Voltage-gated potassium channels and the diversity of electrical signalling

Structural insights into the function, dysfunction and modulation of Kv3 channels

The third subfamily of voltage-gated K+ (Kv) channels includes four members, Kv3.1, Kv3.2, Kv3.3 and Kv3.4. Fast gating and activation at relatively depolarized membrane potentials allows Kv3 channels to be major drivers of fast action potential repolarization in the nervous system. Consequently, they help determine the fast-spiking phenotype of inhibitory interneurons and regulate fast synaptic transmission at glutamatergic synapses and the neuromuscular junction. Recent studies from our group and a team of collaborators have used cryo-EM to demonstrate the surprising gating role of the Kv3.1 cytoplasmic T1 domain, the structural basis of a developmental epileptic encephalopathy caused by the Kv3.2-C125Y variant and the mechanism of action of positive allosteric modulators involving unexpected interactions and conformational changes in Kv3.1 and Kv3.2. Furthermore, our recent work has shown that Kv3.4 regulates use-dependent spike broadening in a manner that depends on gating modulation by phosphorylation of the channel's N-terminal inactivation domain, which can impact activity-dependent synaptic facilitation. Here, we review and integrate these studies to provide a perspective on our current understanding of Kv3 channel function, dysfunction and pain modulation in the nervous system.

The underlying neurobiological basis of gray matter volume alterations in schizophrenia with auditory verbal hallucinations: A meta-analytic investigation

Schizophrenia patients with auditory verbal hallucinations (AVH) frequently exhibit brain structural alterations, particularly reductions in gray matter volume (GMV).Understanding the neurobiological mechanisms underlying the changes is essential for advancing treatment strategies. To address this, a meta-analysis was conducted to identify GMV changes in schizophrenia patients with AVH and their associations with gene expression and neurotransmitter receptor profiles. The results indicated significant GMV reductions in the left and the right insula, as well as the left anterior cingulate cortex. Ontology analysis of genes associated with GMV alternations revealed enrichment in biological processes related to ion transport and synaptic transmission. Hub genes from the KCN, SCN, GN, and PRK families, along with neurotransmitter receptors such as D2, VAChT, and mGluR5, showed significant correlations with GMV changes. Furthermore, multivariate linear regression analysis demonstrated that GNB2, GNB4, PRKCG, D2, and mGluR5 significantly predicted GMV alternations. These findings suggest that GMV reductions in schizophrenia with AVH are linked to disruptions in neurobiological processes involving specific genes and neurotransmitter systems, highlighting the potential targets for therapeutic intervention.

Closed State Structure of the Pore Revealed by Uncoupled Shaker K+ Channel

Voltage gated potassium (Kv) channels play key roles in numerous physiological processes from cellular excitability to immune response and are among the most important pharmaceutical targets. Despite recent advances in the structural determination of Kv channels, the closed state structure of strictly coupled Kv1 family remains elusive. Here, we captured the closed state structure of the pore in the Shaker potassium by uncoupling the voltage sensor domains from the pore domains. Ionic current, gating current and fluorescence measurements show that a conserved isoleucine residue in the S4-S5 linker region, plays a key role controlling the strength of the electromechanical coupling and the channel activation-deactivation equilibrium. Structural determination of completely uncoupled I384R mutant by single particle cryoEM revealed a fully closed pore in the presence of fully activated but non-relaxed voltage sensors. The putative conformational transitions from a fully open pore domain indicates a "roll and turn" movement along the whole length of the pore-forming S6 helices in sharp contrast to canonical gating models based on limited movements of S6. The rotational and translational movement posits two hydrophobic residues, one at inner cavity and the other at the bundle crossing region, directly at the permeation pathway, limiting the pore radius to less than 0.7Å. Voltage clamp fluorimetry of wild type channel incorporating a fluorescent unnatural amino acid strongly supports the cryoEM structural model. Surprisingly, the selectivity filter was captured in a noncanonical state, unlike the previously described dilated or pinched filter conformations. With the present experiment results, we propose a new gating model for strictly coupled Kv1 channels and the molecular mechanism of interactions among different functional states.

Hypertension increases sympathetic neuron activity by enhancing intraganglionic cholinergic collateral connections

Autonomic dysregulation, including sympathetic hyperactivity, is a common feature of hypertension (HT) and other cardiovascular diseases. The CNS plays a role in driving chronic sympathetic activation in disease, but several lines of evidence suggest that neuroplasticity in the periphery may also contribute. The potential contribution of postganglionic sympathetic neurons to sustained sympathetic hyperactivity is not well understood. We recently discovered that noradrenergic sympathetic neurons in the stellate ganglion (SG) have excitatory cholinergic collateral connections to other neurons within the ganglion. We hypothesize that remodelling of these neurons and increased cholinergic collateral transmission contributes to sustained sympathetic hyperactivity in cardiovascular diseases, including HT. To test that hypothesis, we examined the activity of sympathetic neurons in isolated SG under control conditions and after 1 week of HT induced by peripheral angiotensin II infusion, using whole-cell patch clamp recordings. Despite the absence of central inputs, we observed elevated spontaneous activity and synaptic transmission in sympathetic SG neurons from hypertensive mice that required generation of action potentials. Genetically disrupting cholinergic transmission in noradrenergic neurons decreased basal neuronal activity and prevented angiotensin II-mediated enhancement of activity. Similar changes in activity, driven by increased collateral transmission, were identified in cardiac projecting neurons and neurons projecting to brown adipose tissue. These changes were not driven by altered A-type K+ currents. This suggests that HT stimulates increased activity throughout the intraganglionic network of collateral connections, contributing to the sustained sympathetic hyperactivity characteristic in cardiovascular disease. KEY POINTS: Sympathetic neurons in ganglia isolated from angiotensin II-treated hypertensive mice are more active than neurons from control mice despite the absence of central activation. The enhanced activity is the result of a ganglionic network of cholinergic collaterals, rather than altered intrinsic excitability. Increased neuronal activity was observed in both cardiac neurons and brown adipose tissue-projecting neurons, which are not involved in cardiovascular homeostasis.

Voltage sensors

Widely distributed in all kingdoms of life, voltage sensors in the membrane serve important functions via their movements driven by changes in voltage across the membrane (membrane potential). A voltage sensor domain contains 4 transmembrane segments (S1-S4). The S1-S3 helices form a hydrophobic constriction site (HCS, also known as the gating charge transfer center) that spans roughly one-third of the membrane thickness. Flanked by aqueous vestibules connected to the extracellular solution above the HCS or cytoplasmic solution below the HCS, the HCS forms a gating pore for the S4 segment bearing multiple basic residues. Membrane potential changes cause S4 to move through the HCS in a 310 helical conformation. This S4 translocation generates a gating current as the positively charged S4 basic residues traverse the membrane electric field, transferring these gating charges from one aqueous vestibule to the other. For voltage-gated ion channels with their voltage sensor domains connected to pore domains, the HCS in the voltage sensor domain allows S4 but not ions to go through, while the channel pore formed by the pore domains mediates ion permeation. Voltage sensor mutations could result in ω currents that are conducted through the gating pore of mutant voltage-gated ion channels. These ω currents may cause pathological consequences in patients with periodic paralysis. Besides voltage-gated ion channels, the sperm-specific Na+/H+ exchanger and voltage-sensing phosphatases contain voltage sensors for membrane potential regulation. Notably, voltage-gated proton channels that are important for pH homeostasis are formed solely by the voltage sensor domain, which mediates proton permeation. SIGNIFICANCE STATEMENT: Voltage sensors mediate voltage regulation of ion channels, transporters, and phosphatases. The voltage sensor domain composed of 4 transmembrane segments (S1-S4) focuses the membrane electric field to the hydrophobic constriction site. To mediate voltage regulation, S4 basic residues within a 310 helix move across the hydrophobic constriction site without concurrent ion flow through this gating pore. As a counterexample, voltage-gated proton channels are formed by the voltage sensor to mediate proton permeation. These ingeniously engineered voltage sensors are conserved throughout evolution.

