TRPM3 is a nociceptor channel involved in the detection of noxious heat

Sphingosylphosphorylcholine induces itch via activation of TRPM3 and TRPA1 in mice

Itch is a prevalent symptom in atopic dermatitis (AD), often leading to a strong urge to scratch. Elevated levels of sphingosylphosphorylcholine (SPC) are found in the stratum corneum of AD patients, and while SPC is known to induce itch, its molecular targets are not well understood. This study aims to identify the signaling pathway of SPC-induced itch under AD conditions. We demonstrate that SPC specifically activates the Transient Receptor Potential Melastatin 3 (TRPM3) channel in sensory neurons. In HEK293T cells expressing TRPM3, SPC treatment caused a significant increase in intracellular calcium, which was inhibited by TRPM3 antagonists. Among various TRP channels tested, TRPM3 exhibited the highest reactivity to SPC, followed by TRPA1. Molecular docking analysis also supported interactions between SPC and both TRPM3 and TRPA1. In an AD mouse model, SPC-induced responses were dependent on TRPM3 and TRPA1, and the expression of these channels increased in dorsal root ganglion neurons. SPC-induced scratching behaviors were significantly reduced by TRPM3 and TRPA1 antagonists, with TRPM3 playing a critical role in spontaneous scratching. This study identifies TRPM3 and TRPA1 as key mediators of SPC-induced itch, providing potential therapeutic targets for treating itch in AD patients.

Pro-inflammatory mediators sensitise transient receptor potential melastatin 3 cation channel (TRPM3) function in mouse sensory neurons

Pro-inflammatory mediators can directly activate pain-sensing neurons, known as nociceptors. Additionally, these mediators can sensitise ion channels and receptors expressed by these cells through transcriptional and post-translational modulation, leading to nociceptor hypersensitivity. A well-characterised group of ion channels that subserve nociceptor sensitisation is the transient receptor potential (TRP) superfamily of cation channels. For example, the roles of TRP channels vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1) in nociceptor sensitisation and inflammatory pain have been extensively documented. In the case of TRP melastatin 3 (TRPM3), however, despite the increasing recognition of this channel's role in inflammatory pain, the mediators driving its sensitisation during inflammation remain poorly characterised. Here, using Ca2+ imaging, we found that an inflammatory soup of bradykinin, interleukin 1β (IL-1β) and tumour necrosis factor α (TNFα) sensitised TRPM3 function in isolated mouse sensory neurons; IL-1β and TNFα, but not bradykinin, independently potentiated TRPM3 function. TRPM3 expression and translocation to the membrane remained unchanged upon individual or combined exposure to these inflammatory mediators, which suggests that post-translational modification might occur. Finally, using the complete Freund's adjuvant-induced model of knee inflammation, we found that systemic pharmacological blockade of TRPM3 does not alleviate inflammatory pain (as assessed through evaluation of digging behaviour and dynamic weight bearing), which contrasts with previous reports using different pain models. We propose that the nuances of the immune response may determine the relative contribution of TRPM3 to nociceptive signalling in different neuro-immune contexts. Collectively, our findings improve insight into the role of TRPM3 sensitisation in inflammatory pain.

Profiling human iPSC-derived sensory neurons for analgesic drug screening using a multi-electrode array

Chronic pain is a global health issue, yet effective treatments remain limited due to poor preclinical-to-human translation. To address this, we developed a high-content screening (HCS) platform using hiPSC-derived nociceptors to identify analgesics targeting the peripheral nervous system. These cells, cultured on multi-well microelectrode arrays, achieved nearly 100% active electrodes by week 2, maintaining stable activity for at least 2 weeks. After 28 days, we assessed drug effects on neuronal activity, achieving strong assay performance (robust Z' > 0.5). Pharmacological tests confirmed responses to key analgesic targets, including ion channels (Nav, Cav, Kv, and TRPV1), neurotransmitter receptors (AMPAR and GABA-R), and kinase inhibitors (tyrosine and JAK1/2). Transcriptomic analysis validated target expression, though levels differed from primary human DRG cells. The platform was used to screen over 700 natural compounds, demonstrating its potential for analgesic discovery. This HCS platform facilitates the rapid discovery of uncharacterized analgesics, reducing preclinical-to-human translation failure.

Inhibition of TRPM3 channels in the medial prefrontal cortex mitigates OCD symptoms following traumatic brain injury

Although tumor necrosis factor-alpha (TNF-α) plays an important role in the development of obsessive-compulsive disorder (OCD), the pathogenesis remains unclear. Since transient receptor potential melastatin 3 (TRPM3) channels are activated during inflammatory conditions, crosstalk with TNF-α in the progression of OCD has not been investigated yet. We hypothesize that mild traumatic brain injury (mTBI) stimulates TRPM3 channels, thereby enhancing the level of TNF-α in the medial prefrontal cortex (mPFC), a key brain region implicated in OCD pathogenesis. The closed-head weight-drop method was used for mTBI-induced OCD in mice, and neurological assessment was carried out using rotarod and beam-walk tests. Marble-burying test, open-field test, dark-light emergence test, and nest-building behavior test were performed to examine OCD-like symptoms. The mPFC was isolated, and the TNF-α level and TRPM3 immunoreactivity were estimated using ELISA and immunohistochemistry techniques. Additionally, Golgi-Cox staining and HPLC were performed to quantify dendritic arbor and serotonin content. To validate our hypothesis, mTBI mice were treated with a selective TRPM3 inhibitor naringenin (50 mg/kg) via intraperitoneal route, and all the above parameters were screened. Marble-burying and nest-building behaviors were increased in mTBI mice. However, exploratory behavior and time spend in the light chamber were significantly reduced. Moreover, mTBI increases TNF-α concentration and TRPM3 immunoreactivity, while decreasing dendritic arbor and serotonin content. Notably, naringenin treatment reversed these behavioral, biochemical, and molecular abnormalities. Naringenin may inhibit TRPM3-mediated TNF-α production and serotonin transmission, thereby suppressing OCD symptoms. Thus, we propose a novel therapeutic approach for treating OCD associated with traumatic brain injury.

Molecular basis of neurosteroid and anticonvulsant regulation of TRPM3

Transient receptor potential channel subfamily M member 3 (TRPM3) is a Ca2+-permeable cation channel activated by the neurosteroid pregnenolone sulfate (PregS) or heat, serving as a nociceptor in the peripheral sensory system. Recent discoveries of autosomal dominant neurodevelopmental disorders caused by gain-of-function mutations in TRPM3 highlight its role in the central nervous system. Notably, the TRPM3 inhibitor primidone, an anticonvulsant, has proven effective in treating patients with TRPM3-linked neurological disorders and in mouse models of thermal nociception. However, our understanding of neurosteroids, inhibitors and disease mutations on TRPM3 is limited. Here we present cryogenic electron microscopy structures of the mouse TRPM3 in complex with cholesteryl hemisuccinate, primidone and PregS with the synthetic agonist CIM 0216. Our studies identify the binding sites for the neurosteroid, synthetic agonist and inhibitor and offer insights into their effects and disease mutations on TRPM3 gating, aiding future drug development.

