjusting for opioid use, hsa-miR-19b-3p levels were positively associated with pain interference with mood. Because hsa-miR-19 levels have been shown to change in response to exercise, folic acid, and resveratrol, these studies suggest that miRNAs are potential targets of therapeutic interventions.

The Identification of Blood Biomarkers of Chronic Neuropathic Pain by Comparative Transcriptomics

In this study, we recruited 50 chronic pain (neuropathic and nociceptive) and 43 pain-free controls to identify specific blood biomarkers of chronic neuropathic pain (CNP). Affymetrix microarray was carried out on a subset of samples selected 10 CNP and 10 pain-free control participants. The most significant genes were cross-validated using the entire dataset by quantitative real-time PCR (qRT-PCR). In comparative analysis of controls and CNP patients, WLS (P = 4.80 × 10^–7), CHPT1 (P = 7.74 × 10^–7) and CASP5 (P = 2.30 × 10^–5) were highly significant, whilst FGFBP2 (P = 0.00162), STAT1 (P = 0.00223), FCRL6 (P = 0.00335), MYC (P = 0.00335), XCL2 (P = 0.0144) and GZMA (P = 0.0168) were significant in all CNP patients. A three-arm comparative analysis was also carried out with control as the reference group and CNP samples differentiated into two groups of high and low S-LANSS score using a cut-off of 12. STAT1, XCL2 and GZMA were not significant but KIR3DL2 (P = 0.00838), SH2D1B (P = 0.00295) and CXCR31 (P = 0.0136) were significant in CNP high S-LANSS group (S-LANSS score > 12), along with WLS (P = 8.40 × 10^–5), CHPT1 (P = 7.89 × 10^–4), CASP5 (P = 0.00393), FGFBP2 (P = 8.70 × 10^–4) and FCRL6 (P = 0.00199), suggesting involvement of immune pathways in CNP mechanisms. None of the genes was significant in CNP samples with low (< 12) S-LANSS score. The area under the receiver operating characteristic (AUROC) analysis showed that combination of MYC, STAT1, TLR4, CASP5 and WLS gene expression could be potentially used as a biomarker signature of CNP (AUROC − 0.852, (0.773, 0.931 95% CI)).

Interplay between Prokineticins and Histone Demethylase KDM6A in a Murine Model of Bortezomib-Induced Neuropathy

Chemotherapy-induced neuropathy (CIN) is a major adverse effect associated with many chemotherapeutics, including bortezomib (BTZ). Several mechanisms are involved in CIN, and recently a role has been proposed for prokineticins (PKs), a chemokine family that induces proinflammatory/pro-algogen mediator release and drives the epigenetic control of genes involved in cellular differentiation. The present study evaluated the relationships between epigenetic mechanisms and PKs in a mice model of BTZ-induced painful neuropathy. To this end, spinal cord alterations of histone demethylase KDM6A, nuclear receptors PPARα/PPARγ, PK2, and pro-inflammatory cytokines IL-6 and IL-1β were assessed in neuropathic mice treated with the PK receptors (PKRs) antagonist PC1. BTZ treatment promoted a precocious upregulation of KDM6A, PPARs, and IL-6, and a delayed increase of PK2 and IL-1β. PC1 counteracted allodynia and prevented the increase of PK2 and of IL-1β in BTZ neuropathic mice. The blockade of PKRs signaling also opposed to KDM6A increase and induced an upregulation of PPAR gene transcription. These data showed the involvement of epigenetic modulatory enzymes in spinal tissue phenomena associated with BTZ painful neuropathy and underline a role of PKs in sustaining the increase of proinflammatory cytokines and in exerting an inhibitory control on the expression of PPARs through the regulation of KDM6A gene expression in the spinal cord.

KDM6B epigenetically regulated-interleukin-6 expression in the dorsal root ganglia and spinal dorsal horn contributes to the development and maintenance of neuropathic pain following peripheral nerve injury in male rats

The lysine specific demethylase 6B (KDM6B) has been implicated as a coregulator in the expression of proinflammatory mediators, and in the pathogenesis of inflammatory and arthritic pain. However, the role of KDM6B in neuropathic pain has yet to be studied. In the current study, the neuropathic pain was determined by assessing the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) following lumbar 5 spinal nerve ligation (SNL) in male rats. Immunohistochemistry, Western blotting, qRT-PCR, and chromatin immunoprecipitation (ChIP)-PCR assays were performed to investigate the underlying mechanisms. Our results showed that SNL led to a significant increase in KDM6B mRNA and protein in the ipsilateral L4/5 dorsal root ganglia (DRG) and spinal dorsal horn; and this increase correlated a markedly reduction in the level of H3K27me3 methylation in the same tissue. Double immunofluorescence staining revealed that the KDM6B expressed in myelinated A- and unmyelinated C-fibers in the DRG; and located in neuronal cells, astrocytes, and microglia in the dorsal horn. Behavioral data showed that SNL-induced mechanical allodynia and thermal hyperalgesia were impaired by the treatment of prior to i.t. injection of GSK-J4, a specific inhibitor of KDM6B, or KDM6B siRNA. Both microinjection of AAV2-EGFP-KDM6B shRNA in the lumbar 5 dorsal horn and sciatic nerve, separately, alleviated the neuropathic pain following SNL. The established neuropathic pain was also partially attenuated by repeat i.t. injections of GSK-J4 or KDM6B siRNA, started on day 7 after SNL. SNL also resulted in a remarkable increased expression of interleukin-6 (IL-6) in the DRG and dorsal horn. But this increase was dramatically inhibited by i.t. injection of GSK-J4 and KDM6B siRNA; and suppressed by prior to microinjection of AAV2-EGFP-KDM6B shRNA in the dorsal horn and sciatic nerve. Results of ChIP-PCR assay showed that SNL-induced enhanced binding of STAT3 with IL-6 promoter was inhibited by prior to i.t. injection of GSK-J4. Meanwhile, the level of H3K27me3 methylation was also decreased by the treatment. Together, our results indicate that SNL-induced upregulation of KDM6B via demethylating H3K27me3 facilitates the binding of STAT3 with IL-6 promoter, and subsequently mediated-increase in the expression of IL-6 in the DRG and dorsal horn contributes to the development and maintenance of neuropathic pain. Targeting KDM6B might a promising therapeutic strategy to treatment of chronic pain.

