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Knight KM, Krumm BE, Kapolka NJ, Ludlam WG, Cui M, Mani S, Prytkova I, Obarow EG, Lefevre TJ, Wei W, Ma N, Huang XP, Fay JF, Vaidehi N, Smrcka AV, Slesinger PA, Logothetis DE, Martemyanov KA, Roth BL, Dohlman HG. A neurodevelopmental disorder mutation locks G proteins in the transitory pre-activated state. Nat Commun 2024; 15:6643. [PMID: 39103320 DOI: 10.1038/s41467-024-50964-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Accepted: 07/25/2024] [Indexed: 08/07/2024] Open
Abstract
Many neurotransmitter receptors activate G proteins through exchange of GDP for GTP. The intermediate nucleotide-free state has eluded characterization, due largely to its inherent instability. Here we characterize a G protein variant associated with a rare neurological disorder in humans. GαoK46E has a charge reversal that clashes with the phosphate groups of GDP and GTP. As anticipated, the purified protein binds poorly to guanine nucleotides yet retains wild-type affinity for G protein βγ subunits. In cells with physiological concentrations of nucleotide, GαoK46E forms a stable complex with receptors and Gβγ, impeding effector activation. Further, we demonstrate that the mutant can be easily purified in complex with dopamine-bound D2 receptors, and use cryo-electron microscopy to determine the structure, including both domains of Gαo, without nucleotide or stabilizing nanobodies. These findings reveal the molecular basis for the first committed step of G protein activation, establish a mechanistic basis for a neurological disorder, provide a simplified strategy to determine receptor-G protein structures, and a method to detect high affinity agonist binding in cells.
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Affiliation(s)
- Kevin M Knight
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- Department of Neuroscience, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
| | - Brian E Krumm
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Nicholas J Kapolka
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - W Grant Ludlam
- Department of Neuroscience, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
| | - Meng Cui
- Department of Pharmaceutical Sciences Northeastern University, Boston, MA, USA
| | - Sepehr Mani
- Department of Pharmaceutical Sciences Northeastern University, Boston, MA, USA
| | - Iya Prytkova
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Elizabeth G Obarow
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Tyler J Lefevre
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Wenyuan Wei
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, CA, USA
| | - Ning Ma
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, CA, USA
| | - Xi-Ping Huang
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Jonathan F Fay
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, Baltimore, MD, USA
| | - Nagarajan Vaidehi
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, CA, USA
| | - Alan V Smrcka
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Paul A Slesinger
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | | | - Kirill A Martemyanov
- Department of Neuroscience, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
| | - Bryan L Roth
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Henrik G Dohlman
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
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Follmer ML, Isner T, Ozekin YH, Levitt C, Bates EA. Depolarization induces calcium-dependent BMP4 release from mouse embryonic palate mesenchyme. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.11.598333. [PMID: 38915514 PMCID: PMC11195066 DOI: 10.1101/2024.06.11.598333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/26/2024]
Abstract
Ion channels are essential for proper morphogenesis of the craniofacial skeleton. However, the molecular mechanisms underlying this phenomenon are unknown. Loss of the Kcnj2 potassium channel disrupts Bone Morphogenetic Protein (BMP) signaling within the developing palate. BMP signaling is essential for the correct development of several skeletal structures, including the palate, though little is known about the mechanisms that govern BMP secretion. We introduce a tool to image the release of bone morphogenetic protein 4 (BMP4) from mammalian cells. Using this tool, we show that depolarization induces BMP4 release from mouse embryonic palate mesenchyme cells in a calcium-dependent manner. We show native transient changes in intracellular calcium occur in cranial neural crest cells, the cells from which embryonic palate mesenchyme derives. Waves of transient changes in intracellular calcium suggest that these cells are electrically coupled and may temporally coordinate BMP release. These transient changes in intracellular calcium persist in palate mesenchyme cells from embryonic day (E) 9.5 to 13.5 mice. Disruption of Kcnj2 significantly decreases the amplitude of calcium transients and the ability of cells to secrete BMP. Together, these data suggest that temporal control of developmental cues is regulated by ion channels, depolarization, and changes in intracellular calcium for mammalian craniofacial morphogenesis. SUMMARY We show that embryonic palate mesenchyme cells undergo transient changes in intracellular calcium. Depolarization of these cells induces BMP4 release suggesting that ion channels are a node in BMP4 signaling.
