Pharmacological blockade of KV1.3 channel as a promising treatment in autoimmune diseases

Insight into a multifunctional potassium channel Kv1.3 and its novel implication in chronic kidney disease

Chronic kidney disease (CKD), a global public health problem, causes substantial morbidity and mortality worldwide. Innovative therapeutic strategies to mitigate the progression of CKD are needed due to the limitations of existing treatments. Kv1.3, a voltage-gated potassium ion channel, plays a crucial role in multiple biological processes, including cell proliferation, apoptosis, energy homeostasis, and migration. Inhibition of the Kv1.3 channels has shown beneficial effects in the therapy of a wide range of human diseases such as cancer, autoimmune and neuroinflammatory diseases. Increasing evidence reveals a close link between Kv1.3 and CKD. This review summarises the most recent insights into the physiological functions of the Kv1.3 channel and its pharmacological modulators. Furthermore, the therapeutic potential of targeting Kv1.3 for CKD is also discussed. Collectively, these studies suggested that Kv1.3 channels may serve as a novel target for CKD therapy.

Processed Buthus martensii Karsch scorpions ameliorate diet-induced NASH in mice by attenuating Kv1.3-mediated macrophage activation

ETHNOPHARMACOLOGICAL RELEVANCE

Processed Buthus martensii Karsch (BmK) scorpion, also known as Quan-Xie, is a traditional Chinese medicine that is clinically used for the treatment of NAFLD due to its Tong-Luo-San-Jie effects. Our previous study showed that aqueous extract of processed BmK scorpion venom gland (pVg AE) inhibited macrophage inflammation by targeting Kv1.3 and identified the thermostable peptide BmKK2 as a potent Kv1.3 blocker.

AIM OF THE STUDY

This study examined the therapeutic effects of processed BmK scorpions on NASH, specifically focusing on the involvement of their anti-inflammatory effects mediated by macrophage-expressed Kv1.3 in NASH.

MATERIALS AND METHODS

In the present study, the anti-NASH effects of pVg AE were evaluated in high-fat diet (HFD)-induced NASH mouse models. Additionally, the in vitro anti-inflammatory mechanisms of pVg AE and BmKK2 were assessed using a palmitic acid (PA)-induced mouse bone marrow-derived macrophages (BMDMs) inflammation model. Protein and cytokine expression related to the Kv1.3-NF-κB pathway was analyzed by real-time PCR, immunoblotting and ELISA. The effect of pVg AE and BmKK2 on potassium channels was detected by whole-cell voltage-clamp recordings on transfected HEK293T cells or mouse BMDMs. Calcium ion imaging was used to evaluate intracellular calcium signaling. Furthermore, the study utilized Kv1.3 siRNA and a BMDMs and hepatocytes co-culture model to investigate the specific role of Kv1.3 in mediating the anti-NASH effects of pVg AE and BmKK2.

RESULTS

Lipid accumulation upregulated Kv1.3 expression in macrophages in vivo and in vitro. However, pVg AE significantly reduced Kv1.3 expression and Kv1.3-positive macrophage infiltration. Treatment with pVg AE improved obesity, insulin resistance (IR), hepatic steatosis (HS), inflammation, and fibrosis in HFD-fed mice. Mechanistically, pVg AE and BmKK2 inhibited macrophage inflammation by targeting Kv1.3, which reduced PA-induced intracellular Ca2+ levels, resulting in the inhibition of the NF-κB pathway and TNFα release.

CONCLUSIONS

This study demonstrates that Kv1.3-mediated macrophage inflammation is involved in the pathogenesis and treatment of NASH. pVg AE effectively alleviates metabolic stress-induced NASH by inhibiting this inflammation.

