TNFα levels and macrophages expression reflect an inflammatory potential of trigeminal ganglia in a mouse model of familial hemiplegic migraine

Neuron-glia crosstalk and inflammatory mediators in migraine pathophysiology

Migraine is a complex neurological disorder with neuroinflammation playing a crucial role in its pathogenesis. This review provides an overview of the neuroinflammation mechanisms in migraine, focusing on both cellular and molecular aspects. At the cellular level, we examine the role of glial cells, including astrocytes, microglia, oligodendrocytes in the central nervous system, and Schwann cells and satellite glial cells in the peripheral nervous system. On the molecular level, we explore the signaling pathways, including IL-1β, TNF-α, IL-6, and non-coding RNAs, that mediate cell interactions or independent actions. Some of the molecular signaling pathways mentioned, such as TNF-α and IL-1β, have been investigated as druggable targets. Recent advancements, such as [11C] PBR28-targeted imaging for visualizing astrocyte activation and single-cell sequencing for exploring cellular heterogeneity, represent breakthroughs in understanding the mechanisms of neuroinflammation in migraine. By considering factors for personalized treatments, estrogen and TRPM8 emerge as promising therapeutic targets regarding sexual dimorphism. These advancements may help bridge the gap between preclinical findings and clinical applications, ultimately leading to more precise and personalized options for migraine patients.

Causality between multiple autoimmune disorders and migraine and its subtypes: a two-sample Mendelian randomization study

Introduction

Several studies have reported associations between various autoimmune diseases and migraine. Using Mendelian randomization (MR), this study aimed to evaluate the interplay between autoimmune diseases and migraine.

Methods

Here, instrumental variables, exposure factors, and outcome factors for 10 common autoimmune diseases and migraine and its subtypes were screened. This screening utilized comprehensive statistics from Europe's largest genome-wide association study and performed reverse MR analysis on positive results. The causality between autoimmune diseases and migraine was comprehensively assessed using multiple analytical methods. Additionally, sensitivity analyses, such as the horizontal diversity heterogeneity and leave-one-out method, were performed.

Results

Random-effects inverse variance weighting analysis revealed a causal correlation between autoimmune hyperthyroidism and migraine (p = 0.0002), and this association was consistent across both migraine with aura (MA; p = 0.006) and migraine without aura (MO; p = 0.017). In addition, there was a positive causal association between systemic lupus erythematosus (SLE) and MA (p = 0.001) and between hypothyroidism and MO (p = 0.038). There is insufficient evidence to substantiate a causal link between outcomes and other autoimmune-related disorders, and reverse MR results did not reveal a causal relationship between migraines and these autoimmune disorders. The validity of the results was demonstrated by a sensitivity analysis; horizontal pleiotropy and heterogeneity were not observed.

Discussion

This study observed a positive genetic association between autoimmune hyperthyroidism and migraines. In addition, SLE positively affects MA, and hypothyroidism contributes to the incidence of MO. These results have great significance for future research and prevention of migraine.

Models of Trigeminal Activation: Is There an Animal Model of Migraine?

Migraine, recognized as a severe headache disorder, is widely prevalent, significantly impacting the quality of life for those affected. This article aims to provide a comprehensive review of the application of animal model technologies in unraveling the pathomechanism of migraine and developing more effective therapies. It introduces a variety of animal experimental models used in migraine research, emphasizing their versatility and importance in simulating various aspects of the condition. It details the benefits arising from the utilization of these models, emphasizing their role in elucidating pain mechanisms, clarifying trigeminal activation, as well as replicating migraine symptoms and histological changes. In addition, the article consciously acknowledges the inherent limitations and challenges associated with the application of animal experimental models. Recognizing these constraints is a fundamental step toward fine-tuning and optimizing the models for a more accurate reflection of and translatability to the human environment. Overall, a detailed and comprehensive understanding of migraine animal models is crucial for navigating the complexity of the disease. These findings not only provide a deeper insight into the multifaceted nature of migraine but also serve as a foundation for developing effective therapeutic strategies that specifically address the unique challenges arising from migraine pathology.

Causal association between systemic lupus erythematosus and the risk of migraine: A Mendelian randomization study

BACKGROUND

Numerous studies have found that patients with systemic lupus erythematosus (SLE) often have comorbid headache, especially migraine. However, the causal relationship between genetically determined SLE and migraine risk remains unclear. Therefore, we conducted a Mendelian randomization (MR) study to explore this causal association.

METHODS

Genome-wide association studies (GWAS) provided the instrumental variables. We selected summary data from GWAS of SLE as exposure (5201 SLE patients and 9066 controls). Both outcome GWAS data were from the Finnish Gene GWAS, including migraine with aura, migraine with aura and triptan purchases, and migraine without aura. The main MR approach was inverse-variance weighted. Pleiotropy and heterogeneity were detected using the MR pleiotropy residual sum and outlier, MR-Egger intercept test, leave-one-out analysis, and Cochran's Q test.

RESULTS

There was a significant association between genetically predicted SLE susceptibility and increased risk of migraine with aura [odds ratio (OR) = 1.05, 95% confidence interval (CI) = 1.02-1.08, p = .001]. The result was consistent when the outcome was migraine with aura and triptan purchases [OR = 1.05, 95% CI = 1.02-1.08, p = .001]. However, we found no association between SLE and migraine without aura. Our MR study showed no pleiotropy or heterogeneity.

CONCLUSIONS

Our study indicates that genetic susceptibility to SLE increases the incidence of migraine with aura but not migraine without aura. It is necessary for the routine evaluation and early recognition of migraine in patients with SLE in clinical settings.

Role of TNF-α in the Pathogenesis of Migraine

Background

Neurogenic neuroinflammation has a wide role in migraine pathogenesis including the transition from episodic migraine to chronic one. The seed molecule of neurogenic neuroinflammation, i.e., the TNF-α proinflammatory molecule, has gathered a lot of attention. This pleiotropic cytokine is a classical component of inflammatory soup, secreted by the microglial cell, and promotes a wide range of inflammatory reactions.

Aim

In this review, we aimed to provide a culminating and comprehending glimpse into the TNF-α in association with the migraine.

Method

A systematic literature survey method with a mixture of keywords was utilized to grasp the different elements that represent the association between TNF-α and migraine. Discussion. Highlighted the probable involvement of the TNF-α with migraine, the complexity of the matter such as activation of NF-KB signaling cascade, autoactivation, sensitization, and increased likelihood of transition cannot be neglected. Being TNF-α as a core node, it becomes the factor for linking diseases such as chronic inflammatory disorders, including COVID-19, and also interaction with other genes to develop severe conditions.

Conclusion

To this end, TNF-α plays a critical role in chronification, and inhibiting its signaling would likely be a crucial strategy for migraine therapy.

The effect of omega-3 fatty acids supplementation on inflammatory biomarkers in subjects with migraine: a randomized, double-blind, placebo-controlled trial

OBJECTIVE

Imbalances in immune regulation are important features of migraine pathophysiology. In line with this, the current study investigated the efficacy of omega-3 fatty acids supplementation on inflammatory and anti-inflammatory markers in patients with migraines.

MATERIALS AND METHODS

This randomized, double-blind, placebo-controlled trial consisted of 40 patients that were prone to experiencing episodic migraines. For two months, participants were randomized into one group that received omega-3 supplementation (n= 20), 600 mg of EPA and 300 mg of DHA, twice daily) or another group that received a placebo (n= 20). Transforming growth factor β (TGF-β), interleukin (IL)-4, interferon-gamma (IFN-γ), and interleukin (IL)-17 serum levels were assessed using enzyme-linked immunosorbent assay methods at baseline and following the intervention. The current study was registered on ClinicalTrials.gov with the registration number NCT02532023.

