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Wang C, Zhai J, Chen Y. Novel KCNQ2 missense variant expands the genotype spectrum of DEE7. Neurol Sci 2024:10.1007/s10072-024-07655-w. [PMID: 38880853 DOI: 10.1007/s10072-024-07655-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2024] [Accepted: 06/05/2024] [Indexed: 06/18/2024]
Abstract
BACKGROUND KCNQ is a voltage-gated K + channel that controls neuronal excitability and is mutated in epilepsy and autism spectrum disorder (ASD). We focus on the KV7.2 voltage-gated potassium channel gene (KCNQ2), which is known for its association with developmental delay and various seizures (including self-limited benign familial neonatal epilepsy and epileptic encephalopathy). But the pathogenicity of many variants remains unproven, potentially leading to misinterpretation of their functional consequences. METHODS In this study, we studied a patient who visited Nanhua Hospital. Targeted next-generation sequencing and Sanger sequencing were used to identify the pathogenic variants. Meanwhile, computational models, including hydrogen bonding and docking analyses, suggest that variants cause functional impairment. In addition, functional validation was performed in the drosophila to further evaluate the missense variant in the KCNQ2 gene as the cause of this patient. RESULTS A new missense variant in the KCNQ2 gene was identified: NM_172107.4:c.1007C > A(p.ALa336Glu), which resulted in the change from alanine to glutamate at amino acid position 336 in the KCNQ2 gene. After computational modeling, including hydrogen bond analysis and docking analysis, it is indicated that the variants cause functional impairment. Furthermore, RNAi-mediated KCNQ knockout in flies led to the onset of epileptic behavior, lifespan and climbing capacity were affected, expression of the normal human KCNQ2 rescues the in flies RNAi-mediated KCNQ knockout behavioral abnormalities. CONCLUSION Our findings expands the genetic profile of KCNQ2 and enhances the genotype - phenotype link.
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Affiliation(s)
- Chao Wang
- Department of Neurology, the Affiliated Nanhua Hospital, Hengyang Medical School, University of South China, Hengyang, China
| | - JinXia Zhai
- Department of Neurology, the Affiliated Nanhua Hospital, Hengyang Medical School, University of South China, Hengyang, China
| | - YongJun Chen
- Department of Neurology, the Affiliated Nanhua Hospital, Hengyang Medical School, University of South China, Hengyang, China.
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2
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Krüger J, Lerche H. Retigabine and gabapentin restore channel function and neuronal firing in a cellular model of an epilepsy-associated dominant-negative KCNQ5 variant. Neuropharmacology 2024; 250:109892. [PMID: 38428481 DOI: 10.1016/j.neuropharm.2024.109892] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2023] [Revised: 01/19/2024] [Accepted: 02/26/2024] [Indexed: 03/03/2024]
Abstract
KCNQ5 encodes the voltage-gated potassium channel KV7.5, a member of the KV7 channel family, which conducts the M-current. This current is a potent regulator of neuronal excitability by regulating membrane potential in the subthreshold range of action potentials and mediating the medium and slow afterhyperpolarization. Recently, we have identified five loss-of-function variants in KCNQ5 in patients with genetic generalized epilepsy. Using the most severe dominant-negative variant (R359C), we set out to investigate pharmacological therapeutic intervention by KV7 channel openers on channel function and neuronal firing. Retigabine and gabapentin increased R359C-derived M-current amplitudes in HEK cells expressing homomeric or heteromeric mutant KV7.5 channels. Retigabine was most effective in restoring K+ currents. Ten μM retigabine was sufficient to reach the level of WT currents without retigabine, whereas 100 μM of gabapentin showed less than half of this effect and application of 50 μM ZnCl2 only significantly increased M-current amplitude in heteromeric channels. Overexpression of KV7.5-WT potently inhibited neuronal firing by increasing the M-current, whereas R359C overexpression had the opposite effect and additionally decreased the medium afterhyperpolarization current. Both aforementioned drugs and Zn2+ reversed the effect of R359C expression by reducing firing to nearly normal levels at high current injections. Our study shows that a dominant-negative variant with a complete loss-of-function in KV7.5 leads to largely increased neuronal firing which may explain a neuronal hyperexcitability in patients. KV7 channel openers, such as retigabine or gabapentin, could be treatment options for patients currently displaying pharmacoresistant epilepsy and carrying loss-of-function variants in KCNQ5.
