Pico145 - powerful new tool for TRPC1/4/5 channels

Reduction of TRPC1/TRPC3 mediated Ca2+-signaling protects oxidative stress-induced COPD

Oxidative stress is a predisposing factor in Chronic Obstructive Pulmonary Disease (COPD). Specifically, pulmonary epithelial (PE) cells reduce antioxidant capacity during COPD because of the continuous production of reactive oxygen species (ROS). However, the molecular pathogenesis that governs such ROS activity is unclear. Here we show that the dysregulation of intracellular calcium concentration ([Ca2+]i) in PE cells from COPD patients, compared to the healthy PE cells, is associated with the robust functional expressions of Transient Receptor Potential Canonical (TRPC)1 and TRPC3 channels, and Ca2+ entry (SOCE) components, Stromal Interaction Molecule 1 (STIM1) and ORAI1 channels. Additionally, the elevated expression levels of fibrotic, inflammatory, oxidative, and apoptotic markers in cells from COPD patients suggest detrimental pathway activation, thereby reducing the ability of lung remodeling. To further delineate the mechanism, we used human lung epithelial cell line, A549, since the behavior of SOCE and the expression patterns of TRPC1/C3, STIM1, and ORAI1 were much like PE cells. Notably, the knockdown of TRPC1/C3 in A549 cells substantially reduced the SOCE-induced [Ca2+]i rise, and reversed the ROS-mediated oxidative, fibrotic, inflammatory, and apoptotic responses, thus confirming the role of TRPC1/C3 in SOCE driven COPD-like condition. Higher TRPC1/C3, STIM1, and ORAI1 expressions, along with a greater Ca2+ entry, via SOCE in ROS-induced A549 cells, led to the rise in oxidative, fibrotic, inflammatory, and apoptotic gene expression, specifically through the extracellular signal-regulated kinase (ERK) pathway. Abatement of TRPC1 and/or TRPC3 reduced the mobilization of [Ca2+]i and reversed apoptotic gene expression and ERK activation, signifying the involvement of TRPC1/C3. Together these data suggest that TRPC1/C3 and SOCE facilitate the COPD condition through ROS-mediated cell death, thus implicating their likely roles as potential therapeutic targets for COPD. SUMMARY: Alterations in Ca2+ signaling modalities in normal pulmonary epithelial cells exhibit COPD through oxidative stress and cellular injury, compromising repair, which was alleviated through inhibition of store-operated calcium entry. SUBJECT AREA: Calcium, ROS, Cellular signaling, lung disease.

Diacerein modulates TLR4/ NF-κB/IL-1β and TRPC1/CHOP signalling pathways in gentamicin-induced parotid toxicity in rats

The present study aimed to identify the possible protective effect of diacerein (DIA) on gentamicin (GNT)-induced parotid toxicity in rats. DIA was administered in the presence and absence of GNT. Thirty-two Wistar adult male rats were randomly arranged into four groups: control, DIA (50 mg/kg/day), GNT (100 mg/kg) and GNT+DIA groups for 8 days. Parotid oxidative stress parameters, besides inflammatory and apoptotic biomarkers, were evaluated. Salivary flow rate, transient receptor potential canonical 1 (TRCP1), and C/EBP homologous protein (CHOP) in parotid tissue were measured. A parotid histopathological examination and an interleukin-1 beta (IL-1β) immunohistochemical study were also performed. GNT significantly increased parotid oxidative stress, inflammatory, apoptotic and CHOP biomarkers with decreased salivary flow rate and TRCP1 level. A histopathological picture of parotid damage and high IL-1β immunoexpression were detected. DIA significantly normalized the distributed oxidative, inflammatory and apoptotic indicators, CHOP and TRCP1, with a prompt improvement in the histopathological picture and a decrease in IL-1β immunoexpression. These results reported that DIA protects against GNT-induced parotid toxicity via modulation of TLR4/NF-κB/IL-1β and TRPC1/CHOP signalling pathways.

