Structure of the receptor-activated human TRPC6 and TRPC3 ion channels

RNA-binding protein PTENα blocks RIG-I activation to prevent viral inflammation

A timely inflammatory response is crucial for early viral defense, but uncontrolled inflammation harms the host. Retinoic acid-inducible gene I (RIG-I) has a pivotal role in detecting RNA viruses, yet the regulatory mechanisms governing its sensitivity remain elusive. Here we identify PTENα, an N-terminally extended form of PTEN, as an RNA-binding protein with a preference for the CAUC(G/U)UCAU motif. Using both in vivo and in vitro viral infection assays, we demonstrated that PTENα restricted the host innate immune response, relying on its RNA-binding capacity and phosphatase activity. Mechanistically, PTENα directly bound to viral RNA and enzymatically converted its 5'-triphosphate to 5'-monophosphate, thereby reducing RIG-I sensitivity. Physiologically, brain-intrinsic PTENα exerted protective effects against viral inflammation, while peripheral PTENα restricted host antiviral immunity and, to some extent, promoted viral replication. Collectively, our findings underscore the significance of PTENα in modulating viral RNA- and RIG-I-mediated immune recognition, offering potential therapeutic implications for infectious diseases.

TRPC3/6 Channels Mediate Mechanical Pain Hypersensitivity via Enhancement of Nociceptor Excitability and of Spinal Synaptic Transmission

Patients with tissue inflammation or injury often experience aberrant mechanical pain hypersensitivity, one of leading symptoms in clinic. Despite this, the molecular mechanisms underlying mechanical distortion are poorly understood. Canonical transient receptor potential (TRPC) channels confer sensitivity to mechanical stimulation. TRPC3 and TRPC6 proteins, coassembling as heterotetrameric channels, are highly expressed in sensory neurons. However, how these channels mediate mechanical pain hypersensitivity has remained elusive. It is shown that in mice and human, TRPC3 and TRPC6 are upregulated in DRG and spinal dorsal horn under pathological states. Double knockout of TRPC3/6 blunts mechanical pain hypersensitivity, largely by decreasing nociceptor hyperexcitability and spinal synaptic potentiation via presynaptic mechanism. In corroboration with this, nociceptor-specific ablation of TRPC3/6 produces comparable pain relief. Mechanistic analysis reveals that upon peripheral inflammation, TRPC3/6 in primary sensory neurons get recruited via released bradykinin acting on B1/B2 receptors, facilitating BDNF secretion from spinal nociceptor terminals, which in turn potentiates synaptic transmission through TRPC3/6 and eventually results in mechanical pain hypersensitivity. Antagonizing TRPC3/6 in DRG relieves mechanical pain hypersensitivity in mice and nociceptor hyperexcitability in human. Thus, TRPC3/6 in nociceptors is crucially involved in pain plasticity and constitutes a promising therapeutic target against mechanical pain hypersensitivity with minor side effects.

Hyperforin improves matrix stiffness induced nucleus pulposus inflammatory degeneration by activating mitochondrial fission

OBJECTIVE

The continuously increasing extracellular matrix stiffness during intervertebral disc degeneration promotes disease progression. In an attempt to obtain novel treatment methods, this study aims to investigate the changes in nucleus pulposus cells under the stimulation of a stiff microenvironment.

DESIGN

RNA sequencing and metabolomics experiments were combined to evaluate the primary nucleus pulposus and screen key targets under mechanical biological stimulation. Additionally, small molecules work in vitro were used to confirm the target regulatory effect and investigate the mechanism. In vivo, treatment effects were validated using a rat caudal vertebrae compression model.

RESULTS

Our research results revealed that by activating TRPC6, hyperforin, a herbaceous extract can rescue the inflammatory phenotype caused by the stiff microenvironment, hence reducing intervertebral disc degeneration (IDD). Mechanically, it activates mitochondrial fission to inhibit PFKFB3.

CONCLUSION

In summary, this study reveals the important bridging role of TRPC6 between mechanical stiffness, metabolism, and inflammation in the context of nucleus pulposus degeneration. TRPC6 activation with hyperforin may become a promising treatment for IDD.

Distribution of TRPC3 and TRPC6 in the human exocrine and endocrine pancreas

BACKGROUND

Expression and function of TRPC3 and TRPC6 in the pancreas is a controversial topic. Investigation in human tissue is seldom. We aimed to provide here a detailed description of the distribution of TRPC3 and TRPC6 in the human exocrine and endocrine pancreas.

METHODS

We collected healthy samples from cadavers (n = 4) and visceral surgery (n = 4) to investigate the respective expression profiles using immunohistochemical tracing with knockout-validated antibodies.

RESULTS

TRPC3- and TRPC6-proteins were detected in different pancreatic structures including acinar cells, as well as epithelial ductal cells from intercalate, intralobular, and interlobular ducts. Respective connective tissue layers appeared unstained. Endocrine islets of Langerhans were clearly and homogenously immunolabeled by the anti-TRPC3 and anti-TRPC6 antibodies. Insular α, β, γ, and δ cells were conclusively stained, although no secure differentiation of cell types was performed.

CONCLUSIONS

Due to aforementioned antibody specificity verification, protein expression in the immunolabeled localizations can be accepted. Our study in human tissue supports previous investigations especially with respect to acinar and insular α and β cells, while other localizations are here reported for the first time to express TRPC3 and TRPC6, ultimately warranting further research.

PIP2 modulates TRPC3 activity via TRP helix and S4-S5 linker

The transient receptor potential canonical type 3 (TRPC3) channel plays a pivotal role in regulating neuronal excitability in the brain via its constitutive activity. The channel is intricately regulated by lipids and has previously been demonstrated to be positively modulated by PIP2. Using molecular dynamics simulations and patch clamp techniques, we reveal that PIP2 predominantly interacts with TRPC3 at the L3 lipid binding site, located at the intersection of pre-S1 and S1 helices. We demonstrate that PIP2 sensing involves a multistep mechanism that propagates from L3 to the pore domain via a salt bridge between the TRP helix and S4-S5 linker. Notably, we find that both stimulated and constitutive TRPC3 activity require PIP2. These structural insights into the function of TRPC3 are invaluable for understanding the role of the TRPC subfamily in health and disease, in particular for cardiovascular diseases, in which TRPC3 channels play a major role.

