A TRP channel that senses cold stimuli and menthol

Pain research in a petri dish? Advantages and limitations of neuro-glial primary cell cultures from structures of the nociceptive system

How can we learn more about pain without causing pain in humans or animals? This short review focuses on neuro-glial primary cell cultures as models to study neuro-immune interactions in the context of pain and discusses their advantages and limitations. The field of basic pain research places scientists in an ethical dilemma. We aim to understand underlying mechanisms of pain for an improved pain therapy for humans and animals. At the same time, this regularly includes the induction of pain in model animals. Within the field of psychoneuroimmunology, the examination of the complexity of neuro-immune interactions in health and disease as well as the bi-directional communication between the brain and the periphery make animal experiments an inevitable part of pain research. To address ethical and legal considerations as well as the growing societal awareness for animal welfare, scientists push for the identification and characterization of complementary methods to implement the 3R principle of Russel and Burch. As such, methods to replace animal studies, reduce the number of animals used, and refine experiments are tested. Neuro-glial primary cell cultures of structures of the nociceptive system, such as dorsal root ganglia (DRG) or the spinal dorsal horn (SDH) represent useful in vitro tools, when research comes to a cellular and molecular level. They allow for studying mechanisms of neuronal sensitization, glial cell activation, or the role of specific inflammatory mediators and intracellular signaling cascades involved in the development of inflammatory and neuropathic pain. Moreover, DRG/SDH-cultures provide the opportunity to test novel strategies for interventions, such as pharmaceuticals or cell-based therapies targeting neuroinflammatory processes. Thereby, in vitro models contribute to a better understanding of neuron-glia-immune communication in the context of pain and in the advancement of pain therapies. However, this can only be one piece in a large puzzle. Our knowledge about the complexity of pain will depend on studies in humans and animals applied in vitro and in vivo and will benefit from clear and open-minded interdisciplinary communication and transparency in public outreach.

Conservation of the cooling agent binding pocket within the TRPM subfamily

Transient receptor potential (TRP) channels are a large and diverse family of tetrameric cation-selective channels that are activated by many different types of stimuli, including noxious heat or cold, organic ligands such as vanilloids or cooling agents, or intracellular Ca2+. Structures available for all subtypes of TRP channels reveal that the transmembrane domains are closely related despite their unique sensitivity to activating stimuli. Here, we use computational and electrophysiological approaches to explore the conservation of the cooling agent binding pocket identified within the S1-S4 domain of the Melastatin subfamily member TRPM8, the mammalian sensor of noxious cold, with other TRPM channel subtypes. We find that a subset of TRPM channels, including TRPM2, TRPM4, and TRPM5, contain pockets very similar to the cooling agent binding pocket in TRPM8. We then show how the cooling agent icilin modulates activation of mouse TRPM4 to intracellular Ca2+, enhancing the sensitivity of the channel to Ca2+ and diminishing outward-rectification to promote opening at negative voltages. Mutations known to promote or diminish activation of TRPM8 by cooling agents similarly alter activation of TRPM4 by icilin, suggesting that icilin binds to the cooling agent binding pocket to promote opening of the channel. These findings demonstrate that TRPM4 and TRPM8 channels share related ligand binding pockets that are allosterically coupled to opening of the pore.

Neuromodulators in Acute and Chronic Cough in Children: An Update from the Literature

Cough is one of the most common reasons leading to pediatric consultations, negatively impacting the quality of life of patients and caregivers. It is defined as a sudden and forceful expulsion of air from the lungs through the mouth, typically triggered by irritation or the stimulation of sensory nerves in the respiratory tract. This reflex is controlled by a neural pathway that includes sensory receptors, afferent nerves, the brainstem's cough center, efferent nerves, and the muscles involved in coughing. Based on its duration, cough in children may be classified as acute, lasting less than four weeks, and chronic, persisting for more than four weeks. Neuromodulators have shown promise in reducing the frequency and severity of cough by modulating the neural pathways involved in the cough reflex, although they require careful monitoring and patient selection to optimize the outcomes. This review aims to examine the rationale for using neuromodulators in the management of cough in children.

Divergent sensory pathways of sneezing and coughing

Sneezing and coughing are primary symptoms of many respiratory viral infections and allergies. It is generally assumed that sneezing and coughing involve common sensory receptors and molecular neurotransmission mechanisms. Here, we show that the nasal mucosa is innervated by several discrete populations of sensory neurons, but only one population (MrgprC11+MrgprA3-) mediates sneezing responses to a multitude of nasal irritants, allergens, and viruses. Although this population also innervates the trachea, it does not mediate coughing, as revealed by our newly established cough model. Instead, a distinct sensory population (somatostatin [SST+]) mediates coughing but not sneezing, unraveling an unforeseen sensory difference between sneezing and coughing. At the circuit level, sneeze and cough signals are transmitted and modulated by divergent neuropathways. Together, our study reveals the difference in sensory receptors and neurotransmission/modulation mechanisms between sneezing and coughing, offering neuronal drug targets for symptom management in respiratory viral infections and allergies.

Determination of the optimal dose and dosing strategy for effective L-menthol oral rinsing during exercise in hot environments

PURPOSE

This multi-study programme investigated the optimal concentration of L-menthol delivered as an oral mouth rinse to modulate thermo-behaviour during exercise in a hot environment (35 °C).

METHOD

In study 1, 38 participants completed a survey to establish an effective and tolerable range of L-menthol concentration. 31 participants completed an RPE-protocol examining 1. the dose-response effect of L-menthol mouth rinse on exercise performance (n = 16) and 2. the temporal effectiveness of administering L-menthol in an incremental and decremental dosing pattern (n = 15). Power output, heart rate, body core temperature and thermal sensation were reported throughout.

RESULTS

The optimal menthol concentration for peak power was between 0.01 and 0.1% (~ 6% increase, P < 0.05) and 0.5% (~ 9% increase, P < 0.05) with respect to control. Work completed was increased at 0.01% (~ 5%, P < 0.05), at 0.1% (~ 3%, P < 0.05) and had a detrimental effect at 0.5% (- 10% decrease, P < 0.05). There were no differences between an ascending dose protocol (0.01 to 0.5%), descending dose protocol (0.5-0.01%) or a constant 0.01% dose protocol. There were no reported differences in body core temperature or heart rate across trials (P > 0.05).

CONCLUSION

The optimal dose of L-menthol when delivered via oral rinsing is between 0.01 and 0.1%. At lower concentrations, L-menthol appears to be less effective and at higher concentrations (> 0.5%) L-menthol appears to elicit greater irritation and may not positively modulate thermo-behaviour during exercise in a hot environment.

Navigating the Controversies: Role of TRPM Channels in Pain States

Chronic pain is a debilitating condition that affects up to 1.5 billion people worldwide and bears a tremendous socioeconomic burden. The success of pain medicine relies on our understanding of the type of pain experienced by patients and the mechanisms that give rise to it. Ion channels are among the key targets for pharmacological intervention in chronic pain conditions. Therefore, it is important to understand how changes in channel properties, trafficking, and molecular interactions contribute to pain sensation. In this review, we discuss studies that have demonstrated the involvement of transient receptor potential M2, M3, and M8 channels in pain generation and transduction, as well as the controversies surrounding these 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.

Non-verbal effecting - animal research sheds light on human emotion communication

Cracking the non-verbal "code" of human emotions has been a chief interest of generations of scientists. Yet, despite much effort, a dictionary that clearly maps non-verbal behaviours onto meaning remains elusive. We suggest this is due to an over-reliance on language-related concepts and an under-appreciation of the evolutionary context in which a given non-verbal behaviour emerged. Indeed, work in other species emphasizes non-verbal effects (e.g. affiliation) rather than meaning (e.g. happiness) and differentiates between signals, for which communication benefits both sender and receiver, and cues, for which communication does not benefit senders. Against this backdrop, we develop a "non-verbal effecting" perspective for human research. This perspective extends the typical focus on facial expressions to a broadcasting of multisensory signals and cues that emerge from both social and non-social emotions. Moreover, it emphasizes the consequences or effects that signals and cues have for individuals and their social interactions. We believe that re-directing our attention from verbal emotion labels to non-verbal effects is a necessary step to comprehend scientifically how humans share what they feel.

