The cool things to know about TRPM8!

Optical Control of TRPM8 Channels with Photoswitchable Menthol

Transient receptor potential melastatin 8 (TRPM8) channels are well known as sensors for cold temperatures and cooling agents such as menthol and icilin and these channels are tightly regulated by the membrane lipid phosphoinositol-4,5-bisphosphate (PIP2). Since TRPM8 channels emerged as promising drug targets for treating pain, itching, obesity, cancer, dry eye disease, and inflammation, we aimed at developing a high-precision TRPM8 channel activator, to achieve spatiotemporal control of TRPM8 activity with light. In this study, we designed, synthesized and characterized the first photoswitchable TRPM8 activator azo-menthol (AzoM). AzoM enables optical control of endogenously and heterologously expressed TRPM8 channels with UV and blue light which is demonstrated by performing patch-clamp experiments. Moreover, AzoM facilitates the reliable determination of activation, inactivation, and deactivation kinetics thereby providing further insights into the channel gating. Using AzoM, the specific roles of individual amino acids for AzoM or PIP2 binding and for sensitization by PIP2 can be elucidated. Altogether, AzoM represents as a high-precision pharmaceutical tool for reversible control of TRPM8 channel function that enhances our biophysical understanding of TRPM8 channels and holds the potential to support the development of novel pharmaceuticals.

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.

Impact of sex and hypoxia on brain region-specific expression of membrane androgen receptor AR45 in rats

Background

Sex differences in oxidative stress-associated cognitive decline are influenced by sex hormone levels. Notably, oxidative stress-associated neuronal cell death can be exacerbated through testosterone signaling via membrane androgen receptor AR45, which is complexed with G protein Gαq within plasma membrane-associated lipid rafts. The objective of this study was to elucidate the impact of sex on the expression of AR45 and Gαq in brain regions associated with cognitive function, specifically hippocampus subregions and entorhinal cortex. Additionally, we investigated whether chronic intermittent hypoxia (CIH), an oxidative stressor with sex-specific effects, would modulate AR45 and Gαq expression in these brain regions.

Methods

Adult male and female Sprague-Dawley rats were exposed to CIH or normoxia (room air) during their sleep phase for 14 days. We quantified AR45 and Gαq protein expression in various cognition-associated brain regions [dorsal hippocampal CA1, CA3, dentate gyrus (DG), and entorhinal cortex (ETC)] via western blotting. For comparisons, AR45 and Gαq protein expression were also assessed in brain regions outside the hippocampal-ETC circuit [thalamus (TH) and striatum (STR)].

Results

The highest AR45 levels were expressed in the hippocampal CA1 and DG while the lowest expression was observed in the extrahippocampal STR. The highest Gαq levels were expressed in the hippocampal-associated ETC while the lowest expression was observed in the extrahippocampal TH. Females expressed higher levels of AR45 in the hippocampal DG compared to males, while no sex differences in Gαq expression were observed regardless of brain region assessed. Moreover, there was no effect of CIH on AR45 or Gαq expression in any of the brain regions examined. AR45 expression was positively correlated with Gαq expression in the CA1, DG, ETC, TH, and STR in a sex-dependent manner.

Conclusion

Our findings reveal enrichment of AR45 and Gαq protein expression within the hippocampal-ETC circuit, which is vulnerable to oxidative stress and neurodegeneration during cognitive decline. Nonetheless, CIH does not modulate the expression of AR45 or Gαq. Importantly, there are sex differences in AR45 expression and its association with Gαq expression in various brain regions, which may underlie sex-specific differences in cognitive and motor function-associated declines with aging.

Transient Receptor Potential Channels in Sensory Mechanisms of the Lower Urinary Tract

BACKGROUND

Urine storage and excretion require a network of interactions in the urinary tract and the central nervous system, which is mediated by a reservoir of water in the bladder and the outlet to the bladder neck, urethra, and external urethral sphincter. Through communicating and coordinating each other, micturition system eventually showed a switch-like activity pattern.

SUMMARY

At cervicothoracic and lumbosacral spine, the spinal reflex pathway of the lower urinary tract (LUT) received mechanosensory input from the urothelium to regulate the bladder contraction activity, thereby controlled urination voluntarily. Impairment of above-mentioned any level could result in lower urinary tract dysfunction, placed a huge burden on patients and society. Specific expression of purinergic receptors and transient receptor potential (TRP) channels are thought to play an important role in urinary excretion in the LUT.

KEY MESSAGES

This article reviewed the knowledge about the voiding reflex and described the role and function of TRP channels during voiding.