Metabolic heterogeneity in tumor microenvironment - A novel landmark for immunotherapy

The surrounding non-cancer cells and tumor cells that make up the tumor microenvironment (TME) have various metabolic rhythms. TME metabolic heterogeneity is influenced by the intricate network of metabolic control within and between cells. DNA, protein, transport, and microbial levels are important regulators of TME metabolic homeostasis. The effectiveness of immunotherapy is also closely correlated with alterations in TME metabolism. The response of a tumor patient to immunotherapy is influenced by a variety of variables, including intracellular metabolic reprogramming, metabolic interaction between cells, ecological changes within and between tumors, and general dietary preferences. Although immunotherapy and targeted therapy have made great strides, their use in the accurate identification and treatment of tumors still has several limitations. The function of TME metabolic heterogeneity in tumor immunotherapy is summarized in this article. It focuses on how metabolic heterogeneity develops and is regulated as a tumor progresses, the precise molecular mechanisms and potential clinical significance of imbalances in intracellular metabolic homeostasis and intercellular metabolic coupling and interaction, as well as the benefits and drawbacks of targeted metabolism used in conjunction with immunotherapy. This offers insightful knowledge and important implications for individualized tumor patient diagnosis and treatment plans in the future.

Pathophysiological significance and modulation of the transient receptor potential canonical 3 ion channel

Transient receptor potential canonical 3 (TRPC3) protein belongs to the TRP family of nonselective cation channels. Its activation occurs by signaling through a G protein-coupled receptor (GPCR) and a phospholipase C-dependent (PLC) pathway. Perturbations in the expression of TRPC3 are associated with a plethora of pathophysiological conditions responsible for disorders of the cardiovascular, immune, and central nervous systems. The recently solved cryo-EM structure of TRPC3 provides detailed inputs about the underlying mechanistic aspects of the channel, which in turn enables more efficient ways of designing small-molecule modulators. Pharmacologically targeting TRPC3 in animal models has demonstrated great efficacy in treating diseases including cancers, neurological disorders, and cardiovascular diseases. Despite extensive scientific evidence supporting some strong correlations between the expression and activity of TRPC3 and various pathophysiological conditions, therapeutic strategies based on its pharmacological modulations have not led to clinical trials. The development of small-molecule TRPC3 modulators with high safety, sufficient brain penetration, and acceptable drug-like profiles remains in progress. Determining the pathological mechanisms for TRPC3 involvement in human diseases and understanding the requirements for a drug-like TRPC3 modulator will be valuable in advancing small-molecule therapeutics to future clinical trials. In this review, we provide an overview of the origin and activation mechanism of TRPC3 channels, diseases associated with irregularities in their expression, and new development in small-molecule modulators as potential therapeutic interventions for treating TRPC3 channelopathies.

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.

TRPC3 Is Downregulated in Primary Hyperparathyroidism

Transient receptor potential canonical sub-family channel 3 (TRPC3) is considered to play a critical role in calcium homeostasis. However, there are no established findings in this respect with regard to TRPC6. Although the parathyroid gland is a crucial organ in calcium household regulation, little is known about the protein distribution of TRPC channels-especially TRPC3 and TRPC6-in this organ. Our aim was therefore to investigate the protein expression profile of TRPC3 and TRPC6 in healthy and diseased human parathyroid glands. Surgery samples from patients with healthy parathyroid glands and from patients suffering from primary hyperparathyroidism (pHPT) were investigated by immunohistochemistry using knockout-validated antibodies against TRPC3 and TRPC6. A software-based analysis similar to an H-score was performed. For the first time, to our knowledge, TRPC3 and TRPC6 protein expression is described here in the parathyroid glands. It is found in both chief and oxyphilic cells. Furthermore, the TRPC3 staining score in diseased tissue (pHPT) was statistically significantly lower than that in healthy tissue. In conclusion, TRPC3 and TRPC6 proteins are expressed in the human parathyroid gland. Furthermore, there is strong evidence indicating that TRPC3 plays a role in pHPT and subsequently in parathyroid hormone secretion regulation. These findings ultimately require further research in order to not only confirm our results but also to further investigate the relevance of these channels and, in particular, that of TRPC3 in the aforementioned physiological functions and pathophysiological conditions.

The Multifunctional TRPC6 Protein: Significance in the Field of Cardiovascular Studies

Cardiovascular disease is the leading cause of death, medical complications, and healthcare costs. Although recent advances have been in treating cardiovascular disorders linked with a reduced ejection fraction, acutely decompensate cardiac failure remains a significant medical problem. The transient receptor potential cation channel (TRPC6) family responds to neurohormonal and mechanical stress, playing critical roles in cardiovascular diseases. Therefore, TRP C6 channels have great promise as therapeutic targets. Numerous studies have investigated the roles of TRP C6 channels in pain neurons, highlighting their significance in cardiovascular research. The TRPC6 protein exhibits a broad distribution in various organs and tissues, including the brain, nerves, heart, blood vessels, lungs, kidneys, gastrointestinal tract, and other bodily structures. Its activation can be triggered by alterations in osmotic pressure, mechanical stimulation, and diacylglycerol. Consequently, TRPC6 plays a significant role in the pathophysiological mechanisms underlying diverse diseases within living organisms. A recent study has indicated a strong correlation between the disorder known as TRPC6 and the development of cardiovascular diseases. Consequently, investigations into the association between TRPC6 and cardiovascular diseases have gained significant attention in the scientific community. This review explores the most recent developments in the recognition and characterization of TRPC6. Additionally, it considers the field's prospects while examining how TRPC6 might be altered and its clinical applications.

