Long noncoding RNA small nucleolar RNA host gene 5 facilitates neuropathic pain in spinal nerve injury by promoting SCN9A expression via CDK9.

This study aims to explore the functions and mechanisms of long noncoding RNA small nucleolar RNA host gene 5 (SNHG5) in chronic constriction injury (CCI)-induced neuropathic pain (NP). An NP rat model was established using the CCI method and the NP severity was evaluated by paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). The expression of SNHG5, CDK9, and SCN9A was quantified in rat dorsal root ganglion, in addition to the detections of apoptosis, pathological changes, neuron number, and the co-localization of Nav1.7 and cleaved caspase-3 with NeuN. In ND7/23 cells, the apoptosis and lactate dehydrogenase concentration were assessed, as well as the relationship between SNHG5, CDK9, and SCN9A. In the dorsal root ganglion of CCI-treated rats, SNHG5 and SCN9A were upregulated and downregulation of SNHG5 suppressed SCN9A expression, increased the PWT and PWL, blocked neuroinflammation and neuronal apoptosis, and alleviated NP. Mechanistically, SNHG5 recruited CDK9 to enhance SCN9A-encoded Nav1.7 expression and promoted peripheral neuronal apoptosis and injury. In addition, SCN9A overexpression nullified the alleviative effects of SNHG5 deficiency on NP and neuron loss in CCI rats. In conclusion, SNHG5 promotes SCN9A-encoded Nav1.7 expression by recruiting CDK9, thereby facilitating neuron loss and NP after spinal nerve injury, which may offer a promising target for the management of NP.

Metformin Alleviates Pain States by Regulating the Balance of Spinal Synaptic Transmission.

BACKGROUND: Metformin has been shown to have potent analgesic effects; however, the underlying mechanism of synaptic plasticity mediating analgesia remained ambiguous. METHODS: In this study, animal behavioral tests, whole-cell patch­clamp recording, immunofluorescence staining, and network pharmacology techniques were applied to elucidate the mechanisms and potential targets of metformin-induced analgesia. RESULTS: Single or consecutive injections of metformin significantly inhibited spinal nerve ligation (SNL)-induced neuropathic pain, and formalin-induced acute inflammatory pain. Network pharmacology analysis of metformin action targets in pain database-related targets revealed 25 targets, including five hub targets (nitric oxide synthase 1 (NOS1), NOS2, NOS3, epidermal growth factor receptor (EGFR), and plasminogen (PLG)). Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that metformin-induced analgesia was markedly correlated with calcium signaling and synaptic transmission. Intrathecal injection of metformin significantly reversed nerve injury-induced c-Fos (neural activity biomarker) mRNA and protein expression in neuropathic rats by regulating NOS2 expression. In addition, whole-cell recordings of isolated spinal neurons demonstrated that metformin dose-dependently inhibited the enhanced frequency and amplitude of miniature excitatory synaptic currents (mEPSCs) but did not affect those of miniature inhibitory synaptic currents (mIPSCs) in neuropathic pain. CONCLUSIONS: This study further demonstrated that metformin might inhibit spinal glutamatergic transmission and abnormal nociceptive circuit transduction by monitoring synaptic transmission in pain. Results of this work provide an in-depth understanding of metformin analgesia via synaptic plasticity.

Tibetan medicine Ruyi Zhenbao Pill ameliorates neuropathic pain by inhibiting the CXCL10-CXCR3 pathway in spinal cord of spinal nerve ligation model.

