Molecular basis for heat desensitization of TRPV1 ion channels

Chikungunya Particle and RNA Induce Mechanical and Heat Hypersensitivities in a TRPV1-Dependent Manner

Chikungunya virus (CHIKV), the causative agent of the chikungunya fever, is an alphavirus widely transmitted by the bite of the female mosquito of the genus Aedes sp., especially in tropical and subtropical regions. Brazil is the country most affected by the microorganism. CHIKV classically induces articular pain, which can become long lasting for even years in a great number of the infected individuals, reducing their quality of life. The mechanisms of CHIKV-induced pain are poorly understood, but recent evidence indicated a role for the transient receptor potential vanilloid 1 (TRPV1) in this pathology. Herein, we assessed the ability of intra-articularly injected inactivated CHIKV or its RNA to trigger nociception in mice. Both stimuli induced bilateral secondary hyperalgesia to mechanical and heat stimuli. These responses were attenuated by TRPV1 ablation or antagonism. Joint structural alterations and increased cartilage TRPV1 protein expression were detected in the ipsilateral knee joints injected with either CHIKV or viral RNA. However, the lack of this receptor did not influence the histological changes triggered by CHIKV or RNA. The results further support the role of TRPV1 in CHIKV-induced pain and highlight its importance in the chronic phase of the disease.

Genetic Code Expansion: Recent Developments and Emerging Applications

The concept of genetic code expansion (GCE) has revolutionized the field of chemical and synthetic biology, enabling the site-specific incorporation of noncanonical amino acids (ncAAs) into proteins, thus opening new avenues in research and applications across biology and medicine. In this review, we cover the principles of GCE, including the optimization of the aminoacyl-tRNA synthetase (aaRS)/tRNA system and the advancements in translation system engineering. Notable developments include the refinement of aaRS/tRNA pairs, enhancements in screening methods, and the biosynthesis of noncanonical amino acids. The applications of GCE technology span from synthetic biology, where it facilitates gene expression regulation and protein engineering, to medicine, with promising approaches in drug development, vaccine production, and gene editing. The review concludes with a perspective on the future of GCE, underscoring its potential to further expand the toolkit of biology and medicine. Through this comprehensive review, we aim to provide a detailed overview of the current state of GCE technology, its challenges, opportunities, and the frontier it represents in the expansion of the genetic code for novel biological research and therapeutic applications.

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.

Dual Role of TRPV1 Channels in Cerebral Stroke: An Exploration from a Mechanistic and Therapeutic Perspective

Transient receptor potential vanilloid subfamily member 1 (TRPV1) has been strongly implicated in the pathophysiology of cerebral stroke. However, the exact role and mechanism remain elusive. TPRV1 channels are exclusively present in the neurovascular system and involve many neuronal processes. Numerous experimental investigations have demonstrated that TRPV1 channel blockers or the lack of TRPV1 channels may prevent harmful inflammatory responses during ischemia-reperfusion injury, hence conferring neuroprotection. However, TRPV1 agonists such as capsaicin and some other non-specific TRPV1 activators may induce transient/slight degree of TRPV1 channel activation to confer neuroprotection through a variety of mechanisms, including hypothermia induction, improving vascular functions, inducing autophagy, preventing neuronal death, improving memory deficits, and inhibiting inflammation. Another factor in capsaicin-mediated neuroprotection could be the desensitization of TRPV1 channels. Based on the summarized evidence, it may be plausible to suggest that TPRV1 channels have a dual role in ischemia-reperfusion-induced cerebral injury, and thus, both agonists and antagonists may produce neuroprotection depending upon the dose and duration. The current review summarizes the dual function of TRPV1 in ischemia-reperfusion-induced cerebral injury models, explains its mechanism, and predicts the future.

Tubulin interaction at tubulin-binding sequence 1 (TBS1) is required for proper surface expression and TRPV1 channel activity

TRPV1, a polymodal and nonselective cation channel has unique gating mechanisms which is regulated by supramolecular complexes at the plasma membrane formed with membrane proteins, lipids and kinase pathways. Crosstalk between microtubule cytoskeleton with TRPV1 at various level has been established. Previously we demonstrated that the positively-charged residues present at specific tubulin-binding stretch sequences (i.e. TBS1 and TBS2, AA 710-730 and 770-797 respectively) located at the C-terminus of TRPV1 are crucial for tubulin interaction and such sequences have evolutionary origin. The nature of TRPV1-tubulin complex and its functional importance remain poorly understood. Here, we made several mutations in the TBS1 and TBS2 regions and characterized such mutants. Though these mutations reduce tubulin interaction drastically, a low and basal-level of tubulin interaction remains with these mutants. Substitution of positively-charged residues (Lys and Arg) to Ala in the TBS1, but not in TBS2 region results in reduced ligand-sensitivity. Such ligand-sensitivity is altered in response to Taxol or Nocodazole. We suggest that tubulin interaction at the TBS1 region favours channel opening while interaction in TBS2 favours channel closure. We demonstrate for the first time the functional significance of TRPV1-tubulin complex and endorse microtubule dynamics as a parameter that can alter TRPV1 channel functions. These findings can be relevant for several physiological functions and also in the context of chemotherapy-induced neuropathic pain caused by various microtubule stabilizing chemotherapeutic drugs. Thus, this characterization may indicate TRPV1 as a potential therapeutic target relevant for chemotherapeutic drug-induced peripheral neuropathies, neurodegeneration and other 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 (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.

Capsaicin-insensitivity of TRPV1-R575D mutant located at the lipid-water-interface region can be rescued by either extracellular Ca2+-chelation or cholesterol reduction

TRPV1 acts as a unique polymodal ion channel having distinct structure and gating properties. In this context, TRPV1-R575D represents a special mutant located at the inner lipid-water-interface (LWI) region that has less possibility of interaction with membrane cholesterol. In control conditions, this lab-generated mutant of TRPV1 shows no "ligand-sensitivity", reduced surface expression, reduced localization in the lipid rafts, yet induces high cellular lethality. Notably, the cellular lethality induced by TRPV1-R575D expression can be rescued by adding 5'I-RTX (a specific inhibitor of TRPV1) or by introducing another mutation in the next position, i.e. in TRPV1-R575D/D576R. In this work we characterized TRPV1-R575D and TRPV1-R575D/D576R mutants in different cellular conditions and compared with the TRPV1-WT. We report that the "ligand-insensitivity" of TRPV1-R575D can be rescued in certain conditions, such as by chelation of extracellular Ca2+, or by reduction of the membrane cholesterol. Here we show that Ca2+ plays an important role in the channel gating of TRPV1-WT as well as LWI mutants (TRPV1-R575D, TRPV1-R575D/D576R). However, chelation of intracellular Ca2+ or depletion of ER Ca2+ did not have a significant effect on the TRPV1-R575D. Certain properties related to channel gating of mutant TRPV1-R575D/D576R can be rescued partially or fully in a context -dependent manner. Cholesterol depletion also alters these properties. Our data suggests that lower intracellular basal Ca2+ acts as a pre-requisite for further opening of TRPV1-R575D. These findings enable better understanding of the structure-function relationship of TRPV1 and may be critical in comprehending the channelopathies induced by other homologous thermosensitive TRPVs.