Pathway-dependent cold activation of heat-responsive TRPV channels

The homotetrameric thermosensitive transient receptor potential vanilloid 1-4 (TRPV1-4) channels in sensory neurons are highly responsive to heat stimuli. However, their primary heat sensors or triggers for heat activation have not been examined for cold activation. In this study, cold activation of minimal TRPV1 without the pore turret was compared with that of full-length human TRPV3. The former followed a pathway from the putative heat activation starter, while the latter tracked a different pathway starting far from the assumed heat activation point. The results showed that the former shared temperature sensitivity with heat activation while the latter did not. Therefore, this mirrored thermosensitivity can be used to confirm the location of the primary thermal sensor for TRPV1 or TRPV3, and potentially define the primary thermal sensor of other thermosensitive proteins like TRPV2 or TRPV4 once the same heat capacity mechanism is applied.

Stimulus-Transcription Coupling of TRPM3 Channels: A Signaling Pathway from the Plasma Membrane to the Nucleus

Transient receptor potential melastatin-3 (TRPM3) channels are cation channels activated by heat and chemical ligands. TRPM3 regulates heat sensation, secretion, neurotransmitter release, iris constriction, and tumor promotion. Stimulation of TRPM3 triggers an influx of Ca2+ ions into the cells and the initiation of an intracellular signaling cascade. TRPM3 channels are regulated by phosphatidylinositol 4,5-bisphosphate, the βγ subunit of G-protein-coupled receptors, phospholipase C, and calmodulin. Extracellular signal-regulated protein kinase ERK1/2 and c-Jun N-terminal protein kinase (JNK) function as signal transducers. The signaling cascade is negatively regulated by the protein phosphatases MKP-1 and calcineurin and increased concentrations of Zn2+. Stimulation of TRPM3 leads to the activation of stimulus-responsive transcription factors controlled by epigenetic regulators. Potential delayed response genes encoding the pro-inflammatory regulators interleukin-8, calcitonin gene-related peptide, and the prostaglandin-synthesizing enzyme prostaglandin endoperoxide synthase-2 have been identified. Elucidating the TRPM3-induced signaling cascade provides insights into how TRPM3 stimulation alters numerous biochemical and physiological parameters within the cell and throughout the organism and offers intervention points for manipulating TRPM3 signaling and function.

Vestibular neurons link motion sickness, behavioural thermoregulation and metabolic balance in mice

Motion sickness is associated with thermoregulation and metabolic control, but the underlying neural circuitry remains largely unknown. Here we show that neurons in the medial vestibular nuclei parvocellular part (MVePC) mediate the hypothermic responses induced by motion. Reactivation of motion-sensitive MVePC neurons recapitulates motion sickness in mice. We show that motion-activated neurons in the MVePC are glutamatergic (MVePCGlu), and that optogenetic stimulation of MVePCGlu neurons mimics motion-induced hypothermia by signalling to the lateral parabrachial nucleus (LPBN). Acute inhibition of MVePC-LPBN circuitry abrogates motion-induced hypothermia. Finally, we show that chronic inhibition of MVePCGlu neurons prevents diet-induced obesity and improves glucose homeostasis without suppressing food intake. Overall, these findings highlight MVePCGlu neurons as a potential target for motion-sickness treatment and obesity control.

Interaction between thermosensitive TRP channels and anoctamin 1

Some thermosensitive transient receptor potential (TRP) channels form a protein complex with anoctamin 1 (ANO1, also called TMEM16A). TRP channels have high calcium permeability, and the calcium entering cells through TRP channel activation activates ANO1, a calcium-activated chloride channel, involved in many physiological and pathological conditions. The physiological significance of TRP channels is often mediated by their ability to activate ANO1, which controls chloride flux across the plasma membrane. This review summarizes the latest understanding on the interactions between ANO1 and thermosensitive TRP channels, including TRPV1, TRPV3, and TRPV4, which are involved in pain sensitization in primary sensory neurons, proliferation and migration of human keratinocytes, and fluid secretion such as sweat, respectively.

TRPV3 in skin thermosensation and temperature responses

Human skin, as a sophisticated sensory organ, is able to detect subtle changes in ambient temperature. This thermosensory capability is primarily mediated by temperature-sensitive TRP channels expressed in both sensory neurons and keratinocytes. Among these, TRPV3, which responds to warm temperatures and plays a crucial role in various skin functions, is particularly notable. TRPV3 channels not only detect moderate warmth but are also sensitive to chemical ligands that evoke thermal sensations. The activation of TRPV3 by warm temperatures and compounds highlights its importance in the molecular mechanisms underlying skin thermosensation. This review mainly discusses the role of TRPV3, particularly its contribution to skin thermosensation and structural insights into its temperature sensitivity, providing an understanding of how TRPV3 modulates thermal perception at the molecular level.

Phenotype Spectrum of TRPM3-Associated Disorders

OBJECTIVE

Monoallelic variants in the transient receptor potential melastatin-related type 3 gene (TRPM3) have been associated with neurodevelopmental manifestations, but knowledge on the clinical manifestations and treatment options is limited. We characterized the clinical spectrum, highlighting particularly the epilepsy phenotype, and the effect of treatments.

METHODS

We analyzed retrospectively the phenotypes and genotypes of 43 individuals with TRPM3 variants, acquired from GeneMatcher and collaborations (n = 21), and through a systematic literature search (n = 22). We included all patients with a pathogenic TRPM3 variant.

RESULTS

The median age at the time of the study was 10 years, with a preponderance of girls (60%) versus boys (40%). Frequent findings were developmental delay and/or intellectual disability (93%), global or axial hypotonia (77%), ocular involvement (70%), musculoskeletal anomalies (65%), and dysmorphic features (58%). Epilepsy was diagnosed in 31 patients (72%), classified in all as developmental and epileptic encephalopathy with or without spike wave activation in sleep (DEE/DEE-SWAS). Patients with the variant p.Val1002Met (n = 24) significantly more often had developmental delay and epilepsy. The most effective anti-seizure medication was primidone. All treated patients showed an improvement in seizure frequency, motor and speech development, and/or learning capability with this drug.

INTERPRETATION

Developmental delay/intellectual disability and epilepsy are dominant phenotypic features in patients with TRPM3 variants. Given that epilepsy can negatively impact development, screening for awake and sleep electroencephalogram abnormalities and other manifestations are essential to offer early intervention. The TRPM3 channel blocker primidone has shown promising effects and should be considered in every child with a TRPM3 gain-of-function variant. ANN NEUROL 2025;97:561-570.

Modelling inflammation-induced peripheral sensitization in a dish-more complex than expected?

ABSTRACT

Peripheral sensitization of nociceptors is believed to be a key driver of chronic pain states. Here, we sought to study the effects of a modified version of inflammatory soup on the excitability of human stem cell-derived sensory neurons. For this, we used a preexisting and a novel stem cell line, modified to stably express the calcium sensor GCamP6f. Upon treatment with inflammatory soup, we observed no changes in neuronal transcription or functional responses upon calcium imaging and only a very minor increase in resting membrane potential (RMP) via whole cell patch clamping: control RMP (-71.31 ± 1.1 mV) vs inflammatory soup RMP (-67.74 ± 1.29 mV), uncorrected 2-tailed independent samples t test, P = 0.0383. Similarly, small changes were observed when treating mouse primary sensory neurons with inflammatory soup. A semi-systematic reexamination of past literature further indicated that observed effects of inflammatory mediators on dissociated sensory neuron cultures are generally small. We conclude that modelling inflammation-induced peripheral sensitization in vitro is nontrivial and will require careful selection of mediators and/or more complex, longitudinal multicellular setups. Especially in the latter, our novel GCamP6f-induced pluripotent stem cell line may be of value.