ORAI Calcium Channels: Regulation, Function, Pharmacology, and Therapeutic Targets

The changes in intracellular free calcium (Ca2+) levels are one of the most widely regulators of cell function; therefore, calcium as a universal intracellular mediator is involved in very important human diseases and disorders. In many cells, Ca2+ inflow is mediated by store-operated calcium channels, and it is recognized that the store-operated calcium entry (SOCE) is mediated by the two partners: the pore-forming proteins Orai (Orai1-3) and the calcium store sensor, stromal interaction molecule (STIM1-2). Importantly, the Orai/STIM channels are involved in crucial cell signalling processes such as growth factors, neurotransmitters, and cytokines via interaction with protein tyrosine kinase coupled receptors and G protein-coupled receptors. Therefore, in recent years, the issue of Orai/STIM channels as a drug target in human diseases has received considerable attention. This review summarizes and highlights our current knowledge of the Orai/STIM channels in human diseases and disorders, including immunodeficiency, myopathy, tubular aggregate, Stormorken syndrome, York platelet syndrome, cardiovascular and metabolic disorders, and cancers, as well as suggesting these channels as drug targets for pharmacological therapeutic intervention. Moreover, this work will also focus on the pharmacological modulators of Orai/STIM channel complexes. Together, our thoughtful of the biology and physiology of the Orai/STIM channels have grown remarkably during the past three decades, and the next important milestone in the field of store-operated calcium entry will be to identify potent and selective small molecules as a therapeutic agent with the purpose to target human diseases and disorders for patient benefit.

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

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

(-)-Englerin-A Has Analgesic and Anti-Inflammatory Effects Independent of TRPC4 and 5

Recently, we found that the deletion of TRPC5 leads to increased inflammation and pain-related behaviour in two animal models of arthritis. (-)-Englerin A (EA), an extract from the East African plant Phyllanthus engleri has been identified as a TRPC4/5 agonist. Here, we studied whether or not EA has any anti-inflammatory and analgesic properties via TRPC4/5 in the carrageenan model of inflammation. We found that EA treatment in CD1 mice inhibited thermal hyperalgesia and mechanical allodynia in a dose-dependent manner. Furthermore, EA significantly reduced the volume of carrageenan-induced paw oedema and the mass of the treated paws. Additionally, in dorsal root ganglion (DRG) neurons cultured from WT 129S1/SvIm mice, EA induced a dose-dependent cobalt uptake that was surprisingly preserved in cultured DRG neurons from 129S1/SvIm TRPC5 KO mice. Likewise, EA-induced anti-inflammatory and analgesic effects were preserved in the carrageenan model in animals lacking TRPC5 expression or in mice treated with TRPC4/5 antagonist ML204.This study demonstrates that while EA activates a sub-population of DRG neurons, it induces a novel TRPC4/5-independent analgesic and anti-inflammatory effect in vivo. Future studies are needed to elucidate the molecular and cellular mechanisms underlying EA's anti-inflammatory and analgesic effects.

Canonical transient receptor potential channels and their modulators: biology, pharmacology and therapeutic potentials

Canonical transient receptor potential channels (TRPCs) are nonselective, high calcium permeability cationic channels. The TRPCs family includes TRPC1, TRPC2, TRPC3, TRPC4, TRPC5, TRPC6, and TRPC7. These channels are widely expressed in the cardiovascular and nervous systems and exist in many other human tissues and cell types, playing several crucial roles in the human physiological and pathological processes. Hence, the emergence of TRPCs modulators can help investigate these channels’ applications in health and disease. It is worth noting that the TRPCs subfamilies have structural and functional similarities, which presents a significant difficulty in screening and discovering of TRPCs modulators. In the past few years, only a limited number of selective modulators of TRPCs were detected; thus, additional research on more potent and more selective TRPCs modulators is needed. The present review focuses on the striking desired therapeutic effects of TRPCs modulators, which provides intel on the structural modification of TRPCs modulators and further pharmacological research. Importantly, TRPCs modulators can significantly facilitate future studies of TRPCs and TRPCs related diseases.

