The effects of Kv1.3 and IKCa1 potassium channel inhibition on calcium influx of human peripheral T lymphocytes in rheumatoid arthritis

Voltage-gated potassium channel 1.3: A promising molecular target in multiple disease therapy

Voltage-gated potassium channel 1.3 (Kv1.3) has emerged as a pivotal player in numerous biological processes and pathological conditions, sparking considerable interest as a potential therapeutic target across various diseases. In this review, we present a comprehensive examination of Kv1.3 channels, highlighting their fundamental characteristics and recent advancements in utilizing Kv1.3 inhibitors for treating autoimmune disorders, neuroinflammation, and cancers. Notably, Kv1.3 is prominently expressed in immune cells and implicated in immune responses and inflammation associated with autoimmune diseases and chronic inflammatory conditions. Moreover, its aberrant expression in certain tumors underscores its role in cancer progression. While preclinical studies have demonstrated the efficacy of Kv1.3 inhibitors, their clinical translation remains pending. Molecular imaging techniques offer promising avenues for tracking Kv1.3 inhibitors and assessing their therapeutic efficacy, thereby facilitating their development and clinical application. Challenges and future directions in Kv1.3 inhibitor research are also discussed, emphasizing the significant potential of targeting Kv1.3 as a promising therapeutic strategy across a spectrum of diseases.

Kv1.3 in the spotlight for treating immune diseases

INTRODUCTION

Kv1.3 is the main voltage-gated potassium channel of leukocytes from both the innate and adaptive immune systems. Channel function is required for common processes such as Ca2+ signaling but also for cell-specific events. In this context, alterations in Kv1.3 are associated with multiple immune disorders. Excessive channel activity correlates with numerous autoimmune diseases, while reduced currents result in increased cancer prevalence and immunodeficiencies.

AREAS COVERED

This review offers a general view of the role of Kv1.3 in every type of leukocyte. Moreover, diseases stemming from dysregulations of the channel are detailed, as well as current advances in their therapeutic research.

EXPERT OPINION

Kv1.3 arises as a potential immune target in a variety of diseases. Several lines of research focused on channel modulation have yielded positive results. However, among the great variety of specific channel blockers, only one has reached clinical trials. Future investigations should focus on developing simpler administration routes for channel inhibitors to facilitate their entrance into clinical trials. Prospective Kv1.3-based treatments will ensure powerful therapies while minimizing undesired side effects.

A bibliometric analysis: Ca2+ fluxes and inflammatory phenotyping by flow cytometry in peripheral blood mononuclear cells

Background

The immune system, composed of organs, tissues, cells, and proteins, is the key to protecting the body from external biological attacks and inflammation. The latter occurs in several pathologies, such as cancers, type 1 diabetes, and human immunodeficiency virus infection. Immunophenotyping by flow cytometry is the method of choice for diagnosing these pathologies. Under inflammatory conditions, the peripheral blood mononuclear cells (PBMCs) are partially activated and generate intracellular pathways involving Ca2+-dependent signaling cascades leading to transcription factor expression. Ca2+ signaling is typically studied by microscopy in cell lines but can present some limitations to explore human PBMCs, where flow cytometry can be a good alternative.

Objective

In this review, we dived into the research field of inflammation and Ca2+ signaling in PBMCs. We aimed to investigate the structure and evolution of this field in a physio-pathological context, and then we focused our review on flow cytometry analysis of Ca2+ fluxes in PBMCs.

Methods

From 1984 to 2022, 3865 articles on inflammation and Ca2+ signaling in PBMCs were published, according to The Clarivate Web of Science (WOS) database used in this review. A bibliometric study was designed for this collection and consisted of a co-citation and bibliographic coupling analysis.

Results

The co-citation analysis was performed on 133 articles: 4 clusters highlighted the global context of Ca2+ homeostasis, including chemical probe development, identification of the leading players in Ca2+ signaling, and the link with chemokine production in immune cell function. Next, the bibliographic coupling analysis combined 998 articles in 8 clusters. This analysis outlined the mechanisms of PBMC activation, from signal integration to cellular response. Further explorations of the bibliographic coupling network, focusing on flow cytometry, revealed 21 articles measuring cytosolic Ca2+ in PBMCs, with only 5 since 2016. This final query showed that Ca2+ signaling analysis in human PBMCs using flow cytometry is still underdeveloped and investigates mainly the cytosolic Ca2+ compartment.

Conclusion

Our review uncovers remaining knowledge gaps of intracellular players involved in Ca2+ signaling in PBMCs, such as reticulum and mitochondria, and presents flow cytometry as a solid option to supplement gold-standard microscopy studies.

Reduction of Ca2+ Entry by a Specific Block of KCa3.1 Channels Optimizes Cytotoxic Activity of NK Cells against T-ALL Jurkat Cells

Degranulation mediated killing mechanism by NK cells is dependent on store-operated Ca2+ entry (SOCE) and has optimum at moderate intracellular Ca2+ elevations so that partial block of SOCE optimizes the killing process. In this study, we tested the effect of the selective blocker of KCa3.1 channel NS6180 on SOCE and the killing efficiency of NK cells from healthy donors and NK-92 cells against T-ALL cell line Jurkat. Patch-clamp analysis showed that only one-quarter of resting NK cells functionally express KCa3.1 current, which increases 3-fold after activation by interleukins 15 and 2. Nevertheless, blockage of KCa3.1 significantly reduced SOCE and intracellular Ca2+ rise induced by IL-15 or target cell recognition. NS6180 (1 μM) decreased NK degranulation at zero time of coculture with Jurkat cells but already after 1 h, the degranulation reached the same level as in the control. Monitoring of target cell death by flow cytometry and confocal microscopy demonstrated that NS6180 significantly improved the killing ability of NK cells after 1 h in coculture with Jurkat cells and increased the Jurkat cell fraction with apoptotic and necrotic markers. Our data evidence a strong dependence of SOCE on KCa3.1 activity in NK cells and that KCa3.1 specific block can improve NK cytotoxicity.