Identification of novel Kv1.3 channel-interacting proteins using proximity labelling in T-cells

Potassium channels regulate membrane potential, calcium flux, cellular activation and effector functions of adaptive and innate immune cells. The voltage-activated Kv1.3 channel is an important regulator of T cell-mediated autoimmunity and microglia-mediated neuroinflammation. Kv1.3 channels, via protein-protein interactions, are localized with key immune proteins and pathways, enabling functional coupling between K+ efflux and immune mechanisms. To gain insights into proteins and pathways that interact with Kv1.3 channels, we applied a proximity-labeling proteomics approach to characterize protein interactors of the Kv1.3 channel in activated T-cells. Biotin ligase TurboID was fused to either N or C termini of Kv1.3, stably expressed in Jurkat T cells and biotinylated proteins in proximity to Kv1.3 were enriched and quantified by mass spectrometry. We identified over 1,800 Kv1.3 interactors including known interactors (beta-integrins, Stat1) although majority were novel. We found that the N-terminus of Kv1.3 preferentially interacts with protein synthesis and protein trafficking machinery, while the C-terminus interacts with immune signaling and cell junction proteins. T-cell Kv1.3 interactors included 335 cell surface, T-cell receptor complex, mitochondrial, calcium and cytokine-mediated signaling pathway and lymphocyte migration proteins. 178 Kv1.3 interactors in T-cells also represent genetic risk factors of T cell-mediated autoimmunity, including STIM1, which was further validated using co-immunoprecipitation. Our studies reveal novel proteins and molecular pathways that interact with Kv1.3 channels in adaptive (T-cell) and innate immune (microglia), providing a foundation for how Kv1.3 channels may regulate immune mechanisms in autoimmune and neurological diseases.

Staphylococcal superantigens evoke temporary and reversible T cell anergy, but fail to block the development of a bacterium specific cellular immune response

Superantigens (sAgs) are bacterial virulence factors that induce a state of immune hyperactivation by forming a bridge between certain subsets of T cell receptor (TCR) β chains on T lymphocytes, and class II major histocompatibility complex (MHC-II) molecules; this cross-linking leads to indiscriminate T cell activation, cytokine storm and toxic shock. Here we show that sAg exposure drives the preferential expansion of naive and central memory T cell subsets, but not effector or resident memory T cells, which instead, hyper release pro-inflammatory cytokines. A targeted therapeutic approach to minimise cytokine release by effector memory T cells attenuated sAg-induced cytokine release. Irrespective of antigen experience, sAg activation does not render mature T cells permanently dysfunctional, and full restoration of effector function is observed following a transient and reversible anergy. Moreover, we show that in the face of sAg induced immune hyperactivation, an intact bacterium-specific CD4+ T cell response can be mounted.

Application of a modified multifunctional short peptide in the treatment of periodontitis

Periodontitis is a chronic inflammatory disease involving plaque biofilm as a pathogenic factor. Potassium ion plays an important role in cellular homeostasis; a large outflow of potassium may lead to local inflammation progression. In this work, the multifunctional short peptide molecule BmKTX-33 was designed by modifying the BmKTX, a Kv1.3 potassium channel inhibitor. This was to explore its antibacterial properties, capability of maintaining cell ion homeostasis, and bone-forming capacity. The results showed that BmKTX-33 had inhibitory effects on S. gordonii, F. nucleatum, and P. gingivalis. Moreover, BmKTX-33 also inhibited excessive potassium outflow in inflammatory environments. Finally, BmKTX-33 promoted MC3T3-E1 early osteogenesis while suppressing the NLRP3 inflammasome's production. In conclusion, BmKTX-33 not only has antibacterial properties, but also can inhibit the expression of NLRP3 inflammasome and play an anti-inflammatory role.

Interactions of the Kv1.1 Channel with Peptide Pore Blockers: A Fluorescent Analysis on Mammalian Cells

