Structural Pharmacology of TRP Channels

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.

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.

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.

Progress interrogating TRPMPZQ as the target of praziquantel

The drug praziquantel (PZQ) has served as the long-standing drug therapy for treatment of infections caused by parasitic flatworms. These encompass diseases caused by parasitic blood, lung, and liver flukes, as well as various tapeworm infections. Despite a history of clinical usage spanning over 4 decades, the parasite target of PZQ has long resisted identification. However, a flatworm transient receptor potential ion channel from the melastatin subfamily (TRPMPZQ) was recently identified as a target for PZQ action. Here, recent experimental progress interrogating TRPMPZQ is evaluated, encompassing biochemical, pharmacological, genetic, and comparative phylogenetic data that highlight the properties of this ion channel. Various lines of evidence that support TRPMPZQ being the therapeutic target of PZQ are presented, together with additional priorities for further research into the mechanism of action of this important clinical drug.

Silva H, P. de Carvalho R, Ventura ALM, Calaza KC, Silveira MS, Kubrusly RCC, de Melo Reis RA. The Healthy and Diseased Retina Seen through Neuron-Glia Interactions

The retina is the sensory tissue responsible for the first stages of visual processing, with a conserved anatomy and functional architecture among vertebrates. To date, retinal eye diseases, such as diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, glaucoma, and others, affect nearly 170 million people worldwide, resulting in vision loss and blindness. To tackle retinal disorders, the developing retina has been explored as a versatile model to study intercellular signaling, as it presents a broad neurochemical repertoire that has been approached in the last decades in terms of signaling and diseases. Retina, dissociated and arranged as typical cultures, as mixed or neuron- and glia-enriched, and/or organized as neurospheres and/or as organoids, are valuable to understand both neuronal and glial compartments, which have contributed to revealing roles and mechanisms between transmitter systems as well as antioxidants, trophic factors, and extracellular matrix proteins. Overall, contributions in understanding neurogenesis, tissue development, differentiation, connectivity, plasticity, and cell death are widely described. A complete access to the genome of several vertebrates, as well as the recent transcriptome at the single cell level at different stages of development, also anticipates future advances in providing cues to target blinding diseases or retinal dysfunctions.

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.

Mechanosensing in Metabolism

Electrical mechanosensing is a process mediated by specialized ion channels, gated directly or indirectly by mechanical forces, which allows cells to detect and subsequently respond to mechanical stimuli. The activation of mechanosensitive (MS) ion channels, intrinsically gated by mechanical forces, or mechanoresponsive (MR) ion channels, indirectly gated by mechanical forces, results in electrical signaling across lipid bilayers, such as the plasma membrane. While the functions of mechanically gated channels within a sensory context (e.g., proprioception and touch) are well described, there is emerging data demonstrating functions beyond touch and proprioception, including mechanoregulation of intracellular signaling and cellular/systemic metabolism. Both MR and MS ion channel signaling have been shown to contribute to the regulation of metabolic dysfunction, including obesity, insulin resistance, impaired insulin secretion, and inflammation. This review summarizes our current understanding of the contributions of several MS/MR ion channels in cell types implicated in metabolic dysfunction, namely, adipocytes, pancreatic β-cells, hepatocytes, and skeletal muscle cells, and discusses MS/MR ion channels as possible therapeutic targets. © 2024 American Physiological Society. Compr Physiol 14:5269-5290, 2024.

Transient receptor potential-related risk model predicts prognosis of hepatocellular carcinoma patients

BACKGROUND

Members of the transient receptor potential (TRP) protein family shape oncogenic development, but the specific relevance of TRP-related genes in hepatocellular carcinoma (HCC) has yet to be defined.

AIM

To investigate the role of TRP genes in HCC, their association with HCC development and treatment was examined.

