Emerging roles of L-type voltage-gated and other calcium channels in T lymphocytes

Identifying Key Binding Interactions Between the Cardiac L-Type Calcium Channel and Calmodulin Using Molecular Dynamics Simulations

Defects in the binding of the calcium sensing protein calmodulin (CaM) to the L-type calcium channel (CaV1.2) or to the ryanodine receptor type 2 (RyR2) can lead to dangerous cardiac arrhythmias with distinct phenotypes, such as long-QT syndrome (LQTS) and catecholaminergic ventricular tachycardia (CPVT). Certain CaM mutations lead to LQTS while other mutations lead to CPVT, but the mechanisms by which a specific mutation can lead to each disease phenotype are not well-understood. In this study, we use long, 2 μs molecular dynamics simulations and a multitrajectory approach to identify the key binding interactions between the IQ domain of CaV1.2 and CaM. Five key interactions are found between CaV1.2 and CaM in the C-lobe, 1 in the central linker, and 2 in the N-lobe. In addition, while 5 key interactions appear between residues 120-149 in the C-lobe of CaM when it interacts with CaV1.2, only 1 key interaction is found within this region of CaM when it interacts with the RyR2. We show that this difference in the distribution of key interactions correlates with the known distribution of CaM mutations that lead to LQTS or CPVT. This correlation suggests that a disruption of key binding interactions is a plausible mechanism that can lead to these two different disease phenotypes.

The role of ion channels in T cell function and disease

T lymphocytes (T cells) are an important sub-group of cells in our immune system responsible for cell-mediated adaptive responses and maintaining immune homeostasis. Abnormalities in T cell function, lead the way to the persistence of infection, impaired immunosurveillance, lack of suppression of cancer growth, and autoimmune diseases. Ion channels play a critical role in the regulation of T cell signaling and cellular function and are often overlooked and understudied. Little is known about the ion "channelome" and the interaction of ion channels in immune cells. This review aims to summarize the published data on the impact of ion channels on T cell function and disease. The importance of ion channels in health and disease plus the fact they are easily accessible by virtue of being expressed on the surface of plasma membranes makes them excellent drug targets.

Identification of molecular candidates which regulate calcium-dependent CD8+ T-cell cytotoxicity

Cytotoxic CD8⁺ T lymphocytes (CTL) eliminate infected cells or transformed tumor cells by releasing perforin-containing cytotoxic granules at the immunological synapse. The secretion of such granules depends on Ca²⁺-influx through store operated Ca²⁺ channels, formed by STIM (stromal interaction molecule)-activated Orai proteins. Whereas molecular mechanisms of the secretion machinery are well understood, much less is known about the molecular machinery that regulates the efficiency of Ca²⁺-dependent target cell killing. CTL killing efficiency is of high interest considering the number of studies on CD8⁺ T lymphocytes modified for clinical use. Here, we isolated total RNA from primary human cells: natural killer (NK) cells, non-stimulated CD8⁺ T-cells, and from Staphylococcus aureus enterotoxin A (SEA) stimulated CD8⁺ T-cells (SEA-CTL) and conducted whole genome expression profiling by microarray experiments. Based on differential expression analysis of the transcriptome data and analysis of master regulator genes, we identified 31 candidates which potentially regulate Ca²⁺-homeostasis in CTL. To investigate a putative function of these candidates in CTL cytotoxicity, we transfected either SEA-stimulated CTL (SEA-CTL) or antigen specific CD8⁺ T-cell clones (CTL-MART-1) with siRNAs specific against the identified candidates and analyzed the killing capacity using a real-time killing assay. In addition, we complemented the analysis by studying the effect of inhibitory substances acting on the candidate proteins if available. Finally, to unmask their involvement in Ca²⁺ dependent cytotoxicity, candidates were also analyzed under Ca²⁺-limiting conditions. Overall, we identified four hits, CCR5 (C-C chemokine receptor type five), KCNN4 (potassium calcium-activated channel subfamily N), RCAN3 (regulator of calcineurin) and BCL (B-cell lymphoma) 2 which clearly affect the efficiency of Ca²⁺ dependent cytotoxicity in CTL-MART-1 cells, CCR5, BCL2, and KCNN4 in a positive manner, and RCAN3 in a negative way.

Lymphatic-draining nanoparticles deliver Bay K8644 payload to lymphatic vessels and enhance their pumping function

Dysfunction of collecting lymphatic vessel pumping is associated with an array of pathologies. S-(-)-Bay K8644 (BayK), a small-molecule agonist of L-type calcium channels, improves vessel contractility ex vivo but has been left unexplored in vivo because of poor lymphatic access and risk of deleterious off-target effects. When formulated within lymph-draining nanoparticles (NPs), BayK acutely improved lymphatic vessel function, effects not seen from treatment with BayK in its free form. By preventing rapid drug access to the circulation, NP formulation also reduced BayK's dose-limiting side effects. When applied to a mouse model of lymphedema, treatment with BayK formulated in lymph-draining NPs, but not free BayK, improved pumping pressure generated by intact lymphatic vessels and tissue remodeling associated with the pathology. This work reveals the utility of a lymph-targeting NP platform to pharmacologically enhance lymphatic pumping in vivo and highlights a promising approach to treating lymphatic dysfunction.

Concomitant Calcium Channelopathies Involving CACNA1A and CACNA1F: A Case Report and Review of the Literature

Calcium channels are an integral component in maintaining cellular function. Alterations may lead to channelopathies, primarily manifested in the central nervous system. This study describes the clinical and genetic features of a unique 12-year-old boy harboring two congenital calcium channelopathies, involving the CACNA1A and CACNA1F genes, and provides an unadulterated view of the natural history of sporadic hemiplegic migraine type 1 (SHM1) due to the patient's inability to tolerate any preventative medication. The patient presents with episodes of vomiting, hemiplegia, cerebral edema, seizure, fever, transient blindness, and encephalopathy. He is nonverbal, nonambulatory, and forced to have a very limited diet due to abnormal immune responses. The SHM1 manifestations apparent in the subject are consistent with the phenotype described in the 48 patients identified as part of a systematic literature review. The ocular symptoms of CACNA1F align with the family history of the subject. The presence of multiple pathogenic variants make it difficult to identify a clear phenotype-genotype correlation in the present case. Moreover, the detailed case description and natural history along with the comprehensive review of the literature contribute to the understanding of this complex disorder and point to the need for comprehensive clinical assessments of SHM1.

The role of transient receptor potential channels in metastasis

Metastasis is the hallmark of failed tumor treatment and is typically associated with death due to cancer. Transient receptor potential (TRP) channels affect changes in intracellular calcium concentrations and participate at every stage of metastasis. Further, they increase the migratory ability of tumor cells, promote angiogenesis, regulate immune function, and promote the growth of tumor cells through changes in gene expression and function. In this review, we explore the potential mechanisms of action of TRP channels, summarize their role in tumor metastasis, compile inhibitors of TRP channels relevant in tumors, and discuss current challenges in research on TRP channels involved in tumor metastasis.

Proteomic analysis suggests that monoterpenes in lemongrass disrupt Ca2+ homeostasis in Haemaphysalis longicornis leading to mitochondrial depolarization and cytotoxicity

Complex mixtures of bioactive ingredients in plant essential oils present complex chemistries which involve different modes of action. An increasing body of scientific reports has recently focused on the acaricidal activities of plant essential oils attributed to their monoterpene components, but information about their underlying molecular mechanism of action is scarce. Here, after the chemical analysis of lemongrass oil, a proteomic analysis of the ovary, salivary gland, and midgut of Haemaphysalis longicornis exposed to Cymbopogon citratus (lemongrass) essential oil was performed via data-independent acquisition mass spectrometry (DIA-MS) technology to further elucidate the molecular mechanisms involved. Pathway analysis reveals the activation of metabolic pathways mediated by oxidoreductases and transferases. Furthermore, the upregulation of various calcium-associated proteins and the upregulation of cytochrome c1, cytochrome c oxidase polypeptide IV, and programmed cell death protein 6-like isoform X1 suggest a cytotoxic mode of action via the formation of reactive oxygen species (ROS), mitochondrial Ca²⁺ overload, mitochondrial uncoupling, and depolarization, and ATP depletion leading to either apoptotic or necrotic death. Morphological alterations observed after the RNAi of a major detoxification enzyme (glutathione S-transferase) merit further investigation. Hence, the cytotoxic mode of action exhibited by C. citratus oil could be vital for the development of eco-friendly acaricide.