Phosphatase A1 accessory protein PlaS from Serratia marcescens controls cell membrane permeability, fluidity, hydrophobicity, and fatty acid composition in Escherichia coli BL21

Phospholipase A1 (PlaA) plays a pivotal role in diverse applications within the food and biochemical medical industries. Herein, we investigate the impact of the accessory protein encoded by plaS from Serratia marcescens on PlaA activity in Escherichia coli. Notably, PlaS demonstrates the ability to enhance PlaA activity while concurrently exhibiting inhibitory effects on the growth of E. coli BL21 (DE3). Our study revolves around probing the inhibitory action of PlaS on E. coli BL21 (DE3). PlaS exhibits a propensity to heighten both the permeability of outer and inner cell membranes, leading to concomitant reductions in membrane fluidity and surface hydrophobicity. This phenomenon is validated through scanning electron microscopy (SEM) analysis, which highlights PlaS's capacity to compromise membrane integrity. Moreover, through a comprehensive comparative transcriptomic sequencing approach, we identify four down-regulated genes (galM, ybhC, ldtC, and kdpB) alongside two up-regulated genes (rbsB and degP). These genes are intricately associated with processes such as cell membrane synthesis and modification, energy metabolism, and transmembrane transport. Our investigation unveils the intricate gene-level mechanisms underpinning PlaS-mediated growth inhibition and membrane disruption. Consequently, our findings serve as a significant reference for the elucidation of membrane protein mechanisms, shedding light on potential avenues for future exploration.

Non-canonical helical transitions and conformational switching are associated with characteristic flexibility and disorder indices in TRP and Kv channels

Structural evidence and much experimental data have demonstrated the presence of non-canonical helical substructures (π and 3₁₀) in regions of great functional relevance both in TRP as in Kv channels. Through an exhaustive compositional analysis of the sequences underlying these substructures, we find that each of them is associated with characteristic local flexibility profiles, which in turn are implicated in significant conformational rearrangements and interactions with specific ligands. We found that α-to-π helical transitions are associated with patterns of local rigidity whereas α-to-3₁₀ transitions are mainly leagued with high local flexibility profiles. We also study the relationship between flexibility and protein disorder in the transmembrane domain of these proteins. By contrasting these two parameters, we located regions showing a sort of structural discrepancy between these similar but not identical protein attributes. Notably, these regions are presumably implicated in important conformational rearrangements during the gating in those channels. In that sense, finding these regions where flexibility and disorder are not proportional allows us to detect regions with potential functional dynamism. From this point of view, we highlighted some conformational rearrangements that occur during ligand binding events, the compaction, and refolding of the outer pore loops in several TRP channels, as well as the well-known S4 motion in Kv 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.

Selective Activation of a TRPC6 Ion Channel Over TRPC3 by Metalated Type-B Polycyclic Polyprenylated Acylphloroglucinols

Selective modulation of TRPC6 ion channels is a promising therapeutic approach for neurodegenerative diseases and depression. A significant advancement showcases the selective activation of TRPC6 through metalated type-B PPAP, termed PPAP53. This success stems from PPAP53's 1,3-diketone motif facilitating metal coordination. PPAP53 is water-soluble and as potent as hyperforin, the gold standard in this field. In contrast to type-A, type-B PPAPs offer advantages such as gram-scale synthesis, easy derivatization, and long-term stability. Our investigations reveal PPAP53 selectively binding to the C-terminus of TRPC6. Although cryoelectron microscopy has resolved the majority of the TRPC6 structure, the binding site in the C-terminus remained unresolved. To address this issue, we employed state-of-the-art artificial-intelligence-based protein structure prediction algorithms to predict the missing region. Our computational results, validated against experimental data, indicate that PPAP53 binds to the 777LLKL780-region of the C-terminus, thus providing critical insights into the binding mechanism of PPAP53.

Canonical transient receptor potential channel 1 aggravates myocardial ischemia-and-reperfusion injury by upregulating reactive oxygen species

The canonical transient receptor potential channel (TRPC) proteins form Ca2+-permeable cation channels that are involved in various heart diseases. However, the roles of specific TRPC proteins in myocardial ischemia/reperfusion (I/R) injury remain poorly understood. We observed that TRPC1 and TRPC6 were highly expressed in the area at risk (AAR) in a coronary artery ligation induced I/R model. Trpc1-/- mice exhibited improved cardiac function, lower serum Troponin T and serum creatine kinase level, smaller infarct volume, less fibrotic scars, and fewer apoptotic cells after myocardial-I/R than wild-type or Trpc6-/- mice. Cardiomyocyte-specific knockdown of Trpc1 using adeno-associated virus 9 mitigated myocardial I/R injury. Furthermore, Trpc1 deficiency protected adult mouse ventricular myocytes (AMVMs) and HL-1 cells from death during hypoxia/reoxygenation (H/R) injury. RNA-sequencing-based transcriptome analysis revealed differential expression of genes related to reactive oxygen species (ROS) generation in Trpc1-/- cardiomyocytes. Among these genes, oxoglutarate dehydrogenase-like (Ogdhl) was markedly downregulated. Moreover, Trpc1 deficiency impaired the calcineurin (CaN)/nuclear factor-kappa B (NF-κB) signaling pathway in AMVMs. Suppression of this pathway inhibited Ogdhl upregulation and ROS generation in HL-1 cells under H/R conditions. Chromatin immunoprecipitation assays confirmed NF-κB binding to the Ogdhl promoter. The cardioprotective effect of Trpc1 deficiency was canceled out by overexpression of NF-κB and Ogdhl in cardiomyocytes. In conclusion, our findings reveal that TRPC1 is upregulated in the AAR following myocardial I/R, leading to increased Ca2+ influx into associated cardiomyocytes. Subsequently, this upregulates Ogdhl expression through the CaN/NF-κB signaling pathway, ultimately exacerbating ROS production and aggravating myocardial I/R injury.