RESULTS

After two months of intervention, the administration of omega-3 fatty acids resulted in a significant rise in the concentrations of anti-inflammatory cytokine IL-4 (p=0.010) as well as a significant reduction in concentrations of pro-inflammatory cytokine IFN-γ (p=0.001) compared with the placebo. However, no significant changes were observed in serum TGF-β and IL-17 levels.

DISCUSSION

Our findings indicated consumption of omega-3 fatty acids may have a potentially beneficial response on the inflammatory immune response in patients with migraines. Larger trials are needed to corroborate these findings.

Optogenetic cortical spreading depolarization induces headache-related behaviour and neuroinflammatory responses some prolonged in familial hemiplegic migraine type 1 mice

BACKGROUND

Cortical spreading depolarization (CSD), the neurophysiological correlate of the migraine aura, can activate trigeminal pain pathways, but the neurobiological mechanisms and behavioural consequences remain unclear. Here we investigated effects of optogenetically-induced CSDs on headache-related behaviour and neuroinflammatory responses in transgenic mice carrying a familial hemiplegic migraine type 1 (FHM1) mutation.

METHODS

CSD events (3 in total) were evoked in a minimally invasive manner by optogenetic stimulation through the intact skull in freely behaving wildtype (WT) and FHM1 mutant mice. Related behaviours were analysed using mouse grimace scale (MGS) scoring, head grooming, and nest building behaviour. Neuroinflammatory changes were investigated by assessing HMGB1 release with immunohistochemistry and by pre-treating mice with a selective Pannexin-1 channel inhibitor.

RESULTS

In both WT and FHM1 mutant mice, CSDs induced headache-related behaviour, as evidenced by increased MGS scores and the occurrence of oculotemporal strokes, at 30 min. Mice of both genotypes also showed decreased nest building behaviour after CSD. Whereas in WT mice MGS scores had normalized at 24 h after CSD, in FHM1 mutant mice scores were normalized only at 48 h. Of note, oculotemporal stroke behaviour already normalized 5 h after CSD, whereas nest building behaviour remained impaired at 72 h; no genotype differences were observed for either readout. Nuclear HMGB1 release in the cortex of FHM1 mutant mice, at 30 min after CSD, was increased bilaterally in both WT and FHM1 mutant mice, albeit that contralateral release was more pronounced in the mutant mice. Only in FHM1 mutant mice, contralateral release remained higher at 24 h after CSD, but at 48 h had returned to abnormal, elevated, baseline values, when compared to WT mice. Blocking Panx1 channels by TAT-Panx₃₀₈ inhibited CSD-induced headache related behaviour and HMGB1 release.

CONCLUSIONS

CSDs, induced in a minimally invasive manner by optogenetics, investigated in freely behaving mice, cause various migraine relevant behavioural and neuroinflammatory phenotypes that are more pronounced and longer-lasting in FHM1 mutant compared to WT mice. Prevention of CSD-related neuroinflammatory changes may have therapeutic potential in the treatment of migraine.

Targeting the chemokine ligand 2-chemokine receptor 2 axis provides the possibility of immunotherapy in chronic pain

Chronic pain affects patients' physical and psychological health and quality of life, entailing a tremendous public health challenge. Currently, drugs for chronic pain are usually associated with a large number of side effects and poor efficacy. Chemokines in the neuroimmune interface combine with their receptors to regulate inflammation or mediate neuroinflammation in the peripheral and central nervous system. Targeting chemokines and their receptor-mediated neuroinflammation is an effective means to treat chronic pain. In recent years, growing evidence has shown that the expression of chemokine ligand 2 (CCL2) and its main chemokine receptor 2 (CCR2) is involved in its occurrence, development and maintenance of chronic pain. This paper summarises the relationship between the chemokine system, CCL2/CCR2 axis, and chronic pain, and the CCL2/CCR2 axis changes under different chronic pain conditions. Targeting chemokine CCL2 and its chemokine receptor CCR2 through siRNA, blocking antibodies, or small molecule antagonists may provide new therapeutic possibilities for managing chronic pain.

Modulation of Glia Activation by TRPA1 Antagonism in Preclinical Models of Migraine

Preclinical data point to the contribution of transient receptor potential ankyrin 1 (TRPA1) channels to the complex mechanisms underlying migraine pain. TRPA1 channels are expressed in primary sensory neurons, as well as in glial cells, and they can be activated/sensitized by inflammatory mediators. The aim of this study was to investigate the relationship between TRPA1 channels and glial activation in the modulation of trigeminal hyperalgesia in preclinical models of migraine based on acute and chronic nitroglycerin challenges. Rats were treated with ADM_12 (TRPA1 antagonist) and then underwent an orofacial formalin test to assess trigeminal hyperalgesia. mRNA levels of pro- and anti-inflammatory cytokines, calcitonin gene-related peptide (CGRP) and glia cell activation were evaluated in the Medulla oblongata and in the trigeminal ganglia. In the nitroglycerin-treated rats, ADM_12 showed an antihyperalgesic effect in both acute and chronic models, and it counteracted the changes in CGRP and cytokine gene expression. In the acute nitroglycerin model, ADM_12 reduced nitroglycerin-induced increase in microglial and astroglial activation in trigeminal nucleus caudalis area. In the chronic model, we detected a nitroglycerin-induced activation of satellite glial cells in the trigeminal ganglia that was inhibited by ADM_12. These findings show that TRPA1 antagonism reverts experimentally induced hyperalgesia in acute and chronic models of migraine and prevents multiple changes in inflammatory pathways by modulating glial activation.

Could Experimental Inflammation Provide Better Understanding of Migraines?

Migraines constitute a common neurological and headache disorder affecting around 15% of the world’s population. In addition to other mechanisms, neurogenic neuroinflammation has been proposed to play a part in migraine chronification, which includes peripheral and central sensitization. There is therefore considerable evidence suggesting that inflammation in the intracranial meninges could be a key element in addition to calcitonin gene-related peptide (CGRP), leading to sensitization of trigeminal meningeal nociceptors in migraines. There are several studies that have utilized this approach, with a strong focus on using inflammatory animal models. Data from these studies show that the inflammatory process involves sensitization of trigeminovascular afferent nerve terminals. Further, by applying a wide range of different pharmacological interventions, insight has been gained on the pathways involved. Importantly, we discuss how animal models should be used with care and that it is important to evaluate outcomes in the light of migraine pathology.

Leukocyte inflammatory phenotype and function in migraine patients compared with matched non-migraine volunteers: a pilot study

Background

Migraine is a neurological condition characterized by chronic inflammation. However, not much is known about the potential role of peripheral blood immune cells in the pathophysiology of migraine.

Methods

We investigated the status of peripheral blood immune cells of 15 adults with frequent episodic or chronic migraine recruited chronologically from a randomized clinical trial (RCT) on Nutrition for Migraine (NCCIH 5R01AT007813-05) and 15 non-migraine, healthy volunteers (control) matched by age, gender, and Body Mass Index (BMI).

Continuous variables were presented as means ± standard deviationas well as medians, and comparisons between patients and healthy volunteers were performed with non-parametric Wilcoxon signed rank tests. Statistical analysis was performed using Stata (StataCorp. 2019. Stata Statistical Software). Fluorescence-Activated Cell Sorting (FACS) data were processed using FlowJo software (Ashland, OR: Becton, Dickenson and Company; 2019).

Results

We observed that migraineurs had a significantly lower percentage of non-classical monocytes (CD14⁺CD16⁺⁺) in blood circulation, compared to the control group. In addition, Migraineurs also showed a significantly lower percentage of blood CD3⁺CD4⁺ helper T cells and CD4⁺CD25⁺ regulatory T cells, compared to controls. Differences in leukocyte surface markers between chronic migraine patients and their matched controls were more prominent than those between episodic migraine patients and their matched controls.