The powerful potential of amino acid menthyl esters for anti-inflammatory and anti-obesity therapies

Our newly developed menthyl esters of valine and isoleucine exhibit anti-inflammatory properties beyond those of the well-known menthol in macrophages stimulated by lipopolysaccharide (LPS) and in a mouse model of colitis induced by sodium dextran sulfate. Unlike menthol, which acts primarily through the cold-sensitive TRPM8 channel, these menthyl esters displayed unique mechanisms that operate independently of this receptor. They readily penetrated target cells and efficiently suppressed LPS-stimulated tumour necrosis factor-alpha (Tnf) expression mediated by liver X receptor (LXR), a key nuclear receptor that regulates intracellular cholesterol and lipid balance. The menthyl esters showed affinity for LXR and enhanced the transcriptional activity through their non-competitive and potentially synergistic agonistic effect. This effect can be attributed to the crucial involvement of SCD1, an enzyme regulated by LXR, which is central to lipid metabolism and plays a key role in the anti-inflammatory response. In addition, we discovered that the menthyl esters showed remarkable efficacy in suppressing adipogenesis in 3T3-L1 adipocytes at the mitotic clonal expansion stage in an LXR-independent manner as well as in mice subjected to diet-induced obesity. These multiple capabilities of our compounds establish them as formidable allies in the fight against inflammation and obesity, paving the way for a range of potential therapeutic applications.

The ion channel TRPM8 is a direct target of the immunosuppressant rapamycin in primary sensory neurons

BACKGROUND AND PURPOSE

The mechanistic target of rapamycin (mTOR) signalling pathway is a key regulator of cell growth and metabolism. Its deregulation is implicated in several diseases. The macrolide rapamycin, a specific inhibitor of mTOR, has immunosuppressive, anti-inflammatory and antiproliferative properties. Recently, we identified tacrolimus, another macrolide immunosuppressant, as a novel activator of TRPM8 ion channels, involved in cold temperature sensing, thermoregulation, tearing and cold pain. We hypothesized that rapamycin may also have agonist activity on TRPM8 channels.

EXPERIMENTAL APPROACH

Using calcium imaging and electrophysiology in transfected HEK293 cells and wildtype or Trpm8 KO mouse DRG neurons, we characterized rapamycin's effects on TRPM8 channels. We also examined the effects of rapamycin on tearing in mice.

KEY RESULTS

Micromolar concentrations of rapamycin activated rat and mouse TRPM8 channels directly and potentiated cold-evoked responses, effects also observed in human TRPM8 channels. In cultured mouse DRG neurons, rapamycin increased intracellular calcium levels almost exclusively in cold-sensitive neurons. Responses were markedly decreased in Trpm8 KO mice or by TRPM8 channel antagonists. Cutaneous cold thermoreceptor endings were also activated by rapamycin. Topical application of rapamycin to the eye surface evokes tearing in mice by a TRPM8-dependent mechanism.

CONCLUSION AND IMPLICATIONS

These results identify TRPM8 cationic channels in sensory neurons as novel molecular targets of the immunosuppressant rapamycin. These findings may help explain some of its therapeutic effects after topical application to the skin and the eye surface. Moreover, rapamycin could be used as an experimental tool in the clinic to explore cold thermoreceptors.

Conservation of the cooling agent binding pocket within the TRPM subfamily

Transient Receptor Potential (TRP) channels are a large and diverse family of tetrameric cation selective channels that are activated by many different types of stimuli, including noxious heat or cold, organic ligands such as vanilloids or cooling agents, or intracellular Ca2+. Structures available for all subtypes of TRP channels reveal that the transmembrane domains are closely related despite their unique sensitivity to activating stimuli. Here we use computational and electrophysiological approaches to explore the conservation of the cooling agent binding pocket identified within the S1-S4 domain of the Melastatin subfamily member TRPM8, the mammalian sensor of noxious cold, with other TRPM channel subtypes. We find that a subset of TRPM channels, including TRPM2, TRPM4 and TRPM5, contain pockets very similar to the cooling agent binding pocket in TRPM8. We then show how the cooling agent icilin modulates activation of TRPM4 to intracellular Ca2+, enhancing the sensitivity of the channel to Ca2+ and diminishing outward-rectification to promote opening at negative voltages. Mutations known to promote or diminish activation of TRPM8 by cooling agents similarly alter activation of TRPM4 by icilin, suggesting that icilin binds to the cooling agent binding pocket to promote opening of the channel. These findings demonstrate that TRPM4 and TRPM8 channels share related ligand binding pockets that are allosterically coupled to opening of the pore.

Residues of TRPM8 at the Lipid-Water-Interface have Coevolved with Cholesterol Interaction and are Relevant for Diverse Health Disorders

TRPM8 is a non-selective cation channel that is expressed in several tissues and cells and also has a unique property to be activated by low-temperature. In this work, we have analyzed the conservation of amino acids that are present in the lipid-water-interface (LWI) region of TRPM8, the region which experiences a microenvironment near the membrane surface. We demonstrate that the amino acids present in the LWI region are more conserved than the transmembrane or even full-length TRPM8, suggesting strong selection pressure in these residues. TRPM8 also has several conserved cholesterol-binding motifs where cholesterol can bind in different modes and energies. We suggest that mutations and/or physiological conditions can potentially alter these TRPM8-cholesterol complexes and can lead to physiological disorders or even apparently irreversible diseases such as cancer and neurodegeneration.

Complement Component C5a and Fungal Pathogen Induce Diverse Responses through Crosstalk between Transient Receptor Potential Channel (TRPs) Subtypes in Human Conjunctival Epithelial Cells

The conjunctiva has immune-responsive properties to protect the eye from infections. Its innate immune system reacts against external pathogens, such as fungi. The complement factor C5a is an important contributor to the initial immune response. It is known that activation of transient-receptor-potential-vanilloid 1 (TRPV1) and TRP-melastatin 8 (TRPM8) channels is involved in different immune reactions and inflammation in the human body. The aim of this study was to determine if C5a and mucor racemosus e voluminae cellulae (MR) modulate Ca2+-signaling through changes in TRPs activity in human conjunctival epithelial cells (HCjECs). Furthermore, crosstalk was examined between C5a and MR in mediating calcium regulation. Intracellular Ca2+-concentration ([Ca2+]i) was measured by fluorescence calcium imaging, and whole-cell currents were recorded using the planar-patch-clamp technique. MR was used as a purified extract. Application of C5a (0.05-50 ng/mL) increased both [Ca2+]i and whole-cell currents, which were suppressed by either the TRPV1-blocker AMG 9810 or the TRPM8-blocker AMTB (both 20 µM). The N-terminal peptide C5L2p (20-50 ng/mL) blocked rises in [Ca2+]i induced by C5a. Moreover, the MR-induced rise in Ca2+-influx was suppressed by AMG 9810 and AMTB, as well as 0.05 ng/mL C5a. In conclusion, crosstalk between C5a and MR controls human conjunctival cell function through modulating interactions between TRPV1 and TRPM8 channel activity.