METHODS

HCC patient gene expression and clinical data were downloaded from The Cancer Genome Atlas database, and univariate and least absolute shrinkage and selection operator Cox regression models were employed to explore the TRP-related risk spectrum. Based on these analyses, clinically relevant TRP family genes were selected, and the association between the key TRP canonical type 1 (TRPC1) gene and HCC patient prognosis was evaluated.

RESULTS

In total, 28 TRP family genes were screened for clinical relevance, with multivariate analyses ultimately revealing three of these genes (TRPC1, TRP cation channel subfamily M member 2, and TRP cation channel subfamily M member 6) to be significantly associated with HCC patient prognosis (P < 0.05). These genes were utilized to establish a TRP-related risk model. Patients were separated into low- and high-risk groups based on the expression of these genes, and high-risk patients exhibited a significantly poorer prognosis (P = 0.001). Functional analyses highlighted pronounced differences in the immune status of patients in these two groups and associated enriched immune pathways. TRPC1 was identified as a candidate gene in this family worthy of further study, with HCC patients expressing higher TRPC1 levels exhibiting poorer survival outcomes. Consistently, quantitative, immunohistochemistry, and western blot analyses revealed increased TRPC1 expression in HCC.

CONCLUSION

These three TRP genes help determine HCC patient prognosis, providing insight into tumor immune status and immunological composition. These findings will help design combination therapies including immunotherapeutic and anti-TRP agents.

Interaction of Calmodulin with TRPM: An Initiator of Channel Modulation

Transient receptor potential melastatin (TRPM) channels, a subfamily of the TRP superfamily, constitute a diverse group of ion channels involved in mediating crucial cellular processes like calcium homeostasis. These channels exhibit complex regulation, and one of the key regulatory mechanisms involves their interaction with calmodulin (CaM), a cytosol ubiquitous calcium-binding protein. The association between TRPM channels and CaM relies on the presence of specific CaM-binding domains in the channel structure. Upon CaM binding, the channel undergoes direct and/or allosteric structural changes and triggers down- or up-stream signaling pathways. According to current knowledge, ion channel members TRPM2, TRPM3, TRPM4, and TRPM6 are directly modulated by CaM, resulting in their activation or inhibition. This review specifically focuses on the interplay between TRPM channels and CaM and summarizes the current known effects of CaM interactions and modulations on TRPM channels in cellular physiology.

Potential applications of P2X3 receptor antagonists in the treatment of refractory cough

Refractory chronic cough is defined as a clinical condition in which the cause of the cough remains unclear after comprehensive examination and treatment, or the cause is clear but symptomatic treatment is ineffective. Patients with refractory chronic cough experience a variety of physiological and psychological issues that significantly lower their quality of life and place a significant socio-economic burden on society. As a result, research both domestically and internationally has turned heavily toward these patients. Recently, several studies have identified P2X3 receptor antagonists for the treatment of refractory chronic cough, and this paper reviews the background, mechanism of action, evidence-based proof and application prospects of this class of drugs. KEY MESSAGE: There were plenty of studies about P2X3 receptor antagonists in the past, and in recent years this series of drugs are effective in refractory chronic cough. Although review articles summarizing have been published previously, most have focused on their chemical properties rather than their clinical aspects, with some omitting drugs that have been in clinical studies for nearly two years such as Eliapixant and Sivopixant. Focusing on four P2X3 receptor antagonists with proven efficacy in clinical studies, we analyzed the characteristics and disadvantages of each drug by comparing their clinical results of them and theoretically explained the common side effects of these drugs, as well as their potential for treating refractory chronic cough. This article can be used as a reference for the follow-up studies of P2X3 receptor antagonists in chronic cough. Additionally, it also has implications for the clinical focus of the drug and the approaches to relieve some side effects.