Conclusions

Our results suggest that migraine is associated with dysregulated peripheral immune homeostasis and that inflammation and autoimmunity may play a role in its pathophysiology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02781-4.

The role of the meningeal lymphatic system in local meningeal inflammation and trigeminal nociception

A system of lymphatic vessels has been recently characterized in the meninges, with a postulated role in ‘cleaning’ the brain via cerebral fluid drainage. As meninges are the origin site of migraine pain, we hypothesized that malfunctioning of the lymphatic system should affect the local trigeminal nociception. To test this hypothesis, we studied nociceptive and inflammatory mechanisms in the hemiskull preparations (containing the meninges) of K14-VEGFR3-Ig (K14) mice lacking the meningeal lymphatic system. We recorded the spiking activity of meningeal afferents and estimated the local mast cells population, calcitonin gene-related peptide (CGRP) and cytokine levels as well as the dural trigeminal innervation in freshly-isolated hemiskull preparations from K14-VEGFR3-Ig (K14) or wild type C57BL/6 mice (WT). Spiking activity data have been confirmed in an acquired model of meningeal lymphatic dysfunction (AAV-mVEGFR3(1–4)Ig induced lymphatic ablation). We found that levels of the pro-inflammatory cytokine IL12-p70 and CGRP, implicated in migraine, were reduced in the meninges of K14 mice, while the levels of the mast cell activator MCP-1 were increased. The other migraine-related pro-inflammatory cytokines (basal and stimulated), did not differ between the two genotypes. The patterns of trigeminal innervation in meninges remained unchanged and we did not observe alterations in basal or ATP-induced nociceptive firing in the meningeal afferents associated with meningeal lymphatic dysfunction. In summary, the lack of meningeal lymphatic system is associated with a new balance between pro- and anti-migraine mediators but does not directly trigger meningeal nociceptive state.

Changes in Plasma Lipid Levels Following Cortical Spreading Depolarization in a Transgenic Mouse Model of Familial Hemiplegic Migraine

Metabolite levels in peripheral body fluids can correlate with attack features in migraine patients, which underscores the potential of plasma metabolites as possible disease biomarkers. Migraine headache can be preceded by an aura that is caused by cortical spreading depolarization (CSD), a transient wave of neuroglial depolarization. We previously identified plasma amino acid changes after CSD in familial hemiplegic migraine type 1 (FHM1) mutant mice that exhibit increased neuronal excitability and various migraine-related features. Here, we aimed to uncover lipid metabolic pathways affected by CSD, guided by findings on the involvement of lipids in hemiplegic migraine pathophysiology. Using targeted lipidomic analysis, we studied plasma lipid metabolite levels at different time points after CSD in wild-type and FHM1 mutant mice. Following CSD, the most prominent plasma lipid change concerned a transient increase in PGD₂, which lasted longer in mutant mice. In wild-type mice only, levels of anti-inflammatory lipid mediators DPAn-3, EPA, ALA, and DHA were elevated 24 h following CSD compared to Sham-treated animals. Given the role of PGs and neuroinflammation in migraine pathophysiology, our findings underscore the potential of monitoring peripheral changes in lipids to gain insight in central brain mechanisms.

Tissue-resident M2 macrophages directly contact primary sensory neurons in the sensory ganglia after nerve injury

Background

Macrophages in the peripheral nervous system are key players in the repair of nerve tissue and the development of neuropathic pain due to peripheral nerve injury. However, there is a lack of information on the origin and morphological features of macrophages in sensory ganglia after peripheral nerve injury, unlike those in the brain and spinal cord. We analyzed the origin and morphological features of sensory ganglionic macrophages after nerve ligation or transection using wild-type mice and mice with bone-marrow cell transplants.

Methods

After protecting the head of C57BL/6J mice with lead caps, they were irradiated and transplanted with bone-marrow-derived cells from GFP transgenic mice. The infraorbital nerve of a branch of the trigeminal nerve of wild-type mice was ligated or the infraorbital nerve of GFP-positive bone-marrow-cell-transplanted mice was transected. After immunostaining the trigeminal ganglion, the structures of the ganglionic macrophages, neurons, and satellite glial cells were analyzed using two-dimensional or three-dimensional images.

Results

The number of damaged neurons in the trigeminal ganglion increased from day 1 after infraorbital nerve ligation. Ganglionic macrophages proliferated from days 3 to 5. Furthermore, the numbers of macrophages increased from days 3 to 15. Bone-marrow-derived macrophages increased on day 7 after the infraorbital nerve was transected in the trigeminal ganglion of GFP-positive bone-marrow-cell-transplanted mice but most of the ganglionic macrophages were composed of tissue-resident cells. On day 7 after infraorbital nerve ligation, ganglionic macrophages increased in volume, extended their processes between the neurons and satellite glial cells, and contacted these neurons. Most of the ganglionic macrophages showed an M2 phenotype when contact was observed, and little neuronal cell death occurred.

Conclusion

Most of the macrophages that appear after a nerve injury are tissue-resident, and these make direct contact with damaged neurons that act in a tissue-protective manner in the M2 phenotype. These results imply that tissue-resident macrophages signal to neurons directly through physical contact.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02283-z.

Headache in people with epilepsy

Epidemiological estimates indicate that individuals with epilepsy are more likely to experience headaches, including migraine, than individuals without epilepsy. Headaches can be temporally unrelated to seizures, or can occur before, during or after an episode; seizures and migraine attacks are mostly not temporally linked. The pathophysiological links between headaches (including migraine) and epilepsy are complex and have not yet been fully elucidated. Correct diagnoses and appropriate treatment of headaches in individuals with epilepsy is essential, as headaches can contribute substantially to disease burden. Here, we review the insights that have been made into the associations between headache and epilepsy over the past 5 years, including information on the pathophysiological mechanisms and genetic variants that link the two disorders. We also discuss the current best practice for the management of headaches co-occurring with epilepsy and highlight future challenges for this area of research.

Role of Neuroinflammation and Blood-Brain Barrier Permutability on Migraine

Currently, migraine is treated mainly by targeting calcitonin gene-related peptides, although the efficacy of this method is limited and new treatment strategies are desired. Neuroinflammation has been implicated in the pathogenesis of migraine. In patients with migraine, peripheral levels of pro-inflammatory cytokines, such as interleukin-1β (IL-1β) and tumor necrosis factor-α, are known to be increased. Additionally, animal models of headache have demonstrated that immunological responses associated with cytokines are involved in the pathogenesis of migraine. Furthermore, these inflammatory mediators might alter the function of tight junctions in brain vascular endothelial cells in animal models, but not in human patients. Based on clinical findings showing elevated IL-1β, and experimental findings involving IL-1β and both the peripheral trigeminal ganglion and central trigeminal vascular pathways, regulation of the Il-1β/IL-1 receptor type 1 axis might lead to new treatments for migraine. However, the integrity of the blood-brain barrier is not expected to be affected during attacks in patients with migraine.