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Nguyen H, Glaaser IW, Slesinger PA. Direct modulation of G protein-gated inwardly rectifying potassium (GIRK) channels. Front Physiol 2024; 15:1386645. [PMID: 38903913 PMCID: PMC11187414 DOI: 10.3389/fphys.2024.1386645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2024] [Accepted: 04/08/2024] [Indexed: 06/22/2024] Open
Abstract
Ion channels play a pivotal role in regulating cellular excitability and signal transduction processes. Among the various ion channels, G-protein-coupled inwardly rectifying potassium (GIRK) channels serve as key mediators of neurotransmission and cellular responses to extracellular signals. GIRK channels are members of the larger family of inwardly-rectifying potassium (Kir) channels. Typically, GIRK channels are activated via the direct binding of G-protein βγ subunits upon the activation of G-protein-coupled receptors (GPCRs). GIRK channel activation requires the presence of the lipid signaling molecule, phosphatidylinositol 4,5-bisphosphate (PIP2). GIRK channels are also modulated by endogenous proteins and other molecules, including RGS proteins, cholesterol, and SNX27 as well as exogenous compounds, such as alcohol. In the last decade or so, several groups have developed novel drugs and small molecules, such as ML297, GAT1508 and GiGA1, that activate GIRK channels in a G-protein independent manner. Here, we aim to provide a comprehensive overview focusing on the direct modulation of GIRK channels by G-proteins, PIP2, cholesterol, and novel modulatory compounds. These studies offer valuable insights into the underlying molecular mechanisms of channel function, and have potential implications for both basic research and therapeutic development.
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Affiliation(s)
| | | | - Paul A. Slesinger
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, United States
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4
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Jiang X, Zhao K, Sun Y, Song X, Yi C, Xiong T, Wang S, Yu Y, Chen X, Liu R, Yan X, Antos CL. The scale of zebrafish pectoral fin buds is determined by intercellular K+ levels and consequent Ca2+-mediated signaling via retinoic acid regulation of Rcan2 and Kcnk5b. PLoS Biol 2024; 22:e3002565. [PMID: 38527087 PMCID: PMC11018282 DOI: 10.1371/journal.pbio.3002565] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Revised: 04/15/2024] [Accepted: 02/27/2024] [Indexed: 03/27/2024] Open
Abstract
K+ channels regulate morphogens to scale adult fins, but little is known about what regulates the channels and how they control morphogen expression. Using the zebrafish pectoral fin bud as a model for early vertebrate fin/limb development, we found that K+ channels also scale this anatomical structure, and we determined how one K+-leak channel, Kcnk5b, integrates into its developmental program. From FLIM measurements of a Förster Resonance Energy Transfer (FRET)-based K+ sensor, we observed coordinated decreases in intracellular K+ levels during bud growth, and overexpression of K+-leak channels in vivo coordinately increased bud proportions. Retinoic acid, which can enhance fin/limb bud growth, decreased K+ in bud tissues and up-regulated regulator of calcineurin (rcan2). rcan2 overexpression increased bud growth and decreased K+, while CRISPR-Cas9 targeting of rcan2 decreased growth and increased K+. We observed similar results in the adult caudal fins. Moreover, CRISPR targeting of Kcnk5b revealed that Rcan2-mediated growth was dependent on the Kcnk5b. We also found that Kcnk5b enhanced depolarization in fin bud cells via Na+ channels and that this enhanced depolarization was required for Kcnk5b-enhanced growth. Lastly, Kcnk5b-induced shha transcription and bud growth required IP3R-mediated Ca2+ release and CaMKK activity. Thus, we provide a mechanism for how retinoic acid via rcan2 can regulate K+-channel activity to scale a vertebrate appendage via intercellular Ca2+ signaling.
