Human TRPV1 Research Articles

Human TRPV1 is an efficient thermogenetic actuator for chronic neuromodulation

Thermogenetics is a promising neuromodulation technique based on the use of heat-sensitive ion channels. However, on the way to its clinical application, a number of questions have to be addressed. First, to avoid immune response in future human applications, human ion channels should be studied as thermogenetic actuators. Second, heating levels necessary to activate these channels in vivo in brain tissue should be studied and cytotoxicity of these temperatures addressed. Third, the possibility and safety of chronic neuromodulation has to be demonstrated. In this study, we present a comprehensive framework for thermogenetic neuromodulation in vivo using the thermosensitive human ion channel hTRPV1. By targeting hTRPV1 expression to excitatory neurons of the mouse brain and activating them within a non-harmful temperature range with a fiber-coupled infrared laser, we not only induced neuronal firing and stimulated locomotion in mice, but also demonstrated that thermogenetics can be employed for repeated neuromodulation without causing evident brain tissue injury. Our results lay the foundation for the use of thermogenetic neuromodulation in brain research and therapy of neuropathologies.

Interleukin-6 induces nascent protein synthesis in human dorsal root ganglion nociceptors primarily via MNK-eIF4E signaling

Plasticity of dorsal root ganglion (DRG) nociceptors in the peripheral nervous system requires new protein synthesis. This plasticity is believed to be responsible for the physiological changes seen in DRG nociceptors in animal models of chronic pain. Experiments in human DRG (hDRG) neurons also support this hypothesis, but a direct observation of nascent protein synthesis in response to a pain promoting substance, like interleukin-6 (IL-6), has not been measured in these neurons. To fill this gap in knowledge, we used acutely prepared human DRG explants from organ donors. These explants provide a physiologically relevant microenvironment, closer to in vivo conditions, allowing for the examination of functional alterations in DRG neurons reflective of human neuropathophysiology. Using this newly developed assay, we demonstrate upregulation of the target of the MNK1/2 kinases, phosphorylated eIF4E (p-eIF4E), and nascently synthesized proteins in a substantial subset of hDRG neurons following exposure to IL-6. To pinpoint the specific molecular mechanisms driving this IL-6-driven increase in nascent proteins, we used the specific MNK1/2 inhibitor eFT508. Treatment with eFT508 resulted in the inhibition of IL-6-induced increases in p-eIF4E and nascent proteins. Additionally, using TRPV1 as a marker for nociceptors, we found that these effects occurred in a large number of human nociceptors. Our findings provide clear evidence that IL-6 drives nascent protein synthesis in human TRPV1+ nociceptors primarily via MNK1/2-eIF4E signaling. The work links animal findings to human nociception, creates a framework for additional hDRG signaling experiments, and substantiates the continued development of MNK inhibitors for pain

Design and experimental validation of a new radiolabeled analog of N-(3-hydroxy-4-methoxy-phenyl-methyl) ferrocene-carboxamide (VFC) targeting the TRPV1 receptor

The TRPV1 receptor has been recognized to play a role in cancer development, being overexpressed in prostate, breast, lung, and colon cancers. Since TRPV1 activation promotes cancer cell proliferation, invasion, and migration, TRPV1 antagonists may show potential as anti-cancer agents. Capsaicin and capsaicinoids are phytochemicals derived from homovanillic acid found in abundance in chili peppers and responsible for its pungent properties. Capsaicin acts as a potent agonist of TRPV1 with recognized antineoplastic properties. Here, we employ computational approaches including molecular modeling and docking to refine the 3D structure of human TRPV1 and assess its interaction with the newly synthesized N-(3-hydroxy-4-methoxyphenylmethyl)ferrocenecarboxamide (VFC) and its cyclopentadienyl tricarbonyl rhenium and technetium analogs. Radiolabeling of VFC with 99mTc was achieved by double ligand exchange to afford 99mTc-VFC in high radiochemical purity and yield. Biodistribution studies in mice demonstrated preferential accumulation of 99mTc-VFC in the bladder, liver, kidney, and lung. These findings may contribute to developing efficient TRPV1-targeted radiotracers for molecular imaging of tumors by SPECT.

Subcutaneous administration of a novel TRPM8 antagonist reverses cold hypersensitivity while attenuating the drop in core body temperature.