The immunosuppressive effects and mechanisms of loureirin B on collagen-induced arthritis in rats

Introduction

Rheumatoid arthritis (RA) is a common disease mainly affecting joints of the hands and wrists. The discovery of autoantibodies in the serum of patients revealed that RA belonged to the autoimmune diseases and laid a theoretical basis for its immunosuppressive therapy. The pathogenesis of autoimmune diseases mainly involves abnormal activation and proliferation of effector memory T cells, which is closely related to the elevated expression of Kv1.3, a voltage-gated potassium (Kv) channel on the effector memory T cell membrane. Drugs blocking the Kv1.3 channel showed a strong protective effect in RA model animals, suggesting that Kv1.3 is a target for the discovery of specific RA immunosuppressive drugs.

Methods

In the present study, we synthesized LrB and studied the effects of LrB on collagen- induced arthritis (CIA) in rats. The clinical score, paw volume and joint morphology of CIA model rats were compared. The percentage of CD3+, CD4+ and CD8+ T cells in rat peripheral blood mononuclear and spleen were analyzed with flow cytometry. The concentrations of inflammatory cytokines interleukin (IL)-1b, IL-2, IL-4, IL-6, IL-10 and IL-17 in the serum of CIA rats were analyzed with enzyme-linked immunosorbent assay. The IL-1b and IL-6 expression in joints and the Kv1.3 expression in peripheral blood mononuclear cells (PBMCs) were quantified by qPCR. To further study the mechanisms of immunosuppressive effects of LrB, western blot and immunofluorescence were utilized to study the expression of Kv1.3 and Nuclear Factor of Activated T Cells 1 (NFAT1) in two cell models - Jurkat T cell line and extracted PBMCs.

Results

LrB effectively reduced the clinical score and relieved joint swelling. LrB could also decrease the percentage of CD4+ T cells, while increase the percentage of CD8+ T cells in peripheral blood mononuclear and spleen of rats with CIA. The concentrations of inflammatory cytokines interleukin (IL)-1b, IL-2, IL-6, IL-10 and IL-17 in the serum of CIA rats were significantly reduced by LrB. The results of qPCR showed that Kv1.3 mRNA in the PBMCs of CIA rats was significantly higher than that of the control and significantly decreased in the LrB treatment groups. In addition, we confirmed in cell models that LrB significantly decreased Kv1.3 protein on the cell membrane and inhibited the activation of Nuclear Factor of Activated T Cells 1 (NFAT1) with immune stimulus.

Conclusion

In summary, this study revealed that LrB could block NFAT1 activation and reduce Kv1.3 expression in activated T cells, thus inhibiting the proliferation of lymphocytes and the release of inflammatory cytokines, thereby effectively weakening the autoimmune responses in CIA rats. The effects of immunosuppression due to LrB revealed its potential medicinal value in the treatment of RA.

Regulatory role of KCa3.1 in immune cell function and its emerging association with rheumatoid arthritis

Rheumatoid arthritis (RA) is a common autoimmune disease characterized by chronic inflammation. Immune dysfunction is an essential mechanism in the pathogenesis of RA and directly linked to synovial inflammation and cartilage/bone destruction. Intermediate conductance Ca²⁺-activated K⁺ channel (KCa3.1) is considered a significant regulator of proliferation, differentiation, and migration of immune cells by mediating Ca²⁺ signal transduction. Earlier studies have demonstrated abnormal activation of KCa3.1 in the peripheral blood and articular synovium of RA patients. Moreover, knockout of KCa3.1 reduced the severity of synovial inflammation and cartilage damage to a significant extent in a mouse collagen antibody-induced arthritis (CAIA) model. Accumulating evidence implicates KCa3.1 as a potential therapeutic target for RA. Here, we provide an overview of the KCa3.1 channel and its pharmacological properties, discuss the significance of KCa3.1 in immune cells and feasibility as a drug target for modulating the immune balance, and highlight its emerging role in pathological progression of RA.

Potential Target Analysis of Triptolide Based on Transcriptome-Wide m6A Methylome in Rheumatoid Arthritis

