The Up-regulation of TNF-α Maintains Trigeminal Neuralgia by Modulating MAPKs Phosphorylation and BKCa Channels in Trigeminal Nucleus Caudalis

Different mechanisms guide the antinociceptive effect of bone marrow-mononuclear cells and bone marrow-mesenchymal stem/stromal cells in trigeminal neuralgia

AIMS

Trigeminal neuralgia (TN) is a type of chronic orofacial pain evoked by trivial stimuli that manifests as episodes of excruciating and sudden, recurrent paroxysmal pain. Most patients are refractory to pharmacological therapy used for the treatment of TN. Mononuclear cells (MNC) and mesenchymal stem/stromal cells (MSC) have shown therapeutic potential in painful neuropathies, but their mechanism of action is not fully understood. The present work aimed to investigate the antinociceptive effect and mechanism of action of MNC and MSC in experimental TN.

MATERIALS AND METHODS

Mice submitted to the chronic constriction injury of the infraorbital nerve (CCI-ION) mouse model of TN received a single intravenous injection of saline, MNC, or MSC (1 × 106 cells/mouse). The effect of the treatments on the behavioral signs of painful neuropathy, morphological aspects of the infraorbital nerve, and inflammatory and oxidative stress markers in the infraorbital nerve were assessed.

KEY FINDINGS

MNC and MSC improved behavioral painful neuropathy, activated key cell signaling antioxidant pathways by increasing Nrf2 expression, and reduced the proinflammatory cytokines IL-1β and TNF-α. However, treatment with MSC, but not MNC, was associated with a sustained increase of IL-10 and with the re-establishment of the morphometric pattern of the infraorbital nerve, indicating a difference in the mechanism of action between MNC and MSC. In line with this result, in IL-10 knockout mice, MSC transplantation did not induce an antinociceptive effect.

SIGNIFICANCE

Importantly, these data suggest an IL-10-induced disease-modifying profile related to MSC treatment and reinforce cell therapy's potential in treating trigeminal neuralgia.

An experimental model for primary neuropathic corneal pain induced by long ciliary nerve ligation in rats

ABSTRACT

Neuropathic corneal pain (NCP) is a new and ill-defined disease characterized by pain, discomfort, aching, burning sensation, irritation, dryness, and grittiness. However, the mechanism underlying NCP remain unclear. Here, we reported a novel rat model of primary NCP induced by long ciliary nerve (LCN) ligation. After sustained LCN ligation, the rats developed increased corneal mechanical and chemical sensitivity, spontaneous blinking, and photophobia, which were ameliorated by intraperitoneal injection of morphine or gabapentin. However, neither tear reduction nor corneal injury was observed in LCN-ligated rats. Furthermore, after LCN ligation, the rats displayed a significant reduction in corneal nerve density, as well as increased tortuosity and beading nerve ending. Long ciliary nerve ligation also notably elevated corneal responsiveness under resting or menthol-stimulated conditions. At a cellular level, we observed that LCN ligation increased calcitonin gene-related peptide (neuropeptide)-positive cells in the trigeminal ganglion (TG). At a molecular level, upregulated mRNA levels of ion channels Piezo2, TRPM8, and TRPV1, as well as inflammatory factors TNF-α, IL-1β, and IL-6, were also detected in the TG after LCN ligation. Meanwhile, consecutive oral gabapentin attenuated LCN ligation-induced corneal hyperalgesia and increased levels of ion channels and inflammation factors in TG. This study provides a reliable primary NCP model induced by LCN ligation in rats using a simple, minimally invasive surgery technique, which may help shed light on the underlying cellular and molecular bases of NCP and aid in developing a new treatment for the disease.

GFAP-NpHR mediated optogenetic inhibition of trigeminal nucleus caudalis attenuates hypersensitive behaviors and thalamic discharge attributed to infraorbital nerve constriction injury

The significance of hyperactive astrocytes in neuropathic pain is crucial. However, the association between medullary astrocytes and trigeminal neuralgia (TN)-related pain processing is unclear. Here, we examined how optogenetic inhibition of medullary astrocytes in the trigeminal nucleus caudalis (TNC) regulates pain hypersensitivity in an infraorbital nerve (ION) constricted TN model. We used adult Sprague Dawley rats subjected to infraorbital nerve (ION) constriction to mimic TN symptoms, with naive and sham rats serving as controls. For in vivo optogenetic manipulations, rats stereotaxically received AAV8-GFAP-eNpHR3.0-mCherry or AAV8-GFAP-mCherry at the trigeminal nucleus caudalis (TNC). Open field, von Frey, air puff, and acetone tests measured pain behavioral flexibility. In vivo thalamic recordings were obtained simultaneously with optogenetic manipulation in the TNC. Orofacial hyperalgesia and thalamic hyperexcitability were both accompanied by medullary astrocyte hyperactivity, marked by upregulated GFAP. The yellow laser-driven inhibition of TNC astrocytes markedly improved behavioral responses and regulated thalamic neuronal responses. Halorhodopsin-mediated inhibition in medullary astrocytes may modify the nociceptive input transmitted through the trigeminothalamic tract and pain perception. Taken together, these findings imply that this subpopulation in the TNC and its thalamic connections play a significant role in regulating the trigeminal pain circuitry, which might aid in the identification of new therapeutic measures in TN management.

