Thermally activated TRP channels: molecular sensors for temperature detection

Increasing Warmth in Oncological Patients: A Randomized Controlled Cross-Over Pilot Trial Examining the Efficacy of Mustard and Ginger Footbaths

OBJECTIVE

To analyze the thermogenic effects of footbaths with medicinal powders in oncological patients (ON) and healthy controls (HC).

INTERVENTION AND OUTCOMES

Thirty-six participants (23 ON, 13 HC; 24 females; 49.9 ± 13.3 years) received 3 footbaths in a random order with cross-over design: warm water only (WA), warm water plus mustard (MU, Sinapis nigra), and warm water plus ginger (GI, Zingiber officinale). Warmth perception of the feet (Herdecke Warmth Perception Questionnaire, HeWEF) at the follow-up (10 minutes after completion of footbaths, t2) was assessed as the primary outcome measure. Secondary outcome measures included overall warmth as well as self-reported warmth (HeWEF) and measured skin temperature (high resolution thermography) of the face, hands and feet at baseline (t0), post immersion (t1), and follow-up (t2).

RESULTS

With respect to the warmth perception of the feet, GI and MU differed significantly from WA (P's < .05) with the highest effect sizes at t1 (WA vs GI, d = 0.92, WA vs MU, d = 0.73). At t2, perceived warmth tended to be higher with GI compared to WA (d = 0.46). No differences were detected between ON and HC for self-reported warmth. With respect to skin temperatures, face and feet skin temperatures of ON were colder (at t0 and t1, 0.42 ≥ d ≥ 0.68) and tended to have diametrical response patterns than HC (ON vs HC: colder vs warmer after MU).

CONCLUSION

Among adult oncological patients and healthy controls, footbaths with mustard and ginger increased warmth perception of the feet longer than with warm water only. The potential impact of regularly administered thermogenic footbaths over extended periods merits further investigation for the recovery of cancer-related sense of cold.

Gated thermoelectric sensation by nanochannels grafted with thermally responsive polymers

We report that conical PET nanochannels grafted with thermally responsive polymers can mimic the thermosensation of protein channels in living organisms, showing an adjustable gated potential rather than current response to an ambient temperature stimulus, which is more consistent with real biochannels.

Taste the Pain: The Role of TRP Channels in Pain and Taste Perception

Transient receptor potential (TRP) channels are a superfamily of cation transmembrane proteins that are expressed in many tissues and respond to many sensory stimuli. TRP channels play a role in sensory signaling for taste, thermosensation, mechanosensation, and nociception. Activation of TRP channels (e.g., TRPM5) in taste receptors by food/chemicals (e.g., capsaicin) is essential in the acquisition of nutrients, which fuel metabolism, growth, and development. Pain signals from these nociceptors are essential for harm avoidance. Dysfunctional TRP channels have been associated with neuropathic pain, inflammation, and reduced ability to detect taste stimuli. Humans have long recognized the relationship between taste and pain. However, the mechanisms and relationship among these taste-pain sensorial experiences are not fully understood. This article provides a narrative review of literature examining the role of TRP channels on taste and pain perception. Genomic variability in the TRPV1 gene has been associated with alterations in various pain conditions. Moreover, polymorphisms of the TRPV1 gene have been associated with alterations in salty taste sensitivity and salt preference. Studies of genetic variations in TRP genes or modulation of TRP pathways may increase our understanding of the shared biological mediators of pain and taste, leading to therapeutic interventions to treat many diseases.

Photothermoelectric Response of Ti3C2Tx MXene Confined Ion Channels

With recent growing interest in biomimetic smart nanochannels, a biological sensory transduction in response to external stimuli has been of particular interest in the development of biomimetic nanofluidic systems. Here we demonstrate the MXene-based subnanometer ion channels that convert external temperature changes to electric signals via preferential diffusion of cations under a thermal gradient. In particular, coupled with a photothermal conversion feature of MXenes, an array of the nanoconfined Ti3C2Tx ion channels can capture trans-nanochannel diffusion potentials under a light-driven axial temperature gradient. The nonisothermal open-circuit potential across channels is enhanced with increasing cationic permselectivity of confined channels, associated with the ionic concentration or pH of permeant fluids. The photothermoelectric ionic response (evaluated from the ionic Seebeck coefficient) reached up to 1 mV·K-1, which is comparable to biological thermosensory channels, and demonstrated stability and reproducibility in the absence and presence of an ionic concentration gradient. With advantages of physicochemical tunability and easy fabrication process, the lamellar ion conductors may be an important nanofluidic thermosensation platform possibly for biomimetic sensory systems.