Triptolide (TP), a major active component of the herb Tripterygium wilfordii Hook F (TwHF), has been shown to exert therapeutic potential against rheumatoid arthritis (RA). However, its molecular mechanism of action has not been fully elucidated. This study aimed to analyze the potential target of TP based on the discovery of differentially methylated and expressed genes (DMEGs) in RA using methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing (RNA-seq). Five RA samples and ten control samples were obtained from China-Japan Friendship Hospital. The various levels of m⁶A methylation and genes expressed in the RA and control groups were compared by MeRIP-seq and RNA-seq. Bioinformatics explorations were also performed to explore the enriched biological roles and paths of the differentially expressed m⁶A methylation and genes. Molecular networks between TP target proteins and DMEGs were performed using Ingenuity Pathway Analysis (IPA) software. Potential target of TP was determined with Gene Expression Omnibus (GEO) database mining, molecular docking, and in vitro experiment validation. In total, 583 dysregulated m⁶A peaks, of which 295 were greatly upregulated and 288 were greatly downregulated, were identified. Similarly, 1,570 differentially expressed genes were identified by RNA-seq, including 539 upregulated and 1,031 downregulated genes. According to the deeper joint exploration, the m⁶A methylation and mRNA expression degrees of 35 genes varied greatly. Molecular networks between TP target proteins and DMEGs were constructed, and the results revealed that tubulin beta-2A chain (TUBB2A), insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3), cytoplasmic dynein 1 intermediate chain 1 (DYNC1I1), and FOS-like 1 (FOSL1) were the most relevant genes that correlated with the target proteins of TP. The results of the GEO database showed that the gene expression of IGF2BP3 was increased in RA synovial tissue and consistent with the trend of our sequencing results of RA PBMCs. Molecular docking and in vitro experiment suggested that TP and IGF2BP3 had a high binding affinity and TP could decrease the mRNA expression of IGF2BP3 in PBMCs and MH7A.This research established a transcriptional map of m⁶A in RA PBMCs and displayed the hidden association between RNA methylation alterations and associated genes in RA. IGF2BP3 might be a potential therapeutic target of TP during RA treatment.

Optimization of Pichia pastoris Expression System for High-Level Production of Margatoxin

Margatoxin (MgTx) is a high-affinity blocker of voltage-gated potassium (Kv) channels. It inhibits Kv1.1–Kv1.3 ion channels in picomolar concentrations. This toxin is widely used to study physiological function of Kv ion channels in various cell types, including immune cells. Isolation of native MgTx in large quantities from scorpion venom is not affordable. Chemical synthesis and recombinant production in Escherichia coli need in vitro oxidative refolding for proper disulfide bond formation, resulting in a very low yield of peptide production. The Pichia pastoris expression system offers an economical approach to overcome all these limitations and gives a higher yield of correctly refolded recombinant peptides. In this study, improved heterologous expression of recombinant MgTx (rMgTx) in P. pastoris was obtained by using preferential codons, selecting the hyper-resistant clone against Zeocin, and optimizing the culturing conditions. About 36 ± 4 mg/L of >98% pure His-tagged rMgTx (TrMgTx) was produced, which is a threefold higher yield than has been previously reported. Proteolytic digestion of TrMgTx with factor Xa generated untagged rMgTx (UrMgTx). Both TrMgTx and UrMgTx blocked the Kv1.2 and Kv1.3 currents (patch-clamp) (K_d for Kv1.2 were 64 and 14 pM, and for Kv1.3, 86 and 50 pM, respectively) with comparable potency to the native MgTx. The analysis of the binding kinetics showed that TrMgTx had a lower association rate than UrMgTx for both Kv1.2 and Kv1.3. The dissociation rate of both the analogues was the same for Kv1.3. However, in the case of Kv1.2, TrMgTx showed a much higher dissociation rate with full recovery of the block than UrMgTx. Moreover, in a biological functional assay, both peptides significantly downregulated the expression of early activation markers IL2R and CD40L in activated CD4⁺ T_EM lymphocytes whose activation was Kv1.3 dependent. In conclusion, the authors report that the Pichia expression system is a powerful method to produce disulfide-rich peptides, the overexpression of which could be enhanced noticeably through optimization strategies, making it more cost-effective. Since the presence of the His-tag on rMgTx only mildly altered the block equilibrium and binding kinetics, recombinant toxins could be used in ion channel research without removing the tag and could thus reduce the cost and time demand for toxin production.

Discovery of KV 1.3 ion channel inhibitors: Medicinal chemistry approaches and challenges

The KV 1.3 voltage-gated potassium ion channel is involved in many physiological processes both at the plasma membrane and in the mitochondria, chiefly in the immune and nervous systems. Therapeutic targeting KV 1.3 with specific peptides and small molecule inhibitors shows great potential for treating cancers and autoimmune diseases, such as multiple sclerosis, type I diabetes mellitus, psoriasis, contact dermatitis, rheumatoid arthritis, and myasthenia gravis. However, no KV 1.3-targeted compounds have been approved for therapeutic use to date. This review focuses on the presentation of approaches for discovering new KV 1.3 peptide and small-molecule inhibitors, and strategies to improve the selectivity of active compounds toward KV 1.3. Selectivity of dalatazide (ShK-186), a synthetic derivate of the sea anemone toxin ShK, was achieved by chemical modification and has successfully reached clinical trials as a potential therapeutic for treating autoimmune diseases. Other peptides and small-molecule inhibitors are critically evaluated for their lead-like characteristics and potential for progression into clinical development. Some small-molecule inhibitors with well-defined structure-activity relationships have been optimized for selective delivery to mitochondria, and these offer therapeutic potential for the treatment of cancers. This overview of KV 1.3 inhibitors and methodologies is designed to provide a good starting point for drug discovery to identify novel effective KV 1.3 modulators against this target in the future.

Immunological Responses to Envenomation

Venoms are complex mixtures of toxic compounds delivered by bite or sting. In humans, the consequences of envenomation range from self-limiting to lethal. Critical host defence against envenomation comprises innate and adaptive immune strategies targeted towards venom detection, neutralisation, detoxification, and symptom resolution. In some instances, venoms mediate immune dysregulation that contributes to symptom severity. This review details the involvement of immune cell subtypes and mediators, particularly of the dermis, in host resistance and venom-induced immunopathology. We further discuss established venom-associated immunopathology, including allergy and systemic inflammation, and investigate Irukandji syndrome as a potential systemic inflammatory response. Finally, this review characterises venom-derived compounds as a source of immune modulating drugs for treatment of disease.