The voltage-gated potassium channel Kv1.1, which is abundant in the CNS and peripheral nervous system, controls neuronal excitability and neuromuscular transmission and mediates a number of physiological functions in non-excitable cells. The development of some diseases is accompanied by changes in the expression level and/or activity of the channels in particular types of cells. To meet the requirements of studies related to the expression and localization of the Kv1.1 channels, we report on the subnanomolar affinity of hongotoxin 1 N-terminally labeled with Atto 488 fluorophore (A-HgTx) for the Kv1.1 channel and its applicability for fluorescent imaging of the channel in living cells. Taking into consideration the pharmacological potential of the Kv1.1 channel, a fluorescence-based analytical system was developed for the study of peptide ligands that block the ion conductivity of Kv1.1 and are potentially able to correct abnormal activity of the channel. The system is based on analysis of the competitive binding of the studied compounds and A-HgTx to the mKate2-tagged human Kv1.1 (S369T) channel, expressed in the plasma membrane of Neuro2a cells. The system was validated by measuring the affinities of the known Kv1.1-channel peptide blockers, such as agitoxin 2, kaliotoxin 1, hongotoxin 1, and margatoxin. Peptide pore blocker Ce1, from the venom of the scorpion Centruroides elegans, was shown to possess a nanomolar affinity for the Kv1.1 channel. It is reported that interactions of the Kv1.1 channel with the studied peptide blockers are not affected by the transition of the channel from the closed to open state. The conclusion is made that the structural rearrangements accompanying the channel transition into the open state do not change the conformation of the P-loop (including the selectivity filter) involved in the formation of the binding site of the peptide pore blockers.

AgTx2-GFP, Fluorescent Blocker Targeting Pharmacologically Important Kv1.x (x = 1, 3, 6) Channels

The growing interest in potassium channels as pharmacological targets has stimulated the development of their fluorescent ligands (including genetically encoded peptide toxins fused with fluorescent proteins) for analytical and imaging applications. We report on the properties of agitoxin 2 C-terminally fused with enhanced GFP (AgTx2-GFP) as one of the most active genetically encoded fluorescent ligands of potassium voltage-gated K_v1.x (x = 1, 3, 6) channels. AgTx2-GFP possesses subnanomolar affinities for hybrid KcsA-K_v1.x (x = 3, 6) channels and a low nanomolar affinity to KcsA-K_v1.1 with moderate dependence on pH in the 7.0-8.0 range. Electrophysiological studies on oocytes showed a pore-blocking activity of AgTx2-GFP at low nanomolar concentrations for K_v1.x (x = 1, 3, 6) channels and at micromolar concentrations for K_v1.2. AgTx2-GFP bound to K_v1.3 at the membranes of mammalian cells with a dissociation constant of 3.4 ± 0.8 nM, providing fluorescent imaging of the channel membranous distribution, and this binding depended weakly on the channel state (open or closed). AgTx2-GFP can be used in combination with hybrid KcsA-K_v1.x (x = 1, 3, 6) channels on the membranes of E. coli spheroplasts or with K_v1.3 channels on the membranes of mammalian cells for the search and study of nonlabeled peptide pore blockers, including measurement of their affinity.

Current Status of Peptide Medications and the Position of Active Therapeutic Peptides with Scorpion Venom Origin

: Peptides are highly potent, selective, and relatively safe therapeutics. Over the past two decades, natural peptides have been obtained, studied, and eventually approved by the Food and Drug Administration (FDA) due to advancements in identification, production, modification, and analytical technologies. Some peptide therapeutics has been derived from the venom gland of venomous animals, including snake, leech, lizard, snail, and scorpion. Scorpion was identified as a reservoir of important peptides with pharmaceutical properties. The scorpion uses these peptides for capturing prey and defense. However, their pharmacological properties in treating different diseases, including cardiac problems, autoimmune and infectious diseases, and diverse cancers, have been confirmed. Ion channel modifiers are the greatest components of the scorpion venom glands. Due to advances in proteomic and transcriptomic approaches, the identification of new scorpion venom peptides is steadily increasing. In this review, we tried to represent the current status of peptide medicines and describe the last peptide medications approved by FDA in 2022. Moreover, we will further explain potent peptides originating from scorpion venom, which have gone through important steps to be approved.