Pregnenolone sulfate potentiates tetrodotoxin-resistant Na+ channels to increase the excitability of dural afferent neurons in rats

BACKGROUND

Although peripheral administration of pregnenolone sulfate (PS) has been reported to produce pronociceptive effects, the mechanisms by which PS modulates the excitability of nociceptive neurons are poorly understood. Here, we report on the excitatory role of PS in peripheral nociceptive neurons, focusing on its effects on tetrodotoxin-resistant (TTX-R) Na+ channels.

METHODS

TTX-R Na+ current (INa) mediated by NaV1.8 was recorded from acutely isolated small-sized dural afferent neurons of rats, identified with the retrograde fluorescent dye DiI, using a whole-cell patch-clamp technique.

RESULTS

Transcripts for enzymes and transporters involved in PS biosynthesis were detected in the ophthalmic branch of the trigeminal ganglia. In voltage-clamp mode, PS preferentially potentiated the TTX-R persistent INa, a small non-inactivating current during sustained depolarization. PS shifted the voltage-inactivation relationship toward a depolarizing range. PS also delayed the onset of inactivation and accelerated the recovery from inactivation of TTX-R Na+ channels. Additionally, PS decreased the extent of use-dependent inhibition of TTX-R Na+ channels. In current-clamp mode, PS hyperpolarized dural afferent neurons by increasing the leak K+ conductance. Nevertheless, PS decreased the rheobase current-the minimum current required to generate action potentials-and increased the number of action potentials elicited by depolarizing current stimuli.

CONCLUSION

We have shown that the excitatory neurosteroid PS preferentially potentiates TTX-R persistent INa and reduces the inactivation of TTX-R Na+ channels, resulting in increased excitability of dural afferent neurons. The potential role of endogenous PS in migraine pathology warrants further investigation.

Sex difference in TRPM3 channel functioning in nociceptive and vascular systems: an emerging target for migraine therapy in females?

Transient Receptor Potential Melastatin 3 (TRPM3) channels are Ca2+ permeable ion channels that act as polymodal sensors of mechanical, thermal, and various chemical stimuli. TRPM3 channels are highly expressed in the trigeminovascular system, including trigeminal neurons and the vasculature. Their presence in dural afferents suggests that they are potential triggers of migraine pain, which is originating from the meningeal area. This area is densely innervated by autonomous and trigeminal nerves that contain the major migraine mediator calcitonin gene-related peptide (CGRP) in peptidergic nerve fibers. Co-expression of TRPM3 channels and CGRP receptors in meningeal nerves suggests a potential interplay between both signalling systems. Compared to other members of the TRP family, TRPM3 channels have a high sensitivity to sex hormones and to the endogenous neurosteroid pregnenolone sulfate (PregS). The predominantly female sex hormones estrogen and progesterone, of which the levels drop during menses, act as natural inhibitors of TRPM3 channels, while PregS is a known endogenous agonist of these channels. A decrease in sex hormone levels has also been suggested as trigger for attacks of menstrually-related migraine. Notably, there is a remarkable sex difference in TRPM3-mediated effects in trigeminal nociceptive signalling and the vasculature. In line with this, the relaxation of human isolated meningeal arteries induced by the activation of TRPM3 channels is greater in females. Additionally, the sex-dependent vasodilatory responses to CGRP in meningeal arteries seem to be influenced by age-related hormonal changes, which could contribute to sex differences in migraine pathology. Consistent with these observations, activation of TRPM3 channels triggers nociceptive sensory firing much more prominently in female than male mouse meninges, suggesting that pain processing in female patients with migraine may differ. Overall, the combined TRPM3-related neuronal and vascular mechanisms could provide a possible explanation for the higher prevalence and even the more severe quality of migraine attacks in females. This narrative review summarizes recent data on the sex-dependent roles of TRPM3 channels in migraine pathophysiology, the potential interplay between TRPM3 and CGRP signalling, and highlights the prospects for translational therapies targeting TRPM3 channels, which may be of particular relevance for women with migraine.

Muscarinic acetylcholine type 1 receptor antagonism activates TRPM3 to augment mitochondrial function and drive axonal repair in adult sensory neurons

OBJECTIVE

Antagonism of the muscarinic acetylcholine type 1 receptor (M1R) promotes sensory axon repair and is protective in peripheral neuropathy, however, the mechanism remains elusive. We investigated the role of the heat-sensing transient receptor potential melastatin-3 (TRPM3) cation channel in M1R antagonism-mediated nerve regeneration and explored the potential of TRPM3 activation to facilitate axonal plasticity.

METHODS

Dorsal root ganglion (DRG) neurons from adult control or diabetic rats were cultured and treated with TRPM3 agonists (CIM0216, pregnenolone sulfate) and M1R antagonists pirenzepine (PZ) or muscarinic toxin 7 (MT7). Ca2+ transients, mitochondrial respiration, AMP-activated protein kinase (AMPK) expression, and mitochondrial inner membrane potential were analyzed. The effect of M1R activation or blockade on TRPM3 activity mediated by phosphatidylinositol 4,5-bisphosphate (PIP2) was studied. Metabolic profiling of DRG neurons and human neuroblastoma SH-SY5Y cells was conducted.

RESULTS

M1R antagonism induced by PZ or MT7 increased Ca2+ influx in DRG neurons and was inhibited by TRPM3 antagonists or in the absence of extracellular Ca2+. TRPM3 agonists elevated Ca2+ levels, augmented mitochondrial respiration, AMPK activation and neurite outgrowth. M1R antagonism stimulated TRPM3 channel activity through inhibition of PIP2 hydrolysis to activate Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ)/AMPK, leading to augmented mitochondrial function and neuronal metabolism. DRG neurons with AAV-mediated shRNA knockdown of TRPM3 exhibited suppressed antimuscarinic drug-induced neurite outgrowth. TRPM3 agonists increased glycolysis and TCA cycle metabolites, indicating enhanced metabolism in DRG neurons and SH-SY5Y cells.

CONCLUSIONS

Activation of the TRPM3/CaMKKβ/AMPK pathway promoted collateral sprouting of sensory axons, positioning TRPM3 as a promising therapeutic target for peripheral neuropathy.