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Affiliation(s)
- Johanna Krüger
- Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried-Müller-Straße 27, 72076, Tübingen, Germany.
| | - Holger Lerche
- Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried-Müller-Straße 27, 72076, Tübingen, Germany.
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Danačíková Š, Straka B, Daněk J, Kořínek V, Otáhal J. In vitro human cell culture models in a bench-to-bedside approach to epilepsy. Epilepsia Open 2024; 9:865-890. [PMID: 38637998 PMCID: PMC11145627 DOI: 10.1002/epi4.12941] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 03/05/2024] [Accepted: 03/31/2024] [Indexed: 04/20/2024] Open
Abstract
Epilepsy is the most common chronic neurological disease, affecting nearly 1%-2% of the world's population. Current pharmacological treatment and regimen adjustments are aimed at controlling seizures; however, they are ineffective in one-third of the patients. Although neuronal hyperexcitability was previously thought to be mainly due to ion channel alterations, current research has revealed other contributing molecular pathways, including processes involved in cellular signaling, energy metabolism, protein synthesis, axon guidance, inflammation, and others. Some forms of drug-resistant epilepsy are caused by genetic defects that constitute potential targets for precision therapy. Although such approaches are increasingly important, they are still in the early stages of development. This review aims to provide a summary of practical aspects of the employment of in vitro human cell culture models in epilepsy diagnosis, treatment, and research. First, we briefly summarize the genetic testing that may result in the detection of candidate pathogenic variants in genes involved in epilepsy pathogenesis. Consequently, we review existing in vitro cell models, including induced pluripotent stem cells and differentiated neuronal cells, providing their specific properties, validity, and employment in research pipelines. We cover two methodological approaches. The first approach involves the utilization of somatic cells directly obtained from individual patients, while the second approach entails the utilization of characterized cell lines. The models are evaluated in terms of their research and clinical benefits, relevance to the in vivo conditions, legal and ethical aspects, time and cost demands, and available published data. Despite the methodological, temporal, and financial demands of the reviewed models they possess high potential to be used as robust systems in routine testing of pathogenicity of detected variants in the near future and provide a solid experimental background for personalized therapy of genetic epilepsies. PLAIN LANGUAGE SUMMARY: Epilepsy affects millions worldwide, but current treatments fail for many patients. Beyond traditional ion channel alterations, various genetic factors contribute to the disorder's complexity. This review explores how in vitro human cell models, either from patients or from cell lines, can aid in understanding epilepsy's genetic roots and developing personalized therapies. While these models require further investigation, they offer hope for improved diagnosis and treatment of genetic forms of epilepsy.