ETHNOPHARMACOLOGICAL RELEVANCE: Ruyi Zhenbao Pill (RYZBP) is a traditional Tibetan medicine that has been used for over 300 years in China to treat neurological diseases, specifically neuropathic pain (NP). However, its characteristics and mechanism of action in treating NP remains unclear. AIM OF THE STUDY: Based on animal experiments and transcriptomics to evaluate the characteristics and mechanism of RYZBP in treating NP. METHODS: Mice were divided into six groups using random assignment: sham-operation group, spinal nerve ligation (SNL) group, RYZBP low (0.65 g kg-1), medium (1.30 g kg-1), high (2.60 g kg-1) doses groups, and positive drug pregabalin (PGB, 0.05 g kg-1) group. Mice received intragastrical administered for 14 consecutive days. SNL and intrathecal injection models were employed. The analgesic effects were assessed using the Von Frey test, Acetone test, and Hot Plate test. L5 spinal dorsal horns were collected for transcriptomics on day 15. The potential signaling pathways and Hub genes of RYZBP to ameliorate NP were obtained through transcriptomics and network pharmacology. Molecular docking was utilized to evaluate the binding ability of candidate active ingredients with the Hub genes. Finally, western blot (WB) and immunofluorescence (IF) were used to validate the predicted targets. RESULTS: RYZBP demonstrated a dose-dependent alleviation of mechanical allodynia, cold and heat stimulus-induced pain in SNL mice. Transcriptomics analysis identified 24 differentially expressed genes, and pathway enrichment analysis revealed that the CXCL10-CXCR3 signal axis may be the primary biological pathway through which RYZBP relieve NP. Molecular docking test indicated that the active ingredient in RYZBP exhibit a strong affinity for the target protein CXCL10. WB and IF tests showed that RYZBP can significantly inhibit CXCL10 and CXCR3 and its downstream molecules expression in the spinal dorsal horn of SNL mice. Additionally, intrathecal injection of rmCXCL10 worsened pain hypersensitivity, while RYZBP was able to suppress the pain hypersensitivity response induced by rmCXCL10 and reduce the expression levels of CXCL10 and CXCR3 and its downstream molecules. CONCLUSION: RYZBP had a significant analgesic effect on NP model, and this effect may be related to inhibiting the CXCL10-CXCR3 pathway in the spinal dorsal horn.

HSP27 Modulates Neuropathic Pain by Inhibiting P2X3 Degradation.

The role of heat shock protein 27 (HSP27), a chaperone, in neuropathic pain after nerve injury has not been systematically surveyed despite its neuroprotective and regeneration-promoting effects. In this study, we found that HSP27 expression in sensory neurons of the dorsal root ganglia (DRG) mediated nerve injury-induced neuropathic pain. Neuropathic pain behaviors were alleviated by silencing HSP27 in the DRG of a rat spinal nerve ligation (SNL) model. Local injection of an HSP27-overexpression construct into the DRG of naïve rats elicited neuropathic pain behaviors. HSP27 interacted with a purinergic receptor, P2X3, and their expression patterns corroborated the induction and reversal of neuropathic pain according to two lines of evidence: colocalization immunohistochemically and immunoprecipitation biochemically. In a cell model cotransfected with HSP27 and P2X3, the degradation rate of P2X3 was reduced in the presence of HSP27. Such an alteration was mediated by reducing P2X3 ubiquitination in SNL rats and was reversed after silencing HSP27 in the DRGs of SNL rats. In summary, the interaction of HSP27 with P2X3 provides a new mechanism of injury-induced neuropathic pain that could serve as an alternative therapeutic target.

Switching Rat Resident Macrophages from M1 to M2 Phenotype by Iba1 Silencing Has Analgesic Effects in SNL-Induced Neuropathic Pain.

Resident macrophages from dorsal root ganglia are important for the development of traumatic-induced neuropathic pain. In the first 5-7 days after a traumatic sciatic nerve injury (i.e., spinal nerve ligation (SNL), spared nerve injury (SNI), sciatic nerve transection or sciatic nerve ligation and transection), Ionized binding adapter protein 1 (Iba1) (+) resident macrophages cluster around dorsal root ganglia neurons, possibly contributing to nerve injury-induced hypersensitivity. Since infiltrating macrophages gradually recruited to the lesion site peak at about 7 days, the first few days post-lesion offer a window of opportunity when the contribution of Iba1 (+) resident macrophages to neuropathic pain pathogenesis could be investigated. Iba1 is an actin cross-linking cytoskeleton protein, specifically located only in macrophages and microglia. In this study, we explored the contribution of rat Iba1 (+) macrophages in SNL-induced neuropathic pain by using intra-ganglionic injections of naked Iba1-siRNA, delivered at the time the lesion occurred. The results show that 5 days after Iba1 silencing, Iba1 (+) resident macrophages are switched from an M1 (pro-inflammatory) phenotype to an M2 (anti-inflammatory) phenotype, which was confirmed by a significant decrease of M1 markers (CD32 and CD86), a significant increase of M2 markers (CD163 and Arginase-1), a reduced secretion of pro-inflammatory cytokines (IL-6, TNF-α and IL-1ß) and an increased release of pro-regenerative factors (BDNF, NGF and NT-3) which initiated the regrowth of adult DRG neurites and reduced SNL-induced neuropathic pain. Our data show for the first time, that it is possible to induce macrophages towards an anti-inflammatory phenotype by interacting with their cytoskeleton.