Convergent Agonist and Heat Activation of Nociceptor TRPM3

Detecting noxious heat is vital for survival, triggering pain responses that protect against harm1,2. The TRPM3 channel is a key nociceptor for sensing noxious heat and a promising therapeutic target for pain treatment and neurological disorders such as epilepsy3-11. Here, we functionally and structurally characterized TRPM3 in response to diverse stimuli: the synthetic superagonist CIM0216 Ref12, the anticonvulsant antagonist primidone13,14, and heat1,10,15. Our findings reveal that TRPM3 is intrinsically dynamic, with its intracellular domain (ICD) sampling both resting and activated states, though strongly favoring the resting state without stimulation. CIM0216 binds to the S1-S4 domain, inducing conformational changes in the ICD and shifting the equilibrium toward activation. Remarkably, heat induces similar ICD rearrangements, revealing a converged activation mechanism driven by chemical compounds and temperature. This mechanism is supported by functional data showing that mutations facilitating the ICD movement markedly increase the sensitivity of TRPM3 to both chemical and thermal signals. These findings establish a critical role of the ICD in temperature sensing in TRPM3, a mechanism likely conserved across the TRPM family. Finally, we show that primidone binds to the same site as CIM0216 but acts as an antagonist. This study provides a framework for understanding the thermal sensing mechanisms of temperature-sensitive ion channels and offers a structural foundation for developing TRPM3-target therapeutics for pain and neurological disorders.

Protein dynamics underlies strong temperature dependence of heat receptors

Ion channels are generally allosteric proteins, involving specialized stimulus sensor domains conformationally linked to the gate to drive channel opening. Temperature receptors are a group of ion channels from the transient receptor potential family. They exhibit an unprecedentedly strong temperature dependence and are responsible for temperature sensing in mammals. Despite intensive studies, however, the nature of the temperature sensor domain in these channels remains elusive. By direct calorimetry of TRPV1 proteins, we have recently provided a proof of principle that temperature sensing by ion channels may diverge from the conventional allosterity theory; rather it is intimately linked to inherent thermal instability of channel proteins. Here, we tackle the generality of the hypothesis and provide key molecular pieces of evidence on the coupling of thermal transitions in the channels. We show that while wild-type channels possess a single concerted thermal transition peak, the chimera, in which strong temperature dependence becomes disrupted, results in multitransition peaks, and the activation enthalpies are accordingly reduced. The data show that the coupling with protein unfolding drives up the energy barrier of activation, leading to a strong temperature dependence of opening. Furthermore, we pinpoint the proximal N-terminus of the channels as a linchpin in coalescing different parts of the channels into concerted activation. Thus, we suggest that coupled interaction networks in proteins underlie the strong temperature dependence of temperature receptors.

Thermo-TRP regulation by endogenous factors and its physiological function at core body temperature

Transient receptor potential (TRP) channels with temperature sensitivities (thermo-TRPs) are involved in various physiological processes. Thermo-TRPs that detect temperature changes in peripheral sensory neurons possess indispensable functions in thermosensation, eliciting defensive behavior against noxious temperatures and driving autonomic/behavioral thermoregulatory responses to maintain body temperature in mammals. Moreover, most thermo-TRPs are functionally expressed in cells and tissues where the temperature is maintained at a constant core body temperature. To perform physiological functions, the activity of each thermo-TRP channel must be regulated by endogenous mechanisms at body temperature. Dysregulation of this process can lead to various diseases. This review highlights the endogenous factors regulating thermo-TRP activity and physiological functions at constant core body temperature.

Anesthetic- and Analgesic-Related Drugs Modulating Both Voltage-Gated Na+ and TRP Channels

Nociceptive information is transmitted by action potentials (APs) through primary afferent neurons from the periphery to the central nervous system. Voltage-gated Na+ channels are involved in this AP production, while transient receptor potential (TRP) channels, which are non-selective cation channels, are involved in receiving and transmitting nociceptive stimuli in the peripheral and central terminals of the primary afferent neurons. Peripheral terminal TRP vanilloid-1 (TRPV1), ankylin-1 (TRPA1) and melastatin-8 (TRPM8) activation produces APs, while central terminal TRP activation enhances the spontaneous release of L-glutamate from the terminal to spinal cord and brain stem lamina II neurons that play a pivotal role in modulating nociceptive transmission. There is much evidence demonstrating that chemical compounds involved in Na+ channel (or nerve AP conduction) inhibition modify TRP channel functions. Among these compounds are local anesthetics, anti-epileptics, α2-adrenoceptor agonists, antidepressants (all of which are used as analgesic adjuvants), general anesthetics, opioids, non-steroidal anti-inflammatory drugs and plant-derived compounds, many of which are involved in antinociception. This review mentions the modulation of Na+ channels and TRP channels including TRPV1, TRPA1 and TRPM8, both of which modulations are produced by pain-related compounds.

Lipid raft disruption inhibits the activation of Transient Receptor Potential Vanilloid 1, but not TRP Melastatin 3 and the voltage-gated L-type calcium channels in sensory neurons

Transient Receptor Potential (TRP) ion channels like Vanilloid 1 (TRPV1) and Melastatin 3 (TRPM3) are nonselective cation channels expressed in primary sensory neurons and peripheral nerve endings, which are located in cholesterol- and sphingolipid-rich membrane lipid raft regions and have important roles in pain processing. Besides TRP ion channels a wide variety of voltage-gated ion channels were also described in the membrane raft regions of neuronal cells. Here we investigated the effects of lipid raft disruption by methyl-beta-cyclodextrin (MCD) and sphingomyelinase (SMase) on TRPV1, TRPM3 and voltage-gated L-type Ca2+ channel activation in cultured trigeminal neurons and sensory nerve terminals of the trachea. We also examined the mechanism of action of MCD by in silico modeling. Disruption of lipid rafts by MCD or SMase did not alter CIM0216-induced TRPM3 cation channel activation and the voltage-gated L-type Ca2+ channel activation by FPL 64126 or veratridine neither on trigeminal sensory neurons nor sensory nerve terminals. We provided the first structural explanation with in silico modeling that the activation of TRPV1, TRPM3 and voltage-gated L-type Ca2+ channels is affected differently by the cholesterol content surrounding them in the plasma membrane. It is concluded that modifying the hydrophobic interactions between lipid rafts and ion channels might provide a selective novel mechanism for peripheral analgesia.

Profiling Human iPSC-Derived Sensory Neurons for Analgesic Drug Screening Using a Multi-Electrode Array

Chronic pain is a major global health issue, yet effective treatments are limited by poor translation from preclinical studies to humans. To address this, we developed a high-content screening (HCS) platform for analgesic discovery using hiPSC-derived nociceptors. These cells were cultured on multi-well micro-electrode arrays to monitor activity, achieving nearly 100% active electrodes by week two, maintaining stable activity for at least two weeks. After maturation (28 days), we exposed the nociceptors to various drugs, assessing their effects on neuronal activity, with excellent assay performance (Z' values >0.5). Pharmacological tests showed responses to analgesic targets, including ion channels (Nav, Cav, Kv, TRPV1), neurotransmitter receptors (AMPAR, GABA-R), and kinase inhibitors (tyrosine, JAK1/2). Transcriptomic analysis confirmed the presence of these drug targets, although expression levels varied compared to primary human dorsal root ganglion cells. This HCS platform facilitates the rapid discovery of novel analgesics, reducing the risk of preclinical-to-human translation failure.

