Structural basis for human TRPC5 channel inhibition by two distinct inhibitors

Functional determinants of lysophospholipid- and voltage-dependent regulation of TRPC5 channel

Lysophosphatidylcholine (LPC) is a bioactive lipid present at high concentrations in inflamed and injured tissues where it contributes to the initiation and maintenance of pain. One of its important molecular effectors is the transient receptor potential canonical 5 (TRPC5), but the explicit mechanism of the activation is unknown. Using electrophysiology, mutagenesis and molecular dynamics simulations, we show that LPC-induced activation of TRPC5 is modulated by xanthine ligands and depolarizing voltage, and involves conserved residues within the lateral fenestration of the pore domain. Replacement of W577 with alanine (W577A) rendered the channel insensitive to strong depolarizing voltage, but LPC still activated this mutant at highly depolarizing potentials. Substitution of G606 located directly opposite position 577 with tryptophan rescued the sensitivity of W577A to depolarization. Molecular simulations showed that depolarization widens the lower gate of the channel and this conformational change is prevented by the W577A mutation or removal of resident lipids. We propose a gating scheme in which depolarizing voltage and lipid-pore helix interactions act together to promote TRPC5 channel opening.

Dynamic remodeling of TRPC5 channel-caveolin-1-eNOS protein assembly potentiates the positive feedback interaction between Ca2+ and NO signals

The cell signaling molecules nitric oxide (NO) and Ca2+ regulate diverse biological processes through their closely coordinated activities directed by signaling protein complexes. However, it remains unclear how dynamically the multi-component protein assemblies behave within the signaling complexes upon the interplay between NO and Ca2+ signals. Here we demonstrate that TRPC5 channels activated by stimulation of G-protein-coupled ATP receptors mediate Ca2+ influx, that triggers NO production from endothelial NO synthase (eNOS), inducing secondary activation of TRPC5 via cysteine S-nitrosylation and eNOS in vascular endothelial cells. Mutations in the caveolin-1-binding domains of TRPC5 disrupt its association with caveolin-1 and impair Ca2+ influx and NO production, suggesting that caveolin-1 serves primarily as the scaffold for TRPC5 and eNOS to assemble into the signal complex. Interestingly, during ATP receptor activation, eNOS is dissociated from caveolin-1 and in turn directly associates with TRPC5, which accumulates at the plasma membrane dependently on Ca2+ influx and calmodulin (CaM). This protein reassembly likely results in a relief of eNOS from the inhibitory action of caveolin-1 and an enhanced TRPC5 S-nitrosylation by eNOS localized in the proximity, thereby facilitating the secondary activation of Ca2+ influx and NO production. In isolated rat aorta, vasodilation induced by acetylcholine was significantly suppressed by the TRPC5 inhibitor AC1903. Thus, our study provides evidence that dynamic remodeling of the protein assemblies among TRPC5, eNOS, caveolin-1, and CaM determines the ensemble of Ca2+ mobilization and NO production in vascular endothelial cells.

TRPC1: The housekeeper of the hippocampus

The non-selective cation channel TRPC1 is highly expressed in the brain. Recent research shows that neuronal TRPC1 forms heteromeric complexes with TRPC4 and TRPC5, with a small portion existing as homotetramers, primarily in the ER. Given that most studies have focused on the role of heteromeric TRPC1/4/5 complexes, it is crucial to investigate the specific role of homomeric TRPC1 in maintaining brain homeostasis. This review highlights recent findings on TRPC1 in the brain, with a focus on the hippocampus, and compiles the latest data on modulators and their binding sites within the TRPC1/4/5 subfamily to stimulate new research on more selective TRPC1 ligands.

Conservation of the cooling agent binding pocket within the TRPM subfamily

Transient Receptor Potential (TRP) channels are a large and diverse family of tetrameric cation selective channels that are activated by many different types of stimuli, including noxious heat or cold, organic ligands such as vanilloids or cooling agents, or intracellular Ca2+. Structures available for all subtypes of TRP channels reveal that the transmembrane domains are closely related despite their unique sensitivity to activating stimuli. Here we use computational and electrophysiological approaches to explore the conservation of the cooling agent binding pocket identified within the S1-S4 domain of the Melastatin subfamily member TRPM8, the mammalian sensor of noxious cold, with other TRPM channel subtypes. We find that a subset of TRPM channels, including TRPM2, TRPM4 and TRPM5, contain well-conserved cooling agent binding pockets. We then show how the cooling agent icilin modulates activation of TRPM4 to intracellular Ca2+, enhancing the sensitivity of the channel to Ca2+ and diminishing outward-rectification to promote opening at negative voltages. Mutations known to promote or diminish activation of TRPM8 by icilin similarly alter activation of TRPM4 by the cooling agent, suggesting that icilin binds to the cooling agent binding pocket to promote opening of the channel. These findings demonstrate that TRPM4 and TRPM8 channels share related cooling agent binding pockets that are allosterically coupled to opening of the pore.

Redox-Regulated Synthetic Channels: Enabling Reversible Ion Transport by Modulating the Ion-Permeation Pathway

Natural redox-regulated channel proteins often utilize disulfide bonds as redox sensors for adaptive regulation of channel conformations in response to diverse physiological environments. In this study, we developed novel synthetic ion channels capable of reversibly switching their ion-transport capabilities by incorporating multiple disulfide bonds into artificial systems. X-ray structural analysis and electrophysiological experiments demonstrated that these disulfide-bridged molecules possess well-defined tubular cavities and can be efficiently inserted into lipid bilayers to form artificial ion channels. More importantly, the disulfide bonds in these molecules serve as redox-tunable switches to regulate the formation and disruption of ion-permeation pathways, thereby achieving a transition in the transmembrane transport process between the ON and OFF states.

Small molecules targeting canonical transient receptor potential channels: an update

Transient receptor potential canonical (TRPC) channels belong to an important class of non-selective cation channels. This channel family consists of multiple members that widely participate in various physiological and pathological processes. Previous studies have uncovered the intricate regulation of these channels, as well as the spatial arrangement of TRPCs and the binding sites for various small molecule compounds. Multiple small molecules have been identified as selective agonists or inhibitors targeting different subtypes of TRPC, including potential preclinical drug candidates. This review covers recent advancements in the understanding of TRPC regulation and structure and the discovery of TRPC small molecules over the past few years, with the aim of facilitating research on TRPCs and small-molecule drug discovery.