Bridgehead Modifications of Englerin A Reduce TRPC4 Activity and Intravenous Toxicity but not Cell Growth Inhibition

Modifications at the bridgehead position of englerin A were made to explore the effects of variation at this site on the molecule for biological activity, as judged by the NCI 60 screen, in which englerin A is highly potent and selective for renal cancer cells. Replacement of the isopropyl group by other, larger substituents yielded compounds which displayed excellent selectivity and potency comparable to the natural product. Selected compounds were also evaluated for their effect on the ion channel TRPC4 as well as for intravenous toxicity in mice, and these had lower potency in both assays compared to englerin A.

Transient Receptor Potential Canonical (TRPC) Channels: Then and Now

Twenty-five years ago, the first mammalian Transient Receptor Potential Canonical (TRPC) channel was cloned, opening the vast horizon of the TRPC field. Today, we know that there are seven TRPC channels (TRPC1-7). TRPCs exhibit the highest protein sequence similarity to the Drosophila melanogaster TRP channels. Similar to Drosophila TRPs, TRPCs are localized to the plasma membrane and are activated in a G-protein-coupled receptor-phospholipase C-dependent manner. TRPCs may also be stimulated in a store-operated manner, via receptor tyrosine kinases, or by lysophospholipids, hypoosmotic solutions, and mechanical stimuli. Activated TRPCs allow the influx of Ca2+ and monovalent alkali cations into the cytosol of cells, leading to cell depolarization and rising intracellular Ca2+ concentration. TRPCs are involved in the continually growing number of cell functions. Furthermore, mutations in the TRPC6 gene are associated with hereditary diseases, such as focal segmental glomerulosclerosis. The most important recent breakthrough in TRPC research was the solving of cryo-EM structures of TRPC3, TRPC4, TRPC5, and TRPC6. These structural data shed light on the molecular mechanisms underlying TRPCs' functional properties and propelled the development of new modulators of the channels. This review provides a historical overview of the major advances in the TRPC field focusing on the role of gene knockouts and pharmacological tools.

Identification of Novel TRPC5 Inhibitors by Pharmacophore-Based and Structure-Based Approaches

Canonical transient receptor potential-5 (TRPC5), which belongs to the subfamily of transient receptor potential (TRP) channels, is a non-selective cation channel mainly expressed in the central nervous system and shows more restricted expression in the periphery. TRPC5 plays a crucial role in human physiology and pathology, for instance, anxiety, depression, epilepsy, pain, memory and chronic kidney disease (CKD). However, due to lack of the effective and selective inhibitors, its physiological and pathological mechanism remains so far unknown. It is therefore pivotal to identify potential TRPC5 inhibitors. We have applied ligand-based virtual screening (LBVS) and structure-based virtual screening (SBVS) methods. The pharmacophore models of TRPC5 antagonists generated by using the HypoGen and HipHop algorithms were used as a query model for the screening of potential inhibitors against the Specs database. The resultant hits from LBVS were further screened by SBVS. SBVS was carried out based on the homology model generation of human TRPC5, binding site identification, molecular dynamics optimization and molecular docking studies. In our systematic screening approaches, we have identified 7 hits compounds with comparable dock score after Lipinski and Veber rules, ADMET, PAINS analysis, cluster analysis, and similarity analysis. In conclusion, the current research provides novel backbones for the new-generation of TRPC5 inhibitors.

TRPC1/4/5 channels contribute to morphine-induced analgesic tolerance and hyperalgesia by enhancing spinal synaptic potentiation and structural plasticity