Turmeric Bioactive Compounds Alleviate Spinal Nerve Ligation-Induced Neuropathic Pain by Suppressing Glial Activation and Improving Mitochondrial Function in Spinal Cord and Amygdala.

This study examined the effects of turmeric bioactive compounds, curcumin C3 complex® (CUR) and bisdemethoxycurcumin (BDMC), on mechanical hypersensitivity and the gene expression of markers for glial activation, mitochondrial function, and oxidative stress in the spinal cord and amygdala of rats with neuropathic pain (NP). Twenty-four animals were randomly assigned to four groups: sham, spinal nerve ligation (SNL, an NP model), SNL+100 mg CUR/kg BW p.o., and SNL+50 mg BDMC/kg BW p.o. for 4 weeks. Mechanical hypersensitivity was assessed by the von Frey test (VFT) weekly. The lumbosacral section of the spinal cord and the right amygdala (central nucleus) were collected to determine the mRNA expression of genes (IBA-1, CD11b, GFAP, MFN1, DRP1, FIS1, PGC1α, PINK, Complex I, TLR4, and SOD1) utilizing qRT-PCR. Increased mechanical hypersensitivity and increased gene expression of markers for microglial activation (IBA-1 in the amygdala and CD11b in the spinal cord), astrocyte activation (GFAP in the spinal cord), mitochondrial dysfunction (PGC1α in the amygdala), and oxidative stress (TLR4 in the spinal cord and amygdala) were found in untreated SNL rats. Oral administration of CUR and BDMC significantly decreased mechanical hypersensitivity. CUR decreased CD11b and GFAP gene expression in the spinal cord. BDMC decreased IBA-1 in the spinal cord and amygdala as well as CD11b and GFAP in the spinal cord. Both CUR and BDMC reduced PGC1α gene expression in the amygdala, PINK1 gene expression in the spinal cord, and TLR4 in the spinal cord and amygdala, while they increased Complex I and SOD1 gene expression in the spinal cord. CUR and BDMC administration decreased mechanical hypersensitivity in NP by mitigating glial activation, oxidative stress, and mitochondrial dysfunction.

Mitochondrial transplantation attenuates traumatic neuropathic pain, neuroinflammation, and apoptosis in rats with nerve root ligation.

Traumatic neuropathic pain (TNP) is caused by traumatic damage to the somatosensory system and induces the presentation of allodynia and hyperalgesia. Mitochondrial dysfunction, neuroinflammation, and apoptosis are hallmarks in the pathogenesis of TNP. Recently, mitochondria-based therapy has emerged as a potential therapeutic intervention for diseases related to mitochondrial dysfunction. However, the therapeutic effectiveness of mitochondrial transplantation (MT) on TNP has rarely been investigated. Here, we validated the efficacy of MT in treating TNP. Both in vivo and in vitro TNP models by conducting an L5 spinal nerve ligation in rats and exposing the primary dorsal root ganglion (DRG) neurons to capsaicin, respectively, were applied in this study. The MT was operated by administrating 100 µg of soleus-derived allogeneic mitochondria into the ipsilateral L5 DRG in vivo and the culture medium in vitro. Results showed that the viable transplanted mitochondria migrated into the rats' spinal cord and sciatic nerve. MT alleviated the nerve ligation-induced mechanical and thermal pain hypersensitivity. The nerve ligation-induced glial activation and the expression of pro-inflammatory cytokines and apoptotic markers in the spinal cord were also repressed by MT. Consistently, exogenous mitochondria reversed the capsaicin-induced reduction of mitochondrial membrane potential and expression of pro-inflammatory cytokines and apoptotic markers in the primary DRG neurons in vitro. Our findings suggest that MT mitigates the spinal nerve ligation-induced apoptosis and neuroinflammation, potentially playing a role in providing neuroprotection against TNP.

Electroacupuncture inhibits dendritic spine remodeling through the srGAP3-Rac1 signaling pathway in rats with SNL.