Canonical transient receptor potential channels and hypothalamic control of homeostatic functions

Recent molecular biological and electrophysiological studies have identified multiple transient receptor potential (TRP) channels in hypothalamic neurons as critical modulators of homeostatic functions. In particular, the canonical transient receptor potential channels (TRPCs) are expressed in hypothalamic neurons that are vital for the control of fertility and energy homeostasis. Classical neurotransmitters such as serotonin and glutamate and peptide neurotransmitters such as kisspeptin, neurokinin B and pituitary adenylyl cyclase-activating polypeptide signal through their cognate G protein-coupled receptors to activate TPRC 4, 5 channels, which are essentially ligand-gated calcium channels. In addition to neurotransmitters, circulating hormones like insulin and leptin signal through insulin receptor (InsR) and leptin receptor (LRb), respectively, to activate TRPC 5 channels in hypothalamic arcuate nucleus pro-opiomelanocortin (POMC) and kisspeptin (arcuate Kiss1 [Kiss1ARH]) neurons to have profound physiological (excitatory) effects. Besides its overt depolarizing effects, TRPC channels conduct calcium ions into the cytoplasm, which has a plethora of downstream effects. Moreover, not only the expression of Trpc5 mRNA but also the coupling of receptors to TRPC 5 channel opening are regulated in different physiological states. In particular, the mRNA expression of Trpc5 is highly regulated in kisspeptin neurons by circulating estrogens, which ultimately dictates the firing pattern of kisspeptin neurons. In obesity states, InsRs are "uncoupled" from opening TRPC 5 channels in POMC neurons, rendering them less excitable. Therefore, in this review, we will focus on the critical role of TRPC 5 channels in regulating the excitability of Kiss1ARH and POMC neurons in different physiological and pathological states.

Phosphoinositide Regulation of TRP Channels: A Functional Overview in the Structural Era

Transient receptor potential (TRP) ion channels have diverse activation mechanisms including physical stimuli, such as high or low temperatures, and a variety of intracellular signaling molecules. Regulation by phosphoinositides and their derivatives is their only known common regulatory feature. For most TRP channels, phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] serves as a cofactor required for activity. Such dependence on PI(4,5)P2 has been demonstrated for members of the TRPM subfamily and for the epithelial TRPV5 and TRPV6 channels. Intracellular TRPML channels show specific activation by PI(3,5)P2. Structural studies uncovered the PI(4,5)P2 and PI(3,5)P2 binding sites for these channels and shed light on the mechanism of channel opening. PI(4,5)P2 regulation of TRPV1-4 as well as some TRPC channels is more complex, involving both positive and negative effects. This review discusses the functional roles of phosphoinositides in TRP channel regulation and molecular insights gained from recent cryo-electron microscopy structures.

Direct modulation of TRPC ion channels by Gα proteins

GPCR-Gi protein pathways are involved in the regulation of vagus muscarinic pathway under physiological conditions and are closely associated with the regulation of internal visceral organs. The muscarinic receptor-operated cationic channel is important in GPCR-Gi protein signal transduction as it decreases heart rate and increases GI rhythm frequency. In the SA node of the heart, acetylcholine binds to the M2 receptor and the released Gβγ activates GIRK (I(K,ACh)) channel, inducing a negative chronotropic action. In gastric smooth muscle, there are two muscarinic acetylcholine receptor (mAChR) subtypes, M2 and M3. M2 receptor activates the muscarinic receptor-operated nonselective cationic current (mIcat, NSCC(ACh)) and induces positive chronotropic effect. Meanwhile, M3 receptor induces hydrolysis of PIP2 and releases DAG and IP3. This IP3 increases intracellular Ca2+ and then leads to contraction of GI smooth muscles. The activation of mIcat is inhibited by anti-Gi/o protein antibodies in GI smooth muscle, indicating the involvement of Gαi/o protein in the activation of mIcat. TRPC4 channel is a molecular candidate for mIcat and can be directly activated by constitutively active Gαi QL proteins. TRPC4 and TRPC5 belong to the same subfamily and both are activated by Gi/o proteins. Initial studies suggested that the binding sites for G protein exist at the rib helix or the CIRB domain of TRPC4/5 channels. However, recent cryo-EM structure showed that IYY58-60 amino acids at ARD of TRPC5 binds with Gi3 protein. Considering the expression of TRPC4/5 in the brain, the direct G protein activation on TRPC4/5 is important in terms of neurophysiology. TRPC4/5 channels are also suggested as a coincidence detector for Gi and Gq pathway as Gq pathway increases intracellular Ca2+ and the increased Ca2+ facilitates the activation of TRPC4/5 channels. More complicated situation would occur when GIRK, KCNQ2/3 (IM) and TRPC4/5 channels are co-activated by stimulation of muscarinic receptors at the acetylcholine-releasing nerve terminals. This review highlights the effects of GPCR-Gi protein pathway, including dopamine, μ-opioid, serotonin, glutamate, GABA, on various oragns, and it emphasizes the importance of considering TRPC4/5 channels as crucial players in the field of neuroscience.

Structural and accessibility studies highlight the differential binding of clemizole to TRPC5 and TRPC6

Transient Receptor Potential Canonical 5 (T RP C5) and T RP C6 channels play critical physiological roles in various cell types. Their involvement in numerous disease progression mechanisms has led to extensive searches for their inhibitors. Although several potent T RP C inhibitors have been developed and the structure of their binding sites were mapped using cryo electron microscopy, a comprehensive understanding of the molecular interactions within the inhibitor binding site of T RP Cs remains elusive. This study aimed to decipher the structural determinants and molecular mechanisms contributing to the differential binding of clemizole to T RP C5 and T RP C6, with a particular focus on the accessibility of binding site residues. This information can help better understand what molecular features allow for selective binding, which is a key characteristic of clinically effective pharmacological agents. Using computational methodologies, we conducted an in-depth molecular docking analysis of clemizole with T RP C5 and T RP C6 channels. The protein structures were retrieved from publicly accessible protein databases. Discovery Studio 2020 Client Visualizer and Chimera software facilitated our in-silico mutation experiments and enabled us to identify the critical structural elements influencing clemizole binding. Our study reveals key molecular determinants at the clemizole binding site, specifically outlining the role of residues' Accessible Surface Area (ASA) and Relative Accessible Surface Area (RASA) in differential binding. We found that lower accessibility of T RP C6 binding site residues, compared to those in T RP C5, could account for the lower affinity binding of clemizole to T RP C6. This work illuminates the pivotal role of binding site residue accessibility in determining the affinity of clemizole to T RP C5 and T RP C6. A nuanced understanding of the distinct binding properties between these homologous proteins may pave the way for the development of more selective inhibitors, promising improved therapeutic efficacy and fewer off-target effects. By demystifying the structural and molecular subtleties of T RP C inhibitors, this research could significantly accelerate the drug discovery process, offering hope to patients afflicted with T RP C-related diseases.