Methotrexate, a small molecular scaffold targeting Kv1.3 channel extracellular pore region

Methotrexate (MTX) has been widely used for the treatment of many types of autoimmune diseases, such as rheumatoid arthritis, psoriasis and dermatomyositis. However, its pharmacological mechanism is still unclear completely. In this study, we found that MTX is a potent and selective inhibitor of the Kv1.3 channel, a class of potassium channels highly associated with autoimmune diseases. Electrophysiological experiments showed that MTX inhibited human Kv1.3 channel with an IC₅₀ of 41.5 ± 24.9 nM, and 1 μM MTX inhibited 32.6 ± 1.3% and 25.6 ± 2.2% of human Kv1.1 and Kv1.2 channel currents, respectively. These data implied the unique selectivity of MTX towards the Kv1.3 channel. Excitingly, using channel activation and chimeric experiments, we found that MTX bound to the outer pore region of Kv1.3 channel. Mutagenesis experiments in the Kv.3 channel extracellular pore region further showed that the Dsp371, Thr373 and His399 residues of outer pore region of Kv1.3 channel played important roles in MTX inhibiting activities. In conclusion, MTX inhibited Kv1.3 channel by targeting extracellular pore region, which is different form all the report small molecules, such as PAP-1 and 4-AP, but similar with many natural animal toxin peptides, such as ChTX, ShK and BmKTX. To the best of our knowledge, MTX is the first small molecular scaffold targeting the Kv1.3 channel extracellular pore region, suggesting its potential applications for designing novel Kv1.3 lead drugs and treating Kv1.3 channel-associated autoimmune diseases.

Calcium Influx Kinetics and the Characteristics of Potassium Channels in Peripheral T Lymphocytes in Systemic Sclerosis

BACKGROUND

Systemic sclerosis (SSc) is a chronic, immune-mediated, connective tissue disease causing microvascular abnormalities and fibrosis. The cytoplasmic calcium influx kinetics in T lymphocytes governs lymphocyte activation in this inflammatory process. The inhibition of Kv1.3 and IKCa1 potassium channels reduces calcium influx.

METHODS

This study aimed to analyze cytoplasmic calcium influx kinetics following activation in Th1, Th2, and CD8 cells in peripheral blood of 12 healthy individuals and 16 patients with systemic sclerosis using flow cytometry. We also evaluated the effect of the specific inhibition of the Kv1.3 and IKCa1 potassium channels.

RESULTS

We observed higher levels of activation in CD8 compared with Th1 cells in SSc. However, the activation of CD8 cells was lower in SSc compared to healthy controls. Moreover, activation of Th1 lymphocytes was slower in SSc than in healthy controls. The inhibition of IKCa1 channels decreased the activation of Th1 cells, while the inhibition of Kv1.3 channels modified the dynamics of activation of Th1 and Th2 lymphocytes in SSc.

CONCLUSION

Th1 and CD8 cells demonstrate specific activation dynamics and sensitivity to potassium channel inhibition in SSc, distinguishing this condition both from healthy controls and other autoimmune diseases.

Mutual regulation between β-TRCP mediated REST protein degradation and Kv1.3 expression controls vascular smooth muscle cell phenotype switch

BACKGROUND AND AIMS

Phenotypic switch of vascular smooth muscle cells (VSMC) plays a key role in the pathogenesis of atherosclerosis and restenosis after artery intervention. Transcription repressor element 1-silencing transcription factor (REST) has been identified as key regulator of VSMC proliferation. In the present study, we sought to investigate the potential association of E3-ubiquitin ligase β-TRCP mediated REST protein degradation with Kv1.3 expression during VSMC phenotypic switch.

METHODS

Protein and mRNA expression was measured in ex vivo and in vitro models. Protein interaction and ubiquitination were analyzed by immunoprecipitation assays. ChIP assays were performed to assess the relationship between REST and targeted DNA binding site.

RESULTS

We found that the expression level of E3-ubiquitin ligase β-TRCP is significantly increased during VSMC phenotypic switch. REST protein ubiquitination mediated by β-TRCP is critical for VSMC proliferation and migration. We also found that the gene KCNA3 encoding potassium channel protein Kv1.3 contains a functional REST binding site and is repressed by REST. Downregulation of REST by β-TRCP and consequently upregulation of Kv1.3 are important events during VSMC phenotypic switch. Furthermore, upregulated Kv1.3 accelerates β-TRCP modulated REST degradation through Erk1/2 signaling.

CONCLUSIONS

Our results reveal a fundamental role for regulatory interactions between β-TRCP modulated REST degradation and Kv1.3 in the control of the multilayered regulatory programs required for VSMC phenotype switch.

Blockage of Kv1.3 regulates macrophage migration in acute liver injury by targeting δ-catenin through RhoA signaling

Background: Activation of macrophages and infiltration are key events in acute liver injury (ALI). Kv1.3 plays an important role in regulating immunologic functions of macrophages and is extensively recognized as a potential ion channel for immunological diseases. Objective: We hypothesized that blockage of Kv1.3 may influence ALI by inhibiting macrophages infiltration in damaged liver tissues. Methods: Margatoxin was administered into the peritoneal cavity of ALI mice. The impact of this treatment on ALI and macrophage migration in vivo and in vitro was determined using immunohistochemistry, transwell migration, and wound healing assays. Results: MgTX treatment alleviated ALI in mice, as evidenced by reduced macrophage infiltration in liver tissues and lower serum levels of liver ALT and AST. RNA-seq profiling analysis showed that the most obvious change by MgTX treatment was downregulation of δ-catenin, a protein known to be associated with macrophage migration. The effect of MgTX on macrophage migration and involvement of δ-catenin was confirmed by transwell and wound healing assays. Overexpression of δ-catenin in RAW264.7 cells promoted migration, an event that was suppressed upon silencing of δ-catenin. Mechanistically, the expression of RhoA was regulated by the overexpression or knockdown of δ-catenin. Conclusion: These findings suggest a role for blockage of Kv1.3 channel in macrophage migration and reveal a new target in the treatment of ALI.

