The expression of voltage-gated sodium channels in trigeminal nerve following chronic constriction injury in rats.

Objectives: Despite the etiology of trigeminal neuralgia has been verified by microvascular decompression as vascular compression of the trigeminal root, very few researches concerning its underlying pathogenesis has been reported in the literature. The present study focused on those voltage-gated sodium channels, which are the structural basis for generation of ectopic action potentials. Methods: The trigeminal neuralgia modeling was obtained with infraorbital nerve chronic constriction injury (ION-CCI) in rats. Two weeks postoperatively, the infraorbital nerve (TN), the trigeminal ganglion (TG), and the brain stem (BS) were removed and analyzed with a series of molecular biological techniques. Results: Western blot depicted a significant up-regulation of Nav1.3 in TN and TG but not in BS, while none of the other isoforms (Nav1.6, Nav1.7, Nav1.8, or Nav1.9) presented a statistical change. The Nav1.3 from ION-CCI group was quantified as 2.5-fold and 1.7-fold than that from sham group in TN and TG, respectively (p < .05). Immunocytochemistry showed the Nav1.3-IR from ION-CCI group accounted for 21.2 ± 2.3% versus 6.1 ± 1.2% from sham group in TN, while the Nav1.3-positive neurons from ION-CCI group accounted for 34.1 ± 3.5% versus 11.2 ± 1.8% from sham group in TG. Immunohistochemical labeling showed the Nav1.3 was co-localized with CGRP and IB4 but not with GFAP or NF-200 in TG. Conclusion: ION-CCI may give rise to an up-regulation of Nav1.3 in trigeminal nerve as well as in C-type neurons at the trigeminal ganglion. It implied that the ectopic action potential may generate from both the compressed site of the trigeminal nerve and the ganglion rather than from the trigeminal nuclei.

Sodium Channel Nav1.3 Is Expressed by Polymorphonuclear Neutrophils during Mouse Heart and Kidney Ischemia In Vivo and Regulates Adhesion, Transmigration, and Chemotaxis of Human and Mouse Neutrophils In Vitro.

BACKGROUND: Voltage-gated sodium channels generate action potentials in excitable cells, but they have also been attributed noncanonical roles in nonexcitable cells. We hypothesize that voltage-gated sodium channels play a functional role during extravasation of neutrophils. METHODS: Expression of voltage-gated sodium channels was analyzed by polymerase chain reaction. Distribution of Nav1.3 was determined by immunofluorescence and flow cytometry in mouse models of ischemic heart and kidney injury. Adhesion, transmigration, and chemotaxis of neutrophils to endothelial cells and collagen were investigated with voltage-gated sodium channel inhibitors and lidocaine in vitro. Sodium currents were examined with a whole cell patch clamp. RESULTS: Mouse and human neutrophils express multiple voltage-gated sodium channels. Only Nav1.3 was detected in neutrophils recruited to ischemic mouse heart (25 ± 7%, n = 14) and kidney (19 ± 2%, n = 6) in vivo. Endothelial adhesion of mouse neutrophils was reduced by tetrodotoxin (56 ± 9%, unselective Nav-inhibitor), ICA121431 (53 ± 10%), and Pterinotoxin-2 (55 ± 9%; preferential inhibitors of Nav1.3, n = 10). Tetrodotoxin (56 ± 19%), ICA121431 (62 ± 22%), and Pterinotoxin-2 (59 ± 22%) reduced transmigration of human neutrophils through endothelial cells, and also prevented chemotactic migration (n = 60, 3 × 20 cells). Lidocaine reduced neutrophil adhesion to 60 ± 9% (n = 10) and transmigration to 54 ± 8% (n = 9). The effect of lidocaine was not increased by ICA121431 or Pterinotoxin-2. CONCLUSIONS: Nav1.3 is expressed in neutrophils in vivo; regulates attachment, transmigration, and chemotaxis in vitro; and may serve as a relevant target for antiinflammatory effects of lidocaine.

Alteration of Scn3a expression is mediated via CpG methylation and MBD2 in mouse hippocampus during postnatal development and seizure condition.

Increased expression of sodium channel SCN3A, an embryonic-expressed gene, has been identified in epileptic tissues, which is believed to contribute to the development of epilepsy. However, the regulatory mechanism of SCN3A expression under epileptic condition is still unknown. Here we showed a high level of Scn3a mRNA expression in mouse embryonic hippocampus with gradually decreasing to a low level during the postnatal development and a methylation of a specific CpG site (-39C) in the Scn3a promoter was increased in hippocampus during postnatal development, corresponding to the downregulation of Scn3a expression. Furthermore, in vitro methylation and -39C>T mutation of the Scn3a promoter decreased the reporter gene expression, suggesting an important role of the -39C site in regulating gene expression. We then demonstrated that the sequence containing -39C was a MBD2-binding motif and the CpG methylation of the promoter region increased the capability of MBD2's binding to the motif. Knockdown of MBD2 in mouse N1E-115 cells led to the -39C methylation and the downregulation of Scn3a transcription by decreasing the Scn3a promoter activity. In the hippocampus of seizure mice, the expressions of Scn3a and Mbd2 were upregulated after 10-day KA treatment. At the same time point, the -39C site was demethylated and the capability of MBD2's binding to the Scn3a promoter motif was decreased. Taken together, these findings suggest that CpG methylation and MBD2 are involved in altering Scn3a expression during postnatal development and seizure condition.