Goshajinkigan attenuates paclitaxel-induced neuropathic pain via cortical astrocytes

The anticancer agents platinum derivatives and taxanes such as paclitaxel (PCX) often cause neuropathy known as chemotherapy‐induced peripheral neuropathy with high frequency. However, the cellular and molecular mechanisms underlying such neuropathy largely remain unknown. Here, we show new findings that the effect of Goshajinkigan (GJG), a Japanese KAMPO medicine, inhibits PCX‐induced neuropathy by acting on astrocytes. The administration of PCX in mice caused the sustained neuropathy lasting at least 4 weeks, which included mechanical allodynia and thermal hyperalgesia but not cold allodynia. PCX‐evoked pain behaviors were associated with the sensitization of all primary afferent fibers. PCX did not activate microglia or astrocytes in the spinal cord. However, it significantly activated astrocytes in the primary sensory (S1) cortex without affecting S1 microglial activation there. GJG significantly inhibited the PCX‐induced mechanical allodynia by 50% and thermal hyperalgesia by 90%, which was in accordance with the abolishment of astrocytic activation in the S1 cortex. Finally, the inhibition of S1 astrocytes by an astrocyte‐toxin L‐alpha‐aminoadipic acid abolished the PCX‐induced neuropathy. Our findings suggest that astrocytes in the S1 cortex would play an important role in the pathogenesis of PCX‐induced neuropathy and are a potential target for its treatment.

Stem cells from human exfoliated deciduous teeth attenuate mechanical allodynia in mice through distinct from the siglec-9/MCP-1-mediated tissue-repairing mechanism

The effects of stem cells from human exfoliated deciduous teeth (SHED) on mechanical allodynia were examined in mice. A single intravenous injection of SHED and conditioned medium from SHED (SHED-CM) through the left external jugular vein significantly reversed the established mechanical allodynia induced by spinal nerve transection at 6 days after injection. SHED or SHED-CM significantly decreased the mean numbers of activating transcription factor 3-positive neurons and macrophages in the ipsilateral side of the dorsal root ganglion (DRG) at 20 days after spinal nerve transection. SHED or SHED-CM also suppressed activation of microglia and astrocytes in the ipsilateral side of the dorsal spinal cord. A single intravenous injection of secreted ectodomain of sialic acid-binding Ig-like lectin-9 and monocyte chemoattractant protein-1 had no effect on the established mechanical allodynia, whereas a single intravenous injection of protein component(s) contained in SHED-CM with molecular weight of between 30 and 50 kDa reversed the pain. Therefore, it may be concluded that protein component(s) with molecular mass of 30–50 kDa secreted by SHED could protect and/or repair DRG neurons damaged by nerve transection, thereby ameliorating mechanical allodynia.

TTI-101: A competitive inhibitor of STAT3 that spares oxidative phosphorylation and reverses mechanical allodynia in mouse models of neuropathic pain

Signal Transducer and Activator of Transcription (STAT) 3 emerged rapidly as a high-value target for treatment of cancer. However, small-molecule STAT3 inhibitors have been slow to enter the clinic due, in part, to serious adverse events (SAE), including lactic acidosis and peripheral neuropathy, which have been attributed to inhibition of STAT3's mitochondrial function. Our group developed TTI-101, a competitive inhibitor of STAT3 that targets the receptor pY705-peptide binding site within the Src homology 2 (SH2) domain to block its recruitment and activation. TTI-101 has shown target engagement, no toxicity, and evidence of clinical benefit in a Phase I study in patients with solid tumors. Here we report that TTI-101 did not affect mitochondrial function, nor did it cause STAT3 aggregation, chemically modify STAT3 or cause neuropathic pain. Instead, TTI-101 unexpectedly suppressed neuropathic pain induced by chemotherapy or in a spared nerve injury model. Thus, in addition to its direct anti-tumor effect, TTI-101 may be of benefit when administered to cancer patients at risk of developing chemotherapy-induced peripheral neuropathy (CIPN).

Mechanistic Insight into the Effects of Curcumin on Neuroinflammation-Driven Chronic Pain

Chronic pain is a persistent and unremitting condition that has immense effects on patients' quality of life. Studies have shown that neuroinflammation is associated with the induction and progression of chronic pain. The activation of microglia and astrocytes is the major hallmark of spinal neuroinflammation leading to neuronal excitability in the projection neurons. Excessive activation of microglia and astrocytes is one of the major contributing factors to the exacerbation of pain. However, the current chronic pain treatments, mainly by targeting the neuronal cells, remain ineffective and unable to meet the patients' needs. Curcumin, a natural plant product found in the Curcuma genus, improves chronic pain by diminishing the release of inflammatory mediators from the spinal glia. This review details the role of curcumin in microglia and astrocytes both in vitro and in vivo and how it improves pain. We also describe the mechanism of curcumin by highlighting the major glia-mediated cascades in pain. Moreover, the role of curcumin on inflammasome and epigenetic regulation is discussed. Furthermore, we discuss the strategies used to improve the efficacy of curcumin. This review illustrates that curcumin modulating microglia and astrocytes could assure the treatment of chronic pain by suppressing spinal neuroinflammation.

Electroacupuncture ameliorates mechanical hypersensitivity by down-regulating spinal Janus kinase 2/signal transducer and activation of transcription 3 and interleukin 6 in rats with spared nerve injury

BACKGROUND

Evidence shows that the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway participates in the pathogenesis of neuropathic pain. Our previous study revealed that electroacupuncture (EA) attenuated neuropathic pain via activation of alpha-7 nicotinic acetylcholine receptor (α7nAChR) in the spinal cord. However, whether 2 Hz EA alleviates neuropathic pain by regulating the downstream molecules JAK2/STAT3 has not been fully clarified.

METHODS

Paw withdrawal threshold (PWT) was used as a marker of mechanical allodynia in rats with spared nerve injury (SNI). After applying 2 Hz EA on day 3, 7, 14 and 21 post-surgery, spinal expression of JAK2, STAT3 and pro-inflammatory cytokine interleukin (IL)-6 was examined using quantitative reverse transcription and real-time polymerase chain reaction (qRT-PCR) and Western blot analysis. Intrathecal injection of the α7nAChR antagonist alpha-bungarotoxin (α-Bgtx) was used to further explore the mechanism underlying the effects of 2 Hz EA on expression of JAK2/STAT3 in SNI rats.

RESULTS

It was found that levels of spinal STAT3 and IL-6 mRNA, as well as levels of phosphorylated (p)-JAK2, p-STAT3 and IL-6 protein, were markedly increased in SNI rats. 2 Hz EA attenuated the SNI-induced up-regulation of p-JAK2, p-STAT3 and IL-6 expression in the spinal cord. Furthermore, intrathecal injection of α-Bgtx (1.0 μg/kg) not only inhibited the effect of 2 Hz EA on mechanical hypersensitivity but also ameliorated the down-regulation of p-JAK2, p-STAT3 and IL-6 expression induced by 2 Hz EA.

CONCLUSION

This study revealed that 2 Hz EA attenuated SNI-induced mechanical hypersensitivity and the concomitant up-regulation of spinal JAK2, STAT3 and IL-6 in SNI rats, suggesting that suppression of the JAK2/STAT3 signaling pathway might be the mechanism underlying the therapeutic effect of 2 Hz EA on neuropathic pain.