Neural Activity Alterations and Their Association With Neurotransmitter and Genetic Profiles in Schizophrenia: Evidence From Clinical Patients and Unaffected Relatives

BACKGROUND

The pattern of abnormal resting-state brain function has been documented in schizophrenia (SCZ). However, as of yet, it remains unclear whether this pattern is of genetic predisposition or related to the illness itself.

METHODS

A systematical meta-analysis was performed to identify resting-state functional differences in probands and their high-risk first-degree relatives of schizophrenia (FDRs-SCZ) using Seed-based d Mapping software. Subsequently, spatial associations between postmortem gene expression and neurotransmitters distribution data and neural activity alterations were conducted to uncover neural mechanisms underlaying FDRs-SCZ and SCZ from a multidimensional perspective.

RESULTS

A total of 13 studies comprising 503 FDRs-SCZ and 605 healthy controls (HCs) and 129 studies comprising 6506 patients with SCZ and 6982 HCs were included. Compared to HCs, FDRs-SCZ displayed increased spontaneous functional activity in the bilateral anterior cingulate cortex/medial prefrontal cortex (ACC/mPFC); patients with SCZ showed decreased spontaneous functional activity in the bilateral ACC/mPFC, bilateral postcentral gyrus, and right middle temporal gyrus as well as increased spontaneous functional activity in the bilateral striatum. The altered functional activity in FDRs-SCZ and SCZ shared similar spatial associations with genes enriched in potassium ion transmembrane transport, channel activity, and complex. The FDRs-SCZ and SCZ-related brain functional patterns were additionally associated with dopaminergic, serotonergic, and cholinergic neurotransmitter distribution.

CONCLUSIONS

SCZ-related resting-state functional, neuroimaging transcriptomes, and neurotransmitters abnormalities may exist in high-risk unaffected FDRs-SCZ, rather than just in overt SCZ. The study extended the evidence that altered brain function, along with their spatial correlations to genetics and neurotransmitter systems, may associate with genetic vulnerability for SCZ.

Behavioral and genetic markers of susceptibility to escalate fentanyl intake

Background

The "loss of control" over drug consumption, present in opioid use disorder (OUD) and known as escalation of intake, is well-established in preclinical rodent models. However, little is known about how antecedent behavioral characteristics, such as valuation of hedonic reinforcers prior to drug use, may impact the trajectory of fentanyl intake over time. Moreover, it is unclear if distinct escalation phenotypes may be driven by genetic markers predictive of OUD susceptibility.

Methods

Male and female Sprague-Dawley rats (n=63) were trained in a sucrose reinforcement task using a progressive ratio schedule. Individual differences in responsivity to sucrose were hypothesized to predict escalation of fentanyl intake. Rats underwent daily 1-h acquisition sessions for i.v. fentanyl self-administration (2.5 μg/kg; FR1) for 7 days, followed by 21 6-h escalation sessions, then tissue from prefrontal cortex was collected for RNA sequencing and qPCR. Latent growth curve and group-based trajectory modeling were used, respectively, to evaluate the association between sucrose reinforcement and fentanyl self-administration and to identify whether distinct escalation phenotypes can be linked to gene expression patterns.

Results

Sucrose breakpoints were not predictive of fentanyl acquisition nor change during escalation, but did predict fentanyl intake on the first day of extended access to fentanyl. Permutation analyses did not identify associations between behavior and single gene expression when evaluated overall, or between our ascertained phenotypes. However, weighted genome correlation network analysis (WGCNA) and gene set enrichment analysis (GSEA) determined several gene modules linked to escalated fentanyl intake, including genes coding for voltage-gated potassium channels, calcium channels, and genes involved in excitatory synaptic signaling. Transcription factor analyses identified EZH2 and JARID2 as potential transcriptional regulators associated with escalated fentanyl intake. Genome-wide association study (GWAS) term categories were also generated and positively associated with terms relating to substance use disorders.

Discussion

Escalation of opioid intake is largely distinct from motivation for natural reward, such as sucrose. Further, the gene networks associated with fentanyl escalation suggest that engagement of select molecular pathways distinguish individuals with "addiction prone" behavioral endophenotypes, potentially representing druggable targets for opioid use disorder. Our extended in silico identification of SNPs and transcription factors associated with the "addiction prone" high escalating rats highlights the importance of integrating findings from translational preclinical models. Through a precision medicine approach, our results may aid in the development of patient-centered treatment options for those with OUD.

Metal Ion Signaling in Biomedicine

Complex multicellular organisms are composed of distinct tissues involving specialized cells that can perform specific functions, making such life forms possible. Species are defined by their genomes, and differences between individuals within a given species directly result from variations in their genetic codes. While genetic alterations can give rise to disease-causing acquisitions of distinct cell identities, it is now well-established that biochemical imbalances within a cell can also lead to cellular dysfunction and diseases. Specifically, nongenetic chemical events orchestrate cell metabolism and transcriptional programs that govern functional cell identity. Thus, imbalances in cell signaling, which broadly defines the conversion of extracellular signals into intracellular biochemical changes, can also contribute to the acquisition of diseased cell states. Metal ions exhibit unique chemical properties that can be exploited by the cell. For instance, metal ions maintain the ionic balance within the cell, coordinate amino acid residues or nucleobases altering folding and function of biomolecules, or directly catalyze specific chemical reactions. Thus, metals are essential cell signaling effectors in normal physiology and disease. Deciphering metal ion signaling is a challenging endeavor that can illuminate pathways to be targeted for therapeutic intervention. Here, we review key cellular processes where metal ions play essential roles and describe how targeting metal ion signaling pathways has been instrumental to dissecting the biochemistry of the cell and how this has led to the development of effective therapeutic strategies.

Potassium ion channel modulation at cancer-neural interface enhances neuronal excitability in epileptogenic glioblastoma multiforme

The central nervous system (CNS) is increasingly recognized as a critical modulator in the oncogenesis of glioblastoma multiforme (GBM), with interactions between cancer and local neuronal circuits frequently leading to epilepsy; however, the relative contributions of these factors remain unclear. Here, we report a coordinated intratumor shift among distinct cancer subtypes within progenitor-like families of epileptic GBM patients, revealing an accumulation of oligodendrocyte progenitor (OPC)-like subpopulations at the cancer-neuron interface along with heightened electrical signaling activity in the surrounding neuronal networks. The OPC-like cells associated with epilepsy express KCND2, which encodes the voltage-gated K+ channel KV4.2, enhancing neuronal excitability via accumulation of extracellular K+, as demonstrated in patient-derived ex vivo slices, xenografting models, and engineering organoids. Together, we uncovered the essential local circuitry, cellular components, and molecular mechanisms facilitating cancer-neuron interaction at peritumor borders. KCND2 plays a crucial role in mediating nervous system-cancer electrical communication, suggesting potential targets for intervention.

Tools and methods for cell ablation and cell inhibition in Caenorhabditis elegans

To understand the function of cells such as neurons within an organism, it can be instrumental to inhibit cellular function, or to remove the cell (type) from the organism, and thus to observe the consequences on organismic and/or circuit function and animal behavior. A range of approaches and tools were developed and used over the past few decades that act either constitutively or acutely and reversibly, in systemic or local fashion. These approaches make use of either drugs or genetically encoded tools. Also, there are acutely acting inhibitory tools that require an exogenous trigger like light. Here, we give an overview of such methods developed and used in the nematode Caenorhabditis elegans.