The caudal neurosecretory system: A novel thermosensitive tissue and its signal pathway in olive flounder (Paralichthys olivaceus)

Ectotherm animals, such as fish, are vulnerable when facing an extreme temperature fluctuation as a result of their inability to maintain body temperature. The caudal neurosecretory system (CNSS) is unique to fish and has been shown to maintain homeostasis in response to seasonal changes. However, its temperature sensitivity is unknown. Here, we used in vitro electrophysiological and anatomical approaches to investigate a thermosensory pathway in the CNSS. We showed that the CNSS responds directly to local hypothermal challenge via the TRP channel, and transmits this signal using the neurotransmitter, GABA, to the neurosecretory Dahlgren cells of the CNSS. These findings are the first demonstration of the thermal perception of the CNSS and add to our understanding of the physiological role of the CNSS in thermoregulation and seasonal adaptation.

TRPV4: A Physio and Pathophysiologically Significant Ion Channel

Transient Receptor Potential (TRP) channels are a family of ion channels whose members are distributed among all kinds of animals, from invertebrates to vertebrates. The importance of these molecules is exemplified by the variety of physiological roles they play. Perhaps, the most extensively studied member of this family is the TRPV1 ion channel; nonetheless, the activity of TRPV4 has been associated to several physio and pathophysiological processes, and its dysfunction can lead to severe consequences. Several lines of evidence derived from animal models and even clinical trials in humans highlight TRPV4 as a therapeutic target and as a protein that will receive even more attention in the near future, as will be reviewed here.

Disease-associated mutations in the human TRPM3 render the channel overactive via two distinct mechanisms

Transient Receptor Potential Melastatin 3 (TRPM3) is a Ca2+ permeable non-selective cation channel activated by heat and chemical agonists such as pregnenolone sulfate and CIM0216. TRPM3 mutations in humans were recently reported to be associated with intellectual disability and epilepsy; the functional effects of those mutations, however, were not reported. Here, we show that both disease-associated mutations in the human TRPM3 render the channel overactive, but likely via different mechanisms. The Val to Met substitution in the S4-S5 loop induced a larger increase in basal activity and agonist sensitivity at room temperature than the Pro to Gln substitution in the extracellular segment of S6. In contrast, heat activation was increased more by the S6 mutant than by the S4-S5 segment mutant. Both mutants were inhibited by the TRPM3 antagonist primidone, suggesting a potential therapeutic intervention to treat this disease.

Increasing Warmth in Adolescents with Anorexia Nervosa: A Randomized Controlled Crossover Trial Examining the Efficacy of Mustard and Ginger Footbaths

Objective

To analyze the thermogenic effects of footbaths with medicinal powders in adolescents with anorexia nervosa (AN) in comparison to healthy controls (HCs). Intervention and Outcomes. Forty-one female participants (21 AN, 20 HCs; 14.22 ± 1.54 years) received three footbaths-warm water and mustard (MU, Sinapis nigra), warm water and ginger (GI, Zingiber officinale), or warm water only (WA), in random order within a crossover design. Data were collected before (t1), immediately after foot immersion (maximum 20 minutes) (t2), and after 10 minutes subsequently (t3). Actual skin temperature (high resolution thermography) and perceived warmth (HeWEF questionnaire) were assessed at each time point for various body parts. The primary outcome measure was self-perceived warmth at the feet at t3. Secondary outcome measures were objective skin temperature and subjective warmth at the face, hands, and feet.

Results

Perceived warmth at the feet at t3 was significantly higher after GI compared to WA (mean difference -1.02) and MU (-1.07), with no differences between those with AN and HC (-0.29). For the secondary outcome measures, a craniocaudal temperature gradient for the skin temperature (thermography) was noted at t1 for patients with AN and HC (AN with colder feet). The craniocaudal gradient for subjective warmth was only seen for patients with AN.