Effect of intrathecal administration of exogenous noggin on neuropathic pain

OBJECTIVES

To explore the effect of intrathecal administration of exogenous noggin (NOG) on the pain behavior in the neuropathic pain (NP) rats through L5 spinal nerve ligation (SNL), and to examine the regulative role of NOG in astrocyte activation, inflammatory cytokines and downstream signals.

METHODS

A total of 40 adult male Sprague Dawley (SD) rats were randomly divided into 3 groups: a control group (n=10), a SNL group (SNL+intrathecal injection of artificial cerebrospinal fluid, n=15), and a SNL+NOG group (SNL+intrathecal injection of recombinant NOG protein, n=15). Von-Frey filaments were used to test the changes of paw withdrawal threshold (PWT) at Day 1 before operation, and Day 1, Day 4, Day 7 and Day 14 after operation in each group. Immunofluorescence was used to observe the activation of astrocyte located in the dorsal horn of spinal cord in the 3 groups. Western blotting was conducted to detect the expression levels of glial fibrillary acidic protein (GFAP), interleukin-6 (IL-6), signal transducer and activator of transcription (STAT3) and phosphorylation STAT3 (p-STAT3).

RESULTS

Compared with the control group, the PWT in the SNL group was markedly decreased at each time point, together with the increase in GFAP, IL-6 and the ratio of p-STAT3/STAT3 (all P<0.05). Meanwhile, compared with the SNL group, the PWT in the lumbar swelling of spinal cord in the SNL+NOG group was elevated at Day 4 and lasted to Day 14 (P<0.05), accompanied by the decrease in GFAP, IL-6 and the ratio of p-STAT3/STAT3 (all P<0.05).

CONCLUSIONS

The intrathecal administration of NOG may alleviate NP in the SNL rats through inhibiting astrocyte activation and down-regulating the STAT3 signal pathway.

MiR-135-5p Alleviates Bone Cancer Pain by Regulating Astrocyte-Mediated Neuroinflammation in Spinal Cord through JAK2/STAT3 Signaling Pathway

Bone cancer pain (BCP) was associated with microRNA dysregulation. In this study, we intended to clarify the potential role of miR-135-5p in a BCP mouse model, which was established by tumor cell implantation (TCI) in the medullary cavity of the mouse femur. The BCP-related behaviors were tested, including the paw withdrawal mechanical threshold (PWMT) and number of spontaneous flinches (NSF). The miRNA expression profiles in astrocytes of the sham and tumor groups were compared, and miRNA microarray and quantitative real-time PCR (qRT-PCR) assays confirmed that the amount of expression of miR-135-5p was significantly decreased in astrocytes of the tumor group. Gain- and loss-of-function studies showed that miR-135-5p could inhibit astrocyte activation and inflammation cytokine (TNF-α and IL-1β) expression. The relation between miR-135-5p and JAK2 was detected by bioinformatic analysis and dual luciferase reporter gene assay. By conducting in vitro experiments, it was shown that the miR-135-5P mimics lowered the level of JAK2/STAT3 proteins and inflammatory factors in astrocytes. Moreover, in vivo analysis on BCP mice model indicated that the miR-135-5p agonist could sufficiently increase PWMT and decrease NSF. Meanwhile, reduced activation of astrocytes in the spinal cord, as well as decreased expression of JAK2/STAT3 and inflammatory mediators, were found after miR-135-5p agonist treatment. Collectively, the results showed that miR-135-5p could potentially reduce BCP in mice through inhibiting astrocyte-mediated neuroinflammation and blocking of the JAK2/STAT3 signaling pathway, indicating that the upregulation of miR-135-5P could be a therapeutic focus in BCP treatment.

A human isogenic iPSC-derived cell line panel identifies major regulators of aberrant astrocyte proliferation in Down syndrome

Astrocytes exert adverse effects on the brains of individuals with Down syndrome (DS). Although a neurogenic-to-gliogenic shift in the fate-specification step has been reported, the mechanisms and key regulators underlying the accelerated proliferation of astrocyte precursor cells (APCs) in DS remain elusive. Here, we established a human isogenic cell line panel based on DS-specific induced pluripotent stem cells, the XIST-mediated transcriptional silencing system in trisomic chromosome 21, and genome/chromosome-editing technologies to eliminate phenotypic fluctuations caused by genetic variation. The transcriptional responses of genes observed upon XIST induction and/or downregulation are not uniform, and only a small subset of genes show a characteristic expression pattern, which is consistent with the proliferative phenotypes of DS APCs. Comparative analysis and experimental verification using gene modification reveal dose-dependent proliferation-promoting activity of DYRK1A and PIGP on DS APCs. Our collection of human isogenic cell lines provides a comprehensive set of cellular models for further DS investigations.

Keiji Kawatani et al. developed a panel of Down syndrome (DS) isogenic astrocytes derived from iPSCs to observe the consequence of DS on astrocyte precursor proliferation, differentiation, and gene expression. Their results suggest a dose-dependent effect of DYRK1A and PIGP on DS-derived astrocyte precursor proliferation, and represent a valuable resource and cellular model for future DS research.

Serotonin Plays a Key Role in the Development of Opioid-Induced Hyperalgesia in Mice

Opioid usage for pain therapy is limited by its undesirable clinical effects, including paradoxical hyperalgesia, also known as opioid-induced hyperalgesia (OIH). However, the mechanisms associated with the development and maintenance of OIH remain unclear. Here, we investigated the effect of serotonin inhibition by the 5-HT3 receptor antagonist, ondansetron (OND), as well as serotonin deprivation via its synthesis inhibitor para-chlorophenylalanine, on mouse OIH models, with particular focus on astrocyte activation. Co-administering of OND and morphine, in combination with serotonin depletion, inhibited mechanical hyperalgesia and astrocyte activation in the spinal dorsal horn of mouse OIH models. Although previous studies have suggested that activation of astrocytes in the spinal dorsal horn is essential for the development and maintenance of OIH, herein, treatment with carbenoxolone (CBX), a gap junction inhibitor that suppresses astrocyte activation, did not ameliorate mechanical hyperalgesia in mouse OIH models. These results indicate that serotonin in the spinal dorsal horn, and activation of the 5-HT3 receptor play essential roles in OIH induced by chronic morphine, while astrocyte activation in the spinal dorsal horn serves as a secondary effect of OIH. Our findings further suggest that serotonergic regulation in the spinal dorsal horn may be a therapeutic target of OIH. PERSPECTIVE: The current study revealed that the descending serotonergic pain-facilitatory system in the spinal dorsal horn is crucial in OIH, and that activation of astrocytes is a secondary phenotype of OIH. Our study offers new therapeutic targets for OIH and may help reduce inappropriate opioid use.