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.

Human Transient Receptor Potential Ankyrin 1 Channel: Structure, Function, and Physiology

The transient receptor potential ion channel TRPA1 is a Ca2+-permeable nonselective cation channel widely expressed in sensory neurons, but also in many nonneuronal tissues typically possessing barrier functions, such as the skin, joint synoviocytes, cornea, and the respiratory and intestinal tracts. Here, the primary role of TRPA1 is to detect potential danger stimuli that may threaten the tissue homeostasis and the health of the organism. The ability to directly recognize signals of different modalities, including chemical irritants, extreme temperatures, or osmotic changes resides in the characteristic properties of the ion channel protein complex. Recent advances in cryo-electron microscopy have provided an important framework for understanding the molecular basis of TRPA1 function and have suggested novel directions in the search for its pharmacological regulation. This chapter summarizes the current knowledge of human TRPA1 from a structural and functional perspective and discusses the complex allosteric mechanisms of activation and modulation that play important roles under physiological or pathophysiological conditions. In this context, major challenges for future research on TRPA1 are outlined.

Voltage-gated potassium channels KCNQs: Structures, mechanisms, and modulations

KCNQ (Kv7) channels are voltage-gated, phosphatidylinositol 4,5-bisphosphate- (PIP2-) modulated potassium channels that play essential roles in regulating the activity of neurons and cardiac myocytes. Hundreds of mutations in KCNQ channels are closely related to various cardiac and neurological disorders, such as long QT syndrome, epilepsy, and deafness, which makes KCNQ channels important drug targets. During the past several years, the application of single-particle cryo-electron microscopy (cryo-EM) technique in the structure determination of KCNQ channels has greatly advanced our understanding of their molecular mechanisms. In this review, we summarize the currently available structures of KCNQ channels, analyze their special voltage gating mechanism, and discuss their activation mechanisms by both the endogenous membrane lipid and the exogenous synthetic ligands. These structural studies of KCNQ channels will guide the development of drugs targeting KCNQ channels.

Calcium transport and sensing in TRPC channels - New insights into a complex feedback regulation

Canonical TRP (TRPC) channels are a still enigmatic family of signaling molecules with multimodal sensing features. These channels enable Ca2+ influx through the plasma membrane to control a diverse range of cellular functions. Based on both regulatory- and recently uncovered structural features, TRPC channels are considered to coordinate Ca2+ and other divalent cations not only within the permeation path but also at additional sensory sites. Analysis of TRPC structures by cryo-EM identified multiple regulatory ion binding pockets. With this review, we aim at an overview and a critical discussion of the current concepts of divalent sensing by TRPC channels.

Discovery of potential novel TRPC5 inhibitors by virtual screening and bioassay

The transient receptor potential canonical channel 5 (TRPC5), a member of the TRPC family, plays a crucial role in the regulation of various physiological activities and diseases, including those related to the central nervous system, cardiovascular system, kidney, and cancer. As a nonselective cation channel, TRPC5 mainly controls the influx of extracellular Ca2+ into cells, thereby modulating cellular depolarization and intracellular ion concentration. Inhibition of TRPC5 by small molecules presents a promising approach for the treatment of TRPC5-associated diseases. In this study, we conducted a comprehensive virtual screening of more than 1.5 million molecules from the Chemdiv database (https://www.chemdiv.com) to identify potential inhibitors of hTRPC5, utilizing the published structures and binding sites of hTRPC5 as a basis. Lipinski's rule, Veber's rule, PAINS filters, pharmacophore analysis, molecular docking, ADMET evaluation and cluster analysis methods were applied for the screening. From this rigorous screening process, 18 candidates exhibiting higher affinities to hTRPC5 were subsequently evaluated for their inhibitory effects on Ca2+ influx using a fluorescence-based assay. Notably, two molecules, namely SML-1 and SML-13, demonstrated significant inhibition of intracellular Ca2+ levels in hTRPC5-overexpressing HEK 293T cells, with IC50 values of 10.2 μM and 10.3 μM, respectively. These findings highlight SML-1 and SML-13 as potential lead molecules for the development of therapeutics targeting hTRPC5 and its associated physiological activities and diseases.

Modulation and Regulation of Canonical Transient Receptor Potential 3 (TRPC3) Channels

Canonical transient receptor potential 3 (TRPC3) channel is a non-selective cation permeable channel that plays an essential role in calcium signalling. TRPC3 is highly expressed in the brain and also found in endocrine tissues and smooth muscle cells. The channel is activated directly by binding of diacylglycerol downstream of G-protein coupled receptor activation. In addition, TRPC3 is regulated by endogenous factors including Ca2+ ions, other endogenous lipids, and interacting proteins. The molecular and structural mechanisms underlying activation and regulation of TRPC3 are incompletely understood. Recently, several high-resolution cryogenic electron microscopy structures of TRPC3 and the closely related channel TRPC6 have been resolved in different functional states and in the presence of modulators, coupled with mutagenesis studies and electrophysiological characterisation. Here, we review the recent literature which has advanced our understanding of the complex mechanisms underlying modulation of TRPC3 by both endogenous and exogenous factors. TRPC3 plays an important role in Ca2+ homeostasis and entry into cells throughout the body, and both pathological variants and downstream dysregulation of TRPC3 channels have been associated with a number of diseases. As such, TRPC3 may be a valuable therapeutic target, and understanding its regulatory mechanisms will aid future development of pharmacological modulators of the channel.