Involvement of TRPM2 in the Neurobiology of Experimental Migraine: Focus on Oxidative Stress and Apoptosis

Excessive Ca²⁺ influx and mitochondrial oxidative stress (OS) of trigeminal ganglia (TG) have essential roles in the etiology of migraine headache and aura. The stimulation of TRPM2 channel via the generation of OS and ADP-ribose (ADPR) induces pain, inflammatory, and oxidative neurotoxicity, although its inhibition reduces the intensity of pain and neurotoxicity in several neurons. However, the cellular and molecular effects of TRPM2 in the TG of migraine model (glyceryl trinitrate, GTN) on the induction of pain, OS, apoptosis, and inflammation remain elusive. GTN-mediated increases of pain intensity, apoptosis, death, cytosolic reactive oxygen species (ROS), mitochondrial ROS, caspase -3, caspase -9, cytosolic Ca²⁺ levels, and cytokine generations (TNF-α, IL-1β, and IL-6) in the TG of TRPM2 wild-type mouse were further increased by the TRPM2 activation, although they were modulated by the treatments of GSH, PARP-1 inhibitors (PJ34 and DPQ), and TRPM2 blockers (ACA and 2APB). However, the effects of GTN were not observed in the TG of TRPM2 knockout mice. The current data indicate that the maintaining activation of TRPM2 is not only important for the quenching OS, inflammation, and neurotoxicity in the TG neurons of mice with experimental migraine but also equally critical to the modulation of GTN-induced pain.

Chemokines and Pain in the Trigeminal System

Chemotactic cytokines or chemokines are a large family of secreted proteins able to induce chemotaxis. Chemokines are categorized according to their primary amino acid sequence, and in particular their cysteine residues that form disulphide bonds to maintain the structure: CC, CXC, CX3C, and XC, in which X represents variable amino acids. Among their many roles, chemokines are known to be key players in pain modulation in the peripheral and central nervous systems. Thus, they are promising candidates for novel therapeutics that could replace current, often ineffective treatments. The spinal and trigeminal systems are intrinsically different beyond their anatomical location, and it has been suggested that there are also differences in their sensory mechanisms. Hence, understanding the different mechanisms involved in pain modulation for each system could aid in developing appropriate pharmacological alternatives. Here, we aim to describe the current landscape of chemokines that have been studied specifically with regard to trigeminal pain. Searching PubMed and Google Scholar, we identified 30 reports describing chemokines in animal models of trigeminal pain, and 15 reports describing chemokines involved in human pain associated with the trigeminal system. This review highlights the chemokines studied to date at different levels of the trigeminal system, their cellular localization and, where available, their role in a variety of animal pain models.

Migraine and neuroinflammation: the inflammasome perspective

BACKGROUND

Neuroinflammation has an important role in the pathophysiology of migraine, which is a complex neuro-glio-vascular disorder. The main aim of this review is to highlight findings of cortical spreading depolarization (CSD)-induced neuroinflammatory signaling in brain parenchyma from the inflammasome perspective. In addition, we discuss the limited data of the contribution of inflammasomes to other aspects of migraine pathophysiology, foremost the activation of the trigeminovascular system and thereby the generation of migraine pain.

MAIN BODY

Inflammasomes are signaling multiprotein complexes and key components of the innate immune system. Their activation causes the production of inflammatory cytokines that can stimulate trigeminal neurons and are thus relevant to the generation of migraine pain. The contribution of inflammasome activation to pain signaling has attracted considerable attention in recent years. Nucleotide-binding domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) is the best characterized inflammasome and there is emerging evidence of its role in a variety of inflammatory pain conditions, including migraine. In this review, we discuss, from an inflammasome point of view, cortical spreading depolarization (CSD)-induced neuroinflammatory signaling in brain parenchyma, the connection with genetic factors that make the brain vulnerable to CSD, and the relation of the inflammasome with diseases that are co-morbid with migraine, including stroke, epilepsy, and the possible links with COVID-19 infection.

CONCLUSION

Neuroinflammatory pathways, specifically those involving inflammasome proteins, seem promising candidates as treatment targets, and perhaps even biomarkers, in migraine.

Overexpressed Na V 1.7 Channels Confer Hyperexcitability to in vitro Trigeminal Sensory Neurons of Ca V 2.1 Mutant Hemiplegic Migraine Mice

Trigeminal sensory neurons of transgenic knock-in (KI) mice expressing the R192Q missense mutation in the α1A subunit of neuronal voltage-gated Ca_V2.1 Ca²⁺ channels, which leads to familial hemiplegic migraine type 1 (FHM1) in patients, exhibit a hyperexcitability phenotype. Here, we show that the expression of Na_V1.7 channels, linked to pain states, is upregulated in KI primary cultures of trigeminal ganglia (TG), as shown by increased expression of its α1 subunit. In the majority of TG neurons, Na_V1.7 channels are co-expressed with ATP-gated P2X3 receptors (P2X3R), which are important nociceptive sensors. Reversing the trigeminal phenotype with selective Ca_V2.1 channel inhibitor ω-agatoxin IVA inhibited Na_V1.7 overexpression. Functionally, KI neurons revealed a TTX-sensitive inward current of larger amplitude that was partially inhibited by selective Na_V1.7 blocker Tp1a. Under current-clamp condition, Tp1a raised the spike threshold of both wild-type (WT) and KI neurons with decreased firing rate in KI cells. Na_V1.7 activator OD1 accelerated firing in WT and KI neurons, a phenomenon blocked by Tp1a. Enhanced expression and function of Na_V1.7 channels in KI TG neurons resulted in higher excitability and facilitated nociceptive signaling. Co-expression of Na_V1.7 channels and P2X3Rs in TGs may explain how hypersensitivity to local stimuli can be relevant to migraine.

Antidromic Spike Propagation and Dissimilar Expression of P2X, 5-HT, and TRPV1 Channels in Peripheral vs. Central Sensory Axons in Meninges

Background: The terminal branches of the trigeminal nerve in meninges are supposed to be the origin site of migraine pain. The main function of these peripheral sensory axons is the initiation and propagation of spikes in the orthodromic direction to the second order neurons in the brainstem. The stimulation of the trigeminal ganglion induces the release of the neuropeptide CGRP in meninges suggesting the antidromic propagation of excitation in these fibers. However, the direct evidence on antidromic spike traveling in meningeal afferents is missing. Methods: By recording of spikes from peripheral or central parts of the trigeminal nerve in rat meninges, we explored their functional activity and tested the expression of ATP-, serotonin-, and capsaicin-gated receptors in the distal vs. proximal parts of these nerves. Results: We show the significant antidromic propagation of spontaneous spikes in meningeal nerves which was, however, less intense than the orthodromic nociceptive traffic due to higher number of active fibers in the latter. Application of ATP, serotonin and capsaicin induced a high frequency nociceptive firing in peripheral processes while, in central parts, only ATP and capsaicin were effective. Disconnection of nerve from trigeminal ganglion dramatically reduced the tonic antidromic activity and attenuated the excitatory action of ATP. Conclusion: Our data indicate the bidirectional nociceptive traffic and dissimilar expression of P2X, 5-HT and TRPV1 receptors in proximal vs. distal parts of meningeal afferents, which is important for understanding the peripheral mechanisms of migraine pain.

Fruquintinib inhibits VEGF/VEGFR2 axis of choroidal endothelial cells and M1-type macrophages to protect against mouse laser-induced choroidal neovascularization

Wet age-related macular degeneration, which is characterized by choroidal neovascularization (CNV) and induces obvious vision loss. Vascular endothelial growth factor (VEGF) family member VEGF-A (also named as VEGF) and its receptor VEGFR2 contribute to the pathogenesis of CNV. Choroidal endothelial cells (CECs) secret C–C motif chemokine ligand 2 (CCL2), which attracts macrophages to CNV lesion and promotes macrophage M1 polarization. Accordingly, infiltrating macrophages secret inflammatory cytokines to promote CNV. In vivo, intravitreal injection of fruquintinib (HMPL-013), an antitumor neovascularization drug, alleviated mouse CNV formation without obvious ocular toxicity. Meanwhile, HMPL-013 inhibited VEGF/VEGFR2 binding in CECs and macrophages, as well as macrophage M1 polarization. In vitro, noncontact coculture of human choroidal vascular endothelial cells (HCVECs) and macrophages under hypoxia conditions was established. HMPL-013 downregulated VEGF/VEGFR2/phosphoinositide-3-kinase/protein kinase B (AKT)/nuclear factor kappa B pathway and CCL2 secretion in HCVECs, as well as VEGF/VEGFR2-induced macrophage M1 polarization under hypoxia condition. In addition, HMPL-013 inhibited HCEVC derived CCL2-induced macrophage migration and M1 polarization, along with macrophage M1 polarization-induced HCVECs proliferation, migration, and tube formation. Altogether, HMPL-013 alleviated CNV formation might via breaking detrimental cross talk between CECs and macrophages.