Chronic pain and neuroinflammation

In rheumatology, chronic pain most often sets in after a musculoskeletal injury. Its persistence is not always due to the progression of the initial injury, but in some cases to the onset of central sensitization. Much scientific data suggests that this central sensitization is caused by multiple complex interactions between the nervous system and immune system. Afferent nerve fibers carrying pain information are responsible for peripheral sensitization partly linked to inflammation molecules. These afferent fibers release neurotransmitters in the dorsal root ganglion and dorsal horn of the spinal cord, capable of activating microglia, which are the local immune cells. The activated microglia will produce pro-inflammatory cytokines, chemokines and neuropeptides capable of interacting with the second-order neuron, but also segmental and descending inhibitory neurons. This is referred to as neuroinflammation, which will amplify the hypersensitivity of second-order neurons, otherwise called central sensitization. This neuroinflammation will be able to reach the higher brain structures, which are involved in pain modulation and the emotional and cognitive aspects of pain. The aim of this update is to describe the pathophysiology of chronic pain, incorporating the latest scientific data on neuroplasticity and neuroinflammation.

Targeted inhibition of STAT3 in neural stem cells promotes neuronal differentiation and functional recovery in rats with spinal cord injury

STAT3 is expressed in neural stem cells (NSCs), where a number of studies have previously shown that STAT3 is involved in regulating NSC differentiation. However, the possible molecular mechanism and role of STAT3 in spinal cord injury (SCI) remain unclear. In the present study, the potential effect of STAT3 in NSCs was first investigated by using short hairpin RNA (shRNA)-mediated STAT3 knockdown in rat NSCs in vitro. Immunofluorescence of β3-tubulin and glial fibrillary acidic protein staining and western blotting showed that knocking down STAT3 expression promoted NSC neuronal differentiation, where the activity of mTOR was upregulated. Subsequently, rats underwent laminectomy and complete spinal cord transection followed by transplantation of NSCs transfected with control-shRNA or STAT3-shRNA at the injured site in vivo. Spinal cord-evoked potentials and the Basso-Beattie-Bresnahan scores were used to examine functional recovery. In addition, axonal regeneration and tissue repair were assessed using retrograde tracing with FluoroGold, hematoxylin and eosin, Nissl and immunofluorescence staining of β3-tubulin, glial fibrillary acidic protein and microtubule-associated protein 2 following SCI. The results showed that transplantation with NSCs transfected with STAT3-RNA enhanced functional recovery following SCI and promoted tissue repair in rats, in addition to improving neuronal differentiation of the transplanted NSCs in the injury site. Taken together, in vitro and in vivo evidence that inhibiting STAT3 could promote NSC neuronal differentiation was demonstrated in the present study. Therefore, transplantation with NSCs with STAT3 expression knocked down appears to hold promising potential for enhancing the benefit of NSC-mediated regenerative cell therapy for SCI.

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.

Endothelin ETB Receptor-Mediated Astrocytic Activation: Pathological Roles in Brain Disorders

In brain disorders, reactive astrocytes, which are characterized by hypertrophy of the cell body and proliferative properties, are commonly observed. As reactive astrocytes are involved in the pathogenesis of several brain disorders, the control of astrocytic function has been proposed as a therapeutic strategy, and target molecules to effectively control astrocytic functions have been investigated. The production of brain endothelin-1 (ET-1), which increases in brain disorders, is involved in the pathophysiological response of the nervous system. Endothelin B (ET_B) receptors are highly expressed in reactive astrocytes and are upregulated by brain injury. Activation of astrocyte ET_B receptors promotes the induction of reactive astrocytes. In addition, the production of various astrocyte-derived factors, including neurotrophic factors and vascular permeability regulators, is regulated by ET_B receptors. In animal models of Alzheimer’s disease, brain ischemia, neuropathic pain, and traumatic brain injury, ET_B-receptor-mediated regulation of astrocytic activation has been reported to improve brain disorders. Therefore, the astrocytic ET_B receptor is expected to be a promising drug target to improve several brain disorders. This article reviews the roles of ET_B receptors in astrocytic activation and discusses its possible applications in the treatment of brain disorders.

Astrocytic STAT3 activation and chronic itch require IP3R1/TRPC-dependent Ca2+ signals in mice

BACKGROUND

Chronic itch is a debilitating symptom of inflammatory skin diseases, but the underlying mechanism is poorly understood. We have recently demonstrated that astrocytes in the spinal dorsal horn become reactive in models of atopic and contact dermatitis via activation of the transcription factor signal transducer and activator of transcription 3 (STAT3) and critically contribute to chronic itch. In general, STAT3 is transiently activated; however, STAT3 activation in reactive astrocytes of chronic itch model mice persistently occurs via an unknown mechanism.

OBJECTIVE

We aimed to determine the mechanisms of persistent activation of astrocytic STAT3 in chronic itch conditions.

METHODS

To determine the factors that are required for persistent activation of astrocytic STAT3, Western blotting and calcium imaging with cultured astrocytes or spinal cord slices were performed. Thereafter, chronic itch model mice were used for genetic and behavioral experiments to confirm the role of the factors determined to mediate persistent STAT3 activation from in vitro and ex vivo experiments in chronic itch.

RESULTS

IP3 receptor type 1 (IP3R1) knockdown in astrocytes suppressed IL-6-induced persistent STAT3 activation and expression of lipocalin-2 (LCN2), an astrocytic STAT3-dependent inflammatory factor that is required for chronic itch. IP3R1-dependent astrocytic Ca2+ responses involved Ca2+ influx through the cation channel transient receptor potential canonical (TRPC), which was required for persistent STAT3 activation evoked by IL-6. IL-6 expression was upregulated in dorsal root ganglion neurons in a mouse model of chronic itch. Dorsal root ganglion neuron-specific IL-6 knockdown, spinal astrocyte-specific IP3R1 knockdown, and pharmacologic spinal TRPC inhibition attenuated LCN2 expression and chronic itch.

CONCLUSION

Our findings suggest that IP3R1/TRPC channel-mediated Ca2+ signals elicited by IL-6 in astrocytes are necessary for persistent STAT3 activation, LCN2 expression, and chronic itch, and they may also provide new targets for therapeutic intervention.

Combination therapy with semaglutide and rosiglitazone as a synergistic treatment for diabetic retinopathy in rodent animals

OBJECTIVE

To investigate the protective efficacies and potent mechanisms of combination therapy with semaglutide and rosiglitazone (RSG) on the high-glucose incubated human ARPE-19 cells and diabetic retinopathy (DR) model rats.

MAIN METHODS

The CCK-8 methods were used to evaluate the protective effects of semaglutide and RSG alone or combination on the cell viability of high-glucose treated ARPE-19 cells. After the DR rat model was established, the effects of combined treatment on general indexes, retinal morphological changes, retinal Müller cells as well as PI3K/Akt/MTOR related factors of DR model rats were investigated.