Tetherless Optical Neuromodulation: Wavelength from Orange-red to Mid-infrared

Optogenetics, a technique that employs light for neuromodulation, has revolutionized the study of neural mechanisms and the treatment of neurological disorders due to its high spatiotemporal resolution and cell-type specificity. However, visible light, particularly blue and green light, commonly used in conventional optogenetics, has limited penetration in biological tissue. This limitation necessitates the implantation of optical fibers for light delivery, especially in deep brain regions, leading to tissue damage and experimental constraints. To overcome these challenges, the use of orange-red and infrared light with greater tissue penetration has emerged as a promising approach for tetherless optical neuromodulation. In this review, we provide an overview of the development and applications of tetherless optical neuromodulation methods with long wavelengths. We first discuss the exploration of orange-red wavelength-responsive rhodopsins and their performance in tetherless optical neuromodulation. Then, we summarize two novel tetherless neuromodulation methods using near-infrared light: upconversion nanoparticle-mediated optogenetics and photothermal neuromodulation. In addition, we discuss recent advances in mid-infrared optical neuromodulation.

Functional nanotransducer-mediated wireless neural modulation techniques

Functional nanomaterials have emerged as versatile nanotransducers for wireless neural modulation because of their minimal invasion and high spatiotemporal resolution. The nanotransducers can convert external excitation sources (e.g. NIR light, x-rays, and magnetic fields) to visible light (or local heat) to activate optogenetic opsins and thermosensitive ion channels for neuromodulation. The present review provides insights into the fundamentals of the mostly used functional nanomaterials in wireless neuromodulation including upconversion nanoparticles, nanoscintillators, and magnetic nanoparticles. We further discussed the recent developments in design strategies of functional nanomaterials with enhanced energy conversion performance that have greatly expanded the field of neuromodulation. We summarized the applications of functional nanomaterials-mediated wireless neuromodulation techniques, including exciting/silencing neurons, modulating brain activity, controlling motor behaviors, and regulating peripheral organ function in mice. Finally, we discussed some key considerations in functional nanotransducer-mediated wireless neuromodulation along with the current challenges and future directions.

Genetic code expansion, an emerging tool in the Ca2+ ion channel field

Various methods for characterizing binding forces as well as for monitoring and remote control of ion channels are still emerging. A recent innovation is the direct incorporation of unnatural amino acids (UAAs) with corresponding biophysical or biochemical properties, which are integrated using genetic code expansion technology. Minimal changes to natural amino acids, which are achieved by chemical synthesis of corresponding UAAs, are valuable tools to provide insight into the contributions of physicochemical properties of side chains in binding events. To gain unique control over the conformational changes or function of ion channels, a series of light-sensitive, chemically reactive and posttranslationally modified UAAs have been developed and utilized. Here, we present the existing UAA tools, their mode of action, their potential and limitations as well as their previous applications to Ca2+-permeable ion channels.

Nano-optogenetics for Disease Therapies

Optogenetic, known as the method of 21 centuries, combines optic and genetic engineering to precisely control photosensitive proteins for manipulation of a broad range of cellular functions, such as flux of ions, protein oligomerization and dissociation, cellular intercommunication, and so on. In this technique, light is conventionally delivered to targeted cells through optical fibers or micro light-emitting diodes, always suffering from high invasiveness, wide-field illumination facula, strong absorption, and scattering by nontargeted endogenous substance. Light-transducing nanomaterials with advantages of high spatiotemporal resolution, abundant wireless-excitation manners, and easy functionalization for recognition of specific cells, recently have been widely explored in the field of optogenetics; however, there remain a few challenges to restrain its clinical applications. This review summarized recent progress on light-responsive genetically encoded proteins and the myriad of activation strategies by use of light-transducing nanomaterials and their disease-treatment applications, which is expected for sparking helpful thought to push forward its preclinical and translational uses.

Thermo-ring basis for heat unfolding-induced inactivation in TRPV1

Transient receptor potential vanilloid-1 (TRPV1) is a capsaicin receptor and employs the use-dependent desensitization to protect mammals from noxious heat damage in response to repeated or constant heat stimuli. However, the underlying structural factor or motif has not been resolved precisely. In this computational study, the graph theory-based grid thermodynamic model was used to reveal how the temperature-dependent noncovalent interactions as identified in the 3D structures of rat TRPV1 could develop a well-organized fluidic grid-like mesh network, featuring various topological grids constrained as the thermo-rings that range in size from the biggest to the smallest to govern distinct structural and functional traits of the channel in response to varying temperature degrees. Following the findings that the heat unfolding of three specific biggest grids, one in the closed state and two in the open state, was respectively responsible for the reversible activation at 43 °C and thermal inactivation from 56 °C to 61 °C, a random smaller grid was further identified for the irreversible inactivation and the relevant use-dependent desensitization from the pre-open closed state between 43 °C and 61 °C. Thus, these two distinct inactivation pathways of TRPV1 may be involved in protecting mammals against noxious heat damages.

A journey from molecule to physiology and in silico tools for drug discovery targeting the transient receptor potential vanilloid type 1 (TRPV1) channel

The heat and capsaicin receptor TRPV1 channel is widely expressed in nerve terminals of dorsal root ganglia (DRGs) and trigeminal ganglia innervating the body and face, respectively, as well as in other tissues and organs including central nervous system. The TRPV1 channel is a versatile receptor that detects harmful heat, pain, and various internal and external ligands. Hence, it operates as a polymodal sensory channel. Many pathological conditions including neuroinflammation, cancer, psychiatric disorders, and pathological pain, are linked to the abnormal functioning of the TRPV1 in peripheral tissues. Intense biomedical research is underway to discover compounds that can modulate the channel and provide pain relief. The molecular mechanisms underlying temperature sensing remain largely unknown, although they are closely linked to pain transduction. Prolonged exposure to capsaicin generates analgesia, hence numerous capsaicin analogs have been developed to discover efficient analgesics for pain relief. The emergence of in silico tools offered significant techniques for molecular modeling and machine learning algorithms to indentify druggable sites in the channel and for repositioning of current drugs aimed at TRPV1. Here we recapitulate the physiological and pathophysiological functions of the TRPV1 channel, including structural models obtained through cryo-EM, pharmacological compounds tested on TRPV1, and the in silico tools for drug discovery and repositioning.

The role of TRPV ion channels in adipocyte differentiation: What is the evidence?