Sex-specific differences in mortality and neurocardiac interactions in the Kv1.1 knockout mouse model of sudden unexpected death in epilepsy (SUDEP)

Sudden unexpected death in epilepsy (SUDEP) is a devastating complication of epilepsy with possible sex-specific risk factors, although the exact relationship between sex and SUDEP remains unclear. To investigate this, we studied Kcna1 knockout (Kcna1-/-) mice, which lack voltage-gated Kv1.1 channel subunits and are widely used as a SUDEP model that mirrors key features in humans. To assess sex differences, we first performed survival analysis, EEG-ECG recordings, seizure threshold testing and retrospective analysis of previous intracardiac pacing data. We then applied a novel modelling approach across organs (organomics) to uncover potential sex-specific differences in brain-heart communication. Our findings revealed female Kcna1-/- mice have significantly longer lifespans than males, suggesting lower SUDEP rates. Although no sex differences were found in seizure frequency, duration, burden, susceptibility or interictal heart rate variability, females showed a higher incidence of bradycardia during spontaneous seizures than males, as well as resistance to inducible ventricular tachyarrhythmias in response to programmed electrical stimulation. Two captured SUDEP events, one per sex, displayed similar patterns of ictal bradycardia in both sexes, progressing to postictal cardiorespiratory failure. Going beyond traditional seizure and cardiac metrics, organomics analysis revealed that seizures affect brain-heart communication differently between sexes. Females exhibited more effective resetting of brain-heart interactions postictally than males. This finding may contribute to the lower SUDEP risk in females and underscores the complex interplay between sex, cardiac function and brain-heart communication in determining SUDEP susceptibility. Furthermore, seizure-resetting measures could represent a promising class of biomarkers for SUDEP risk stratification. KEY POINTS: Female Kcna1-/- mice live longer than males, suggesting lower sudden unexpected death in epilepsy (SUDEP) rates. There are no sex differences in seizure metrics or interictal heart rate variability. Females show more bradycardia during seizures and are resistant to inducible ventricular tachyarrhythmias. Seizures affect brain-heart communication differently between the sexes. Seizures in females reset brain-heart interactions more effectively postictally, potentially lowering SUDEP risk.

Competition of two time scales determines the performance of a voltage-gated potassium channel

The dynamics of a voltage-gated potassium channel in real environments represents a crucial bridge between its molecular structure and functions. However, it is still missing due to the mathematical difficulty that arises from the high dimensionality and nonlinear interregulation. Here we present a method for solving the stationary distribution of a hybrid process that contains two negatively interregulating kinetics: channel gating and voltage decay. The results can be summarized as follows: first, the voltage distribution is determined by the competition of their time scales; second, the fluctuation structures in parameter space illustrate that, to perform the voltage-controlling task, the channel gating is elastic while the membrane produces the stabilizing function; third, the power dissipated by the capacitive currents and the internal battery current are calculated and explained. Based on these findings, we examine the manner in which macroscopic functions of potassium channels are manifested. Our methodology provides an accurate characterization of hybrid processes that are pervasive in the life sciences.

Kv3.1 Interaction with UBR5 Is Required for Chronic Inflammatory Pain

Chronic inflammatory pain caused by neuronal hyperactivity is a common and refractory disease. Kv3.1, a member of the Kv3 family of voltage-dependent K+ channels, is a major determinant of the ability of neurons to generate high-frequency action potentials. However, little is known about its role in chronic inflammatory pain. Here, we show that although Kv3.1 mRNA expression was unchanged, Kv3.1 protein expression was decreased in the dorsal spinal horn of mice after plantar injection of complete Freund's adjuvant (CFA), a mouse model of inflammatory pain. Upregulating Kv3.1 expression alleviated CFA-induced mechanical allodynia and heat hyperalgesia, whereas downregulating Kv3.1 induced nociception-like behaviors. Additionally, we found that ubiquitin protein ligase E3 component n-recognin 5 (UBR5), a key factor in the initiation of chronic pain, binds directly to Kv3.1 to drive its ubiquitin degradation. Intrathecal injection of the peptide TP-CH-401, a Kv3.1 ubiquitination motif sequence, rescued the decrease in Kv3.1 expression and Kv currents through competitive binding to UBR5, and consequently attenuated mechanical and thermal hypersensitivity. These findings demonstrate a previously unrecognized pathway of Kv3.1 abrogation by UBR5 and indicate that Kv3.1 is critically involved in the regulation of nociceptive behavior. Kv3.1 is thus a promising new target for treating inflammatory pain.

Conotoxin KM-RIIIJ reveals interplay between Kv1-channels and persistent sodium currents in proprioceptive DRG neurons

Voltage-gated potassium channels (VGKCs) comprise the largest and most complex families of ion channels. Approximately 70 genes encode VGKC alpha subunits, which assemble into functional tetrameric channel complexes. These subunits can also combine to form heteromeric channels, significantly expanding the potential diversity of VGKCs. The functional expression and physiological role of heteromeric K-channels have remained largely unexplored due to the lack of tools to probe their functions. Conotoxins, from predatory cone snails, have high affinity and specificity for heteromeric combinations of K-channels and show great promise for defining their physiological roles. In this work, using conotoxin KM-RIIIJ as a pharmacological probe, we explore the expression and physiological functions of heteromeric Kv1.2 channels using constellation pharmacology platform. We report that heteromers of Kv1.2/1.1 are highly expressed in proprioceptive neurons found in the dorsal root ganglion (DRG). Inhibition of Kv1.2/1.1 heteromers leads to an influx of calcium ions, suggesting that these channels regulate neuronal excitability. We also present evidence that Kv1.2/1.1 heteromers counteract persistent sodium currents, and that inhibiting these channels leads to tonic firing of action potentials. Additionally, KM-RIIIJ impaired proprioception in mice, uncovering a previously unrecognized physiological function of heteromeric Kv1.2/1.1 channels in proprioceptive sensory neurons of the DRG.

Structural biology and molecular pharmacology of voltage-gated ion channels

Voltage-gated ion channels (VGICs), including those for Na+, Ca2+ and K+, selectively permeate ions across the cell membrane in response to changes in membrane potential, thus participating in physiological processes involving electrical signalling, such as neurotransmission, muscle contraction and hormone secretion. Aberrant function or dysregulation of VGICs is associated with a diversity of neurological, psychiatric, cardiovascular and muscular disorders, and approximately 10% of FDA-approved drugs directly target VGICs. Understanding the structure-function relationship of VGICs is crucial for our comprehension of their working mechanisms and role in diseases. In this Review, we discuss how advances in single-particle cryo-electron microscopy have afforded unprecedented structural insights into VGICs, especially on their interactions with clinical and investigational drugs. We present a comprehensive overview of the recent advances in the structural biology of VGICs, with a focus on how prototypical drugs and toxins modulate VGIC activities. We explore how these structures elucidate the molecular basis for drug actions, reveal novel pharmacological sites, and provide critical clues to future drug discovery.

Electrophysiological correlates of divergent projections in the avian superior olivary nucleus

The physiological diversity of inhibitory neurons provides ample opportunity to influence a wide range of computational roles through their varied activity patterns, especially via feedback loops. In the avian auditory brain stem, inhibition originates primarily from the superior olivary nucleus (SON), and so it is critical to understand the intrinsic physiological properties and processing capabilities of these neurons. Neurons in the SON receive ascending input via the cochlear nuclei: directly from the intensity-coding cochlear nucleus angularis (NA) and indirectly via the interaural timing nucleus laminaris (NL), which itself receives input from cochlear nucleus magnocellularis (NM). Two distinct populations of SON neurons provide inhibitory feedback either to ipsilateral NA, NL, and the timing cochlear nucleus NM or to the contralateral SON. To determine whether these populations correspond to distinct response types, we investigated their electrophysiology in brain stem slices, using patch-clamp electrophysiology. We identified three phenotypes: single-spiking, chattering tonic, and regular tonic neurons. The two tonic phenotypes displayed distinct firing patterns and different membrane properties. Fluctuating "noisy" currents used to probe the capability of SON neurons to encode temporal features showed that each phenotype differed in sensitivity to temporally modulated input. By using cell fills and anatomical reconstructions, we could correlate the firing phenotypes with their axonal projection patterns. We found that SON axons exited via three fiber tracts, with each tract composed of specific phenotypes. These results provide a basis for understanding the role of specific inhibitory cell types in auditory function and elucidate the organization of the SON outputs.NEW & NOTEWORTHY Inhibitory inputs for the avian brain stem originate primarily from the superior olivary nucleus (SON). We describe three intrinsic phenotypes of SON neurons and show how they differ in their temporal processing and projection patterns. We propose that the two types of tonic firing neurons (including one novel type) and the single-spiking neurons in SON comprise separate feedback circuits that may differentially influence the auditory information flowing via the cochlear nuclei and nucleus laminaris.