We extend the characterization of the TRPM8 antagonist VBJ103 with tests of selectivity, specificity and distribution, therapeutic efficacy of systemic administration against oxaliplatin-induced cold hyperalgesia and the impact of systemic administration on core body temperature (CBT). Selectivity at human TRPA1 and TRPV1 as well as in vitro safety profiling was determined. Effects of systemic administration of VBJ103 were evaluated in a model of oxaliplatin-induced cold hyperalgesia. Both peripheral and centrally mediated effects of VBJ103 on CBT were assessed with radiotelemetry. VBJ103 had no antagonist activity at TRPV1 and TRPA1, but low potency TRPA1 activation. The only safety liability detected was partial inhibition of the dopamine transporter (DAT). VBJ103 delivered subcutaneously dose-dependently attenuated cold hypersensitivity in oxaliplatin-treated mice at 3, 10 and 30 mg·kg-1 (n = 7, P < 0.05). VBJ103 (30 mg·kg-1) antinociception was influenced by neither the TRPA1 antagonist HC-030031 nor the DAT antagonist GBR12909. Subcutaneous administration of VBJ103 (3, 10 and 30 mg·kg-1, but not 100 or 300 mg·kg-1, n = 7) decreased CBT (2°C). Intraperitoneal (i.p.) administration of VBJ103 (3, 10 and 30 mg·kg-1) dose-dependently decreased CBT to an extent larger than that detected with subcutaneous administration. Intracerebroventricular (i.c.v.) administration (306 nmol/1 μL; n = 5) did not alter CBT. We achieve therapeutic efficacy with subcutaneous administration of a novel TRPM8 antagonist that attenuates deleterious influences on CBT, a side effect that has largely prevented the translation of TRPM8 as a target.

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.

Structural Pharmacology of TRPV4 Antagonists.

The nonselective calcium-permeable Transient Receptor Potential Cation Channel Subfamily V Member4 (TRPV4)channel regulates various physiological activities. Dysfunction of TRPV4 is linked to many severe diseases, including edema, pain, gastrointestinal disorders, lung diseases, and inherited neurodegeneration. Emerging TRPV4 antagonists show potential clinical benefits. However, the molecular mechanisms of TRPV4 antagonism remain poorly understood. Here, cryo-electron microscopy (cryo-EM) structures of human TRPV4 are presented in-complex with two potent antagonists, revealing the detailed binding pockets and regulatory mechanisms of TRPV4 gating. Both antagonists bind to the voltage-sensing-like domain (VSLD) and stabilize the channel in closed states. These two antagonists induce TRPV4 to undergo an apparent fourfold to twofold symmetry transition. Moreover, it is demonstrated that one of the antagonists binds to the VSLD extended pocket, which differs from the canonical VSLD pocket. Complemented with functional and molecular dynamics simulation results, this study provides crucial mechanistic insights into TRPV4 regulation by small-molecule antagonists, which may facilitate future drug discovery targeting TRPV4.