Obesity is a complex disorder, and the incidence of obesity continues to rise at an alarming rate worldwide. In particular, the growing incidence of overweight and obesity in children is a major health concern. However, the underlying mechanisms of obesity remain unclear and the efficacy of several approaches for weight loss is limited. As an important calcium-permeable temperature-sensitive cation channel, transient receptor potential vanilloid (TRPV) ion channels directly participate in thermo-, mechano-, and chemosensory responses. Modulation of TRPV ion channel activity can alter the physiological function of the ion channel, leading to neurodegenerative diseases, chronic pain, cancer, and skin disorders. In recent years, increasing studies have demonstrated that TRPV ion channels are abundantly expressed in metabolic organs, including the liver, adipose tissue, skeletal muscle, pancreas, and central nervous system, which has been implicated in various metabolic diseases, including obesity and diabetes mellitus. In addition, as an important process for the pathophysiology of adipocyte metabolism, adipocyte differentiation plays a critical role in obesity. In this review, we focus on the role of TRPV ion channels in adipocyte differentiation to broaden the ideas for prevention and control strategies for obesity.

Temperature-Dependent Activation of Thermosensitive Transient Receptor Potential Channels

Temperature detection is essential for the survival and perpetuation of any species. Thermoreceptors in the skin sense the body temperature and also the temperatures of the ambient air and the objects. In 1997, Dr. David Julius and his colleagues found that a receptor expressed in small-diameter primary sensory neurons was activated by capsaicin (the pungent chemical in hot pepper). This receptor was also activated by temperature above 42 °C. That was the first time that a thermal receptor in primary sensory neurons has been identified. This receptor is named transient receptor potential vanilloid 1 (TRPV1). Now, 11 thermosensitive TRP channels are known. In this chapter, we summarize the reports and analyze thermosensitive TRP channels in a variety of ways to clarify the activation mechanisms by which temperature changes are sensed.

Thermoring basis for the TRPV3 bio-thermometer

The thermosensitive transient receptor potential (TRP) channels are well-known as bio-thermometers with specific temperature thresholds and sensitivity. However, their precise structural origins are still mysterious. Here, graph theory was used to test how the temperature-dependent non-covalent interactions as identified in the 3D structures of thermo-gated TRPV3 could form a systematic fluidic grid-like mesh network with the constrained thermo-rings from the biggest grids to the smallest ones as necessary structural motifs for the variable temperature thresholds and sensitivity. The results showed that the heat-evoked melting of the biggest grids may control the specific temperature thresholds to initiate channel gating while the smaller grids may be required to secure heat efficacy. Together, all the grids along the lipid-dependent minimal gating pathway may be necessary to change with molar heat capacity for the specific temperature sensitivity. Therefore, this graph theory-based grid thermodynamic model may provide an extensive structural basis for the thermo-gated TRP channels.

Implications of a temperature-dependent heat capacity for temperature-gated ion channels

Temperature influences dynamics and state-equilibrium distributions in all molecular processes, and only a relatively narrow range of temperatures is compatible with life-organisms must avoid temperature extremes that can cause physical damage or metabolic disruption. Animals evolved a set of sensory ion channels, many of them in the family of transient receptor potential cation channels that detect biologically relevant changes in temperature with remarkable sensitivity. Depending on the specific ion channel, heating or cooling elicits conformational changes in the channel to enable the flow of cations into sensory neurons, giving rise to electrical signaling and sensory perception. The molecular mechanisms responsible for the heightened temperature-sensitivity in these ion channels, as well as the molecular adaptations that make each channel specifically heat- or cold-activated, are largely unknown. It has been hypothesized that a heat capacity difference (ΔCp) between two conformational states of these biological thermosensors can drive their temperature-sensitivity, but no experimental measurements of ΔCp have been achieved for these channel proteins. Contrary to the general assumption that the ΔCp is constant, measurements from soluble proteins indicate that the ΔCp is likely to be a function of temperature. By investigating the theoretical consequences for a linearly temperature-dependent ΔCp on the open-closed equilibrium of an ion channel, we uncover a range of possible channel behaviors that are consistent with experimental measurements of channel activity and that extend beyond what had been generally assumed to be possible for a simple two-state model, challenging long-held assumptions about ion channel gating models at equilibrium.

Analgesic effects of main indole alkaloid of kratom, mitragynine in acute pain animal model

Mitragynine exerts its analgesic effect mainly via opioid receptors activation. Additionally, the effect may be mediated via mitragynine's anti-inflammatory property and non-opioid receptor pain pathways, namely through the TRPV1 receptor. No studies identify hitherto, hence, the current study aimed to investigate the mitragynine's analgesic effect via the anti-inflammatory property, non-opioid receptor (TRPV1) and the effective dose (ED) to alleviate pain. Male and female Sprague Dawley rats were pre-treated intraperitoneally with either mitragynine (1, 5, 10, 13, 15 or 30 mg/kg), vehicle, or indomethacin (1 mg/kg) 30 min before inducing inflammatory pain using acetic acid. The writhes and pain-related withdrawal behaviour occurrence were counted within a 1-h duration. Percentage of writhes inhibition, pain-related withdrawal behaviour aggregate, ED50 and ED95 were determined. The body temperature was recorded and TRPV1 expression in the rats' brains was measured. Mitragynine (except 1 mg/kg) significantly reduced the number of writhes compared with the vehicle administered group. Mitragynine (30 mg/kg) demonstrated 99.5% inhibition of writhing behaviour and low withdrawal behaviour score compared with vehicle and indomethacin and successfully blocked the hypothermia induced by acetic acid. The overall ED50 and ED95 values of mitragynine were 3.62 and 20.84 mg/kg, respectively. The percentage of writhing inhibition and withdrawal behaviour were similar in both genders. Mitragynine (15 and 30 mg/kg) significantly reduced the TRPV1 expression in the brain of the rats. Mitragynine alleviated pain-like behaviour and showed analgesic effects via anti-inflammatory and non-opioid receptor pathways. The findings also suggest that mitragynine might regulate some physiological functions of the rat.

Molecular Physiology of TRPV Channels: Controversies and Future Challenges

The ability to detect stimuli from the environment plays a pivotal role in our survival. The molecules that allow the detection of such signals include ion channels, which are proteins expressed in different cells and organs. Among these ion channels, the transient receptor potential (TRP) family responds to the presence of diverse chemicals, temperature, and osmotic changes, among others. This family of ion channels includes the TRPV or vanilloid subfamily whose members serve several physiological functions. Although these proteins have been studied intensively for the last two decades, owing to their structural and functional complexities, a number of controversies regarding their function still remain. Here, we discuss some salient features of their regulation in light of these controversies and outline some of the efforts pushing the field forward.

Efficiency of cutaneous heat diffusion after local hyperthermia for the treatment of itch

BACKGROUND

Today, itching is understood as an independent sensory perception, which is based on a complex etiology of a disturbed neuronal activity and leads to clinical symptoms. The primary afferents (pruriceptors) have functional overlaps with afferents of thermoregulation (thermoceptors). Thus, an antipruritic effect can be caused by antagonizing heat-sensitive receptors of the skin. The ion channel TRP-subfamily V member 1 (TRPV1) is of particular importance in this context. Repeated heat application can induce irreversible inactivation by unfolding of the protein, causing a persistent functional deficit and thus clinically and therapeutically reducing itch sensation.