Roles of KCNA2 in Neurological Diseases: from Physiology to Pathology

Potassium voltage-gated channel subfamily a member 2 (Kv1.2, encoded by KCNA2) is highly expressed in the central and peripheral nervous systems. Based on the patch clamp studies, gain-of function (GOF), loss-of-function (LOF), and a mixed type (GOF/LOF) variants can cause different conditions/disorders. KCNA2-related neurological diseases include epilepsy, intellectual disability (ID), attention deficit/hyperactive disorder (ADHD), autism spectrum disorder (ASD), pain as well as autoimmune and movement disorders. Currently, the molecular mechanisms for the reported variants in causing diverse disorders are unknown. Consequently, this review brings up to date the related information regarding the structure and function of Kv1.2 channel, expression patterns, neuronal localizations, and tetramerization as well as important cell and animal models. In addition, it provides updates on human genetic variants, genotype-phenotype correlations especially highlighting the deep insight into clinical prognosis of KCNA2-related developmental and epileptic encephalopathy, mechanisms, and the potential treatment targets for all KCNA2-related neurological disorders.

Voltage-Gated Ion Channel Compensatory Effect in DEE: Implications for Future Therapies

Developmental and Epileptic Encephalopathies (DEEs) represent a clinically and genetically heterogeneous group of rare and severe epilepsies. DEEs commonly begin early in infancy with frequent seizures of various types associated with intellectual disability and leading to a neurodevelopmental delay or regression. Disease-causing genomic variants have been identified in numerous genes and are implicated in over 100 types of DEEs. In this context, genes encoding voltage-gated ion channels (VGCs) play a significant role, and part of the large phenotypic variability observed in DEE patients carrying VGC mutations could be explained by the presence of genetic modifier alleles that can compensate for these mutations. This review will focus on the current knowledge of the compensatory effect of DEE-associated voltage-gated ion channels and their therapeutic implications in DEE. We will enter into detailed considerations regarding the sodium channels SCN1A, SCN2A, and SCN8A; the potassium channels KCNA1, KCNQ2, and KCNT1; and the calcium channels CACNA1A and CACNA1G.

The potential of marine natural products and their synthetic derivatives as drugs targeting ion channels

Ion channels are a type of protein channel that play a vital role in numerous physiological functions by facilitating the passage of ions through cell membranes, thereby enabling ion and electrical signal transmission. As a crucial target for drug action, ion channels have been implicated in various diseases. Many natural products from marine organisms, such as fungi, algae, sponges, and sea cucumber, etc. have been found to have activities related to ion channels for decades. These interesting natural product molecules undoubtedly bring good news for the treatment of neurological and cardiovascular diseases. In this review, 92 marine natural products and their synthetic derivatives with ion channel-related activities that were identified during the period 2000-2024 were systematically reviewed. The synthesis and mechanisms of action of selected compounds were also discussed, aiming to offer insights for the development of drugs targeting ion channels.

The downregulation of Kv1 channels in Lgi1-/-mice is accompanied by a profound modification of its interactome and a parallel decrease in Kv2 channels

In animal models of LGI1-dependent autosomal dominant lateral temporal lobe epilepsy, Kv1 channels are downregulated, suggesting their crucial involvement in epileptogenesis. The molecular basis of Kv1 channel-downregulation in LGI1 knock-out mice has not been elucidated and how the absence of this extracellular protein induces an important modification in the expression of Kv1 remains unknown. In this study we analyse by immunofluorescence the modifications in neuronal Kv1.1 and Kv1.2 distribution throughout the hippocampal formation of LGI1 knock-out mice. We show that Kv1 downregulation is not restricted to the axonal compartment, but also takes place in the somatodendritic region and is accompanied by a drastic decrease in Kv2 expression levels. Moreover, we find that the downregulation of these Kv channels is associated with a marked increase in bursting patterns. Finally, mass spectrometry uncovered key modifications in the Kv1 interactome that highlight the epileptogenic implication of Kv1 downregulation in LGI1 knock-out animals.

Voltage-gated ion channels as novel regulators of epithelial ion transport in the osmoregulatory organs of insects

Voltage-gated ion channels (VGICs) respond to changes in membrane potential (Vm) and typically exhibit fast kinetic properties. They play an important role in signal detection and propagation in excitable tissues. In contrast, the role of VGICs in non-excitable tissues like epithelia is less studied and less clear. Studies in epithelia of vertebrates and invertebrates demonstrate wide expression of VGICs in epithelia of animals. Recently, VGICs have emerged as regulators of ion transport in the Malpighian tubules (MTs) and other osmoregulatory organs of insects. This mini-review aims to concisely summarize which VGICs have been implicated in the regulation of ion transport in the osmoregulatory epithelia of insects to date, and highlight select groups for further study. We have also speculated on the roles VGICs may potentially play in regulating processes connected directly to ion transport in insects (e.g., acid-base balance, desiccation, thermal tolerance). This review is not meant to be exhaustive but should rather serve as a thought-provoking collection of select existing highlights on VGICs, and to emphasize how understudied this mechanism of ion transport regulation is in insect epithelia.

Synthetic ShK-like Peptide from the Jellyfish Nemopilema nomurai Has Human Voltage-Gated Potassium-Channel-Blocking Activity

We identified a new human voltage-gated potassium channel blocker, NnK-1, in the jellyfish Nemopilema nomurai based on its genomic information. The gene sequence encoding NnK-1 contains 5408 base pairs, with five introns and six exons. The coding sequence of the NnK-1 precursor is 894 nucleotides long and encodes 297 amino acids containing five presumptive ShK-like peptides. An electrophysiological assay demonstrated that the fifth peptide, NnK-1, which was chemically synthesized, is an effective blocker of hKv1.3, hKv1.4, and hKv1.5. Multiple-sequence alignment with cnidarian Shk-like peptides, which have Kv1.3-blocking activity, revealed that three residues (3Asp, 25Lys, and 34Thr) of NnK-1, together with six cysteine residues, were conserved. Therefore, we hypothesized that these three residues are crucial for the binding of the toxin to voltage-gated potassium channels. This notion was confirmed by an electrophysiological assay with a synthetic peptide (NnK-1 mu) where these three peptides were substituted with 3Glu, 25Arg, and 34Met. In conclusion, we successfully identified and characterized a new voltage-gated potassium channel blocker in jellyfish that interacts with three different voltage-gated potassium channels. A peptide that interacts with multiple voltage-gated potassium channels has many therapeutic applications in various physiological and pathophysiological contexts.

The binding and mechanism of a positive allosteric modulator of Kv3 channels

Small-molecule modulators of diverse voltage-gated K+ (Kv) channels may help treat a wide range of neurological disorders. However, developing effective modulators requires understanding of their mechanism of action. We apply an orthogonal approach to elucidate the mechanism of action of an imidazolidinedione derivative (AUT5), a highly selective positive allosteric modulator of Kv3.1 and Kv3.2 channels. AUT5 modulation involves positive cooperativity and preferential stabilization of the open state. The cryo-EM structure of the Kv3.1/AUT5 complex at a resolution of 2.5 Å reveals four equivalent AUT5 binding sites at the extracellular inter-subunit interface between the voltage-sensing and pore domains of the channel's tetrameric assembly. Furthermore, we show that the unique extracellular turret regions of Kv3.1 and Kv3.2 essentially govern the selective positive modulation by AUT5. High-resolution apo and bound structures of Kv3.1 demonstrate how AUT5 binding promotes turret rearrangements and interactions with the voltage-sensing domain to favor the open conformation.

KCNA2 IgG autoimmunity in neuropsychiatric diseases

BACKGROUND

Autoantibodies against the potassium voltage-gated channel subfamily A member 2 (KCNA2) have been described in a few cases of neuropsychiatric disorders, but their diagnostic and pathophysiological role is currently unknown, imposing challenges to medical practice.

DESIGN / METHODS

We retrospectively collected comprehensive clinical and paraclinical data of 35 patients with KCNA2 IgG autoantibodies detected in cell-based and tissue-based assays. Patients' sera and cerebrospinal fluid (CSF) were used for characterization of the antigen, clinical-serological correlations, and determination of IgG subclasses.