The modes of action of ion-channel-targeting neurotoxic insecticides: lessons from structural biology

Insecticides are indispensable tools for plant protection in modern agriculture. Despite having highly heterogeneous structures, many neurotoxic insecticides use similar principles to inhibit or deregulate neuronal ion channels. Insecticides targeting pentameric ligand-gated channels are structural mimetics of neurotransmitters or manipulate and deregulate the proteins. Those binding to (pseudo-)tetrameric voltage-gated(-like) channels, on the other hand, are natural or synthetic compounds that directly block the ion-conducting pore or prevent conformational changes in the transmembrane domain necessary for opening and closing the pore. The use of a limited number of inhibition mechanisms can be problematic when resistances arise and become more widespread. Therefore, there is a rising interest in the development of insecticides with novel mechanisms that evade resistance and are pest-insect-specific. During the last decade, most known insecticide targets, many with bound compounds, have been structurally characterized, bringing the rational design of novel classes of agrochemicals within closer reach than ever before.

Neurotoxin-Derived Optical Probes for Biological and Medical Imaging

The superb specificity and potency of biological toxins targeting various ion channels and receptors are of major interest for the delivery of therapeutics to distinct cell types and subcellular compartments. Fused with reporter proteins or labelled with fluorophores and nanocomposites, animal toxins and their detoxified variants also offer expanding opportunities for visualisation of a range of molecular processes and functions in preclinical models, as well as clinical studies. This article presents state-of-the-art optical probes derived from neurotoxins targeting ion channels, with discussions of their applications in basic and translational biomedical research. It describes the design and production of probes and reviews their applications with advantages and limitations, with prospects for future improvements. Given the advances in imaging tools and expanding research areas benefiting from the use of optical probes, described here resources should assist the discovery process and facilitate high-precision interrogation and therapeutic interventions.

A review of the pathophysiology and the role of ion channels on bronchial asthma

Asthma is one of the main non-communicable chronic diseases and affects a huge portion of the population. It is a multifactorial disease, classified into several phenotypes, being the allergic the most frequent. The pathophysiological mechanism of asthma involves a Th2-type immune response, with high concentrations of allergen-specific immunoglobulin E, eosinophilia, hyperreactivity and airway remodeling. These mechanisms are orchestrated by intracellular signaling from effector cells, such as lymphocytes and eosinophils. Ion channels play a fundamental role in maintaining the inflammatory response on asthma. In particular, transient receptor potential (TRP), stock-operated Ca2+ channels (SOCs), Ca2+-activated K+ channels (IKCa and BKCa), calcium-activated chloride channel (TMEM16A), cystic fibrosis transmembrane conductance regulator (CFTR), piezo-type mechanosensitive ion channel component 1 (PIEZO1) and purinergic P2X receptor (P2X). The recognition of the participation of these channels in the pathological process of asthma is important, as they become pharmacological targets for the discovery of new drugs and/or pharmacological tools that effectively help the pharmacotherapeutic follow-up of this disease, as well as the more specific mechanisms involved in worsening asthma.

Intrinsically disordered regions in TRPV2 mediate protein-protein interactions

Transient receptor potential (TRP) ion channels are gated by diverse intra- and extracellular stimuli leading to cation inflow (Na+, Ca2+) regulating many cellular processes and initiating organismic somatosensation. Structures of most TRP channels have been solved. However, structural and sequence analysis showed that ~30% of the TRP channel sequences, mainly the N- and C-termini, are intrinsically disordered regions (IDRs). Unfortunately, very little is known about IDR 'structure', dynamics and function, though it has been shown that they are essential for native channel function. Here, we imaged TRPV2 channels in membranes using high-speed atomic force microscopy (HS-AFM). The dynamic single molecule imaging capability of HS-AFM allowed us to visualize IDRs and revealed that N-terminal IDRs were involved in intermolecular interactions. Our work provides evidence about the 'structure' of the TRPV2 IDRs, and that the IDRs may mediate protein-protein interactions.

TRP Channels: The Neglected Culprits in Breast Cancer Chemotherapy Resistance?