Modulation of Adaptive Immunity and Viral Infections by Ion Channels

Most cellular functions require of ion homeostasis and ion movement. Among others, ion channels play a crucial role in controlling the homeostasis of anions and cations concentration between the extracellular and intracellular compartments. Calcium (Ca2+) is one of the most relevant ions involved in regulating critical functions of immune cells, allowing the appropriate development of immune cell responses against pathogens and tumor cells. Due to the importance of Ca2+ in inducing the immune response, some viruses have evolved mechanisms to modulate intracellular Ca2+ concentrations and the mobilization of this cation through Ca2+ channels to increase their infectivity and to evade the immune system using different mechanisms. For instance, some viral infections require the influx of Ca2+ through ionic channels as a first step to enter the cell, as well as their replication and budding. Moreover, through the expression of viral proteins on the surface of infected cells, Ca2+ channels function can be altered, enhancing the pathogen evasion of the adaptive immune response. In this article, we review those ion channels and ion transporters that are essential for the function of immune cells. Specifically, cation channels and Ca2+ channels in the context of viral infections and their contribution to the modulation of adaptive immune responses.

Calcium Signaling Mechanisms Across Kingdoms

Calcium (Ca²⁺) is a unique mineral that serves as both a nutrient and a signal in all eukaryotes. To maintain Ca²⁺ homeostasis for both nutrition and signaling purposes, the toolkit for Ca²⁺ transport has expanded across kingdoms of eukaryotes to encode specific Ca²⁺ signals referred to as Ca²⁺ signatures. In parallel, a large array of Ca²⁺-binding proteins has evolved as specific sensors to decode Ca²⁺ signatures. By comparing these coding and decoding mechanisms in fungi, animals, and plants, both unified and divergent themes have emerged, and the underlying complexity will challenge researchers for years to come. Considering the scale and breadth of the subject, instead of a literature survey, in this review we focus on a conceptual framework that aims to introduce to readers to the principles and mechanisms of Ca²⁺ signaling. We finish with several examples of Ca²⁺-signaling pathways, including polarized cell growth, immunity and symbiosis, and systemic signaling, to piece together specific coding and decoding mechanisms in plants versus animals. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

GABAergic signaling by cells of the immune system: more the rule than the exception

Gamma-aminobutyric acid (GABA) is best known as an essential neurotransmitter in the evolved central nervous system (CNS) of vertebrates. However, GABA antedates the development of the CNS as a bioactive molecule in metabolism and stress-coupled responses of prokaryotes, invertebrates and plants. Here, we focus on the emerging findings of GABA signaling in the mammalian immune system. Recent reports show that mononuclear phagocytes and lymphocytes, for instance dendritic cells, microglia, T cells and NK cells, express a GABAergic signaling machinery. Mounting evidence shows that GABA receptor signaling impacts central immune functions, such as cell migration, cytokine secretion, immune cell activation and cytotoxic responses. Furthermore, the GABAergic signaling machinery of leukocytes is implicated in responses to microbial infection and is co-opted by protozoan parasites for colonization of the host. Peripheral GABA signaling is also implicated in inflammatory conditions and diseases, such as type 1 diabetes, rheumatoid arthritis and cancer cell metastasis. Adding to its role in neurotransmission, growing evidence shows that the non-proteinogenic amino acid GABA acts as an intercellular signaling molecule in the immune system and, as an interspecies signaling molecule in host–microbe interactions. Altogether, the data raise the assumption of conserved GABA signaling in a broad range of mammalian cells and diversification of function in the immune system.

IonoBiology: The functional dynamics of the intracellular metallome, with lessons from bacteria

Metal ions are essential for life and represent the second most abundant constituent (after water) of any living cell. While the biological importance of inorganic ions has been appreciated for over a century, we are far from a comprehensive understanding of the functional roles that ions play in cells and organisms. In particular, recent advances are challenging the traditional view that cells maintain constant levels of ion concentrations (ion homeostasis). In fact, the ionic composition (metallome) of cells appears to be purposefully dynamic. The scientific journey that started over 60 years ago with the seminal work by Hodgkin and Huxley on action potentials in neurons is far from reaching its end. New evidence is uncovering how changes in ionic composition regulate unexpected cellular functions and physiology, especially in bacteria, thereby hinting at the evolutionary origins of the dynamic metallome. It is an exciting time for this field of biology, which we discuss and refer to here as IonoBiology.

Neurokinin-1 Receptor Signaling Is Required for Efficient Ca2+ Flux in T-Cell-Receptor-Activated T Cells

Efficient Ca²⁺ flux induced during cognate T cell activation requires signaling the T cell receptor (TCR) and unidentified G-protein-coupled receptors (GPCRs). T cells express the neurokinin-1 receptor (NK1R), a GPCR that mediates Ca²⁺ flux in excitable and non-excitable cells. However, the role of the NK1R in TCR signaling remains unknown. We show that the NK1R and its agonists, the neuropeptides substance P and hemokinin-1, co-localize within the immune synapse during cognate activation of T cells. Simultaneous TCR and NK1R stimulation is necessary for efficient Ca²⁺ flux and Ca²⁺-dependent signaling that sustains the survival of activated T cells and helper 1 (Th1) and Th17 bias. In a model of contact dermatitis, mice with T cells deficient in NK1R or its agonists exhibit impaired cellular immunity, due to high mortality of activated T cells. We demonstrate an effect of the NK1R in T cells that is relevant for immunotherapies based on pro-inflammatory neuropeptides and its receptors.

The neurokinin 1 receptor (NK1R) induces Ca²⁺ flux in excitable cells. Here, Morelli et al. show that NK1R signaling in T cells promotes optimal Ca²⁺ flux triggered by TCR stimulation, which is necessary to sustain T cell survival and the efficient Th1- and Th17-based immunity that is relevant for immunotherapies based on pro-inflammatory neuropeptides.

Cellular calcium in bipolar disorder: systematic review and meta-analysis

Calcium signalling has long been implicated in bipolar disorder, especially by reports of altered intracellular calcium ion concentrations ([Ca²⁺]). However, the evidence has not been appraised critically. We carried out a systematic review and meta-analysis of studies of cellular calcium indices in bipolar disorder. 2281 records were identified and 117 screened, of which 32 were eligible and 21 were suitable for meta-analyses. The latter each involved up to 642 patients and 404 control subjects. We found that basal free intracellular [Ca²⁺] is increased in bipolar disorder, both in platelets and in lymphocytes. The effect size is 0.55, with an estimated elevation of 29%. It is observed in medication-free patients. It is present in mania and bipolar depression, but data are equivocal for euthymia. Cells from bipolar disorder individuals also show an enhanced [Ca²⁺] response to stimulation with 5-HT or thrombin, by an estimated 25%, with an effect size of 0.63. In studies which included other diagnoses, intracellular basal [Ca²⁺] was higher in bipolar disorder than in unipolar depression, but not significantly different from schizophrenia. Functional parameters of cellular Ca²⁺ (e.g. calcium transients), and neuronal [Ca²⁺], have been much less investigated, and no firm conclusions can be drawn. In summary, there is a robust, medium effect size elevation of basal and stimulated free intracellular [Ca²⁺] in bipolar disorder. The results suggest altered calcium functioning in the disorder, and encourage further investigations into the underlying mechanisms, and the implications for pathophysiology and therapeutics.