RESULTS

KCNA2 autoantibody-positive patients (n = 35, median age at disease onset of 65 years, range of 16-83 years, 74 % male) mostly presented with cognitive impairment and/or epileptic seizures but also ataxia, gait disorder and personality changes. Serum autoantibodies belonged to IgG3 and IgG1 subclasses and titers ranged from 1:32 to 1:10,000. KCNA2 IgG was found in the CSF of 8/21 (38 %) patients and in the serum of 4/96 (4.2 %) healthy blood donors. KCNA2 autoantibodies bound to characteristic anatomical areas in the cerebellum and hippocampus of mammalian brain and juxtaparanodal regions of peripheral nerves but reacted exclusively with intracellular epitopes. A subset of four KCNA2 autoantibody-positive patients responded markedly to immunotherapy alongside with conversion to seronegativity, in particular those presenting an autoimmune encephalitis phenotype and receiving early immunotherapy. An available brain biopsy showed strong immune cell invasion. KCNA2 autoantibodies occurred in less than 10 % in association with an underlying tumor.

CONCLUSION

Our data suggest that KCNA2 autoimmunity is clinically heterogeneous. Future studies should determine whether KCNA2 autoantibodies are directly pathogenic or develop secondarily. Early immunotherapy should be considered, in particular if autoantibodies occur in CSF or if clinical or diagnostic findings suggest ongoing inflammation. Suspicious clinical phenotypes include autoimmune encephalitis, atypical dementia, new-onset epilepsy and unexplained epileptic seizures.

Design of Ultrapotent Genetically Encoded Inhibitors of Kv4.2 for Gating Neural Plasticity

The Kv4.2 potassium channel plays established roles in neuronal excitability, while also being implicated in plasticity. Current means to study the roles of Kv4.2 are limited, motivating us to design a genetically encoded membrane tethered Heteropodatoxin-2 (MetaPoda). We find that MetaPoda is an ultrapotent and selective gating-modifier of Kv4.2. We narrow its site of contact with the channel to two adjacent residues within the voltage sensitive domain (VSD) and, with docking simulations, suggest that the toxin binds the VSD from within the membrane. We also show that MetaPoda does not require an external linker of the channel for its activity. In neurons (obtained from female and male rat neonates), MetaPoda specifically, and potently, inhibits all Kv4 currents, leaving all other A-type currents unaffected. Inhibition of Kv4 in hippocampal neurons does not promote excessive excitability, as is expected from a simple potassium channel blocker. We do find that MetaPoda's prolonged expression (1 week) increases expression levels of the immediate early gene cFos and prevents potentiation. These findings argue for a major role of Kv4.2 in facilitating plasticity of hippocampal neurons. Lastly, we show that our engineering strategy is suitable for the swift engineering of another potent Kv4.2-selective membrane-tethered toxin, Phrixotoxin-1, denoted MetaPhix. Together, we provide two uniquely potent genetic tools to study Kv4.2 in neuronal excitability and plasticity.

A structurally precise mechanism links an epilepsy-associated KCNC2 potassium channel mutation to interneuron dysfunction

De novo heterozygous variants in KCNC2 encoding the voltage-gated potassium (K+) channel subunit Kv3.2 are a recently described cause of developmental and epileptic encephalopathy (DEE). A de novo variant in KCNC2 c.374G > A (p.Cys125Tyr) was identified via exome sequencing in a patient with DEE. Relative to wild-type Kv3.2, Kv3.2-p.Cys125Tyr induces K+ currents exhibiting a large hyperpolarizing shift in the voltage dependence of activation, accelerated activation, and delayed deactivation consistent with a relative stabilization of the open conformation, along with increased current density. Leveraging the cryogenic electron microscopy (cryo-EM) structure of Kv3.1, molecular dynamic simulations suggest that a strong π-π stacking interaction between the variant Tyr125 and Tyr156 in the α-6 helix of the T1 domain promotes a relative stabilization of the open conformation of the channel, which underlies the observed gain of function. A multicompartment computational model of a Kv3-expressing parvalbumin-positive cerebral cortex fast-spiking γ-aminobutyric acidergic (GABAergic) interneuron (PV-IN) demonstrates how the Kv3.2-Cys125Tyr variant impairs neuronal excitability and dysregulates inhibition in cerebral cortex circuits to explain the resulting epilepsy.

Transparent Intracellular Sensing Platform with Si Needles for Simultaneous Live Imaging

Vertically ordered Si needles are of particular interest for long-term intracellular recording owing to their capacity to infiltrate living cells with negligible damage and minimal toxicity. Such intracellular recordings could greatly benefit from simultaneous live cell imaging without disrupting their culture, contributing to an in-depth understanding of cellular function and activity. However, the use of standard live imaging techniques, such as inverted and confocal microscopy, is currently impeded by the opacity of Si wafers, typically employed for fabricating vertical Si needles. Here, we introduce a transparent intracellular sensing platform that combines vertical Si needles with a percolated network of Au-Ag nanowires on a transparent elastomeric substrate. This sensing platform meets all prerequisites for simultaneous intracellular recording and imaging, including electrochemical impedance, optical transparency, mechanical compliance, and cell viability. Proof-of-concept demonstrations of this sensing platform include monitoring electrical potentials in cardiomyocyte cells and in three-dimensionally engineered cardiovascular tissue, all while conducting live imaging with inverted and confocal microscopes. This sensing platform holds wide-ranging potential applications for intracellular research across various disciplines such as neuroscience, cardiology, muscle physiology, and drug screening.

Eukaryotic Kv channel Shaker inactivates through selectivity filter dilation rather than collapse

Eukaryotic voltage-gated K+ channels have been extensively studied, but the structural bases for some of their most salient functional features remain to be established. C-type inactivation, for example, is an auto-inhibitory mechanism that confers temporal resolution to their signal-firing activity. In a recent breakthrough, studies of a mutant of Shaker that is prone to inactivate indicated that this process entails a dilation of the selectivity filter, the narrowest part of the ion conduction pathway. Here, we report an atomic-resolution cryo-electron microscopy structure that demonstrates that the wild-type channel can also adopt this dilated state. All-atom simulations corroborate this conformation is congruent with the electrophysiological characteristics of the C-type inactivated state, namely, residual K+ conductance and altered ion specificity, and help rationalize why inactivation is accelerated or impeded by certain mutations. In summary, this study establishes the molecular basis for an important self-regulatory mechanism in eukaryotic K+ channels, laying a solid foundation for further studies.

Modeling methamphetamine use disorder and relapse in animals: short- and long-term epigenetic, transcriptional., and biochemical consequences in the rat brain

Methamphetamine use disorder (MUD) is a neuropsychiatric disorder characterized by binge drug taking episodes, intervals of abstinence, and relapses to drug use even during treatment. MUD has been modeled in rodents and investigators are attempting to identify its molecular bases. Preclinical experiments have shown that different schedules of methamphetamine self-administration can cause diverse transcriptional changes in the dorsal striatum of Sprague-Dawley rats. In the present review, we present data on differentially expressed genes (DEGs) identified in the rat striatum following methamphetamine intake. These include genes involved in transcription regulation, potassium channel function, and neuroinflammation. We then use the striatal data to discuss the potential significance of the molecular changes induced by methamphetamine by reviewing concordant or discordant data from the literature. This review identified potential molecular targets for pharmacological interventions. Nevertheless, there is a need for more research on methamphetamine-induced transcriptional consequences in various brain regions. These data should provide a more detailed neuroanatomical map of methamphetamine-induced changes and should better inform therapeutic interventions against MUD.

Determination of single-molecule transport activity of OATP2B1 by measuring the number of transporter molecules using electrophysiological approach

Transporter-mediated clearance is determined by two factors, its single-molecule clearance, and expression level. However, no reliable method has been developed to evaluate them separately. This study aimed to develop a reliable method for evaluating the single-molecule activity of membrane transporters, such as organic anion transporting polypeptide (OATP) 2B1. HEK293 cells that co-expressed large conductance calcium-activated potassium (BK) channel and OATP2B1 were established and used for the following experiments. i) BK channel-mediated whole-cell conductance was measured using patch-clamp technique and divided by its unitary conductance to estimate the number of channels on plasma membrane (QI). ii) Using plasma membrane fraction, quantitative targeted absolute proteomics determined the stoichiometric ratio (ρ) of OATP2B1 to BK channel. iii) The uptake of estrone 3-sulfate was evaluated to calculate the Michaelis constant and uptake clearance (CL) per cell. Single-molecule clearance (CLint) was calculated by dividing CL by QI·ρ. QI and ρ values were estimated to be 916 and 2.16, respectively, yielding CLint of 5.23 fL/min/molecule. We successfully developed a novel method to reliably measure the single-molecule activity of a transporter, which could be used to evaluate the influences of factors such as genetic variations and post-translational modifications on the intrinsic activity of transporters.