TRP (transient receptor potential) ion channel family: structures, biological functions and therapeutic interventions for diseases

Transient receptor potential (TRP) channels are sensors for a variety of cellular and environmental signals. Mammals express a total of 28 different TRP channel proteins, which can be divided into seven subfamilies based on amino acid sequence homology: TRPA (Ankyrin), TRPC (Canonical), TRPM (Melastatin), TRPML (Mucolipin), TRPN (NO-mechano-potential, NOMP), TRPP (Polycystin), TRPV (Vanilloid). They are a class of ion channels found in numerous tissues and cell types and are permeable to a wide range of cations such as Ca²⁺, Mg²⁺, Na⁺, K⁺, and others. TRP channels are responsible for various sensory responses including heat, cold, pain, stress, vision and taste and can be activated by a number of stimuli. Their predominantly location on the cell surface, their interaction with numerous physiological signaling pathways, and the unique crystal structure of TRP channels make TRPs attractive drug targets and implicate them in the treatment of a wide range of diseases. Here, we review the history of TRP channel discovery, summarize the structures and functions of the TRP ion channel family, and highlight the current understanding of the role of TRP channels in the pathogenesis of human disease. Most importantly, we describe TRP channel-related drug discovery, therapeutic interventions for diseases and the limitations of targeting TRP channels in potential clinical applications.

Molecular architecture of the Gαi-bound TRPC5 ion channel

G-protein coupled receptors (GPCRs) and ion channels serve as key molecular switches through which extracellular stimuli are transformed into intracellular effects, and it has long been postulated that ion channels are direct effector molecules of the alpha subunit of G-proteins (Gα). However, no complete structural evidence supporting the direct interaction between Gα and ion channels is available. Here, we present the cryo-electron microscopy structures of the human transient receptor potential canonical 5 (TRPC5)-Gα_i3 complexes with a 4:4 stoichiometry in lipid nanodiscs. Remarkably, Gα_i3 binds to the ankyrin repeat edge of TRPC5 ~ 50 Å away from the cell membrane. Electrophysiological analysis shows that Gα_i3 increases the sensitivity of TRPC5 to phosphatidylinositol 4,5-bisphosphate (PIP₂), thereby rendering TRPC5 more easily opened in the cell membrane, where the concentration of PIP₂ is physiologically regulated. Our results demonstrate that ion channels are one of the direct effector molecules of Gα proteins triggered by GPCR activation-providing a structural framework for unraveling the crosstalk between two major classes of transmembrane proteins: GPCRs and ion channels.

Radiosynthesis and Evaluation of a C-11 Radiotracer for Transient Receptor Potential Canonical 5 in the Brain

PURPOSE

TRPC5 belongs to the mammalian superfamily of transient receptor potential (TRP) Ca2+-permeable cationic channels and it has been implicated in various CNS disorders. As part of our ongoing interest in the development of a PET radiotracer for imaging TRPC5, herein, we explored the radiosynthesis, and in vitro and in vivo evaluation of a new C-11 radiotracer [11C]HC070 in rodents and nonhuman primates.

PROCEDURES

[11C]HC070 was radiolabeled utilizing the corresponding precursor and [11C]CH3I via N-methylation protocol. Ex vivo biodistribution study of [11C]HC070 was performed in Sprague-Dawley rats. In vitro autoradiography study was conducted for the rat brain sections to characterize the radiotracer distribution in the brain regionals. MicroPET brain imaging studies of [11C]HC070 were done for 129S1/SvImJ wild-type mice and 129S1/SvImJ TRPC5 knockout mice for 0-60-min dynamic data acquisition after intravenous administration of the radiotracer. Dynamic PET scans (0-120 min) for the brain of cynomolgus male macaques were performed after the radiotracer injection.

RESULTS

[11C]HC070 was efficiently prepared with good radiochemical yield (45 ± 5%, n = 15), high chemical and radiochemical purity (> 99%), and high molar activity (320.6 ± 7.4 GBq/μmol, 8.6 ± 0.2 Ci/μmol) at the end of bombardment (EOB). Radiotracer [11C]HC070 has good solubility in the aqueous dose solution. The ex vivo biodistribution study showed that [11C]HC070 had a quick rat brain clearance. Autoradiography demonstrated that [11C]HC070 specifically binds to TRPC5-enriched regions in rat brain. MicroPET study showed the peak brain uptake (SUV value) was 0.63 in 129S1/SvImJ TRPC5 knockout mice compared to 1.13 in 129S1/SvImJ wild-type mice. PET study showed that [11C]HC070 has good brain uptake with maximum SUV of ~ 2.2 in the macaque brain, followed by rapid clearance.

CONCLUSIONS

Our data showed that [11C]HC070 is a TRPC5-specific radiotracer with high brain uptake and good brain washout pharmacokinetics in both rodents and nonhuman primates. The radiotracer is worth further investigating of its suitability to be a PET radiotracer for imaging TRPC5 in animals and human subjects in vivo.

Hydrophobic interactions within the C terminus pole helices tunnel regulate calcium-dependent inactivation of TRPC3 in a calmodulin-dependent manner

Recent structural studies have shown that the carboxyl-terminus of many TRP channels, including TRPC3, are folded into a horizontal rib helix that is connected to the vertical pole helix, which play roles in inter-structural interactions and multimerization. In a previous work we identified I807 located in the pole helix with a role in regulation of TRPC3 by STIM1 (Lee et al., 2014, Liu et al., 2022). To further determine the role of the pole helix in TRPC3 function, here we identified key hydrophobic residues in the pole helix that form tight tunnel-like structure and used mutations to probe their role in TRPC3 regulation by Ca2+ and Calmodulin. Our findings suggest that the hydrophobic starch formed by the I807-L818 residues has several roles, it modulates gating of TRPC3 by Ca2+, affects channel selectivity and the channel Ca2+ permeability. Mutations of I807, I811, L814 and L818 all attenuated the Ca2+-dependent inactivation (CDI) of TRPC3, with I807 having the most prominent effect. The extent of modulation of the CDI depended on the degree of hydrophobicity of I807. Moreover, the TRPC3(I807S) mutant showed altered channel monovalent ion selectivity and increased Ca2+ permeability, without affecting the channel permeability to Mg2+ and Ba2+ and without changing the pore diameter. The CDI of TRPC3 was reduced by an inactive calmodulin mutant and by a pharmacological inhibitor of calmodulin, which was eliminated by the I807S mutation. Notably, deletion of STIM1 caused similar alteration of TRPC3 properties. Taken together, these findings reveal a role of the pole helix in CDI, in addition to its potential role in channel multimerization that required gating of TRPC3 by STIM1. Since all TRPC and most TRP channels have pole helix structures, our findings raise the possibility that the pole helix may have similar roles in all the TRP family.