Margatoxin mitigates CCl4‑induced hepatic fibrosis in mice via macrophage polarization, cytokine secretion and STAT signaling

A number of macrophage phenotypes have been previously identified as crucial regulators in the progression of hepatic fibrosis (HF). Cytokines from macrophages or Kupffer cells (KCs) have also been identified to be important regulators in HF. Blocking Kv1.3 in models of HF, regulating macrophage polarization and cytokine secretion have not yet been assessed as potential treatments options for this condition. In the current study, a model of carbon tetrachloride (CCl4)-induced HF was established and examined the effects of margatoxin (MgTX; an inhibitor of Kv1.3) on HF. Hematoxylin and eosin, Masson's trichrome and immunohistochemistry staining were performed to determine whether MgTX can alleviate liver fibrosis. To elucidate the mechanisms through which MgTX attenuates liver injury, reverse transcription-quantitative PCR and western blot analysis were used to detect polarized macrophage markers in RAW264.7 cells and cytokines were examined using ELISA. Furthermore, macrophage polarization signal transducer and activator of transcription (STAT) signaling, which is associated with macrophage polarization, was identified in RAW264.7 cells. The results revealed that MgTX protected the mice from CCl4-induced liver fibrosis. Furthermore, MgTX decreased the expression of M1 phenotype biomarkers, and increased the expression of M2 phenotype biomarkers in CCl4-induced HF. Additionally, the production of pro-inflammatory cytokines was decreased and interleukin-10 production was increased in the serum of mice with HF injected with MgTX. Furthermore, MgTX was found to regulate the expression of M1 markers by suppressing p-STAT1 activity and increasing the expression of M2 markers by promoting p-STAT6 activity. On the whole, the findings of this study demonstrate that MgTX is able to alleviate CCl4-induced HF in mice, possibly via macrophage polarization, cytokine secretion and STAT signaling.

Alleviating airway inflammation by inhibiting ERK-NF-κB signaling pathway by blocking Kv1.3 channels

Allergic asthma is a chronic inflammatory disease of the airways. T lymphocytes play an important role in the pathogenesis of asthma. The voltage-gated Kv1.3 potassium channel is a target for the preferential inhibition of T_EM cells. In this study, we investigate the effects of PAP-1, a selective inhibitor of Kv1.3 channel, on the treatment of the neutrophilic asthma model. PAP-1 (40 mg/kg) was injected intraperitoneally into ovalbumin (OVA)-lipopolysaccharide (LPS)-challenged BALB/c mice. We found that the expression of the Kv1.3 channel in the lung tissues, and the intensity of the Kv current in the asthmatic mice increased clearly compared with those in normal control. PAP-1 significantly reduced airway hyperresponsiveness (AHR), inflammatory cell count in the bronchoalveolar lavage fluids (BALF) and serum, and attenuated airway inflammation in a histological examination of the asthmatic mice. Moreover, PAP-1 inhibited the OVA-LPS-induced imbalance of Th1/Th2, Treg/Th17 lymphocytes, and reduced levels of IL-4 and IL-17, inducing an increase in the production of IFN-γ and IL-10. Furthermore, the activation of the extracellular signal-regulated kinase (ERK)/nuclear factor-κB (NF-κB) pathway in the lungs of the asthmatic mice was suppressed by PAP-1. We also found that PD-98059, an inhibitor of ERK, had a similar effect with PAP-1 in terms of regulating the imbalance of Th1/Th2, Treg/Th17 cytokines. However, PD-98059 could not further influence cytokine changes when the cells were treated with PAP-1. The results suggest that ERK acts as a downstream regulator of inhibitors of the Kv1.3 channel in neutrophilic asthma. In conclusion, the inhibitor of the Kv1.3 channel has therapeutic potential for treating asthma.

Human T cells in silico: Modelling dynamic intracellular calcium and its influence on cellular electrophysiology

A network of ion currents influences basic cellular T cell functions. After T cell receptor activation, changes in highly regulated calcium levels play a central role in triggering effector functions and cell differentiation. A dysregulation of these processes might be involved in the pathogenesis of several diseases. We present a mathematical model based on the NEURON simulation environment that computes dynamic calcium levels in combination with the current output of diverse ion channels (K_V1.3, K_Ca3.1, K_2P channels (TASK1-3, TRESK), VRAC, TRPM7, CRAC). In line with experimental data, the simulation shows a strong increase in intracellular calcium after T cell receptor stimulation before reaching a new, elevated calcium plateau in the T cell's activated state. Deactivation of single ion channel modules, mimicking the application of channel blockers, reveals that two types of potassium channels are the main regulators of intracellular calcium level: calcium-dependent potassium (K_Ca3.1) and two-pore-domain potassium (K_2P) channels.