Conclusion

Footbaths with ginger increased warmth perception at the feet longer than with mustard or warm water only for adolescents with AN as well as for HC. The impact of ginger footbaths on recovery of thermoregulatory disturbances in patients with AN repeated over extended periods merits further investigation.

Structural biology of thermoTRPV channels

Essential for physiology, transient receptor potential (TRP) channels constitute a large and diverse family of cation channels functioning as cellular sensors responding to a vast array of physical and chemical stimuli. Detailed understanding of the inner workings of TRP channels has been hampered by a lack of atomic structures, though structural biology of TRP channels has been an enthusiastic endeavor since their molecular identification two decades ago. These multi-domain integral membrane proteins, exhibiting complex polymodal gating behavior, have been a challenge for traditional X-ray crystallography, which requires formation of well-ordered protein crystals. X-ray structures remain limited to a few TRP channel proteins to date. Fortunately, recent breakthroughs in single-particle cryo-electron microscopy (cryo-EM) have enabled rapid growth of the number of TRP channel structures, providing tremendous insights into channel gating and regulation mechanisms and serving as foundations for further mechanistic investigations. This brief review focuses on recent exciting developments in structural biology of a subset of TRP channels, the calcium-permeable, non-selective and thermosensitive vanilloid subfamily of TRP channels (TRPV1-4), and the permeation and gating mechanisms revealed by structures.

Voltage vs. Ligand I: Structural basis of the intrinsic flexibility of S3 segment and its significance in ion channel activation

We systematically predict the internal flexibility of the S3 segment, one of the most mobile elements in the voltage-sensor domain. By analyzing the primary amino acid sequences of V-sensor containing proteins, including Hv1, TPC channels and the voltage-sensing phosphatases, we established correlations between the local flexibility and modes of activation for different members of the VGIC superfamily. Taking advantage of the structural information available, we also assessed structural aspects to understand the role played by the flexibility of S3 during the gating of the pore. We found that S3 flexibility is mainly determined by two specific regions: (1) a short NxxD motif in the N-half portion of the helix (S3a), and (2) a short sequence at the beginning of the so-called paddle motif where the segment has a kink that, in some cases, divide S3 into two distinct helices (S3a and S3b). A good correlation between the flexibility of S3 and the reported sensitivity to temperature and mechanical stretch was found. Thus, if the channel exhibits high sensitivity to heat or membrane stretch, local S3 flexibility is low. On the other hand, high flexibility of S3 is preferentially associated to channels showing poor heat and mechanical sensitivities. In contrast, we did not find any apparent correlation between S3 flexibility and voltage or ligand dependence. Overall, our results provide valuable insights into the dynamics of channel-gating and its modulation.

A Cold-Sensing Receptor Encoded by a Glutamate Receptor Gene

In search of the molecular identities of cold-sensing receptors, we carried out an unbiased genetic screen for cold-sensing mutants in C. elegans and isolated a mutant allele of glr-3 gene that encodes a kainate-type glutamate receptor. While glutamate receptors are best known to transmit chemical synaptic signals in the CNS, we show that GLR-3 senses cold in the peripheral sensory neuron ASER to trigger cold-avoidance behavior. GLR-3 transmits cold signals via G protein signaling independently of its glutamate-gated channel function, suggesting GLR-3 as a metabotropic cold receptor. The vertebrate GLR-3 homolog GluK2 from zebrafish, mouse, and human can all function as a cold receptor in heterologous systems. Mouse DRG sensory neurons express GluK2, and GluK2 knockdown in these neurons suppresses their sensitivity to cold but not cool temperatures. Our study identifies an evolutionarily conserved cold receptor, revealing that a central chemical receptor unexpectedly functions as a thermal receptor in the periphery.