RAR-related orphan receptor A: One gene with multiple functions related to migraine

Aims

RAR‐related orphan receptor (RORA) involves in regulation of several biological processes including inflammation and circadian rhythm that probably are involved in migraine pathophysiology. In the current study, the association between RORA rs11639084 and rs4774388 variants and susceptibility to migraine were investigated in a sample of Iranian migraine patients for the first time.

Methods

In a case‐control study including 400 participants, 200 migraineurs and 200 healthy controls, genotyping of RORA rs4774388 and rs11639084 polymorphisms was performed using tetra‐primer amplification refractory mutation system–polymerase chain reaction (TP‐ARMS‐PCR).

Results

The distribution of rs4774388 C/T and T/T genotypes differed significantly between the studied groups. Moreover, an association was observed between rs4774388 and migraine under the recessive mode of inheritance (P = 0.002; OR = 1.89.; CI = 1.25‐2.87). The distribution of rs11639084 alleles and genotypes was not significantly different between migraineurs and healthy controls.

Conclusion

Current results suggest RORA, as a molecular link, may explain inflammation and circadian rhythm dysfunction in migraine. Further studies in different ethnicities are required to confirm the function of RORA in migraine development.

Retrograde Labeling of Different Distribution Features of DRG P2X2 and P2X3 Receptors in a Neuropathic Pain Rat Model

The distributions of P2X subtypes during peripheral neuropathic pain conditions and their differential roles are not fully understood. To explore these characteristics, the lumbosacral dorsal root ganglion (DRG) in the chronic constriction injury (CCI) sciatic nerve rat model was studied. Retrograde trace labeling combined with immunofluorescence technology was applied to analyze the distribution of neuropathic nociceptive P2X1-6 receptors. Our results suggest that Fluoro-Gold (FG) retrograde trace labeling is an efficient method for studying lumbosacral DRG neurons in the CCI rat model, especially when the DRG neurons are divided into small, medium, and large subgroups. We found that neuropathic nociceptive lumbosacral DRG neurons (i.e., FG-positive cells) were significantly increased in medium DRG neurons, while they declined in the large DRG neurons in the CCI group. P2X3 receptors were markedly upregulated in medium while P2X2 receptors were significantly decreased in small FG-positive DRG neurons. There were no significant changes in other P2X receptors (including P2X1, P2X4, P2X5, and P2X6). We anticipate that P2X receptors modulate nociceptive sensitivity primarily through P2X3 subtypes that are upregulated in medium neuropathic nociceptive DRG neurons and/or via the downregulation of P2X2 cells in neuropathic nociceptive small DRG neurons.

Orofacial skin inflammation increases the number of macrophages in the maxillary subregion of the rat trigeminal ganglion in a corticosteroid-reversible manner

Inflammation of the cutaneous orofacial tissue can lead to a prolonged alteration of neuronal and nonneuronal cellular functions in trigeminal nociceptive pathways. In this study, we investigated the effects of experimentally induced skin inflammation by dithranol (anthralin) on macrophage activation in the rat trigeminal ganglion. Tissue localization and protein expression levels of ionized calcium-binding adaptor molecule 1 (Iba1), a macrophage/microglia-specific marker, and proliferation/mitotic marker antigen identified by the monoclonal antibody Ki67 (Ki67), were quantitatively analyzed using immunohistochemistry and western blots in control, dithranol-treated, dithranol- and corticosteroid-treated, and corticosteroid-treated trigeminal ganglia. Chronic orofacial dithranol treatment elicited a strong pro-inflammatory effect in the ipsilateral trigeminal ganglion. Indeed, daily dithranol treatment of the orofacial skin for 3-5 days increased the number of macrophages and Iba1 protein expression in the maxillary subregion of the ipsilateral ganglion. In the affected ganglia, none of the Iba1-positive cells expressed Ki67. This absence of mitotically active cells suggested that the accumulation of macrophages in the ganglion was not the result of resident microglia proliferation but rather the extravasation of hematogenous monocytes from the periphery. Subsequently, when a 5-day-long anti-inflammatory corticosteroid therapy was employed on the previously dithranol-treated orofacial skin, Iba1 immunoreactivity was substantially reduced in the ipsilateral ganglion. Collectively, our findings indicate that both peripheral inflammation and subsequent anti-inflammatory therapy affect macrophage activity and thus interfere with the functioning of the affected sensory ganglion neurons.

The fifth cranial nerve in headaches

The fifth cranial nerve is the common denominator for many headaches and facial pain pathologies currently known. Projecting from the trigeminal ganglion, in a bipolar manner, it connects to the brainstem and supplies various parts of the head and face with sensory innervation. In this review, we describe the neuroanatomical structures and pathways implicated in the sensation of the trigeminal system. Furthermore, we present the current understanding of several primary headaches, painful neuropathies and their pharmacological treatments. We hope that this overview can elucidate the complex field of headache pathologies, and their link to the trigeminal nerve, to a broader field of young scientists.

Mouse Models of Familial Hemiplegic Migraine for Studying Migraine Pathophysiology

Migraine, an extremely disabling neurological disorder, has a strong genetic component. Since monogenic mi-graines (resulting from mutations or changes in a single gene) may help researchers discover migraine pathophysiology, transgenic mice models harboring gene mutations identified in Familial Hemiplegic Migraine (FHM) patients have been gen-erated. Studies in these FHM mutant mice models have shed light on the mechanisms of migraine and may aid in the identifi-cation of novel targets for treatment. More specifically, the studies shed light on how gene mutations, hormones, and other factors impact the pathophysiology of migraine. The models may also be of relevance to researchers outside the field of mi-graine as some of their aspects are relevant to pain in general. Additionally, because of the comorbidities associated with mi-graine, they share similarities with the mutant mouse models of epilepsy, stroke, and perhaps depression. Here, we review the experimental data obtained from these mutant mice and focus on how they can be used to investigate the pathophysiology of migraine, including synaptic plasticity, neuroinflammation, metabolite alterations, and molecular and behavioral mecha-nisms of pain.

Mechanisms of migraine as a chronic evolutive condition

Understanding the mechanisms of migraine remains challenging as migraine is not a static disorder, and even in its episodic form migraine remains an "evolutive" chronic condition. Considerable progress has been made in elucidating the pathophysiological mechanisms of migraine, associated genetic factors that may influence susceptibility to the disease, and functional and anatomical changes during the progression of a migraine attack or the transformation of episodic to chronic migraine. Migraine is a life span neurological disorder that follows an evolutive age-dependent change in its prevalence and even clinical presentations. As a disorder, migraine involves recurrent intense head pain and associated unpleasant symptoms. Migraine attacks evolve over different phases with specific neural mechanisms and symptoms being involved during each phase. In some patients, migraine can be transformed into a chronic form with daily or almost daily headaches. The mechanisms behind this evolutive process remain unknown, but genetic and epigenetic factors, inflammatory processes and central sensitization may play an important role.