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Affiliation(s)
- Šárka Danačíková
- Laboratory of Developmental EpileptologyInstitute of Physiology of the Czech Academy of SciencesPragueCzech Republic
- Department of Pathophysiology, Second Faculty of MedicineCharles UniversityPragueCzech Republic
- Laboratory of Cell and Developmental BiologyInstitute of Molecular Genetics of the Czech Academy of SciencesPragueCzech Republic
- Department of Physiology, Faculty of ScienceCharles UniversityPragueCzech Republic
| | - Barbora Straka
- Neurogenetics Laboratory of the Department of Paediatric Neurology, Second Faculty of MedicineCharles University and Motol University Hospital, Full Member of the ERN EpiCAREPragueCzech Republic
| | - Jan Daněk
- Laboratory of Developmental EpileptologyInstitute of Physiology of the Czech Academy of SciencesPragueCzech Republic
| | - Vladimír Kořínek
- Laboratory of Cell and Developmental BiologyInstitute of Molecular Genetics of the Czech Academy of SciencesPragueCzech Republic
| | - Jakub Otáhal
- Laboratory of Developmental EpileptologyInstitute of Physiology of the Czech Academy of SciencesPragueCzech Republic
- Department of Pathophysiology, Second Faculty of MedicineCharles UniversityPragueCzech Republic
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4
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Celentano C, Carotenuto L, Miceli F, Carleo G, Corrado B, Baroli G, Iervolino S, Vecchione R, Taglialatela M, Barrese V. Kv7 channel activation reduces brain endothelial cell permeability and prevents kainic acid-induced blood-brain barrier damage. Am J Physiol Cell Physiol 2024; 326:C893-C904. [PMID: 38284124 PMCID: PMC11193483 DOI: 10.1152/ajpcell.00709.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 01/22/2024] [Accepted: 01/22/2024] [Indexed: 01/30/2024]
Abstract
Ion channels in the blood-brain barrier (BBB) play a main role in controlling the interstitial fluid composition and cerebral blood flow, and their dysfunction contributes to the disruption of the BBB occurring in many neurological diseases such as epilepsy. In this study, using morphological and functional approaches, we evaluated the expression and role in the BBB of Kv7 channels, a family of voltage-gated potassium channels including five members (Kv7.1-5) that play a major role in the regulation of cell excitability and transmembrane flux of potassium ions. Immunofluorescence experiments showed that Kv7.1, Kv7.4, and Kv7.5 were expressed in rat brain microvessels (BMVs), as well as brain primary- and clonal (BEND-3) endothelial cells (ECs). Kv7.5 localized at the cell-to-cell junction sites, whereas Kv7.4 was also found in pericytes. The Kv7 activator retigabine increased transendothelial electrical resistance (TEER) in both primary ECs and BEND-3 cells; moreover, retigabine reduced paracellular dextran flux in BEND-3 cells. These effects were prevented by the selective Kv7 blocker XE-991. Exposure to retigabine also hyperpolarized cell membrane and increased tight junctions (TJs) integrity in BEND-3 cells. BMVs from rats treated with kainic acid (KA) showed a disruption of TJs and a selective reduction of Kv7.5 expression. In BEND-3 cells, retigabine prevented the increase of cell permeability and the reduction of TJs integrity induced by KA. Overall, these findings demonstrate that Kv7 channels are expressed in the BBB, where they modulate barrier properties both in physiological and pathological conditions.NEW & NOTEWORTHY This study describes for the first time the expression and the functional role of Kv7 potassium channels in the blood-brain barrier. We show that the opening of Kv7 channels reduces endothelial cell permeability both in physiological and pathological conditions via the hyperpolarization of cell membrane and the sealing of tight junctions. Therefore, activation of endothelial Kv7 channels might be a useful strategy to treat epilepsy and other neurological disorders characterized by blood-brain barrier dysfunction.