Modulation of TRPV2 by endogenous and exogenous ligands: A computational study

Transient receptor potential vanilloid (TRPV) channels play various important roles in human physiology. As membrane proteins, these channels are modulated by their endogenous lipid environment as the recent wealth of structural studies has revealed functional and structural lipid binding sites. Additionally, it has been shown that exogenous ligands can exchange with some of these lipids to alter channel gating. Here, we used molecular dynamics simulations to examine how one member of the TRPV family, TRPV2, interacts with endogenous lipids and the pharmacological modulator cannabidiol (CBD). By computationally reconstituting TRPV2 into a typical plasma membrane environment, which includes phospholipids, cholesterol, and phosphatidylinositol (PIP) in the inner leaflet, we showed that most of the interacting surface lipids are phospholipids without strong specificity for headgroup types. Intriguingly, we observed that the C-terminal membrane proximal region of the channel binds preferentially to PIP lipids. We also modelled two structural lipids in the simulation: one in the vanilloid pocket and the other in the voltage sensor-like domain (VSLD) pocket. The simulation shows that the VSLD lipid dampens the fluctuation of the VSLD residues, while the vanilloid lipid exhibits heterogeneity both in its binding pose and in its influence on protein dynamics. Addition of CBD to our simulation system led to an open selectivity filter and a structural rearrangement that includes a clockwise rotation of the ankyrin repeat domains, TRP helix, and VSLD. Together, these results reveal the interplay between endogenous lipids and an exogenous ligand and their effect on TRPV2 stability and channel gating.

Subunit composition, molecular environment, and activation of native TRPC channels encoded by their interactomes

In the mammalian brain TRPC channels, a family of Ca²⁺-permeable cation channels, are involved in a variety of processes from neuronal growth and synapse formation to transmitter release, synaptic transmission and plasticity. The molecular appearance and operation of native TRPC channels, however, remained poorly understood. Here, we used high-resolution proteomics to show that TRPC channels in the rodent brain are macro-molecular complexes of more than 1 MDa in size that result from the co-assembly of the tetrameric channel core with an ensemble of interacting proteins (interactome). The core(s) of TRPC1-, C4-, and C5-containing channels are mostly heteromers with defined stoichiometries for each subtype, whereas TRPC3, C6, and C7 preferentially form homomers. In addition, TRPC1/C4/C5 channels may co-assemble with the metabotropic glutamate receptor mGluR1, thus guaranteeing both specificity and reliability of channel activation via the phospholipase-Ca²⁺ pathway. Our results unveil the subunit composition of native TRPC channels and resolve the molecular details underlying their activation.

[Overexpression of miR-607 inhibits hepatocellular carcinoma cell growth and metastasis by down-regulating TRPC5]

OBJECTIVE

To investigate the clinical implications of abnormal expression of miR-607 in hepatocellular carcinoma (HCC) and its influence on HCC cell proliferation and migration.

METHODS

The expression of miR-607 in 45 pairs of HCC and adjacent tissues were detected with real-time PCR, and the correlation between miR-607 expression and clinicopathological features of the patients was analyzed. The effects of transfection with miR-607 mimics on proliferation, apoptosis, migration and invasion of two HCC cell lines (Huh-7 and HCCLM3) were evaluated using CCK-8 assay, flow cytometry, wound-healing assay and Transwell assay. A dual-luciferase reporter system was used to detect the direct binding between miR-607 and 3'-UTR of TRPC5 mRNA. Western blotting was used to measure the expressions of TRPC5, CCND1, MMP2 and phosphorylated Akt in the HCC cells.

RESULTS

The expression of miR-607 was significantly decreased in HCC tissues (P=0.029) and HCC cell lines (P < 0.05). In HCC patients, a low expression of miR-607 was associated with a larger tumor size (>5 cm, P=0.031), vascular invasion (P=0.027) and advanced TNM stages (Ⅲ + Ⅳ, P=0.015). In the two HCC cell line, overexpression of miR-607 significantly inhibited cell proliferation, migration, and invasion and enhanced cell apoptosis (P < 0.05). The results of dualluciferase reporter assay confirmed that TRPC5 was a direct target of miR- 607 in HCC cells. Overexpression of miR-607 significantly inhibited the expressions of TRPC5, CCND1, and MMP2 and suppressed Akt phosphorylation in HCC cells (P < 0.05).

CONCLUSION

A low expression of miR-607 in HCC is associated with poor clinicopathological phenotypes of HCC. Overexpression of miR-607 inhibits HCC growth and metastasis possibly by down- regulating TRPC5, which causes Akt signaling inactivation.

Interactions between the Polysialylated Neural Cell Adhesion Molecule and the Transient Receptor Potential Canonical Channels 1, 4, and 5 Induce Entry of Ca2+ into Neurons

The neural cell adhesion molecule (NCAM) plays important functional roles in the developing and mature nervous systems. Here, we show that the transient receptor potential canonical (TRPC) ion channels TRPC1, -4, and -5 not only interact with the intracellular domains of the transmembrane isoforms NCAM140 and NCAM180, but also with the glycan polysialic acid (PSA) covalently attached to the NCAM protein backbone. NCAM antibody treatment leads to the opening of TRPC1, -4, and -5 hetero- or homomers at the plasma membrane and to the influx of Ca²⁺ into cultured cortical neurons and CHO cells expressing NCAM, PSA, and TRPC1 and -4 or TRPC1 and -5. NCAM-stimulated Ca²⁺ entry was blocked by the TRPC inhibitor Pico145 or the bacterial PSA homolog colominic acid. NCAM-stimulated Ca²⁺ influx was detectable neither in NCAM-deficient cortical neurons nor in TRPC1/4- or TRPC1/5-expressing CHO cells that express NCAM, but not PSA. NCAM-induced neurite outgrowth was reduced by TRPC inhibitors and a function-blocking TRPC1 antibody. A characteristic signaling feature was that extracellular signal-regulated kinase 1/2 phosphorylation was also reduced by TRPC inhibitors. Our findings indicate that the interaction of NCAM with TRPC1, -4, and -5 contributes to the NCAM-stimulated and PSA-dependent Ca²⁺ entry into neurons thereby influencing essential neural functions.