Opioid analgesics remain the mainstay for managing intractable chronic pain, but their use is limited by detrimental side effects such as analgesic tolerance and hyperalgesia. Calcium-dependent synaptic plasticity is a key determinant in opiates tolerance and hyperalgesia. However, the exact substrates for this calcium-dependent synaptic plasticity in mediating these maladaptive processes are largely unknown. Canonical transient receptor potential 1, 4, and 5 (TRPC1, 4, 5) proteins assemble into heteromultimeric nonselective cation channels with high Ca2+ permeability and influence various neuronal functions. However, whether and how TRPC1/4/5 channels contribute to the development of opiates tolerance and hyperalgesia remains elusive. Here, we show that TRPC1/4/5 channels contribute to the generation of morphine tolerance and hyperalgesia. Chronic morphine exposure leads to upregulation of TRPC1/4/5 channels in the spinal cord. Spinally expressed TRPC1, TPRC4, and TRPC5 are required for chronic morphine-induced synaptic long-term potentiation (LTP) as well as remodeling of synaptic spines in the dorsal horn, thereby orchestrating functional and structural plasticity during the course of morphine-induced hyperalgesia and tolerance. These effects are attributed to TRPC1/4/5-mediated Ca2+ elevation in the spinal dorsal horn induced by chronic morphine treatment. This study identifies TRPC1/4/5 channels as a promising novel target to prevent the unwanted morphine tolerance and hyperalgesia.

Regulation of Vessel Permeability by TRP Channels

The vascular endothelium constitutes a semi-permeable barrier between blood and interstitial fluids. Since an augmented endothelial permeability is often associated to pathological states, understanding the molecular basis for its regulation is a crucial biomedical and clinical challenge. This review focuses on the processes controlling paracellular permeability that is the permeation of fluids between adjacent endothelial cells (ECs). Cytosolic calcium changes are often detected as early events preceding the alteration of the endothelial barrier (EB) function. For this reason, great interest has been devoted in the last decades to unveil the molecular mechanisms underlying calcium fluxes and their functional relationship with vessel permeability. Beyond the dicotomic classification between store-dependent and independent calcium entry at the plasma membrane level, the search for the molecular components of the related calcium-permeable channels revealed a difficult task for intrinsic and technical limitations. The contribution of redundant channel-forming proteins including members of TRP superfamily and Orai1, together with the very complex intracellular modulatory pathways, displays a huge variability among tissues and along the vascular tree. Moreover, calcium-independent events could significantly concur to the regulation of vascular permeability in an intricate and fascinating multifactorial framework.

Canonical Transient Receptor Potential (TRPC) Channels in Nociception and Pathological Pain

Chronic pathological pain is one of the most intractable clinical problems faced by clinicians and can be devastating for patients. Despite much progress we have made in understanding chronic pain in the last decades, its underlying mechanisms remain elusive. It is assumed that abnormal increase of calcium levels in the cells is a key determinant in the transition from acute to chronic pain. Exploring molecular players mediating Ca²⁺ entry into cells and molecular mechanisms underlying activity-dependent changes in Ca²⁺ signaling in the somatosensory pain pathway is therefore helpful towards understanding the development of chronic, pathological pain. Canonical transient receptor potential (TRPC) channels form a subfamily of nonselective cation channels, which permit the permeability of Ca²⁺ and Na+ into the cells. Initiation of Ca²⁺ entry pathways by these channels triggers the development of many physiological and pathological functions. In this review, we will focus on the functional implication of TRPC channels in nociception with the elucidation of their role in the detection of external stimuli and nociceptive hypersensitivity.

Targeting the Endothelial Ca2+ Toolkit to Rescue Endothelial Dysfunction in Obesity Associated-Hypertension

BACKGROUND

Obesity is a major cardiovascular risk factor which dramatically impairs endothelium- dependent vasodilation and leads to hypertension and vascular damage. The impairment of the vasomotor response to extracellular autacoids, e.g., acetylcholine, mainly depends on the reduced Nitric Oxide (NO) bioavailability, which hampers vasorelaxation in large conduit arteries. In addition, obesity may affect Endothelium-Dependent Hyperpolarization (EDH), which drives vasorelaxation in small resistance arteries and arterioles. Of note, endothelial Ca2+ signals drive NO release and trigger EDH.

METHODS

A structured search of bibliographic databases was carried out to retrieve the most influential, recent articles on the impairment of vasorelaxation in animal models of obesity, including obese Zucker rats, and on the remodeling of the endothelial Ca2+ toolkit under conditions that mimic obesity. Furthermore, we searched for articles discussing how dietary manipulation could be exploited to rescue Ca2+-dependent vasodilation.