RESULTS

The CCK-8 assay showed obviously enhanced protective efficacies of combination therapy with semaglutide and RSG on the ARPE-19 with oxidative stress induced by high-glucose with combination index all below 1.5 demonstrating obvious synergistic effects. Combined incubation could also effectively decrease the expression of inflammatory factors, including TNF-α, IL-1β, IL-6, and the increase of ROS content in ARPE cell culture supernatant induced by high-glucose. Combined use of the antioxidant, PI3K/Akt and mTOR inhibitors, we further demonstrated that combined incubation of semaglutide and RSG could effectively by reduce high glucose-induced inflammatory injury inhibiting ROS/PI3K/Akt/mTOR signaling. Furthermore, chronic combination treatment effectively improved the histopathological characteristics and down-regulated the GFAP expression in Müller cells as well as PI3K/Akt/MTOR signaling pathway-related factors in retina which was better than any monomer treatment group.

CONCLUSIONS

Combined semaglutide with RSG exhibited synergistically protective efficacies on retinal cells by decreasing the GFAP expression, inhibiting oxidative stress and PI3K/Akt/MTOR signaling-transduction in DR model rats.

Angiotensin receptors and neuropathic pain

Growing evidence implicates the renin-angiotensin system (RAS) in multiple facets of neuropathic pain (NP). This narrative review focuses primarily on the major bioactive RAS peptide, Angiotensin II (Ang II), and its receptors, namely type 1 (AT1R) and type 2 (AT2R). Both receptors are involved in the development of NP and represent potential therapeutic targets. We first discuss the potential role of Ang II receptors in modulation of NP in the central nervous system. Ang II receptor expression is widespread in circuits associated with the perception and modulation of pain, but more studies are required to fully characterize receptor distribution, downstream signaling, and therapeutic potential of targeting the central nervous system RAS in NP. We then describe the peripheral neuronal and nonneuronal distribution of the RAS, and its contribution to NP. Other RAS modulators (such as Ang (1-7)) are briefly reviewed as well. AT1R antagonists are analgesic across different pain models, including NP. Several studies show neuronal protection and outgrowth downstream of AT2R activation, which may lead to the use of AT2R agonists in NP. However, blockade of AT2R results in analgesia. Furthermore, expression of the RAS in the immune system and a growing appreciation of neuroimmune crosstalk in NP add another layer of complexity and therapeutic potential of targeting this pathway. A growing number of human studies also hint at the analgesic potential of targeting Ang II signaling. Altogether, Ang II receptor signaling represents a promising, far-reaching, and novel strategy to treat NP.

Gene expression profiling of the spinal cord at the chronic pain phase identified CDKL5 as a candidate gene for neural remodeling

BACKGROUND

Chronic pain is a highly refractory and complicated condition that persists even without nociception. Several genome-wide gene expression analyses have shown that the immune response and inflammatory cytokines affect chronic pain establishment in the acute pain phase. However, compared with the acute phase, the chronic phase has a poorly elucidated gene expression profile. This study aimed to determine the gene expression profile in the spinal cord of a neuropathic pain mouse model in the chronic phase to elucidate the chronic pain characteristics.

METHODS

We established a sciatic nerve cuff mouse model as a neuropathic pain model by placing a 2-mm section of a split PE-20 polyethylene tube around the sciatic nerve. The spinal cord was harvested at the L4-6 level at 28 postoperative days. Next, we examined differentially expressed genes (DEGs) through RNA sequencing (RNA-seq) compared with the sham group; moreover, we conducted enrichment analyses of the expressed genes. To reveal the chronic pain characteristics, we compared the gene expression profiles of the spinal cord between the acute and chronic phases in the neuropathic pain model. Among the chronic pain-related genes categorized in the dendrites, we focused on cyclin-dependent kinase-like 5 (CDKL5). We analyzed CDKL5 expression and function using real-time polymerase chain reaction (PCR), immunohistochemistry, and neurite extension assay in Neuro 2a (N2a) cells. We used three types of CDKL5 plasmids: wild type, nuclear localization signal-attached, and K42R kinase-dead CDKL5.

RESULTS

We identified 403 DEGs, including 104 upregulated and 43 downregulated genes (false discovery rate < 0.01). Rather than inflammation or immune response, the most enriched terms in the chronic phase were "regulation of plasma membrane-bounded cell projection organization" and "dendrite." Real-time PCR assay confirmed increased CDKL5 expression in the ipsilateral dorsal horn. CDKL5 was broadly expressed in the ipsilateral dorsal horn across all layers. The neurite extension assay revealed that the cytoplasmic kinase function of CDKL5 was necessary for neurite outgrowth in N2a cells.

CONCLUSION

RNA-seq of the spinal cord revealed that the most enriched genes during the chronic pain phase were involved in regulating axon and dendrite morphogenesis, including CDKL5. Our findings suggest that neural remodeling affects chronic pain establishment. Since patients with CDKL5 mutations have shown reduced pain perception, our findings suggest that CDKL5 in the spinal cord could result in neural remodeling during the chronic pain phase through cytoplasmic kinase activity.

Mir21 modulates inflammation and sensorimotor deficits in cervical myelopathy: data from humans and animal models

Degenerative cervical myelopathy is a common condition resulting from chronic compression of the spinal cord by degenerating structures of the spine. Degenerative cervical myelopathy present a wide range of outcomes, and the biological factors underlying this variability are poorly understood. Previous studies have found elevated MIR21-5p in the sub-acute and chronic neuroinflammatory environment after spinal cord injury. As chronic spinal cord neuroinflammation is a major feature of degenerative cervical myelopathy, we hypothesized that MIR21-5p may be particularly relevant to disease pathobiology, and could serve as a potential biomarker. A prospective cohort study of 69 human degenerative cervical myelopathy patients (36 male:33 female) between the ages of 30 and 78 years was performed to identify the relationship between MIR21-5p expression, symptom severity and treatment outcomes. Results from this study identified a positive correlation between elevated plasma MIR21-5p expression, initial symptom severity and poor treatment outcomes. Subsequent validation of these relationships using a mouse model of degenerative cervical myelopathy identified a similar elevation of MIR21-5p expression at 6 and 12 weeks after onset, corresponding to moderate to severe neurological deficits. To further determine how MIR21-5p affects cervical myelopathy pathobiology, this mouse model was applied to a Mir21 knockout mouse line. Deletion of the Mir21 gene preserved locomotor function on rotarod and forced swim tests, but also resulted in increased nociception based on tail flick, Von Frey filament and electrophysiological testing. Critically, Mir21 knockout mice also had reduced spinal cord inflammation, demonstrated by the reduction of Iba1+ microglia by ∼50% relative to wild-type controls. In vitro experiments using primary microglial cultures confirmed that MIR21-5p expression was greatly increased after exposure to lipopolysaccharide (pro-inflammatory), Il4 (anti-inflammatory) and hypoxia. Mir21 knockout did not appear to alter the ability of microglia to respond to these stimuli, as expression of key pro- and anti-inflammatory response genes was not significantly altered. However, target prediction algorithms identified the IL6/STAT3 pathway as a potential downstream target of MIR21-5p, and subsequent in vitro testing found that expression of components of the IL6 receptor complex, Il6ra and Il6st, were significantly higher in Mir21 knockout microglia. In aggregate, these data show that Mir21 plays a role in the progression of motor deficits and neuroinflammatory modulation in degenerative cervical myelopathy. Given this role in neuroinflammation, and its association with poor patient outcomes, MIR21-5p represents a potential therapeutic target and a new marker for prognostication.