Virus-Mediated Knockdown of Nav1.3 in Dorsal Root Ganglia of STZ-Induced Diabetic Rats Alleviates Tactile Allodynia.

Diabetic neuropathic pain affects a substantial number of people and represents a major public health problem. Available clinical treatments for diabetic neuropathic pain remain only partially effective and many of these treatments carry the burden of side effects or the risk of dependence. The misexpression of sodium channels within nociceptive neurons contributes to abnormal electrical activity associated with neuropathic pain. Voltage-gated sodium channel Nav1.3 produces tetrodotoxin-sensitive sodium currents with rapid repriming kinetics and has been shown to contribute to neuronal hyperexcitability and ectopic firing in injured neurons. Suppression of Nav1.3 activity can attenuate neuropathic pain induced by peripheral nerve injury. Previous studies have shown that expression of Nav1.3 is upregulated in dorsal root ganglion (DRG) neurons of diabetic rats that exhibit neuropathic pain. Here, we hypothesized that viral-mediated knockdown of Nav1.3 in painful diabetic neuropathy would reduce neuropathic pain. We used a validated recombinant adeno-associated virus (AAV)-shRNA-Nav1.3 vector to knockdown expression of Nav1.3, via a clinically applicable intrathecal injection method. Three weeks following vector administration, we observed a significant rate of transduction in DRGs of diabetic rats that concomitantly reduced neuronal excitability of dorsal horn neurons and reduced behavioral evidence of tactile allodynia. Taken together, these findings offer a novel gene therapy approach for addressing chronic diabetic neuropathic pain.

Intrathecal miR-96 inhibits Nav1.3 expression and alleviates neuropathic pain in rat following chronic construction injury.

MicroRNAs (miRNAs) are short non-coding RNAs that regulate gene expression post-transcriptionally by binding to their cognate target mRNAs. Emerging evidence suggests that miRNAs are critical regulators of neuronal functions. The expression pattern of miRNAs in the peripheral nervous system after peripheral nerve injury suggest that miRNAs may have important and yet unknown roles in the mechanisms of pain. Thus, we examined the role of miR-96 in neuropathic pain using a rat model of the condition chronic constriction sciatic nerve injury (CCI). We found that miR-96 alleviated neuropathic pain. The level of miR-96 was decreased within the ipsilateral dorsal root ganglion (DRG) after peripheral nerve injury but the Nav1.3 level was increased. Specifically, Intrathecal administration of miR-96 suppressed the expression of Nav1.3 induced by CCI. Further examination revealed that miR-96 inhibited the Nav1.3 mRNA expression in the embryonic DRG neurons in vitro. Our findings suggest that miR-96 participate in the regulation of neuropathic pain through inhibiting the expression of Nav1.3 in the DRG of CCI rats.

miR-384-5p ameliorates neuropathic pain by targeting SCN3A in a rat model of chronic constriction injury.

Objective: To explore the potential regulation mechanisms of miR-384-5p in Neuropathic pain (NP).Methods: Rat model of chronic constriction injury (CCI) was established to induce NP in vivo. NP levels were assessed using Withdrawal Threshold (PWT) and Paw Withdrawal Latency (PWL). qPCR and Western blotting were used to determine the relative expression of miR-384-5p and SCN3A. The inflammation response in spinal microglia cells was determined by ELISA assay. Immunofluorescence assay was used to demonstrate the co-localization of miR-384-5p with SCN3A in rat dorsal root ganglions (DRGs). The target genes of miR-384-5p were verified by dual-luciferase report assays.Results: In the current study, the miR-384-5p expression level was significantly downregulated in CCI rats when comparing to the sham group. In addition, miR-384-5p agomir significantly repressed mechanical allodynia and heat hyperalgesia in CCI rats. Meanwhile, the current study indicated miR-384-5p could decrease inflammation progress in spinal microglia cells incubated in lipopolysaccharide. Consistently, overexpression of miR-384-5p obviously depressed inflammation cytokine levels in CCI rats. Dual-luciferase reporter assays indicated that SCN3A is a target gene of miR-384-5p.Conclusion: miR-384-5p is a negative regulator in the development of neuropathic pain by regulating SCN3A, indicating that miR-384-5p might be a promising therapeutic target in the treatment of neuropathic pain.Abbreviations: CCI: Chronic constriction injury; ZEB1: Zinc finger E box binding protein-1; MAPK6: Mitogen-activated protein kinase 6; COX-2: cyclooxygenase-2.

GAPDH-mediated posttranscriptional regulations of sodium channel Scn1a and Scn3a genes under seizure and ketogenic diet conditions.