RESULTS

We found evidence that the endothelial Ca2+ could be severely affected by obese vessels. This rearrangement could contribute to endothelial damage and is likely to be involved in the disruption of vasorelaxant mechanisms. However, several Ca2+-permeable channels, including Vanilloid Transient Receptor Potential (TRPV) 1, 3 and 4 could be stimulated by several food components to stimulate vasorelaxation in obese individuals.

CONCLUSION

The endothelial Ca2+ toolkit could be targeted to reduce vascular damage and rescue endothelium- dependent vasodilation in obese vessels. This hypothesis remains, however, to be probed on truly obese endothelial cells.

Xanthine-based photoaffinity probes allow assessment of ligand engagement by TRPC5 channels

Diazirine-containing photoaffinity probes, based on the potent and selective TRPC1/4/5 channel inhibitor Pico145, allowed the development of an assay to probe cellular interactions between TRPC5 protein and xanthine-based TRPC5 channel modulators.

Structure-Function Relationship and Physiological Roles of Transient Receptor Potential Canonical (TRPC) 4 and 5 Channels

The study of the structure–function relationship of ion channels has been one of the most challenging goals in contemporary physiology. Revelation of the three-dimensional (3D) structure of ion channels has facilitated our understanding of many of the submolecular mechanisms inside ion channels, such as selective permeability, voltage dependency, agonist binding, and inter-subunit multimerization. Identifying the structure–function relationship of the ion channels is clinically important as well since only such knowledge can imbue potential therapeutics with practical possibilities. In a sense, recent advances in the understanding of the structure–relationship of transient receptor potential canonical (TRPC) channels look promising since human TRPC channels are calcium-permeable, non-selective cation channels expressed in many tissues such as the gastrointestinal (GI) tract, kidney, heart, vasculature, and brain. TRPC channels are known to regulate GI contractility and motility, pulmonary hypertension, right ventricular hypertrophy, podocyte injury, seizure, fear, anxiety-like behavior, and many others. In this article, we tried to elaborate recent findings of Cryo-EM (cryogenic-electron microscopy) based structural information of TRPC 4 and 5 channels and domain-specific functions of the channel, such as G-protein mediated activation mechanism, extracellular modification of the channel, homo/hetero-tetramerization, and pharmacological gating mechanisms.

Potent, selective, and subunit-dependent activation of TRPC5 channels by a xanthine derivative

BACKGROUND AND PURPOSE

The TRPC1, TRPC4, and TRPC5 proteins form homotetrameric or heterotetrameric, calcium-permeable cation channels that are involved in various disease states. Recent research has yielded specific and potent xanthine-based TRPC1/4/5 inhibitors. Here, we investigated the possibility of xanthine-based activators of these channels.

EXPERIMENTAL APPROACH

An analogue of the TRPC1/4/5 inhibitor Pico145, AM237, was synthesized and its activity was investigated using HEK cells overexpressing TRPC4, TRPC5, TRPC4-C1, TRPC5-C1, TRPC1:C4 or TRPC1:C5 channels, and in A498 cells expressing native TRPC1:C4 channels. TRPC1/4/5 channel activities were assayed by measuring intracellular concentration of Ca2+ ([Ca2+ ]i ) and by patch-clamp electrophysiology. Selectivity of AM237 was tested against TRPC3, TRPC6, TRPV4, or TRPM2 channels.

KEY RESULTS

AM237 potently activated TRPC5:C5 channels (EC50 15-20 nM in [Ca2+ ]i assay) and potentiated their activation by sphingosine-1-phosphate but suppressed activation evoked by (-)-englerin A (EA). In patch-clamp studies, AM237 activated TRPC5:C5 channels, with greater effect at positive voltages, but with lower efficacy than EA. Pico145 competitively inhibited AM237-induced TRPC5:C5 activation. AM237 did not activate TRPC4:C4, TRPC4-C1, TRPC5-C1, TRPC1:C5, and TRPC1:C4 channels, or native TRPC1:C4 channels in A498 cells, but potently inhibited EA-dependent activation of these channels with IC50 values ranging from 0.9 to 7 nM. AM237 (300 nM) did not activate or inhibit TRPC3, TRPC6, TRPV4, or TRPM2 channels.