Structure of human TRPV4 in complex with GTPase RhoA

Structure of human TRPV4 in complex with GTPase RhoA

MOLECULAR INSIGHTS INTO PROPOXAZEPAM INTERACTION WITH TRPV1 RECEPTORS: A DOCKING ANALYSIS

Problem. Pain therapy has remained conceptually stagnant since the opioid crisis, which highlighted the dangers of treating pain with opioids. TRPV1 receptors and their ligands have emerged as promising targets for the management of various pain conditions, including inflammatory and neuropathic pain. Further investigation into the activation and desensitization mechanisms of TRPV1 receptors, as well as the exploration of novel ligands with enhanced selectivity and efficacy, holds the potential to alleviate the burden of chronic pain. Aim. The study of interactions of ligands with the TRPV1 receptor by molecular docking and analysis of components of these interactions. Methods. In order to study the binding energy of the TRPV1 receptor with the researched compounds 8GFA – Cryo-EM structure of human TRPV1 in complex with the analgesic drug SB-366791 was utilized. The docking and QSAR prediction were carried out with propoxazepam, its possible metabolite 3-hydroxopropoxazepam, diazepam, oxazepam, SB-366791, RTX, capsazepin, capsaicin. The docking and QSAR build model using the Maestro Schrödinger Suite. The main results. Propoxazepam has the necessary pharmacophoric features to bind with TRPV1 recepor: region A-benzene ring; region B – the amide group (NH-C=O); region C – alkoxy group. The docking score of propoxazepam (-7.30 kcal/mol) indicates a stronger interaction with the TRPV1 receptor compared to oxazepam (-6.82 kcal/mol), 3-hydroxopropoxazepam (-6.49 kcal/mol), and capsazepin (-6.39 kcal/mol). When considering the increase in the free energy of interactions, the ligands can be ranked as follows: SB-366791 &gt; Capsaicin &gt; RTX &gt; Capsazepin &gt; Propoxazepam &gt; Diazepam &gt; 3-hydroxopropoxazepam &gt; Oxazepam. Propoxazepam establishes two hydrogen bonds: one involving the NH group of the amide (resulting in a hydrogen bond interaction with the linker-neck) and THR550 of the protein, and another between oxygen of the alkoxy group (hydrophobic tail) and TYR511 of the TRPV1 receptor. Ligands with confirmed effects on the TRPV1 receptor also engage in interactions with the protein by forming hydrogen bonds with the same amino acids as the benzodiazepines, namely THR550 and TYR511. Propoxazepam is predicted to have relatively low potency or affinity for TRPV1 (predicted pIC50 value of –1.115), but this value is higher than other ligands. Conclusions. As propoxazepam has the necessary pharmacophoric features of the pharmacophore model of TRPV1 ligands, it could theoretically bind with this receptor. Propoxazepam creates hydrogen bond with TYR511 of the TRPV1 receptor as referent ligand SB-366791. Propoxazepam exhibits one of the largest contributions of hydrogen bonds in the energy of interaction with the receptor. According to QSAR modelling, all studied compounds (3-hydroxopropoxazepam, diazepam, oxazepam, propoxazepam) have low pIC50 values, which could indicate a relatively low potency or affinity for TRPV1. But propoxazepam has the highest predicted pIC50, it means that the model predicts it to be the most potent among the compounds.

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.

PH-dependent modulation of TRPV1 by modality-selective antagonists.

Antagonists of TRPV1 that inhibit all activation modes cause hyperthermia, hampering their medical use as novel analgesics. TRPV1 antagonists that do not (fully) inhibit responses to low pH do not cause hyperthermia, but it remains incompletely understood how such antagonists affect channel gating. We tested the hypothesis that pH-sparing antagonists act in a modality-selective manner on TRPV1, differentially affecting channel activation by protons and capsaicin. Using whole-cell patch-clamp and calcium imaging to measure channel activity in cells expressing wild type human TRPV1 or the pH-insensitive mutant F660A. Responses to protons and capsaicin were measured at different pH values in the presence of antagonists that reportedly partially spare (A-1165442) or potentiate (AMG7905) acid-evoked channel activation. At pH5.5, A-1165442 was equipotent at blocking acid- and capsaicin-evoked responses of wild type TRPV1. Its potency to inhibit acid-evoked responses was attenuated at pH ≤ 5.0. AMG7905, at a concentration (1μM) that fully inhibits capsaicin-evoked responses, potentiated proton-evoked (pH5.5) responses of wild type TRPV1. In the F660A mutant, the inhibitory efficacy of A-1165442 and AMG7905 towards capsaicin-evoked responses was reduced at lower pH values and AMG7905 acted as a partial agonist. Our findings show that A-1165442 and AMG7905 interact in a pH-dependent manner with TRPV1, but this pH dependence is not strictly modality-selective. Reduced TRPV1 antagonism at acidic pH may limit analgesic efficacy in injured tissue and needs to be considered in models explaining the effects of antagonists on core body temperature.

Activation of renal vascular smooth muscle TRPV4 channels by 5-hydroxytryptamine impairs kidney function in neonatal pigs.

Control of microvascular reactivity by 5-hydroxytryptamine (5-HT; serotonin) is complex and may depend on vascular bed type and 5-HT receptors. 5-HT receptors consist of seven families (5-HT1-5-HT7), with 5-HT2 predominantly mediating renal vasoconstriction. Cyclooxygenase (COX) and smooth muscle intracellular Ca2+ levels ([Ca2+]i) have been implicated in 5-HT-induced vascular reactivity. Although 5-HT receptor expression and circulating 5-HT levels are known to be dependent on postnatal age, control of neonatal renal microvascular function by 5-HT is unclear. In the present study, we demonstrate that 5-HT stimulated human TRPV4 transiently expressed in Chinese hamster ovary cells. 5-HT2A is the predominant 5-HT2 receptor subtype in freshly isolated neonatal pig renal microvascular smooth muscle cells (SMCs). HC-067047 (HC), a selective TRPV4 blocker, attenuated cation currents induced by 5-HT in the SMCs. HC also inhibited the 5-HT-induced increase in renal microvascular [Ca2+]i and constriction. Intrarenal artery infusion of 5-HT had minimal effects on systemic hemodynamics but reduced renal blood flow (RBF) and increased renal vascular resistance (RVR) in the pigs. Transdermal measurement of glomerular filtration rate (GFR) indicated that kidney infusion of 5-HT reduced GFR. HC and 5-HT2 receptor antagonist ritanserin attenuated 5-HT effects on RBF, RVR, and GFR. Moreover, the serum and urinary COX-1 and COX-2 levels in 5-HT-treated piglets were unchanged compared with the control. These data suggest that activation of renal microvascular SMC TRPV4 channels by 5-HT impairs kidney function in neonatal pigs independently of COX production.

