Transient receptor potential melastatin 8 is required for nitroglycerin- and calcitonin gene-related peptide-induced migraine-like pain behaviors in mice

Activation of central and peripheral transient receptor potential melastatin 8 increases susceptibility to spreading depolarization and facilitates trigeminal neuroinflammation

BACKGROUND

Transient receptor potential melastatin 8 (TRPM8), a gene encoding a nonselective cation channel responsive to cold stimuli, has been implicated in migraine susceptibility. Despite this association, the role of TRPM8 to migraine pathogenesis remains elusive. This study aims to elucidate the potential role of TRPM8 in migraine pathophysiology.

METHODS

TRPM8 expression in the cortex and primary trigeminal ganglion (TG) cells was analyzed via immunostaining. The central role of TRPM8 was assessed using a spreading depolarization (SD) model, where intracerebroventricular injections or topical applications of TRPM8 agonists and antagonists were administered to rats to investigate their effects on KCl-evoked SD and SD-induced cortical inflammation. The peripheral role of TRPM8 in migraine was evaluated using primary cultures of rat TG cells by analyzing the effects of TRPM8 activation on calcitonin gene-related peptide (CGRP) expression, release, and trigeminal neuroinflammation.

RESULTS

TRPM8 was homogeneously distributed in the cerebral cortex, predominantly co-localizing with cortical neurons. Activation of cortical TRPM8 increased the frequency of KCl-evoked SD and exacerbated SD-induced cortical inflammation. Interestingly. Interestingly, inhibition of cerebral TRPM8 had negligible effects. In TG primary cultures, TRPM8 activation upregulated CGRP expression and release and induced cyclooxygenase-2 (Cox2) upregulation via a calmodulin kinase II (CaMKII)-dependent mechanism.

CONCLUSIONS

TRPM8 activation increased susceptibility to SD and facilitated the effects of CGRP and trigeminal neuroinflammation, implicating that TRPM8 may contribute to migraine pathophysiology through central and peripheral mechanisms.

The neurotrophic factor artemin and its receptor GFRα3 mediate migraine-like pain via the ion channel TRPM8

BACKGROUND

Migraine has a strong genetic foundation, including both monogenic and polygenic types. The former are rare, with most migraine considered polygenic, supported by genome-wide association studies (GWAS) identifying numerous genetic variants linked with migraine risk. Surprisingly, some of the most common mutations are associated with transient receptor potential melastatin 8 (TRPM8), a non-selective cation channel that is the primary sensor of cold temperatures in cutaneous primary afferents of the somatosensory system. However, it is unlikely that the temperature sensitivity of TRPM8 is relevant in migraine-related tissues, such as the meninges, suggesting other activation mechanisms underly its role in migraine pathogenesis. Thus, to define the basis of the channel's involvement, we reasoned that cellular processes that increase cold sensitivity in the skin, such as the neurotrophic factor artemin, via its receptor glial cell-line derived neurotrophic factor family receptor alpha-3 (GFRα3), also mediate TRPM8-associated migraine-like pain in the meninges.

METHODS

To investigate the role of artemin and GFRα3 in preclinical rodent migraine models, we infused nitroglycerin acutely and chronically, and measured changes in periorbital and hind paw mechanical sensitivity in male and female mice lacking GFRα3, after neutralization of free artemin with specific monoclonal antibodies, or by systemic treatment with a TRPM8-specific antagonist. Further, in mice lacking GFRα3 we tested the effects of supradural infusions of a mix of inflammatory mediators, as well as tested if dura stimulation with artemin or a TRPM8-specific agonist induce migraine-related pain in mice.

RESULTS

We find that mechanical allodynia induced by systemic nitroglycerin, or supradural infusion of inflammatory mediators, involves GFRα3. In addition, neutralization of circulating artemin reduces the nitroglycerin phenotype, demonstrating the importance of this neurotrophic pathway in headaches. Further, we show TRPM8 expression in the meninges, and that direct supradural infusion of either a TRPM8-specific agonist or artemin itself produces mechanical allodynia, with the latter dependent on TRPM8 and ameliorated by concurrent treatment with sumatriptan.

CONCLUSIONS

These results indicate that neuroinflammatory events in the meninges can produce migraine-like pain in mice via artemin and GFRα3, likely acting upstream of TRPM8, providing a novel pathway that may contribute to headaches or migraine pathogenesis.

Animal Models of Chronic Migraine: From the Bench to Therapy

PURPOSE OF REVIEW

Chronic migraine is a disabling progressive disorder without effective management approaches. Animal models have been developed and used in chronic migraine research. However, there are several problems with existing models. Therefore, we aimed to summarize and analyze existing animal models to facilitate translation from basic to clinical.