Breast cancer is a major health concern worldwide, and resistance to therapies remains a significant challenge in treating this disease. In breast cancer, Transient Receptor Potential (TRP) channels are well studied and constitute key players in nearly all carcinogenesis hallmarks. Recently, they have also emerged as important actors in resistance to therapy by modulating the response to various pharmaceutical agents. Targeting TRP channels may represent a promising approach to overcome resistance to therapies in breast cancer patients.

The Role of TRPM4 in Cardiac Electrophysiology and Arrhythmogenesis

The transient receptor potential melastatin 4 (TRPM4) channel is a non-selective cation channel that activates in response to increased intracellular Ca²⁺ levels but does not allow Ca²⁺ to pass through directly. It plays a crucial role in regulating diverse cellular functions associated with intracellular Ca²⁺ homeostasis/dynamics. TRPM4 is widely expressed in the heart and is involved in various physiological and pathological processes therein. Specifically, it has a significant impact on the electrical activity of cardiomyocytes by depolarizing the membrane, presumably via Na⁺ loading. The TRPM4 channel likely contributes to the development of cardiac arrhythmias associated with specific genetic backgrounds and cardiac remodeling. This short review aims to overview what is known so far about the TRPM4 channel in cardiac electrophysiology and arrhythmogenesis, highlighting its potential as a novel therapeutic target to effectively prevent and treat cardiac arrhythmias.

Molecular architecture and gating mechanisms of the Drosophila TRPA1 channel

The transient receptor potential channel subfamily A member 1 (TRPA1) ion channel is an evolutionary conserved polymodal sensor responding to noxious temperature or chemical stimuli. Notably, the thermosensitivity of TRPA1 varies among different species or even different isoforms in the same species. However, the underlying molecular basis of its thermo-gating remains largely unknown. Here, we determine the structures of a heat-sensitive isoform of TRPA1 in Drosophila melanogaster in two distinct conformations with cryo-samples prepared at 8 °C. Large conformational changes are observed in the ankyrin repeat domain (ARD) and the coiled-coil domain between the two states. Remarkably, all 17 ankyrin repeats are mapped in the newly resolved conformation, forming a propeller-like architecture. Two intersubunit interfaces are identified in the amino (N)-terminal domain, and play vital roles during both heat and chemical activation as shown by electrophysiological analysis. With cryo-samples prepared at 35 °C, only one conformation is resolved, suggesting possible state transitions during heat responses. These findings provide a basis for further understanding how the ARD regulates channel functions, and insights into the gating mechanism of TRPA1.

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.

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.

Cannabinoid non-cannabidiol site modulation of TRPV2 structure and function

TRPV2 is a ligand-operated temperature sensor with poorly defined pharmacology. Here, we combine calcium imaging and patch-clamp electrophysiology with cryo-electron microscopy (cryo-EM) to explore how TRPV2 activity is modulated by the phytocannabinoid Δ⁹-tetrahydrocannabiorcol (C16) and by probenecid. C16 and probenecid act in concert to stimulate TRPV2 responses including histamine release from rat and human mast cells. Each ligand causes distinct conformational changes in TRPV2 as revealed by cryo-EM. Although the binding for probenecid remains elusive, C16 associates within the vanilloid pocket. As such, the C16 binding location is distinct from that of cannabidiol, partially overlapping with the binding site of the TRPV2 inhibitor piperlongumine. Taken together, we discover a new cannabinoid binding site in TRPV2 that is under the influence of allosteric control by probenecid. This molecular insight into ligand modulation enhances our understanding of TRPV2 in normal and pathophysiology.