Role of Neuronal TRPC6 Channels in Synapse Development, Memory Formation and Animal Behavior

The transient receptor potential cation channel, subfamily C, member 6 (TRPC6), has been believed to adjust the formation of an excitatory synapse. The positive regulation of TRPC6 engenders synapse enlargement and improved learning and memory in animal models. TRPC6 is involved in different synaptoprotective signaling pathways, including antagonism of N-methyl-D-aspartate receptor (NMDAR), activation of brain-derived neurotrophic factor (BDNF) and postsynaptic store-operated calcium entry. Positive regulation of TRPC6 channels has been repeatedly shown to be good for memory formation and storage. TRPC6 is mainly expressed in the hippocampus, particularly in the dentate granule cells, cornu Ammonis 3 (CA3) pyramidal cells and gamma-aminobutyric acid (GABA)ergic interneurons. It has been observed that TRPC6 agonists have a great influence on animal behavior including memory formation and storage The purpose of this review is to collect the available information on the role of TRPC6 in memory formation in various parts of the brain to understand how TRPC6-specific pharmaceutical agents will affect memory in distinct parts of the central nervous system (CNS).

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.

Current advancements and future perspectives of long noncoding RNAs in lipid metabolism and signaling

BACKGROUND

The investigation of lncRNAs has provided a novel perspective for elucidating mechanisms underlying diverse physiological and pathological processes. Compelling evidence has revealed an intrinsic link between lncRNAs and lipid metabolism, demonstrating that lncRNAs-induced disruption of lipid metabolism and signaling contribute to the development of multiple cancers and some other diseases, including obesity, fatty liver disease, and cardiovascular disease.

AIMOF REVIEW

The current review summarizes the recent advances in basic research about lipid metabolism and lipid signaling-related lncRNAs. Meanwhile, the potential and challenges of targeting lncRNA for the therapy of cancers and other lipid metabolism-related diseases are also discussed.

KEY SCIENTIFIC CONCEPT OF REVIEW

Compared with the substantial number of lncRNA loci, we still know little about the role of lncRNAs in metabolism. A more comprehensive understanding of the function and mechanism of lncRNAs may provide a new standpoint for the study of lipid metabolism and signaling. Developing lncRNA-based therapeutic approaches is an effective strategy for lipid metabolism-related diseases.

Transient Receptor Potential Canonical 6 (TRPC6) Channel in the Pathogenesis of Diseases: A Jack of Many Trades

The mammalian Transient Receptor Potential Canonical (TRPC) subfamily comprises seven transmembrane proteins (TRPC1-7) forming cation channels in the plasma membrane of mammalian cells. TRPC channels mediate Ca²⁺ and Na⁺ influx into the cells. Amongst TRPCs, TRPC6 deficiency or increased activity due to gain-of-function mutations has been associated with a multitude of diseases, such as kidney disease, pulmonary disease, and neurological disease. Indeed, the TRPC6 protein is expressed in various organs and is involved in diverse signalling pathways. The last decade saw a surge in the investigative studies concerning the physiological roles of TRPC6 and describing the development of new pharmacological tools modulating TRPC6 activity. The current review summarizes the progress achieved in those investigations.

Transient receptor potential canonical type 6 (TRPC6) O-GlcNAcylation at Threonine-221 plays potent role in channel regulation

Transient receptor potential canonical type 6 (TRPC6) is a non-voltage-gated channel that principally conducts calcium. Elevated channel activation contributes to fibrosis, hypertrophy, and proteinuria, often coupled to stimulation of nuclear factor of activated T-cells (NFAT). TRPC6 is post-translationally regulated, but a role for O-linked β-N-acetyl glucosamine (O-GlcNAcylation) as elevated by diabetes, is unknown. Here we show TRPC6 is constitutively O-GlcNAcylated at Ser14, Thr70, and Thr221 in the N-terminus ankryn-4 (AR4) and linker (LH1) domains. Mutagenesis to alanine reveals T221 as a critical controller of resting TRPC6 conductance, and associated NFAT activity and pro-hypertrophic signaling. T→A mutations at sites homologous in closely related TRPC3 and TRPC7 also increases their activity. Molecular modeling predicts interactions between Thr221-O-GlcNAc and Ser199, Glu200, and Glu246, and combined alanine substitutions of the latter similarly elevates resting NFAT activity. Thus, O-GlcNAcylated T221 and interactions with coordinating residues is required for normal TRPC6 channel conductance and NFAT activation.

Clenbuterol Prevents Mechanical Unloading-Induced Myocardial Atrophy via Upregulation of Transient Receptor Potential Channel-3

Left ventricular assist device in combination with clenbuterol has been demonstrated to significantly improve heart function in patients with advanced heart failure. However, the roles of clenbuterol in mechanical unloading and its underlying mechanism are poorly understood. A rat abdominal heart transplantation model has been developed to mimic mechanical unloading of the heart. The recipient rats were randomly segregated into experimental groups for the daily administration of either saline (the "Trans" group; n = 13) or clenbuterol (2 mg/kg, the "Trans + CB" group; n = 12). Another group of 10 rats served as a treatment mimic control/sham animals (the "Sham" group). All interventions were performed via intraperitoneal injections once daily for 4 weeks. The Trans group animals exhibited myocardial atrophy and dysfunction with decreased expression levels of transient receptor potential channel 3 (TRPC3) and phospholipase C-β1 (PLC-β1) at 4 weeks post-transplantation. Administration of clenbuterol improved cardiac function, prevented myocardial atrophy, and restored expression of TRPC3 and PLC-β1 in the unloaded hearts of the "Trans + CB" animals at 4 weeks post-transplantation. Silencing of the TRPC3 gene by siRNA inhibited the pro-hypertrophic effect of clenbuterol in the rat primary cardiomyocytes in vitro. Furthermore, U73122, an inhibitor of the PLC-β1/diacylglycerol (DAG) pathway, significantly attenuated clenbuterol-induced upregulation of TRPC3 in cardiomyocytes. These findings suggest that the anti-atrophic effect of clenbuterol may be dependent on the upregulation of TRPC3 through the activation of the PLC-β1/DAG pathway during mechanical unloading. The results of our study reveal a potential target for the prevention and treatment of mechanical unloading-induced myocardial atrophy.