RECENT FINDINGS

The most commonly used models are the inflammatory soup induction model and the nitric oxide donor induction model. In addition, KATP openers have also been used in model induction. Based on the above models, some molecular targets have been identified, such as glutamate receptors. However, each model has its shortcomings and characteristics, and there are still some common problems that need to be solved, such as spontaneous headache, evaluation criteria after model establishment, and identification methods. In this review, we summarized and highlighted the advantages and limitations of the currently commonly used animal models of chronic migraine with a special focus on drug discovery and current therapeutic strategies, and discussed the directions that can be worked on in the future.

Neuroimmune interactions in the development and chronification of migraine headache

Migraine is highly prevalent and debilitating. The persistent headaches in this condition are thought to arise from the activation and sensitization of the trigeminovascular pathway. Both clinical and animal model studies have suggested that neuroimmune interactions contribute to the pathophysiology of migraine headache. In this review, we first summarize the findings from human studies implicating the dysregulation of the immune system in migraine, including genetic analyses, measurement of circulatory factors, and neuroimaging data. We next discuss recent advances from rodent studies aimed at elucidating the neuroimmune interactions that manifest at various levels of the trigeminovascular pathway and lead to the recruitment of innate and adaptive immune cells as well as immunocompetent glial cells. These cells reciprocally modulate neuronal activity via multiple pro- and anti-inflammatory mediators, thereby regulating peripheral and central sensitization. Throughout the discussions, we highlight the potential clinical and translational implications of the findings.

The neurotrophic factor artemin and its receptor GFRα3 mediate migraine-like pain via the ion channel TRPM8

Background

Migraine has a strong genetic foundation, including both monogenic and polygenic types. The former are rare, with most migraine considered polygenic, supported by genome-wide association studies (GWAS) identifying numerous genetic variants associated with migraine risk. Surprisingly, some of the most common mutations are associated with TRPM8, a non-selective cation channel that is the primary sensor of cold temperatures in primary afferent neurons of the somatosensory system. However, it is unlikely that the temperature sensitivity of TRPM8 underlies its role in migraine pathogenesis. To define the basis of the channel's involvement, we reasoned that cellular processes that increase cold sensitivity in the skin, such as the neurotrophic factor artemin, via its receptor GFRα3, also mediate TRPM8-associated migraine-like pain in the meninges.

Methods

To investigate the role of artemin and GFRα3 in preclinical rodent migraine models, we infused nitroglycerin acutely and chronically, and measured changes in periorbital and hind paw mechanical sensitivity in male and female mice lacking GFRα3, after neutralization of free artemin with specific monoclonal antibodies, or by systemic treatment with a TRPM8-specific antagonist. Further, in wildtypes and mice lacking either GFRα3 or TRPM8, we tested the effects of supradural infusions of a mix of inflammatory mediators, artemin, and a TRPM8-specific agonist on migraine-related pain in mice.

Results

We find that mechanical allodynia induced by systemic nitroglycerin, or supradural infusion of inflammatory mediators, involves GFRα3. In addition, neutralization of circulating artemin reduces the nitroglycerin phenotype, demonstrating the importance of this neurotrophic pathway. Further, we show TRPM8 expression in the meninges and that direct supradural infusion of either a TRPM8-specific agonist or artemin itself produces mechanical allodynia, the latter dependent on TRPM8 and ameliorated by concurrent treatment with sumatriptan.

Conclusions

These results indicate that neuroinflammatory events in the meninges can produce migraine-like pain in mice via artemin and GFRα3, likely acting upstream of TRPM8, providing a novel pathway that may contribute to migraine pathogenesis.

Menthol dural application alters meningeal arteries tone and enhances excitability of trigeminocervical neurons in rats

Headaches, including migraines, can have a causal relationship to exposure to cold, and this relationship may be both positive and negative, as cold can both provoke and alleviate cephalgia. The role of thermoreceptors responsible for transduction of low temperatures belongs to the transient receptor potential cation channel subfamily melastatin member 8 (TRPM8). These channels mediate normal cooling sensation and have a role in both cold pain and cooling-mediated analgesia; they are seen as a potential target for principally new anti-migraine pharmaceuticals. Using a validated animal migraine models, we evaluated effects of menthol, the TRPM8-agonist, on trigeminovascular nociception. In acute experiments on male rats, effects of applied durally menthol solution in various concentrations on the neurogenic dural vasodilatation (NDV) and firing rate of dura-sensitive neurons of the trigeminocervical complex (TCC) were assessed. Application of menthol solution in concentrations of 5 % and 10 % was associated with NDV suppression, however amplitude reduction of the dilatation response caused not by the vascular dilatation degree decrease, but rather due to the significant increase of the meningeal arterioles' basal tone. In electrophysiological experiments the 1 % and 30 % menthol solutions intensified TCC neuron responses to the dural electrical stimulation while not changing their background activity. Revealed in our study excitatory effects of menthol related to the vascular as well as neuronal branches of the trigeminovascular system indicate pro-cephalalgic effects of TRPM8-activation and suggest feasibility of further search for new anti-migraine substances among TRPM8-antagonists.