Previous studies have shown that peripheral nerve injury can lead to abnormal dendritic spine remodeling in spinal dorsal horn neurons. Inhibition of abnormal dendritic spine remodeling can relieve neuropathic pain. Electroacupuncture (EA) has a beneficial effect on the treatment of neuropathic pain, but the specific mechanism remains unclear. Evidence has shown that slit-robo GTPase activating protein 3 (srGAP3) and Rho GTPase (Rac1) play very important roles in dendritic spine remodeling. Here, we used srGAP3 siRNA and Rac1 activator CN04 to confirm the relationship between SrGAP3 and Rac1 and their roles in improving neuropathic pain with EA. Spinal nerve ligation (SNL) was used as the experimental model, and thermal withdrawal latency (TWL), mechanical withdrawal threshold (MWT), Western blotting, immunohistochemistry and Golgi-Cox staining were used to examine changes in behavioral performance, protein expression and dendritic spines. More dendritic spines and higher expression levels of srGAP3 were found in the initial phase of neuropathic pain. During the maintenance phase, dendritic spines were more mature, which was consistent with lower expression levels of srGAP3 and higher expression levels of Rac1-GTP. EA during the maintenance phase reduced the density and maturity of dendritic spines of rats with SNL, increased the levels of srGAP3 and reduced the levels of Rac1-GTP, while srGAP3 siRNA and CN04 reversed the therapeutic effects of EA. These results suggest that dendritic spines have different manifestations in different stages of neuropathic pain and that EA may inhibit the abnormal dendritic spine remodeling by regulating the srGAP3/Rac1 signaling pathway to alleviate neuropathic pain.

The Novel Gabapentinoid Mirogabalin Prevents Upregulation of α2δ-1 Subunit of Voltage-Gated Calcium Channels in Spinal Dorsal Horn in a Rat Model of Spinal Nerve Ligation.

Gabapentinoids are specific ligands for the α2δ-1 subunit of voltage-gated calcium channels. This class of drugs, including gabapentin and pregabalin, exert various pharmacological effects and are widely used for the treatment of epilepsy, anxiety, and chronic pain. The mechanism of action of gabapentinoids involves both direct modulation of calcium channel kinetics and inhibition of channel trafficking and expression, which contribute to the above pharmacological effects. In the present study, we investigated the effects of mirogabalin, a novel potent gabapentinoid, on expression levels of the α2δ-1 subunit in the spinal dorsal horn in a rat model of spinal nerve ligation (SNL) as an experimental animal model for peripheral neuropathic pain. The neuropathic pain state was induced by SNL in male Sprague - Dawley rats. After the development of mechanical hypersensitivity, the animals received 10 mg/kg mirogabalin or vehicle orally for 5 consecutive days and were subjected to immunohistochemical analysis of α2δ-1 subunit expression in the spinal cord. In the SNL model rats, expression of the α2δ-1 subunit significantly increased in the spinal dorsal horn at the ipsilateral side of nerve injury, while mirogabalin inhibited this increase. In conclusion, the α2δ-1 subunit was upregulated in the spinal dorsal horn of SNL model rats, and repeated administration of mirogabalin inhibited this upregulation. The inhibitory effect of mirogabalin on upregulation of the α2δ-1 subunit after nerve injury is considered to contribute to its analgesic effects in peripheral neuropathic pain.

Effect and underlying mechanisms of spirocyclopiperazinium salt compound DXL-A-24 in rats following spinal nerve ligation.