Abnormal expressions of sodium channel SCN1A and SCN3A genes alter neural excitability that are believed to contribute to the pathogenesis of epilepsy, a long-term risk of recurrent seizures. Ketogenic diet (KD), a high-fat and low-carbohydrate treatment for difficult-to-control (refractory) epilepsy in children, has been suggested to reverse gene expression patterns. Here, we reveal a novel role of GAPDH on the posttranscriptional regulation of mouse Scn1a and Scn3a expressions under seizure and KD conditions. We show that GAPDH binds to a conserved region in the 3' UTRs of human and mouse SCN1A and SCN3A genes, which decreases and increases genes' expressions by affecting mRNA stability through SCN1A 3' UTR and SCN3A 3' UTR, respectively. In seizure mice, the upregulation and phosphorylation of GAPDH enhance its binding to the 3' UTR, which lead to downregulation of Scn1a and upregulation of Scn3a. Furthermore, administration of KD generates ß-hydroxybutyric acid which rescues the abnormal expressions of Scn1a and Scn3a by weakening the GAPDH's binding to the element. Taken together, these data suggest that GAPDH-mediated expression regulation of sodium channel genes may be associated with epilepsy and the anticonvulsant action of KD.

Blockage of the upregulation of voltage-gated sodium channel nav1.3 improves outcomes after experimental traumatic brain injury.

Excessive active voltage-gated sodium channels are responsible for the cellular abnormalities associated with secondary brain injury following traumatic brain injury (TBI). We previously presented evidence that significant upregulation of Nav1.3 expression occurs in the rat cortex at 2 h and 12 h post-TBI and is correlated with TBI severity. In our current study, we tested the hypothesis that blocking upregulation of Nav1.3 expression in vivo in the acute stage post-TBI attenuates the secondary brain injury associated with TBI. We administered either antisense oligodeoxynucleotides (ODN) targeting Nav1.3 or artificial cerebrospinal fluid (aCSF) at 2 h, 4 h, 6 h, and 8 h following TBI. Control sham animals received aCSF administration at the same time points. At 12 h post-TBI, Nav1.3 messenger ribonucleic acid (mRNA) levels in bilateral hippocampi of the aCSF group were significantly elevated, compared with the sham and ODN groups (p<0.01). However, the Nav1.3 mRNA levels in the uninjured contralateral hippocampus of the ODN group were significantly lowered, compared with the sham group (p<0.01). Treatment with antisense ODN significantly decreased the number of degenerating neurons in the ipsilateral hippocampal CA3 and hilar region (p<0.01). A set of left-to-right ratio value analyzed by magnetic resonance imaging T2 image on one day, three days, and seven days post-TBI showed marked edema in the ipsilateral hemisphere of the aCSF group, compared with that of the ODN group (p<0.05). The Morris water maze memory retention test showed that both the aCSF and ODN groups took longer to find a hidden platform, compared with the sham group (p<0.01). However, latency in the aCSF group was significantly higher than in the ODN group (p<0.05). Our in vivo Nav1.3 inhibition studies suggest that therapeutic strategies to block upregulation of Nav1.3 expression in the brain may improve outcomes following TBI.

Expression of voltage-gated sodium channel Nav1.3 is associated with severity of traumatic brain injury in adult rats.

During the secondary injury period after traumatic brain injury (TBI), depolarization of neurons mediated by voltage-gated sodium channels (VGSCs) leads to cellular abnormalities and neurological dysfunction. Alterations in expression of different α subunits of VGSCs can affect early brain pathology following TBI. This study detected the expression of Nav1.3 mRNA and protein in the rat cortex post-TBI. Adult male Sprague-Dawley rats were randomly assigned to sham-TBI, mild-TBI (mTBI), or severe-TBI (sTBI) groups. TBI was induced using a fluid percussion device at magnitudes of 1.5-1.6 atm (mTBI) and 2.9-3.0 atm (sTBI). Nav1.3 mRNA and protein levels in the ipsilateral-injured cortex were examined at 2 h, 12 h, 24 h, and 72 h post-TBI by real-time reverse transcriptase quantitative polymerase chain reaction and Western blot. Brains were collected at 24 h, 72 h, and 7 days post-TBI for TUNEL staining and cell count analysis. Immunofluorescence was performed to localize expression of Nav1.3 protein in the ipsilateral-injured cortex. Expression of Nav1.3 mRNA and protein were significantly upregulated in mTBI and sTBI groups when compared with the sham-TBI group at 2 h and 12 h post-TBI. Nav1.3 mRNA and protein levels in the sTBI group were much higher than in the mTBI group at 12 h post-TBI. TUNEL-positive cell numbers were significantly higher in the sTBI group than in the mTBI at 24 h, 72 h, and 7 days post-TBI. Expression of Nav1.3 was observed predominantly in neurons of the cortex. These findings indicated significant upregulation in the expression of Nav1.3 mRNA and protein in the rat ipsilateral-injured cortex at the very early stage post-TBI, and were also correlated with TBI severity.