Nonopioid GTS-21 Mitigates Burn Injury Pain in Rats by Decreasing Spinal Cord Inflammatory Responses

BACKGROUND

Burn injury (BI) pain consists of inflammatory and neuropathic components and activates microglia. Nicotinic alpha 7 acetylcholine receptors (α7AChRs) expressed in microglia exhibit immunomodulatory activity during agonist stimulation. Efficacy of selective α7AChR agonist GTS-21 to mitigate BI pain and spinal pain-mediators was tested.

METHODS

Anesthetized rats after hind-paw BI received intraperitoneal GTS-21 or saline daily. Allodynia and hyperalgesia were tested on BI and contralateral paw for 21 days. Another group after BI receiving GTS-21 or saline had lumbar spinal cord segments harvested (day 7 or 14) to quantify spinal inflammatory-pain transducers or microglia activation using fluorescent marker, ionized calcium-binding adaptor protein (Iba1).

RESULTS

BI significantly decreased allodynia withdrawal threshold from baseline of ~9-10 to ~0.5-1 g, and hyperalgesia latency from ~16-17 to ~5-6 seconds by day 1. Both doses of GTS-21 (4 or 8 mg/kg) mitigated burn-induced allodynia from ~0.5-1 to ~2-3 g threshold (P = .089 and P = .010), and hyperalgesia from ~5-6 to 8-9 seconds (P < .001 and P < .001) by day 1. The GTS-21 group recovered to baseline pain threshold by day 15-17 compared to saline-treated, where the exaggerated nociception persisted beyond 15-17 days. BI significantly (P < .01) increased spinal cord microgliosis (identified by fluorescent Iba1 staining), microglia activation (evidenced by the increased inflammatory cytokine), and pain-transducer (protein and/or messenger RNA [mRNA]) expression (tumor necrosis factor-α [TNF-α], interleukin-1β [IL-1β], nuclear factor-kappa B [NF-κB], interleukin-6 [IL-6], Janus-associated kinase signal transducer and activator of transcription 3 [JAK-STAT3], and/or N-methyl-D-aspartate receptor [NMDAR]). GTS-21 mitigated pain-transducer changes. The α7AChR antagonist methyllycaconitine nullified the beneficial effects of GTS-21 on both increased nociception and pain-biomarker expression.

CONCLUSIONS

Nonopioid, α7AChR agonist GTS-21 elicits antinociceptive effects at least in part by decreased activation spinal-cord pain-inducers. The α7AChR agonist GTS-21 holds promise as potential therapeutic adjunct to decrease BI pain by attenuating both microglia changes and expression of exaggerated pain transducers.

Reorganization of synaptic inputs to spinal dorsal horn neurons in neuropathic pain

Peripheral nerve injuries produce a variety of negative structural and functional changes in the central terminal sites of damaged axons, as well as the injured primary afferents. Such changes have been shown to be involved in the development of neuropathic pain, which includes abnormal pain sensations such as allodynia and hyperalgesia. Since the spinal dorsal horn is the first central site where signals from peripheral sensory nerves are transmitted and shows a variety of changes after peripheral nerve injury or chronic inflammation of peripheral tissues, it is one of the most important sites contributing to the mechanisms underlying the development of neuropathic pain. The functional disruption of inhibitory interneurons and glial activation in the spinal dorsal horn after peripheral nerve injury cause reorganization of neuronal circuits and changes in the excitability of second-order neurons. These events are involved in the development or maintenance of neuropathic pain. Here, we describe the interactions of primary afferents, interneurons, and glial cells that may cause reorganization of synaptic inputs to spinal dorsal horn neurons after peripheral nerve injury.

Valproic acid mitigates spinal nerve ligation-induced neuropathic pain in rats by modulating microglial function and inhibiting neuroinflammatory response

Spinal inflammation is a pathophysiological state of neuropathic pain (NP). The subsequent microglial activation and neuroinflammatory response are contributing factors for long-lasting behavioral hypersensitivity. Valproic acid (VPA), a histone deacetylase inhibitor, has promising anti-inflammatory and neuroprotective properties for clinical use in the treatment of neurological disorders. However, the underlying mechanisms of its effects on NP have not been determined. This study aimed to clarify the possible mechanisms by which VPA alleviates NP in rat models induced by spinal nerve ligation (SNL). Intraperitoneal injection of VPA (300 mg/kg) efficiently attenuated mechanical allodynia in rats with NP. VPA exerted anti-inflammatory effects by downregulating proinflammatory cytokines (tumor necrosis factor-α, cytokines interleukin-1β, cytokines interleukin-6; TNF-α, IL-1β, and IL-6) and upregulating anti-inflammatory cytokines (transforming growth factor-β, cytokines interleukin-10, cytokines interleukin-4; TGF-β, IL-10 and IL-4). Additionally, VPA suppressed spinal microgliosis and promoted the polarization of microglia towards the M2 phenotype to further ameliorate spinal neuroinflammation. VPA also exerted neuroprotective effects by decreasing spinal cell apoptosis. The anti-inflammatory and neuroprotective effects may have depended on changes in nuclear histone deacetylase 3 (HDAC3) expression following VPA treatment. Moreover, VPA treatment inhibited nuclear factor-κB (NF-κB) p65 nuclear expression and upregulated acetylated the signal transducer and activator of transcription 1 (STAT1). In addition, VPA suppressed SNL-induced phosphorylation of Janus Kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3). Taken together, our results demonstrate that VPA is a promising anti-inflammatory agent suitable for NP therapy that regulates microglial function and suppresses spinal neuroinflammation via the STAT1/NF-κB and JAK2/STAT3 signaling pathways.