PURPOSE: Neuropathic pain represents a significant public health problem and its effective management remains a challenge. The present study is designed to evaluate the analgesic effect of the spirocyclopiperazinium salt compound DXL-A-24 in spinal nerve ligation (SNL) model, and further to explore the possible molecular mechanisms. METHODS: SNL model was established on rats, and mechanical allodynia and thermal hyperalgesia were estimated with the von Frey and hot plate tests; the expression of CaMKIIα, CREB, JAK2, STAT3 and c-fos was determined by western blotting; the protein level of TNF-α was analysed by ELISA; the mRNA expression of TNF-α and c-fos was detected using qRT-PCR analysis and the receptor blocking test was used for target searching. RESULTS: Administration of DXL-A-24 (1, 0.5, 0.25 mg/kg, i.g.) obviously relieved SNL-induced mechanical allodynia and thermal hyperalgesia in rats (P < 0.01), with the percentage of pain threshold elevation (PTE%) was 103 %, 68 % and 47 %, respectively, in mechanical allodynia; the percentage of maximal possible effect (MPE%) was 56 %, 34 % and 21 %, respectively, in thermal hyperalgesia on day 7 after SNL. Pretreatment with peripheral α7 nicotinic or M4 muscarinic receptor antagonist, the effect of DXL-A-24 was completely blocked (P > 0.05). DXL-A-24 significantly reduced the upregulated pCaMKIIα, pCREB, pJAK2, pSTAT3 and TNF-α protein (P < 0.01), which could be blocked by α7 nicotinic receptor or M4 muscarinic receptor antagonist. In addition, administration of DXL-A-24 attenuated the mRNA and protein expression of c-fos and TNF-α mRNA in DRG of SNL rat. We did not observe significant acute toxicity and chronic hepatorenal impairment at effective dose and high dose. CONCLUSIONS: We report firstly that administration of DXL-A-24 displays obvious antineuropathic pain effects in SNL rats. The underlying mechanism may involve the reduction of the CaMKIIα/CREB and JAK2/STAT3 signalling pathways, and the suppression of TNF-α and c-fos expression, which may be mediated by activating peripheral α7 nicotinic and M4 muscarinic receptors. This study may provide a new perspective for developing new antineuralgic drug.

Radiocaine: An Imaging Marker of Neuropathic Injury.

Voltage-gated sodium channels (Navs) play a crucial electrical signaling role in neurons. Nav-isoforms present in peripheral sensory neurons and dorsal root ganglia of the spinal cord are critically involved in pain perception and transmission. While these isoforms, particularly Nav1.7, are implicated in neuropathic pain disorders, changes in the functional state and expression levels of these channels have not been extensively studied in vivo. Radiocaine, a fluorine-18 radiotracer based on the local anesthetic lidocaine, a non-selective Nav blocker, has previously been used for cardiac Nav1.5 imaging using positron-emission tomography (PET). In the present study, we used Radiocaine to visualize changes in neuronal Nav expression after neuropathic injury. In rats that underwent unilateral spinal nerve ligation, PET/MR imaging demonstrated significantly higher uptake of Radiocaine into the injured sciatic nerve, as compared to the uninjured sciatic nerve, for up to 32 days post-surgery. Radiocaine, due to its high translational potential, may serve as a novel diagnostic tool for neuropathic pain conditions using PET imaging.

Downregulation of Sp1 Inhibits the Expression of HDAC1/SOX10 to Alleviate Neuropathic Pain-like Behaviors after Spinal Nerve Ligation in Mice.

Specific protein 1 (Sp1) is a member of the Sp/Kruppel-like factor family, which regulates cellular processes of neurons in the nervous system. This study was performed to examine the regulatory role and the underlying mechanism of transcription factor Sp1 in neuropathic pain (NP)-like behaviors after spinal nerve ligation (SNL). Sp1 and histone deacetylase 1(HDAC1) expressions were determined in the C57BL6 mouse model with NP-like behaviors after SNL, which demonstrated that Sp1 and HDAC1 elevation occurred in neurons in the spinal dorsal horn of SNL mice. The chromatin immunoprecipitation assay verified that Sp1 was bound to the HDAC1 promoter region and HDAC1 to the SRY-box-containing gene 10 (SOX10) promoter region in the spinal dorsal horn. Immunofluorescence was performed to determine Sp1, HDAC1, and SOX10 in the spinal dorsal horn neurons as well as the neuronal marker (NeuN), microglial marker (Iba-1), and astrocyte marker (GFAP). The nociceptive test was performed to characterize the hindlimb paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) of mice 0-10 days after model establishment. Loss- and gain-of-function assays revealed that Sp1 promoted HDAC1 expression, and HDAC1 in turn promoted SOX10 expression. HDAC1 elevation reversed the effects of Sp1 silencing, and the increased PWT and PWL of SNL mice were negated after SOX10 overexpression. Meanwhile, SOX10 also restored the results by Sp1 knockdown. Collectively, downregulating Sp1 alleviates NP-like behaviors after SNL via the HDAC1/SOX10 axis.

MicroRNA-489-3p attenuates neuropathic allodynia by regulating oncoprotein DEK/TET1-dependent epigenetic modification in the dorsal horn.