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Affiliation(s)
- Camilla Celentano
- Department of Neuroscience, Reproductive Sciences and Dentistry, University of Naples Federico II, Naples, Italy
| | - Lidia Carotenuto
- Department of Neuroscience, Reproductive Sciences and Dentistry, University of Naples Federico II, Naples, Italy
| | - Francesco Miceli
- Department of Neuroscience, Reproductive Sciences and Dentistry, University of Naples Federico II, Naples, Italy
| | - Giusy Carleo
- Department of Neuroscience, Reproductive Sciences and Dentistry, University of Naples Federico II, Naples, Italy
| | - Brunella Corrado
- Interdisciplinary Research Centre on Biomaterials, University of Naples Federico II, Naples, Italy
- Center for Advanced Biomaterials for Health Care, Istituto Italiano di Tecnologia, Naples, Italy
| | - Giulia Baroli
- Department of Neuroscience, Reproductive Sciences and Dentistry, University of Naples Federico II, Naples, Italy
| | - Stefania Iervolino
- Department of Neuroscience, Reproductive Sciences and Dentistry, University of Naples Federico II, Naples, Italy
| | - Raffaele Vecchione
- Center for Advanced Biomaterials for Health Care, Istituto Italiano di Tecnologia, Naples, Italy
| | - Maurizio Taglialatela
- Department of Neuroscience, Reproductive Sciences and Dentistry, University of Naples Federico II, Naples, Italy
| | - Vincenzo Barrese
- Department of Neuroscience, Reproductive Sciences and Dentistry, University of Naples Federico II, Naples, Italy
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5
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Tsvetkov D, Schleifenbaum J, Wang Y, Kassmann M, Polovitskaya MM, Ali M, Schütze S, Rothe M, Luft FC, Jentsch TJ, Gollasch M. KCNQ5 Controls Perivascular Adipose Tissue-Mediated Vasodilation. Hypertension 2024; 81:561-571. [PMID: 38354270 DOI: 10.1161/hypertensionaha.123.21834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2023] [Accepted: 12/12/2023] [Indexed: 02/16/2024]
Abstract
BACKGROUND Small arteries exhibit resting tone, a partially contracted state that maintains arterial blood pressure. In arterial smooth muscle cells, potassium channels control contraction and relaxation. Perivascular adipose tissue (PVAT) has been shown to exert anticontractile effects on the blood vessels. However, the mechanisms by which PVAT signals small arteries, and their relevance remain largely unknown. We aimed to uncover key molecular components in adipose-vascular coupling. METHODS A wide spectrum of genetic mouse models targeting Kcnq3, Kcnq4, and Kcnq5 genes (Kcnq3-/-, Kcnq4-/-, Kcnq5-/-, Kcnq5dn/dn, Kcnq4-/-/Kcnq5dn/dn, and Kcnq4-/-/Kcnq5-/-), telemetry blood pressure measurements, targeted lipidomics, RNA-Seq profiling, wire-myography, patch-clamp, and sharp-electrode membrane potential measurements was used. RESULTS We show that PVAT causes smooth muscle cell KV7.5 family of voltage-gated potassium (K+) channels to hyperpolarize the membrane potential. This effect relaxes small arteries and regulates blood pressure. Oxygenation of polyunsaturated fats generates oxylipins, a superclass of lipid mediators. We identified numerous oxylipins released by PVAT, which potentiate vasodilatory action in small arteries by opening smooth muscle cell KV7.5 family of voltage-gated potassium (K+) channels. CONCLUSIONS Our results reveal a key molecular function of the KV7.5 family of voltage-gated potassium (K+) channels in the adipose-vascular coupling, translating PVAT signals, particularly oxylipins, to the central physiological function of vasoregulation. This novel pathway opens new therapeutic perspectives.
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Affiliation(s)
- Dmitry Tsvetkov
- Department of Internal Medicine and Geriatrics, University Medicine Greifswald, Germany (D.T., M.K., M.A., M.G.)
| | - Johanna Schleifenbaum
- Institute of Vegetative Physiology, Charité-Universitätsmedizin Berlin, Germany (J.S.)
| | - Yibin Wang
- Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine, Berlin, Germany (Y.W., F.C.L.)
| | - Mario Kassmann
- Department of Internal Medicine and Geriatrics, University Medicine Greifswald, Germany (D.T., M.K., M.A., M.G.)
| | - Maya M Polovitskaya
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany (M.M.P., S.S., T.J.J.)
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (M.M.P., S.S., T.J.J.)
| | - Mohamed Ali
- Department of Internal Medicine and Geriatrics, University Medicine Greifswald, Germany (D.T., M.K., M.A., M.G.)
| | - Sebastian Schütze
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany (M.M.P., S.S., T.J.J.)
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (M.M.P., S.S., T.J.J.)
| | | | - Friedrich C Luft
- Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine, Berlin, Germany (Y.W., F.C.L.)
| | - Thomas J Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany (M.M.P., S.S., T.J.J.)