TRESK K+ Channel Activity Regulates Trigeminal Nociception and Headache

Although TWIK-related spinal cord K⁺ (TRESK) channel is expressed in all primary afferent neurons in trigeminal ganglia (TG) and dorsal root ganglia (DRG), whether TRESK activity regulates trigeminal pain processing is still not established. Dominant-negative TRESK mutations are associated with migraine but not with other types of pain in humans, suggesting that genetic TRESK dysfunction preferentially affects the generation of trigeminal pain, especially headache. Using TRESK global knock-out mice as a model system, we found that loss of TRESK in all TG neurons selectively increased the intrinsic excitability of small-diameter nociceptors, especially those that do not bind to isolectin B4 (IB4^-). Similarly, loss of TRESK resulted in hyper-excitation of the small IB4^- dural afferent neurons but not those that bind to IB4 (IB4⁺). Compared with wild-type littermates, both male and female TRESK knock-out mice exhibited more robust trigeminal nociceptive behaviors, including headache-related behaviors, whereas their body and visceral pain responses were normal. Interestingly, neither the total persistent outward current nor the intrinsic excitability was altered in adult TRESK knock-out DRG neurons, which may explain why genetic TRESK dysfunction is not associated with body and/or visceral pain in humans. We reveal for the first time that, among all primary afferent neurons, TG nociceptors are the most vulnerable to the genetic loss of TRESK. Our findings indicate that endogenous TRESK activity regulates trigeminal nociception, likely through controlling the intrinsic excitability of TG nociceptors. Importantly, we provide evidence that genetic loss of TRESK significantly increases the likelihood of developing headache.

Genetic mouse models of migraine

Mouse models of rare monogenic forms of migraine provide a unique experimental system to study the cellular and circuit mechanisms of the primary brain dysfunctions causing a migraine disorder. Here, we discuss the migraine-relevant phenotypes and the migraine-relevant functional alterations in the brain of five genetic mouse models of migraine, four of which carry mutations derived from patients with familial hemiplegic migraine (FHM) and the fifth carry a mutation from patients with both phenotypically normal MA and familial advanced sleep phase syndrome (FASPS). We focus on the latter mouse model, in which a ubiquitous serine-threonine kinase is mutated, and on two mouse models of pure FHM, in which a voltage-gated calcium channel controlling neurotransmitter release at most brain synapses and a Na/K ATPase that is expressed mainly in astrocytes in the adult brain are mutated, respectively. First, we describe the behavioral phenotypes of the genetic animal models and review the evidence that an increased susceptibility to experimentally induced cortical spreading depression (CSD) is a key migraine-relevant phenotype common to the five models. Second, we review the synaptic alterations in the cerebral cortex of the genetic models of migraine and discuss the mechanisms underlying their increased susceptibility to CSD. Third, we review the alterations in the trigeminovascular pain pathway and discuss possible implications for migraine pain mechanisms. Finally, we discuss the insights into migraine pathophysiology obtained from the genetic models of migraine, in particular regarding the mechanisms that make the brain of migraineurs susceptible to the ignition of “spontaneous” CSDs. Although the reviewed functional studies support the view of migraine as a disorder of the brain characterized by dysfunctional regulation of the excitatory/inhibitory balance in specific neuronal circuits, much work remains to be done in the genetic mouse models e.g. to identfy the relevant dysfunctional circuits and to establish whether and how the alterations in the function of specific circuits (in the cerebral cortex and/or other brain areas) are state-dependent and may, in certain conditions, favor CSD ignition and the migraine attack.

Basal astrocyte and microglia activation in the central nervous system of Familial Hemiplegic Migraine Type I mice

Background

Gain-of-function missense mutations in the α1A subunit of neuronal CaV2.1 channels, which define Familial Hemiplegic Migraine Type 1 (FHM1), result in enhanced cortical glutamatergic transmission and a higher susceptibility to cortical spreading depolarization. It is now well established that neurons signal to surrounding glial cells, namely astrocytes and microglia, in the central nervous system, which in turn become activated and in pathological conditions can sustain neuroinflammation. We and others previously demonstrated an increased activation of pro-algogenic pathways, paralleled by augmented macrophage infiltration, in both isolated trigeminal ganglia and mixed trigeminal ganglion neuron-satellite glial cell cultures of FHM1 mutant mice. Hence, we hypothesize that astrocyte and microglia activation may occur in parallel in the central nervous system.

Methods

We have evaluated signs of reactive glia in brains from naïve FHM1 mutant mice in comparison with wild type animals by immunohistochemistry and Western blotting.

Results

Here we show for the first time signs of reactive astrogliosis and microglia activation in the naïve FHM1 mutant mouse brain.

Conclusions

Our data reinforce the involvement of glial cells in migraine, and suggest that modulating such activation may represent an innovative approach to reduce pathology.

A clinical model for identifying an inflammatory phenotype in mood disorders

Increasingly, clinical research has found inflammatory correlates of psychiatric disorders, particularly mood symptomatology. Biological measures may provide greater precision in many cases and may capture clinically-relevant inflammatory signposts, such as central obesity risk, inflammation-associated co-morbid medical conditions, or proinflammatory lifestyle choices. In order to expand understanding of the role of inflammation in mood disorders, we propose a more inclusive clinical model for capturing an inflammatory phenotype of depression by identifying clinically-relevant inflammatory phenotypes grounded in biology. Our model includes chronic conditions and lifestyle behaviors associated with clinically elevated inflammation in mood disorders. Elements of this "inflamed depression" model include: obesity, low HDL concentrations, elevated triglyceride concentrations, chronically elevated blood pressure, clinical diagnosis of hypothyroidism, migraines, rheumatoid arthritis, adult onset diabetes, inflammatory bowel diseases, inflammatory skin conditions, and lifestyle factors including smoking cigarettes and chronic stress.

Investigating macrophage-mediated inflammation in migraine using ultrasmall superparamagnetic iron oxide-enhanced 3T magnetic resonance imaging

Background

Initiating mechanisms of migraine headache remain poorly understood and a biomarker of migraine does not exist. Inflammation pertaining to the wall of cerebral arteries and brain parenchyma has been suggested to play a role in migraine pathophysiology.

Objective

We conducted the first experimental human study to investigate macrophage-mediated inflammation as a possible biomarker of migraine.

Methods

Using ultrasmall superparamagnetic iron oxide (USPIO)-enhanced 3T magnetic resonance imaging (MRI), we investigated the presence of macrophages in cerebral artery walls and in brain parenchyma of patients with migraine without aura. We used the phosphodiesterase-3-inhibitor cilostazol as an experimental migraine trigger, and investigated both patients who received sumatriptan treatment, and patients who did not. To validate our use of USPIO-enhanced MRI, we included a preclinical mouse model with subcutaneous capsaicin injection in the trigeminal V1 area. The study is registered at ClinicalTrials.gov with the identifier NCT02549898.

Results

A total of 28 female patients with migraine without aura underwent a baseline MRI scan, ingested cilostazol, developed a migraine-like attack, and underwent an USPIO-enhanced MRI scan > 24 hours after intravenous administration of USPIO. Twelve patients treated their attack with 6 mg s.c. sumatriptan, while the remaining 16 patients received no migraine-specific rescue medication. The preclinical model confirmed that USPIO-enhanced MRI detects macrophage-mediated inflammation. In patients, however, migraine attacks were not associated with increased USPIO signal on the pain side of the head compared to the non-pain side.

Conclusion

Our findings suggest that migraine without aura is not associated with macrophage-mediated inflammation specific to the head pain side.