Role of ion channels in the mechanism of proteinuria (Review)

Proteinuria is a common clinical manifestation of kidney diseases, such as glomerulonephritis, nephrotic syndrome, immunoglobulin A nephropathy and diabetic nephropathy. Therefore, proteinuria is considered to be a risk factor for renal dysfunction. Furthermore, proteinuria is also significantly associated with the progression of kidney diseases and increased mortality. Its occurrence is closely associated with damage to the structure of the glomerular filtration membrane. An impaired glomerular filtration membrane can affect the selective filtration function of the kidneys; therefore, several macromolecular substances, such as proteins, may pass through the filtration membrane and promote the manifestation of proteinuria. It has been reported that ion channels play a significant role in the mechanisms underlying proteinuria. Ion channel mutations or other dysfunctions have been implicated in several diseases, therefore ion channels could be used as major therapeutic targets. The mechanisms underlying the action of ion channels and ion transporters in proteinuria have been overlooked in the literature, despite their importance in identifying novel targets for treating proteinuria and delaying the progression of kidney diseases. The current review article focused on the four key ion channel groups, namely Na⁺, Ca²⁺, Cl^- and K⁺ ion channels and the associated ion transporters.

The SOCE Machinery: An Unbalanced Knowledge between Left and Right Ventricular Pathophysiology

Right ventricular failure (RVF) is the most important prognostic factor for morbidity and mortality in pulmonary arterial hypertension (PAH) or pulmonary hypertension (PH) caused by left heart diseases. However, right ventricle (RV) remodeling is understudied and not targeted by specific therapies. This can be partly explained by the lack of basic knowledge of RV remodeling. Since the physiology and hemodynamic function of the RV differ from those of the left ventricle (LV), the mechanisms of LV dysfunction cannot be generalized to that of the RV, albeit a knowledge of these being helpful to understanding RV remodeling and dysfunction. Store-operated Ca²⁺ entry (SOCE) has recently emerged to participate in the LV cardiomyocyte Ca²⁺ homeostasis and as a critical player in Ca²⁺ mishandling in a pathological context. In this paper, we highlight the current knowledge on the SOCE contribution to the LV and RV dysfunctions, as SOCE molecules are present in both compartments. he relative lack of studies on RV dysfunction indicates the necessity of further investigations, a significant challenge over the coming years.

Quaternary structure independent folding of voltage-gated ion channel pore domain subunits

Every voltage-gated ion channel (VGIC) has a pore domain (PD) made from four subunits, each comprising an antiparallel transmembrane helix pair bridged by a loop. The extent to which PD subunit structure requires quaternary interactions is unclear. Here, we present crystal structures of a set of bacterial voltage-gated sodium channel (BacNa_V) 'pore only' proteins that reveal a surprising collection of non-canonical quaternary arrangements in which the PD tertiary structure is maintained. This context-independent structural robustness, supported by molecular dynamics simulations, indicates that VGIC-PD tertiary structure is independent of quaternary interactions. This fold occurs throughout the VGIC superfamily and in diverse transmembrane and soluble proteins. Strikingly, characterization of PD subunit-binding Fabs indicates that non-canonical quaternary PD conformations can occur in full-length VGICs. Together, our data demonstrate that the VGIC-PD is an autonomously folded unit. This property has implications for VGIC biogenesis, understanding functional states, de novo channel design, and VGIC structural origins.

On the Connections between TRPM Channels and SOCE

Plasma membrane protein channels provide a passageway for ions to access the intracellular milieu. Rapid entry of calcium ions into cells is controlled mostly by ion channels, while Ca2+-ATPases and Ca2+ exchangers ensure that cytosolic Ca2+ levels ([Ca2+]cyt) are maintained at low (~100 nM) concentrations. Some channels, such as the Ca2+-release-activated Ca2+ (CRAC) channels and voltage-dependent Ca2+ channels (CACNAs), are highly Ca2+-selective, while others, including the Transient Receptor Potential Melastatin (TRPM) family, have broader selectivity and are mostly permeable to monovalent and divalent cations. Activation of CRAC channels involves the coupling between ORAI1-3 channels with the endoplasmic reticulum (ER) located Ca2+ store sensor, Stromal Interaction Molecules 1-2 (STIM1/2), a pathway also termed store-operated Ca2+ entry (SOCE). The TRPM family is formed by 8 members (TRPM1-8) permeable to Mg2+, Ca2+, Zn2+ and Na+ cations, and is activated by multiple stimuli. Recent studies indicated that SOCE and TRPM structure-function are interlinked in some instances, although the molecular details of this interaction are only emerging. Here we review the role of TRPM and SOCE in Ca2+ handling and highlight the available evidence for this interaction.