Targeting TRP Channels for Pain, Itch and Neurogenic Inflammation

Transient receptor potential (TRP) channels are multifunctional signaling molecules with important roles in health and disease [...].

Peripheral CCL2-CCR2 signalling contributes to chronic headache-related sensitization

Migraine, especially chronic migraine, is highly debilitating and still lacks effective treatment. The persistent headache arises from activation and sensitization of primary afferent neurons in the trigeminovascular pathway, but the underlying mechanisms remain incompletely understood. Animal studies indicate that signalling through chemokine C-C motif ligand 2 (CCL2) and C-C motif chemokine receptor 2 (CCR2) mediates the development of chronic pain after tissue or nerve injury. Some migraine patients had elevated CCL2 levels in CSF or cranial periosteum. However, whether the CCL2-CCR2 signalling pathway contributes to chronic migraine is not clear. Here, we modelled chronic headache with repeated administration of nitroglycerin (NTG, a reliable migraine trigger in migraineurs) and found that both Ccl2 and Ccr2 mRNA were upregulated in dura and trigeminal ganglion (TG) tissues that are implicated in migraine pathophysiology. In Ccl2 and Ccr2 global knockout mice, repeated NTG administration did not evoke acute or persistent facial skin hypersensitivity as in wild-type mice. Intraperitoneal injection of CCL2 neutralizing antibodies inhibited chronic headache-related behaviours induced by repeated NTG administration and repetitive restraint stress, suggesting that the peripheral CCL2-CCR2 signalling mediates headache chronification. We found that CCL2 was mainly expressed in TG neurons and cells associated with dura blood vessels, whereas CCR2 was expressed in subsets of macrophages and T cells in TG and dura but not in TG neurons under both control and disease states. Deletion of Ccr2 gene in primary afferent neurons did not alter NTG-induced sensitization, but eliminating CCR2 expression in either T cells or myeloid cells abolished NTG-induced behaviours, indicating that both CCL2-CCR2 signalling in T cells and macrophages are required to establish chronic headache-related sensitization. At cellular level, repeated NTG administration increased the number of TG neurons that responded to calcitonin-gene-related peptide (CGRP) and pituitary adenylate cyclase activating polypeptide (PACAP) as well as the production of CGRP in wild-type but not Ccr2 global knockout mice. Lastly, co-administration of CCL2 and CGRP neutralizing antibodies was more effective in reversing NTG-induced behaviours than individual antibodies. Taken together, these results suggest that migraine triggers activate CCL2-CCR2 signalling in macrophages and T cells. This consequently enhances both CGRP and PACAP signalling in TG neurons, ultimately leading to persistent neuronal sensitization underlying chronic headache. Our work not only identifies the peripheral CCL2 and CCR2 as potential targets for chronic migraine therapy, but also provides proof-of-concept that inhibition of both peripheral CGRP and CCL2-CCR2 signalling is more effective than targeting either pathway alone.

Levcromakalim provokes an acute rapid-onset migraine-like phenotype without inducing cortical spreading depolarization

BACKGROUND

Migraine headache attacks and accompanying sensory augmentation can be induced by several agents including levcromakalim (LVC), that is also capable of provoking aura-like symptoms in migraineurs. We investigated whether single LVC injection causes acute migraine-like phenotype in rats and induces/modulates cortical spreading depolarization (CSD), a rodent model of migraine aura.

METHODS

Wistar rats were administered LVC (1 mg/kg, i.p.) and compared to control (CTRL, vehicle, i.p.) and nitroglycerin (NTG, 10 mg/kg, i.p.) groups. Von Frey filaments were used to examine the periorbital and hind paw mechanical allodynia. Dark-light box (DLB), elevated plus maze (EPM), and open field arena (OFA) were used to evaluate light sensitivity and anxiety-related behaviors. The effects of LVC on CSD parameters, somatosensory evoked potentials, and baseline dural EEG (electroencephalography) were investigated. Possible CSD-induced c-fos expression was studied with Western Blot. Blood-brain barrier integrity in cortex was examined with Evans blue assay.