Cellular Mechanisms Mediating the Antinociceptive Effect of Botulinum Toxin A in a Rodent Model of Trigeminal Irritation by a Foreign Body

Although numerous studies have described botulinum toxin type A (BTX-A) efficacy against trigeminal neuralgia (TN), the underlying cellular mechanisms remain unclear. We have investigated cellular mechanisms that mediate the antinociceptive effect of BTX-A in a rodent model of TN produced by compression of the trigeminal nerve root (TNR). Anesthetized male Sprague-Dawley rats were fixed in a stereotaxic instrument and compression of the TNR was then achieved with a 4% agar solution. This model produced a significant mechanical allodynia and increased the expression of hypoxia-inducible factor (HIF)-1α and cytokines levels including interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in the trigeminal ganglion (TG) by postoperative day (POD) 7. Single or double treatments with a high BTX-A dose (3 U/kg) led to significantly prolonged antinociceptive effects. Furthermore, a single treatment with BTX-A (3 U/kg) significantly suppressed the upregulation of HIF-1α expression and IL-1β, IL-6, and TNF-α concentrations in the TG. Intraganglionic injection of PX-12, a HIF-1α inhibitor, led to significant anti-allodynic effects and lowered the IL-1β, IL-6, and TNF-α levels in the TG. These findings indicate that the antinociceptive effect of BTX-A is mediated via HIF-1α associated cytokines modulation in the TG and is therefore a potentially relevant treatment strategy for TN. PERSPECTIVE: The antinociceptive properties of BTX-A in a rat model of trigeminal neuralgia are mediated through the regulation of the HIF-1α associated cytokine pathway in the trigeminal ganglion. BTX-A is therefore a potentially effective treatment strategy for trigeminal neuralgia.

Mechanism of Glucose Water as a Neural Injection: A Perspective on Neuroinflammation

The entrapment of peripheral nerves is associated with chronic neuroinflammation and neuropathic pain, and perineural injection therapy with glucose is emerging as an effective treatment for peripheral entrapment neuropathy. However, the mechanism underlying the pharmacological effect of glucose on nerves remains unclear. One of the hypothesized mechanisms is that glucose reduces neurogenic inflammation. Therefore, we investigated the effects of high glucose concentrations on cytokine-induced neuroinflammation in vitro. Human SH-SY5Y neuronal cells were challenged with 10 ng/mL TNF-α for 16 h and subsequently treated with different glucose concentrations (0–25 mM) for 24 h. Cell viability was evaluated using the diphenyltetrazolium bromide assay, and proinflammatory cytokine levels were assessed using ELISA and quantitative PCR. In addition, mRNA levels of NF-κB and cyclooxygenase-2 were analyzed using quantitative PCR. Exposure to 10 ng/mL TNF-α resulted in decreased viability of SH-SY5Y cells and significant upregulation of IL-6, IL-1β, NF-κB, and cyclooxygenase-2. Subsequent exposure to high glucose levels (25 mM) markedly reduced the upregulation of IL-6, IL-1β, cyclooxygenase-2, and NF-κB, and restored the functional metabolism of SH-SY5Y cells, compared with that of the normal glucose control. Our findings suggest that high glucose concentrations can mitigate TNF-α-induced NF-κB activation, upregulation of proinflammatory cytokines, and metabolic dysfunction.

Olfactory Ensheathing Cells Alleviate Facial Pain in Rats with Trigeminal Neuralgia by Inhibiting the Expression of P2X7 Receptor

Trigeminal neuralgia (TN) is a common facial neuropathic pain that is mainly characterized by spontaneous or induced needling or electric shock pain in the innervation area of the trigeminal nerve. It is also referred to as “the cancer that never dies”. The olfactory ensheathing cell (OEC) is a special glial cell in the nervous system that has a strong supportive function in nerve regeneration. Cell transplantation therapy is a useful treatment modality that we believe can be applied in TN management. In this study, OECs were transplanted into the ligation site of the infraorbital nerve of rats. We found that after the OEC transplantation, mechanical pain threshold in the face of the rats was significantly increased. Western blotting, immunofluorescence assay, and reverse transcription-quantitative polymerase chain reaction were performed on the trigeminal ganglia (TG) of model rats. The results revealed a decrease in the expression of P2X7 receptor (P2X7R) in the trigeminal ganglia. Our findings show that OEC transplantation has a good therapeutic effect on TN in rats, and that can reduce the expression of P2X7R in trigeminal ganglia. Therefore, we think that OEC transplantation may be a suitable treatment for TN.

Screening and Validation of p38 MAPK Involved in Ovarian Development of Brachymystax lenok

Brachymystax lenok (lenok) is a rare cold-water fish native to China that is of high meat quality. Its wild population has declined sharply in recent years, and therefore, exploring the molecular mechanisms underlying the development and reproduction of lenoks for the purposes of artificial breeding and genetic improvement is necessary. The lenok comparative transcriptome was analyzed by combining single molecule, real-time, and next generation sequencing (NGS) technology. Differentially expressed genes (DEGs) were identified in five tissues (head kidney, spleen, liver, muscle, and gonad) between immature [300 days post-hatching (dph)] and mature [three years post-hatching (ph)] lenoks. In total, 234,124 and 229,008 full-length non-chimeric reads were obtained from the immature and mature sequencing data, respectively. After NGS correction, 61,405 and 59,372 non-redundant transcripts were obtained for the expression level and pathway enrichment analyses, respectively. Compared with the mature group, 719 genes with significantly increased expression and 1,727 genes with significantly decreased expression in all five tissues were found in the immature group. Furthermore, DEGs and pathways involved in the endocrine system and gonadal development were identified, and p38 mitogen-activated protein kinases (MAPKs) were identified as potentially regulating gonadal development in lenok. Inhibiting the activity of p38 MAPKs resulted in abnormal levels of gonadotropin-releasing hormone, follicle-stimulating hormone, and estradiol, and affected follicular development. The full-length transcriptome data obtained in this study may provide a valuable reference for the study of gene function, gene expression, and evolutionary relationships in B. lenok and may illustrate the basic regulatory mechanism of ovarian development in teleosts.