Sensory TRP Channels in Three Dimensions

Transient receptor potential (TRP) ion channels are sophisticated signaling machines that detect a wide variety of environmental and physiological signals. Every cell in the body expresses one or more members of the extended TRP channel family, which consists of over 30 subtypes, each likely possessing distinct pharmacological, biophysical, and/or structural attributes. While the function of some TRP subtypes remains enigmatic, those involved in sensory signaling are perhaps best characterized and have served as models for understanding how these excitatory ion channels serve as polymodal signal integrators. With the recent resolution revolution in cryo-electron microscopy, these and other TRP channel subtypes are now yielding their secrets to detailed atomic analysis, which is beginning to reveal structural underpinnings of stimulus detection and gating, ion permeation, and allosteric mechanisms governing signal integration. These insights are providing a framework for designing and evaluating modality-specific pharmacological agents for treating sensory and other TRP channel-associated disorders. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Druggable Lipid Binding Sites in Pentameric Ligand-Gated Ion Channels and Transient Receptor Potential Channels

Lipids modulate the function of many ion channels, possibly through direct lipid-protein interactions. The recent outpouring of ion channel structures by cryo-EM has revealed many lipid binding sites. Whether these sites mediate lipid modulation of ion channel function is not firmly established in most cases. However, it is intriguing that many of these lipid binding sites are also known sites for other allosteric modulators or drugs, supporting the notion that lipids act as endogenous allosteric modulators through these sites. Here, we review such lipid-drug binding sites, focusing on pentameric ligand-gated ion channels and transient receptor potential channels. Notable examples include sites for phospholipids and sterols that are shared by anesthetics and vanilloids. We discuss some implications of lipid binding at these sites including the possibility that lipids can alter drug potency or that understanding protein-lipid interactions can guide drug design. Structures are only the first step toward understanding the mechanism of lipid modulation at these sites. Looking forward, we identify knowledge gaps in the field and approaches to address them. These include defining the effects of lipids on channel function in reconstituted systems using asymmetric membranes and measuring lipid binding affinities at specific sites using native mass spectrometry, fluorescence binding assays, and computational approaches.

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

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

The effects of cannabidiol via TRPV2 channel in chronic myeloid leukemia cells and its combination with imatinib

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by accumulation of immature cells in bone marrow and peripheral blood. Although successful results were obtained with tyrosine kinase inhibitors, several patients showed resistance. For this reason, the identification of new strategies and therapeutic biomarkers represents an attractive goal. The role of transient receptor potential (TRP) ion channels as possible drug targets has been elucidated in different types of cancer. Among natural compounds known to activate TRPs, cannabidiol (CBD) displays anticancer properties. By using FACS analysis, confocal microscopy, gene silencing, and cell growth assay, we demonstrated that CBD, through TRPV2, inhibits cell proliferation and cell cycle in CML cells. It promoted mitochondria dysfunction and mitophagy as shown by mitochondrial mass reduction and up‐regulation of several mitophagy markers. These effects were associated with changes in the expression of octamer‐binding transcription factor 4 and PU.1 markers regulated during cellular differentiation. Interestingly, a synergistic effect by combining CBD with the standard drug imatinib was found and imatinib‐resistant cells remain susceptible to CBD effects. Therefore, the targeting of TRPV2 by using CBD, through the activation of mitophagy and the reduction in stemness, could be a promising strategy to enhance conventional therapy and improve the prognosis of CML patients.