CONCLUSIONS AND IMPLICATIONS

This study suggests the possibility for selective activation of TRPC5 channels by xanthine derivatives and supports the general principle that xanthine-based compounds can activate, potentiate, or inhibit these channels depending on subunit composition.

Photopharmacology and opto-chemogenetics of TRPC channels-some therapeutic visions

Non-selective cation conductances formed by transient receptor potential canonical (TRPC) proteins govern the function and fate of a wide range of human cell types. In the past decade, evidence has accumulated for a pivotal role of these channels in human diseases, raising substantial interest in their therapeutic targeting. As yet, an appreciable number of small molecules for block and modulation of recombinant TRPC conductances have been identified. However, groundbreaking progress in TRPC pharmacology towards therapeutic applications is lagging behind due to incomplete understanding of their molecular pharmacology and their exact role in disease. A major breakthrough that is expected to overcome these hurdles is the recent success in obtaining high-resolution structure information on TRPC channel complexes and the advent of TRP photopharmacology and optogenetics. Here, we summarize current concepts of enhancing the precision of therapeutic interference with TRPC signaling and TRPC-mediated pathological processes.

Treasure troves of pharmacological tools to study transient receptor potential canonical 1/4/5 channels

Canonical or classical transient receptor potential 4 and 5 proteins (TRPC4 and TRPC5) assemble as homomers or heteromerize with TRPC1 protein to form functional nonselective cationic channels with high calcium permeability. These channel complexes, TRPC1/4/5, are widely expressed in nervous and cardiovascular systems, also in other human tissues and cell types. It is debatable that TRPC1 protein is able to form a functional ion channel on its own. A recent explosion of molecular information about TRPC1/4/5 has emerged including knowledge of their distribution, function, and regulation suggesting these three members of the TRPC subfamily of TRP channels play crucial roles in human physiology and pathology. Therefore, these ion channels represent potential drug targets for cancer, epilepsy, anxiety, pain, and cardiac remodelling. In recent years, a number of highly selective small-molecule modulators of TRPC1/4/5 channels have been identified as being potent with improved pharmacological properties. This review will focus on recent remarkable small-molecule agonists: (-)-englerin A and tonantzitlolone and antagonists: Pico145 and HC7090, of TPRC1/4/5 channels. In addition, this work highlights other recently identified modulators of these channels such as the benzothiadiazine derivative, riluzole, ML204, clemizole, and AC1903. Together, these treasure troves of agonists and antagonists of TRPC1/4/5 channels provide valuable hints to comprehend the functional importance of these ion channels in native cells and in vivo animal models. Importantly, human diseases and disorders mediated by these proteins can be studied using these compounds to perhaps initiate drug discovery efforts to develop novel therapeutic agents.

TRPC-mediated Ca2+ signaling and control of cellular functions

Canonical members of the TRP superfamily of ion channels have long been recognized as key elements of Ca²⁺ handling in a plethora of cell types. The emerging role of TRPC channels in human physiopathology has generated considerable interest in their pharmacological targeting, which requires detailed understanding of their molecular function. Although consent has been reached that receptor-phospholipase C (PLC) pathways and generation of lipid mediators constitute the prominent upstream signaling process that governs channel activity, multimodal sensing features of TRPC complexes have been demonstrated repeatedly. Downstream signaling by TRPC channels is similarly complex and involves the generation of local and global cellular Ca²⁺ rises, which are well-defined in space and time to govern specific cellular functions. These TRPC-mediated Ca²⁺ signals rely in part on Ca²⁺ permeation through the channels, but are essentially complemented by secondary mechanisms such as Ca²⁺ mobilization from storage sites and Na⁺/Ca²⁺ exchange, which involve coordinated interaction with signaling partners. Consequently, the control of cell functions by TRPC molecules is critically determined by dynamic assembly and subcellular targeting of the TRPC complexes. The very recent availability of high-resolution structure information on TRPC channel complexes has paved the way towards a comprehensive understanding of signal transduction by TRPC channels. Here, we summarize current concepts of cation permeation in TRPC complexes, TRPC-mediated shaping of cellular Ca²⁺ signals and the associated control of specific cell functions.