The effects of Kv1.3 and IKCa1 channel inhibition on cytokine production and calcium influx of T lymphocytes in rheumatoid arthritis and ankylosing spondylitis

Kv1.3 and IKCa1 lymphocyte potassium channels have been implicated as important targets of selective immunomodulation. We compared the alterations in cytokine production upon selective inhibition of Kv1.3 or IKCa1 channels (by MGTX and TRAM, respectively) in healthy donors (HD), RA and AS patients. We also determined calcium influx kinetics and its sensitivity to Kv1.3 and IKCa1 channel inhibition following PHA activation in CD4, Th1, Th2 and CD8 cells as well as monocytes. The application of TRAM resulted in a lower production of TNF-a and IL1-RA in all three study groups. Inhibition by TRAM had contrary effects on the production of IL-1b and IL-5: While their production was increased by PBMCs of RA patients, this effect was not observed in HD and AS PBMCs. While treatment with MGTX resulted in a similar decrease in calcium influx in the CD4 and Th2 subsets across all study groups, TRAM treatment had opposite effects on RA and HD samples: It decreased calcium influx in the Th2 and CD8 subsets in RA, while only Th1 cells were affected in HDs. The effects of IKCa1 channel inhibition are controversial in samples of RA and AS patients, since it shifts the inflammatory balance into the pro-inflammatory direction.

Margatoxin-bound quantum dots as a novel inhibitor of the voltage-gated ion channel Kv1.3

Venom-derived ion channel inhibitors have strong channel selectivity, potency, and stability; however, tracking delivery to their target can be challenging. Herein, we utilized luminescent quantum dots (QDs) conjugated to margatoxin (MgTx) as a traceable vehicle to target a voltage-dependent potassium channel, Kv1.3, which has a select distribution and well-characterized role in immunity, glucose metabolism, and sensory ability. We screened both unconjugated (MgTx) and conjugated MgTx (QD-MgTx) for their ability to inhibit Shaker channels Kv1.1 to Kv1.7 using patch-clamp electrophysiology in HEK293 cells. Our data indicate that MgTx inhibits 79% of the outward current in Kv1.3-transfected cells and that the QD-MgTx conjugate is able to achieve a similar level of block, albeit a slightly reduced efficacy (66%) and at a slower time course (50% block by 10.9 ± 1.1 min, MgTx; vs. 15.3 ± 1.2 min, QD-MgTx). Like the unbound peptide, the QD-MgTx conjugate inhibits both Kv1.3 and Kv1.2 at a 1 nM concentration, whereas it does not inhibit other screened Shaker channels. We tested the ability of QD-MgTx to inhibit native Kv1.3 expressed in the mouse olfactory bulb (OB). In brain slices of the OB, the conjugate acted similarly to MgTx to inhibit Kv1.3, causing an increased action potential firing frequency attributed to decreased intraburst duration rather than interspike interval. Our data demonstrate a retention of known biophysical properties associated with block of the vestibule of Kv1.3 by QD-MgTx conjugate compared to that of MgTx, inferring QDs could provide a useful tool to deliver ion channel inhibitors to targeted tissues in vivo.

Lack of effect of Z-butylidenephthalide on presynaptic N-type Ca²⁺ channels in isolated guinea-pig ileum

Z-Butylidenephthalide (Bdph) was reported to more potently inhibit electrically induced twitch responses than acetylcholine-induced tonic contraction in isolated guinea-pig ileum (GPI). The aim of the present study was to investigate the inhibitory effects of Z-Bdph on Ca2+ and K+ channels on GPI. In Locke-Ringer’s solution, both responses were isometrically recorded on a polygraph. Incubation of ω-conotoxin MVIIC, but not Z-Bdph, in the electrically stimulated GPI prior to adding ω-conotoxin GVIA, an irreversible blocker of N-type voltage-dependent Ca2+ channels (VDCCs), protected the binding sites and resulted in the twitch responses reversible by washing, suggesting that Z-Bdph did not bind to the N-type VDCCs. Interestingly, we found Z-Bdph concentration dependently delayed the onsets of K+-induced twitch responses, suggesting that Z-Bdph may be a blocker of K+ channels to interfere extracellular K+ across through the pre-junctional membrane of nerve ending in K+-free medium. Z-Bdph similar to nifedipine non-competitively inhibited cumulative ACh-induced phasic contractions, suggesting that Z-Bdph may bind to L-type of inositol-1,4,5-trisphosphate (IP3)-sensitive Ca2+ channels on the endoplasmic reticulum (ER) membrane. In the presence of verapamil, a L-type Ca2+ channel blocker or Z-Bdph, the twitch inhibitions by either were effectively reversed by exogenous Ca2+, suggesting that they may freely pass through pre-junctional N-type, but not L-type which was blocked at least a part by either, of VDDCs open when each electrical coaxial stimulation (ECS) into intracellular space of cholinergic nerve terminal and trigger release of transmitters. In conclusion, results confirm that Z-Bdph more potently inhibits ECS-induced twitch responses than ACh-induced PCs in GPI and suggest that this effect is not mediated by interaction with presynaptic N-type VDCCs.

Human T cells in silico: Modelling their electrophysiological behaviour in health and disease

Although various types of ion channels are known to have an impact on human T cell effector functions, their exact mechanisms of influence are still poorly understood. The patch clamp technique is a well-established method for the investigation of ion channels in neurons and T cells. However, small cell sizes and limited selectivity of pharmacological blockers restrict the value of this experimental approach. Building a realistic T cell computer model therefore can help to overcome these kinds of limitations as well as reduce the overall experimental effort. The computer model introduced here was fed off ion channel parameters from literature and new experimental data. It is capable of simulating the electrophysiological behaviour of resting and activated human CD4(+) T cells under basal conditions and during extracellular acidification. The latter allows for the very first time to assess the electrophysiological consequences of tissue acidosis accompanying most forms of inflammation.