Pharmacology and Mechanism of Action of HSK16149, a Selective Ligand of α2δ Subunit of Voltage-Gated Calcium Channel with Analgesic Activity in Animal Models of Chronic Pain

Chronic pain is a public health problem because current treatments are unsatisfactory with small therapeutic index. Although pregabalin is effective for treating chronic pain, the clinical use is limited because of its side effects. Therefore, improving its therapeutic index is essential. In this study, HSK16149 was found to be a novel ligand of voltage-gated calcium channel (VGCC) α ₂ δ subunit. HSK16149 inhibited [³H]gabapentin binding to the α ₂ δ subunit and was 23 times more potent than pregabalin. In two rat models of neuropathic pain, the minimum effective dose (MED) of HSK16149 was 10 mg/kg, and the efficacy was similar to that of 30 mg/kg pregabalin. Moreover, the efficacy of HSK16149 could persist up to 24 hours postadministration at 30 mg/kg, whereas the efficacy of pregabalin lasted only for 12 hours at 30 mg/kg in streptozotocin-induced diabetic neuropathy model, indicating that HSK16149 might be a longer-acting drug candidate. HSK16149 could also inhibit mechanical allodynia in intermittent cold stress model and decrease phase II pain behaviors in formalin-induced nociception model. In addition, the locomotor activity test showed that the MED of HSK16149 was similar to that of pregabalin, whereas in the Rotarod test, the MEDs of HSK16149 and pregabalin were 100 and 30 mg/kg, respectively. These findings indicated that HSK16149 might have a better safety profile on the central nervous system. In summary, HSK16149 is a potent ligand of VGCC α ₂ δ subunit with a better therapeutic index than pregabalin. Hence, it could be an effective and safe drug candidate for treating chronic pain. SIGNIFICANCE STATEMENT: As a novel potent ligand of voltage-gated calcium channel α ₂ δ subunit, HSK16149 has the potential to be an effective and safe drug candidate for the treatment of chronic pain.

LncRNA KCNA2-AS regulates spinal astrocyte activation through STAT3 to affect postherpetic neuralgia

Objectives

Postherpetic neuralgia (PHN) is the most common complication of herpes zoster, but the mechanism of PHN is still unclear. Activation of spinal astrocytes is involved in PHN. Our study aims to explore whether lncRNA KCNA2 antisense RNA (KCNA2-AS) regulates spinal astrocytes in PHN through signal transducers and activators of transcription 3 (STAT3).

Methods

Varicella zoster virus (VZV)-infected CV-1 cells were injected into rats to construct a PHN model. Primary spinal cord astrocytes were activated using S-Nitrosoglutathione (GSNO). Glial fibrillary acidic protein (GFAP; marker of astrocyte activation), phosphorylated STAT3 (pSTAT3), and KCNA2-AS were analyzed by immunofluorescence and RNA fluorescence in situ hybridization. RNA pull-down and RNA immunoprecipitation were used to detect binding of KCNA2-AS to pSTAT3.

Results

KCNA2-AS was highly expressed in the spinal cord tissue of PHN model rats, and was positively correlated with GFAP expression. GFAP was significantly increased in GSNO-induced cells, but the knockdown of KCNA2-AS reversed this result. Meanwhile, pSTAT3 was significantly increased in GSNO-induced cells, but knockdown of KCNA2-AS reduced pSTAT3 within the nucleus while the total pSTAT3 did not change significantly. pSTAT3 bound to KCNA2-AS and this binding increased with GSNO treatment. Furthermore, knockdown of KCNA2-AS in PHN model rats relieved mechanical allodynia.

Conclusion

Down-regulation of KCNA2-AS alleviates PHN partly by reducing the translocation of pSTAT3 cytoplasm to the nucleus and then inhibiting the activation of spinal astrocytes.

Neuroinflammation, oxidative stress and their interplay in neuropathic pain: Focus on specialized pro-resolving mediators and NADPH oxidase inhibitors as potential therapeutic strategies

Neuropathic pain (NP) is a chronic condition that results from a lesion or disease of the nervous system, greatly impacting patients' quality of life. Current pharmacotherapy options deliver inadequate and/or insufficient responses and thus a significant unmet clinical need remains for alternative treatments in NP. Neuroinflammation, oxidative stress and their reciprocal relationship are critically involved in NP pathophysiology. In this context, new pharmacological approaches, aiming at enhancing the resolution phase of inflammation and/or restoring redox balance by targeting specific reactive oxygen species (ROS) sources, are emerging as potential therapeutic strategies for NP, with improved efficacy and safety profiles. Several reports have demonstrated that administration of exogenous specialized pro-resolving mediators (SPMs) ameliorates NP pathophysiology. Likewise, deletion or inhibition of the ROS-generating enzyme NADPH oxidase (NOX), particularly its isoforms 2 and 4, results in beneficial effects in NP models. Notably, SPMs also modulate oxidative stress and NOX also regulates neuroinflammation. By targeting neuroinflammatory and oxidative pathways, both SPMs analogues and isoform-specific NOX inhibitors are promising therapeutic strategies for NP.

Mechanical pain of the lower extremity after compression of the upper spinal cord involves signal transducer and activator of transcription 3-dependent reactive astrocytes and interleukin-6

Chronic pain is one of the main symptoms of spinal disorders such as spinal canal stenosis. A major cause of this pain is related to compression of the spinal cord, and chronic pain can develop at the level of the compressed spinal segment. However, in many patients chronic pain arises in an area that does not correspond to the compressed segment, and the underlying mechanism involved remains unknown. This was investigated in the present study using a mouse model of spinal cord compression in which mechanical pain of the hindpaws develops after compression of the first lumbar segment (L1) of the spinal cord. Compression induced the activation of astrocytes in the L1 spinal dorsal horn (SDH)-but not the L4 SDH that corresponds to the hindpaws-and activated signal transducer and activator of transcription 3 (STAT3). Suppressing reactive astrocytes by expressing a dominant negative form of STAT3 (dnSTAT3) in the compressed SDH prevented mechanical pain. Expression of interleukin (IL)-6 was also upregulated in the compressed SDH, and it was inhibited by astrocytic expression of dnSTAT3. Intrathecal administration of a neutralizing anti-IL-6 antibody reversed the compression-induced mechanical pain. These results suggest that astrocytic STAT3 and IL-6 in the compressed SDH are involved in remote mechanical pain observed in the lower extremity, and may provide a target for treating chronic pain associated with spinal cord compression such as spinal canal stenosis.

Acupuncture attenuates the development of diabetic peripheral neuralgia by regulating P2X4 expression and inflammation in rat spinal microglia

Diabetic peripheral neuropathy (DPN) is a chronic microvascular complication of diabetes. The purpose of this study is to find the underlying mechanism for the effects of acupuncture in DPN rats. Rats were rendered diabetic with a single injection of 35 mg/kg streptozotocin (STZ). These STZ-diabetic rats were treated with acupuncture for 20 min once daily. The therapeutic efficacy of acupuncture was assessed using mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) evaluations. After 14 days treatment, acupuncture markedly reduced the pathological injury in STZ-diabetic rats. Moreover, it significantly down-regulated P2X4 and OX42 expression along with the reduced levels of inflammatory factors (CXCR3, TNF-α, IL-1β, IL-6), GSP and lipid metabolisms in the spinal cord of the DPN rats. Acupuncture could relieve DPN in rats by regulating P2X4 expression and inflammation in spinal microglia.