Originally characterized as an oncoprotein overexpressed in many forms of cancer that participates in numerous cellular pathways, DEK has since been well described regarding the regulation of epigenetic markers and transcription factors in neurons. However, its role in neuropathic allodynia processes remain elusive and intriguingly complex. Here, we show that DEK, which is induced in spinal dorsal horn neurons after spinal nerve ligation (SNL), is regulated by miR-489-3p. Moreover, SNL-induced decrease in miR-489-3p expression increased the expression of DEK, which recruited TET1 to the promoter fragments of the Bdnf, Grm5, and Stat3 genes, thereby enhancing their transcription in the dorsal horn. Remarkably, these effects were also induced by intrathecally administering naïve animals with miR-489-3p inhibitor, which could be inhibited by knockdown of TET1 siRNA or DEK siRNA. Conversely, delivery of intrathecal miR-489-3p-mimic into SNL rats attenuated allodynia behavior and reversed protein expression coupled to the promoter segments in the dorsal horn. Thus, a spinal miR-489-3p/DEK/TET1 transcriptional axis may contribute to neuropathic allodynia. These results may provide a new target for treating neuropathic allodynia.

Electroacupuncture suppresses spinal nerve ligation-induced neuropathic pain via regulation of synaptic plasticity through upregulation of basic fibroblast growth factor expression.

BACKGROUND: Improving synaptic plasticity is a good way to alleviate neuropathic pain. Electroacupuncture (EA) is currently used worldwide to treat this disease, but its specific mechanisms of action need further investigation. Evidence has suggested that basic fibroblast growth factor (bFGF) plays an important role in promoting nerve regeneration and can promote the expression of vascular endothelial growth factor (VEGF). OBJECTIVE: In this study, we examined the effects of EA on synaptic plasticity and its underlying mechanism. METHODS: A spinal nerve ligation (SNL) rat model was established. NSC37204 (a specific inhibitor of bFGF) was used to determine the relationship between bFGF and putative EA-mediated improvements in synaptic plasticity. Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were assessed to evaluate hyperalgesia in rats with SNL. Tissue morphology was detected by hematoxylin-eosin (HE) and Nissl staining, while neural plasticity and its molecular mechanisms were examined by Western blotting, quantitative real-time polymerase chain reaction (qPCR), dual-label immunohistochemistry and transmission electron microscopy. RESULTS: We found that EA improved synaptic plasticity, consistent with higher levels of expression of bFGF and VEGF. Contrary to the beneficial effects of EA, NSC37204 promoted synaptic reconstruction. Furthermore, EA-induced improvements in the neurobehavioral state and improved synaptic plasticity were blocked by NSC37204, consistent with lower expression levels of bFGF and VEGF. CONCLUSION: These findings indicate that EA suppresses SNL-induced neuropathic pain by improving synaptic plasticity via upregulation of bFGF expression.

Effect of surgical damage to spinal nerve on dorsal-root ganglion gene expressions: Comprehensive analysis of differentially expressed genes.

BACKGROUND: Neuropathic pain can cause significant physical and economic burden, and there are no effective long-term treatments. We conducted a bioinformatics analysis to identify mechanisms to determine strategies for more effective treatments of neuropathic pain. METHOD: GSE24982 and GSE63442 microarray datasets were extracted from the Gene Expression Omnibus database to analyze transcriptome differences of neuropathic pain in the dorsal root ganglions (DRGs). We filtered the differentially expressed genes (DEGs) in the two datasets and conducted Gene Ontology (GO) functional analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of the shared DEGs. The Protein-Protein Interaction network was used to determine the hub genes, which were verified in the GSE30691 dataset. miRDB and miRWalk Databases were used to predict potential miRNA of the selected DEGs. We made the spinal nerve ligation (SNL) rat model and qPCR was used to verify the differential expression of hub genes. RESULTS: A total of 182 overlapped DEGs were found between GSE24982 and GSE63442 datasets. The GO and KEGG analysis showed that the selected DEGs were enriched in infection, transmembrane transport of ion channels, and synaptic transmission. We identified seven hub genes (Atf3, Aif1, Ctss, Gfap, Scg2, Jun, and Vgf). qPCR verified the expression differences of the hub genes in the DRGs after SNL model. Predicted miRNA targeting each selected hub genes were identified. CONCLUSIONS: Seven hub genes related to the pathogenesis of neuropathic pain and potential targeting miRNA were identified, expanding understanding of the mechanism of neuropathic pain and facilitating treatment development.