Kv1.3 K+ Channel Physiology Assessed by Genetic and Pharmacological Modulation

Potassium channels are widespread over all kingdoms and play an important role in the maintenance of cellular ionic homeostasis. Kv1.3 is a voltage-gated potassium channel of the Shaker family with a wide tissue expression and a well-defined pharmacology. In recent decades, experiments mainly based on pharmacological modulation of Kv1.3 have highlighted its crucial contribution to different fundamental processes such as regulation of proliferation, apoptosis, and metabolism. These findings link channel function to various pathologies ranging from autoimmune diseases to obesity and cancer. In the present review, we briefly summarize studies employing Kv1.3 knockout animal models to confirm such roles and discuss the findings in comparison to the results obtained by pharmacological modulation of Kv1.3 in various pathophysiological settings. We also underline how these studies contributed to our understanding of channel function in vivo and propose possible future directions.

Combining mKate2-Kv1.3 Channel and Atto488-Hongotoxin for the Studies of Peptide Pore Blockers on Living Eukaryotic Cells

The voltage-gated potassium Kv1.3 channel is an essential component of vital cellular processes which is also involved in the pathogenesis of some autoimmune, neuroinflammatory and oncological diseases. Pore blockers of the Kv1.3 channel are considered as potential drugs and are used to study Kv1 channels' structure and functions. Screening and study of the blockers require the assessment of their ability to bind the channel. Expanding the variety of methods used for this, we report on the development of the fluorescent competitive binding assay for measuring affinities of pore blockers to Kv1.3 at the membrane of mammalian cells. The assay constituents are hongotoxin 1 conjugated with Atto488, fluorescent mKate2-tagged Kv1.3 channel, which was designed to improve membrane expression of the channel in mammalian cells, confocal microscopy, and a special protocol of image processing. The assay is implemented in the "mix and measure", format and allows the screening of Kv1.3 blockers, such as peptide toxins, that bind to the extracellular vestibule of the K⁺-conducting pore, and analyzing their affinity.

Atto488-Agitoxin 2—A Fluorescent Ligand with Increased Selectivity for Kv1.3 Channel Binding Site

Fluorescently labeled peptide blockers of ion channels are useful probes in studying the localization and functioning of the channels and in the performance of a search for new channel ligands with bioengineering screening systems. Here, we report on the properties of Atto488-agitoxin 2 (A-AgTx2), a derivative of the Kv1 channel blocker agitoxin 2 (AgTx2), which was N-terminally labeled with Atto 488 fluorophore. The interactions of A-AgTx2 with the outer binding sites of the potassium voltage-gated Kv1.x (x = 1, 3, 6) channels were studied using bioengineered hybrid KcsA–Kv1.x (x = 1, 3, 6) channels. In contrast to AgTx2, A-AgTx2 was shown to lose affinity for the Kv1.1 and Kv1.6 binding sites but to preserve it for the Kv1.3 site. Thus, Atto488 introduces two new functionalities to AgTx2: fluorescence and the selective targeting of the Kv1.3 channel, which is known for its pharmacological significance. In the case of A-AgTx2, fluorescent labeling served as an alternative to site-directed mutagenesis in modulating the pharmacological profile of the channel blocker. Although the affinity of A-AgTx2 for the Kv1.3 binding site was decreased as compared to the unlabeled AgTx2, its dissociation constant value was within a low nanomolar range (4.0 nM). The properties of A-AgTx2 allow one to use it for the search and study of Kv1.3 channel blockers as well as to consider it for the imaging of the Kv1.3 channel in cells and tissues.

Biological Effects of Animal Venoms on the Human Immune System

Venoms are products of specialized glands and serve many living organisms to immobilize and kill prey, start digestive processes and act as a defense mechanism. Venoms affect different cells, cellular structures and tissues, such as skin, nervous, hematological, digestive, excretory and immune systems, as well as the heart, among other structures. Components of both the innate and adaptive immune systems can be stimulated or suppressed. Studying the effects on the cells and molecules produced by the immune system has been useful in many biomedical fields. The effects of venoms can be the basis for research and development of therapeutic protocols useful in the modulation of the immunological system, including different autoimmune diseases. This review focuses on the understanding of biological effects of diverse venom on the human immune system and how some of their components can be useful for the study and development of immunomodulatory drugs.