Loss of transient receptor potential channel 5 causes obesity and postpartum depression

Hypothalamic neural circuits regulate instinctive behaviors such as food seeking, the fight/flight response, socialization, and maternal care. Here, we identified microdeletions on chromosome Xq23 disrupting the brain-expressed transient receptor potential (TRP) channel 5 (TRPC5). This family of channels detects sensory stimuli and converts them into electrical signals interpretable by the brain. Male TRPC5 deletion carriers exhibited food seeking, obesity, anxiety, and autism, which were recapitulated in knockin male mice harboring a human loss-of-function TRPC5 mutation. Women carrying TRPC5 deletions had severe postpartum depression. As mothers, female knockin mice exhibited anhedonia and depression-like behavior with impaired care of offspring. Deletion of Trpc5 from oxytocin neurons in the hypothalamic paraventricular nucleus caused obesity in both sexes and postpartum depressive behavior in females, while Trpc5 overexpression in oxytocin neurons in knock-in mice reversed these phenotypes. We demonstrate that TRPC5 plays a pivotal role in mediating innate human behaviors fundamental to survival, including food seeking and maternal care.

Draft Genome of Akame (Lates Japonicus) Reveals Possible Genetic Mechanisms for Long-Term Persistence and Adaptive Evolution with Low Genetic Diversity

It is known that some endangered species have persisted for thousands of years despite their very small effective population sizes and low levels of genetic polymorphisms. To understand the genetic mechanisms of long-term persistence in threatened species, we determined the whole genome sequences of akame (Lates japonicus), which has survived for a long time with extremely low genetic variations. Genome-wide heterozygosity in akame was estimated to be 3.3 to 3.4 × 10-4/bp, one of the smallest values in teleost fishes. Analysis of demographic history revealed that the effective population size in akame was around 1,000 from 30,000 years ago to the recent past. The relatively high ratio of nonsynonymous to synonymous heterozygosity in akame indicated an increased genetic load. However, a detailed analysis of genetic diversity in the akame genome revealed that multiple genomic regions, including genes involved in immunity, synaptic development, and olfactory sensory systems, have retained relatively high nucleotide polymorphisms. This implies that the akame genome has preserved the functional genetic variations by balancing selection, to avoid a reduction in viability and loss of adaptive potential. Analysis of synonymous and nonsynonymous nucleotide substitution rates has detected signs of positive selection in many akame genes, suggesting adaptive evolution to temperate waters after the speciation of akame and its close relative, barramundi (Lates calcarifer). Our results indicate that the functional genetic diversity likely contributed to the long-term persistence of this species by avoiding the harmful effects of the population size reduction.

Capsaicin: Emerging Pharmacological and Therapeutic Insights

Capsaicin, the most prominent pungent compound of chilli peppers, has been used in traditional medicine systems for centuries; it already has a number of established clinical and industrial applications. Capsaicin is known to act through the TRPV1 receptor, which exists in various tissues; capsaicin is hepatically metabolised, having a half-life correlated with the method of application. Research on various applications of capsaicin in different formulations is still ongoing. Thus, local capsaicin applications have a pronounced anti-inflammatory effect, while systemic applications have a multitude of different effects because their increased lipophilic character ensures their augmented bioavailability. Furthermore, various teams have documented capsaicin's anti-cancer effects, proven both in vivo and in vitro designs. A notable constraint in the therapeutic effects of capsaicin is its increased toxicity, especially in sensitive tissues. Regarding the traditional applications of capsaicin, apart from all the effects recorded as medicinal effects, the application of capsaicin in acupuncture points has been demonstrated to be effective and the combination of acupuncture and capsaicin warrants further research. Finally, capsaicin has demonstrated antimicrobial effects, which can supplement its anti-inflammatory and anti-carcinogenic actions.

Evaluation of the mechanism of action of paracetamol, drotaverine, and peppermint oil and their effects in combination with hyoscine butylbromide on colonic motility: human ex-vivo study

Introduction

Drotaverine, paracetamol, and peppermint oil are often prescribed for the treatment of gastrointestinal spasm and pain. This study aimed to evaluate the effect of these drugs alone and combined with the well-known antispasmodic hyoscine butylbromide on the human colon.

Methods

Colon samples were obtained from macroscopically normal regions of 68 patients undergoing surgery and studied in muscle bath. Drotaverine, paracetamol, and peppermint oil were tested alone and in combination with hyoscine butylbromide on (1) spontaneous contractility induced by isometric stretch (in the presence of 1 µM tetrodotoxin) and (2) contractility induced by 10-5 M carbachol and after (3) electrical field stimulation-induced selective stimulation of excitatory (in the presence of 1 mM Nω-nitro-L-arginine and 10 µM MRS2179) and (4) inhibitory (under non-adrenergic, non-cholinergic conditions) pathways. (5) Drotaverine alone was also tested on cAMP-dependent pathway activated by forskolin.

Results

Compared with the vehicle, drotaverine and paracetamol (10-9-10-5 M) did not modify spontaneous contractions, carbachol-induced contractions, and responses attributed to selective activation of excitatory pathways. The addition of hyoscine butylbromide (10-7-10-5 M), concentration-dependently reduced myogenic contractions and carbachol- and electrical field stimulation-induced contractile responses. The association of paracetamol (10-4 M) and hyoscine butylbromide (10-7-10-5 M) was not different from hyoscine butylbromide alone (10-7-10-5 M). At higher concentrations (10-3M-3*10-3 M), paracetamol decreased myogenic and carbachol-induced contractions. The adenylate cyclase activator, forskolin, concentration-dependently reduced contractility, leading to smooth muscle relaxation. The effect of forskolin 10-7 M was concentration-dependently enhanced by drotaverine (10-6M-10-5M).

Discussion

Peppermint oil reduced myogenic activity and carbachol- and electrical field stimulation-induced contractions. The association of hyoscine butylbromide and peppermint oil was synergistic since the interaction index measured with the isobologram was lower than 1. No effect was seen on the neural-mediated inhibitory responses with any of the drugs studied although peppermint oil reduced the subsequent off-contraction. Drotaverine and hyoscine butylbromide have a complementary effect on human colon motility as one stimulates the cAMP inhibitory pathway and the other inhibits the excitatory pathway. Peppermint oil is synergic with hyoscine butylbromide suggesting that a combination therapy may be more effective in treating patients. In contrast, at therapeutic concentrations, paracetamol does not modify colonic contractility, suggesting that the association of paracetamol and hyoscine butylbromide has independent analgesic and antispasmodic properties.

Current Update on Categorization of Migraine Subtypes on the Basis of Genetic Variation: a Systematic Review

Migraine is a complex neurovascular disorder that is characterized by severe behavioral, sensory, visual, and/or auditory symptoms. It has been labeled as one of the ten most disabling medical illnesses in the world by the World Health Organization (Aagaard et al Sci Transl Med 6(237):237ra65, 2014). According to a recent report by the American Migraine Foundation (Shoulson et al Ann Neurol 25(3):252-9, 1989), around 148 million people in the world currently suffer from migraine. On the basis of presence of aura, migraine is classified into two major subtypes: migraine with aura (Aagaard et al Sci Transl Med 6(237):237ra65, 2014) and migraine without aura. (Aagaard K et al Sci Transl Med 6(237):237ra65, 2014) Many complex genetic mechanisms have been proposed in the pathophysiology of migraine but specific pathways associated with the different subtypes of migraine have not yet been explored. Various approaches including candidate gene association studies (CGAS) and genome-wide association studies (Fan et al Headache: J Head Face Pain 54(4):709-715, 2014). have identified the genetic markers associated with migraine and its subtypes. Several single nucleotide polymorphisms (Kaur et al Egyp J Neurol, Psychiatry Neurosurg 55(1):1-7, 2019) within genes involved in ion homeostasis, solute transport, synaptic transmission, cortical excitability, and vascular function have been associated with the disorder. Currently, the diagnosis of migraine is majorly behavioral with no focus on the genetic markers and thereby the therapeutic intervention specific to subtypes. Therefore, there is a need to explore genetic variants significantly associated with MA and MO as susceptibility markers in the diagnosis and targets for therapeutic interventions in the specific subtypes of migraine. Although the proper characterization of pathways based on different subtypes is yet to be studied, this review aims to make a first attempt to compile the information available on various genetic variants and the molecular mechanisms involved with the development of MA and MO. An attempt has also been made to suggest novel candidate genes based on their function to be explored by future research.