Motivation

Chronic pain affects approximately 1.5 billion people worldwide, yet effective treatments remain elusive. A significant barrier to progress in analgesic drug discovery is the limited translation of preclinical findings to human clinical outcomes. Traditional rodent models, although widely used, often fail to accurately predict human responses, while human primary tissues are limited by scarcity, technical difficulties, and ethical concerns. Recent advancements have identified human induced pluripotent stem cell (hiPSC)-derived nociceptors as promising alternatives; however, current differentiation protocols produce cells with inconsistent and physiologically questionable phenotypes.To address these challenges, our study introduces a novel high-content screening (HCS) platform using hiPSC-derived nociceptors cultured on multi-well micro-electrode arrays (MEAs). The "Anatomic" protocol, used to generate these nociceptors, ensures cells with transcriptomic profiles closely matching human primary sensory neurons. Our platform achieves nearly 100% active electrode yield within two weeks and demonstrates sustained, stable activity over time. Additionally, robust Z' factor analysis (exceeding 0.5) confirms the platform's reliability, while pharmacological validation establishes the functional expression of critical analgesic targets. This innovative approach improves both the efficiency and clinical relevance of analgesic drug screening, potentially bridging the translational gap between preclinical studies and human clinical trials, and offering new hope for effective pain management.

Protein Dynamics Underlies Strong Temperature Dependence of Heat Receptors

Ion channels are generally allosteric proteins, involving specialized stimulus sensor domains conformationally linked to the gate to drive channel opening. Temperature receptors are a group of ion channels from the transient receptor potential (TRP) family. They exhibit an unprecedentedly strong temperature dependence and are responsible for temperature sensing in mammals. Despite intensive studies, however, the nature of the temperature sensor domain in these channels remains elusive. By direct calorimetry of TRPV1 proteins, we have recently provided a proof of principle that temperature sensing by ion channels may diverge from the conventional allosterity theory; rather it is intimately linked to inherent thermal instability of channel proteins. Here we tackle the generality of the hypothesis and provide key molecular evidences on the coupling of thermal transitions in the channels. We show that while wild-type channels possess a single concerted thermal transition peak, the chimera, in which strong temperature dependence becomes disrupted, results in multi-transition peaks, and the activation enthalpies are accordingly reduced. The data show that the coupling with protein unfolding drives up the energy barrier of activation, leading to a strong temperature dependence of opening. Furthermore, we pinpoint the proximal N-terminus of the channels as a linchpin in coalescing different parts of the channels into concerted activation. Thus, we suggest that coupled interaction networks in proteins underlie the strong temperature dependence of temperature receptors.

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.

Implications of TRPM3 and TRPM8 for sensory neuron sensitisation

Sensory neurons serve to receive and transmit a wide range of information about the conditions of the world around us as well as the external and internal state of our body. Sensitisation of these nerve cells, i.e. becoming more sensitive to stimuli or the emergence or intensification of spontaneous activity, for example in the context of inflammation or nerve injury, can lead to chronic diseases such as neuropathic pain. For many of these disorders there are only very limited treatment options and in order to find and establish new therapeutic approaches, research into the exact causes of sensitisation with the elucidation of the underlying mechanisms and the identification of the molecular components is therefore essential. These components include plasma membrane receptors and ion channels that are involved in signal reception and transmission. Members of the transient receptor potential (TRP) channel family are also expressed in sensory neurons and some of them play a crucial role in temperature perception. This review article focuses on the heat-sensitive TRPM3 and the cold-sensitive TRPM8 (and TRPA1) channels and their importance in sensitisation of dorsal root ganglion sensory neurons is discussed based on studies related to inflammation and injury- as well as chemotherapy-induced neuropathy.

Genome of Russian Snow-White Chicken Reveals Genetic Features Associated with Adaptations to Cold and Diseases

Russian Snow White (RSW) chickens are characterized by high egg production, extreme resistance to low temperatures, disease resistance, and by the snow-white color of the day-old chicks. Studying the genome of this unique chicken breed will reveal its evolutionary history and help to understand the molecular genetic mechanisms underlying the unique characteristics of this breed, which will open new breeding opportunities and support future studies. We have sequenced and made a de novo assembly of the whole RSW genome using deep sequencing (250×) by the short reads. The genome consists of 40 chromosomes with a total length of 1.1 billion nucleotide pairs. Phylogenetic analysis placed the RSW near the White Leghorn, Fayoumi, and Houdan breeds. Comparison with other chicken breeds revealed a wide pool of mutations unique to the RSW. The functional annotation of these mutations showed the adaptation of genes associated with the development of the nervous system, thermoreceptors, purine receptors, and the TGF-beta pathway, probably caused by selection for low temperatures. We also found adaptation of the immune system genes, likely driven by selection for resistance to viral diseases. Integration with previous genome-wide association studies (GWAS) suggested several causal single nucleotide polymorphisms (SNPs). Specifically, we identified an RSW-specific missense mutation in the RALYL gene, presumably causing the snow-white color of the day-old chicks, and an RSW-specific missense mutation in the TLL1 gene, presumably affecting the egg weight.

Topical menthol, a pharmacological cold mimic, induces cold sensitivity, adaptive thermogenesis and brown adipose tissue activation in mice

AIM

Brown adipose tissue (BAT) thermogenesis has profound energy-expanding potential, which makes it an attractive target tissue to combat ever-increasing obesity and its other associated metabolic complications. Although it is fairly accepted that cold is a potent inducer of BAT activation and function, there are limited studies on the mechanisms of pharmacological cold-mimicking agents, such as the TRPM8 agonist, menthol, on BAT thermogenesis and activation.

METHODS

Herein, we sought to determine the effect of topical application of menthol (10% w/v [4 g/kg] cream formulation/day for 15 days) on temperature sensitivity behaviour (thermal gradient assay, nesting behaviour), adaptive thermogenesis (infrared thermography, core body temperature), BAT sympathetic innervation (tyrosine hydroxylase immunohistochemistry) and activation (18F-FDG PET-CT analysis, Uncoupling Protein 1 immunohistochemistry and BAT gene expression), whole-body energy expenditure (indirect calorimetry) and other metabolic variables in male C57BL/6N mice.

RESULTS

We show that male C57BL/6N mice: (a) develop a warm-seeking and cold-avoiding thermal preference phenotype; (b) display increased locomotor activity and adaptive thermogenesis; (c) show augmented sympathetic innervation in BAT and its activation; (d) exhibit enhanced gluconeogenic capacity (increased glucose excursion in response to pyruvate) and insulin sensitivity; and (e) show enhanced whole-body energy expenditure and induced lipid-utilizing phenotype after topical menthol application.

CONCLUSIONS

Taken together, our findings highlight that pharmacological cold mimicking using topical menthol application presents a potential therapeutic strategy to counter weight gain and related complications.

Functions of TRPs in retinal tissue in physiological and pathological conditions

The Transient Receptor Potential (TRP) constitutes a family of channels subdivided into seven subfamilies: Ankyrin (TRPA), Canonical (TRPC), Melastatin (TRPM), Mucolipin (TRPML), no-mechano-potential C (TRPN), Polycystic (TRPP), and Vanilloid (TRPV). Although they are structurally similar to one another, the peculiarities of each subfamily are key to the response to stimuli and the signaling pathway that each one triggers. TRPs are non-selective cation channels, most of which are permeable to Ca2+, which is a well-established second messenger that modulates several intracellular signaling pathways and is involved in physiological and pathological conditions in various cell types. TRPs depolarize excitable cells by increasing the influx of Ca2+, Na+, and other cations. Most TRP families are activated by temperature variations, membrane stretching, or chemical agents and, therefore, are defined as polymodal channels. All TPRs are expressed, at some level, in the central nervous system (CNS) and ocular-related structures, such as the retina and optic nerve (ON), except the TRPP in the ON. TRPC, TRPM, TRPV, and TRPML are found in the retinal pigmented cells, whereas only TRPA1 and TRPM are detected in the uvea. Accordingly, several studies have focused on the search to unravel the role of TRPs in physiological and pathological conditions related to the eyes. Thus, this review aims to shed light on endogenous and exogenous modulators, triggered cell signaling pathways, and localization and roles of each subfamily of TRP channels in physiological and pathological conditions in the retina, optic nerve, and retinal pigmented epithelium of vertebrates.