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (M.M.P., S.S., T.J.J.)
- NeuroCure Cluster of Excellence, Charité-Universitätsmedizin Berlin, Berlin, Germany (T.J.J.)
| | - Maik Gollasch
- Department of Internal Medicine and Geriatrics, University Medicine Greifswald, Germany (D.T., M.K., M.A., M.G.)
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6
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Soto-Perez J, Cleary CM, Sobrinho CR, Mulkey SB, Carroll JL, Tzingounis AV, Mulkey DK. Phox2b-expressing neurons contribute to breathing problems in Kcnq2 loss- and gain-of-function encephalopathy models. Nat Commun 2023; 14:8059. [PMID: 38052789 PMCID: PMC10698053 DOI: 10.1038/s41467-023-43834-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Accepted: 11/21/2023] [Indexed: 12/07/2023] Open
Abstract
Loss- and gain-of-function variants in the gene encoding KCNQ2 channels are a common cause of developmental and epileptic encephalopathy, a condition characterized by seizures, developmental delays, breathing problems, and early mortality. To understand how KCNQ2 dysfunction impacts behavior in a mouse model, we focus on the control of breathing by neurons expressing the transcription factor Phox2b which includes respiratory neurons in the ventral parafacial region. We find Phox2b-expressing ventral parafacial neurons express Kcnq2 in the absence of other Kcnq isoforms, thus clarifying why disruption of Kcnq2 but not other channel isoforms results in breathing problems. We also find that Kcnq2 deletion or expression of a recurrent gain-of-function variant R201C in Phox2b-expressing neurons increases baseline breathing or decreases the central chemoreflex, respectively, in mice during the light/inactive state. These results uncover mechanisms underlying breathing abnormalities in KCNQ2 encephalopathy and highlight an unappreciated vulnerability of Phox2b-expressing ventral parafacial neurons to KCNQ2 pathogenic variants.
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Affiliation(s)
- J Soto-Perez
- Dept of Physiology and Neurobiology, University of Connecticut, Storrs, CT, USA
| | - C M Cleary
- Dept of Physiology and Neurobiology, University of Connecticut, Storrs, CT, USA
| | - C R Sobrinho
- Dept of Physiology and Neurobiology, University of Connecticut, Storrs, CT, USA
| | - S B Mulkey
- Prenatal Pediatrics Institute, Children's National Hospital, Departments of Neurology and Pediatrics, The George Washington Univ. School of Medicine and Health Sciences, Washington, DC, USA
| | - J L Carroll
- Dept. of Pediatrics, Univ. Arkansas for Medical Sciences, Little Rock, AR, USA
| | - A V Tzingounis
- Dept of Physiology and Neurobiology, University of Connecticut, Storrs, CT, USA.
| | - D K Mulkey
- Dept of Physiology and Neurobiology, University of Connecticut, Storrs, CT, USA.
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7
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Bortolami A, Sesti F. Ion channels in neurodevelopment: lessons from the Integrin-KCNB1 channel complex. Neural Regen Res 2023; 18:2365-2369. [PMID: 37282454 PMCID: PMC10360111 DOI: 10.4103/1673-5374.371347] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023] Open
Abstract
Ion channels modulate cellular excitability by regulating ionic fluxes across biological membranes. Pathogenic mutations in ion channel genes give rise to epileptic disorders that are among the most frequent neurological diseases affecting millions of individuals worldwide. Epilepsies are triggered by an imbalance between excitatory and inhibitory conductances. However, pathogenic mutations in the same allele can give rise to loss-of-function and/or gain-of-function variants, all able to trigger epilepsy. Furthermore, certain alleles are associated with brain malformations even in the absence of a clear electrical phenotype. This body of evidence argues that the underlying epileptogenic mechanisms of ion channels are more diverse than originally thought. Studies focusing on ion channels in prenatal cortical development have shed light on this apparent paradox. The picture that emerges is that ion channels play crucial roles in landmark neurodevelopmental processes, including neuronal migration, neurite outgrowth, and synapse formation. Thus, pathogenic channel mutants can not only cause epileptic disorders by altering excitability, but further, by inducing morphological and synaptic abnormalities that are initiated during neocortex formation and may persist into the adult brain.