Spearmint targets microtubules by (-)-carvone

Allelopathy can provide sustainable alternatives to herbicides because it is based on specific signals rather than generic toxicity. We show that the allelopathic activity of Spearmint and Watermint is linked with their main compounds, (-)-carvone and (+)-menthofuran, both deriving from (-)-limonene. Germination of Poppy and Cress, and root growth of Arabidopsis thaliana are inhibited by very low concentrations of (-)-carvone, acting even through the gas phase. (+)-Menthofuran is active as well, but at lower efficacy. Using fluorescently tagged marker lines in tobacco BY-2 cells and Arabidopsis roots, we demonstrate a rapid degradation of microtubules and a remodeling of actin filaments in response to (-)-carvone and, to a milder extent, to (+)-menthofuran. This cytoskeletal response is followed by cell death. By means of a Root Chip system, we can follow the tissue dependent response of the cytoskeleton and show a cell-type dependent gradient of sensitivity between meristem and distal elongation zone, accompanied by programmed cell death.

Evidence that the cold- and menthol-sensing functions of the human TRPM8 channel evolved separately

Transient receptor potential melastatin 8 (TRPM8) is a temperature- and menthol-sensitive ion channel that contributes to diverse physiological roles, including cold sensing and pain perception. Clinical trials targeting TRPM8 have faced repeated setbacks predominantly due to the knowledge gap in unraveling the molecular underpinnings governing polymodal activation. A better understanding of the molecular foundations between the TRPM8 activation modes may aid the development of mode-specific, thermal-neutral therapies. Ancestral sequence reconstruction was used to explore the origins of TRPM8 activation modes. By resurrecting key TRPM8 nodes along the human evolutionary trajectory, we gained valuable insights into the trafficking, stability, and function of these ancestral forms. Notably, this approach unveiled the differential emergence of cold and menthol sensitivity over evolutionary time, providing a fresh perspective on complex polymodal behavior. These studies provide a paradigm for understanding polymodal behavior in TRPM8 and other proteins with the potential to enhance our understanding of sensory receptor biology and pave the way for innovative therapeutic interventions.

Effects of Mucosal Decongestion on Nasal Aerodynamics: A Pilot Study

OBJECTIVE

Mucosal decongestion with nasal sprays is a common treatment for nasal airway obstruction. However, the impact of mucosal decongestion on nasal aerodynamics and the physiological mechanism of nasal airflow sensation are incompletely understood. The objective of this study is to compare nasal airflow patterns in nasal airway obstruction (NAO) patients with and without mucosal decongestion and nondecongested healthy subjects.

STUDY DESIGN

Cross-sectional study of a convenience sample.

SETTING

Academic tertiary medical center.

METHODS

Forty-five subjects were studied (15 nondecongested healthy subjects, 15 nondecongested NAO patients, and 15 decongested NAO patients). Three-dimensional models of the nasal anatomy were created from computed tomography scans. Steady-state simulations of airflow and heat transfer were conducted at 15 L/min inhalation rate using computational fluid dynamics.

RESULTS

In the narrow side of the nose, unilateral nasal resistance was similar in decongested NAO patients and nondecongested healthy subjects, but substantially higher in nondecongested NAO patients. The vertical airflow distribution within the nasal cavity (inferior vs middle vs superior) was also similar in decongested NAO patients and nondecongested healthy subjects, but nondecongested NAO patients had substantially less middle airflow. Mucosal cooling, quantified by the surface area where heat flux exceeds 50 W/m2, was significantly higher in decongested NAO patients than in nondecongested NAO patients.

CONCLUSION

This pilot study suggests that mucosal decongestion improves objective measures of nasal airflow, which is consistent with improved subjective sensation of nasal patency after decongestion.

Physiological temperature drives TRPM4 ligand recognition and gating

Temperature profoundly affects macromolecular function, particularly in proteins with temperature sensitivity1,2. However, its impact is often overlooked in biophysical studies that are typically performed at non-physiological temperatures, potentially leading to inaccurate mechanistic and pharmacological insights. Here we demonstrate temperature-dependent changes in the structure and function of TRPM4, a temperature-sensitive Ca2+-activated ion channel3-7. By studying TRPM4 prepared at physiological temperature using single-particle cryo-electron microscopy, we identified a 'warm' conformation that is distinct from those observed at lower temperatures. This conformation is driven by a temperature-dependent Ca2+-binding site in the intracellular domain, and is essential for TRPM4 function in physiological contexts. We demonstrated that ligands, exemplified by decavanadate (a positive modulator)8 and ATP (an inhibitor)9, bind to different locations of TRPM4 at physiological temperatures than at lower temperatures10,11, and that these sites have bona fide functional relevance. We elucidated the TRPM4 gating mechanism by capturing structural snapshots of its different functional states at physiological temperatures, revealing the channel opening that is not observed at lower temperatures. Our study provides an example of temperature-dependent ligand recognition and modulation of an ion channel, underscoring the importance of studying macromolecules at physiological temperatures. It also provides a potential molecular framework for deciphering how thermosensitive TRPM channels perceive temperature changes.

Chief Complaint: Nasal Congestion

Nasal obstruction is the subjective perception and objective state of insufficient airflow through the nose. Nasal congestion, conversely, describes a state of not just inadequate airflow or obstructive phenomena but also pressure- and mucus-related states to the patient. Nasal receptors belonging to the transient receptor potential (TRP) protein family mediate the sense of nasal patency via the trigeminal nerve. The transient receptor potential melastatin-8 (TRPM8) responds to temperatures around 8°C to 22°C, and is stimulated by menthol and other cooling agents. The radiant effects of airflow create heat loss to activate these receptors and humans perceive this as nasal patency rather than the direct detection of airflow. The thermovascular state of the mucosa, in conditions such as rhinitis, influence TRPM8 activation. Nasal endoscopy can show signs of rhinitis and should be considered an essential part of the workup of nasal congestion. Efforts to relieve nasal congestion need to manage the mucosal state and surgery needs to ensures that the nasal cavity mucosa is exposed to the cooling effects of airflow rather than simply creating a passage to the nasopharynx.

Signal Transduction of Transient Receptor Potential TRPM8 Channels: Role of PIP5K, Gq-Proteins, and c-Jun

Transient receptor potential melastatin-8 (TRPM8) is a cation channel that is activated by cold and "cooling agents" such as menthol and icilin, which induce a cold sensation. The stimulation of TRPM8 activates an intracellular signaling cascade that ultimately leads to a change in the gene expression pattern of the cells. Here, we investigate the TRPM8-induced signaling pathway that links TRPM8 channel activation to gene transcription. Using a pharmacological approach, we show that the inhibition of phosphatidylinositol 4-phosphate 5 kinase α (PIP5K), an enzyme essential for the biosynthesis of phosphatidylinositol 4,5-bisphosphate, attenuates TRPM8-induced gene transcription. Analyzing the link between TRPM8 and Gq proteins, we show that the pharmacological inhibition of the βγ subunits impairs TRPM8 signaling. In addition, genetic studies show that TRPM8 requires an activated Gα subunit for signaling. In the nucleus, the TRPM8-induced signaling cascade triggers the activation of the transcription factor AP-1, a complex consisting of a dimer of basic region leucine zipper (bZIP) transcription factors. Here, we identify the bZIP protein c-Jun as an essential component of AP-1 within the TRPM8-induced signaling cascade. In summary, with PIP5K, Gq subunits, and c-Jun, we identified key molecules in TRPM8-induced signaling from the plasma membrane to the nucleus.