MATERIAL AND METHODS

To demonstrate relevant heat diffusion after local application of heat (45°C to 52°C for 3 and 5 seconds) by a technical medical device, the temperature profile for the relevant skin layer was recorded synchronously on ex vivo human skin using an infrared microscope.

RESULTS

The results showed that the necessary activation temperature for TRPV1 of (≥43°C) in the upper relevant skin layers was safely reached after 3 and 5 seconds of application time. There were no indications of undesirable thermal effects.

CONCLUSION

The test results show that the objectified performance of the investigated medical device can be expected to provide the necessary temperature input for the activation of heat-sensitive receptors in the skin. Clinical studies are necessary to prove therapeutic efficacy in the indication pruritus.

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.

Rapid Regulation of Local Temperature and Transient Receptor Potential Vanilloid 1 Ion Channels with Wide-Field Plasmonic Thermal Microscopy

Plasmonic absorption of light can create significant local heat and has become a promising tool for rapid temperature regulation in diverse fields, from biomedical technology to optoelectronics. Current plasmonic heating usually relies on specially designed nanomaterials randomly distributed in the space and barely provides uniform temperature regulation in a wide field. Herein, we report a rapid temperature regulation strategy on a plain gold-coated glass slip using a plasmonic scattering microscopy, which can be referred to as wide-field plasmonic thermal microscopy (W-PTM). We calibrated the W-PTM by monitoring the phase transition of the temperature-sensitive polymer solutions, showing that it can provide a temperature regulation range of 33-80 °C. Moreover, the W-PTM provides imaging capability, thus allowing the statistical analysis of the phase-transitioned polymeric nanoparticles. Finally, we demonstrated that W-PTM can be used for noninvasive and local regulation of the transient receptor potential vanilloid 1 (TRPV1) ion channels in the living cells, which can be monitored by simultaneous fluorescence imaging of the calcium influx. With the nondestructive local temperature-regulating and concurrent fluorescence imaging capability, we anticipate that W-PTM can be a powerful tool to study cellular activities associated with cellular membrane temperature changes.

Supplementation with artificial sweetener and capsaicin alters metabolic flexibility and performance in heat-stressed and feed-restricted pigs

Substantial economic losses in animal agriculture result from animals experiencing heat stress (HS). Pigs are especially susceptible to HS, resulting in reductions in growth, altered body composition, and compromised substrate metabolism. In this study, an artificial high-intensity sweetener and capsaicin (CAPS-SUC; Pancosma, Switzerland) were supplemented in combination to mitigate the adverse effects of HS on pig performance. Forty cross-bred barrows (16.2 ± 6 kg) were assigned to one of five treatments: thermal neutral controls (TN) (22 ± 1.2 °C; 38%-73% relative humidity) with ad libitum feed, HS conditions with ad libitum feed with (HS+) or without (HS-) supplementation, and pair-fed to HS with (PF+) or without supplementation (PF-). Pigs in heat-stressed treatments were exposed to a cyclical environmental temperature of 12 h at 35 ± 1.2 °C with 27%-45% relative humidity and 12 h at 30 ± 1.1 °C with 24%-35% relative humidity for 21 d. Supplementation (0.1 g/kg feed) began 7 d before and persisted through the duration of environmental or dietary treatments (HS/PF), which lasted for 21 d. Rectal temperatures and respiration rates (RR; breaths/minute) were recorded thrice daily, and feed intake (FI) was recorded daily. Before the start and at the termination of environmental treatments (HS/PF), a muscle biopsy of the longissimus dorsi was taken for metabolic analyses. Blood samples were collected weekly, and animals were weighed every 3 d during treatment. Core temperature (TN 39.2 ± 0.02 °C, HS- 39.6 ± 0.02 °C, and HS+ 39.6 ± 0.02 °C, P < 0.001) and RR (P < 0.001) were increased in both HS- and HS+ groups, but no difference was detected between HS- and HS+. PF- pigs exhibited reduced core temperature (39.1 ± 0.02 °C, P < 0.001), which was restored in PF+ pigs (39.3 ± 0.02 °C) to match TN. Weight gain and feed efficiency were reduced in PF- pigs (P < 0.05) but not in the PF+ or the HS- or HS+ groups. Metabolic flexibility was decreased in the HS- group (-48.4%, P < 0.05) but maintained in the HS+ group. CAPS-SUC did not influence core temperature or weight gain in HS pigs but did restore core temperature, weight gain, and feed efficiency in supplemented PF pigs. In addition, supplementation restored metabolic flexibility during HS and improved weight gain and feed efficiency during PF, highlighting CAPS-SUC's therapeutic metabolic effects.

Bioactive Peptides and Proteins from Centipede Venoms

Venoms are a complex cocktail of biologically active molecules, including peptides, proteins, polyamide, and enzymes widely produced by venomous organisms. Through long-term evolution, venomous animals have evolved highly specific and diversified peptides and proteins targeting key physiological elements, including the nervous, blood, and muscular systems. Centipedes are typical venomous arthropods that rely on their toxins primarily for predation and defense. Although centipede bites are frequently reported, the composition and effect of centipede venoms are far from known. With the development of molecular biology and structural biology, the research on centipede venoms, especially peptides and proteins, has been deepened. Therefore, we summarize partial progress on the exploration of the bioactive peptides and proteins in centipede venoms and their potential value in pharmacological research and new drug development.

The acquisition of cold sensitivity during TRPM8 ion channel evolution

SignificanceAdaptation to more severe ambient temperature fluctuations can be considered one of the key innovations of terrestrial tetrapods. Our study shows the formation of the functional MHR1-3 domain in transient receptor potential melastatin 8 (TRPM8) bestowed the channel with cold sensitivity during the water-to-land transition. The evolved MHR1-3 domain found in terrestrial tetrapods serves as an independent apparatus with cold sensitivity. Furthermore, this domain with independent cold sensitivity is necessary for the regulatory mechanism of the pore domain, where the efficacy of cold activation is largely altered by evolutionary tuning of the hydrophobicity of several residues during the diversification of terrestrial tetrapods. Our findings advance the understanding of cold-sensing emergence during evolution and the thermodynamic basis of TRPM8 cold activation.

CRISPR/Cas12a-based technology: A powerful tool for biosensing in food safety

BACKGROUND

In the context of the current pandemic caused by the novel coronavirus, molecular detection is not limited to the clinical laboratory, but also faces the challenge of the complex and variable real-time detection fields. A series of novel coronavirus events were detected in the process of food cold chain packaging and transportation, making the application of molecular diagnosis in food processing, packaging, transportation, and other links urgent. There is an urgent need for a rapid detection technology that can adapt to the diversity and complexity of food safety.

SCOPE AND APPROACH

This review introduces a new molecular diagnostic technology-biosensor analysis technology based on CRISPR-Cas12a. Systematic clarification of its development process and detection principles. It summarizes and systematically organizes its applications in viruses, food-borne pathogenic bacteria, small molecule detection, etc. In the past four years, which provides a brand-new and comprehensive solution for food detection. Finally, this article puts forward the challenges and the prospects for food safety.