A randomized, double-blinded, vehicle-controlled clinical trial of topical cryosim-1, a synthetic TRPM8 agonist, in prurigo nodularis

BACKGROUND

Prurigo nodularis (PN) is an intensively pruritic skin disease that negatively influences quality of life. Cryosim-1 (Intrinsic IB Spot) is a synthetic, selective transient receptor potential melastatin 8 agonist.

AIMS

To investigate the efficacy and safety of cryosim-1 in PN patients.

PATIENTS/METHODS

A randomized, double-blinded, placebo-controlled clinical trial including 30 patients was conducted. The numerical rating scale (NRS) of pruritus was evaluated before and 2 h after cryosim-1 application at every visit.

RESULTS

At week 8, the mean pruritus NRS before serum application (4.7 ± 0.4 treatment, 6.1 ± 0.5 placebo; p = 0.045) and 2 h after serum application (2.8 ± 0.4 treatment, 4.3 ± 0.5 placebo; p = 0.031) were significantly lower in the treatment group, and the mean NRS for sleep disorder was significantly lower in the treatment group (2.2 ± 0.5 treatment, 4.2 ± 0.8 placebo; p = 0.031). The mean satisfaction scales for pruritus improvement were significantly higher in the treatment group (7.2 ± 0.6) than in the placebo group (4.0 ± 0.9; p = 0.005). There was no difference in TEWL between the two groups, and no adverse reactions were reported.

CONCLUSIONS

Cryosim-1 is a safe and effective topical treatment for PN patients.

Structure of human TRPM8 channel

TRPM8 is a non-selective cation channel permeable to both monovalent and divalent cations that is activated by multiple factors, such as temperature, voltage, pressure, and changes in osmolality. It is a therapeutic target for anticancer drug development, and its modulators can be utilized for several pathological conditions. Here, we present a cryo-electron microscopy structure of a human TRPM8 channel in the closed state that was solved at 2.7 Å resolution. Our structure comprises the most complete model of the N-terminal pre-melastatin homology region. We also visualized several lipids that are bound by the protein and modeled how the human channel interacts with icilin. Analyses of pore helices in available TRPM structures showed that all these structures can be grouped into different closed, desensitized and open state conformations based on the register of the pore helix S6 which positions particular amino acid residues at the channel constriction.

Interaction of Calmodulin with TRPM: An Initiator of Channel Modulation

Transient receptor potential melastatin (TRPM) channels, a subfamily of the TRP superfamily, constitute a diverse group of ion channels involved in mediating crucial cellular processes like calcium homeostasis. These channels exhibit complex regulation, and one of the key regulatory mechanisms involves their interaction with calmodulin (CaM), a cytosol ubiquitous calcium-binding protein. The association between TRPM channels and CaM relies on the presence of specific CaM-binding domains in the channel structure. Upon CaM binding, the channel undergoes direct and/or allosteric structural changes and triggers down- or up-stream signaling pathways. According to current knowledge, ion channel members TRPM2, TRPM3, TRPM4, and TRPM6 are directly modulated by CaM, resulting in their activation or inhibition. This review specifically focuses on the interplay between TRPM channels and CaM and summarizes the current known effects of CaM interactions and modulations on TRPM channels in cellular physiology.

Thermoregulation and thermal sensation during whole-body water immersion at different water temperatures in healthy individuals: A scoping review

BACKGROUND

Severe thermal discomfort may increase risk of drowning due to hypothermia or hyperthermia from prolonged exposure to noxious water temperatures. The importance of using a behavioral thermoregulation model with thermal sensation may predict the thermal load that the human body receives when exposed to various immersive water conditions. However, there is no thermal sensation "gold standard" model specific for water immersion. This scoping review aims to present a comprehensive overview regarding human physiological and behavioral thermoregulation during whole-body water immersion and explore the feasibility for an accepted defined sensation scale for cold and hot water immersion.

METHODS

A standard literary search was performed on PubMed, Google Scholar, and SCOPUS. The words "Water Immersion," "Thermoregulation," "Cardiovascular responses" were used either as independent searched terms and MeSH terms (Medical Subject Headings) or in combination with other text words. The inclusion criteria for clinical trials terms to thermoregulatory measurements (core or skin temperature), whole-body immersion, 18-60 years old and healthy individuals. The prementioned data were analyzed narratively to achieve the overall study objective.

RESULTS

Twenty-three published articles fulfilled the review inclusion/exclusion criteria (with nine measured behavioral responses). Our outcomes illustrated a homogenous thermal sensation in a variety of water temperatures ranges, that was strongly associated with thermal balance, and observed different thermoregulatory responses. This scoping review highlights the impact of water immersion duration on human thermoneutral zone, thermal comfort zone, and thermal sensation.