TRPC channels as emerging targets for seizure disorders

Epilepsy is characterized by seizures of diverse types that affect about 1-2% of the population worldwide. Current antiseizure medications are unsatisfactory, as they merely provide symptomatic relief, are ineffective in about one-third of patients, and cause unbearable adverse effects. Transient receptor potential canonical (TRPC) channels are a group of nonselective cation channels involved in many physiological functions. In this review, we provide an overview of recent preclinical studies using both genetic and pharmacological strategies that reveal these receptor-operated calcium-permeable channels may also play fundamental roles in many aspects of epileptic seizures. We also propose that TRPC channels represent appealing targets for epilepsy treatment, with a goal of helping to advance the discovery and development of new antiseizure and/or antiepileptogenic therapies.

TRP channel function in platelets and megakaryocytes: basic mechanisms and pathophysiological impact

Transient receptor potential (TRP) proteins form a superfamily of cation channels that are expressed in a wide range of tissues and cell types. During the last years, great progress has been made in understanding the molecular complexity and the functions of TRP channels in diverse cellular processes, including cell proliferation, migration, adhesion and activation. The diversity of functions depends on multiple regulatory mechanisms by which TRP channels regulate Ca²⁺ entry mechanisms and intracellular Ca²⁺ dynamics, either through membrane depolarization involving cation influx or store- and receptor-operated mechanisms. Abnormal function or expression of TRP channels results in vascular pathologies, including hypertension, ischemic stroke and inflammatory disorders through effects on vascular cells, including the components of blood vessels and platelets. Moreover, some TRP family members also regulate megakaryopoiesis and platelet production, indicating a complex role of TRP channels in pathophysiological conditions. In this review, we describe potential roles of TRP channels in megakaryocytes and platelets, as well as their contribution to diseases such as thrombocytopenia, thrombosis and stroke. We also critically discuss the potential of TRP channels as possible targets for disease prevention and treatment.

Activity dependent inhibition of TRPC1/4/5 channels by duloxetine involves voltage sensor-like domain

Transient receptor potential canonical 5 (TRPC5) is a polymodal, calcium-permeable, nonselective ion channel that is expressed in the brain and 75 % of human sensory neurons. Its pharmacological or genetic inhibition leads to the relief of neuropathic and inflammatory pain. The clinically approved drug duloxetine is superior to other serotonin and norepinephrine reuptake inhibitors at managing painful neuropathies, but it is not known why. Here we ask whether the TRPC5 receptor is modulated by duloxetine and may contribute to its analgesic effect. Electrophysiological measurements of heterologously expressed human TRPC5 in HEK293T cells were performed to evaluate the effect of duloxetine. The interaction site was identified by molecular docking and molecular dynamics simulations in combination with point mutagenesis. We found that duloxetine inhibits TRPC5 in a concentration-dependent manner with a high potency (IC₅₀ = 0.54 ± 0.03 µM). Our data suggest that duloxetine binds into a voltage sensor-like domain. For the interaction, Glu⁴¹⁸ exhibited particular importance due to putative hydrogen bond formation. Duloxetine effectively inhibits TRPC5 currents induced by cooling, voltage, direct agonists and by the stimulation of the PLC pathway. The finding that this TRPC5 inhibitor is widely used and well tolerated provides a scaffold for new pain treatment strategies.

TRP channels: a journey towards a molecular understanding of pain

The perception of nociceptive signals, which are translated into pain, plays a fundamental role in the survival of organisms. Because pain is linked to a negative sensation, animals learn to avoid noxious signals. These signals are detected by receptors, which include some members of the transient receptor potential (TRP) family of ion channels that act as transducers of exogenous and endogenous noxious cues. These proteins have been in the focus of the field of physiology for several years, and much knowledge of how they regulate the function of the cell types and organs where they are expressed has been acquired. The last decade has been especially exciting because the 'resolution revolution' has allowed us to learn the molecular intimacies of TRP channels using cryogenic electron microscopy. These findings, in combination with functional studies, have provided insights into the role played by these channels in the generation and maintenance of pain.

Diacylglycerols interact with the L2 lipidation site in TRPC3 to induce a sensitized channel state

Coordination of lipids within transient receptor potential canonical channels (TRPCs) is essential for their Ca2+ signaling function. Single particle cryo-EM studies identified two lipid interaction sites, designated L1 and L2, which are proposed to accommodate diacylglycerols (DAGs). To explore the role of L1 and L2 in TRPC3 function, we combined structure-guided mutagenesis and electrophysiological recording with molecular dynamics (MD) simulations. MD simulations indicate rapid DAG accumulation within both L1 and L2 upon its availability within the plasma membrane. Electrophysiological experiments using a photoswitchable DAG-probe reveal potentiation of TRPC3 currents during repetitive activation by DAG. Importantly, initial DAG exposure generates a subsequently sensitized channel state that is associated with significantly faster activation kinetics. TRPC3 sensitization is specifically promoted by mutations within L2, with G652A exhibiting sensitization at very low levels of active DAG. We demonstrate the ability of TRPC3 to adopt a closed state conformation that features partial lipidation of L2 sites by DAG and enables fast activation of the channel by the phospholipase C-DAG pathway.

Simulation and Machine Learning Methods for Ion-Channel Structure Determination, Mechanistic Studies and Drug Design

Ion channels are expressed in almost all living cells, controlling the in-and-out communications, making them ideal drug targets, especially for central nervous system diseases. However, owing to their dynamic nature and the presence of a membrane environment, ion channels remain difficult targets for the past decades. Recent advancement in cryo-electron microscopy and computational methods has shed light on this issue. An explosion in high-resolution ion channel structures paved way for structure-based rational drug design and the state-of-the-art simulation and machine learning techniques dramatically improved the efficiency and effectiveness of computer-aided drug design. Here we present an overview of how simulation and machine learning-based methods fundamentally changed the ion channel-related drug design at different levels, as well as the emerging trends in the field.