KEY FINDINGS AND CONCLUSIONS

The novel coronavirus hazards infiltrated every step of the food industry, from processing to packaging to transportation. The biosensor analytical technology based on CRISPR-Cas12a has great potential in the qualitative and quantitative analysis of infectious pathogens. CRISPR-Cas12a can effectively identify the presence of the specific nucleic acid targets and the small changes in sequences, which is particularly important for nucleic acid identification and pathogen detection. In addition, the CRISPR-Cas12a method can be adjusted and reconfigured within days to detect other viruses, providing equipment for nucleic acid diagnostics in the field of food safety. The future work will focus on the development of portable microfluidic devices for multiple detection. Shao et al. employed physical separation methods to separate Cas proteins in different microfluidic channels to achieve multiple detection, and each channel simultaneously detected different targets by adding crRNA with different spacer sequences. Although CRISPR-Cas12a technology has outstanding advantages in detection, there are several technical barriers in the transformation from emerging technologies to practical applications. The newly developed CRISPR-Cas12a-based applications and methods promote the development of numerous diagnostic and detection solutions, and have great potential in medical diagnosis, environmental monitoring, and especially food detection.

DIC/Oxyma-based accelerated synthesis and oxidative folding studies of centipede toxin RhTx

Coupling reagents play crucial roles in the iterative construction of amide bonds for the synthesis of peptides and peptide-based derivatives. The novel DIC/Oxyma condensation system featured with the low risk of explosion displayed remarkable abilities to inhibit racemization, along with efficient coupling efficiency in both manual and automated syntheses. Nevertheless, an ideal reaction molar ratio in DIC/Oxyma condensation system and the moderate reaction temperature by manual synthesis remain to be further investigated. Herein, the synthetic efficiencies of different reaction ratios between DIC and Oxyma under moderate reaction temperature were systematically evaluated. The robustness and efficiency of DIC/Oxyma condensation system are validated by the rapid synthesis of linear centipede toxin RhTx. Different folding strategies were applied for the construction of disulfide bridges in RhTx, which was further confirmed in assays of circular dichroism and patch-clamp electrophysiology evaluation. This work establishes the DIC/Oxyma-based accelerated synthesis of peptides under moderate condensation conditions, which is especially useful for the manual synthesis of peptides. Besides, the strategy presented here provides robust technical supports for the large-scale synthesis and oxidative folding of RhTx.

Transient Receptor Potential (TRP) and Thermoregulation in Animals: Structural Biology and Neurophysiological Aspects

This review presents and analyzes recent scientific findings on the structure, physiology, and neurotransmission mechanisms of transient receptor potential (TRP) and their function in the thermoregulation of mammals. The aim is to better understand the functionality of these receptors and their role in maintaining the temperature of animals, or those susceptible to thermal stress. The majority of peripheral receptors are TRP cation channels formed from transmembrane proteins that function as transductors through changes in the membrane potential. TRP are classified into seven families and two groups. The data gathered for this review include controversial aspects because we do not fully know the mechanisms that operate the opening and closing of the TRP gates. Deductions, however, suggest the intervention of mechanisms related to G protein-coupled receptors, dephosphorylation, and ligands. Several questions emerge from the review as well. For example, the future uses of these data for controlling thermoregulatory disorders and the invitation to researchers to conduct more extensive studies to broaden our understanding of these mechanisms and achieve substantial advances in controlling fever, hyperthermia, and hypothermia.

OUP accepted manuscript

Animals rely on their sensory systems to inform them of ecologically relevant environmental variation. In the Southern Ocean, the thermal environment has remained between −1.9 and 5 °C for 15 Myr, yet we have no knowledge of how an Antarctic marine organism might sense their thermal habitat as we have yet to discover a thermosensitive ion channel that gates (opens/closes) below 10 °C. Here, we investigate the evolutionary dynamics of transient receptor potential (TRP) channels, which are the primary thermosensors in animals, within cryonotothenioid fishes—the dominant fish fauna of the Southern Ocean. We found cryonotothenioids have a similar complement of TRP channels as other teleosts (∼28 genes). Previous work has shown that thermosensitive gating in a given channel is species specific, and multiple channels act together to sense the thermal environment. Therefore, we combined evidence of changes in selective pressure, gene gain/loss dynamics, and the first sensory ganglion transcriptome in this clade to identify the best candidate TRP channels that might have a functional dynamic range relevant for frigid Antarctic temperatures. We concluded that TRPV1a, TRPA1b, and TRPM4 are the likeliest putative thermosensors, and found evidence of diversifying selection at sites across these proteins. We also put forward hypotheses for molecular mechanisms of other cryonotothenioid adaptations, such as reduced skeletal calcium deposition, sensing oxidative stress, and unusual magnesium homeostasis. By completing a comprehensive and unbiased survey of these genes, we lay the groundwork for functional characterization and answering long-standing thermodynamic questions of thermosensitive gating and protein adaptation to low temperatures.

Spinal integration of hot and cold nociceptive stimuli by wide-dynamic-range neurons in anesthetized adult rats

Introduction

Early neuronal processing of thermal noxious information relies mostly on molecular detectors of the transient receptor potential family expressed by specific subpopulation of sensory neurons. This information may converge to second-order wide-dynamic-range (WDR) neurons located in the deep layer of the dorsal horn of the spinal cord.

Method

Using a micro-Peltier thermode thermal contact stimulator II delivering various cold and hot noxious stimulations, we have characterized the extracellular electrophysiological responses of mechanosensitive WDR neurons in anesthetized adult male and female Wistar rats.

Results

Most of the WDR neurons were activated after hot and cold noxious stimulations, at mean temperature thresholds corresponding to 43 and 20°C, respectively. If the production of action potential was not different in frequency between the 2 thermal modalities, the latency to observe the first action potential was significantly different (cold: 212 ms; hot: 490 ms, unpaired Student t-test: t = 8.041; df = 32; P < 0.0001), suggesting that different fiber types and circuits were involved. The temporal summation was also different because no facilitation was seen for cold noxious stimulations contrary to hot noxious ones.

Conclusion

Altogether, this study helps better understand how short-lasting and long-lasting hot or cold noxious stimuli are integrated by mechanosensitive WDR neurons. In our experimental conditions, we found WDR neurons to be nociceptive specific for C-fiber-mediated hot stimuli. We also found that cold nonnoxious and noxious information, triggered at glabrous skin areas, are likely taken in charge by A-type sensory neurons. This study will be helpful to establish working hypothesis explaining the thermal pain symptoms displayed by animal models and patients in a translational extent.

Transient receptor potential V1 modulates neuroinflammation in Parkinson's disease dementia: Molecular implications for electroacupuncture and rivastigmine

OBJECTIVES

Parkinson's disease (PD) is a common progressive neurodegeneration disease. Its incidence increases with age and affects about 1% of people over 60. Incidentally, transient receptor potential V1 (TRPV1) and its relation with neuroinflammation in mouse brain has been widely reported.