CACNA1S haploinsufficiency confers resistance to New World arenavirus infection

Understanding the genetics of susceptibility to infectious agents is of great importance to our ability to combat disease. Here, we show that voltage-gated calcium channels (VGCCs) are critical for cellular binding and entry of the New World arenaviruses Junín and Tacaribe virus, suggesting that zoonosis via these receptors could occur. Moreover, we demonstrate that α1s haploinsufficiency renders cells and mice more resistant to infection by these viruses. In addition to being more resistant to infection, haploinsufficient cells and mice required a lower dosage of VGCC antagonists to block infection. These studies underscore the importance of genetic variation in susceptibility to both viruses and pharmaceutics.

Phosphate Transporter Profiles in Murine and Human Thymi Identify Thymocytes at Distinct Stages of Differentiation

Thymocyte differentiation is dependent on the availability and transport of metabolites in the thymus niche. As expression of metabolite transporters is a rate-limiting step in nutrient utilization, cell surface transporter levels generally reflect the cell's metabolic state. The GLUT1 glucose transporter is upregulated on actively dividing thymocytes, identifying thymocytes with an increased metabolism. However, it is not clear whether transporters of essential elements such as phosphate are modulated during thymocyte differentiation. While PiT1 and PiT2 are both phosphate transporters in the SLC20 family, we show here that they exhibit distinct expression profiles on both murine and human thymocytes. PiT2 expression distinguishes thymocytes with high metabolic activity, identifying immature murine double negative (CD4⁻CD8⁻) DN3b and DN4 thymocyte blasts as well as immature single positive (ISP) CD8 thymocytes. Notably, the absence of PiT2 expression on RAG2-deficient thymocytes, blocked at the DN3a stage, strongly suggests that high PiT2 expression is restricted to thymocytes having undergone a productive TCRβ rearrangement at the DN3a/DN3b transition. Similarly, in the human thymus, PiT2 was upregulated on early post-β selection CD4⁺ISP and TCRαβ⁻CD4^hiDP thymocytes co-expressing the CD71 transferrin receptor, a marker of metabolic activity. In marked contrast, expression of the PiT1 phosphate importer was detected on mature CD3⁺ murine and human thymocytes. Notably, PiT1 expression on CD3⁺DN thymocytes was identified as a biomarker of an aging thymus, increasing from 8.4 ± 1.5% to 42.4 ± 9.4% by 1 year of age (p < 0.0001). We identified these cells as TCRγδ and, most significantly, NKT, representing 77 ± 9% of PiT1⁺DN thymocytes by 1 year of age (p < 0.001). Thus, metabolic activity and thymic aging are associated with distinct expression profiles of the PiT1 and PiT2 phosphate transporters.

Ca2+ signaling in T lymphocytes: the interplay of the endoplasmic reticulum, mitochondria, membrane potential, and CRAC channels on transcription factor activation

T cell receptor stimulation initiates a cascade of reactions that cause an increase in intracellular calcium (Ca2+) concentration mediated through inositol 1,4,5-trisphosphate (IP3). To understand the basic mechanisms by which the immune response in T cells is activated, it is useful to understand the signaling pathways that contain important targets for drugs in a quantitative fashion. A computational model helps us to understand how the selected elements in the pathways interact with each other, and which component plays the crucial role in systems. We have developed a mathematical model to explore the mechanism for controlling transcription factor activity, which regulates gene expression, by the modulation of calcium signaling triggered during T cell activation. The model simulates the activation and modulation of Ca2+ release-activated Ca2+ (CRAC) channels by mitochondrial dynamics and depletion of endoplasmic reticulum (ER) store, and also includes membrane potential in T-cells. The model simulates the experimental finding that increases in Ca2+ current enhances the activation of transcription factors and the Ca2+ influx through CRAC is also essential for the NFAT and NFκB activation. The model also suggests that plasma membrane Ca2+-ATPase (PMCA) controls a majority of the extrusion of Ca2+ and modulates the activation of CRAC channels. Furthermore, the model simulations explain how the complex interaction of the endoplasmic reticulum, membrane potential, mitochondria, and ion channels such as CRAC channels control T cell activation.

Vitamin B Complex Treatment Attenuates Local Inflammation after Peripheral Nerve Injury

Peripheral nerve injury (PNI) leads to a series of cellular and molecular events necessary for axon regeneration and reinnervation of target tissues, among which inflammation is crucial for the orchestration of all these processes. Macrophage activation underlies the pathogenesis of PNI and is characterized by morphological/phenotype transformation from proinflammatory (M1) to an anti-inflammatory (M2) type with different functions in the inflammatory and reparative process. The aim of this study was to evaluate influence of the vitamin B (B1, B2, B3, B5, B6, and B12) complex on the process of neuroinflammation that is in part regulated by l-type Ca_V1.2 calcium channels. A controlled transection of the motor branch of the femoral peripheral nerve was used as an experimental model. Animals were sacrificed after 1, 3, 7, and 14 injections of vitamin B complex. Isolated nerves were used for immunofluorescence analysis. Treatment with vitamin B complex decreased expression of proinflammatory and increased expression of anti-inflammatory cytokines, thus contributing to the resolution of neuroinflammation. In parallel, B vitamins decreased the number of M1 macrophages that expressed the Ca_V1.2 channel, and increased the number of M2 macrophages that expressed this channel, suggesting their role in M1/M2 transition after PNI. In conclusion, B vitamins had the potential for treatment of neuroinflammation and neuroregeneration and thereby might be an effective therapy for PNI in humans.

Calcium signalling in T cells

Calcium (Ca²⁺) signalling is of paramount importance to immunity. Regulated increases in cytosolic and organellar Ca²⁺ concentrations in lymphocytes control complex and crucial effector functions such as metabolism, proliferation, differentiation, antibody and cytokine secretion and cytotoxicity. Altered Ca²⁺ regulation in lymphocytes leads to various autoimmune, inflammatory and immunodeficiency syndromes. Several types of plasma membrane and organellar Ca²⁺-permeable channels are functional in T cells. They contribute highly localized spatial and temporal Ca²⁺ microdomains that are required for achieving functional specificity. While the mechanistic details of these Ca²⁺ microdomains are only beginning to emerge, it is evident that through crosstalk, synergy and feedback mechanisms, they fine-tune T cell signalling to match complex immune responses. In this article, we review the expression and function of various Ca²⁺-permeable channels in the plasma membrane, endoplasmic reticulum, mitochondria and endolysosomes of T cells and their role in shaping immunity and the pathogenesis of immune-mediated diseases.

Mutation of an L-Type Calcium Channel Gene Leads to T Lymphocyte Dysfunction

Calcium (Ca²⁺) is a vital secondary messenger in T lymphocytes regulating a vast array of important events including maturation, homeostasis, activation, and apoptosis and can enter the cell through CRAC, TRP, and Ca_V channels. Here we describe a mutation in the L-type Ca²⁺ channel Ca_V1.4 leading to T lymphocyte dysfunction, including several hallmarks of immunological exhaustion. Ca_V1.4-deficient mice exhibited an expansion of central and effector memory T lymphocytes, and an upregulation of inhibitory receptors on several T cell subsets. Moreover, the sustained elevated levels of activation markers on B lymphocytes suggest that they are in a chronic state of activation. Functionally, T lymphocytes exhibited a reduced store-operated Ca²⁺ flux compared to wild-type controls. Finally, modifying environmental conditions by herpes virus infection exacerbated the dysfunctional immune phenotype of the Ca_V1.4-deficient mice. This is the first example where the mutation of a Ca_V channel leads to T lymphocyte dysfunction, including the upregulation of several inhibitory receptors, hallmarks of T cell exhaustion, and establishes the physiological importance of Ca_V channel signaling in maintaining a nimble immune system.