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Affiliation(s)
- Alessandro Bortolami
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Rutgers University, West Piscataway, NJ, USA
| | - Federico Sesti
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Rutgers University, West Piscataway, NJ, USA
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8
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Rockley K, Roberts R, Jennings H, Jones K, Davis M, Levesque P, Morton M. An integrated approach for early in vitro seizure prediction utilizing hiPSC neurons and human ion channel assays. Toxicol Sci 2023; 196:126-140. [PMID: 37632788 DOI: 10.1093/toxsci/kfad087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/28/2023] Open
Abstract
Seizure liability remains a significant cause of attrition throughout drug development. Advances in stem cell biology coupled with an increased understanding of the role of ion channels in seizure offer an opportunity for a new paradigm in screening. We assessed the activity of 15 pro-seizurogenic compounds (7 CNS active therapies, 4 GABA receptor antagonists, and 4 other reported seizurogenic compounds) using automated electrophysiology against a panel of 14 ion channels (Nav1.1, Nav1.2, Nav1.6, Kv7.2/7.3, Kv7.3/7.5, Kv1.1, Kv4.2, KCa4.1, Kv2.1, Kv3.1, KCa1.1, GABA α1β2γ2, nicotinic α4β2, NMDA 1/2A). These were selected based on linkage to seizure in genetic/pharmacological studies. Fourteen compounds demonstrated at least one "hit" against the seizure panel and 11 compounds inhibited 2 or more ion channels. Next, we assessed the impact of the 15 compounds on electrical signaling using human-induced pluripotent stem cell neurons in microelectrode array (MEA). The CNS active therapies (amoxapine, bupropion, chlorpromazine, clozapine, diphenhydramine, paroxetine, quetiapine) all caused characteristic changes to electrical activity in key parameters indicative of seizure such as network burst frequency and duration. The GABA antagonist picrotoxin increased all parameters, but the antibiotics amoxicillin and enoxacin only showed minimal changes. Acetaminophen, included as a negative control, caused no changes in any of the parameters assessed. Overall, pro-seizurogenic compounds showed a distinct fingerprint in the ion channel/MEA panel. These studies highlight the potential utility of an integrated in vitro approach for early seizure prediction to provide mechanistic information and to support optimal drug design in early development, saving time and resources.
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Affiliation(s)
| | - Ruth Roberts
- ApconiX, Macclesfield SK10 4TG, UK
- Department of Biosciences, University of Birmingham, Edgbaston B15 1TT, UK
| | | | | | - Myrtle Davis
- Bristol Myers Squibb, Princeton, New Jersey, USA
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9
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Okamura Y, Yoshioka D. What voltage-sensing phosphatases can reveal about the mechanisms of ion channel regulation by phosphoinositides. Biochem Soc Trans 2023; 51:827-839. [PMID: 37052219 DOI: 10.1042/bst20221065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 03/20/2023] [Accepted: 03/30/2023] [Indexed: 04/14/2023]
Abstract
Many membrane proteins including ion channels and ion transporters are regulated by membrane phospholipids such as phosphoinositides in cell membranes and organelles. Voltage-sensing phosphatase, VSP, is a voltage-sensitive phosphoinositide phosphatase which dephosphorylates PI(4,5)P2 into PI(4)P. VSP rapidly reduces the level of PI(4,5)P2 upon membrane depolarization, thus serving as a useful tool to quantitatively study phosphoinositide-regulation of ion channels and ion transporters using a cellular electrophysiology system. In this review, we focus on the application of VSPs to Kv7 family potassium channels, which have been important research targets in biophysics, pharmacology and medicine.