Neuroanatomy of the Cutaneous Nervous System Regarding Wound Healing

Wound healing is an important topic in modern medicine across many disciplines. Healing of all cutaneous wounds, whether accidentally sustained or intentionally created, requires the common yet complex set of interactions between the immune, circulatory, nervous, endocrine, and integumentary systems. Deficits in any of these systems or the molecular factors that mediate their communications can contribute to impaired healing of cutaneous wounds. While the stages of wound repair, angiogenesis, growth factors, and cytokines involved have been extensively studied, the role of the cutaneous nervous system in wound healing has not been well outlined. We have provided a basic overview of cutaneous innervation and wound repair for the dermatologic surgeon by outlining the normal cutaneous nervous anatomy and function and discussing the most important neuropeptides that mediate the wound healing process.

Honokiol targeting ankyrin repeat domain of TRPV4 ameliorates endothelial permeability in mice inflammatory bowel disease induced by DSS

ETHNOPHARMACOLOGICAL RELEVANCE

As a classic traditional Chinese medicine, Magnolia officinalis (M. officinalis) is widely used in digestive diseases. It has rich gastrointestinal activity including inflammatory bowel disease (IBD) treatment, but the mechanism is not clear.

AIM OF THE STUDY

In recent years, there has been a growing interest in investigating the regulatory effects of herbal compounds on transient receptor potential (TRP) channel proteins. Transient receptor potential vanilloid 4 (TRPV4), a subtype involved in endothelial permeability regulation, was discussed as the target of M. officinalis in the treatment of IBD in the study. Based on the targeting effect of TRPV4, this study investigated the active ingredients and mechanism of M. officinalis extract in treating IBD.

MATERIALS AND METHODS

To reveal the connection between the active ingredients in M. officinalis and TRPV4, a bioactivity-guided high performance liquid chromatography system coupled with mass spectrometry identification was utilized to screen for TRPV4 antagonists. TRPV4 siRNA knockdown experiment was employed to validate the significance of TRPV4 as a crucial target in regulating endothelial permeability by honokiol (HON). The interaction of the active ingredient representing HON with TRPV4 was confirmed by molecular docking, fluorescence-based thermal shift and live cell calcium imaging experiments. The potential binding sites and inhibitory mechanisms of HON in TRPV4 were analyzed by molecular dynamics simulation and microscale thermophoresis. The therapeutic effect of HON based on TRPV4 was discussed in DSS-IBD mice.

RESULTS

Our finding elucidated that the inhibitory activity of M. officinalis against TRPV4 is primarily attributed to HON analogues. The knockdown of TRPV4 expression significantly impaired the calcium regulation and permeability protection in endothelial cells. The mechanism study revealed that HON specifically targets the Q239 residue located in the ankyrin repeat domain of TRPV4, and competitively inhibits channel opening with adenosine triphosphate (ATP) binding. The immunofluorescence assay demonstrated that the administration of HON enhances the expression and location of VE-Cadherin to protect the endothelial barrier and attenuates immune cell infiltration.

CONCLUSIONS

The finding suggested that HON alleviates IBD by improving endothelial permeability through TRPV4. The discovery provides valuable insights into the potential therapeutic strategy of active natural products for alleviating IBD.

Supramolecular Structure of the β-Cyclodextrin Metal-Organic Framework Optimizes Iodine Stability and Its Co-delivery with l-Menthol for Antibacterial Applications

The spread of upper respiratory tract (URT) infections harms people's health and causes social burdens. Developing targeted treatment strategies for URT infections that exhibit good biocompatibility, stability, and strong antimicrobial effects remains challenging. The dual antimicrobial and antiviral effects of iodine (I2) in combination with the cooling sensation of l-menthol in the respiratory tract can simultaneously alleviate URT inflammation symptoms. However, as both I2 and l-menthol are volatile, addressing stability issues is crucial. In this study, a potassium iodide β-cyclodextrin metal-organic framework [β-CD-POF(I)] with appropriate particle size was used to coload and deliver I2 and l-menthol. Primarily, β-CD-POF(I) was employed as the most efficient carrier to significantly enhance the stability of I2, surpassing any other known protection strategies in the pharmaceutical field (CD complexations, PVP conjugations, and cadexomer iodine). The mechanism underlying the improvement in stability of I2 by β-CD-POF(I) was investigated through scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and molecular docking. The results revealed that the key processes involved in improving stability were the inclusion of I2 by β-CD cavities in β-CD-POF(I) and the formation of polyiodide anion between iodine ions and I2. Furthermore, the potential of β-CD-POF(I) to load and deliver drugs was validated, and coloading of l-menthol and I2 demonstrated reliable stability. β-CD-POF(I) achieved a rate of URT deposition ≥95% in vitro, and the combined antibacterial effects of coloaded I2 and l-menthol was better than I2 or PVP-I alone, with no irritation noted following URT administration in rabbits. Therefore, the stable coloading of drugs by β-CD-POF(I), leading to enhanced antimicrobial effects, provides a new strategy for treating URT infections.

Anti-Nociceptive Effects of Sphingomyelinase and Methyl-Beta-Cyclodextrin in the Icilin-Induced Mouse Pain Model

The thermo- and pain-sensitive Transient Receptor Potential Melastatin 3 and 8 (TRPM3 and TRPM8) ion channels are functionally associated in the lipid rafts of the plasma membrane. We have already described that cholesterol and sphingomyelin depletion, or inhibition of sphingolipid biosynthesis decreased the TRPM8 but not the TRPM3 channel opening on cultured sensory neurons. We aimed to test the effects of lipid raft disruptors on channel activation on TRPM3- and TRPM8-expressing HEK293T cells in vitro, as well as their potential analgesic actions in TRPM3 and TRPM8 channel activation involving acute pain models in mice. CHO cell viability was examined after lipid raft disruptor treatments and their effects on channel activation on channel expressing HEK293T cells by measurement of cytoplasmic Ca2+ concentration were monitored. The effects of treatments were investigated in Pregnenolone-Sulphate-CIM-0216-evoked and icilin-induced acute nocifensive pain models in mice. Cholesterol depletion decreased CHO cell viability. Sphingomyelinase and methyl-beta-cyclodextrin reduced the duration of icilin-evoked nocifensive behavior, while lipid raft disruptors did not inhibit the activity of recombinant TRPM3 and TRPM8. We conclude that depletion of sphingomyelin or cholesterol from rafts can modulate the function of native TRPM8 receptors. Furthermore, sphingolipid cleavage provided superiority over cholesterol depletion, and this method can open novel possibilities in the management of different pain conditions.

TRPA5 encodes a thermosensitive ankyrin ion channel receptor in a triatomine insect

As ectotherms, insects need heat-sensitive receptors to monitor environmental temperatures and facilitate thermoregulation. We show that TRPA5, a class of ankyrin transient receptor potential (TRP) channels absent in dipteran genomes, may function as insect heat receptors. In the triatomine bug Rhodnius prolixus (order: Hemiptera), a vector of Chagas disease, the channel RpTRPA5B displays a uniquely high thermosensitivity, with biophysical determinants including a large channel activation enthalpy change (72 kcal/mol), a high temperature coefficient (Q10 = 25), and in vitro temperature-induced currents from 53°C to 68°C (T0.5 = 58.6°C), similar to noxious TRPV receptors in mammals. Monomeric and tetrameric ion channel structure predictions show reliable parallels with fruit fly dTRPA1, with structural uniqueness in ankyrin repeat domains, the channel selectivity filter, and potential TRP functional modulator regions. Overall, the finding of a member of TRPA5 as a temperature-activated receptor illustrates the diversity of insect molecular heat detectors.