Involvement of Voltage-Gated Calcium Channels in Inflammation and Inflammatory Pain

Voltage-gated calcium channels (VGCCs) are classified into high-voltage-activated (HVA) channels and low-voltage-activated channels consisting of Ca_v3.1-3.3, known as T ("transient")-type VGCC. There is evidence that certain types of HVA channels are involved in neurogenic inflammation and inflammatory pain, in agreement with reports indicating the therapeutic effectiveness of gabapentinoids, ligands for the α₂δ subunit of HVA, in treating not only neuropathic, but also inflammatory, pain. Among the Ca_v3 family members, Ca_v3.2 is abundantly expressed in the primary afferents, regulating both neuronal excitability at the peripheral terminals and spontaneous neurotransmitter release at the spinal terminals. The function and expression of Ca_v3.2 are modulated by a variety of inflammatory mediators including prostanoids and hydrogen sulfide (H₂S), a gasotransmitter. The increased activity of Ca_v3.2 by H₂S participates in colonic, bladder and pancreatic pain, and regulates visceral inflammation. Together, VGCCs are involved in inflammation and inflammatory pain, and Ca_v3.2 T-type VGCC is especially a promising therapeutic target for the treatment of visceral inflammatory pain in patients with irritable bowel syndrome, interstitial cystitis/bladder pain syndrome, pancreatitis, etc., in addition to neuropathic pain.

What role does multiple sclerosis play in the development of untreatable painful conditions?

Clinical data outline the high incidence of pain syndromes in patients with multiple sclerosis, with a significant prevalence of craniofacial manifestations, including trigeminal neuralgia and migraine, which are very difficult to be managed pharmacologically. The common explanation of a localization of demyelinating plaques in areas devoted to pain modulation and integration as a trigger for pain development seems now partially unsatisfactory, since pain is often manifested well before the clinical signs of the pathology and its severity does not correlate with disease progression. This review focuses on additional mechanisms which could be at the basis of pain development in multiple sclerosis, whose identification will help identifying new targets to design more effective analgesic strategies.

In situ imaging reveals properties of purinergic signalling in trigeminal sensory ganglia in vitro

Chronic pain is supported by sterile inflammation that induces sensitisation of sensory neurons to ambient stimuli including extracellular ATP acting on purinergic P2X receptors. The development of in vitro methods for drug screening would be useful to investigate cell crosstalk and plasticity mechanisms occurring during neuronal sensitisation and sterile neuroinflammation. Thus, we studied, at single-cell level, membrane pore dilation based on the uptake of a fluorescent probe following sustained ATP-gated P2X receptor function in neurons and non-neuronal cells of trigeminal ganglion cultures from wild-type (WT) and R192Q CaV2.1 knock-in (KI) mice, a model of familial hemiplegic migraine type 1 characterised by neuronal sensitisation and higher release of soluble mediators. In WT cultures, pore responses were mainly evoked by ATP rather than benzoyl-ATP (BzATP) and partly inhibited by the P2X antagonist TNP-ATP. P2X7 receptors were expressed in trigeminal ganglia mainly by non-neuronal cells. In contrast, KI cultures showed higher expression of P2X7 receptors, stronger responses to BzATP, an effect largely prevented by prior administration of CaV2.1 blocker ω-agatoxin IVA, small interfering RNA (siRNA)-based silencing of P2X7 receptors or the P2X7 antagonist A-804598. No cell toxicity was detected with the protocols. Calcitonin gene-related peptide (CGRP), a well-known migraine mediator, potentiated BzATP-evoked membrane permeability in WT as well as R192Q KI cultures, demonstrating its modulatory role on trigeminal sensory ganglia. Our results show an advantageous experimental approach to dissect pharmacological properties potentially relevant to chronic pain and suggest that CGRP is a soluble mediator influencing purinergic P2X pore dilation and regulating inflammatory responses.

Inflammatory pain assessment in the arthritis of the temporomandibular joint in rats: A comparison between two phlogistic agents

Temporomandibular joint (TMJ) disorders are a group of conditions that result in TMJ pain, which frequently limits basic daily activities. Experimental models that allow the study of the mechanisms underlying these inflammatory and pain conditions are of great clinical relevance. The aim of this study was to evaluate nociception, inflammation and participation of the macrophage/microglia cells in the arthritis of the TMJ induced by two phlogistic agents. 84 rats were divided into 2 groups: Zy, which received zymosan intra-articularly, or Cg, which received carrageenan intra-articularly. Mechanical nociception, total leukocyte influx to the synovial fluid and histopathological analyses were evaluated in the TMJ. The participation of macrophage/microglia located in trigeminal ganglia (TG) and in the subnucleus caudalis (V-SnC) was assessed immunohistochemically. Both agents induced mechanical hyperalgesia 6h after the induction, but a more persistent algesic state was perceived in the Cg group, which lasted for 120h. Even though both groups presented increased leukocyte influx, the Zy-group presented a more intense influx. Zymosan recruited resident macrophage in the trigeminal ganglia 24h after the injection. In the V-SnC, the group Cg presented a more prolonged immunolabeling pattern in comparison with the group Zy. It can be concluded that zymosan induced a more intense infiltrate and peripheral nervous changes, while Cg lead to a moderate TMJ inflammation with prominent changes in the V-SnC.

Comorbid association of antiphospholipid antibodies and migraine: A systematic review and meta-analysis

BACKGROUND

Antiphospholipid antibodies (aPLs) namely anticardiolipin (aCL) antibody, anti-β2-glycoprotein I (β2GPI) antibody and lupus anticoagulant (LA) are autoantibodies produced against anionic phospholipids and proteins on plasma membranes. Migraine is a primary headache disorder which has growing evidences of autoimmune-mediated pathogenesis and previous studies suggested the presence of aPLs in migraine patients.

AIMS

The aim of this study was to evaluate the comorbid association between aPLs (aCL, anti-β2GPI and LA) and migraine compared to healthy controls.

METHODS

Studies were searched through PubMed, ISI Web of Science and Google Scholar databases without restricting the languages and year (up to October 2016) and were selected based on the inclusion criteria. Two authors independently extracted data from the included studies. All analyses were conducted by using random effects model to calculate the odds ratio (OR) and 95% confidence interval (CI). Quality assessment was carried out by using the modified Newcastle-Ottawa Scale (NOS). Publication bias was evaluated via visualization of funnel plots, Begg's and Egger's tests.

RESULTS

The database searches produced 1995 articles, 13 of which were selected (912 migraineurs and 822 healthy controls). 8.59%, 15.21% and 4.11% of the migraineurs exhibited aCL, anti-β2GPI and LA which was 4.83, 1.63 and 3.03 times higher, respectively, than healthy controls. A significant presence of aCL (OR: 3.55, 95% CI: 1.59-7.95; p=0.002) or anti-β2GPI antibodies (OR: 2.02, 95% CI: 1.20-3.42; p=0.008) was observed in migraine patients, however, LA was not significantly associated (OR: 2.02, 95% CI: 0.50-8.37; p=0.320). Majority of the studies (n=10 of 13) demonstrated NOS score of 7 or above and no significant publication bias was observed.

CONCLUSION

Migraine might be an autoimmune-associated neurologic disorder. The presence of aCL or anti-β2GPI antibodies was significant in migraine patients compared to healthy controls, suggesting an involvement of these autoantibodies in migraine attack.