MATERIALS AND METHODS

We used 6-hydroxydopamine (6-OHDA) to induce PDD in mice. We then used the Morris water maze and Bio-Plex to test learning and inflammatory mediators in mouse plasma. Western blotting and immunostaining were used to examine TRPV1 pathway in the hippocampus and medial prefrontal cortex (mPFC).

RESULTS

On acquisition days 3 (Control = 4.40 ± 0.8 sec, PDD = 9.82 ± 1.52 sec, EA = 5.04 ± 0.58 sec, Riva = 4.75 ± 0.87 sec; P=0.001) and 4, reversal learning days 1, 2, 3 (Control = 2.86 ± 0.46 sec, PDD = 9.80 ± 1.83 sec, EA = 4.6 ± 0.82 sec, Riva = 4.6 ± 1.03 sec; P=0.001) and 4, PDD mice showed significantly longer escape latency than the other three groups. Results showed that several cytokines were up-regulated in PDD mice and reversed by EA and rivastigmine. TRPV1 and downstream molecules were up-regulated in PDD mice and further reversed by EA and rivastigmine. Interestingly, α7 nicotinic receptors and parvalbumin levels in both the hippocampus and prefrontal cortex increased in EA-treated mice, but not in rivastigmine-treated mice.

CONCLUSION

Our results showed that TRPV1 played a role in the modulation of neuroinflammation of PDD, and could potentially be a new target for treatment.

TRPV1 Ion Channel: Structural Features, Activity Modulators, and Therapeutic Potential

Although TRPV1 ion channel has been attracting researchers' attention for many years, its functions in animal organisms, the principles of regulation, and the involvement in pathological processes have not yet been fully clarified. Mutagenesis experiments and structural studies have identified the structural features of the channel and binding sites for its numerous ligands; however, these studies are far from conclusion. This review summarizes recent achievements in the TRPV1 research with special focus on structural and functional studies of the channel and on its ligands, which are extremely diverse in their nature and interaction specificity to TRPV1. Particular attention was given to the effects of numerous endogenous agonists and antagonists that can fine-tune the channel sensitivity to its usual activators, such as capsaicin, heat, acids, or their combination. In addition to the pain sensing not covered in this review, the TRPV1 channel was found to be involved in the regulation of many important physiological and pathological processes and, therefore, can be considered as a promising therapeutic target in the treatment of various diseases, such as pneumonia, ischemia, diabetes, epilepsy, schizophrenia, psoriasis, etc.

Molecular sensors for temperature detection during behavioral thermoregulation in turtle embryos

Temperature sensing is essential for the survival of living organisms. Some reptile embryos can reposition themselves within the egg to seek optimal temperatures, but the molecular sensors involved in this temperature detection remain unknown. Here, we show that such thermotaxic behavior is directly determined by the activation of two heat-sensitive ion channels of the turtle: the transient receptor potential ankyrin 1 (MrTRPA1) and transient receptor potential vanilloid-1 (MrTRPV1). These two TRP channels were found to exhibit distinctive distributions among turtle dorsal root ganglion (DRG) neurons. Additionally, our laser irradiation assays illustrated that the heat activation thresholds of MrTRPA1 and MrTRPV1 are consistent with the mild (28-33°C) and noxious (>33°C) heat determined by behavioral tests, respectively. Further pharmacological studies have demonstrated that ligand-induced intervention of MrTRPA1 or MrTRPV1 is sufficient to mimic heat stimuli or block temperature signaling, causing changes in embryo movement. These findings indicate that the initiation of thermotaxic response in turtle embryos relies on a delicate functional balance between the heat activation of MrTRPA1 and MrTRPV1. Our study reveals, for the first time, a unique molecular mechanism underlying thermal detection: the two TRP channels act as a physiological tandem to control the thermotaxic behavior of turtle embryos.

ANAP: A versatile, fluorescent probe of ion channel gating and regulation

Fluorescence spectroscopy and microscopy are non-destructive methods that provide real-time measurements of ion channel structural dynamics. As such, they constitute a direct path linking the high-resolution structural models from X-ray crystallography and cryo-electron microscopy with the high-resolution functional data from ionic current measurements. The utility of fluorescence as a reporter of channel structure is limited by the palette of available fluorophores. Thiol-reactive fluorophores are small and bright, but are restricted in terms of the positions on a protein that can be labeled and present significant issues with background incorporation. Genetically encoded fluorescent protein tags are specific to a protein of interest, but are very large and usually only used to label the free N- and C-termini of proteins. L-3-(6-acetylnaphthalen-2-ylamino)-2-aminopropionic acid (ANAP) is a fluorescent amino acid that can be specifically incorporated into virtually any site on a protein of interest using amber stop-codon suppression. Due to its environmental sensitivity and potential as a donor in fluorescence resonance energy transfer experiments, it has been adopted by numerous investigators to study voltage, ligand, and temperature-dependent activation of a host of ion channels. Simultaneous measurements of ionic currents and ANAP fluorescence yield exceptional mechanistic insights into channel function. In this chapter, I will summarize the current literature regarding ANAP and ion channels and discuss the practical aspects of using ANAP, including potential pitfalls and confounds.

A plant-derived TRPV3 inhibitor suppresses pain and itch

BACKGROUND AND PURPOSE

Itching is the most frequent pathology in dermatology that has significant impacts on people's mental health and social life. Transient receptor potential vanilloid 3 (TRPV3) channel is a promising target for treating pruritus. However, few selecetive and potent antagonists have been reported. This study was designed to identify selective TRPV3 antagonist and elucidate its anti-pruritus pharmacology.

EXPERIMENTAL APPROACH

FlexStation and calcium fluorescence imaging were conducted to track the functional compounds. Whole-cell patch clamp was used to record itch-related ion channel currents. Homologous recombination and site-directed mutagenesis were employed to construct TRPV3 channel chimeras and point mutations for exploring pharmacological mechanism. Mouse models were used for in vivo anti-pruritus assay.

KEY RESULTS

An acridone alkaloid (citrusinine-II) was purified and characterized from Atalantia monophylla. It directly interacts with Y564 within S4 helix of TRPV3 to selectively inhibit the channel with a half maximal inhibitory concentration (IC₅₀ ) of 12.43 μM. Citrusinine-II showed potential efficacy to attenuate both chronic and acute itch. Intradermal administration of citrusinine-II (143 ng/skin site) nearly completely inhibited itch behaviours. It also shows significant analgesic effects. Little side effects of the compound are observed.

CONCLUSION AND IMPLICATIONS

By acting as a selective and potent inhibitor of TRPV3 channel, citrusinine-II shows valuable therapeutic effects in pruritus animal models and is a promising candidate drug and/or lead molecule for the development of anti-pruritus drugs.