Current understanding of the molecular mechanisms of chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is the most common off-target adverse effects caused by various chemotherapeutic agents, such as cisplatin, oxaliplatin, paclitaxel, vincristine and bortezomib. CIPN is characterized by a substantial loss of primary afferent sensory axonal fibers leading to sensory disturbances in patients. An estimated of 19-85% of patients developed CIPN during the course of chemotherapy. The lack of preventive measures and limited treatment options often require a dose reduction or even early termination of life-saving chemotherapy, impacting treatment efficacy and patient survival. In this Review, we summarized the current understanding on the pathogenesis of CIPN. One prominent change induced by chemotherapeutic agents involves the disruption of neuronal cytoskeletal architecture and axonal transport dynamics largely influenced by the interference of microtubule stability in peripheral neurons. Due to an ineffective blood-nerve barrier in our peripheral nervous system, exposure to some chemotherapeutic agents causes mitochondrial swelling in peripheral nerves, which lead to the opening of mitochondrial permeability transition pore and cytochrome c release resulting in degeneration of primary afferent sensory fibers. The exacerbated nociceptive signaling and pain transmission in CIPN patients is often linked the increased neuronal excitability largely due to the elevated expression of various ion channels in the dorsal root ganglion neurons. Another important contributing factor of CIPN is the neuroinflammation caused by an increased infiltration of immune cells and production of inflammatory cytokines. In the central nervous system, chemotherapeutic agents also induce neuronal hyperexcitability in the spinal dorsal horn and anterior cingulate cortex leading to the development of central sensitization that causes CIPN. Emerging evidence suggests that the change in the composition and diversity of gut microbiota (dysbiosis) could have direct impact on the development and progression of CIPN. Collectively, all these aspects contribute to the pathogenesis of CIPN. Recent advances in RNA-sequencing offer solid platform for in silico drug screening which enable the identification of novel therapeutic agents or repurpose existing drugs to alleviate CIPN, holding immense promises for enhancing the quality of life for cancer patients who undergo chemotherapy and improve their overall treatment outcomes.

Observations of cold-induced vasodilation in persons with spinal cord injuries

STUDY DESIGN

Acute experimental study.

OBJECTIVES

Cold-induced vasodilation is a local mechanism of protection against frostbite in non-injured persons. We assessed whether an increase in skin blood flow (SkBF) during local cooling (LC) was observed in individuals with spinal cord injuries (SCIs) and if the response patterns differed between region levels or sites.

SETTING

Laboratory of Wakayama Medical University and the affiliated clinics, Japan.

METHODS

A local cooler device (diameter 4 cm) was placed on the chest (sensate) and right thigh (non-sensate) in persons with cervical (SCIC; n = 9) and thoracolumbar SCIs (SCITL; n = 9). After the surface temperature under the device was controlled at 33 °C for 10 min (baseline), LC (-0.045 °C/s) was applied and the skin temperature was maintained at 15 and 8 °C for 15 min of each stage. SkBF (laser Doppler flowmetry) was monitored using a 1-mm needle-type probe inserted into its center.

RESULTS

The percent change in SkBF (%ΔSkBF) on the chest remained unchanged until the end of 15 °C stage; thereafter, it increased to a level at least 70% greater than the baseline during the 8 °C stage in both groups. The %ΔSkBF on the thigh in both SCIC and SCITL notably increased from 8 and 6 min respectively, during the 8°C stage, compared to 1 min before the stage; however, it did not exceed the baseline level.

CONCLUSIONS

An increase in SkBF during LC was observed both in the sensate and non-sensate areas in SCIs, although the magnitude was larger in the sensate area.

A computationally informed distinction of interoception and exteroception

While interoception is of major neuroscientific interest, its precise definition and delineation from exteroception continue to be debated. Here, we propose a functional distinction between interoception and exteroception based on computational concepts of sensor-effector loops. Under this view, the classification of sensory inputs as serving interoception or exteroception depends on the sensor-effector loop they feed into, for the control of either bodily (physiological and biochemical) or environmental states. We explain the utility of this perspective by examining the perception of skin temperature, one of the most challenging cases for distinguishing between interoception and exteroception. Specifically, we propose conceptualising thermoception as inference about the thermal state of the body (including the skin), which is directly coupled to thermoregulatory processes. This functional view emphasises the coupling to regulation (control) as a defining property of perception (inference) and connects the definition of interoception to contemporary computational theories of brain-body interactions.

The kainate receptor GluK2 mediates cold sensing in mice

Thermosensors expressed in peripheral somatosensory neurons sense a wide range of environmental temperatures. While thermosensors detecting cool, warm and hot temperatures have all been extensively characterized, little is known about those sensing cold temperatures. Though several candidate cold sensors have been proposed, none has been demonstrated to mediate cold sensing in somatosensory neurons in vivo, leaving a knowledge gap in thermosensation. Here we characterized mice lacking the kainate-type glutamate receptor GluK2, a mammalian homolog of the Caenorhabditis elegans cold sensor GLR-3. While GluK2 knockout mice respond normally to heat and mechanical stimuli, they exhibit a specific deficit in sensing cold but not cool temperatures. Further analysis supports a key role for GluK2 in sensing cold temperatures in somatosensory DRG neurons in the periphery. Our results reveal that GluK2-a glutamate-sensing chemoreceptor mediating synaptic transmission in the central nervous system-is co-opted as a cold-sensing thermoreceptor in the periphery.

Hypothalamic TRPM8 and TRPA1 ion channel genes in the regulation of temperature homeostasis at water balance changes

The role of the hypothalamic cold-sensitive ion channels - transient receptor potential melastatin 8 (TRPM8) and transient receptor potential ankyrin 1 (TRPA1) in homeostatic systems of thermoregulation and water-salt balance - is not clear. The interaction of homeostatic systems of thermoregulation and water-salt balance without additional temperature load did not receive due attention, too. On the models of water-balance disturbance, we tried to elucidate some aspect of these problems. Body temperature (Tbody), O2 consumption, CO2 excretion, electrical muscle activity (EMA), temperature of tail skin (Ttail), plasma osmolality, as well as gene expression of hypothalamic TRPM8 and TRPA1 have been registered in rats of 3 groups: control; water-deprived (3 days under dry-eating); and hyperhydrated (6 days without dry food, drinking liquid 4 % sucrose). No relationship was observed between plasma osmolality and gene expression of Trpm8 and Trpa1. In water-deprived rats, the constriction of skin vessels, increased fat metabolism by 10 % and increased EMA by 48 % allowed the animals to maintain Tbody unchanged. The hyperhydrated rats did not develop sufficient mechanisms, and their Tbody decreased by 0.8 °C. The development of reactions was correlated with the expression of genes of thermosensitive ion channels in the anterior hypothalamus. Ttail had a direct correlation with the expression of the Trpm8 gene, whereas EMA directly correlated with the expression of the Trpa1 gene in water-deprived group. The obtained data attract attention from the point of view of management and correction of physiological functions by modulating the ion channel gene expression.

A mouse DRG genetic toolkit reveals morphological and physiological diversity of somatosensory neuron subtypes

Dorsal root ganglia (DRG) somatosensory neurons detect mechanical, thermal, and chemical stimuli acting on the body. Achieving a holistic view of how different DRG neuron subtypes relay neural signals from the periphery to the CNS has been challenging with existing tools. Here, we develop and curate a mouse genetic toolkit that allows for interrogating the properties and functions of distinct cutaneous targeting DRG neuron subtypes. These tools have enabled a broad morphological analysis, which revealed distinct cutaneous axon arborization areas and branching patterns of the transcriptionally distinct DRG neuron subtypes. Moreover, in vivo physiological analysis revealed that each subtype has a distinct threshold and range of responses to mechanical and/or thermal stimuli. These findings support a model in which morphologically and physiologically distinct cutaneous DRG sensory neuron subtypes tile mechanical and thermal stimulus space to collectively encode a wide range of natural stimuli.