CONCLUSION

Our findings enlighten the significance of thermal sensation as a health indicator for establishing a behavioral thermal model applicable for water immersion. This scoping review provides insight for the needed development of subjective thermal model of thermal sensation in relation to human thermal physiology specific to immersive water temperature ranges within and outside the thermal neutral and comfort zone.

Age-dependent and modality-specific changes in the phenotypic markers Nav1.8, ASIC3, P2X3 and TRPM8 in male rat primary sensory neurons during healthy aging

The effects during healthy aging of the tetrodotoxin-resistant voltage-gated sodium channel 1.8 (Nav1.8), the acid-sensing ion channel-3 (ASIC3), the purinergic-receptor 2X3 (P2X3) and transient receptor potential of melastatin-8 (TRPM8) on responses to non-noxious stimuli are poorly understood. These effects will influence the transferability to geriatric subjects of findings obtained using young animals. To evaluate the involvement of these functional markers in mechanical and cold sensitivity to non-noxious stimuli and their underlying mechanisms, we used a combination of immunohistochemistry and quantitation of immunostaining in sub-populations of neurons of the dorsal root ganglia (DRG), behavioral tests, pharmacological interventions and Western-blot in healthy male Wistar rats from 3 to 24 months of age. We found significantly decreased sensitivity to mechanical and cold stimuli in geriatric rats. These behavioural alterations occurred simultaneously with differing changes in the expression of Nav1.8, ASIC3, P2X3 and TRPM8 in the DRG at different ages. Using pharmacological blockade in vivo we demonstrated the involvement of ASIC3 and P2X3 in normal mechanosensation and of Nav1.8 and ASIC3 in cold sensitivity. Geriatric rats also exhibited reductions in the number of A-like large neurons and in the proportion of peptidergic to non-peptidergic neurons. The changes in normal sensory physiology in geriatric rats we report here strongly support the inclusion of aged rodents as an important group in the design of pre-clinical studies evaluating pain treatments.

Progress in the Structural Basis of thermoTRP Channel Polymodal Gating

The thermosensory transient receptor potential (thermoTRP) family of ion channels is constituted by several nonselective cation channels that are activated by physical and chemical stimuli functioning as paradigmatic polymodal receptors. Gating of these ion channels is achieved through changes in temperature, osmolarity, voltage, pH, pressure, and by natural or synthetic chemical compounds that directly bind to these proteins to regulate their activity. Given that thermoTRP channels integrate diverse physical and chemical stimuli, a thorough understanding of the molecular mechanisms underlying polymodal gating has been pursued, including the interplay between stimuli and differences between family members. Despite its complexity, recent advances in cryo-electron microscopy techniques are facilitating this endeavor by providing high-resolution structures of these channels in different conformational states induced by ligand binding or temperature that, along with structure-function and molecular dynamics, are starting to shed light on the underlying allosteric gating mechanisms. Because dysfunctional thermoTRP channels play a pivotal role in human diseases such as chronic pain, unveiling the intricacies of allosteric channel gating should facilitate the development of novel drug-based resolving therapies for these disorders.

Association Between Experimental Pain Thresholds and Trajectories of Postoperative Recovery Measures After Benign Hysterectomy

Purpose

Quantitative sensory testing (QST) can be applied to quantify the sensitivity to different painful stimuli. This study aims to evaluate the association between preoperative pressure and thermal pain thresholds and trajectories of measurements of postoperative recovery (patient-reported daily maximum and average pain intensity, sum score of symptoms, and analgesic consumption) after benign hysterectomy.

Patients and Methods

A prospective, longitudinal single-blinded, observational multicenter study was conducted in five hospitals in the southeast of Sweden between 2011 and 2017. A total of 406 women scheduled for abdominal or vaginal hysterectomy for benign conditions were enrolled in the study. QST measuring pressure (PPT), heat (HPT), and cold pain thresholds (CPT) were performed preoperatively. The cut-off levels for dichotomizing the pain thresholds (low/high) were set at the 25-percentile for PPT and HPT and the 75-percentile for CPT. The Swedish Postoperative Symptom Questionnaire was used to measure postoperative pain and other symptoms of discomfort (symptom sum score) on 13 occasions for six weeks postoperatively. Daily analgesic consumption of opioids and non-opioids was registered.

Results

A CPT above the 75-percentile was associated with high postoperative maximum pain intensity (p = 0.04), high symptom sum score (p = 0.03) and greater consumption of non-opioids (p = 0.03). A HPT below the 25-percentile was only associated with greater consumption of non-opioids (p = 0.02). PPT was not associated with any of the outcome measures.