The Mysteries of Capsaicin-Sensitive Afferents

A fundamental subdivision of nociceptive sensory neurons is named after their unique sensitivity to capsaicin, the pungent ingredient in hot chili peppers: these are the capsaicin-sensitive afferents. The initial excitation by capsaicin of these neurons manifested as burning pain sensation is followed by a lasting refractory state, traditionally referred to as "capsaicin desensitization," during which the previously excited neurons are unresponsive not only to capsaicin but a variety of unrelated stimuli including noxious heat. The long sought-after capsaicin receptor, now known as TRPV1 (transient receptor potential cation channel, subfamily V member 1), was cloned more than two decades ago. The substantial reduction of the inflammatory phenotype of Trpv1 knockout mice has spurred extensive efforts in the pharmaceutical industry to develop small molecule TRPV1 antagonists. However, adverse effects, most importantly hyperthermia and burn injuries, have so far prevented any compounds from progressing beyond Phase 2. There is increasing evidence that these limitations can be at least partially overcome by approaches outside of the mainstream pharmaceutical development, providing novel therapeutic options through TRPV1. Although ablation of the whole TRPV1-expressing nerve population by high dose capsaicin, or more selectively by intersectional genetics, has allowed researchers to investigate the functions of capsaicin-sensitive afferents in health and disease, several "mysteries" remain unsolved to date, including the molecular underpinnings of "capsaicin desensitization," and the exact role these nerves play in thermoregulation and heat sensation. This review tries to shed some light on these capsaicin mechanisms.

Activation of the archaeal ion channel MthK is exquisitely regulated by temperature

Physiological response to thermal stimuli in mammals is mediated by a structurally diverse class of ion channels, many of which exhibit polymodal behavior. To probe the diversity of biophysical mechanisms of temperature-sensitivity, we characterized the temperature-dependent activation of MthK, a two transmembrane calcium-activated potassium channel from thermophilic archaebacteria. Our functional complementation studies show that these channels are more efficient at rescuing K+ transport at 37°C than at 24°C. Electrophysiological activity of the purified MthK is extremely sensitive (Q10 >100) to heating particularly at low-calcium concentrations whereas channels lacking the calcium-sensing RCK domain are practically insensitive. By analyzing single-channel activities at limiting calcium concentrations, we find that temperature alters the coupling between the cytoplasmic RCK domains and the pore domain. These findings reveal a hitherto unexplored mechanism of temperature-dependent regulation of ion channel gating and shed light on ancient origins of temperature-sensitivity.

Engineering and Rewiring of a Calcium-Dependent Signaling Pathway

An important feature of synthetic biological circuits is their response to physicochemical signals, which enables the external control of cellular processes. Calcium-dependent regulation is an attractive approach for achieving such control, as diverse stimuli induce calcium influx by activating membrane channel receptors. Most calcium-dependent gene circuits use the endogenous nuclear factor of activated T-cells (NFAT) signaling pathway. Here, we employed engineered NFAT transcription factors to induce the potent and robust activation of exogenous gene expression in HEK293T cells. Furthermore, we designed a calcium-dependent transcription factor that does not interfere with NFAT-regulated promoters and potently activates transcription in several mammalian cell types. Additionally, we demonstrate that coupling the circuit to a calcium-selective ion channel resulted in capsaicin- and temperature-controlled gene expression. This engineered calcium-dependent signaling pathway enables tightly controlled regulation of gene expression through different stimuli in mammalian cells and is versatile, adaptable, and useful for a wide range of therapeutic and diagnostic applications.

Different Therapeutic Effects of CO2 and Diode Laser Irradiation on Tooth Movement-Related Pain

Although orthodontic treatment is common, orthodontic force often induced pain. Low-level laser therapy (LLLT) has been investigated to improve therapeutic comfort. In dentistry, LLLT is mainly applied using two types of lasers, CO₂ and diode lasers, whose biological actions are thought to be associated with wavelength (CO₂: 10,600 nm; diode: 808 nm). The analgesic effect of LLLT on orthodontic treatment-related pain is widely reported but inconsistent. This study aimed to (1) determine whether irradiation with a CO₂ or diode laser attenuates orthodontic treatment-related pain using the jaw-opening reflex model, (2) elucidate the optimal irradiation protocol for both lasers to obtain the maximal analgesic effect, (3) evaluate the effects of laser irradiation on other biological features [e.g., tooth movement, glial fibrillary acidic protein (GFAP) expression, and temperature alterations] and (4) investigate the mechanism underlying the analgesic effect of laser irradiation. In this animal model, orthodontic treatment-induced pain manifested as a significantly reduced the threshold for inducing the jaw-opening reflex on the orthodontically treated side compared with the contralateral side. GFAP expression in the bilateral trigeminal ganglia (TGs) was significantly increased by the application of orthodontic force. CO₂ laser irradiation of the orthodontically treated region significantly increased the threshold for inducing the jaw-opening reflex and the peripheral temperature. Similar reductions in jaw-opening reflex excitability were induced by surface anesthesia and thermal stimulation but not, the diode laser. Neither CO₂ nor diode laser irradiation altered GFAP expression in the TGs. Infiltration anesthesia also significantly increased the threshold for inducing the jaw-opening reflex on each anesthetized side. Irradiation (30 s) by either laser immediately after orthodontic force application (preirradiation) significantly decreased jaw-opening reflex excitability and GFAP expression in the bilateral TGs the next day. However, thermal stimulation immediately after orthodontic force application failed to alter jaw-opening reflex excitability the next day. Laser irradiation did not alter tooth movement; however, an optimized irradiation protocol for aiding tooth movement is suggested. In conclusion, both CO₂ and diode lasers are able to prevent orthodontic treatment-related pain. Furthermore, the involvement of temperature alterations and surface anesthesia in the analgesic effect induced by CO₂ laser irradiation is suggested.

A specialized pore turret in the mammalian cation channel TRPV1 is responsible for distinct and species-specific heat activation thresholds

The transient receptor potential vanilloid 1 (TRPV1) channel is a heat-activated cation channel that plays a crucial role in ambient temperature detection and thermal homeostasis. Although several structural features of TRPV1 have been shown to be involved in heat-induced activation of the gating process, the physiological significance of only a few of these key elements has been evaluated in an evolutionary context. Here, using transient expression in HEK293 cells, electrophysiological recordings, and molecular modeling, we show that the pore turret contains both structural and functional determinants that set the heat activation thresholds of distinct TRPV1 orthologs in mammals whose body temperatures fluctuate widely. We found that TRPV1 from the bat Carollia brevicauda exhibits a lower threshold temperature of channel activation than does its human ortholog and three bat-specific amino acid substitutions located in the pore turret are sufficient to determine this threshold temperature. Furthermore, the structure of the TRPV1 pore turret appears to be of physiological and evolutionary significance for differentiating the heat-activated threshold among species-specific TRPV1 orthologs. These findings support a role for the TRPV1 pore turret in tuning the heat-activated threshold, and they suggest that its evolution was driven by adaption to specific physiological traits among mammals exposed to variable temperatures.

Variations in the TRPV1 gene are associated to exertional heat stroke

OBJECTIVES

Exertional Heat Stroke (EHS) is one of the top three causes of sudden death in athletes. Extrinsic and intrinsic risk factors have been identified but the genetic causes still remain unclear. Our aim was to identify genes responsible for EHS, which is a necessary step to identify patients at risk and prevent crises.