Characterization of human iPSC-derived sensory neurons and their functional assessment using multi electrode array

Sensory neurons are afferent neurons in sensory systems that convert stimuli and transmit information to the central nervous system as electrical signals. Primary afferent neurons that are affected by non-noxious and noxious stimuli are present in the dorsal root ganglia (DRG), and the DRG sensory neurons are used as an in vitro model of the nociceptive response. However, DRG derived from mouse or rat give a low yield of neurons, and they are difficult to culture. To help alleviate this problem, we characterized human induced pluripotent stem cell (hiPSC) derived sensory neurons. They can solve the problems of interspecies differences and supply stability. We investigated expressions of sensory neuron related proteins and genes, and drug responses by Multi-Electrode Array (MEA) to analyze the properties and functions of sensory neurons. They expressed nociceptor, mechanoreceptor and proprioceptor related genes and proteins. They constitute a heterogeneous population of their subclasses. We confirmed that they could respond to both noxious and non-noxious stimuli. We showed that histamine inhibitors reduced histamine-induced neuronal excitability. Furthermore, incubation with a ProTx-II and Nav1.7 inhibitor reduced the spontaneous neural activity in hiPSC-derived sensory neurons. Their responsiveness was different from each drug. We have demonstrated that hiPSC-derived sensory neurons combined with MEA are good candidates for drug discovery studies where DRG in vitro modeling is necessary.

Caldendrin Is a Repressor of PIEZO2 Channels and Touch Sensation in Mice

The sense of touch is crucial for cognitive, emotional, and social development and relies on mechanically activated (MA) ion channels that transduce force into an electrical signal. Despite advances in the molecular characterization of these channels, the physiological factors that control their activity are poorly understood. Here, we used behavioral assays, electrophysiological recordings, and various mouse strains (males and females analyzed separately) to investigate the role of the calmodulin-like Ca2+ sensor, caldendrin, as a key regulator of MA channels and their roles in touch sensation. In mice lacking caldendrin (Cabp1 KO), heightened responses to tactile stimuli correlate with enlarged MA currents with lower mechanical thresholds in dorsal root ganglion neurons (DRGNs). The expression pattern of caldendrin in the DRG parallels that of the major MA channel required for touch sensation, PIEZO2. In transfected cells, caldendrin interacts with and inhibits the activity of PIEZO2 in a manner that requires an alternatively spliced sequence in the N-terminal domain of caldendrin. Moreover, targeted genetic deletion of caldendrin in Piezo2-expressing DRGNs phenocopies the tactile hypersensitivity of complete Cabp1 KO mice. We conclude that caldendrin is an endogenous repressor of PIEZO2 channels and their contributions to touch sensation in DRGNs.

Cold temperature induces a TRPM8-independent calcium release from the endoplasmic reticulum in human platelets

The detection of temperature by the human sensory system is life-preserving and highly evolutionarily conserved. Platelets are sensitive to temperature changes and are activated by a decrease in temperature, akin to sensory neurons. However, the molecular mechanism of this temperature-sensing ability is unknown. Yet, platelet activation by temperature could contribute to numerous clinical sequelae, most importantly to reduced quality of ex vivo-stored platelets for transfusion. In this multidisciplinary study, we present evidence for the expression of the temperature-sensitive ion channel transient receptor potential cation channel subfamily member 8 (TRPM8) in human platelets and precursor cells. We found the TRPM8 mRNA and protein in MEG-01 cells and platelets. Inhibition of TRPM8 prevented temperature-induced platelet activation and shape change. However, chemical agonists of TRPM8 did not seem to have an acute effect on platelets. When exposing platelets to below-normal body temperature, we detected a cytosolic calcium increase which was independent of TRPM8 but was completely dependent on the calcium release from the endoplasmic reticulum. Because of the high interindividual variability of TRPM8 expression, a population-based approach should be the focus of future studies. Our study suggests that the cold response of platelets is complex and TRPM8 appears to play a role in early temperature-induced activation of platelets, while other mechanisms likely contribute to later stages of temperature-mediated platelet response.

TRPM channels in health and disease

Different cell channels and transporters tightly regulate cytoplasmic levels and the intraorganelle distribution of cations. Perturbations in these processes lead to human diseases that are frequently associated with kidney impairment. The family of melastatin-related transient receptor potential (TRPM) channels, which has eight members in mammals (TRPM1-TRPM8), includes ion channels that are highly permeable to divalent cations, such as Ca2+, Mg2+ and Zn2+ (TRPM1, TRPM3, TRPM6 and TRPM7), non-selective cation channels (TRPM2 and TRPM8) and monovalent cation-selective channels (TRPM4 and TRPM5). Three family members contain an enzymatic protein moiety: TRPM6 and TRPM7 are fused to α-kinase domains, whereas TRPM2 is linked to an ADP-ribose-binding NUDT9 homology domain. TRPM channels also function as crucial cellular sensors involved in many physiological processes, including mineral homeostasis, blood pressure, cardiac rhythm and immunity, as well as photoreception, taste reception and thermoreception. TRPM channels are abundantly expressed in the kidney. Mutations in TRPM genes cause several inherited human diseases, and preclinical studies in animal models of human disease have highlighted TRPM channels as promising new therapeutic targets. Here, we provide an overview of this rapidly evolving research area and delineate the emerging role of TRPM channels in kidney pathophysiology.

TRP channels associated with macrophages as targets for the treatment of obese asthma

Globally, obesity and asthma pose significant health challenges, with obesity being a key factor influencing asthma. Despite this, effective treatments for obese asthma, a distinct phenotype, remain elusive. Since the discovery of transient receptor potential (TRP) channels in 1969, their value as therapeutic targets for various diseases has been acknowledged. TRP channels, present in adipose tissue cells, influence fat cell heat production and the secretion of adipokines and cytokines, which are closely associated with asthma and obesity. This paper aims to investigate the mechanisms by which obesity exacerbates asthma-related inflammation and suggests that targeting TRP channels in adipose tissue could potentially suppress obese asthma and offer novel insights into its treatment.

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.

Phosphoinositide Regulation of TRP Channels: A Functional Overview in the Structural Era

Transient receptor potential (TRP) ion channels have diverse activation mechanisms including physical stimuli, such as high or low temperatures, and a variety of intracellular signaling molecules. Regulation by phosphoinositides and their derivatives is their only known common regulatory feature. For most TRP channels, phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] serves as a cofactor required for activity. Such dependence on PI(4,5)P2 has been demonstrated for members of the TRPM subfamily and for the epithelial TRPV5 and TRPV6 channels. Intracellular TRPML channels show specific activation by PI(3,5)P2. Structural studies uncovered the PI(4,5)P2 and PI(3,5)P2 binding sites for these channels and shed light on the mechanism of channel opening. PI(4,5)P2 regulation of TRPV1-4 as well as some TRPC channels is more complex, involving both positive and negative effects. This review discusses the functional roles of phosphoinositides in TRP channel regulation and molecular insights gained from recent cryo-electron microscopy structures.

Intragastric administration of cinnamaldehyde induces changes in body temperature via TRPA1

The transient receptor potential (TRP) channel family, including TRPA1, is known to be involved in temperature sensing and response. Previous studies have shown that intragastric administration of cinnamaldehyde (a typical TRPA1 agonist) can change body temperature, but the role of TRPA1 in this response is not clear. In this study, we found that intragastric administration of cinnamaldehyde increased in the intrascapular brown adipose tissue (IBAT) and rectal temperatures. However, this effect was not observed in TRPA1 knockout mice, suggesting that TRPA1 is involved in these temperature changes. Intravenous cinnamaldehyde also increased IBAT and rectal temperatures, only in the presence of TRPA1. We also explored the contribution of the vagus nerve to these temperature changes and found that it played a limited role. These results suggest that cinnamaldehyde can affect body temperature through TRPA1 activation, with the vagus nerve having a minor influence.

Discovery of flavone-derivatives as the new skeleton of transient receptor potential vanilloid 3 channel antagonists

Transient receptor potential vanilloid 3 (TRPV3) channel is a temperature-sensitive and Ca2+-permeable nonselective cation channel, which is abundantly expressed in skin keratinocyte and plays an important role in skin homeostasis and repair. However, only a few TRPV3 inhibitors were reported. Few selective and potent modulators of the TRPV3 channel have hindered the progress of the investigation and clinical application. TRPV3 channel research still faces challenges and requires the new inhibitors. Flavonoids are a kind of natural compounds with various biological and pharmacological activities including anti-inflammatory and anti allergic effects, which is associated with some physiological effects mediated by TRPV3 channel. Herein, our group designed and synthesized a range of flavone derivatives, and investigated their inhibitory properties on the human TRPV3 channel by electrophysiology technique. Then, we identified a new potent TRPV3 antagonist 2d with IC50 of 0.62 μM. It also showed good selectivity on TRPV1, TRPV4, TRPA1 and TRPM8.