Structural and Mechanistic Insights of CRAC Channel as a Drug Target in Autoimmune Disorder

BACKGROUND

Calcium (Ca2+) ion is a major intracellular signaling messenger, controlling a diverse array of cellular functions like gene expression, secretion, cell growth, proliferation, and apoptosis. The major mechanism controlling this Ca2+ homeostasis is store-operated Ca2+ release-activated Ca2+ (CRAC) channels. CRAC channels are integral membrane protein majorly constituted via two proteins, the stromal interaction molecule (STIM) and ORAI. Following Ca2+ depletion in the Endoplasmic reticulum (ER) store, STIM1 interacts with ORAI1 and leads to the opening of the CRAC channel gate and consequently allows the influx of Ca2+ ions. A plethora of studies report that aberrant CRAC channel activity due to Loss- or gain-of-function mutations in ORAI1 and STIM1 disturbs this Ca2+ homeostasis and causes several autoimmune disorders. Hence, it clearly indicates that the therapeutic target of CRAC channels provides the space for a new approach to treat autoimmune disorders.

OBJECTIVE

This review aims to provide the key structural and mechanical insights of STIM1, ORAI1 and other molecular modulators involved in CRAC channel regulation.

RESULTS AND CONCLUSION

Understanding the structure and function of the protein is the foremost step towards improving the effective target specificity by limiting their potential side effects. Herein, the review mainly focusses on the structural underpinnings of the CRAC channel gating mechanism along with its biophysical properties that would provide the solid foundation to aid the development of novel targeted drugs for an autoimmune disorder. Finally, the immune deficiencies caused due to mutations in CRAC channel and currently used pharmacological blockers with their limitation are briefly summarized.

Drug discovery for psychiatric disorders using high-content single-cell screening of signaling network responses ex vivo

There is a paucity of efficacious new compounds to treat neuropsychiatric disorders. We present a novel approach to neuropsychiatric drug discovery based on high-content characterization of druggable signaling network responses at the single-cell level in patient-derived lymphocytes ex vivo. Primary T lymphocytes showed functional responses encompassing neuropsychiatric medications and central nervous system ligands at established (e.g., GSK-3β) and emerging (e.g., CrkL) drug targets. Clinical application of the platform to schizophrenia patients over the course of antipsychotic treatment revealed therapeutic targets within the phospholipase Cγ1-calcium signaling pathway. Compound library screening against the target phenotype identified subsets of L-type calcium channel blockers and corticosteroids as novel therapeutically relevant drug classes with corresponding activity in neuronal cells. The screening results were validated by predicting in vivo efficacy in an independent schizophrenia cohort. The approach has the potential to discern new drug targets and accelerate drug discovery and personalized medicine for neuropsychiatric conditions.

Calling in the CaValry-Toxoplasma gondii Hijacks GABAergic Signaling and Voltage-Dependent Calcium Channel Signaling for Trojan horse-Mediated Dissemination

Dendritic cells (DCs) are regarded as the gatekeepers of the immune system but can also mediate systemic dissemination of the obligate intracellular parasite Toxoplasma gondii. Here, we review the current knowledge on how T. gondii hijacks the migratory machinery of DCs and microglia. Shortly after active invasion by the parasite, infected cells synthesize and secrete the neurotransmitter γ-aminobutyric acid (GABA) and activate GABA-A receptors, which sets on a hypermigratory phenotype in parasitized DCs in vitro and in vivo. The signaling molecule calcium plays a central role for this migratory activation as signal transduction following GABAergic activation is mediated via the L-type voltage-dependent calcium channel (L-VDCC) subtype Cav1.3. These studies have revealed that DCs possess a GABA/L-VDCC/Cav1.3 motogenic signaling axis that triggers migratory activation upon T. gondii infection. Moreover, GABAergic migration can cooperate with chemotactic responses. Additionally, the parasite-derived protein Tg14-3-3 has been associated with hypermigration of DCs and microglia. We discuss the interference of T. gondii infection with host cell signaling pathways that regulate migration. Altogether, T. gondii hijacks non-canonical signaling pathways in infected immune cells to modulate their migratory properties, and thereby promote its own dissemination.

The Oxford study of Calcium channel Antagonism, Cognition, Mood instability and Sleep (OxCaMS): study protocol for a randomised controlled, experimental medicine study

Background

The discovery that voltage-gated calcium channel genes such as CACNA1C are part of the aetiology of psychiatric disorders has rekindled interest in the therapeutic potential of L-type calcium channel (LTCC) antagonists. These drugs, licensed to treat hypertension and angina, have previously been used in bipolar disorder, but without clear results. Neither is much known about the broader effects of these drugs on the brain and behaviour.

Methods

The Oxford study of Calcium channel Antagonism, Cognition, Mood instability and Sleep (OxCaMS) is a high-intensity randomised, double-blind, placebo-controlled experimental medicine study on the effect of the LTCC antagonist nicardipine in healthy young adults with mood instability. An array of cognitive, psychiatric, circadian, physiological, biochemical and neuroimaging (functional magnetic resonance imaging and magnetoencephalography) parameters are measured during a 4-week period, with randomisation to drug or placebo on day 14. We are interested in whether nicardipine affects the stability of these measures, as well as its overall effects. Participants are genotyped for the CACNA1C risk polymorphism rs1006737.

Discussion

The results will clarify the potential of LTCC antagonists for repurposing or modification for use in psychiatric disorders in which cognition, mood and sleep are affected.

Trial registration

ISRCTN, ISRCTN33631053. Retrospectively registered on 8 June 2018 (applied 17 May 2018).

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3175-0) contains supplementary material, which is available to authorized users.

Ion Channels and Transporters in Inflammation: Special Focus on TRP Channels and TRPC6

Allergy and autoimmune diseases are characterised by a multifactorial pathogenic background. Several genes involved in the control of innate and adaptive immunity have been associated with diseases and variably combine with each other as well as with environmental factors and epigenetic processes to shape the characteristics of individual manifestations. Systemic or local perturbations in salt/water balance and in ion exchanges between the intra- and extracellular spaces or among tissues play a role. In this field, usually referred to as elementary immunology, novel evidence has been recently acquired on the role of members of the transient potential receptor (TRP) channel family in several cellular mechanisms of potential significance for the pathophysiology of the immune response. TRP canonical channel 6 (TRPC6) is emerging as a functional element for the control of calcium currents in immune-committed cells and target tissues. In fact, TRPC6 influences leukocytes’ tasks such as transendothelial migration, chemotaxis, phagocytosis and cytokine release. TRPC6 also modulates the sensitivity of immune cells to apoptosis and influences tissue susceptibility to ischemia-reperfusion injury and excitotoxicity. Here, we provide a view of the interactions between ion exchanges and inflammation with a focus on the pathogenesis of immune-mediated diseases and potential future therapeutic implications.

Ion channelopathies of the immune system

Ion channels and transporters move ions across membrane barriers and are essential for a host of cell functions in many organs. They conduct K+, Na+ and Cl-, which are essential for regulating the membrane potential, H+ to control intracellular and extracellular pH and divalent cations such as Ca2+, Mg2+ and Zn2+, which function as second messengers and cofactors for many proteins. Inherited channelopathies due to mutations in ion channels or their accessory proteins cause a variety of diseases in the nervous, cardiovascular and other tissues, but channelopathies that affect immune function are not as well studied. Mutations in ORAI1 and STIM1 genes that encode the Ca2+ release-activated Ca2+ (CRAC) channel in immune cells, the Mg2+ transporter MAGT1 and the Cl- channel LRRC8A all cause immunodeficiency with increased susceptibility to infection. Mutations in the Zn2+ transporters SLC39A4 (ZIP4) and SLC30A2 (ZnT2) result in nutritional Zn2+ deficiency and immune dysfunction. These channels, however, only represent a fraction of ion channels that regulate immunity as demonstrated by immune dysregulation in channel knockout mice. The immune system itself can cause acquired channelopathies that are associated with a variety of diseases of nervous, cardiovascular and endocrine systems resulting from autoantibodies binding to ion channels. These autoantibodies highlight the therapeutic potential of functional anti-ion channel antibodies that are being developed for the treatment of autoimmune, inflammatory and other diseases.