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Affiliation(s)
- Yasushi Okamura
- Laboratory of Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Yamada Oka 2-2, Suita, Osaka 565-0871, Japan
| | - Daisuke Yoshioka
- Laboratory of Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Yamada Oka 2-2, Suita, Osaka 565-0871, Japan
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10
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Potassium channelopathies associated with epilepsy-related syndromes and directions for therapeutic intervention. Biochem Pharmacol 2023; 208:115413. [PMID: 36646291 DOI: 10.1016/j.bcp.2023.115413] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 01/06/2023] [Accepted: 01/09/2023] [Indexed: 01/15/2023]
Abstract
A number of mutations to members of several CNS potassium (K) channel families have been identified which result in rare forms of neonatal onset epilepsy, or syndromes of which one prominent characteristic is a form of epilepsy. Benign Familial Neonatal Convulsions or Seizures (BFNC or BFNS), also referred to as Self-Limited Familial Neonatal Epilepsy (SeLNE), results from mutations in 2 members of the KV7 family (KCNQ) of K channels; while generally self-resolving by about 15 weeks of age, these mutations significantly increase the probability of generalized seizure disorders in the adult, in some cases they result in more severe developmental syndromes. Epilepsy of Infancy with Migrating Focal Seizures (EIMSF), or Migrating Partial Seizures of Infancy (MMPSI), is a rare severe form of epilepsy linked primarily to gain of function mutations in a member of the sodium-dependent K channel family, KCNT1 or SLACK. Finally, KCNMA1 channelopathies, including Liang-Wang syndrome (LIWAS), are rare combinations of neurological symptoms including seizure, movement abnormalities, delayed development and intellectual disabilities, with Liang-Wang syndrome an extremely serious polymalformative syndrome with a number of neurological sequelae including epilepsy. These are caused by mutations in the pore-forming subunit of the large-conductance calcium-activated K channel (BK channel) KCNMA1. The identification of these rare but significant channelopathies has resulted in a resurgence of interest in their treatment by direct pharmacological or genetic modulation. We will briefly review the genetics, biophysics and pharmacology of these K channels, their linkage with the 3 syndromes described above, and efforts to more effectively target these syndromes.
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11
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Krüger J, Schubert J, Kegele J, Labalme A, Mao M, Heighway J, Seebohm G, Yan P, Koko M, Aslan-Kara K, Caglayan H, Steinhoff BJ, Weber YG, Keo-Kosal P, Berkovic SF, Hildebrand MS, Petrou S, Krause R, May P, Lesca G, Maljevic S, Lerche H. Loss-of-function variants in the KCNQ5 gene are implicated in genetic generalized epilepsies. EBioMedicine 2022; 84:104244. [PMID: 36088682 PMCID: PMC9471468 DOI: 10.1016/j.ebiom.2022.104244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 08/09/2022] [Accepted: 08/16/2022] [Indexed: 11/17/2022] Open
Abstract
Background De novo missense variants in KCNQ5, encoding the voltage-gated K+ channel KV7.5, have been described to cause developmental and epileptic encephalopathy (DEE) or intellectual disability (ID). We set out to identify disease-related KCNQ5 variants in genetic generalized epilepsy (GGE) and their underlying mechanisms. Methods 1292 families with GGE were studied by next-generation sequencing. Whole-cell patch-clamp recordings, biotinylation and phospholipid overlay assays were performed in mammalian cells combined with homology modelling. Findings We identified three deleterious heterozygous missense variants, one truncation and one splice site alteration in five independent families with GGE with predominant absence seizures; two variants were also associated with mild to moderate ID. All missense variants displayed a strongly decreased current density indicating a loss-of-function (LOF). When mutant channels were co-expressed with wild-type (WT) KV7.5 or KV7.5 and KV7.3 channels, three variants also revealed a significant dominant-negative effect on WT channels. Other gating parameters were unchanged. Biotinylation assays indicated a normal surface expression of the variants. The R359C variant altered PI(4,5)P2-interaction. Interpretation Our study identified deleterious KCNQ5 variants in GGE, partially combined with mild to moderate ID. The disease mechanism is a LOF partially with dominant-negative effects through functional deficits. LOF of KV7.5 channels will reduce the M-current, likely resulting in increased excitability of KV7.5-expressing neurons. Further studies on network level are necessary to understand which circuits are affected and how this induces generalized seizures. Funding DFG/FNR Research Unit FOR-2715 (Germany/Luxemburg), BMBF rare disease network Treat-ION (Germany), foundation ‘no epilep’ (Germany).