Activation of TRPC1 Channel by Metabotropic Glutamate Receptor mGluR5 Modulates Synaptic Plasticity and Spatial Working Memory

Group I metabotropic glutamate receptors, in particular mGluR5, have been implicated in various forms of synaptic plasticity that are believed to underlie declarative memory. We observed that mGluR5 specifically activated a channel containing TRPC1, an isoform of the canonical family of transient receptor potential (TRPC) channels highly expressed in CA1-3 regions of the hippocampus. TRPC1 is able to form tetrameric complexes with TRPC4 and/or TRPC5 isoforms. TRPC1/4/5 complexes have recently been involved in the efficiency of synaptic transmission in the hippocampus. We therefore used a mouse model devoid of TRPC1 expression to investigate the involvement of mGluR5-TRPC1 pathway in synaptic plasticity and memory formation. Trpc1^-/- mice showed alterations in spatial working memory and fear conditioning. Activation of mGluR increased synaptic excitability in neurons from WT but not from Trpc1^-/- mice. LTP triggered by a theta burst could not maintain over time in brain slices from Trpc1^-/- mice. mGluR-induced LTD was also impaired in these mice. Finally, acute inhibition of TRPC1 by Pico145 on isolated neurons or on brain slices mimicked the genetic depletion of Trpc1 and inhibited mGluR-induced entry of cations and subsequent effects on synaptic plasticity, excluding developmental or compensatory mechanisms in Trpc1^-/- mice. In summary, our results indicate that TRPC1 plays a role in synaptic plasticity and spatial working memory processes.

Tonantzitlolone is a nanomolar potency activator of transient receptor potential canonical 1/4/5 channels

BACKGROUND AND PURPOSE

The diterpene ester tonantzitlolone (TZL) is a natural product, which displays cytotoxicity towards certain types of cancer cell such as renal cell carcinoma cells. The effect is similar to that of (-)-englerin A, and so, although it is chemically distinct, we investigated whether TZL also targets transient receptor potential canonical (TRPC) channels of the 1, 4 and 5 type (TRPC1/4/5 channels).

EXPERIMENTAL APPROACH

The effects of TZL on renal cell carcinoma A498 cells natively expressing TRPC1 and TRPC4, modified HEK293 cells overexpressing TRPC4, TRPC5, TRPC4-TRPC1 or TRPC5-TRPC1 concatemer, TRPC3 or TRPM2, or CHO cells overexpressing TRPV4 were studied by determining changes in intracellular Ca²⁺ , or whole-cell or excised membrane patch-clamp electrophysiology.

KEY RESULTS

TZL induced an elevation of intracellular Ca²⁺ in A498 cells, similar to that evoked by englerin A. TZL activated overexpressed channels with EC₅₀ values of 123 nM (TRPC4), 83 nM (TRPC5), 140 nM (TRPC4-TRPC1) and 61 nM (TRPC5-TRPC1). These effects of TZL were reversible on wash-out and potently inhibited by the TRPC1/4/5 inhibitor Pico145. TZL activated TRPC5 channels when bath-applied to excised outside-out but not inside-out patches. TZL failed to activate endogenous store-operated Ca²⁺ entry or overexpressed TRPC3, TRPV4 or TRPM2 channels in HEK 293 cells.

CONCLUSIONS AND IMPLICATIONS

TZL is a novel potent agonist for TRPC1/4/5 channels, which should be useful for testing the functionality of this type of ion channel and understanding how TRPC1/4/5 agonists achieve selective cytotoxicity against certain types of cancer cell.