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.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

TRPC Channels in the Physiology and Pathophysiology of the Renal Tubular System: What Do We Know?

The study of transient receptor potential (TRP) channels has dramatically increased during the past few years. TRP channels function as sensors and effectors in the cellular adaptation to environmental changes. Here, we review literature investigating the physiological and pathophysiological roles of TRPC channels in the renal tubular system with a focus on TRPC3 and TRPC6. TRPC3 plays a key role in Ca²⁺ homeostasis and is involved in transcellular Ca²⁺ reabsorption in the proximal tubule and the collecting duct. TRPC3 also conveys the osmosensitivity of principal cells of the collecting duct and is implicated in vasopressin-induced membrane translocation of AQP-2. Autosomal dominant polycystic kidney disease (ADPKD) can often be attributed to mutations of the PKD2 gene. TRPC3 is supposed to have a detrimental role in ADPKD-like conditions. The tubule-specific physiological functions of TRPC6 have not yet been entirely elucidated. Its pathophysiological role in ischemia-reperfusion injuries is a subject of debate. However, TRPC6 seems to be involved in tumorigenesis of renal cell carcinoma. In summary, TRPC channels are relevant in multiples conditions of the renal tubular system. There is a need to further elucidate their pathophysiology to better understand certain renal disorders and ultimately create new therapeutic targets to improve patient care.

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.

New Positive TRPC6 Modulator Penetrates Blood-Brain Barrier, Eliminates Synaptic Deficiency and Restores Memory Deficit in 5xFAD Mice

Synapse loss in the brain of Alzheimer's disease patients correlates with cognitive dysfunctions. Drugs that limit synaptic loss are promising pharmacological agents. The transient receptor potential cation channel, subfamily C, member 6 (TRPC6) regulates the formation of an excitatory synapse. Positive regulation of TRPC6 results in increased synapse formation and enhances learning and memory in animal models. The novel selective TRPC6 agonist, 3-(3-,4-Dihydro-6,7-dimethoxy-3,3-dimethyl-1-isoquinolinyl)-2H-1-benzopyran-2-one, has recently been identified. Here we present in silico, in vitro, ex vivo, pharmacokinetic and in vivo studies of this compound. We demonstrate that it binds to the extracellular agonist binding site of the human TRPC6, protects hippocampal mushroom spines from amyloid toxicity in vitro, efficiently recovers synaptic plasticity in 5xFAD brain slices, penetrates the blood-brain barrier and recovers cognitive deficits in 5xFAD mice. We suggest that C20 might be recognized as the novel TRPC6-selective drug suitable to treat synaptic deficiency in Alzheimer's disease-affected hippocampal neurons.

Mechanosensitive cation currents through TRPC6 and Piezo1 channels in human pulmonary arterial endothelial cells

Mechanosensitive cation channels and Ca2+ influx through these channels play an important role in the regulation of endothelial cell functions. Transient receptor potential canonical channel 6 (TRPC6) is a diacylglycerol-sensitive nonselective cation channel that forms receptor-operated Ca2+ channels in a variety of cell types. Piezo1 is a mechanosensitive cation channel activated by membrane stretch and shear stress in lung endothelial cells. In this study, we report that TRPC6 and Piezo1 channels both contribute to membrane stretch-mediated cation currents and Ca2+ influx or increase in cytosolic-free Ca2+ concentration ([Ca2+]cyt) in human pulmonary arterial endothelial cells (PAECs). The membrane stretch-mediated cation currents and increase in [Ca2+]cyt in human PAECs were significantly decreased by GsMTX4, a blocker of Piezo1 channels, and by BI-749327, a selective blocker of TRPC6 channels. Extracellular application of 1-oleoyl-2-acetyl-sn-glycerol (OAG), a membrane permeable analog of diacylglycerol, rapidly induced whole cell cation currents and increased [Ca2+]cyt in human PAECs and human embryonic kidney (HEK)-cells transiently transfected with the human TRPC6 gene. Furthermore, membrane stretch with hypo-osmotic or hypotonic solution enhances the cation currents in TRPC6-transfected HEK cells. In HEK cells transfected with the Piezo1 gene, however, OAG had little effect on the cation currents, but membrane stretch significantly enhanced the cation currents. These data indicate that, while both TRPC6 and Piezo1 are involved in generating mechanosensitive cation currents and increases in [Ca2+]cyt in human PAECs undergoing mechanical stimulation, only TRPC6 (but not Piezo1) is sensitive to the second messenger diacylglycerol. Selective blockers of these channels may help develop novel therapies for mechanotransduction-associated pulmonary vascular remodeling in patients with pulmonary arterial hypertension.

Unfolding and identification of membrane proteins in situ

Single-molecule force spectroscopy (SMFS) uses the cantilever tip of an AFM to apply a force able to unfold a single protein. The obtained force-distance curve encodes the unfolding pathway, and from its analysis it is possible to characterize the folded domains. SMFS has been mostly used to study the unfolding of purified proteins, in solution or reconstituted in a lipid bilayer. Here, we describe a pipeline for analyzing membrane proteins based on SMFS, that involves the isolation of the plasma membrane of single cells and the harvesting of force-distance curves directly from it. We characterized and identified the embedded membrane proteins combining, within a Bayesian framework, the information of the shape of the obtained curves, with the information from Mass Spectrometry and proteomic databases. The pipeline was tested with purified/reconstituted proteins and applied to five cell types where we classified the unfolding of their most abundant membrane proteins. We validated our pipeline by overexpressing 4 constructs, and this allowed us to gather structural insights of the identified proteins, revealing variable elements in the loop regions. Our results set the basis for the investigation of the unfolding of membrane proteins in situ, and for performing proteomics from a membrane fragment.

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.