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Bauer CK, Holling T, Horn D, Laço MN, Abdalla E, Omar OM, Alawi M, Kutsche K. Clinically Relevant KCNQ1 Variants Causing KCNQ1-KCNE2 Gain-of-Function Affect the Ca2+ Sensitivity of the Channel. Int J Mol Sci 2022; 23:ijms23179690. [PMID: 36077086 PMCID: PMC9456291 DOI: 10.3390/ijms23179690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 08/18/2022] [Accepted: 08/22/2022] [Indexed: 11/16/2022] Open
Abstract
Dominant KCNQ1 variants are well-known for underlying cardiac arrhythmia syndromes. The two heterozygous KCNQ1 missense variants, R116L and P369L, cause an allelic disorder characterized by pituitary hormone deficiency and maternally inherited gingival fibromatosis. Increased K+ conductance upon co-expression of KCNQ1 mutant channels with the beta subunit KCNE2 is suggested to underlie the phenotype; however, the reason for KCNQ1-KCNE2 (Q1E2) channel gain-of-function is unknown. We aimed to discover the genetic defect in a single individual and three family members with gingival overgrowth and identified the KCNQ1 variants P369L and V185M, respectively. Patch-clamp experiments demonstrated increased constitutive K+ conductance of V185M-Q1E2 channels, confirming the pathogenicity of the novel variant. To gain insight into the pathomechanism, we examined all three disease-causing KCNQ1 mutants. Manipulation of the intracellular Ca2+ concentration prior to and during whole-cell recordings identified an impaired Ca2+ sensitivity of the mutant KCNQ1 channels. With low Ca2+, wild-type KCNQ1 currents were efficiently reduced and exhibited a pre-pulse-dependent cross-over of current traces and a high-voltage-activated component. These features were absent in mutant KCNQ1 channels and in wild-type channels co-expressed with calmodulin and exposed to high intracellular Ca2+. Moreover, co-expression of calmodulin with wild-type Q1E2 channels and loading the cells with high Ca2+ drastically increased Q1E2 current amplitudes, suggesting that KCNE2 normally limits the resting Q1E2 conductance by an increased demand for calcified calmodulin to achieve effective channel opening. Our data link impaired Ca2+ sensitivity of the KCNQ1 mutants R116L, V185M and P369L to Q1E2 gain-of-function that is associated with a particular KCNQ1 channelopathy.
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Affiliation(s)
- Christiane K. Bauer
- Department of Cellular and Integrative Physiology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
- Correspondence:
| | - Tess Holling
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Denise Horn
- Department of Medical Genetics and Human Genetics, Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt Universität zu Berlin and Berlin Institute of Health, 13353 Berlin, Germany
| | - Mário Nôro Laço
- Medical Genetics Unit, Hospital Pediátrico, Centro Hospitalar e Universitário de Coimbra, 3004-561 Coimbra, Portugal
| | - Ebtesam Abdalla
- Department of Human Genetics, Medical Research Institute, Alexandria University, Alexandria 5422031, Egypt
- Genetics Department, Armed Forces College of Medicine (AFCM), Cairo 4460015, Egypt
| | - Omneya Magdy Omar
- Department of Pediatrics, Faculty of Medicine, Alexandria University, Alexandria 5422031, Egypt
| | - Malik Alawi
- Bioinformatics Core, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Kerstin Kutsche
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
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