Structural mechanism of TRPV3 channel inhibition by the anesthetic dyclonine

Pathology of pain and its implications for therapeutic interventions

Pain is estimated to affect more than 20% of the global population, imposing incalculable health and economic burdens. Effective pain management is crucial for individuals suffering from pain. However, the current methods for pain assessment and treatment fall short of clinical needs. Benefiting from advances in neuroscience and biotechnology, the neuronal circuits and molecular mechanisms critically involved in pain modulation have been elucidated. These research achievements have incited progress in identifying new diagnostic and therapeutic targets. In this review, we first introduce fundamental knowledge about pain, setting the stage for the subsequent contents. The review next delves into the molecular mechanisms underlying pain disorders, including gene mutation, epigenetic modification, posttranslational modification, inflammasome, signaling pathways and microbiota. To better present a comprehensive view of pain research, two prominent issues, sexual dimorphism and pain comorbidities, are discussed in detail based on current findings. The status quo of pain evaluation and manipulation is summarized. A series of improved and innovative pain management strategies, such as gene therapy, monoclonal antibody, brain-computer interface and microbial intervention, are making strides towards clinical application. We highlight existing limitations and future directions for enhancing the quality of preclinical and clinical research. Efforts to decipher the complexities of pain pathology will be instrumental in translating scientific discoveries into clinical practice, thereby improving pain management from bench to bedside.

TRPV3 activation by different agonists accompanied by lipid dissociation from the vanilloid site

TRPV3 represents both temperature- and ligand-activated transient receptor potential (TRP) channel. Physiologically relevant opening of TRPV3 channels by heat has been captured structurally, while opening by agonists has only been observed in structures of mutant channels. Here, we present cryo-EM structures that illuminate opening and inactivation of wild-type human TRPV3 in response to binding of two types of agonists: either the natural cannabinoid tetrahydrocannabivarin (THCV) or synthetic agonist 2-aminoethoxydiphenylborane (2-APB). We found that THCV binds to the vanilloid site, while 2-APB binds to the S1-S4 base and ARD-TMD linker sites. Despite binding to distally located sites, both agonists induce similar pore opening and cause dissociation of a lipid that occupies the vanilloid site in their absence. Our results uncover different but converging allosteric pathways through which small-molecule agonists activate TRPV3 and provide a framework for drug design and understanding the role of lipids in ion channel function.

Molecular details of ruthenium red pore block in TRPV channels

Transient receptor potential vanilloid (TRPV) channels play a critical role in calcium homeostasis, pain sensation, immunological response, and cancer progression. TRPV channels are blocked by ruthenium red (RR), a universal pore blocker for a wide array of cation channels. Here we use cryo-electron microscopy to reveal the molecular details of RR block in TRPV2 and TRPV5, members of the two TRPV subfamilies. In TRPV2 activated by 2-aminoethoxydiphenyl borate, RR is tightly coordinated in the open selectivity filter, blocking ion flow and preventing channel inactivation. In TRPV5 activated by phosphatidylinositol 4,5-bisphosphate, RR blocks the selectivity filter and closes the lower gate through an interaction with polar residues in the pore vestibule. Together, our results provide a detailed understanding of TRPV subfamily pore block, the dynamic nature of the selectivity filter and allosteric communication between the selectivity filter and lower gate.

Selective inhibition of overactive warmth-sensitive Ca2+-permeable TRPV3 channels by antispasmodic agent flopropione for alleviation of skin inflammation

The temperature-sensitive Ca2+-permeable TRPV3 ion channel is robustly expressed in the skin keratinocytes, and its gain-of-function mutations are involved in the pathology of skin lesions. Here, we report the identification of an antispasmodic agent flopropione that alleviates skin inflammation by selective inhibition of TRPV3. In whole-cell patch clamp recordings, flopropione selectively inhibits macroscopic TRPV3 currents in a concentration-dependent manner with an IC50 value of 17.8 ± 3.5 μM. At the single-channel level, flopropione inhibits TRPV3 channel open probability without alteration of its unitary conductance. In an in vivo mouse model of skin inflammation induced by the skin sensitizer DNFB, flopropione also alleviates dorsal skin lesions and ear skin swelling. Further molecular docking combined with site-directed mutagenesis reveals that two residues E501 and I505 in the channel S2-helix are critical for flopropione-mediated inhibition of TRPV3. Taken together, our findings demonstrate that the spasmolytic drug flopropione as a selective inhibitor of TRPV3 channel not only provides a valuable tool molecule for understanding of TRPV3 channel pharmacology but also holds repurposing potential for therapy of skin disorders, such as dermatitis and pruritus.