What is new about mild temperature sensing? A review of recent findings

The superfamily of Transient Receptor Potential (TRP) channels is composed by a group of calcium-permeable ionic channels with a generally shared topology. The thermoTRP channels are a subgroup of 11 members, found in the TRPA, TRPV, TRPC, and TRPM subfamilies. Historically, members of this subgroup have been classified as cold, warm or hot-specific temperature sensors. Recently, new experimental results have shown that the role that has been given to the thermoTRPs in thermosensation is not necessarily strict. In addition, it has been shown that these channels activate over temperature ranges, which can have variations depending on the species and the interaction with a specific biological context. Investigation of these interactions could help to elucidate the mechanisms of activation by temperature, which remains uncertain. Abbreviations: Cryo-EM: Cryogenic electron microscopy; DRG: Dorsal root ganglia; H: Human; ROS: Reactive Oxygen Species; TG: Trigeminal ganglia; TRP: Transient Receptor Potential; TRPA: TRP ankyrin; TRPV: TRP vanilloid; TRPC: TRP canonical; TRPM: TRP melastatin.

Effects of Footbaths with Mustard, Ginger, or Warm Water Only on Objective and Subjective Warmth Distribution in Healthy Subjects: A Randomized Controlled Trial

OBJECTIVE

To analyze the short-term thermogenic effects of footbaths with warm water alone (WA) versus when combined with medicinal powders.

DESIGN

Randomized controlled trial with cross-over.

INTERVENTIONS AND OUTCOMES

Seventeen healthy volunteers (mean age 22.1 years, SD = 2.4; 11 female) received three footbaths with WA or WA combined with mustard (MU) or ginger (GI) in a randomized order. Self-perceived warmth (Herdecke warmth perception questionnaire) and actual skin temperatures (thermography) were assessed before (t0), immediately after footbaths (t1), and 10 minutes later (t2). The primary outcome was perceived warmth in the feet. Secondary outcomes were warmth perception in the face, hands and overall, as well as actual skin temperature in the feet, face, and hands.

RESULTS

Perceived warmth at the feet (primary outcome) increased significantly (all p's < .001) for MU and GI at t1 as well as for GI at t2 when compared to t0 with high effect sizes. At t2, GI differed significantly from WA (p < .001) and MU (p = .048). With regards to the secondary measures of outcome, no significant effects were seen for perceived warmth at the face or hands. Overall warmth was significantly higher at t1 compared to t0 (p = .01). Thermography assessments of skin temperature at the feet at t1 increased after all conditions (p < .001). No effects were seen in the face. At the hands, temperature decreased at t1 (p = .02) and t2 compared to t0 (p < .001).

CONCLUSION

The present study provides preliminary evidence that mustard and ginger increase warmth perception at the feet more than warm water alone, with only the effects for GI enduring at the brief follow-up.

Structural Basis of TRPV4 N Terminus Interaction with Syndapin/PACSIN1-3 and PIP2

Transient receptor potential (TRP) channels are polymodally regulated ion channels. TRPV4 (vanilloid 4) is sensitized by PIP₂ and desensitized by Syndapin3/PACSIN3, which bind to the structurally uncharacterized TRPV4 N terminus. We determined the nuclear magnetic resonance structure of the Syndapin3/PACSIN3 SH3 domain in complex with the TRPV4 N-terminal proline-rich region (PRR), which binds as a class I polyproline II (PPII) helix. This PPII conformation is broken by a conserved proline in a cis conformation. Beyond the PPII, we find that the proximal TRPV4 N terminus is unstructured, a feature conserved across species thus explaining the difficulties in resolving it in previous structural studies. Syndapin/PACSIN SH3 domain binding leads to rigidification of both the PRR and the adjacent PIP₂ binding site. We determined the affinities of the TRPV4 N terminus for PACSIN1, 2, and 3 SH3 domains and PIP₂ and deduce a hierarchical interaction network where Syndapin/PACSIN binding influences the PIP₂ binding site but not vice versa.

Irreversible temperature gating in trpv1 sheds light on channel activation

Temperature-activated TRP channels or thermoTRPs are among the only proteins that can directly convert temperature changes into changes in channel open probability. In spite of a wealth of functional and structural information, the mechanism of temperature activation remains unknown. We have carefully characterized the repeated activation of TRPV1 by thermal stimuli and discovered a previously unknown inactivation process, which is irreversible. We propose that this form of gating in TRPV1 channels is a consequence of the heat absorption process that leads to channel opening.