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.

TRPM3, TRPM4, and TRPM5 as thermo-sensitive channels

Temperature detection is essential for the survival and perpetuation of any species. Thermoreceptors in the skin sense body temperature as well as the temperatures of ambient air and objects. Since Dr. David Julius and his colleagues discovered that TRPV1 is expressed in small-diameter primary sensory neurons, and activated by temperatures above 42 °C, 11 of thermo-sensitive TRP channels have been identified. TRPM3 expressed in sensory neurons acts as a sensor for noxious heat. TRPM4 and TRPM5 are Ca2⁺-activated monovalent cation channels, and their activity is drastically potentiated by temperature increase. This review aims to summarize the expression patterns, electrophysiological properties, and physiological roles of TRPM3, TRPM4, and TRPM5 associated with thermosensation.

TLR4 induced TRPM2 mediated neuropathic pain

Ion channels play an important role in mediating pain through signal transduction, regulation, and control of responses, particularly in neuropathic pain. Transient receptor potential channel superfamily plays an important role in cation permeability and cellular signaling. Transient receptor potential channel Melastatin 2 (TRPM2) subfamily regulates Ca2+ concentration in response to various chemicals and signals from the surrounding environment. TRPM2 has a role in several physiological functions such as cellular osmosis, temperature sensing, cellular proliferation, as well as the manifestation of many disease processes such as pain process, cancer, apoptosis, endothelial dysfunction, angiogenesis, renal and lung fibrosis, and cerebral ischemic stroke. Toll-like Receptor 4 (TLR4) is a critical initiator of the immune response to inflammatory stimuli, particularly those triggered by Lipopolysaccharide (LPS). It activates downstream pathways leading to the production of oxidative molecules and inflammatory cytokines, which are modulated by basal and store-operated calcium ion signaling. The cytokine production and release cause an imbalance of antioxidant enzymes and redox potential in the Endoplasmic Reticulum and mitochondria due to oxidative stress, which results from TLR-4 activation and consequently induces the production of inflammatory cytokines in neuronal cells, exacerbating the pain process. Very few studies have reported the role of TRPM2 and its association with Toll-like receptors in the context of neuropathic pain. However, the molecular mechanism underlying the interaction between TRPM2 and TLR-4 and the quantum of impact in acute and chronic neuropathic pain remains unclear. Understanding the link between TLR-4 and TRPM2 will provide more insights into pain regulation mechanisms for the development of new therapeutic molecules to address neuropathic pain.

Functional Upregulation of TRPM3 Channels Contributes to Acute Pancreatitis-associated Pain and Inflammation

Transient receptor potential melastatin M3 (TRPM3) channels have been recognized as a pain transducer in dorsal root ganglion (DRG) neurons in recent years. TRPM3 activation initiates neurogenic inflammation and is required for the development of inflammatory hyperalgesia. We aimed to evaluate the role of TRPM3 in pancreas sensory afferents in pancreatic nociception, neurogenic inflammation, and acute pancreatitis (AP)-associated pain. AP was induced by intraperitoneal (i.p.) injection of L-arginine in rats. TRPM3 expression in pancreatic DRG neurons, spontaneous or mechanical-stimulation-evoked pain behaviors, and the extent of inflammation were evaluated. We found that TRPM3 channels were expressed on pancreatic primary afferent nerve terminals containing calcitonin gene-related peptide (CGRP). Activation of TRPM3 in the pancreas by injection of its specific agonist CIM0216 (10 μM) induced pain, CGRP and substance P release, and neurogenic inflammation, as evidenced by edema, plasma extravasation, and inflammatory cell accumulation in the pancreas. Increased TRPM3 functional expression was detected in pancreatic DRG neurons from AP rats, and blocking TRPM3 activity with its antagonist (Primidone, 5 mg/kg, i.p.) attenuated AP-associated pain behaviors and pancreatic inflammation. Pre-incubation of pancreatic DRG neurons with nerve growth factor (NGF) enhanced the increase in intracellular Ca2+ induced by the TRPM3 agonist (CIM0216, 1 μM). Our findings indicate that, in addition to TRPV1 and TRPA1 channels, TRPM3 is another pain channel that has a critical role in pancreatic nociception, neurogenic inflammation, and AP-associated pain behaviors. TRPM3 may be a promising pharmaceutical target for AP pain treatment.

Human heat sensation: A randomized crossover trial

Sensing of noxious heat has been reported to be mediated by TRPV1, TRPA1, TRPM3, and ANO1 in mice, and this is redundant so that the loss of one receptor is at least partially compensated for by others. We have established an infusion-based human heat pain model. Heat-induced pain probed with antagonists for the four receptors did not match the redundancy found in mice. In healthy participants, only TRPV1 contributes to the detection of noxious heat; none of the other three receptors are involved. TRPV1 inhibition reduced the pain at all noxious temperatures, which can also be seen as an increase in the temperature that causes a particular level of pain. However, even if the TRPV1-dependent shift in heat detection is about 1°C, at the end of the temperature ramp to 52°C, most heat-induced pain remains unexplained. This difference between species reopens the quest for the molecular safety net for the detection of noxious heat in humans.

Melastatin subfamily Transient Receptor Potential channels support spermatogenesis in planarian flatworms

The Transient Receptor Potential superfamily of proteins (TRPs) form cation channels that are abundant in animal sensory systems. Amongst TRPs, the Melastatin-related subfamily (TRPMs) is composed of members that respond to temperature, pH, sex hormones, and various other stimuli. Some TRPMs exhibit enriched expression in gonads of vertebrate and invertebrate species, but their contributions to germline development remain to be determined. We identified twenty-one potential TRPMs in the planarian flatworm Schmidtea mediterranea and analyzed their anatomical distribution of expression by whole-mount in situ hybridization. Enriched expression of two TRPMs (Smed-TRPM-c and Smed-TRPM-l) was detected in testis, whereas eight TRPM genes had detectable expression in patterns representative of neuronal and/or sensory cell types. Functional analysis of TRPM homologs by RNA-interference (RNAi) revealed that disruption of Smed-TRPM-c expression results in reduced sperm development, indicating a role for this receptor in supporting spermatogenesis. Smed-TRPM-l RNAi did not result in a detectable phenotype, but it increased sperm development deficiencies when combined with Smed-TRPM-c RNAi. Fluorescence in situ hybridization revealed expression of Smed-TRPM-c in early spermatogenic cells within testes, suggesting cell-autonomous regulatory functions in germ cells for this gene. In addition, Smed-TRPM-c RNAi resulted in reduced numbers of presumptive germline stem cell clusters in asexual planarians, suggesting that Smed-TRPM-c supports establishment, maintenance, and/or expansion of spermatogonial germline stem cells. While further research is needed to identify the factors that trigger Smed-TRPM-c activity, these findings reveal one of few known examples for TRPM function in direct regulation of sperm development.