Inactivation of the Kv2.1 channel through electromechanical coupling

The Kv2.1 voltage-activated potassium (Kv) channel is a prominent delayed-rectifier Kv channel in the mammalian central nervous system, where its mechanisms of activation and inactivation are critical for regulating intrinsic neuronal excitability1,2. Here we present structures of the Kv2.1 channel in a lipid environment using cryo-electron microscopy to provide a framework for exploring its functional mechanisms and how mutations causing epileptic encephalopathies3-7 alter channel activity. By studying a series of disease-causing mutations, we identified one that illuminates a hydrophobic coupling nexus near the internal end of the pore that is critical for inactivation. Both functional and structural studies reveal that inactivation in Kv2.1 results from dynamic alterations in electromechanical coupling to reposition pore-lining S6 helices and close the internal pore. Consideration of these findings along with available structures for other Kv channels, as well as voltage-activated sodium and calcium channels, suggests that related mechanisms of inactivation are conserved in voltage-activated cation channels and likely to be engaged by widely used therapeutics to achieve state-dependent regulation of channel activity.

Cell-cycle arrest at the G1/S boundary enhances transient voltage-gated ion channel expression in human and insect cells

Heterologous expression of recombinant ion channel subunits in cell lines is often limited by the presence of a low number of channels at the cell surface level. Here, we introduce a combination of two techniques: viral expression using the baculovirus system plus cell-cycle arrest at the G1/S boundary using either thymidine or hydroxyurea. This method achieved a manifold increase in the peak current density of expressed ion channels compared with the classical liposome-mediated transfection methods. The enhanced ionic current was accompanied by an increase in the density of gating charges, confirming that the increased yield of protein and ionic current reflects the functional localization of channels in the plasma membrane. This modified method of viral expression coordinated with the cell cycle arrest will pave the way to better decipher the structure and function of ion channels and their association with ion channelopathies.

Potassium channels in behavioral brain disorders. Molecular mechanisms and therapeutic potential: A narrative review

Potassium channels (K+-channels) selectively control the passive flow of potassium ions across biological membranes and thereby also regulate membrane excitability. Genetic variants affecting many of the human K+-channels are well known causes of Mendelian disorders within cardiology, neurology, and endocrinology. K+-channels are also primary targets of many natural toxins from poisonous organisms and drugs used within cardiology and metabolism. As genetic tools are improving and larger clinical samples are being investigated, the spectrum of clinical phenotypes implicated in K+-channels dysfunction is rapidly expanding, notably within immunology, neurosciences, and metabolism. K+-channels that previously were considered to be expressed in only a few organs and to have discrete physiological functions, have recently been found in multiple tissues and with new, unexpected functions. The pleiotropic functions and patterns of expression of K+-channels may provide additional therapeutic opportunities, along with new emerging challenges from off-target effects. Here we review the functions and therapeutic potential of K+-channels, with an emphasis on the nervous system, roles in neuropsychiatric disorders and their involvement in other organ systems and diseases.

Potassium Channels in Parkinson's Disease: Potential Roles in Its Pathogenesis and Innovative Molecular Targets for Treatment

Parkinson's disease (PD) is a neurodegenerative disorder characterized by selective loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) region of the midbrain. The loss of neurons results in a subsequent reduction of dopamine in the striatum, which underlies the core motor symptoms of PD. To date, there are no effective treatments to stop, slow, or reverse the pathologic progression of dopaminergic neurodegeneration. This unfortunate predicament is because of the current early stages in understanding the biologic targets and pathways involved in PD pathogenesis. Ion channels have become emerging targets for new therapeutic development for PD due to their essential roles in neuronal function and neuroinflammation. Potassium channels are the most prominent ion channel family and have been shown to be critically important in PD pathology because of their roles in modulating neuronal excitability, neurotransmitter release, synaptic transmission, and neuroinflammation. In this review, members of the subfamilies of voltage-gated K+ channels, inward rectifying K+ channels, and Ca2+-activated K+ channels are described. Evidence of the role of these channels in PD etiology is discussed together with the latest views on related pathologic mechanisms and their potential as biologic targets for developing neuroprotective drugs for PD. SIGNIFICANCE STATEMENT: Parkinson's disease (PD) is the second most common neurodegenerative disorder, featuring progressive degeneration of dopaminergic neurons in the midbrain. It is a multifactorial disease involving multiple risk factors and complex pathobiological mechanisms. Mounting evidence suggests that ion channels play vital roles in the pathogenesis and progression of PD by regulating neuronal excitability and immune cell function. Therefore, they have become "hot" biological targets for PD, as demonstrated by multiple clinical trials of drug candidates targeting ion channels for PD therapy.

Heterogeneity of voltage gated sodium current density between neurons decorrelates spiking and suppresses network synchronization in Scn1b null mouse models

Voltage gated sodium channels (VGSCs) are required for action potential initiation and propagation in mammalian neurons. As with other ion channel families, VGSC density varies between neurons. Importantly, sodium current (INa) density variability is reduced in pyramidal neurons of Scn1b null mice. Scn1b encodes the VGSC β1/ β1B subunits, which regulate channel expression, trafficking, and voltage dependent properties. Here, we investigate how variable INa density in cortical layer 6 and subicular pyramidal neurons affects spike patterning and network synchronization. Constitutive or inducible Scn1b deletion enhances spike timing correlations between pyramidal neurons in response to fluctuating stimuli and impairs spike-triggered average current pattern diversity while preserving spike reliability. Inhibiting INa with a low concentration of tetrodotoxin similarly alters patterning without impairing reliability, with modest effects on firing rate. Computational modeling shows that broad INa density ranges confer a similarly broad spectrum of spike patterning in response to fluctuating synaptic conductances. Network coupling of neurons with high INa density variability displaces the coupling requirements for synchronization and broadens the dynamic range of activity when varying synaptic strength and network topology. Our results show that INa heterogeneity between neurons potently regulates spike pattern diversity and network synchronization, expanding VGSC roles in the nervous system.

Novel Genetic Variants Expand the Functional, Molecular, and Pathological Diversity of KCNA1 Channelopathy

The KCNA1 gene encodes Kv1.1 voltage-gated potassium channel α subunits, which are crucial for maintaining healthy neuronal firing and preventing hyperexcitability. Mutations in the KCNA1 gene can cause several neurological diseases and symptoms, such as episodic ataxia type 1 (EA1) and epilepsy, which may occur alone or in combination, making it challenging to establish simple genotype-phenotype correlations. Previous analyses of human KCNA1 variants have shown that epilepsy-linked mutations tend to cluster in regions critical for the channel's pore, whereas EA1-associated mutations are evenly distributed across the length of the protein. In this review, we examine 17 recently discovered pathogenic or likely pathogenic KCNA1 variants to gain new insights into the molecular genetic basis of KCNA1 channelopathy. We provide the first systematic breakdown of disease rates for KCNA1 variants in different protein domains, uncovering potential location biases that influence genotype-phenotype correlations. Our examination of the new mutations strengthens the proposed link between the pore region and epilepsy and reveals new connections between epilepsy-related variants, genetic modifiers, and respiratory dysfunction. Additionally, the new variants include the first two gain-of-function mutations ever discovered for KCNA1, the first frameshift mutation, and the first mutations located in the cytoplasmic N-terminal domain, broadening the functional and molecular scope of KCNA1 channelopathy. Moreover, the recently identified variants highlight emerging links between KCNA1 and musculoskeletal abnormalities and nystagmus, conditions not typically associated with KCNA1. These findings improve our understanding of KCNA1 channelopathy and promise to enhance personalized diagnosis and treatment for individuals with KCNA1-linked disorders.