Conclusion

CPT seemed to be predictive for postoperative pain and symptoms of discomfort after benign hysterectomy. Preoperative QST may be used to individualize the management of postoperative recovery for low pain threshold individuals.

Distinct neural networks derived from galanin-containing nociceptors and neurotensin-expressing pruriceptors

Pain and itch are distinct sensations arousing evasion and compulsive desire for scratching, respectively. It's unclear whether they could invoke different neural networks in the brain. Here, we use the type 1 herpes simplex virus H129 strain to trace the neural networks derived from two types of dorsal root ganglia (DRG) neurons: one kind of polymodal nociceptors containing galanin (Gal) and one type of pruriceptors expressing neurotensin (Nts). The DRG microinjection and immunosuppression were performed in transgenic mice to achieve a successful tracing from specific types of DRG neurons to the primary sensory cortex. About one-third of nuclei in the brain were labeled. More than half of them were differentially labeled in two networks. For the ascending pathways, the spinothalamic tract was absent in the network derived from Nts-expressing pruriceptors, and the two networks shared the spinobulbar projections but occupied different subnuclei. As to the motor systems, more neurons in the primary motor cortex and red nucleus of the somatic motor system participated in the Gal-containing nociceptor-derived network, while more neurons in the nucleus of the solitary tract (NST) and the dorsal motor nucleus of vagus nerve (DMX) of the emotional motor system was found in the Nts-expressing pruriceptor-derived network. Functional validation of differentially labeled nuclei by c-Fos test and chemogenetic inhibition suggested the red nucleus in facilitating the response to noxious heat and the NST/DMX in regulating the histamine-induced scratching. Thus, we reveal the organization of neural networks in a DRG neuron type-dependent manner for processing pain and itch.

[Correlation between nasal mucosal temperature change and nasal airflow perception]

The mechanism of nasal airflow perception remains little known. It is currently believed that the main mechanism for perceiving nasal patency is to activate transient receptor potential melastatin subtype 8. Computer fluent dynamics show that increased airflow and heat flux are associated with higher subjective scores. Similarly, physical measurements of the nasal cavity using a temperature probe show a correlation between the lower nasal mucosa temperature and better results. Trigeminal function detection also indirectly confirms this. This literature review aimed to explore the role of nasal mucosal temperature change in the subjective perception of nasal patency and the secondary aim was to appraise the relevant evidence about the mechanism.

Ocular Surface Ion-Channels Are Closely Related to Dry Eye: Key Research Focus on Innovative Drugs for Dry Eye

Abundant ion-channels, including various perceptual receptors, chloride channels, purinergic receptor channels, and water channels that exist on the ocular surface, play an important role in the pathogenesis of dry eye. Channel-targeting activators or inhibitor compounds, which have shown positive effects in in vivo and in vitro experiments, have become the focus of the dry eye drug research and development, and individual compounds have been applied in clinical experimental treatment. This review summarized various types of ion-channels on the ocular surface related to dry eye, their basic functions, and spatial distribution, and discussed basic and clinical research results of various channel receptor regulatory compounds. Therefore, further elucidating the relationship between ion-channels and dry eye will warrant research of dry eye targeted drug therapy.

TaSCA, an Agile Survey on Chemosensory Impairments for Self-Monitoring of COVID-19 Patients: A Pilot Study

Background/Objective: During the COVID-19 pandemic, smell and taste disorders emerged as key non-respiratory symptoms. Due to widespread presence of the disease and to difficult objective testing of positive persons, the use of short surveys became mandatory. Most of the existing resources are focused on smell, very few on taste or trigeminal chemosensation called chemesthesis. However, it is possible that the three submodalities are affected differently by COVID-19.

Methods: We prepared a short survey (TaSCA) that can be administered at the telephone or through online resources to explore chemosensation. It is composed of 11 items on olfaction, taste, and chemesthesis, in order to discriminate the three modalities. We avoided abstract terms, and the use of semiquantitative scales because older patients may be less engaged. Statistical handling included descriptive statistics, Pearson's chi-squared test and cluster analysis.

Results: The survey was completed by 83 persons (60 females and 23 males), which reported diagnosis of COVID-19 by clinical (n = 7) or molecular (n = 18) means, the others being non-COVID subjects. Cluster analysis depicted the existence of two groups, one containing mostly asymptomatic and one mostly symptomatic subjects. All swab-positive persons fell within this second group. Only one item, related to trigeminal temperature perception, did not discriminate between the two groups.

Conclusions: These preliminary results indicate that TaSCA may be used to easily track chemosensory symptoms related to COVID-19 in an agile way, giving a picture of three different chemosensory modalities.