Mechanism involved of post-exercise cold water immersion: Blood redistribution and increase in energy expenditure during rewarming

Thermogenesis is well understood, but the relationships between cold water immersion (CWI), the post-CWI rewarming and the associated physiological changes are not. This study investigated muscle and systemic oxygenation, cardiorespiratory and hemodynamic responses, and gastrointestinal temperature during and after CWI. 21 healthy men completed randomly 2 protocols. Both protocols consisted of a 48 minutes heating cycling exercise followed by 3 recovery periods (R1-R3), but they differed in R2. R1 lasted 20 minutes in a passive semi-seated position on a physiotherapy table at ambient room temperature. Depending on the protocol, R2 lasted 15 minutes at either ambient condition (R2_AMB) or in a CWI condition at 10°C up to the iliac crest (R2_CWI). R3 lasted 40 minutes at AMB while favoring rewarming after R2_CWI. This was followed by 10 minutes of cycling. Compared to R2_AMB, R2_CWI ended at higherV ˙ O2 in the non-immersed body part due to thermogenesis (7.16(2.15) vs. 4.83(1.62) ml.min-1.kg-1) and lower femoral artery blood flow (475(165) vs. 704(257) ml.min-1) (p < 0.001). Only after CWI, R3 showed a progressive decrease in vastus and gastrocnemius medialis O2 saturation, significant after 34 minutes (p < 0.001). As blood flow did not differ from the AMB protocol, this indicated local thermogenesis in the immersed part of the body. After CWI, a lower gastrointestinal temperature on resumption of cycling compared to AMB (36.31(0.45) vs. 37.30(0.49) °C, p < 0.001) indicated incomplete muscle thermogenesis. In conclusion, the rewarming period after CWI was non-linear and metabolically costly. Immersion and rewarming should be considered as a continuum rather than separate events.

Targeting TRP channels: recent advances in structure, ligand binding, and molecular mechanisms

Transient receptor potential (TRP) channels are a large and diverse family of transmembrane ion channels that are widely expressed, have important physiological roles, and are associated with many human diseases. These proteins are actively pursued as promising drug targets, benefitting greatly from advances in structural and mechanistic studies of TRP channels. At the same time, the complex, polymodal activation and regulation of TRP channels have presented formidable challenges. In this short review, we summarize recent progresses toward understanding the structural basis of TRP channel function, as well as potential ligand binding sites that could be targeted for therapeutics. A particular focus is on the current understanding of the molecular mechanisms of TRP channel activation and regulation, where many fundamental questions remain unanswered. We believe that a deeper understanding of the functional mechanisms of TRP channels will be critical and likely transformative toward developing successful therapeutic strategies targeting these exciting proteins. This endeavor will require concerted efforts from computation, structural biology, medicinal chemistry, electrophysiology, pharmacology, drug safety and clinical studies.

Molecular and circuit mechanisms underlying avoidance of rapid cooling stimuli in C. elegans

The mechanisms by which animals respond to rapid changes in temperature are largely unknown. Here, we found that polymodal ASH sensory neurons mediate rapid cooling-evoked avoidance behavior within the physiological temperature range in C. elegans. ASH employs multiple parallel circuits that consist of stimulatory circuits (AIZ, RIA, AVA) and disinhibitory circuits (AIB, RIM) to respond to rapid cooling. In the stimulatory circuit, AIZ, which is activated by ASH, releases glutamate to act on both GLR-3 and GLR-6 receptors in RIA neurons to promote reversal, and ASH also directly or indirectly stimulates AVA to promote reversal. In the disinhibitory circuit, AIB is stimulated by ASH through the GLR-1 receptor, releasing glutamate to act on AVR-14 to suppress RIM activity. RIM, an inter/motor neuron, inhibits rapid cooling-evoked reversal, and the loop activities thus equally stimulate reversal. Our findings elucidate the molecular and circuit mechanisms underlying the acute temperature stimuli-evoked avoidance behavior.

Thermosensation and TRP Channels

Somatosensory neurons can sense external temperature by converting sensation of temperature information to neural activity via afferent input to the central nervous system. Various populations of somatosensory neurons have specialized gene expression, including expression of thermosensitive transient receptor potential (TRP) ion channels. Thermosensitive TRP channels are responsible for thermal transduction at the peripheral ends of somatosensory neurons and can sense a wide range of temperatures. Here we focus on several thermosensitive TRP channels including TRPV1, TRPV4, TRPM2, TRPM3, TRPM8, TRPC5, and TRPA1 in sensory neurons. TRPV3, TRPV4, and TRPC5 are also involved in somatosensation in nonneuronal cells and tissues. In particular, we discuss whether skin senses ambient temperatures through TRPV3 and TRPV4 activation in skin keratinocytes and the involvement of TRPM2 expressed by hypothalamic neurons in thermosensation in the brain.

A new gene for autosomal dominant facial palsy/migraine identified in a family by whole exome sequencing

BACKGROUND

Facial palsy manifests as unilateral or bilateral weakness and inability to move some of the facial muscles. The aetiology may be different including idiopathic, trauma, infections or brain tumours or it can be associated with chronic neurological diseases. For instance, in recurrent migraine, an increased risk of idiopathic facial palsy (often unilateral) has been observed. Migraine is a neurovascular disorder characterized by mild to severe intensity of headaches, often associated with neuro-ophthalmological symptoms.

METHODS

A family is reported where five members were affected by facial palsy associated with other clinical features including migraine, diplopia, facial swelling, eye conjunctivitis following a vertical transmission. Whole exome sequencing was performed in three members (two affected and one healthy) in order to identify potential variants causative of their phenotype.

RESULTS

A missense variant c.304G>A was found leading to the p.(Ala102Thr) substitution in the TRPM8 gene, previously related to migraine by genome wide association studies. This variant was classified as deleterious by several predictor tools, and the mutant residue was predicted to alter the protein structure in terms of flexibility and interactions with the surrounding residues.

CONCLUSION

These findings suggest that TRPM8 could be a new causative gene further linking migraine and recurrent facial palsy.

Topical application of L-Menthol - Physiological and genetic considerations to assist in developing female athlete research: A narrative review

L-menthol is a cyclic monoterpene derived from aromatic plants, which gives a cooling sensation upon application. With this in mind, L-menthol is beginning to be considered as a potential ergogenic aid for exercise and sporting competitions, particularly in hot environments, however female-specific research is lacking. The aim of this narrative review is to summarize available literature relating to topical application of L-menthol and provide commentary on avenues of consideration relating to future research developments of topical L-menthol in female athletes. From available studies in male participants, L-menthol topical application results in no endurance exercise performance improvements, however decreases in thermal sensation are observed. Mixed results are observed within strength performance parameters. Several genetic variations and single nucleotide polymorphisms have been identified in relation to sweat production, fluid loss and body mass changes - factors which may influence topical application of L-menthol. More specifically to female athletes, genetic variations relating to sweat responses and skin thickness, phases of the menstrual cycle, and body composition indices may affect the ergogenic effects of L-menthol topical application, via alterations in thermogenic responses, along with differing tissue distribution compared to their male counterparts. This narrative review concludes that further development of female athlete research and protocols for topical application of L-menthol is warranted due to physiological and genetic variations. Such developments would benefit research and practitioners alike with further personalized sport science strategies around phases of the menstrual cycle and body composition indices, with a view to optimize ergogenic effects of L-menthol.