Gain-of-function, focal segmental glomerulosclerosis Trpc6 mutation minimally affects susceptibility to renal injury in several mouse models

Mutations in TRPC6 are a cause of autosomal dominant focal segmental glomerulosclerosis in humans. Many of these mutations are known to have a gain-of-function effect on the non-specific cation channel function of TRPC6. In vitro studies have suggested these mutations affect several signaling pathways, but in vivo studies have largely compared wild-type and Trpc6-deficient rodents. We developed mice carrying a gain-of-function Trpc6 mutation encoding an E896K amino acid change, corresponding to a known FSGS mutation in TRPC6. Homozygous mutant Trpc6 animals have no appreciable renal pathology, and do not develop albuminuria until very advanced age. The Trpc6E896K mutation does not impart susceptibility to PAN nephrosis. The animals show a slight delay in recovery from the albumin overload model. In response to chronic angiotensin II infusion, Trpc6E896K/E896K mice have slightly greater albuminuria initially compared to wild-type animals, an effect that is lost at later time points, and a statistically non-significant trend toward more glomerular injury. This phenotype is nearly opposite to that of Trpc6-deficient animals previously described. The Trpc6 mutation does not appreciably impact renal interstitial fibrosis in response to either angiotensin II infusion, or folate-induced kidney injury. TRPC6 protein and TRPC6-agonist induced calcium influx could not be detected in glomeruli. In sum, these findings suggest that a gain-of-function Trpc6 mutation confers only a mild susceptibility to glomerular injury in the mouse.

Critical contributions of pre-S1 shoulder and distal TRP box in DAG-activated TRPC6 channel by PIP2 regulation

Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂ or PIP₂) regulates the activities of numerous membrane proteins, including diacylglycerol(DAG)-activated TRPC3/6/7 channels. Although PIP₂ binding is known to support DAG-activated TRP channel activity, its binding site remains unknown. We screened for PIP₂ binding sites within TRPC6 channels through extensive mutagenesis. Using voltage-sensitive phosphatase (DrVSP), we found that Arg437 and Lys442, located in the channel’s pre-S1 domain/shoulder, are crucial for interaction with PIP₂. To gain structural insights, we conducted computer protein–ligand docking simulations with the pre-S1 domain/shoulder of TRPC6 channels. Further, the functional significance of PIP₂ binding to the pre-S1 shoulder was assessed for receptor-operated channel functions, cross-reactivity to DAG activation, and the kinetic model simulation. These results revealed that basic residues in the pre-S1 domain/shoulder play a central role in the regulation of PIP₂-dependent gating. In addition, neutralizing mutation of K771 in the distal TRP box reversed the effect of PIP₂ depletion from inhibiting to potentiating channel activity. A similar effect was seen in TRPV1 channels, which suggests that TRPC6 possesses a common but robust polarity switch mediating the PIP₂-dependent effect. Overall, these mutagenesis studies reveal functional and structural insights for how basic residues and channel segments in TRP channels are controlled through phosphoinositides recognition.

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.

Further exploration of the benzimidazole scaffold as TRPC5 inhibitors: identification of 1-alkyl-2-(pyrrolidin-1-yl)-1H-benzo[d]imidazoles as potent and selective inhibitors

The transient receptor potential cation channel 5 (TRPC5) plays an important role in numerous cellular processes. Due to this, it has gained considerable attention over the past few years as a potential therapeutic target. Recently, TRPC5 has been shown to be involved in the regulation of podocyte survival, indicating a potential treatment option for chronic kidney disease. In addition, a recent study has shown TRPC5 to be expressed in human sensory neurons and suggests that TRPC5 inhibition could be an effective treatment for spontaneous and tactile pain. To understand these processes more fully, potent and selective tool compounds are needed. Herein we report further exploration of the 2‐aminobenzimidazole scaffold as a potent TRPC5 inhibitor, culminating in the discovery of 16 f as a potent and selective TRPC5 inhibitor.

Identification of an arthropod molecular target for plant-derived natural repellents

Rational control of arthropod pests is important for animal and human health as well as biodiversity preservation. As an alternative to synthetic chemical pesticides, natural repellents represent an ecological method of pest control. Through an exceptional gene library screening in Mesobuthus martensii scorpions, we here uncover a transient receptor potential ion channel as the chemosensory sensor for plant-derived repellents. Its ortholog ion channel in Drosophila melanogaster also acts as a molecular receptor of natural repellents and mediates avoidance behavior. This work thus identifies a molecular basis for arthropod chemosensing and should help update the ecological strategies for pest control while preserving biodiversity.

Arthropods maintain ecosystem balance while also contributing to the spread of disease. Plant-derived natural repellents represent an ecological method of pest control, but their direct molecular targets in arthropods remain to be further elucidated. Occupying a critical phylogenetic niche in arthropod evolution, scorpions retain an ancestral genetic profile. Here, using a behavior-guided screening of the Mesobuthus martensii genome, we identified a scorpion transient receptor potential (sTRP1) channel that senses Cymbopogon-derived natural repellents, while remaining insensitive to the synthetic chemical pesticide DEET. Scrutinizing orthologs of sTRP1 in Drosophila melanogaster, we further demonstrated dTRPγ ion channel as a chemosensory receptor of natural repellents to mediate avoidance behavior. This study sheds light on arthropod molecular targets of natural repellents, exemplifying the arthropod–plant adaptation. It should also help the rational design of insect control strategy and in conserving biodiversity.

Irisin mediates beiging of adipose-derived mesenchymal stem cells through binding to TRPC3

BACKGROUND

Beiging of white fat plays an important role in energy metabolism. Beige adipocytes contribute to the regulation of body weight and body temperature through expenditure of chemical energy to produce heat, and they have therefore recently attracted considerable attention as potential targets for therapeutic approaches in metabolic disorders, including obesity. All adipocytes, including beige adipocytes, differentiate from mesenchymal stem cells (MSCs), which may provide an important path for clinical intervention; however, the mechanism of beiging of human adipose cell-derived MSCs is not fully understood. Here, we provide insights on the role of IRISIN, which is known to be secreted by skeletal muscle and promote beiging of white fat.