Understanding autoimmunity: The ion channel perspective

Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions. Malfunction of these channels results in debilitating diseases collectively termed channelopathies. In this review, we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarizes the ion channels that could be used as molecular targets in the development of new therapeutics against autoimmune disorders.

Usefulness of targeting lymphocyte Kv1.3-channels in the treatment of respiratory diseases

T lymphocytes predominantly express delayed rectifier K(+)-channels (Kv1.3) in their plasma membranes. Patch-clamp studies revealed that the channels play crucial roles in facilitating the calcium influx necessary to trigger lymphocyte activation and proliferation. Using selective channel inhibitors in experimental animal models, in vivo studies further revealed the clinically relevant relationship between the channel expression and the development of chronic respiratory diseases, in which chronic inflammation or the overstimulation of cellular immunity in the airways is responsible for the pathogenesis. In chronic respiratory diseases, such as chronic obstructive pulmonary disease, asthma, diffuse panbronchiolitis and cystic fibrosis, in addition to the supportive management for the symptoms, the anti-inflammatory effects of macrolide antibiotics were shown to be effective against the over-activation or proliferation of T lymphocytes. Recently, we provided physiological and pharmacological evidence that macrolide antibiotics, together with calcium channel blockers, HMG-CoA reductase inhibitors, and nonsteroidal anti-inflammatory drugs, effectively suppress the Kv1.3-channel currents in lymphocytes, and thus exert anti-inflammatory or immunomodulatory effects. In this review article, based on the findings obtained from recent in vivo and in vitro studies, we address the novel therapeutic implications of targeting the lymphocyte Kv1.3-channels for the treatment of chronic or acute respiratory diseases.

Toxins Targeting the Kv1.3 Channel: Potential Immunomodulators for Autoimmune Diseases

Autoimmune diseases are usually accompanied by tissue injury caused by autoantigen-specific T-cells. K_V1.3 channels participate in modulating calcium signaling to induce T-cell proliferation, immune activation and cytokine production. Effector memory T (T_EM)-cells, which play major roles in many autoimmune diseases, are controlled by blocking K_V1.3 channels on the membrane. Toxins derived from animal venoms have been found to selectively target a variety of ion channels, including K_V1.3. By blocking the K_V1.3 channel, these toxins are able to suppress the activation and proliferation of T_EM cells and may improve T_EM cell-mediated autoimmune diseases, such as multiple sclerosis and type I diabetes mellitus.

Roles of lymphocyte kv1.3-channels in the pathogenesis of renal diseases and novel therapeutic implications of targeting the channels

Delayed rectifier K⁺-channels (Kv1.3) are predominantly expressed in T lymphocytes. Based on patch-clamp studies, the channels play crucial roles in facilitating the calcium influx necessary to trigger lymphocyte activation and proliferation. Using selective channel inhibitors in experimental animal models, in vivo studies then revealed the clinically relevant relationship between the channel expression and the pathogenesis of autoimmune diseases. In renal diseases, in which “chronic inflammation” or “the overstimulation of cellular immunity” is responsible for the pathogenesis, the overexpression of Kv1.3-channels in lymphocytes promotes their cellular proliferation and thus contributes to the progression of tubulointerstitial fibrosis. We recently demonstrated that benidipine, a potent dihydropyridine calcium channel blocker, which also strongly and persistently inhibits the lymphocyte Kv1.3-channel currents, suppressed the proliferation of kidney lymphocytes and actually ameliorated the progression of renal fibrosis. Based on the recent in vitro evidence that revealed the pharmacological properties of the channels, the most recent studies have revealed novel therapeutic implications of targeting the lymphocyte Kv1.3-channels for the treatment of renal diseases.

Physiological significance of delayed rectifier K(+) channels (Kv1.3) expressed in T lymphocytes and their pathological significance in chronic kidney disease

T lymphocytes predominantly express delayed rectifier K(+) channels (Kv1.3) in their plasma membranes. More than 30 years ago, patch-clamp studies revealed that the channels play crucial roles in facilitating the calcium influx necessary to trigger lymphocyte activation and proliferation. In addition to selective channel inhibitors that have been developed, we recently showed physiological evidence that drugs such as nonsteroidal anti-inflammatory drugs, antibiotics, and anti-hypertensives effectively suppress the channel currents in lymphocytes, and thus exert immunosuppressive effects. Using experimental animal models, previous studies revealed the pathological relevance between the expression of ion channels and the progression of renal diseases. As an extension, we recently demonstrated that the overexpression of lymphocyte Kv1.3 channels contributed to the progression of chronic kidney disease (CKD) by promoting cellular proliferation and interstitial fibrosis. Together with our in-vitro results, the studies indicated the therapeutic potency of Kv1.3-channel inhibitors in the treatment or the prevention of CKD.

Regulation of the voltage gated K channel Kv1.3 by recombinant human klotho protein

BACKGROUND/AIMS

Klotho, a protein mainly produced in the kidney and released into circulating blood, contributes to the negative regulation of 1,25(OH)2D3 formation and is thus a powerful regulator of mineral metabolism. As β-glucuronidase, alpha Klotho protein further regulates the stability of several carriers and channels in the plasma membrane and thus regulates channel and transporter activity. Accordingly, alpha Klotho protein participates in the regulation of diverse functions seemingly unrelated to mineral metabolism including lymphocyte function. The present study explored the impact of alpha Klotho protein on the voltage gated K+ channel Kv1.3.