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.

Functional relationship between peripheral thermosensation and behavioral thermoregulation

Thermoregulation is a fundamental mechanism for maintaining homeostasis in living organisms because temperature affects essentially all biochemical and physiological processes. Effector responses to internal and external temperature cues are critical for achieving effective thermoregulation by controlling heat production and dissipation. Thermoregulation can be classified as physiological, which is observed primarily in higher organisms (homeotherms), and behavioral, which manifests as crucial physiological functions that are conserved across many species. Neuronal pathways for physiological thermoregulation are well-characterized, but those associated with behavioral regulation remain unclear. Thermoreceptors, including Transient Receptor Potential (TRP) channels, play pivotal roles in thermoregulation. Mammals have 11 thermosensitive TRP channels, the functions for which have been elucidated through behavioral studies using knockout mice. Behavioral thermoregulation is also observed in ectotherms such as the fruit fly, Drosophila melanogaster. Studies of Drosophila thermoregulation helped elucidate significant roles for thermoreceptors as well as regulatory actions of membrane lipids in modulating the activity of both thermosensitive TRP channels and thermoregulation. This review provides an overview of thermosensitive TRP channel functions in behavioral thermoregulation based on results of studies involving mice or Drosophila melanogaster.

Potential pathophysiological role of the ion channel TRPM3 in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and the therapeutic effect of low-dose naltrexone

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a debilitating disease with a broad overlap of symptomatology with Post-COVID Syndrome (PCS). Despite the severity of symptoms and various neurological, cardiovascular, microvascular, and skeletal muscular findings, no biomarkers have been identified. The Transient receptor potential melastatin 3 (TRPM3) channel, involved in pain transduction, thermosensation, transmitter and neuropeptide release, mechanoregulation, vasorelaxation, and immune defense, shows altered function in ME/CFS. Dysfunction of TRPM3 in natural killer (NK) cells, characterized by reduced calcium flux, has been observed in ME/CFS and PCS patients, suggesting a role in ineffective pathogen clearance and potential virus persistence and autoimmunity development. TRPM3 dysfunction in NK cells can be improved by naltrexone in vitro and ex vivo, which may explain the moderate clinical efficacy of low-dose naltrexone (LDN) treatment. We propose that TRPM3 dysfunction may have a broader involvement in ME/CFS pathophysiology, affecting other organs. This paper discusses TRPM3's expression in various organs and its potential impact on ME/CFS symptoms, with a focus on small nerve fibers and the brain, where TRPM3 is involved in presynaptic GABA release.

Across two continents: The genomic basis of environmental adaptation in house mice (Mus musculus domesticus) from the Americas

Replicated clines across environmental gradients can be strong evidence of adaptation. House mice (Mus musculus domesticus) were introduced to the Americas by European colonizers and are now widely distributed from Tierra del Fuego to Alaska. Multiple aspects of climate, such as temperature, vary predictably across latitude in the Americas. Past studies of North American populations across latitudinal gradients provided evidence of environmental adaptation in traits related to body size, metabolism, and behavior and identified candidate genes using selection scans. Here, we investigate genomic signals of environmental adaptation on a second continent, South America, and ask whether there is evidence of parallel adaptation across multiple latitudinal transects in the Americas. We first identified loci across the genome showing signatures of selection related to climatic variation in mice sampled across a latitudinal transect in South America, accounting for neutral population structure. Consistent with previous results, most candidate SNPs were in putatively regulatory regions. Genes that contained the most extreme outliers relate to traits such as body weight or size, metabolism, immunity, fat, eye function, and the cardiovascular system. We then compared these results with the results of analyses of published data from two transects in North America. While most candidate genes were unique to individual transects, we found significant overlap among candidate genes identified independently in the three transects. These genes are diverse, with functions relating to metabolism, immunity, cardiac function, and circadian rhythm, among others. We also found parallel shifts in allele frequency in candidate genes across latitudinal gradients. Finally, combining data from all three transects, we identified several genes associated with variation in body weight. Overall, our results provide strong evidence of shared responses to selection and identify genes that likely underlie recent environmental adaptation in house mice across North and South America.

Understanding the role of temperature in seasonal timing: Effects on behavioural, physiological and molecular phenotypes

Organisms adapt to daily and seasonal environmental changes to maximise their metabolic and reproductive fitness. For seasonally breeding animals, photoperiod is considered the most robust cue to drive these changes. It, however, does not explain the interannual variations in different seasonal phenotypes. Several studies have repeatedly shown the influence of ambient temperature on the timing of different seasonal physiologies including the timing of migration, reproduction and its associated behaviours, etc. In the present review, we have discussed the effects of changes in ambient temperature on different seasonal events in endotherms with a focus on migratory birds as they have evolved to draw benefits from distinct but largely predictable seasonal patterns of natural resources. We have further discussed the physiological and molecular mechanisms by which temperature affects seasonal timings. The primary brain area involved in detecting temperature changes is the hypothalamic preoptic area. This area receives thermal inputs via sensory neurons in the peripheral ganglia that measure changes in thermoregulatory tissues such as the skin and spinal cord. For the input signals, several thermal sensory TRP (transient receptor potential ion channels) channels have been identified across different classes of vertebrates. These channels are activated at specific thermal ranges. Once perceived, this information should activate an effector function. However, the link between temperature sensation and the effector pathways is not properly understood yet. Here, we have summarised the available information that may help us understand how temperature information is translated into seasonal timing.

Exploring oak processionary caterpillar induced lepidopterism (part 2): ex vivo bio-assays unmask the role of TRPV1

As human skin comes into contact with the tiny hairs or setae of the oak processionary caterpillar, Thaumetopoea processionea, a silent yet intense chemical confrontation occurs. The result is a mix of issues: skin rashes and an intense itching that typically lasts days and weeks after the contact. This discomfort poses a significant health threat not only to humans but also to animals. In Western Europe, the alarming increase in outbreaks extends beyond areas near infested trees due to the dispersion of the setae. Predictions indicate a sustained rise in outbreaks, fueled by global changes favoring the caterpillar's survival and distribution. Currently, the absence of an efficient treatment persists due to significant gaps in our comprehension of the pathophysiology associated with this envenomation. Here, we explored the interaction between the venom extract derived from the setae of T. processionea and voltage- and ligand-gated ion channels and receptors. By conducting electrophysiological analyses, we discovered ex vivo evidence highlighting the significant role of TPTX1-Tp1, a peptide toxin from T. processionea, in modulating TRPV1. TPTX1-Tp1 is a secapin-like peptide and demonstrates a unique ability to modulate TRPV1 channels in the presence of capsaicin, leading to cell depolarization, itch and inflammatory responses. This discovery opens new avenues for developing a topical medication, suggesting the incorporation of a TRPV1 blocker as a potential solution for the local effects caused by T. processionea.