RESULTS

We established an IRISIN-induced mesenchymal stem cell beiging model and found that IRISIN protein interacts with the MSC membrane protein TRPC3. This interaction results in calcium influx and consequential activation of Erk and Akt signaling pathways, which causes phosphorylation of PPARγ. The phosphorylated PPARγ enters the nucleus and binds the UCP1 promoter region. Furthermore, the role of TRPC3 in the beiging of MSCs was largely abolished in Trpc3^-/- mice. We additionally demonstrate that the calcium concentration in the brain of mice increases upon IRISIN stimulation, followed by an increase in the content of excitatory amino acids and norepinephrine, while Trpc3^-/- mice exhibit the reverse effect.

CONCLUSIONS

We found that TRPC3 is a key factor in irisin-induced beiging of MSCs, which may provide a new target pathway in addressing metabolic disorders. Our results additionally suggest that the interaction of irisin with TRPC3 may affect multiple tissues, including the brain.

A Pharmacokinetic and Metabolism Study of the TRPC6 Inhibitor SH045 in Mice by LC-MS/MS

TRPC6, the sixth member of the family of canonical transient receptor potential (TRP) channels, contributes to a variety of physiological processes and human pathologies. This study extends the knowledge on the newly developed TRPC6 blocker SH045 with respect to its main target organs beyond the description of plasma kinetics. According to the plasma concentration-time course in mice, SH045 is measurable up to 24 h after administration of 20 mg/kg BW (i.v.) and up to 6 h orally. The short plasma half-life and rather low oral bioavailability are contrasted by its reported high potency. Dosage limits were not worked out, but absence of safety concerns for 20 mg/kg BW supports further dose exploration. The disposition of SH045 is described. In particular, a high extravascular distribution, most prominent in lung, and a considerable renal elimination of SH045 were observed. SH045 is a substrate of CYP3A4 and CYP2A6. Hydroxylated and glucuronidated metabolites were identified under optimized LC-MS/MS conditions. The results guide a reasonable selection of dose and application route of SH045 for target-directed preclinical studies in vivo with one of the rare high potent and subtype-selective TRPC6 inhibitors available.

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.

Structure of the ancient TRPY1 channel from Saccharomyces cerevisiae reveals mechanisms of modulation by lipids and calcium

Transient receptor potential (TRP) channels emerged in fungi as mechanosensitive osmoregulators. The Saccharomyces cerevisiae vacuolar TRP yeast 1 (TRPY1) is the most studied TRP channel from fungi, but the structure and details of channel modulation remain elusive. Here, we describe the full-length cryoelectron microscopy structure of TRPY1 at 3.1 Å resolution in a closed state. The structure, despite containing an evolutionarily conserved and archetypical transmembrane domain, reveals distinctive structural folds for the cytosolic N and C termini, compared with other eukaryotic TRP channels. We identify an inhibitory phosphatidylinositol 3-phosphate (PI(3)P) lipid-binding site, along with two Ca2+-binding sites: a cytosolic site, implicated in channel activation and a vacuolar lumen site, implicated in inhibition. These findings, together with data from microsecond-long molecular dynamics simulations and a model of a TRPY1 open state, provide insights into the basis of TRPY1 channel modulation by lipids and Ca2+, and the molecular evolution of TRP channels.

Roles of Intramolecular Interactions in the Regulation of TRP Channels

The transient receptor potential (TRP) channels, classified into six (-A, -V, -P, -C, -M, -ML, -N and -Y) subfamilies, are important membrane sensors and mediators of diverse stimuli including pH, light, mechano-force, temperature, pain, taste, and smell. The mammalian TRP superfamily of 28 members share similar membrane topology with six membrane-spanning helices (S1-S6) and cytosolic N-/C-terminus. Abnormal function or expression of TRP channels is associated with cancer, skeletal dysplasia, immunodeficiency, and cardiac, renal, and neuronal diseases. The majority of TRP members share common functional regulators such as phospholipid PIP2, 2-aminoethoxydiphenyl borate (2-APB), and cannabinoid, while other ligands are more specific, such as allyl isothiocyanate (TRPA1), vanilloids (TRPV1), menthol (TRPM8), ADP-ribose (TRPM2), and ML-SA1 (TRPML1). The mechanisms underlying the gating and regulation of TRP channels remain largely unclear. Recent advances in cryogenic electron microscopy provided structural insights into 19 different TRP channels which all revealed close proximity of the C-terminus with the N-terminus and intracellular S4-S5 linker. Further studies found that some highly conserved residues in these regions of TRPV, -P, -C and -M members mediate functionally critical intramolecular interactions (i.e., within one subunit) between these regions. This review provides an overview on (1) intramolecular interactions in TRP channels and their effect on channel function; (2) functional roles of interplays between PIP2 (and other ligands) and TRP intramolecular interactions; and (3) relevance of the ligand-induced modulation of intramolecular interaction to diseases.

Structure-function relationships of the disease-linked A218T oxytocin receptor variant

Various single nucleotide polymorphisms (SNPs) in the oxytocin receptor (OXTR) gene have been associated with behavioral traits, autism spectrum disorder (ASD) and other diseases. The non-synonymous SNP rs4686302 results in the OXTR variant A218T and has been linked to core characteristics of ASD, trait empathy and preterm birth. However, the molecular and intracellular mechanisms underlying those associations are still elusive. Here, we uncovered the molecular and intracellular consequences of this mutation that may affect the psychological or behavioral outcome of oxytocin (OXT)-treatment regimens in clinical studies, and provide a mechanistic explanation for an altered receptor function. We created two monoclonal HEK293 cell lines, stably expressing either the wild-type or A218T OXTR. We detected an increased OXTR protein stability, accompanied by a shift in Ca²⁺ dynamics and reduced MAPK pathway activation in the A218T cells. Combined whole-genome and RNA sequencing analyses in OXT-treated cells revealed 7823 differentially regulated genes in A218T compared to wild-type cells, including 429 genes being associated with ASD. Furthermore, computational modeling provided a molecular basis for the observed change in OXTR stability suggesting that the OXTR mutation affects downstream events by altering receptor activation and signaling, in agreement with our in vitro results. In summary, our study provides the cellular mechanism that links the OXTR rs4686302 SNP with genetic dysregulations associated with aspects of ASD.