The scaffold protein calcium/calmodulin-dependent serine protein kinase controls ATP release in sensory ganglia upon P2X3 receptor activation and is part of an ATP keeper complex

P2X3 receptors, gated by extracellular ATP, are expressed by sensory neurons and are involved in peripheral nociception and pain sensitization. The ability of P2X3 receptors to transduce extracellular stimuli into neuronal signals critically depends on the dynamic molecular partnership with the calcium/calmodulin-dependent serine protein kinase (CASK). The present work used trigeminal sensory neurons to study the impact that activation of P2X3 receptors (evoked by the agonist α,β-meATP) has on the release of endogenous ATP and how CASK modulates this phenomenon. P2X3 receptor function was followed by ATP efflux via Pannexin1 (Panx1) hemichannels, a mechanism that was blocked by the P2X3 receptor antagonist A-317491, and by P2X3 silencing. ATP efflux was enhanced by nerve growth factor, a treatment known to potentiate P2X3 receptor function. Basal ATP efflux was not controlled by CASK, and carbenoxolone or Pannexin silencing reduced ATP release upon P2X3 receptor function. CASK-controlled ATP efflux followed P2X3 receptor activity, but not depolarization-evoked ATP release. Molecular biology experiments showed that CASK was essential for the transactivation of Panx1 upon P2X3 receptor activation. These data suggest that P2X3 receptor function controls a new type of feed-forward purinergic signaling on surrounding cells, with consequences at peripheral and spinal cord level. Thus, P2X3 receptor-mediated ATP efflux may be considered for the future development of pharmacological strategies aimed at containing neuronal sensitization. P2X3 receptors are involved in sensory transduction and associate to CASK. We have studied in primary sensory neurons the molecular mechanisms downstream P2X3 receptor activation, namely ATP release and partnership with CASK or Panx1. Our data suggest that CASK and P2X3 receptors are part of an ATP keeper complex, with important feed-forward consequences at peripheral and central level.

The Revolution in Migraine Genetics: From Aching Channels Disorders to a Next-Generation Medicine

Channelopathies are a heterogeneous group of neurological disorders resulting from dysfunction of ion channels located in cell membranes and organelles. The clinical scenario is broad and symptoms such as generalized epilepsy (with or without fever), migraine (with or without aura), episodic ataxia and periodic muscle paralysis are some of the best known consequences of gain- or loss-of-function mutations in ion channels. We review the main clinical effects of ion channel mutations associated with a significant impact on migraine headache. Given the increasing and evolving use of genetic analysis in migraine research-greater emphasis is now placed on genetic markers of dysfunctional biological systems-we also show how novel information in rare monogenic forms of migraine might help to clarify the disease mechanisms in the general population of migraineurs. Next-generation sequencing (NGS) and more accurate and precise phenotyping strategies are expected to further increase understanding of migraine pathophysiology and genetics.

Targeted overexpression of tumor necrosis factor-α increases cyclin-dependent kinase 5 activity and TRPV1-dependent Ca2+ influx in trigeminal neurons

We reported earlier that TNF-α, a proinflammatory cytokine implicated in many inflammatory disorders causing orofacial pain, increases the activity of Cdk5, a key kinase involved in brain development and function and recently found to be involved in pain signaling. To investigate a potential mechanism underlying inflammatory pain in trigeminal ganglia (TGs), we engineered a transgenic mouse model (TNF) that can conditionally overexpresses TNF-α upon genomic recombination by Cre recombinase. TNF mice were bred with Nav1.8-Cre mouse line that expresses the Cre recombinase in sensory neurons to obtain TNF-α:Nav1.8-Cre (TNF-α cTg) mice. Although TNF-α cTg mice appeared normal without any gross phenotype, they displayed a significant increase in TNF-α levels after activation of NFκB signaling in the TG. IL-6 and MCP-1 levels were also increased along with intense immunostaining for Iba1 and GFAP in TG, indicating the presence of infiltrating macrophages and the activation of satellite glial cells. TNF-α cTg mice displayed increased trigeminal Cdk5 activity, and this increase was associated with elevated levels of phospho-T407-TRPV1 and capsaicin-evocated Ca influx in cultured trigeminal neurons. Remarkably, this effect was prevented by roscovitine, an inhibitor of Cdk5, which suggests that TNF-α overexpression induced sensitization of the TRPV1 channel. Furthermore, TNF-α cTg mice displayed more aversive behavior to noxious thermal stimulation (45°C) of the face in an operant pain assessment device as compared with control mice. In summary, TNF-α overexpression in the sensory neurons of TNF-α cTg mice results in inflammatory sensitization and increased Cdk5 activity; therefore, this mouse model would be valuable for investigating the mechanism of TNF-α involved in orofacial pain.

Inefficient constitutive inhibition of P2X3 receptors by brain natriuretic peptide system contributes to sensitization of trigeminal sensory neurons in a genetic mouse model of familial hemiplegic migraine

BACKGROUND

On trigeminal ganglion neurons, pain-sensing P2X3 receptors are constitutively inhibited by brain natriuretic peptide via its natriuretic peptide receptor-A. This inhibition is associated with increased P2X3 serine phosphorylation and receptor redistribution to non-lipid raft membrane compartments. The natriuretic peptide receptor-A antagonist anantin reverses these effects. We studied whether P2X3 inhibition is dysfunctional in a genetic familial hemiplegic migraine type-1 model produced by introduction of the human pathogenic R192Q missense mutation into the mouse CACNA1A gene (knock-in phenotype). This model faithfully replicates several properties of familial hemiplegic migraine type-1, with gain-of-function of CaV2.1 Ca(2+) channels, raised levels of the algogenic peptide calcitonin gene-related peptide, and enhanced activity of P2X3 receptors in trigeminal ganglia.

RESULTS

In knock-in neurons, anantin did not affect P2X3 receptor activity, membrane distribution, or serine phosphorylation level, implying ineffective inhibition by the constitutive brain natriuretic peptide/natriuretic peptide receptor-A pathway. However, expression and functional properties of this pathway remained intact together with its ability to downregulate TRPV1 channels. Reversing the familial hemiplegic migraine type-1 phenotype with the CaV2.1-specific antagonist, ω-agatoxin IVA restored P2X3 activity to wild-type level and enabled the potentiating effects of anantin again. After blocking calcitonin gene-related peptide receptors, P2X3 receptors exhibited wild-type properties and were again potentiated by anantin.

CONCLUSIONS

P2X3 receptors on mouse trigeminal ganglion neurons are subjected to contrasting modulation by inhibitory brain natriuretic peptide and facilitatory calcitonin gene-related peptide that both operate via complex intracellular signaling. In the familial hemiplegic migraine type-1 migraine model, the action of calcitonin gene-related peptide appears to prevail over brain natriuretic peptide, thus suggesting that peripheral inhibition of P2X3 receptors becomes insufficient and contributes to trigeminal pain sensitization.

Animal models of monogenic migraine

Migraine is a highly prevalent and disabling neurological disorder with a strong genetic component. Rare monogenic forms of migraine, or syndromes in which migraine frequently occurs, help scientists to unravel pathogenetic mechanisms of migraine and its comorbidities. Transgenic mouse models for rare monogenic mutations causing familial hemiplegic migraine (FHM), cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and familial advanced sleep-phase syndrome (FASPS), have been created. Here, we review the current state of research using these mutant mice. We also discuss how currently available experimental approaches, including epigenetic studies, biomolecular analysis and optogenetic technologies, can be used for characterization of migraine genes to further unravel the functional and molecular pathways involved in migraine.

From migraine genes to mechanisms

Migraine is a common multifactorial episodic brain disorder with strong genetic basis. Monogenic subtypes include rare familial hemiplegic migraine, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, familial advanced sleep-phase syndrome (FASPS), and retinal vasculopathy with cerebral leukodystrophy. Functional studies of disease-causing mutations in cellular and/or transgenic models revealed enhanced (glutamatergic) neurotransmission and abnormal vascular function as key migraine mechanisms. Common forms of migraine (both with and without an aura), instead, are thought to have a polygenic makeup. Genome-wide association studies have already identified over a dozen genes involved in neuronal and vascular mechanisms. Here, we review the current state of molecular genetic research in migraine, also with respect to functional and pathway analyses. We will also discuss how novel experimental approaches for the identification and functional characterization of migraine genes, such as next-generation sequencing, induced pluripotent stem cell, and optogenetic technologies will further our understanding of the molecular pathways involved in migraine pathogenesis.