Potassium Ion Channels in Glioma: From Basic Knowledge into Therapeutic Applications

Ion channels, specifically those controlling the flux of potassium across cell membranes, have recently been shown to exhibit an important role in the pathophysiology of glioma, the most common primary central nervous system tumor with a poor prognosis. Potassium channels are grouped into four subfamilies differing by their domain structure, gating mechanisms, and functions. Pertinent literature indicates the vital functions of potassium channels in many aspects of glioma carcinogenesis, including proliferation, migration, and apoptosis. The dysfunction of potassium channels can result in pro-proliferative signals that are highly related to calcium signaling as well. Moreover, this dysfunction can feed into migration and metastasis, most likely by increasing the osmotic pressure of cells allowing the cells to initiate the "escape" and "invasion" of capillaries. Reducing the expression or channel blockage has shown efficacy in reducing the proliferation and infiltration of glioma cells as well as inducing apoptosis, priming several approaches to target potassium channels in gliomas pharmacologically. This review summarizes the current knowledge on potassium channels, their contribution to oncogenic transformations in glioma, and the existing perspectives on utilizing them as potential targets for therapy.

Bioelectricity in Developmental Patterning and Size Control: Evidence and Genetically Encoded Tools in the Zebrafish Model

Developmental patterning is essential for regulating cellular events such as axial patterning, segmentation, tissue formation, and organ size determination during embryogenesis. Understanding the patterning mechanisms remains a central challenge and fundamental interest in developmental biology. Ion-channel-regulated bioelectric signals have emerged as a player of the patterning mechanism, which may interact with morphogens. Evidence from multiple model organisms reveals the roles of bioelectricity in embryonic development, regeneration, and cancers. The Zebrafish model is the second most used vertebrate model, next to the mouse model. The zebrafish model has great potential for elucidating the functions of bioelectricity due to many advantages such as external development, transparent early embryogenesis, and tractable genetics. Here, we review genetic evidence from zebrafish mutants with fin-size and pigment changes related to ion channels and bioelectricity. In addition, we review the cell membrane voltage reporting and chemogenetic tools that have already been used or have great potential to be implemented in zebrafish models. Finally, new perspectives and opportunities for bioelectricity research with zebrafish are discussed.

Mechanism underlying delayed rectifying in human voltage-mediated activation Eag2 channel

The transmembrane voltage gradient is a general physico-chemical cue that regulates diverse biological function through voltage-gated ion channels. How voltage sensing mediates ion flows remains unknown at the molecular level. Here, we report six conformations of the human Eag2 (hEag2) ranging from closed, pre-open, open, and pore dilation but non-conducting states captured by cryo-electron microscopy (cryo-EM). These multiple states illuminate dynamics of the selectivity filter and ion permeation pathway with delayed rectifier properties and Cole-Moore effect at the atomic level. Mechanistically, a short S4-S5 linker is coupled with the constrict sites to mediate voltage transducing in a non-domain-swapped configuration, resulting transitions for constrict sites of F464 and Q472 from gating to open state stabilizing for voltage energy transduction. Meanwhile, an additional potassium ion occupied at positions S6 confers the delayed rectifier property and Cole-Moore effects. These results provide insight into voltage transducing and potassium current across membrane, and shed light on the long-sought Cole-Moore effects.

Gene mutations in comorbidity of epilepsy and arrhythmia

Epilepsy is one of the most common neurological disorders, and sudden unexpected death in epilepsy (SUDEP) is the most severe outcome of refractory epilepsy. Arrhythmia is one of the heterogeneous factors in the pathophysiological mechanism of SUDEP with a high incidence in patients with refractory epilepsy, increasing the risk of premature death. The gene co-expressed in the brain and heart is supposed to be the genetic basis between epilepsy and arrhythmia, among which the gene encoding ion channel contributes to the prevalence of "cardiocerebral channelopathy" theory. Nevertheless, this theory could only explain the molecular mechanism of comorbid arrhythmia in part of patients with epilepsy (PWE). Therefore, we summarized the mutant genes that can induce comorbidity of epilepsy and arrhythmia and the possible corresponding treatments. These variants involved the genes encoding sodium, potassium, calcium and HCN channels, as well as some non-ion channel coding genes such as CHD4, PKP2, FHF1, GNB5, and mitochondrial genes. The relationship between genotype and clinical phenotype was not simple linear. Indeed, genes co-expressed in the brain and heart could independently induce epilepsy and/or arrhythmia. Mutant genes in brain could affect cardiac rhythm through central or peripheral regulation, while in the heart it could also affect cerebral electrical activity by changing the hemodynamics or internal environment. Analysis of mutations in comorbidity of epilepsy and arrhythmia could refine and expand the theory of "cardiocerebral channelopathy" and provide new insights for risk stratification of premature death and corresponding precision therapy in PWE.

A KCNC1-related neurological disorder due to gain of Kv3.1 function

OBJECTIVE

To further clarify genotype:phenotype correlations associated with variants in KCNC1 encoding the voltage-gated potassium (K+) channel subunit Kv3.1 and which are an emerging cause of a spectrum of neurological disease including intellectual disability, isolated myoclonus, progressive myoclonus epilepsy, and developmental and epileptic encephalopathy.

METHODS

We describe the clinical and genetic characteristics of a series of three patients with de novo heterozygous missense variants in KCNC1 associated with nonspecific developmental delay/intellectual disability and central hypotonia without epilepsy or ataxia. All three variants lead to amino acids alterations with mild predicted differences in physicochemical properties yet are localized to the S6 pore region of the Kv3.1 protein between the selectivity filter and PXP motif important for K+ channel gating. We performed whole-cell voltage clamp electrophysiological recording of wild-type versus variants in a heterologous mammalian expression system.

RESULTS

We demonstrate a prominent leftward (hyperpolarized) shift in the voltage dependence of activation and slowed deactivation of all variants in the clinically defined series.

INTERPRETATION

Electrophysiological recordings are consistent with a gain of K+ channel function that is predicted to exert a loss of function on the excitability of Kv3-expressing high frequency- firing neurons based on the unique electrophysiological properties of Kv3 channels. These results define a clinical-genetic syndrome within the spectrum of KCNC1-related neurological disorders.

Identification of novel genes by targeted exome sequencing in Retinoblastoma

BACKGROUND

Retinoblastoma (RB) is initiated by mutation in both alleles of RB1 gene. However, few cases may occur even in the absence of RB1 mutation suggesting the role of genes other than RB1.

METHODOLOGY

The current study was planned to utilize targeted exome sequencing in Indian RB patients affected with unilateral non-familial RB. 75 unilateral RB patients below 5 years of age were enrolled. Genomic DNA was extracted from blood and tumor tissue. From peripheral blood DNA, all coding and exon/intron regions were amplified using PCR and direct sequencing. Cases which did not harbor pathogenic variants in peripheral blood DNA were further screened for mutations in their tumor tissue DNA using targeted exome sequencing. Three pathogenicity prediction tools (Mutation Taster, SIFT, and PolyPhen-2) were used to determine the pathogenicity of non-synonymous variations. An in-house bioinformatics pipeline was devised for the mutation screening by targeted exome sequencing. Protein modeling studies were also done to predict the effect of the mutations on the protein structure and function.

RESULTS

Using the mentioned approach, we found two novel variants (g.69673_69674insT and g.48373314C>A) in RB1 gene in peripheral blood DNA. We also found novel variants in eight genes (RB1, ACAD11, GPR151, KCNA1, OTOR, SOX30, ARL11, and MYCT1) that may be associated with RB pathogenesis.

CONCLUSION

The present study expands our current knowledge regarding the genomic landscape of RB and also highlights the importance of NGS technologies to detect genes and novel variants that may play an important role in cancer initiation, progression, and prognosis.