Role of Store-Operated Ca2+ Entry in the Pulmonary Vascular Remodeling Occurring in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe and multifactorial disease. PAH pathogenesis mostly involves pulmonary arterial endothelial and pulmonary arterial smooth muscle cell (PASMC) dysfunction, leading to alterations in pulmonary arterial tone and distal pulmonary vessel obstruction and remodeling. Unfortunately, current PAH therapies are not curative, and therapeutic approaches mostly target endothelial dysfunction, while PASMC dysfunction is under investigation. In PAH, modifications in intracellular Ca2+ homoeostasis could partly explain PASMC dysfunction. One of the most crucial actors regulating Ca2+ homeostasis is store-operated Ca2+ channels, which mediate store-operated Ca2+ entry (SOCE). This review focuses on the main actors of SOCE in human and experimental PASMC, their contribution to PAH pathogenesis, and their therapeutic potential in PAH.

A potential role for cannabichromene in modulating TRP channels during acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a life-threatening clinical syndrome whose potential to become one of the most grievous challenges of the healthcare system evidenced by the COVID-19 pandemic. Considering the lack of target-specific treatment for ARDS, it is absolutely exigent to have an effective therapeutic modality to reduce hospitalization and mortality rate as well as to improve quality of life and outcomes for ARDS patients. ARDS is a systemic inflammatory disease starting with the pulmonary system and involves all other organs in a morbid bidirectional fashion. Mounting evidence including our findings supporting the notion that cannabinoids have potential to be targeted as regulatory therapeutic modalities in the treatment of inflammatory diseases. Therefore, it is plausible to test their capabilities as alternative therapies in the treatment of ARDS. In this study, we investigated the potential protective effects of cannabichromene (CBC) in an experimental model of ARDS.

METHODS

We used, for the first time, an inhalant CBC treatment as a potential therapeutic target in a murine model of ARDS-like symptoms. ARDS was induced by intranasal administration of Poly(I:C), a synthetic mismatched double-stranded RNA, into the C57BL/6 mice (6-10 male mice/group, including sham, placebo, and CBC treated), three once-daily doses followed by a daily dose of inhalant CBC or placebo for the period of 8 days starting the first dose 2 h after the second Poly(I:C) treatment. We employed histologic, immunohistochemistry, and flow cytometry methods to assess the findings. Statistical analysis was performed by using one way analysis of variance (ANOVA) followed by Newman-Keuls post hoc test to determine the differences among the means of all experimental groups and to establish significance (p < 0.05) among all groups.

RESULTS

Our data showed that CBC was able to reverse the hypoxia (increasing blood O₂ saturation by 8%), ameliorate the symptoms of ARDS (reducing the pro-inflammatory cytokines by 50% in lung and blood), and protect the lung tissues from further destruction. Further analysis showed that CBC may wield its protective effects through transient receptor potential (TRP) cation channels, TRPA1 and TRPV1, increasing their expression by 5-folds in lung tissues compared to sham and untreated mice, re-establishing the homeostasis and immune balance.

CONCLUSION

Our findings suggest that inhalant CBC may be an effective alternative therapeutic target in the treatment of ARDS. In addition, Increased expression of TRPs cation channels after CBC treatment proposes a novel role for TRPs (TRPA1 and TRPV2) as new potential mechanism to interpret the beneficial effects of CBC as well as other cannabinoids in the treatment of ARDS as well as other inflammatory diseases. Importantly, delivering CBC through an inhaler device is a translational model supporting the feasibility of trial with human subjects, authorizing further research.