Akt/Aquaporin-4 Signaling Aggravates Neuropathic Pain by Activating Astrocytes after Spinal Nerve Ligation in Rats.

Aquaporins (AQPs) play critical physiological roles in water balance in the central nervous system (CNS). Aquaporin-4 (AQP4), the principal aquaporin expressed in the CNS, has been implicated in the processing of sensory and pain transmission. Akt signaling is also involved in pain mediation, such as neuroinflammatory pain and bone cancer pain. Previously, we found that expression of AQP4 and p-Akt was altered in the rat spinal cord after spinal nerve ligation (SNL). Here, we further investigated the effects of the AQP4 and Akt pathways in the spinal dorsal horn (SDH) on the pathogenesis of neuropathic pain (NP). Spinal AQP4 was significantly upregulated after SNL and was primarily expressed in astrocytes in the SDH. Inhibition of AQP4 with TGN-020 attenuated the development and maintenance of NP by inhibiting glial activation and anti-neuroinflammatory mechanisms. Moreover, inhibition of AQP4 suppressed astrocyte activation both in the SDH and in primary cultures. Similar to AQP4, we found that p-Akt was also significantly elevated after SNL. Inhibition of Akt with MK2206 suppressed AQP4 upregulation and astrocyte activation both in vivo and in vitro. Furthermore, Akt blockade with MK2206 alleviated NP in the early and late phases after SNL. These results elucidate the mechanisms involved in the roles of Akt/AQP4 signaling in the development and maintenance of NP. AQP4 is likely to be a novel therapeutic target for NP management.

Effect of sympathetic sprouting on the excitability of dorsal root ganglion neurons and afferents in a rat model of neuropathic pain.

Increased sympathetic nerve excitability has been reported to aggravate a variety of chronic pain conditions, and an increase in the number of sympathetic nerve fibers in the dorsal root ganglion (DRG) has been found in neuropathic pain (NP) models. However, the mechanism of the neurotransmitter norepinephrine (NE) released by sympathetic nerve fiber endings on the excitability of DRG neurons is still controversial, and the adrenergic receptor subtypes involved in this biological process are also controversial. In our study, we have two objectives: (1) To determine the effect of the neurotransmitter NE on the excitability of different neurons in DRG; (2) To determine which adrenergic receptors are involved in the excitability of DRG neurons by NE released by sprouting sympathetic fibers. In this experiment, a unique field potential recording method of spinal cord dorsal horn was innovatively adopted, which can be used for electrophysiological study in vivo. The results showed that： Forty days after SNI, patch clamp and field potential recording methods confirmed that NE enhanced the excitability of ipsilateral DRG large neurons, and then our in vivo electrophysiological results showed that the α2 receptor blocker Yohimbine could block the excitatory effect of NE on A-fiber and the inhibitory effect on C-fiber, while the α2A-adrenergic receptor agonist guanfacine (100 µM) had the same biological effect as NE. Finally, we concluded that NE from sympathetic fiber endings is involved in the regulation of pain signaling by acting on α2A-adrenergic receptors in DRG.

CircRNA_01477 influences axonal growth via regulating miR-3075/FosB/Stat3 axis.

Circular RNAs (circRNAs) are important for the development and regeneration of the nervous system. We investigated the differential expression profiles of circRNA induced by spinal cord injury and reported that circRNA_01477 facilitates spinal astrocyte proliferation and migration after injury in rats. In this study, we further clarified the function and possible mechanism of action of circRNA_01477 in neurons. Fluorescence in situ hybridization assay revealed that circRNA_01477 is mainly localized in the neuronal cytoplasm. Knockdown of circRNA_01477 significantly increased axonal length. The circRNA_01477/microRNAs (miRNA)/messenger RNA (mRNA) interaction network was investigated using RNA sequencing. miRNA-3075 showed a remarkable increase after circRNA_01477 depletion, and either overexpression of miRNA-3075 or downregulation of its target gene FosB significantly promoted axonal growth. Luciferase reporter assay showed that miRNA-3075 could directly bind to the 3'UTR of FosB and negatively regulated FosB transcription. Dual silencing of circRNA_01477 and miR-3075 revealed that miR-3075 inhibition rescued the increased axon length caused by siCircRNA_01477. Finally, we verified that the Stat3 pathway was activated after FosB protein depletion in rat spinal neurons, while the NF-κB pathway was not altered. In summary, our study is the first to report that circRNA_01477 contributes to axon growth by functioning as miRNA sponge by regulating the miRNA-3075/FosB/Stat3 axis.