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

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

Molecular pharmacology of the onco-TRP channel TRPV6

TRPV6, a representative of the vanilloid subfamily of TRP channels, serves as the principal calcium uptake channel in the gut. Dysregulation of TRPV6 results in disturbed calcium homeostasis leading to a variety of human diseases, including many forms of cancer. Inhibitors of this oncochannel are therefore particularly needed. In this review, we provide an overview of recent advances in structural pharmacology that uncovered the molecular mechanisms of TRPV6 inhibition by a variety of small molecules, including synthetic and natural, plant-derived compounds as well as some prospective and clinically approved drugs.

Spatio-Temporal Analysis of Anesthetics in Mice by Solid-Phase Microextraction: Dielectric Barrier Discharge Ionization Mass Spectrometry

Local anesthetics, drugs that only affect a restricted area of the body, are widely used in daily clinical practice. Less studied but equally important is the distribution of local anesthetics inside organisms. Here, we present a rapid in situ testing method of drug distribution in various organs. The temporal and spatial distribution of anesthetics in mice was measured by solid-phase microextraction (SPME), thermal desorption (TD), and dielectric barrier discharge ionization (DBDI) atmospheric pressure mass spectrometry. A coated SPME probe using a tungsten wire as the support covered with a carbonaceous material was prepared by a simple, low-cost flame method. An in-line structure of the inlet allows TD and DBDI to share the same capillary tube, which greatly improves the transmission efficiency. Nine kinds of anesthetics, such as lidocaine and dyclonine, were detected, and the limit of detection was determined to be as low as 13 pg/mL. In addition, the time-dependent distribution of drugs in mice organs was studied. We also found that macromolecules in organisms do not noticeably interfere with the detection. This method is convenient and efficient because it does not require tissue homogenates and allows direct in situ detection. Compared with the conventional analytical methods, this method is simple and rapid, works in situ, and allows microscale analysis of trace analytes in biological organisms with high sensitivity.

Molecular pathway and structural mechanism of human oncochannel TRPV6 inhibition by the phytocannabinoid tetrahydrocannabivarin

The calcium-selective oncochannel TRPV6 is an important driver of cell proliferation in human cancers. Despite increasing interest of pharmacological research in developing synthetic inhibitors of TRPV6, natural compounds acting at this channel have been largely neglected. On the other hand, pharmacokinetics of natural small-molecule antagonists optimized by nature throughout evolution endows these compounds with a medicinal potential to serve as potent and safe next-generation anti-cancer drugs. Here we report the structure of human TRPV6 in complex with tetrahydrocannabivarin (THCV), a natural cannabinoid inhibitor extracted from Cannabis sativa. We use cryo-electron microscopy combined with electrophysiology, calcium imaging, mutagenesis, and molecular dynamics simulations to identify THCV binding sites in the portals that connect the membrane environment surrounding the protein to the central cavity of the channel pore and to characterize the allosteric mechanism of TRPV6 inhibition. We also propose the molecular pathway taken by THCV to reach its binding site. Our study provides a foundation for the development of new TRPV6-targeting drugs.

Structure of human TRPV4 in complex with GTPase RhoA

Transient receptor potential (TRP) channel TRPV4 is a polymodal cellular sensor that responds to moderate heat, cell swelling, shear stress, and small-molecule ligands. It is involved in thermogenesis, regulation of vascular tone, bone homeostasis, renal and pulmonary functions. TRPV4 is implicated in neuromuscular and skeletal disorders, pulmonary edema, and cancers, and represents an important drug target. The cytoskeletal remodeling GTPase RhoA has been shown to suppress TRPV4 activity. Here, we present a structure of the human TRPV4-RhoA complex that shows RhoA interaction with the membrane-facing surface of the TRPV4 ankyrin repeat domains. The contact interface reveals residues that are mutated in neuropathies, providing an insight into the disease pathogenesis. We also identify the binding sites of the TRPV4 agonist 4α-PDD and the inhibitor HC-067047 at the base of the S1-S4 bundle, and show that agonist binding leads to pore opening, while channel inhibition involves a π-to-α transition in the pore-forming helix S6. Our structures elucidate the interaction interface between hTRPV4 and RhoA, as well as residues at this interface that are involved in TRPV4 disease-causing mutations. They shed light on TRPV4 activation and inhibition and provide a template for the design of future therapeutics for treatment of TRPV4-related diseases.