TRPV4-Rho GTPase complex structures reveal mechanisms of gating and disease

Crosstalk between ion channels and small GTPases is critical during homeostasis and disease, but little is known about the structural underpinnings of these interactions. TRPV4 is a polymodal, calcium-permeable cation channel that has emerged as a potential therapeutic target in multiple conditions. Gain-of-function mutations also cause hereditary neuromuscular disease. Here, we present cryo-EM structures of human TRPV4 in complex with RhoA in the ligand-free, antagonist-bound closed, and agonist-bound open states. These structures reveal the mechanism of ligand-dependent TRPV4 gating. Channel activation is associated with rigid-body rotation of the intracellular ankyrin repeat domain, but state-dependent interaction with membrane-anchored RhoA constrains this movement. Notably, many residues at the TRPV4-RhoA interface are mutated in disease and perturbing this interface by introducing mutations into either TRPV4 or RhoA increases TRPV4 channel activity. Together, these results suggest that RhoA serves as an auxiliary subunit for TRPV4, regulating TRPV4-mediated calcium homeostasis and disruption of TRPV4-RhoA interactions can lead to TRPV4-related neuromuscular disease. These insights will help facilitate TRPV4 therapeutics development.

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.

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.

Blockade of TRPV channels by intracellular spermine.

The Vanilloid thermoTRP (TRPV1-4) subfamily of TRP channels are involved in thermoregulation, osmoregulation, itch and pain perception, (neuro)inflammation and immune response, and tight control of channel activity is required for perception of noxious stimuli and pain. Here we report voltage-dependent modulation of each of human TRPV1, 3, and 4 by the endogenous intracellular polyamine spermine. As in inward rectifier K channels, currents are blocked in a strongly voltage-dependent manner, but, as in cyclic nucleotide-gated channels, the blockade is substantially reduced at more positive voltages, with maximal blockade in the vicinity of zero voltage. A kinetic model of inhibition suggests two independent spermine binding sites with different affinities as well as different degrees of polyamine permeability in TRPV1, 3, and 4. Given that block and relief occur over the physiological voltage range of action potentials, voltage-dependent polyamine block may be a potent modulator of TRPV-dependent excitability in multiple cell types.

Drosophila pain sensitization and modulation unveiled by a novel pain model and analgesic drugs.

In mammals, pain is regulated by the combination of an ascending stimulating and descending inhibitory pain pathway. It remains an intriguing question whether such pain pathways are of ancient origin and conserved in invertebrates. Here we report a new Drosophila pain model and use it to elucidate the pain pathways present in flies. The model employs transgenic flies expressing the human capsaicin receptor TRPV1 in sensory nociceptor neurons, which innervate the whole fly body, including the mouth. Upon capsaicin sipping, the flies abruptly displayed pain-related behaviors such as running away, scurrying around, rubbing vigorously, and pulling at their mouth parts, suggesting that capsaicin stimulated nociceptors in the mouth via activating TRPV1. When reared on capsaicin-containing food, the animals died of starvation, demonstrating the degree of pain experienced. This death rate was reduced by treatment both with NSAIDs and gabapentin, analgesics that inhibit the sensitized ascending pain pathway, and with antidepressants, GABAergic agonists, and morphine, analgesics that strengthen the descending inhibitory pathway. Our results suggest Drosophila to possess intricate pain sensitization and modulation mechanisms similar to mammals, and we propose that this simple, non-invasive feeding assay has utility for high-throughput evaluation and screening of analgesic compounds.

Hydrophobic gating in bundle-crossing ion channels: A case study of TRPV4.