Contribution of non-selective membrane channels and receptors in epilepsy

Overcoming refractory epilepsy's resistance to the combination of antiepileptic drugs (AED), mitigating side effects, and preventing sudden unexpected death in epilepsy are critical goals for therapy of this disorder. Current therapeutic strategies are based primarily on neurocentric mechanisms, overlooking the participation of astrocytes and microglia in the pathophysiology of epilepsy. This review is focused on a set of non-selective membrane channels (permeable to ions and small molecules), including channels and ionotropic receptors of neurons, astrocytes, and microglia, such as: the hemichannels formed by Cx43 and Panx1; the purinergic P2X7 receptors; the transient receptor potential vanilloid (TRPV1 and TRPV4) channels; calcium homeostasis modulators (CALHMs); transient receptor potential canonical (TRPC) channels; transient receptor potential melastatin (TRPM) channels; voltage-dependent anion channels (VDACs) and volume-regulated anion channels (VRACs), which all have in common being activated by epileptic activity and the capacity to exacerbate seizure intensity. Specifically, we highlight evidence for the activation of these channels/receptors during epilepsy including neuroinflammation and oxidative stress, discuss signaling pathways and feedback mechanisms, and propose the functions of each of them in acute and chronic epilepsy. Studying the role of these non-selective membrane channels in epilepsy and identifying appropriate blockers for one or more of them could provide complementary therapies to better alleviate the disease.

The Combined Effect of Branching and Elongation on the Bioactivity Profile of Phytocannabinoids. Part I: Thermo-TRPs

The affinity of cannabinoids for their CB₁ and CB₂ metabotropic receptors is dramatically affected by a combination of α-branching and elongation of their alkyl substituent, a maneuver exemplified by the n-pentyl -> α,α-dimethylheptyl (DMH) swap. The effect of this change on other cannabinoid end-points is still unknown, an observation surprising since thermo-TRPs are targeted by phytocannabinoids with often sub-micromolar affinity. To fill this gap, the α,α-dimethylheptyl analogues of the five major phytocannabinoids [CBD (1a), Δ⁸-THC (6a), CBG (7a), CBC (8a) and CBN (9a)] were prepared by total synthesis, and their activity on thermo-TRPs (TRPV1-4, TRPM8, and TRPA1) was compared with that of one of their natural analogues. Surprisingly, the DMH chain promoted a shift in the selectivity toward TRPA1, a target involved in pain and inflammatory diseases, in all investigated compounds. A comparative study of the putative binding modes at TRPA1 between DMH-CBC (8b), the most active compound within the series, and CBC (8a) was carried out by molecular docking, allowing the rationalization of their activity in terms of structure–activity relationships. Taken together, these observations qualify DMH-CBC (8b) as a non-covalent TRPA1-selective cannabinoid lead that is worthy of additional investigation as an analgesic and anti-inflammatory agent.

The expanded effects of sevoflurane on the nervous system: the harmful effect of residual concentration of sevoflurane on the respiratory system through neurogenic inflammation

Background

Neurogenic inflammation caused by sevoflurane may not only limite to the nervous system, but also expand to the respiratory system. The purpose of this study was to investigate the expression changes of transient receptor potential vanilloid 1 (TRPV1), neurokinin A (NKA), neurokinin B (NKB), calcitonin gene related peptide (CGRP) and substance P (SP) in 14, 21 and 42-day-old rats after inhaling 0.4% sevoflurane, in order to evaluate whether the residual sevoflurane be harmful to the respiratory system through neurogenic inflammation.

Methods

The anesthetic inhalation device was designed to allow 14, 21 and 42-day-old rats inhale 0.4% sevoflurane, while rats in the control group inhaled 40% O2 for 1h. Rats in the antagonist group inhaled 0.4% sevoflurane or 40% O2 for 1 h after Capsazepine (CPZ) pretreatment. The expression of TRPV1 in lung tissue was detected by western blot, and the expression of NKA, NKB, CGRP and SP in trachea was detected by immunohistochemistry.

Results

After inhaling 0.4% sevoflurane, the expression of TRPV1 in lung tissue of 14 and 21-day-old rats was significantly higher than that of the control group, as well as increased the expression of CGRP and SP in the trachea of 14-day-old rats and NKA, NKB, CGRP and SP in the trachea of 21-day-old rats. CPZ pretreatment could antagonize these effects.

Conclusion

Residual sevoflurane during resuscitation of inhalation anesthesia could induce neurogenic inflammation by activating TRPV1, which damaged to the developing respiratory system, but has no significant effect on the respiratory system in adulthood.