Transient receptor potential (TRP) channels in Sebastes schlegelii: Genome-wide identification and ThermoTRP expression analysis under high-temperature

Transient Receptor Potential (TRP) channels, essential for sensing environmental stimuli, are widely distributed. Among them, thermosensory TRP channels play a crucial role in temperature sensing and regulation. Sebastes schlegelii, a significant aquatic economic species, exhibits sensitivity to temperature across multiple aspects. In this study, we identified 18 SsTRP proteins using whole-genome scanning. Motif analysis revealed motif 2 in all TRP proteins, with conserved motifs in subfamilies. TRP-related domains, anchored repeats, and ion-transmembrane domains were found. Chromosome analysis showed 18 TRP genes on 11 chromosomes and a scaffold. Phylogenetics classified SsTRPs into four subfamilies: TRPM, TRPA, TRPV, and TRPC. In diverse organisms, four monophyletic subfamilies were identified. Additionally, we identified key TRP genes with significantly upregulated transcription levels under short-term (30 min) and long-term (3 days) exposure at 24 °C (optimal elevated temperature) and 27 °C (critical high temperature). We propose that genes upregulated at 30 min may be involved in the primary response process of temperature sensing, while genes upregulated at 3 days may participate in the secondary response process of temperature perception. This study lays the foundation for understanding the regulatory mechanisms of TRPs responses to environmental stimuli in S. schlegelii and other fishes.

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.

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.

Neurodevelopmental disorders caused by variants in TRPM3

Developmental and epileptic encephalopathies (DEE) are a broad and varied group of disorders that affect the brain and are characterized by epilepsy and comorbid intellectual disability (ID). These conditions have a broad spectrum of symptoms and can be caused by various underlying factors, including genetic mutations, infections, and other medical conditions. The exact cause of DEE remains largely unknown in the majority of cases. However, in around 25 % of patients, rare nonsynonymous coding variants in genes encoding ion channels, cell-surface receptors, and other neuronally expressed proteins are identified. This review focuses on a subgroup of DEE patients carrying variations in the gene encoding the Transient Receptor Potential Melastatin 3 (TRPM3) ion channel, where recent data indicate that gain-of-function of TRPM3 channel activity underlies a spectrum of dominant neurodevelopmental disorders.

Role of thermosensitive transient receptor potential (TRP) channels in thermal preference of male and female mice

Transient Receptor Potential (TRP) ion channels are important for sensing environmental temperature. In rodents, TRPV4 senses warmth (25-34 °C), TRPV1 senses heat (>42 °C), TRPA1 putatively senses cold (<17 °C), and TRPM8 senses cool-cold (18-26 °C). We investigated if knockout (KO) mice lacking these TRP channels exhibited changes in thermal preference. Thermal preference was tested using a dual hot-cold plate with one thermoelectric surface set at 30 °C and the adjacent surface at a temperature of 15-45 °C in 5 °C increments. Blinded observers counted the number of times mice crossed through an opening between plates and the percentage of time spent on the 30 °C plate. In a separate experiment, observers blinded as to genotype also assessed the temperature at the location on a thermal gradient (1.83 m, 4-50 °C) occupied by the mouse at 5- or 10-min intervals over 2 h. Male and female wildtype mice preferred 30 °C and significantly avoided colder (15-20 °C) and hotter (40-45 °C) temperatures. Male TRPV1KOs and TRPA1KOs, and TRPV4KOs of both sexes, were similar, while female WTs, TRPV1KOs, TRPA1KOs and TRPM8KOs did not show significant thermal preferences across the temperature range. Male and female TRPM8KOs did not significantly avoid the coldest temperatures. Male mice (except for TRPM8KOs) exhibited significantly fewer plate crossings at hot and cold temperatures and more crossings at thermoneutral temperatures, while females exhibited a similar but non-significant trend. Occupancy temperatures along the thermal gradient exhibited a broad distribution that shrank somewhat over time. Mean occupancy temperatures (recorded at 90-120 min) were significantly higher for females (30-34 °C) compared to males (26-27 °C) of all genotypes, except for TRPA1KOs which exhibited no sex difference. The results indicate (1) sex differences with females (except TRPA1KOs) preferring warmer temperatures, (2) reduced thermosensitivity in female TRPV1KOs, and (3) reduced sensitivity to cold and innocuous warmth in male and female TRPM8KOs consistent with previous studies.

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.

Similarities and differences in peripheral itch and pain pathways in atopic dermatitis

Atopic dermatitis (AD) is predominantly characterized by intense itching, but concomitant skin pain is experienced by more than 40% of patients. Patients with AD display considerable somatosensory aberrations, including increased nerve sensitivity to itch stimuli (hyperknesis), perception of itch from innocuous stimuli (alloknesis), or perception of pain from innocuous stimuli (allodynia). This review summarizes the current understanding of the similarities and differences in the peripheral mechanisms underlying itch and pain in AD. These distinct yet reciprocal sensations share many similarities in the peripheral nervous system, including common mediators (such as serotonin, endothelin-1, IL-33, and thymic stromal lymphopoietin), receptors (such as members of the G protein-coupled receptor family and Toll-like receptors), and ion channels for signal transduction (such as certain members of the transient receptor potential [TRP] cation channels). Itch-responding neurons are also sensitive to pain stimuli. However, there are distinct differences between itch and pain signaling. For example, specific immune responses are associated with pain (type 1 and/or type 3 cytokines and certain chemokine C-C [CCL2, CCL5] and C-X-C [CXCL] motif ligands) and itch (type 2 cytokines, including IL-31, and periostin). The TRP melastatin channels TRPM2 and TRPM3 have a role in pain but no known role in itch. Activation of μ-opioid receptors is known to alleviate pain but exacerbate itch. Understanding the connection between itch and pain mechanisms may offer new insights into the treatment of chronic pain and itch in AD.

Targeting TRP channels for pain relief: A review of current evidence from bench to bedside

Several decades of research support the involvement of transient receptor potential (TRP) channels in nociception. Despite the disappointments of early TRPV1 antagonist programs, the TRP family remains a promising therapeutic target in pain disorders. High-dose capsaicin patches are already in clinical use to relieve neuropathic pain. At present, localized injections of the side-directed TRPV1 agonist capsaicin and resiniferatoxin are undergoing clinical trials in patients with osteoarthritis and bone cancer pain. TRPA1, TRPM3, and TRPC5 channels are also of significant interest. This review discusses the role of TRP channels in human pain conditions.

Lipid raft disruption as an opportunity for peripheral analgesia

Chronic pain conditions are unmet medical needs, since the available drugs, opioids, non-steroidal anti-inflammatory/analgesic drugs and adjuvant analgesics do not provide satisfactory therapeutic effect in a great proportion of patients. Therefore, there is an urgent need to find novel targets and novel therapeutic approaches that differ from classical pharmacological receptor antagonism. Most ion channels and receptors involved in pain sensation and processing such as Transient Receptor Potential ion channels, opioid receptors, P2X purinoreceptors and neurokinin 1 receptor are located in the lipid raft regions of the plasma membrane. Targeting the membrane lipid composition and structure by sphingolipid or cholesterol depletion might open future perspectives for the therapy of chronic inflammatory, neuropathic or cancer pain, most importantly acting at the periphery.