Many transmembrane (TM) ion channels regulate ion permeation by forming bundle crossing of the pore-lining TM helices when deactivated. The resulting physical constriction is generally believed to serve as the “gate” and impose the major free energy barrier to ion permeation. On the other hand, many ion channels have been observed contain inner pores that are highly hydrophobic and can undergo spontaneous dewetting transitions. The resulting “vapor” region can block ion flow even in the absence of physical constriction. However, it is not clear whether such hydrophobic gating mechanism could be involved in channels with bundle-crossing in the deactivated state. Using atomistic simulations, we show that the human TRPV4 (hTRPV4) channel in the bundle-crossing closed state can readily undergoes hydrophobic dewetting transition and forms a vapor region in the lower pore region. Importantly, free energy analysis reveals that the major barrier for ion permeation is not located at the most constricted site, but within the vapor region. Furthermore, a single hydrophilic mutation I715N in the lower pore region significantly increases pore hydration without affecting the physical opening near bundle crossing; yet it largely removes the free energy barrier of ion permeation in hTRPV4, consistent with a previous experimental study showing that I715N leads to a constitutively conductive channel. Therefore, hTRPV4 is a hydrophobic gating channel despite the presence of bundle-crossing in the deactivated state. We anticipate that hydrophobic gating may play a key role in other bundle-crossing ion channels with hydrophobic inner pores.

Delivery of nonbiologically-compatible membrane protein constructs to mammalian cells for functional characterization.

A hallmark of integral membrane protein biogenesis is the various cellular pathways that identify and tightly regulate protein fates. These quality control mechanisms identify misfolded from well-folded membrane proteins and target them for degradation or trafficking to the appropriate cellular membrane. A current limitation in membrane protein biophysics is that many engineered membrane proteins used in structural, molecular, and mechanistic studies; including mutations, truncations, and chimeras, do not satisfy cellular quality control requirements, limiting their ability for cellular characterization. Our recently developed membrane delivery method enables recombinantly expressed and purified membrane proteins to be delivered back to cells for functional and other characterization. Here we extend these methods to characterize the delivery and evaluate the function of a minimal TRPV1 ion channel by whole-cell patch-clamp electrophysiology and other techniques. This minimal construct is ∼35% of the full-length human TRPV1 receptor and does not satisfy cellular quality control, and is thereby excluded from trafficking to the plasma membrane. Delivery of minimal TRPV1 directly to the plasma membrane enables its characterization and shows that it retains polymodal activation by heat, protons, and capsaicin, analogously to the full-length TRPV1 protein. These outcomes are validated with other methods such as electron microscopy and NMR data, enabling a bridge between cellular and biophysical studies by bypassing cellular quality control and trafficking pathways.

Voltage-dependent inhibition of thermo-TRPV channels by intracellular spermine.

The Vanilloid TRP (TRPV1-4) subfamily of channels is involved in thermoregulation, osmoregulation, itch and pain perception, immune response and (neuro)inflammation, and tight control of channel activity is required for perception of pain and noxious stimuli. TRPV1, 2, 4 have been shown to be overexpressed in various cancer cell types and suggested to serve as a marker of cancer progression and, in some cases, as an anti-cancer drug target. The polyamines (PAs) putrescine, spermidine and spermine, are present in sub-millimolar concentrations in the cytoplasm of virtually all cells and in the extracellular fluid. Intracellular PA levels decrease with age, while pathological alterations of PA levels affect cognitive functions and have been linked to brain ageing and degeneration, as well as to cancer. We have discovered a previously unrecognized physiological modulation of human TRPV1, 3 and 4 by the endogenous intracellular polyamine spermine. As in inward rectifier K channels, currents are blocked in a strongly voltage-dependent manner, but, as in cyclic nucleotide-gated channels, the block is substantially relieved at more positive voltages. Consistent with block relief resulting from spermine permeation, there is much weaker relief of block by the analog 1-naphthyl-acetyl spermine, with a bulky aromatic group at one end of the molecule. A kinetic model of inhibition suggests two independent spermine binding sites with different affinities as well as significantly different degrees of PA permeability in TRPV1, 3, and 4. Since block, relief, and permeation occur over the physiological voltage range of action potentials and PA concentrations, voltage-dependent PA block may be a potent modulator of TRPV-dependent excitability in multiple cell types, and at least some TRPV channels may contribute to polyamine transport. Thermo-TRPV structural insights and available literature also hint at a common mechanism of PA block of different TRP channel sub-families.