Staphylococcal Superantigens Use LAMA2 as a Coreceptor To Activate T Cells

Canonical Ag-dependent TCR signaling relies on activation of the src-family tyrosine kinase LCK. However, staphylococcal superantigens can trigger TCR signaling by activating an alternative pathway that is independent of LCK and utilizes a Gα11-containing G protein-coupled receptor (GPCR) leading to PLCβ activation. The molecules linking the superantigen to GPCR signaling are unknown. Using the ligand-receptor capture technology LRC-TriCEPS, we identified LAMA2, the α2 subunit of the extracellular matrix protein laminin, as the coreceptor for staphylococcal superantigens. Complementary binding assays (ELISA, pull-downs, and surface plasmon resonance) provided direct evidence of the interaction between staphylococcal enterotoxin E and LAMA2. Through its G4 domain, LAMA2 mediated the LCK-independent T cell activation by these toxins. Such a coreceptor role of LAMA2 involved a GPCR of the calcium-sensing receptor type because the selective antagonist NPS 2143 inhibited superantigen-induced T cell activation in vitro and delayed the effects of toxic shock syndrome in vivo. Collectively, our data identify LAMA2 as a target of antagonists of staphylococcal superantigens to treat toxic shock syndrome.

Anti-apolipoprotein A-1 autoantibodies are associated with immunodeficiency and systemic inflammation in HIV patients

OBJECTIVES

To determine the existence of autoantibodies against apolipoprotein A-1 (anti-apoA-1 IgG) in HIV patients and explore their association with biological features of HIV infection and different inflammatory biomarkers. We also evaluated their impact on CD4⁺ lymphocytes survival.

METHODS

Anti-apoA-1 IgG plasma levels were assessed by ELISA in 237 HIV positive patients from a national prospective cohort with no current lipid-lowering therapy.

RESULTS

58% of patients were found positive for anti-apoA-1 IgG and were associated with lower CD4⁺ counts, but higher viremia and systemic inflammation. Logistic regression analyses indicated that high anti-apoA-1 IgG levels were associated with a 16-fold increased risk of displaying low CD4⁺ levels, independent of HIV RNA levels and treatment (adjusted Odds ratio [OR]:16.1, 95% Confidence Interval [95%CI]:1.80-143.6; p = 0.01), and a 6-fold increased risk of having a detectable viremia, independent of antiretroviral treatment (OR:5.47; 95% CI:1.63-18.36; p = 0.006). In vitro, anti-apoA-1 IgG induced dose and time-dependent CD4⁺ apoptosis that was increased by exposure to HIV RNA.

CONCLUSIONS

In HIV patients, anti-apoA-1 IgG levels are associated with low CD4+ counts, high viremia and a pro-inflammatory systemic profile. Anti-apoA-1 IgG can promote CD4+ lymphocyte apoptosis via undefined pathways.

Down-regulation of the Wnt/β-catenin signaling pathway by Cacnb4

The β4 isoform of the β-subunits of voltage-gated calcium channel regulates cell proliferation and cell cycle progression. Herein we show that coexpression of the β4-subunit with actors of the canonical Wnt/β-catenin signaling pathway in a hepatoma cell line inhibits Wnt-responsive gene transcription and decreases cell division, in agreement with the role of the Wnt pathway in cell proliferation. β4-subunit-mediated inhibition of Wnt signaling is observed in the presence of LiCl, an inhibitor of glycogen synthase kinase (GSK3) that promotes β-catenin translocation to the nucleus. Expression of β4-subunit mutants that lost the ability to translocate to the nucleus has no effect on Wnt signaling, suggesting that β4-subunit inhibition of Wnt signaling occurs downstream from GSK3 and requires targeting of β4-subunit to the nucleus. β4-subunit coimmunoprecipitates with the TCF4 transcription factor and overexpression of TCF4 reverses the effect of β4-subunit on the Wnt pathway. We thus propose that the interaction of nuclear β4-subunit with TCF4 prevents β-catenin binding to TCF4 and leads to the inhibition of the Wnt-responsive gene transcription. Thereby, our results show that β4-subunit is a TCF4 repressor and therefore appears as an interesting candidate for the regulation of this pathway in neurons where β4-subunit is specifically expressed.

Introducing Membrane Charge and Membrane Potential to T Cell Signaling

While membrane models now include the heterogeneous distribution of lipids, the impact of membrane charges on regulating the association of proteins with the plasma membrane is often overlooked. Charged lipids are asymmetrically distributed between the two leaflets of the plasma membrane, resulting in the inner leaflet being negatively charged and a surface potential that attracts and binds positively charged ions, proteins, and peptide motifs. These interactions not only create a transmembrane potential but they can also facilitate the formation of charged membrane domains. Here, we reference fields outside of immunology in which consequences of membrane charge are better characterized to highlight important mechanisms. We then focus on T cell receptor (TCR) signaling, reviewing the evidence that membrane charges and membrane-associated calcium regulate phosphorylation of the TCR–CD3 complex and discuss how the immunological synapse exhibits distinct patterns of membrane charge distribution. We propose that charged lipids, ions in solution, and transient protein interactions form a dynamic equilibrium during T cell activation.

The cooling compound icilin attenuates autoimmune neuroinflammation through modulation of the T-cell response

The synthetic supercooling drug, icilin, and its primary receptor target, the cation channel transient receptor potential (TRP) melastatin-8 (TRPM8), have been described as potent negative regulators of inflammation in the colon. The aim of this study was to determine whether the anti-inflammatory action of icilin could potentially be used to treat autoimmune neuroinflammatory disorders, such as multiple sclerosis (MS). During experimental autoimmune encephalomyelitis (EAE)-a CD4⁺ T cell-driven murine model of MS-we found that both wild-type (WT) and TRPM8-deficient EAE mice were protected from disease progression during icilin treatment, as evidenced by delays in clinical onset and reductions in neuroinflammation. In vitro, icilin potently inhibited the proliferation of murine and human CD4⁺ T cells, with the peripheral expansion of autoantigen-restricted T cells similarly diminished by the administration of icilin in mice. Attenuation of both TRPM8^-/- and TRP ankyrin-1^-/- T-cell proliferation by icilin was consistent with the WT phenotype, which suggests a mechanism that is independent of these channels. In addition, icilin treatment altered the expressional profile of activated CD4⁺ T cells to one that was indicative of restricted effector function and limited neuroinflammatory potential. These findings identify a potent anti-inflammatory role for icilin in lymphocyte-mediated neuroinflammation and highlight clear pleiotropic effects of the compound beyond classic TRP channel activation.-Ewanchuk, B. W., Allan, E. R. O., Warren, A. L., Ramachandran, R., Yates, R. M. The cooling compound icilin attenuates autoimmune neuroinflammation through modulation of the T-cell response.

A complex of Neuroplastin and Plasma Membrane Ca2+ ATPase controls T cell activation

The outcome of T cell activation is determined by mechanisms that balance Ca²⁺ influx and clearance. Here we report that murine CD4 T cells lacking Neuroplastin (Nptn ^-/-), an immunoglobulin superfamily protein, display elevated cytosolic Ca²⁺ and impaired post-stimulation Ca²⁺ clearance, along with increased nuclear levels of NFAT transcription factor and enhanced T cell receptor-induced cytokine production. On the molecular level, we identified plasma membrane Ca²⁺ ATPases (PMCAs) as the main interaction partners of Neuroplastin. PMCA levels were reduced by over 70% in Nptn ^-/- T cells, suggesting an explanation for altered Ca²⁺ handling. Supporting this, Ca²⁺ extrusion was impaired while Ca²⁺ levels in internal stores were increased. T cells heterozygous for PMCA1 mimicked the phenotype of Nptn ^-/- T cells. Consistent with sustained Ca²⁺ levels, differentiation of Nptn ^-/- T helper cells was biased towards the Th1 versus Th2 subset. Our study thus establishes Neuroplastin-PMCA modules as important regulators of T cell activation.