Role of reactive astrocytes in the spinal dorsal horn under chronic itch conditions

Astrocytes are the most abundant glial cells in the central nervous system (CNS), including the spinal cord. Neuronal damage induces astrocytes to become reactive and contribute to various CNS pathologies. Recent studies have demonstrated that astrocytes in the spinal dorsal horn (SDH) become reactive in a transcription factor signal transducer and activator of transcription 3-dependent manner without neuronal damage under chronic itch conditions, causing release of the factor lipocalin-2, leading to induction of sensitization of gastrin releasing peptide-induced chemical itch signaling in the SDH. In this review, we describe recent advances in our understanding of SDH neuronal pathways for itch transmission, the mechanisms of SDH astrocytic activation and its contribution to abnormal itch processing and discuss the role of reactive astrocytes in the SDH in abnormal sensory processing under chronic itch conditions.

The CB2 Agonist β-Caryophyllene in Male and Female Rats Exposed to a Model of Persistent Inflammatory Pain

Cannabinoids help in pain treatment through their action on CB1 and CB2 receptors. β-caryophyllene (BCP), an ancient remedy to treat pain, is a sesquiterpene found in large amounts in the essential oils of various spice and food plants such as oregano, cinnamon, and black pepper. It binds to the CB2 receptor, acting as a full agonist. Sex differences in the BCP-induced analgesic effect were studied by exposing male and female rats to a persistent/repeated painful stimulation. To simulate treatment of a repeated inflammatory condition, after the first formalin injection (FT1; 50 μl, 2.5%), rats received BCP per os for 7 days at two dosages: 5 and 10 mg/kg dissolved in olive oil (OIL). The control group was treated with OIL for 7 days. On day 8, the formalin test was repeated (FT2) with a lower formalin concentration (50 μl, 1%). During the first and second formalin tests, pain-induced responses (licking, flexing, and paw jerk) and spontaneous behaviors were recorded and analyzed. In the FT1 (before the beginning of treatment with BCP), females displayed higher pain responses than did males in terms of flexing duration during the first part of the test (I phase and interphase), while during the second part (II phase early and late) males showed higher levels than did females in licking duration. In the FT2, the pain responses generally decreased in the BCP groups in a dose-dependent manner (i.e., greater effect of BCP10), with a more pronounced reduction in males than in females; moreover, the pain responses remained high in the OIL groups and in the female BCP5 group. In conclusion, long-term intake of BCP appears to be able to decrease pain behaviors in a model of repeated inflammatory pain in both sexes, but to a greater degree in males.

Gut microbiota regulates neuropathic pain: potential mechanisms and therapeutic strategy

Neuropathic pain (NP) is a sustained and nonreversible condition characterized by long-term devastating physical and psychological damage. Therefore, it is urgent to identify an effective treatment for NP. Unfortunately, the precise pathogenesis of NP has not been elucidated. Currently, the microbiota-gut-brain axis has drawn increasing attention, and the emerging role of gut microbiota is investigated in numerous diseases including NP. Gut microbiota is considered as a pivotal regulator in immune, neural, endocrine, and metabolic signaling pathways, which participates in forming a complex network to affect the development of NP directly or indirectly. In this review, we conclude the current understanding of preclinical and clinical findings regarding the role of gut microbiota in NP and provide a novel therapeutic method for pain relief by medication and dietary interventions.

The lncRNA H19 binding to let-7b promotes hippocampal glial cell activation and epileptic seizures by targeting Stat3 in a rat model of temporal lobe epilepsy

Objectives

Glial cell activation contributes to the inflammatory response and occurrence of epilepsy. Our preliminary study demonstrated that the long non‐coding RNA, H19, promotes hippocampal glial cell activation during epileptogenesis. However, the precise mechanisms underlying this effect remain unclear.

Materials and methods

H19 and let‐7b were overexpressed or silenced using an adeno‐associated viral vector in vivo. Their expression in a kainic acid‐induced epilepsy model was evaluated by real‐time quantitative PCR, fluorescence in situ hybridization, and cytoplasmic and nuclear RNA isolation. A dual‐luciferase reporter assay was used to evaluate the direct binding of let‐7b to its target genes and H19. Western blot, video camera monitoring and Morris water maze were performed to confirm the role of H19 and let7b on epileptogenesis.

Results

H19 was increased in rat hippocampus neurons after status epilepticus, which might be due to epileptic seizure‐induced hypoxia. Increased H19 aggravated the epileptic seizures, memory impairment and mossy fibre sprouting of the epileptic rats. H19 could competitively bind to let‐7b to suppress its expression. Overexpression of let‐7b inhibited hippocampal glial cell activation, inflammatory response and epileptic seizures by targeting Stat3. Moreover, overexpressed H19 reversed the inhibitory effect of let‐7b on glial cell activation.

Conclusions

LncRNA H19 could competitively bind to let‐7b to promote hippocampal glial cell activation and epileptic seizures by targeting Stat3 in a rat model of temporal lobe epilepsy.

Mechanisms Involved in Superiority of Angiotensin Receptor Blockade over ACE Inhibition in Attenuating Neuropathic Pain Induced in Rats

Although previous reports described the beneficial role of angiotensin-converting enzyme inhibitors (ACE-Is) or AT1 receptor blockers (ARBs) in attenuating neuropathic pain (NP), no study has yet explored the exact underlying mechanisms, as well as the superiority of using centrally versus peripherally acting renin-angiotensin-aldosterone system (RAAS) drugs in NP. We investigated the effects of 14 days of treatment with centrally (telmisartan and ramipril) or peripherally (losartan and enalapril) acting ARBs and ACE-Is, respectively, in attenuating peripheral NP induced by sciatic nerve chronic constriction injury (CCI) in rats. We also compared these with the effects of pregabalin, the standard treatment for NP. Behavioral changes, inflammatory markers (NFкB, TNF-α, COX-2, PGE2, and bradykinin), oxidative stress markers (NADPH oxidase and catalase), STAT3 activation, levels of phosphorylated P38-MAPK, ACE, AT1 receptor (AT1R), and AT2 receptor (AT2R), as well as histopathological features, were assessed in the brainstem and sciatic nerve. CCI resulted in clear pain-related behavior along with increased levels of inflammatory and oxidative stress markers, and STAT3 activity, as well as increased levels of phosphorylated P38-MAPK, ACE, AT1R, and AT2R, along with worsened histopathological findings in both the brainstem and sciatic nerve. ARBs improved both animal behavior and all measured parameters in CCI rats and were more effective than ACE-Is. At the tested doses, centrally acting ARBs or ACE-Is were not superior to the peripherally acting drugs of the same category. These findings suggest that ARBs (centrally or peripherally acting) are an effective treatment modality for NP.