DESIGN

Genetic and functional laboratory studies METHODS: Whole Exome Sequencing (WES) was performed to search for candidate genes in a cohort of 15 soldiers who had a documented EHS episode. In silico and in vitro functional studies were performed to evaluate the effect of mutations identified in the candidate gene TRPV1.

RESULTS

WES led to the identification of two missense variations in the TRPV1 gene. These variations were very rare or unreported in control databases and located in critical domains of the protein. In vitro functional studies revealed that both variations induce a strong modification of the channel response to one of its natural agonist, the capsaicin.

CONCLUSIONS

We evidenced mutations altering channel properties of the TRPV1 gene and demonstrated that TRPV1, which is involved in thermoregulation and nociception, is a new candidate gene for EHS. Our data provide the bases to explore genetic causes and molecular mechanisms governing the pathophysiology of EHS.

A centipede toxin causes rapid desensitization of nociceptor TRPV1 ion channel

The nociceptive transient receptor potential vanilloid 1 (TRPV1) ion channel is a polymodal receptor for multiple painful stimuli, hence actively pursued as a target for analgesic drugs. We identified a small peptide toxin RhTx2 from the Chinese red-headed centipede that strongly modulates TRPV1 activities. RhTx2, a 31-amino-acid peptide, is similar to a TRPV1-activating toxin RhTx we have previously discovered but with four extra amino acids at the N terminus. We observed that, like RhTx, RhTx2 activated TRPV1, but RhTx2 rapidly desensitized the channel upon prolonged exposure. Desensitization was achieved by reducing both the open probability and the single-channel conductance. RhTx2 is not only a tool to study the desensitization mechanism of TRPV1, but also a promising starting molecule for developing novel analgesics.

A paradigm of thermal adaptation in penguins and elephants by tuning cold activation in TRPM8

Sensing temperature is critical for the survival of all living beings. Here, we show that during cold-induced activation of the archetypical temperature-sensitive TRPM8 ion channel, there are hydrophobic residues in the pore domain stabilized in the exposed state. Tuning hydrophobicity of these residues specifically alters cold response in TRPM8. Furthermore, TRPM8 orthologs in vertebrates evolved to employ such a mechanism, which physiologically tunes cold tolerance for better thermal adaptation. Our findings not only advance the understanding of the cold-induced activation mechanism of TRPM8 but also bring insights to the molecular evolution strategy for ambient-temperature adaptation in vertebrates.

To adapt to habitat temperature, vertebrates have developed sophisticated physiological and ecological mechanisms through evolution. Transient receptor potential melastatin 8 (TRPM8) serves as the primary sensor for cold. However, how cold activates TRPM8 and how this sensor is tuned for thermal adaptation remain largely unknown. Here we established a molecular framework of how cold is sensed in TRPM8 with a combination of patch-clamp recording, unnatural amino acid imaging, and structural modeling. We first observed that the maximum cold activation of TRPM8 in eight different vertebrates (i.e., African elephant and emperor penguin) with distinct side-chain hydrophobicity (SCH) in the pore domain (PD) is tuned to match their habitat temperature. We further showed that altering SCH for residues in the PD with solvent-accessibility changes leads to specific tuning of the cold response in TRPM8. We also observed that knockin mice expressing the penguin’s TRPM8 exhibited remarkable tolerance to cold. Together, our findings suggest a paradigm of thermal adaptation in vertebrates, where the evolutionary tuning of the cold activation in the TRPM8 ion channel through altering SCH and solvent accessibility in its PD largely contributes to the setting of the cold-sensitive/tolerant phenotype.

CRISPR/Cas12a-Mediated Interfacial Cleaving of Hairpin DNA Reporter for Electrochemical Nucleic Acid Sensing

A rapid and sensitive isothermal method is crucial for point-of-care (POC) nucleic acid testing. Recently, RNA-guided CRISPR/Cas12a proteins were discovered to exhibit target-triggered nonspecific single-stranded deoxyribonuclease (ssDNase) activity. Herein, the ssDNase cleavage capacity of the CRISPR/Cas12a system for interfacial hairpin DNA (hpDNA) and linear DNA was investigated in detailed. A novel electrochemical DNA biosensor was then developed via target-induced Cas12a cleaving interfacial hpDNA. In this strategy, the RNA-guided target DNA binding activates the robust Cas12a ssDNase activity. The immobilized hpDNA electrochemical reporters with a low surface coverage and incompact morphological structure present accessible substrates for highly efficient Cas12a cleavage, leading to a highly sensitive electrochemical DNA biosensor. Under the optimal conditions, as low as 30 pM target DNA was detected in about 60 min with 3.5 orders of magnitude dynamic range from 50 pM to 100 nM. Furthermore, the practical application ability of the established sensing method for detecting the target in complex matrices was also demonstrated. The proposed strategy enables rapid and sensitive DNA determination, providing a potential tool for POC molecular diagnostics.

Structural insights into the gating mechanisms of TRPV channels

Transient Receptor Potential channels from the vanilloid subfamily (TRPV) are a group of cation channels modulated by a variety of endogenous stimuli as well as a range of natural and synthetic compounds. Their roles in human health make them of keen interest, particularly from a pharmacological perspective. However, despite this interest, the complexity of these channels has made it difficult to obtain high resolution structures until recently. With the cryo-EM resolution revolution, TRPV channel structural biology has blossomed to produce dozens of structures, covering every TRPV family member and a variety of approaches to examining channel modulation. Here, we review all currently available TRPV structures and the mechanistic insights into gating that they reveal.

TRPA1 modulation by piperidine carboxamides suggests an evolutionarily conserved binding site and gating mechanism

The transient receptor potential ankyrin 1 (TRPA1) channel functions as an irritant sensor and is a therapeutic target for treating pain, itch, and respiratory diseases. As a ligand-gated channel, TRPA1 can be activated by electrophilic compounds such as allyl isothiocyanate (AITC) through covalent modification or activated by noncovalent agonists through ligand binding. However, how covalent modification leads to channel opening and, importantly, how noncovalent binding activates TRPA1 are not well-understood. Here we report a class of piperidine carboxamides (PIPCs) as potent, noncovalent agonists of human TRPA1. Based on their species-specific effects on human and rat channels, we identified residues critical for channel activation; we then generated binding modes for TRPA1-PIPC interactions using structural modeling, molecular docking, and mutational analysis. We show that PIPCs bind to a hydrophobic site located at the interface of the pore helix 1 (PH1) and S5 and S6 transmembrane segments. Interestingly, this binding site overlaps with that of known allosteric modulators, such as A-967079 and propofol. Similar binding sites, involving π-helix rearrangements on S6, have been recently reported for other TRP channels, suggesting an evolutionarily conserved mechanism. Finally, we show that for PIPC analogs, predictions from computational modeling are consistent with experimental structure-activity studies, thereby suggesting strategies for rational drug design.