Cellular and Molecular Targets of Menthol Actions

Menthol belongs to monoterpene class of a structurally diverse group of phytochemicals found in plant-derived essential oils. Menthol is widely used in pharmaceuticals, confectionary, oral hygiene products, pesticides, cosmetics, and as a flavoring agent. In addition, menthol is known to have antioxidant, anti-inflammatory, and analgesic effects. Recently, there has been renewed awareness in comprehending the biological and pharmacological effects of menthol. TRP channels have been demonstrated to mediate the cooling actions of menthol. There has been new evidence demonstrating that menthol can significantly influence the functional characteristics of a number of different kinds of ligand and voltage-gated ion channels, indicating that at least some of the biological and pharmacological effects of menthol can be mediated by alterations in cellular excitability. In this article, we examine the results of earlier studies on the actions of menthol with voltage and ligand-gated ion channels.

Relevance of tissue specific subunit expression in channelopathies

Channelopathies are a diverse group of human disorders that are caused by mutations in genes coding for ion channels or channel-regulating proteins. Several dozen channelopathies have been identified that involve both non-excitable cells as well as electrically active tissues like brain, skeletal and smooth muscle or the heart. In this review, we start out from the general question which ion channel genes are expressed tissue-selectively. We mined the human gene expression database Human Protein Atlas (HPA) for tissue-enriched ion channel genes and found 85 genes belonging to the ion channel families. Most of these genes were enriched in brain, testis and muscle and a complete list of the enriched ion channel genes is provided. We further focused on the tissue distribution of voltage-gated calcium channel (VGCC) genes including different brain areas and the retina based on the human gene expression from the FANTOM5 dataset. The expression data is complemented by an overview of the tissue-dependent aspects of L-type calcium channel (LTCC) function, dysfunction and pharmacology, as well as of their splice variants. Finally, we focus on the pathology of tissue-restricted LTCC channelopathies and their treatment options. This article is part of the Special Issue entitled 'Channelopathies.'

Chloroquine inhibits Ca2+ permeable ion channels-mediated Ca2+ signaling in primary B lymphocytes

BACKGROUND

Chloroquine, a bitter tastant, inhibits Ca²⁺ signaling, resulting in suppression of B cell activation; however, the inhibitory mechanism remains unclear.

RESULTS

In this study, thapsigargin (TG), but not caffeine, induced sustained intracellular Ca²⁺ increases in mouse splenic primary B lymphocytes, which were markedly inhibited by chloroquine. Under Ca²⁺-free conditions, TG elicited transient Ca²⁺ increases, which additionally elevated upon the restoration of 2 mM Ca²⁺. The former were from release of intracellular Ca²⁺ store and the latter from Ca²⁺ influx. TG-induced release was inhibited by 2-APB (an inhibitor of inositol-3-phosphate receptors, IP₃Rs) and chloroquine, and TG-caused influx was inhibited by pyrazole (Pyr3, an inhibitor of transient receptor potential C3 (TRPC3) and stromal interaction molecule (STIM)/Orai channels) and chloroquine. Moreover, chloroquine also blocked Ca²⁺ increases induced by the engagement of B cell receptor (BCR) with anti-IgM.

CONCLUSIONS

These results indicate that chloroquine inhibits Ca²⁺ elevations in splenic B cells through inhibiting Ca²⁺ permeable IP₃R and TRPC3 and/or STIM/Orai channels. These findings suggest that chloroquine would be a potent immunosuppressant.

Altering calcium influx for selective destruction of breast tumor

Background

Human triple-negative breast cancer has limited therapeutic choices. Breast tumor cells have depolarized plasma membrane potential. Using this unique electrical property, we aim to develop an effective selective killing of triple-negative breast cancer.

Methods

We used an engineered L-type voltage-gated calcium channel (Cec), activated by membrane depolarization without inactivation, to induce excessive calcium influx in breast tumor cells. Patch clamp and flow cytometry were used in testing the killing selectivity and efficiency of human breast tumor cells in vitro. Bioluminescence and ultrasound imaging were used in studies of human triple-negative breast cancer cell MDA-MB-231 xenograft in mice. Histological staining, immunoblotting and immunohistochemistry were used to investigate mechanism that mediates Cec-induced cell death.

Results

Activating Cec channels expressed in human breast cancer MCF7 cells produced enormous calcium influx at depolarized membrane. Activating the wild-type Cav1.2 channels expressed in MCF7 cells also produced a large calcium influx at depolarized membrane, but this calcium influx was diminished at the sustained membrane depolarization due to channel inactivation. MCF7 cells expressing Cec died when the membrane potential was held at -10 mV for 1 hr, while non-Cec-expressing MCF7 cells were alive. MCF7 cell death was 8-fold higher in Cec-expressing cells than in non-Cec-expressing cells. Direct injection of lentivirus containing Cec into MDA-MB-231 xenograft in mice inhibited tumor growth. Activated caspase-3 protein was detected only in MDA-MB-231 cells expressing Cec, along with a significantly increased expression of activated caspase-3 in xenograft tumor treated with Cec.

Conclusions

We demonstrated a novel strategy to induce constant calcium influx that selectively kills human triple-negative breast tumor cells.

Immunological Disorders: Regulation of Ca2+ Signaling in T Lymphocytes

Engagement of T cell receptors (TCRs) with cognate antigens triggers cascades of signaling pathways in helper T cells. TCR signaling is essential for the effector function of helper T cells including proliferation, differentiation, and cytokine production. It also modulates effector T cell fate by inducing cell death, anergy (nonresponsiveness), exhaustion, and generation of regulatory T cells. One of the main axes of TCR signaling is the Ca²⁺-calcineurin-nuclear factor of activated T cells (NFAT) signaling pathway. Stimulation of TCRs triggers depletion of intracellular Ca²⁺ store and, in turn, activates store-operated Ca²⁺ entry (SOCE) to raise the intracellular Ca²⁺ concentration. SOCE in T cells is mediated by the Ca²⁺ release-activated Ca²⁺ (CRAC) channels, which have been very well characterized in terms of their electrophysiological properties. Identification of STIM1 as a sensor to detect depletion of the endoplasmic reticulum (ER) Ca²⁺ store and Orai1 as the pore subunit of CRAC channels has dramatically advanced our understanding of the regulatory mechanism of Ca²⁺ signaling in T cells. In this review, we discuss our current understanding of Ca²⁺ signaling in T cells with specific focus on the mechanism of CRAC channel activation and regulation via protein interactions. In addition, we will discuss the role of CRAC channels in effector T cells, based on the analyses of genetically modified animal models.