Analysis of hyperforin (St. John's wort) action at TRPC6 channel leads to the development of a new class of antidepressant drugs

St. John's wort is an herb, long used in folk medicine for the treatment of mild depression. Its antidepressant constituent, hyperforin, has properties such as chemical instability and induction of drug-drug interactions that preclude its use for individual pharmacotherapies. Here we identify the transient receptor potential canonical 6 channel (TRPC6) as a druggable target to control anxious and depressive behavior and as a requirement for hyperforin antidepressant action. We demonstrate that TRPC6 deficiency in mice not only results in anxious and depressive behavior, but also reduces excitability of hippocampal CA1 pyramidal neurons and dentate gyrus granule cells. Using electrophysiology and targeted mutagenesis, we show that hyperforin activates the channel via a specific binding motif at TRPC6. We performed an analysis of hyperforin action to develop a new antidepressant drug that uses the same TRPC6 target mechanism for its antidepressant action. We synthesized the hyperforin analog Hyp13, which shows similar binding to TRPC6 and recapitulates TRPC6-dependent anxiolytic and antidepressant effects in mice. Hyp13 does not activate pregnan-X-receptor (PXR) and thereby loses the potential to induce drug-drug interactions. This may provide a new approach to develop better treatments for depression, since depression remains one of the most treatment-resistant mental disorders, warranting the development of effective drugs based on naturally occurring compounds.

Computer-Based Drug Design of Positive Modulators of Store-Operated Calcium Channels to Prevent Synaptic Dysfunction in Alzheimer's Disease

Store-operated calcium entry (SOCE) constitutes a fine-tuning mechanism responsible for the replenishment of intracellular stores. Hippocampal SOCE is regulated by store-operated channels (SOC) organized in tripartite complex TRPC6/ORAI2/STIM2. It is suggested that in neurons, SOCE maintains intracellular homeostatic Ca2+ concentration at resting conditions and is needed to support the structure of dendritic spines. Recent evidence suggests that positive modulators of SOC are prospective drug candidates to treat Alzheimer’s disease (AD) at early stages. Although STIM2 and ORAI2 are definitely involved in the regulation of nSOC amplitude and a play major role in AD pathogenesis, growing evidence suggest that it is not easy to target these proteins pharmacologically. Existing positive modulators of TRPC6 are unsuitable for drug development due to either bad pharmacokinetics or side effects. Thus, we concentrate the review on perspectives to develop specific nSOC modulators based on available 3D structures of TRPC6, ORAI2, and STIM2. We shortly describe the structural features of existing models and the methods used to prepare them. We provide commonly used steps applied for drug design based on 3D structures of target proteins that might be used to develop novel AD preventing therapy.

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.

GSK1702934A and M085 directly activate TRPC6 via a mechanism of stimulating the extracellular cavity formed by the pore helix and transmembrane helix S6

Transient receptor potential canonical (TRPC) channels, as important membrane proteins regulating intracellular calcium (Ca2+i) signaling, are involved in a variety of physiological and pathological processes. Activation and regulation of TRPC are more dependent on membrane or intracellular signals. However, how extracellular signals regulate TRPC6 function remains to be further investigated. Here, we suggest that two distinct small molecules, M085 and GSK1702934A, directly activate TRPC6, both through a mechanism of stimulation of extracellular sites formed by the pore helix (PH) and transmembrane (TM) helix S6. In silico docking scanning of TRPC6 identified three extracellular sites that can bind small molecules, of which only mutations on residues of PH and S6 helix significantly reduced the apparent affinity of M085 and GSK1702934A and attenuated the maximal response of TRPC6 to these two chemicals by altering channel gating of TRPC6. Combing metadynamics, molecular dynamics simulations, and mutagenesis, we revealed that W679, E671, E672, and K675 in the PH and N701 and Y704 in the S6 helix constitute an orthosteric site for the recognition of these two agonists. The importance of this site was further confirmed by covalent modification of amino acid residing at the interface of the PH and S6 helix. Given that three structurally distinct agonists M085, GSK1702934A, and AM-0883, act at this site, as well as the occupancy of lipid molecules at this position found in other TRP subfamilies, it is suggested that the cavity formed by the PH and S6 has an important role in the regulation of TRP channel function by extracellular signals.

Reprint of: Mechanosensitive ion channels in cell migration

Cellular processes are initiated and regulated by different stimuli, including mechanical forces. Cell membrane mechanosensors represent the first step towards the conversion of mechanical stimuli to a biochemical or electrical response. Mechanosensitive (MS) ion channels form a growing family of ion gating channels that respond to direct physical force or plasma membrane deformations. A number of calcium (Ca²⁺) permeable MS channels are known to regulate the initiation, direction, and persistence of cell migration during development and tumour progression. While the evidence that links individual MS ion channels to cell migration is growing, a unified analysis of the molecular mechanisms regulated downstream of MS ion channel activation is lacking. In this review, we describe the MS ion channel families known to regulate cell migration. We discuss the molecular mechanisms that act downstream of MS ion channels with an emphasis on Ca²⁺ mediated processes. Finally, we propose the future directions and impact of MS ion channel activity in the field of cell migration.

Structural Pharmacology of TRP Channels

Transient receptor potential (TRP) ion channels are a super-family of ion channels that mediate transmembrane cation flux with polymodal activation, ranging from chemical to physical stimuli. Furthermore, due to their ubiquitous expression and role in human diseases, they serve as potential pharmacological targets. Advances in cryo-EM TRP channel structural biology has revealed general, as well as diverse, architectural elements and regulatory sites among TRP channel subfamilies. Here, we review the endogenous and pharmacological ligand-binding sites of TRP channels and their regulatory mechanisms.