METHODS

cRNA encoding Kv1.3 (KCNA3) was injected into Xenopus oocytes and depolarization induced outward current in Kv1.3 expressing Xenopus oocytes determined utilizing dual electrode voltage clamp. Experiments were performed without or with prior treatment with recombinant human Klotho protein (50 ng/ml, 24 hours) in the absence or presence of a β-glucuronidase inhibitor D-saccharic acid-1,4-lactone (DSAL, 10 µM). Moreover, the voltage gated K+ current was determined in Jcam lymphoma cells by whole cell patch clamp following 24 hours incubation without or with recombinant human Klotho protein (50 ng/ml, 24 hours). Kv1.3 protein abundance in Jcam cells was determined utilising fluorescent antibodies in flow cytometry.

RESULTS

In Kv1.3 expressing Xenopus oocytes the Kv1.3 currents and the protein abundance of Kv1.3 were both significantly enhanced after treatment with recombinant human Klotho protein (50 ng/ml, 24 hours), an effect reversed by presence of DSAL. Moreover, treatment with recombinant human Klotho protein increased Kv currents and Kv1.3 protein abundance in Jcam cells.

CONCLUSION

Alpha Klotho protein enhances Kv1.3 channel abundance and Kv1.3 currents in the plasma membrane, an effect depending on its β-glucuronidase activity.

Margatoxin is a non-selective inhibitor of human Kv1.3 K+ channels

Margatoxin (MgTx), an alpha-KTx scorpion toxin, is considered a selective inhibitor of the Kv1.3K + channel. This peptide is widely used in ion channel research; however, a comprehensive study of its selectivity with electrophysiological methods has not been published yet. The lack of selectivity might lead to undesired side effects upon therapeutic application or may lead to incorrect conclusion regarding the role of a particular ion channel in a physiological or pathophysiological response either in vitro or in vivo. Using the patch-clamp technique we characterized the selectivity profile of MgTx using L929 cells expressing mKv1.1 channels, human peripheral lymphocytes expressing Kv1.3 channels and transiently transfected tsA201 cells expressing hKv1.1, hKv1.2, hKv1.3, hKv1.4-IR, hKv1.5, hKv1.6, hKv1.7, rKv2.1, Shaker-IR, hERG, hKCa1.1, hKCa3.1 and hNav1.5 channels. MgTx is indeed a high affinity inhibitor of Kv1.3 (Kd = 11.7 pM) but is not selective, it inhibits the Kv1.2 channel with similar affinity (Kd = 6.4 pM) and Kv1.1 in the nanomolar range (Kd = 4.2 nM). Based on our comprehensive data MgTX has to be considered a non-selective Kv1.3 inhibitor, and thus, experiments aiming at elucidating the significance of Kv1.3 in in vitro or in vivo physiological responses have to be carefully evaluated.

Physiological role of Kv1.3 channel in T lymphocyte cell investigated quantitatively by kinetic modeling

Kv1.3 channel is a delayed rectifier channel abundant in human T lymphocytes. Chronic inflammatory and autoimmune disorders lead to the over-expression of Kv1.3 in T cells. To quantitatively study the regulatory mechanism and physiological function of Kv1.3 in T cells, it is necessary to have a precise kinetic model of Kv1.3. In this study, we firstly established a kinetic model capable to precisely replicate all the kinetic features for Kv1.3 channels, and then constructed a T-cell model composed of ion channels including Ca²⁺-release activated calcium (CRAC) channel, intermediate K⁺ (IK) channel, TASK channel and Kv1.3 channel for quantitatively simulating the changes in membrane potentials and local Ca²⁺ signaling messengers during activation of T cells. Based on the experimental data from current-clamp recordings, we successfully demonstrated that Kv1.3 dominated the membrane potential of T cells to manipulate the Ca²⁺ influx via CRAC channel. Our results revealed that the deficient expression of Kv1.3 channel would cause the less Ca²⁺ signal, leading to the less efficiency in secretion. This was the first successful attempt to simulate membrane potential in non-excitable cells, which laid a solid basis for quantitatively studying the regulatory mechanism and physiological role of channels in non-excitable cells.

Targeting potassium channels Kv1.3 and KC a 3.1: routes to selective immunomodulators in autoimmune disorder treatment?

The Kv1.3 and KC a 3.1 potassium channels are promising targets for the treatment of autoimmune disorders. Many Kv1.3 and KC a 3.1 blockers have a more favorable adverse event profiles than existing immunosuppressants, suggesting the selectivity of Kv1.3 and KC a 3.1 blockade. The Kv1.3 and KC a 3.1 blockers exert differential effects in different autoimmune diseases. The Kv1.3 inhibitors or gene deletion have been shown to have benefits in multiple sclerosis, type 1 diabetes, rheumatoid arthritis, psoriasis, and rapidly progressive glomerulonephritis. The KC a 3.1 blockers have demonstrated efficacy in human primary biliary cirrhosis and showed protective effects in animal models of severe colitis, allergic encephalomyelitis, inflammatory bowel disease, and multiple sclerosis. The KC a 3.1 blockers are not considered candidates for treatment of multiple sclerosis. The selective immunosuppressive effects of the Kv1.3 and KC a 3.1 blockers are due to the differences in their distribution on autoimmune-related immune cells and tissues and β1 integrin (very late activating antigen)-Kv1.3 channel cross-talk.