Distinct patterns of cytolytic T-cell activation by different tumour cells revealed by Ca2+ signalling and granule mobilization

Cancer-germline genes in both humans and mice have been shown to encode antigens susceptible to targeting by cytotoxic CD8 T effector cells (CTL). We analysed the ability of CTL to kill different tumour cell lines expressing the same cancer-germline gene P1A (Trap1a). We previously demonstrated that CTL expressing a T-cell receptor specific for the P1A_35-43 peptide associated with H-2L^d , although able to induce regression of P1A-expressing P815 mastocytoma cells, were much less effective against P1A-expressing melanoma cells. Here, we analysed parameters of the in vitro interaction between P1A-specific CTL and mastocytoma or melanoma cells expressing similar levels of the P1A gene and of surface H-2L^d . The mastocytoma cells were more sensitive to cytolysis than the melanoma cells in vitro. Analysis by video-microscopy of early events required for target cell killing showed that similar patterns of increase in cytoplasmic Ca²⁺ concentration ([Ca²⁺ ]i) were induced by both types of P1A-expressing tumour cells. However, the use of CTL expressing a fluorescent granzyme B (GZMB-Tom) showed a delay in the migration of cytotoxic granules to the tumour interaction site, as well as a partially deficient GZMB-Tom exocytosis in response to the melanoma cells. Among surface molecules possibly affecting tumour-CTL interactions, the mastocytoma cells were found to express intercellular adhesion molecule-1, the ligand for LFA-1, which was not detected on the melanoma cells.

Transient receptor potential vanilloid 1 expression and function in splenic dendritic cells: a potential role in immune homeostasis

Neuro-immune interactions, particularly those driven by neuropeptides, are increasingly implicated in immune responses. For instance, triggering calcium-channel transient receptor potential vanilloid 1 (TRPV1) on sensory nerves induces the release of calcitonin-gene-related peptide (CGRP), a neuropeptide known to moderate dendritic cell activation and T helper cell type 1 polarization. Despite observations that CGRP is not confined to the nervous system, few studies have addressed the possibility that immune cells can respond to well-documented 'neural' ligands independently of peripheral nerves. Here we have identified functionally relevant TRPV1 on primary antigen-presenting cells of the spleen and have demonstrated both calcium influx and CGRP release in three separate strains of mice using natural agonists. Furthermore, we have shown down-regulation of activation markers CD80/86 on dendritic cells, and up-regulation of interleukin-6 and interleukin-10 in response to CGRP treatment. We suggest that dendritic cell responses to neural ligands can amplify neuropeptide release, but more importantly that variability in CGRP release across individuals may have important implications for immune cell homeostasis.

Low-Voltage-Activated CaV3.1 Calcium Channels Shape T Helper Cell Cytokine Profiles

Activation of T cells is mediated by the engagement of T cell receptors (TCRs) followed by calcium entry via store-operated calcium channels. Here we have shown an additional route for calcium entry into T cells-through the low-voltage-activated T-type CaV3.1 calcium channel. CaV3.1 mediated a substantial current at resting membrane potentials, and its deficiency had no effect on TCR-initiated calcium entry. Mice deficient for CaV3.1 were resistant to the induction of experimental autoimmune encephalomyelitis and had reduced productions of the granulocyte-macrophage colony-stimulating factor (GM-CSF) by central nervous system (CNS)-infiltrating T helper 1 (Th1) and Th17 cells. CaV3.1 deficiency led to decreased secretion of GM-CSF from in vitro polarized Th1 and Th17 cells. Nuclear translocation of the nuclear factor of activated T cell (NFAT) was also reduced in CaV3.1-deficient T cells. These data provide evidence for T-type channels in immune cells and their potential role in shaping the autoimmune response.

T Cell Receptor Mediated Calcium Entry Requires Alternatively Spliced Cav1.1 Channels

The process of calcium entry in T cells is a multichannel and multi-step process. We have studied the requirement for L-type calcium channels (Ca_v1.1) α1S subunits during calcium entry after TCR stimulation. High expression levels of Ca_v1.1 channels were detected in activated T cells. Sequencing and cloning of Ca_v1.1 channel cDNA from T cells revealed that a single splice variant is expressed. This variant lacks exon 29, which encodes the linker region adjacent to the voltage sensor, but contains five new N-terminal exons that substitute for exons 1 and 2, which are found in the Ca_v1.1 muscle counterpart. Overexpression studies using cloned T cell Ca_v1.1 in 293HEK cells (that lack TCR) suggest that the gating of these channels was altered. Knockdown of Ca_v1.1 channels in T cells abrogated calcium entry after TCR stimulation, suggesting that Ca_v1.1 channels are controlled by TCR signaling.

Transient Receptor Potential (TRP) channels in T cells

The transient receptor potential (TRP) family of ion channels is widely expressed in many cell types and plays various physiological roles. Growing evidence suggests that certain TRP channels are functionally expressed in the immune system. Indeed, an increasing number of reports have demonstrated the functional expression of several TRP channels in innate and adaptive immune cells and have highlighted their critical role in the activation and function of these cells. However, very few reviews have been entirely dedicated to this subject. Here, we will summarize the recent findings with regards to TRP channel expression in T cells and discuss their emerging role as regulators of T cell activation and functions. Moreover, these studies suggest that beyond their pharmaceutical interest in pain management, certain TRP channels may represent potential novel therapeutic targets for various immune-related diseases.

Signature Channels of Excitability no More: L-Type Channels in Immune Cells

Although the concept of Ca(2+) as a universal messenger is well established, it was assumed that the regulatory mechanisms of Ca(2+)-signaling were divided along the line of electric excitability. Recent advances in molecular biology and genomics have, however, provided evidence that non-excitable cells such as immunocytes also express a wide and diverse pool of ion channels that does not differ as significantly from that of excitable cells as originally assumed. Ion channels and transporters are involved in virtually all aspects of immune response regulation, from cell differentiation and development to activation, and effector functions such as migration, antibody-secretion, phagosomal maturation, or vesicular delivery of bactericidal agents. This comprises TRP channel family members, voltage- and Ca(2+)-gated K(+)- and Na(+)-channels, as well as unexpectedly, components of the CaV1-subfamily of voltage-gated L-type Ca(2+)-channels, originally thought to be signature molecules of excitability. This article provides an overview of recent observations made in the field of CaV1 L-type channel function in the immune context, as well as presents results we obtained studying these channels in B-lymphocytes.

Inhibition of Gαs/cAMP Signaling Decreases TCR-Stimulated IL-2 transcription in CD4(+) T Helper Cells

BACKGROUND

The role of cAMP in regulating T cell activation and function has been controversial. cAMP is generally known as an immunosuppressant, but it is also required for generating optimal immune responses. As the effect of cAMP is likely to depend on its cellular context, the current study investigated whether the mechanism of activation of Gαs and adenylyl cyclase influences their effect on T cell receptor (TCR)-stimulated interleukin-2 (IL-2) mRNA levels.

METHODS

The effect of blocking Gs-coupled receptor (GsPCR)-mediated Gs activation on TCR-stimulated IL-2 mRNA levels in CD4(+) T cells was compared with that of knocking down Gαs expression or inhibiting adenylyl cyclase activity. The effect of knocking down Gαs expression on TCR-stimulated cAMP accumulation was compared with that of blocking GsPCR signaling.

RESULTS

ZM-241385, an antagonist to the Gs-coupled A2A adenosine receptor (A2AR), enhanced TCR-stimulated IL-2 mRNA levels in primary human CD4(+) T helper cells and in Jurkat T cells. A dominant negative Gαs construct, GαsDN3, also enhanced TCR-stimulated IL-2 mRNA levels. Similar to GsPCR antagonists, GαsDN3 blocked GsPCR-dependent activation of both Gαs and Gβγ. In contrast, Gαs siRNA and 2',5'-dideoxyadenosine (ddA), an adenylyl cyclase inhibitor, decreased TCR-stimulated IL-2 mRNA levels. Gαs siRNA, but not GαsDN3, decreased TCR-stimulated cAMP synthesis. Potentiation of IL-2 mRNA levels by ZM-241385 required at least two days of TCR stimulation, and addition of ddA after three days of TCR stimulation enhanced IL-2 mRNA levels.

CONCLUSIONS

GsPCRs play an inhibitory role in the regulation of TCR-stimulated IL-2 mRNA levels whereas Gαs and cAMP can play a stimulatory one. Additionally, TCR-dependent activation of Gαs does not appear to involve GsPCRs. These results suggest that the context of Gαs/cAMP activation and the stage of T cell activation and differentiation determine the effect on TCR-stimulated IL-2 mRNA levels.