TRPV3 Ion Channel: From Gene to Pharmacology

Transient receptor potential vanilloid subtype 3 (TRPV3) is an ion channel with a sensory function that is most abundantly expressed in keratinocytes and peripheral neurons. TRPV3 plays a role in Ca²⁺ homeostasis due to non-selective ionic conductivity and participates in signaling pathways associated with itch, dermatitis, hair growth, and skin regeneration. TRPV3 is a marker of pathological dysfunctions, and its expression is increased in conditions of injury and inflammation. There are also pathogenic mutant forms of the channel associated with genetic diseases. TRPV3 is considered as a potential therapeutic target of pain and itch, but there is a rather limited range of natural and synthetic ligands for this channel, most of which do not have high affinity and selectivity. In this review, we discuss the progress in the understanding of the evolution, structure, and pharmacology of TRPV3 in the context of the channel's function in normal and pathological states.

Structural mechanism of human oncochannel TRPV6 inhibition by the natural phytoestrogen genistein

Calcium-selective oncochannel TRPV6 is the major driver of cell proliferation in human cancers. While significant effort has been invested in the development of synthetic TRPV6 inhibitors, natural channel blockers have been largely neglected. Here we report the structure of human TRPV6 in complex with the plant-derived phytoestrogen genistein, extracted from Styphnolobium japonicum, that was shown to inhibit cell invasion and metastasis in cancer clinical trials. Despite the pharmacological value, the molecular mechanism of TRPV6 inhibition by genistein has remained enigmatic. We use cryo-EM combined with electrophysiology, calcium imaging, mutagenesis, and molecular dynamics simulations to show that genistein binds in the intracellular half of the TRPV6 pore and acts as an ion channel blocker and gating modifier. Genistein binding to the open channel causes pore closure and a two-fold symmetrical conformational rearrangement in the S4-S5 and S6-TRP helix regions. The unprecedented mechanism of TRPV6 inhibition by genistein uncovers new possibilities in structure-based drug design.

Human TRPV1 structure and inhibition by the analgesic SB-366791

Pain therapy has remained conceptually stagnant since the opioid crisis, which highlighted the dangers of treating pain with opioids. An alternative addiction-free strategy to conventional painkiller-based treatment is targeting receptors at the origin of the pain pathway, such as transient receptor potential (TRP) ion channels. Thus, a founding member of the vanilloid subfamily of TRP channels, TRPV1, represents one of the most sought-after pain therapy targets. The need for selective TRPV1 inhibitors extends beyond pain treatment, to other diseases associated with this channel, including psychiatric disorders. Here we report the cryo-electron microscopy structures of human TRPV1 in the apo state and in complex with the TRPV1-specific nanomolar-affinity analgesic antagonist SB-366791. SB-366791 binds to the vanilloid site and acts as an allosteric hTRPV1 inhibitor. SB-366791 binding site is supported by mutagenesis combined with electrophysiological recordings and can be further explored to design new drugs targeting TRPV1 in disease conditions.

Multidisciplinary Advances Address the Challenges in Developing Drugs against Transient Receptor Potential Channels to Treat Metabolic Disorders

Transient receptor potential (TRP) channels are cation channels that regulate key physiological and pathological processes in response to a broad range of stimuli. Moreover, they systemically regulate the release of hormones, metabolic homeostasis, and complications of diabetes, which positions them as promising therapeutic targets to combat metabolic disorders. Nevertheless, there are significant challenges in the design of TRP ligands with high potency and durability. Herein we summarize the four challenges as hydrophobicity, selectivity, mono-target therapy, and interspecies discrepancy. We present 1134 TRP ligands with diversified modes of TRP-ligand interaction and provide a detailed discussion of the latest strategies, especially cryogenic electron microscopy (cryo-EM) and computational methods. We propose solutions to address the challenges with a critical analysis of advances in membrane partitioning, polypharmacology, biased agonism, and biochemical screening of transcriptional modulators. They are fueled by the breakthrough from cryo-EM, chemoinformatics and bioinformatics. The discussion is aimed to shed new light on designing next-generation drugs to treat obesity, diabetes and its complications, with optimal hydrophobicity, higher mode selectivity, multi-targeting and consistent activities between human and rodents.

TRPV3-ANO1 interaction positively regulates wound healing in keratinocytes

Transient receptor potential vanilloid 3 (TRPV3) belongs to the TRP ion channel super family and functions as a nonselective cation channel that is highly permeable to calcium. This channel is strongly expressed in skin keratinocytes and is involved in warmth sensation, itch, wound healing and secretion of several cytokines. Previous studies showed that anoctamin1 (ANO1), a calcium-activated chloride channel, was activated by calcium influx through TRPV1, TRPV4 or TRPA1 and that these channel interactions were important for TRP channel-mediated physiological functions. We found that ANO1 was expressed by normal human epidermal keratinocytes (NHEKs). We observed that ANO1 mediated currents upon TRPV3 activation of NHEKs and mouse skin keratinocytes. Using an in vitro wound-healing assay, we observed that either a TRPV3 blocker, an ANO1 blocker or low chloride medium inhibited cell migration and proliferation through p38 phosphorylation, leading to cell cycle arrest. These results indicated that chloride influx through ANO1 activity enhanced wound healing by keratinocytes.