Mutations within the selectivity filter reveal that Kv1 channels have distinct propensities to slow inactivate

Voltage-activated potassium (Kv) channels open in response to membrane depolarization and subsequently inactivate through distinct mechanisms. For the model Shaker Kv channel from Drosophila, fast N-type inactivation is thought to occur by a mechanism involving blockade of the internal pore by the N-terminus, whereas slow C-type inactivation results from conformational changes in the ion selectivity filter in the external pore. Kv channel inactivation plays critical roles in shaping the action potential and regulating firing frequency, and has been implicated in a range of diseases including episodic ataxia and arrhythmias. Although structures of the closely related Shaker and Kv1.2 channels containing mutations that promote slow inactivation both support a mechanism involving dilation of the outer selectivity filter, mutations in the outer pores of these two Kv channels have been reported to have markedly distinct effects on slow inactivation, raising questions about the extent to which slow inactivation is related in both channels. In this study, we characterized the influence of a series of mutations within the external pore of Shaker and Kv1.2 channels and observed many distinct mutant phenotypes. We find that mutations at four positions near the selectivity filter promote inactivation less dramatically in Kv1.2 when compared to Shaker, and they identify one key variable position (T449 in Shaker and V381 in Kv1.2) underlying the different phenotypes in the two channels. Collectively, our results suggest that Kv1.2 is less prone to inactivate compared to Shaker, yet support a common mechanism of inactivation in the two channels.

Genetic Knockout of TRPM2 Increases Neuronal Excitability of Hippocampal Neurons by Inhibiting Kv7 Channel in Epilepsy

Epilepsy is a chronic brain disease that makes serious cognitive and motor retardation. Ion channels affect the occurrence of epilepsy in various ways, but the mechanisms have not yet been fully elucidated. Transient receptor potential melastain2 (TRPM2) ion channel is a non-selective cationic channel that can permeate Ca²⁺ and critical for epilepsy. Here, TRPM2 gene knockout mice were used to generate a chronic kindling epilepsy model by PTZ administration in mice. We found that TRPM2 knockout mice were more susceptible to epilepsy than WT mice. Furthermore, the neuronal excitability in the hippocampal CA1 region of TRPM2 knockout mice was significantly increased. Compared with WT group, there were no significant differences in the input resistance and after hyperpolarization of CA1 neurons in TRPM2 knockout mice. Firing adaptation rate of hippocampal CA1 pyramidal neurons of TRPM2 knockout mice was lower than that of WT mice. We also found that activation of Kv7 channel by retigabine reduced the firing frequency of action potential in the hippocampal pyramidal neurons of TRPM2 knockout mice. However, inhibiting Kv7 channel increased the firing frequency of action potential in hippocampal pyramidal neurons of WT mice. The data suggest that activation of Kv7 channel can effectively reduce epileptic seizures in TRPM2 knockout mice. We conclude that genetic knockout of TRPM2 in hippocampal CA1 pyramidal neurons may increase neuronal excitability by inhibiting Kv7 channel, affecting the susceptibility to epilepsy. These findings may provide a potential therapeutic target for epilepsy.

Epilepsy Characteristics in Neurodevelopmental Disorders: Research from Patient Cohorts and Animal Models Focusing on Autism Spectrum Disorder

Epilepsy, a heterogeneous group of brain-related diseases, has continued to significantly burden society and families. Epilepsy comorbid with neurodevelopmental disorders (NDDs) is believed to occur due to multifaceted pathophysiological mechanisms involving disruptions in the excitation and inhibition (E/I) balance impeding widespread functional neuronal circuitry. Although the field has received much attention from the scientific community recently, the research has not yet translated into actionable therapeutics to completely cure epilepsy, particularly those comorbid with NDDs. In this review, we sought to elucidate the basic causes underlying epilepsy as well as those contributing to the association of epilepsy with NDDs. Comprehensive emphasis is put on some key neurodevelopmental genes implicated in epilepsy, such as MeCP2, SYNGAP1, FMR1, SHANK1-3 and TSC1, along with a few others, and the main electrophysiological and behavioral deficits are highlighted. For these genes, the progress made in developing appropriate and valid rodent models to accelerate basic research is also detailed. Further, we discuss the recent development in the therapeutic management of epilepsy and provide a briefing on the challenges and caveats in identifying and testing species-specific epilepsy models.

Kv Channel Ancillary Subunits: Where Do We Go from Here?

Voltage-gated potassium (Kv) channels each comprise four pore-forming α-subunits that orchestrate essential duties such as voltage sensing and K+ selectivity and conductance. In vivo, however, Kv channels also incorporate regulatory subunits-some Kv channel specific, others more general modifiers of protein folding, trafficking, and function. Understanding all the above is essential for a complete picture of the role of Kv channels in physiology and disease.

Axonal ion homeostasis and glial differentiation

The brain is the ultimate control unit of the body. It conducts accurate, fast and reproducible calculations to control motor actions affecting mating, foraging and flight or fight decisions. Therefore, during evolution, better and more efficient brains have emerged. However, even simple brains are complex organs. They are formed by glial cells and neurons that establish highly intricate networks to enable information collection, processing and eventually, a precise motor control. Here, we review and connect some well-established and some hidden pieces of information to set the focus on ion homeostasis as a driving force in glial differentiation promoting signalling speed and accuracy.

A missense mutation in Kcnc3 causes hippocampal learning deficits in mice

Although a wide variety of genetic tools has been developed to study learning and memory, the molecular basis of memory encoding remains incompletely understood. Here, we undertook an unbiased approach to identify novel genes critical for memory encoding. From a large-scale, in vivo mutagenesis screen using contextual fear conditioning, we isolated in mice a mutant, named Clueless, with spatial learning deficits. A causative missense mutation (G434V) was found in the voltage-gated potassium channel, subfamily C member 3 (Kcnc3) gene in a region that encodes a transmembrane voltage sensor. Generation of a Kcnc3^G434V CRISPR mutant mouse confirmed this mutation as the cause of the learning defects. While G434V had no effect on transcription, translation, or trafficking of the channel, electrophysiological analysis of the G434V mutant channel revealed a complete loss of voltage-gated conductance, a broadening of the action potential, and decreased neuronal firing. Together, our findings have revealed a role for Kcnc3 in learning and memory.

General Pharmacological Activation Mechanism of K+ Channels Bypassing Channel Gates

Under the known pharmacological activation mechanisms, activators allosterically or directly open potassium channel gates. However, herein, molecular dynamics simulations on TREK-1, a member of the channel class gated at the filter, suggested that negatively charged activators act with a gate-independent mechanism where compounds increase currents by promoting ions passing through the central cavity. Then, based on studies of KCNQ2, we uncovered that this noncanonical activation mechanism is shared by the other channel class gated at the helix-bundle crossing. Rational drug design found a novel KCNQ2 agonist, CLE030, which stably binds to the central cavity. Functional analysis, molecular dynamics simulations, and calculations of the potential of mean force revealed that the carbonyl oxygen of CLE030 influences permeant ions in the central cavity to contribute to its activation effects. Together, this study discovered a ligand-to-ion activation mechanism for channels that bypasses their gates and thus is conserved across subfamilies with different gates.

Mechanisms Underlying C-type Inactivation in Kv Channels: Lessons From Structures of Human Kv1.3 and Fly Shaker-IR Channels

Voltage-gated potassium (Kv) channels modulate the function of electrically-excitable and non-excitable cells by using several types of “gates” to regulate ion flow through the channels. An important gating mechanism, C-type inactivation, limits ion flow by transitioning Kv channels into a non-conducting inactivated state. Here, we highlight two recent papers, one on the human Kv1.3 channel and the second on the Drosophila Shaker Kv channel, that combined cryogenic electron microscopy and molecular dynamics simulation to define mechanisms underlying C-type inactivation. In both channels, the transition to the non-conducting inactivated conformation begins with the rupture of an intra-subunit hydrogen bond that fastens the selectivity filter to the pore helix. The freed filter swings outwards and gets tethered to an external residue. As a result, the extracellular end of the selectivity filter dilates and K⁺ permeation through the pore is impaired. Recovery from inactivation may entail a reversal of this process. Such a reversal, at least partially, is induced by the peptide dalazatide. Binding of dalazatide to external residues in Kv1.3 frees the filter to swing inwards. The extracellular end of the selectivity filter narrows allowing K⁺ to move in single file through the pore typical of conventional knock-on conduction. Inter-subunit hydrogen bonds that stabilize the outer pore in the dalazatide-bound structure are equivalent to those in open-conducting conformations of Kv channels. However, the intra-subunit bond that fastens the filter to the pore-helix is absent, suggesting an incomplete reversal of the process. These mechanisms define how Kv channels self-regulate the flow of K⁺ by changing the conformation of the selectivity filter.