Inhibition of G-Protein βγ Signaling Decreases Levels of Messenger RNAs Encoding Proinflammatory Cytokines in T Cell Receptor-Stimulated CD4(+) T Helper Cells

Background: Inhibition of G-protein βγ (Gβγ) signaling was found previously to enhance T cell receptor (TCR)-stimulated increases in interleukin 2 (IL-2) mRNA in CD4⁺ T helper cells, suggesting that Gβγ might be a useful drug target for treating autoimmune diseases, as low dose IL-2 therapy can suppress autoimmune responses. Because IL-2 may counteract autoimmunity in part by shifting CD4⁺ T helper cells away from the Type 1 T helper cell (TH1) and TH17 subtypes towards the TH2 subtype, the purpose of this study was to determine if blocking Gβγ signaling affected the balance of TH1, TH17, and TH2 cytokine mRNAs produced by CD4⁺ T helper cells.

Methods: Gallein, a small molecule inhibitor of Gβγ, and siRNA-mediated silencing of the G-protein β₁ subunit (Gβ₁) were used to test the effect of blocking Gβγ on mRNA levels of cytokines in primary human TCR-stimulated CD4⁺ T helper cells.

Results: Gallein and Gβ₁ siRNA decreased interferon-γ (IFN-γ) and IL-17A mRNA levels in TCR-stimulated CD4⁺ T cells grown under TH1-promoting conditions. Inhibiting Gβγ also decreased mRNA levels of STAT4, which plays a positive role in TH1 differentiation and IL-17A production. Moreover, mRNA levels of the STAT4-regulated TH1-associated proteins, IL-18 receptor β chain (IL-18Rβ), mitogen-activated protein kinase kinase kinase 8 (MAP3K8), lymphocyte activation gene 3 (LAG-3), natural killer cell group 7 sequence (NKG7), and oncostatin M (OSM) were also decreased upon Gβγ inhibition. Gallein also increased IL-4, IL-5, IL-9, and IL-13 mRNA levels in TCR-stimulated memory CD4⁺ T cells grown in TH2-promoting conditions.

Conclusions: Inhibiting Gβγ to produce these shifts in cytokine mRNA production might be beneficial for patients with autoimmune diseases such as rheumatoid arthritis (RA), Crohn’s disease (CD), psoriasis, multiple sclerosis (MS), and Hashimoto’s thyroiditis (HT), in which both IFN-γ and IL-17A are elevated.

Effects of monoterpenes on ion channels of excitable cells

Monoterpenes are a structurally diverse group of phytochemicals and a major constituent of plant-derived 'essential oils'. Monoterpenes such as menthol, carvacrol, and eugenol have been utilized for therapeutical purposes and food additives for centuries and have been reported to have anti-inflammatory, antioxidant and analgesic actions. In recent years there has been increasing interest in understanding the pharmacological actions of these molecules. There is evidence indicating that monoterpenes can modulate the functional properties of several types of voltage and ligand-gated ion channels, suggesting that some of their pharmacological actions may be mediated by modulations of ion channel function. In this report, we review the literature concerning the interaction of monoterpenes with various ion channels.

Inhibition of G-protein βγ signaling enhances T cell receptor-stimulated interleukin 2 transcription in CD4+ T helper cells

G-protein-coupled receptor (GPCR) signaling modulates the expression of cytokines that are drug targets for immune disorders. However, although GPCRs are common targets for other diseases, there are few GPCR-based pharmaceuticals for inflammation. The purpose of this study was to determine whether targeting G-protein βγ (Gβγ) complexes could provide a useful new approach for modulating interleukin 2 (IL-2) levels in CD4⁺ T helper cells. Gallein, a small molecule inhibitor of Gβγ, increased levels of T cell receptor (TCR)-stimulated IL-2 mRNA in primary human naïve and memory CD4⁺ T helper cells and in Jurkat human CD4⁺ leukemia T cells. Gβ₁ and Gβ₂ mRNA accounted for >99% of Gβ mRNA, and small interfering RNA (siRNA)-mediated silencing of Gβ₁ but not Gβ₂ enhanced TCR-stimulated IL-2 mRNA increases. Blocking Gβγ enhanced TCR-stimulated increases in IL-2 transcription without affecting IL-2 mRNA stability. Blocking Gβγ also enhanced TCR-stimulated increases in nuclear localization of nuclear factor of activated T cells 1 (NFAT1), NFAT transcriptional activity, and levels of intracellular Ca²⁺. Potentiation of IL-2 transcription required continuous Gβγ inhibition during at least two days of TCR stimulation, suggesting that induction or repression of additional signaling proteins during T cell activation and differentiation might be involved. The potentiation of TCR-stimulated IL-2 transcription that results from blocking Gβγ in CD4⁺ T helper cells could have applications for autoimmune diseases.

Calcium channels in Fc receptor signaling

The calcium ion (Ca(2+)) is the main common second messenger involved in signaling transduction subsequent to immunoreceptor activation. Its rapid intracellular elevation induces multiple cellular responses, such as secretion, proliferation, mobility, and gene transcription. Intracellular levels of Ca(2+) need to reach a specific threshold to efficiently transduce the signal to activate transcription factors through the recruitment of Ca(2+)-binding molecules. However, since Ca(2+) cannot be metabolized, its intracellular concentration is tightly regulated to avoid the induction of programmed cell death. This highly controlled regulation of Ca(2+) homeostasis has recently been clarified by the uncovering of new ion channels. The regulation of these channels allows the role of Ca(2+) in Fc receptor transduction pathways to be more precisely defined.

Verapamil modulates interleukin-5 and interleukin-6 secretion in organotypic human sinonasal polyp explants

BACKGROUND

Verapamil is an L-type calcium channel blocker (CCB) that has been shown to have immunomodulatory properties in a variety of tissues. The goal of this study was determine whether verapamil is capable of regulating cytokine secretion in sinonasal polyps and to compare this effect to dexamethasone, an established immunosuppressive corticosteroid.

METHODS

This was an institutional review board (IRB)-approved study in sinonasal polyp explants derived from 8 patients with chronic rhinosinusitis with nasal polyps (CRSwNP). Polyps were incubated with dexamethasone or verapamil for 24 hours followed by an additional 24 hours with Staphylococcal enterotoxin B (SEB). Concentrations of secreted cytokines over each exposure period were determined by enzyme-linked immunosorbent assay (ELISA) and are expressed as a percent. Results were compared using a 2-tailed Student t test.

RESULTS

The percent of SEB-stimulated interleukin-5 (IL-5) secretion (mean ± standard deviation [SD], 339.94% ± 315.48%) between the second and first treatment periods was significantly reduced following exposure to dexamethasone (74.08% ± 26.77%, p < 0.05) and verapamil (119.99% ± 69.32%, p < 0.05). The percent of SEB-stimulated IL-6 secretion (217.53% ± 89.51%) was also significantly reduced following exposure to verapamil (148.82% ± 79.15%, p < 0.05) but not dexamethasone (148.86% ± 145.24%). Finally, the percent of SEB-stimulated thymic stromal lymphopoietin (TSLP) secretion (37.86% ± 18.88%) demonstrated a nonsignificant trend toward reduction with both dexamethasone (31.15% ± 35.28%) and verapamil (20.14% ± 12.10%).

CONCLUSION

Although the mechanism has yet to be fully understood, L-type CCBs are capable of reducing inflammation in multiple tissues. Verapamil was specifically found to reduce airway goblet cell hyperplasia and eosinophilic infiltration in a murine asthma model. Our data support these findings suggesting that verapamil can modulate T-helper cell type 2 (Th2)-associated cytokine secretion in sinonasal polyp explants. This data points to a possible therapeutic role for CCBs in the management of CRSwNP.