TRPV3: Structure, Diseases and Modulators

Transient receptor potential vanillin 3 (TRPV3) is a member of the transient receptor potential (TRP) superfamily. As a Ca²⁺-permeable nonselective cation channel, TRPV3 can recognize thermal stimulation (31-39 °C), and it plays an important regulatory role in temperature perception, pain transduction, skin physiology, inflammation, cancer and other diseases. TRPV3 is not only activated by the changes in the temperature, but it also can be activated by a variety of chemical and physical stimuli. Selective TRPV3 agonists and antagonists with regulatory effects and the physiological functions for clinical application are highly demanded. In recent years, significant progress has been made in the study of TRPV3, but there is still a lack of modulators with a strong affinity and excellent selectivity. This paper reviews the functional characteristics of TRPV3 in terms of the structure, diseases and the research on TRPV3 modulators.

Structural basis of TRPV3 inhibition by an antagonist

The TRPV3 channel plays vital roles in skin physiology. Dysfunction of TRPV3 causes skin diseases, including Olmsted syndrome. However, the lack of potent and selective inhibitors impedes the validation of TRPV3 as a therapeutic target. In this study, we identified Trpvicin as a potent and subtype-selective inhibitor of TRPV3. Trpvicin exhibits pharmacological potential in the inhibition of itch and hair loss in mouse models. Cryogenic electron microscopy structures of TRPV3 and the pathogenic G573S mutant complexed with Trpvicin reveal detailed ligand-binding sites, suggesting that Trpvicin inhibits the TRPV3 channel by stabilizing it in a closed state. Our G573S mutant structures demonstrate that the mutation causes a dilated pore, generating constitutive opening activity. Trpvicin accesses additional binding sites inside the central cavity of the G573S mutant to remodel the channel symmetry and block the channel. Together, our results provide mechanistic insights into the inhibition of TRPV3 by Trpvicin and support TRPV3-related drug development.

TRPV3 and Itch: The Role of TRPV3 in Chronic Pruritus according to Clinical and Experimental Evidence

Itching is a sensory phenomenon characterized by an unpleasant sensation that makes you want to scratch the skin, and chronic itching diminishes the quality of life. In recent studies, multiple transient receptor potential (TRP) channels present in keratinocytes or nerve endings have been shown to engage in the propagation of itch signals in chronic dermatological or pruritic conditions, such as atopic dermatitis (AD) and psoriasis (PS). TRPV3, a member of the TRP family, is highly expressed in the epidermal keratinocytes. Normal TRPV3 signaling is essential for maintaining epidermal barrier homeostasis. In recent decades, many studies have suggested that TRPV3 contributes to detecting pruritus signals. Gain-of-function mutations in TRPV3 in mice and humans are characterized by severe itching, hyperkeratosis, and elevated total IgE levels. These studies suggest that TRPV3 is an important channel for skin itching. Preclinical studies have provided evidence to support the development of TRPV3 antagonists for treating inflammatory skin conditions, itchiness, and pain. This review explores the role of TRPV3 in chronic pruritus, collating clinical and experimental evidence. We also discuss underlying cellular and molecular mechanisms and explore the potential of TRPV3 antagonists as therapeutic agents.

Structural snapshots of the mechanism of TRPV2 channel activation by small-molecule agonists

Transient receptor potential (TRP) channels are polymodal sensors that play critical roles in various physiological processes in living organisms. These cation-permeable channels respond to a variety of physical and chemical stimuli, including cold and hot temperatures, acidic pH, and mechanical stress, often determining a sensory frontier of defense against hostile environments. Vanilloid (V) subfamily is the most studied category of TRP channels that includes six closely related members: highly calcium-selective TRPV5-6 and non-selective TRPV1-4. A remarkable feature of TRPV1-4 is their ability to sense heat, which makes them temperature-sensitive TRP channels or thermo-TRPs. TRPV channels are associated with a multitude of human diseases, including cancers, chronic pain, cardiovascular, neurological and nociceptive disorders. Despite the great clinical interest, pharmacology of TRPV channels remains largely undeveloped because of insufficient knowledge about the mechanisms of their regulation. For instance, activation of TRPV channels by small molecules or heat remains poorly understood. Numerous identified TRPV channel agonists, while effective in physiological experiments, appear limited in their ability to act in the conditions of structural biology experiments. In this regard, the recent study by Pumroy et al. [1] makes a significant contribution towards our understanding of TRPV2 structural dynamics that leads to opening of this channel in physiological conditions.