Remarkable Progress with Small-Molecule Modulation of TRPC1/4/5 Channels: Implications for Understanding the Channels in Health and Disease

Proteins of the TRPC family can form many homo- and heterotetrameric cation channels permeable to Na⁺, K⁺ and Ca2+. In this review, we focus on channels formed by the isoforms TRPC1, TRPC4 and TRPC5. We review evidence for the formation of different TRPC1/4/5 tetramers, give an overview of recently developed small-molecule TRPC1/4/5 activators and inhibitors, highlight examples of biological roles of TRPC1/4/5 channels in different tissues and pathologies, and discuss how high-quality chemical probes of TRPC1/4/5 modulators can be used to understand the involvement of TRPC1/4/5 channels in physiological and pathophysiological processes.

Identification of an (-)-englerin A analogue, which antagonizes (-)-englerin A at TRPC1/4/5 channels

BACKGROUND AND PURPOSE

(-)-Englerin A (EA) is a potent cytotoxic agent against renal carcinoma cells. It achieves its effects by activation of transient receptor potential canonical (TRPC)4/TRPC1 heteromeric channels. It is also an agonist at channels formed by the related protein, TRPC5. Here, we sought an EA analogue, which might enable a better understanding of these effects of EA.

EXPERIMENTAL APPROACH

An EA analogue, A54, was synthesized by chemical elaboration of EA. The effects of EA and A54 on the activity of human TRPC4 or TRPC5 channels overexpressed on A498 and HEK 293 cells were investigated, firstly, by measuring intracellular Ca²⁺ and, secondly, current using whole-cell patch clamp recordings.

KEY RESULTS

A54 had weak or no agonist activity at endogenous TRPC4/TRPC1 channels in A498 cells or TRPC4 or TRPC5 homomeric channels overexpressed in HEK 293 cells. A54 strongly inhibited EA-mediated activation of TRPC4/TRPC1 or TRPC5 and weakly inhibited activation of TRPC4. Studies of TRPC5 showed that A54 shifted the EA concentration-response curve to the right without changing its slope, consistent with competitive antagonism. In contrast, Gd³⁺ -activated TRPC5 or sphingosine-1-phosphate-activated TRPC4 channels were not inhibited but potentiated by A54. A54 did not activate TRPC3 channels or affect the activation of these channels by the agonist 1-oleoyl-2-acetyl-sn-glycerol.

CONCLUSIONS AND IMPLICATIONS

This study has revealed a new tool compound for EA and TRPC1/4/5 channel research, which could be useful for characterizing endogenous TRPC1/4/5 channels and understanding EA-binding sites and their physiological relevance.

Endothelial Ca2+ Signaling and the Resistance to Anticancer Treatments: Partners in Crime

Intracellular Ca²⁺ signaling drives angiogenesis and vasculogenesis by stimulating proliferation, migration, and tube formation in both vascular endothelial cells and endothelial colony forming cells (ECFCs), which represent the only endothelial precursor truly belonging to the endothelial phenotype. In addition, local Ca²⁺ signals at the endoplasmic reticulum (ER)-mitochondria interface regulate endothelial cell fate by stimulating survival or apoptosis depending on the extent of the mitochondrial Ca²⁺ increase. The present article aims at describing how remodeling of the endothelial Ca²⁺ toolkit contributes to establish intrinsic or acquired resistance to standard anti-cancer therapies. The endothelial Ca²⁺ toolkit undergoes a major alteration in tumor endothelial cells and tumor-associated ECFCs. These include changes in TRPV4 expression and increase in the expression of P2X7 receptors, Piezo2, Stim1, Orai1, TRPC1, TRPC5, Connexin 40 and dysregulation of the ER Ca²⁺ handling machinery. Additionally, remodeling of the endothelial Ca²⁺ toolkit could involve nicotinic acetylcholine receptors, gasotransmitters-gated channels, two-pore channels and Na⁺/H⁺ exchanger. Targeting the endothelial Ca²⁺ toolkit could represent an alternative adjuvant therapy to circumvent patients' resistance to current anti-cancer treatments.