Cellular context determines primary characteristics of human TRPC5 as a cold-activated channel

The human transient receptor potential canonical 5 (TRPC5) is a calcium-permeable, nonselective cation channel expressed in the central and peripheral nervous system and also in other tissues such as the kidney, synovium, and odontoblasts. TRPC5 has been recently confirmed to play a key role in spontaneous, inflammatory mechanical, and cold pain. Although TRPC5 activation is known to be cold sensitive, it is unclear whether this property is intrinsic to the channel protein and whether or to what extent it may be determined by the cellular environment. In this study, we explored the cold sensitivity of human TRPC5 at the single-channel level using transiently transfected HEK293T cells. Upon decreasing the temperature, the channel demonstrated prolonged mean open dwell times and a robust increase in the open probability (P_o ), whereas the amplitude of unitary currents decreased ~1.5-fold per 10°C of temperature difference. In the absence of any agonists, the temperature dependence of P_o was sigmoidal, with a steep slope within the temperature range of 16°C-11°C, and exhibited saturation below 8-5°C. Thermodynamic analysis revealed significant changes in enthalpy and entropy, suggesting that substantial conformational changes accompany cold-induced gating. The mutant channel T970A, in which the regulation downstream of G-protein coupled receptor signaling was abrogated, exhibited higher basal activity at room temperature and a less steep temperature response profile, with an apparent threshold below 22°C. An even more pronounced decrease in the activation threshold was observed in a mutant that disrupted the electrostatic interaction of TRPC5 with the endoplasmic reticulum calcium sensor stromal interaction molecule 1. Thus, TRPC5 exhibits features of an intrinsically cold-gated channel; its sensitivity to cold tightly depends on the phosphorylation status of the protein and intracellular calcium homeostasis.

Sequence and structural conservation reveal fingerprint residues in TRP channels

Transient receptor potential (TRP) proteins are a large family of cation-selective channels, surpassed in variety only by voltage-gated potassium channels. Detailed molecular mechanisms governing how membrane voltage, ligand binding, or temperature can induce conformational changes promoting the open state in TRP channels are still a matter of debate. Aiming to unveil distinctive structural features common to the transmembrane domains within the TRP family, we performed phylogenetic reconstruction, sequence statistics, and structural analysis over a large set of TRP channel genes. Here, we report an exceptionally conserved set of residues. This fingerprint is composed of twelve residues localized at equivalent three-dimensional positions in TRP channels from the different subtypes. Moreover, these amino acids are arranged in three groups, connected by a set of aromatics located at the core of the transmembrane structure. We hypothesize that differences in the connectivity between these different groups of residues harbor the apparent differences in coupling strategies used by TRP subgroups.

Ligand-Binding Sites in Vanilloid-Subtype TRP Channels

Vanilloid-subfamily TRP channels TRPV1-6 play important roles in various physiological processes and are implicated in numerous human diseases. Advances in structural biology, particularly the "resolution revolution" in cryo-EM, have led to breakthroughs in molecular characterization of TRPV channels. Structures with continuously improving resolution uncover atomic details of TRPV channel interactions with small molecules and protein-binding partners. Here, we provide a classification of structurally characterized binding sites in TRPV channels and discuss the progress that has been made by structural biology combined with mutagenesis, functional recordings, and molecular dynamics simulations toward understanding of the molecular mechanisms of ligand action. Given the similarity in structural architecture of TRP channels, 16 unique sites identified in TRPV channels may be shared between TRP channel subfamilies, although the chemical identity of a particular ligand will likely depend on the local amino-acid composition. The characterized binding sites and molecular mechanisms of ligand action create a diversity of druggable targets to aid in the design of new molecules for tuning TRP channel function in disease conditions.

TRPC3 channel gating by lipids requires localization at the ER/PM junctions defined by STIM1

TRPC3, a member of the transient receptor potential (TRP) superfamily of cation channels, is a lipid-regulated, Ca²⁺-permeable channel that mediates essential components of the receptor evoked Ca²⁺ signal. The modes and mechanisms by which lipids regulate TRPC3 and other members of the TRPC channel family are not well understood. Here, we report that PI(4,5)P₂ regulates TRPC3 in three independent modes. PLC-dependent hydrolysis generates diacylglycerol (DAG) that interacts with lipid-binding site 2 in the channel pore. PI(4,5)P₂ interacts with lipid site 1 to inhibit TRPC3 opening and regulate access of DAG to the pore lipid site 2. PI(4,5)P₂ is required for regulating pore ionic selectivity by receptor stimulation. Notably, the activation and regulation of TRPC3 by PI(4,5)P₂ require recruitment of TRPC3 to the ER/PM junctions at a PI(4,5)P₂-rich domain. Accordingly, we identified an FFAT site at the TRPC3 N-terminal loop within the linker helices that envelope the C-terminus pole helix. The FFAT site interacts with the ER-resident VAPB to recruit TRPC3 to the ER/PM junctions and control its receptor-mediated activation. The TRPC3’s lipid interacting sites are fully conserved in TRPC6 and TRPC7 and in part in other TRPC channels. These findings inform on multiple modes of regulation of ion channels by lipids that may be relevant to diseases affected by aberrant TRPC channel functions.

The Role of Membrane Lipids in Light-Activation of Drosophila TRP Channels

Transient Receptor Potential (TRP) channels constitute a large superfamily of polymodal channel proteins with diverse roles in many physiological and sensory systems that function both as ionotropic and metabotropic receptors. From the early days of TRP channel discovery, membrane lipids were suggested to play a fundamental role in channel activation and regulation. A prominent example is the Drosophila TRP and TRP-like (TRPL) channels, which are predominantly expressed in the visual system of Drosophila. Light activation of the TRP and TRPL channels, the founding members of the TRP channel superfamily, requires activation of phospholipase Cβ (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP₂) into Diacylglycerol (DAG) and Inositol 1, 4,5-trisphosphate (IP₃). However, the events required for channel gating downstream of PLC activation are still under debate and led to several hypotheses regarding the mechanisms by which lipids gate the channels. Despite many efforts, compelling evidence of the involvement of DAG accumulation, PIP₂ depletion or IP₃-mediated Ca²⁺ release in light activation of the TRP/TRPL channels are still lacking. Exogeneous application of poly unsaturated fatty acids (PUFAs), a product of DAG hydrolysis was demonstrated as an efficient way to activate the Drosophila TRP/TRPL channels. However, compelling evidence for the involvement of PUFAs in physiological light-activation of the TRP/TRPL channels is still lacking. Light-induced mechanical force generation was measured in photoreceptor cells prior to channel opening. This mechanical force depends on PLC activity, suggesting that the enzymatic activity of PLC converting PIP₂ into DAG generates membrane tension, leading to mechanical gating of the channels. In this review, we will present the roles of membrane lipids in light activation of Drosophila TRP channels and present the many advantages of this model system in the exploration of TRP channel activation under physiological conditions.