The Role of NF-κB/NLRP3 Inflammasome Signaling Pathway in Attenuating Pyroptosis by Melatonin Upon Spinal Nerve Ligation Models.

Accumulated evidence has demonstrated causative links between neuropathic pain (NP) and immune-mediated inflammatory disorders. However, the role of inflammasome-induced pyroptosis in NP remains elusive. Melatonin possesses a well-documented analgesic action in various pain models. The current study aimed to test our hypothesis that melatonin regulated pyroptosis to alleviate NP by inhibiting NF-κB/NLRP3-dependent signaling. A rat model of spinal nerve ligation (SNL) was established to explore the potential association between melatonin and pyroptosis. Behavioral experiments revealed that SNL provoked severe allodynia which was suppressed by the administration of melatonin, a caspase-1 inhibitor (VX-765), or an NF-κB inhibitor (BAY 11-7085). SNL significantly up-regulated the inflammatory cytokines associated with the excessive activation of NLRP3 components and NF-κB signaling, as well as a marked pyroptosis activation. These effects were partially inhibited by melatonin, VX-765 or BAY 11-7085, and when melatonin and inhibitors were added together, the effect was enhanced. In conclusion, melatonin has potent analgesic and anti-inflammatory effects in SNL models through preventing pyroptosis via the NF-κB/NLRP3 inflammasome signaling pathway.

Microglial Activation of GLP-1R Signaling in Neuropathic Pain Promotes Gene Expression Adaption Involved in Inflammatory Responses.

Background: Neuropathic pain is a common chronic pain, which is related to hypersensitivity to stimulus and greatly affects the quality of life of patients. Maladaptive gene changes and molecular signaling underlie the sensitization of nociceptive pathways. We previously found that the activation of microglial glucagon-like peptide 1 receptor (GLP-1R) could potently relieve formalin-, bone cancer-, peripheral nerve injury-, and diabetes-induced pain hypersensitivity. So far, little is known about how the gene profile changes upon the activation of GLP-1R signaling in the pathophysiology of neuropathic pain. Methods: Spinal nerve ligation (SNL) was performed to induce neuropathic pain in rats. Mechanical allodynia was assessed using von Frey filaments. The expression of IL-10, ß-endorphin, and µ-opioid receptor (MOR) was examined by real-time quantitative polymerase chain reaction (qPCR) and whole-cell recording. Measurements of cellular excitability of the substantia gelatinosa (SG) neurons by whole-cell recording were carried out. R packages of differential gene expression analysis based on the negative binomial distribution (DESeq2) and weighted correlation network analysis (WGCNA) were used to analyze differential gene expression and the correlated modules among GLP-1R clusters in neuropathic pain. Results: The GLP-1R agonist, exenatide, has an antiallodynic effect on neuropathic pain, which could be reversed by intrathecal injections of the microglial inhibitor minocycline. Furthermore, differential gene expression analysis (WGCNA) indicated that intrathecal injections of exenatide could reverse the abnormal expression of 591 genes in the spinal dorsal horn induced by nerve injury. WGCNA revealed 58 modules with a close relationship between the microglial GLP-1R pathway and features of nerve injuries, including pain, ligation, paw withdrawal latency (PWL), and anxiety. The brown module was identified as the highest correlated module, and the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that inflammatory responses were most correlated with PWL. To further unravel the changes of hyperalgesia-related neuronal electrophysiological activity mediated by microglia GLP-1 receptors, whole-cell recording identified that MOR agonism stimulated a robust outward current in the sham groups compared with the spinal nerve ligation (SNL) groups. This inhibitory effect on the SNL group was more sensitive than that of the sham group after bath application of ß-endorphin. Conclusions: Our results further confirmed that the GLP-1R pathway is involved in alleviating pain hypersensitivity mediated by spinal microglia activation, and inflammatory responses were the most correlated pathway associated with PWL changes in response to exenatide treatment. We found that the identification of gene regulation in response to GLP-1R activation is an effective strategy for identifying new therapeutic targets for neuropathic pain. Investigation for the activation of spinal microglial GLP-1R which might ameliorate inflammatory responses through gene expression and structural changes is providing a potential biomarker in pain management.