RESULTS

LVC and NTG administration robustly reduced periorbital mechanical thresholds in rats and induced anxiety-like behaviors and photophobia within 30 and 120 min, respectively. LVC induced migraine-like phenotype recovered in 2 h while NTG group did not fully recover before 4 h. Both LVC and NTG did not provoke DC (direct current) shift, EEG alterations or cortical c-fos expression characteristic to CSD. LVC did not induce de novo CSD and affect KCl (potassium chloride)-induced CSD parameters except for an increase in propagation failure. However, NTG significantly increased both CSD susceptibility and propagation failure. Somatosensory evoked potential (SSEP) configurations were not altered in both LVC and NTG groups, but SSEP latencies were prolonged after CSD. Acute LVC or NTG injection did not increase cortical BBB permeability.

CONCLUSIONS

Single LVC administration induced the fastest manifestation and recovery of acute migraine-like phenotype which was not mediated by CSD waves in the cerebral cortex. We suppose LVC triggered rapid-onset migraine-like symptoms are probably related to functional alterations in the trigeminal nociceptive system and K⁺ channel opening properties of LVC. Understanding the neurobiological mechanisms of this nociceptive window, may provide a novel target in migraine treatment.

Targeting Nociceptive Neurons and Transient Receptor Potential Channels for the Treatment of Migraine

Migraine is a neurovascular disorder that affects approximately 12% of the global population. While its exact causes are still being studied, researchers believe that nociceptive neurons in the trigeminal ganglia play a key role in the pain signals of migraine. These nociceptive neurons innervate the intracranial meninges and convey pain signals from the meninges to the thalamus. Targeting nociceptive neurons is considered promising due to their accessibility and distinct molecular profile, which includes the expression of several transient receptor potential (TRP) channels. These channels have been linked to various pain conditions, including migraine. This review discusses the role and mechanisms of nociceptive neurons in migraine, the challenges of current anti-migraine drugs, and the evidence for well-studied and emerging TRP channels, particularly TRPC4, as novel targets for migraine prevention and treatment.

TRP Channels: Recent Development in Translational Research and Potential Therapeutic Targets in Migraine

Migraine is a chronic neurological disorder that affects approximately 12% of the population. The cause of migraine headaches is not yet known, however, when the trigeminal system is activated, neuropeptides such as calcitonin gene-related peptide (CGRP) and substance P (SP) are released, which cause neurogenic inflammation and sensitization. Advances in the understanding of migraine pathophysiology have identified new potential pharmacological targets. In recent years, transient receptor potential (TRP) channels have been the focus of attention in the pathophysiology of various pain disorders, including primary headaches. Genetic and pharmacological data suggest the role of TRP channels in pain sensation and the activation and sensitization of dural afferents. In addition, TRP channels are widely expressed in the trigeminal system and brain regions which are associated with the pathophysiology of migraine and furthermore, co-localize several neuropeptides that are implicated in the development of migraine attacks. Moreover, there are several migraine trigger agents known to activate TRP channels. Based on these, TRP channels have an essential role in migraine pain and associated symptoms, such as hyperalgesia and allodynia. In this review, we discuss the role of the certain TRP channels in migraine pathophysiology and their therapeutic applicability.

ThermoTRP channels in pain sexual dimorphism: new insights for drug intervention

Chronic pain is a major burden for the society and remains more prevalent and severe in females. The presence of chronic pain is linked to persistent alterations in the peripheral and the central nervous system. One of the main types of peripheral pain transducers are the transient receptor potential channels (TRP), also known as thermoTRP channels, which intervene in the perception of hot and cold external stimuli. These channels, and especially TRPV1, TRPA1 and TRPM8, have been subjected to profound investigation because of their role as thermosensors and also because of their implication in acute and chronic pain. Surprisingly, their sensitivity to endogenous signaling has been far less studied. Cumulative evidence suggests that the function of these channels may be differently modulated in males and females, in part through sexual hormones, and this could constitute a significant contributor to the sex differences in chronic pain. Here, we review the exciting advances in thermoTRP pharmacology for males and females in two paradigmatic types of chronic pain with a strong peripheral component: chronic migraine and chemotherapy-induced peripheral neuropathy (CIPN). The possibilities of peripheral druggability offered by these channels and the differential exploitation for men and women represent a development opportunity that will lead to a significant increment of the armamentarium of analgesic medicines for personalized chronic pain treatment.