Discovery of pyridazinone analogs as potent transient receptor potential canonical channel 5 inhibitors

A deepening understanding of the relationship between transient receptor potential canonical channel 5 (TRPC5) and chronic kidney disease (CKD), has led to the emergence of several types of TRPC5 inhibitors displaying clear therapeutic effect. Herein, we report the synthesis and biological evaluation of a series of pyrroledione TRPC5 inhibitors, culminating in the discovery of compound 16g with subtype selectivity. Compared with GFB-8438, a potent TRPC5 inhibitor (Goldfinch Bio), compound 16g showed improved inhibition of TRPC5 and enhanced protective effect against protamine sulfates (PS)-induced podocyte injury in vitro. In addition, compound 16g did not induce cell death in primary cultured hepatocytes and immortalized podocytes in a preliminary toxicity assessment, indicating its utility as a potent and safe inhibitor for studying the function of TRPC5.

Nonselective TRPC channel inhibition and suppression of aminoglycoside-induced premature termination codon readthrough by the small molecule AC1903

Nonsense mutations, which occur in ∼11% of patients with genetic disorders, introduce premature termination codons (PTCs) that lead to truncated proteins and promote nonsense-mediated mRNA decay. Aminoglycosides such as G418 permit PTC readthrough and so may be used to address this problem. However, their effects are variable between patients, making clinical use of aminoglycosides challenging. In this study, we tested whether TRPC nonselective cation channels contribute to the variable PTC readthrough effect of aminoglycosides by controlling their cellular uptake. Indeed, a recently reported selective TRPC5 inhibitor, AC1903, consistently suppressed G418 uptake and G418-induced PTC readthrough in the DMS-114 cancer cell line and junctional epidermolysis bullosa (JEB) patient-derived keratinocytes. Interestingly, the effect of AC1903 in DMS-114 cells was mimicked by nonselective TRPC inhibitors, but not by well-characterized inhibitors of TRPC1/4/5 (Pico145, GFB-8438) or TRPC3/6/7 (SAR7334), suggesting that AC1903 may work through additional or undefined targets. Indeed, in our experiments, AC1903 inhibited multiple TRPC channels including TRPC3, TRPC4, TRPC5, TRPC6, TRPC4-C1, and TRPC5-C1, as well as endogenous TRPC1:C4 channels in A498 renal cancer cells, all with low micromolar IC50 values (1.8-18 μM). We also show that AC1903 inhibited TRPV4 channels, but had weak or no effects on TRPV1 and no effect on the nonselective cation channel PIEZO1. Our study reveals that AC1903 has previously unrecognized targets, which need to be considered when interpreting results from experiments with this compound. In addition, our data strengthen the hypothesis that nonselective calcium channels are involved in aminoglycoside uptake.

Structural mechanism of human TRPC3 and TRPC6 channel regulation by their intracellular calcium-binding sites

TRPC3 and TRPC6 channels are calcium-permeable non-selective cation channels that are involved in many physiological processes. The gain-of-function (GOF) mutations of TRPC6 lead to familial focal segmental glomerulosclerosis (FSGS) in humans, but their pathogenic mechanism remains elusive. Here, we report the cryo-EM structures of human TRPC3 in both high-calcium and low-calcium conditions. Based on these structures and accompanying electrophysiological studies, we identified both inhibitory and activating calcium-binding sites in TRPC3 that couple intracellular calcium concentrations to the basal channel activity. These calcium sensors are also structurally and functionally conserved in TRPC6. We uncovered that the GOF mutations of TRPC6 activate the channel by allosterically abolishing the inhibitory effects of intracellular calcium. Furthermore, structures of human TRPC6 in complex with two chemically distinct inhibitors bound at different ligand-binding pockets reveal different conformations of the transmembrane domain, providing templates for further structure-based drug design targeting TRPC6-related diseases such as FSGS.

Pharmacology of TRPC Channels and Its Potential in Cardiovascular and Metabolic Medicine

Transient receptor potential canonical (TRPC) proteins assemble to form homo- or heterotetrameric, nonselective cation channels permeable to K⁺, Na⁺, and Ca²⁺. TRPC channels are thought to act as complex integrators of physical and chemical environmental stimuli. Although the understanding of essential physiological roles of TRPC channels is incomplete, their implication in various pathological mechanisms and conditions of the nervous system, kidneys, and cardiovascular system in combination with the lack of major adverse effects of TRPC knockout or TRPC channel inhibition is driving the search of TRPC channel modulators as potential therapeutics. Here, we review the most promising small-molecule TRPC channel modulators, the understanding of their mode of action, and their potential in the study and treatment of cardiovascular and metabolic disease.

Transient receptor potential canonical 5 mediates inflammatory mechanical and spontaneous pain in mice

Tactile and spontaneous pains are poorly managed symptoms of inflammatory and neuropathic injury. Here, we found that transient receptor potential canonical 5 (TRPC5) is a chief contributor to both of these sensations in multiple rodent pain models. Use of TRPC5 knockout mice and inhibitors revealed that TRPC5 selectively contributes to the mechanical hypersensitivity associated with CFA injection, skin incision, chemotherapy induced peripheral neuropathy, sickle cell disease, and migraine, all of which were characterized by elevated concentrations of lysophosphatidylcholine (LPC). Accordingly, exogenous application of LPC induced TRPC5-dependent behavioral mechanical allodynia, neuronal mechanical hypersensitivity, and spontaneous pain in naïve mice. Lastly, we found that 75% of human sensory neurons express TRPC5, the activity of which is directly modulated by LPC. On the basis of these results, TRPC5 inhibitors might effectively treat spontaneous and tactile pain in conditions characterized by elevated LPC.

A greasy business: Identification of a diacylglycerol binding site in human TRPC5 channels by cryo-EM

The transient receptor potential classical or canonical (TRPC) 5 channel is a non-selective calcium-permeable cation channel that recently emerged as a promising target for the treatment of various diseases such as mental disorders and kidney diseases. Thus, detailed insight into the structural properties of TRPC5 channels is of utmost importance to further advance TRPC5 channels as drug targets. Recently, Song et al. (2021) have presented cryo-EM structures of the human TRPC5 channel alone or in complex with two different inhibitors thereby revealing two new distinct drug binding sites. Moreover, a binding site for the second messenger diacylglycerol (DAG) has been identified commensurate with a key role of DAG for TRPC5 channel activation.