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Affiliation(s)
- Xiaowen Jiang
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Kun Zhao
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Yi Sun
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Xinyue Song
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Chao Yi
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Tianlong Xiong
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Sen Wang
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Yi Yu
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
- Center for Quantitative Biology, Peking University, Beijing, People’s Republic of China
| | - Xiduo Chen
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Run Liu
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Xin Yan
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
| | - Christopher L. Antos
- School of Life Sciences and Technology, ShanghaiTech University, Shanghai, People’s Republic of China
- Institut für Pharmakologie und Toxikologie, Technische Universität Dresden, Dresden, Germany
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5
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van Eyk CL, Fahey MC, Gecz J. Redefining cerebral palsies as a diverse group of neurodevelopmental disorders with genetic aetiology. Nat Rev Neurol 2023; 19:542-555. [PMID: 37537278 DOI: 10.1038/s41582-023-00847-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/28/2023] [Indexed: 08/05/2023]
Abstract
Cerebral palsy is a clinical descriptor covering a diverse group of permanent, non-degenerative disorders of motor function. Around one-third of cases have now been shown to have an underlying genetic aetiology, with the genetic landscape overlapping with those of neurodevelopmental disorders including intellectual disability, epilepsy, speech and language disorders and autism. Here we review the current state of genomic testing in cerebral palsy, highlighting the benefits for personalized medicine and the imperative to consider aetiology during clinical diagnosis. With earlier clinical diagnosis now possible, we emphasize the opportunity for comprehensive and early genomic testing as a crucial component of the routine diagnostic work-up in people with cerebral palsy.
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Affiliation(s)
- Clare L van Eyk
- Adelaide Medical School, The University of Adelaide, Adelaide, South Australia, Australia
- Robinson Research Institute, The University of Adelaide, Adelaide, South Australia, Australia
| | - Michael C Fahey
- Department of Paediatrics, Monash University, Melbourne, Victoria, Australia
| | - Jozef Gecz
- Adelaide Medical School, The University of Adelaide, Adelaide, South Australia, Australia.
- Robinson Research Institute, The University of Adelaide, Adelaide, South Australia, Australia.
- South Australian Health and Medical Research Institute, Adelaide, South Australia, Australia.
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6
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Badonyi M, Marsh JA. Buffering of genetic dominance by allele-specific protein complex assembly. SCIENCE ADVANCES 2023; 9:eadf9845. [PMID: 37256959 PMCID: PMC10413657 DOI: 10.1126/sciadv.adf9845] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2023] [Accepted: 04/24/2023] [Indexed: 06/02/2023]
Abstract
Protein complex assembly often occurs while subunits are being translated, resulting in complexes whose subunits were translated from the same mRNA in an allele-specific manner. It has thus been hypothesized that such cotranslational assembly may counter the assembly-mediated dominant-negative effect, whereby co-assembly of mutant and wild-type subunits "poisons" complex activity. Here, we show that cotranslationally assembling subunits are much less likely to be associated with autosomal dominant relative to recessive disorders, and that subunits with dominant-negative disease mutations are significantly depleted in cotranslational assembly compared to those associated with loss-of-function mutations. We also find that complexes with known dominant-negative effects tend to expose their interfaces late during translation, lessening the likelihood of cotranslational assembly. Finally, by combining complex properties with other features, we trained a computational model for predicting proteins likely to be associated with non-loss-of-function disease mechanisms, which we believe will be of considerable utility for protein variant interpretation.
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Affiliation(s)
- Mihaly Badonyi
- MRC Human Genetics Unit, Institute of Genetics and Cancer, University of Edinburgh, Edinburgh, UK
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7
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van Midden VM, Kinsley L, Fraint A, Krainc D, Mencacci NE. Expanding the spectrum of KCNJ6-related disorders: Milder phenotype with pathological startle responses. Clin Genet 2023; 103:103-108. [PMID: 36071510 PMCID: PMC10087234 DOI: 10.1111/cge.14226] [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: 06/30/2022] [Revised: 08/29/2022] [Accepted: 09/01/2022] [Indexed: 12/13/2022]
Abstract
Keppen-Lubinsky syndrome is caused by pathogenic variants in KCNJ6, which encodes the inwardly rectifying channel subfamily J6. The four confirmed cases reported to date were characterized by severe intellectual disability, global developmental delay, feeding difficulties, and dysmorphic features. All but one of the cases also had a severe form of lipodystrophy, resulting in tightly adherent facial skin and appearance of premature aging. Here, we describe a 36-year-old female with a de novo pathogenic variant in KCNJ6 (NM_002240.5: c.460G>T; p.(Gly154Cys)) presenting with mild intellectual disability, subtle dysmorphic features, obsessive-compulsive disorder, and an exaggerated startle response. This case indicates that KCNJ6-related disorders should be considered in patients with less pronounced dysmorphic features and milder cognitive impairment, as well as in patients with startle disorders.
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Affiliation(s)
- Vesna Marija van Midden
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.,Department of Neurology, University Medical Centre Ljubljana, Ljubljana, Slovenia
| | - Lisa Kinsley
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
| | - Avram Fraint
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
| | - Dimitri Krainc
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
| | - Niccolò E Mencacci
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
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8
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Araújo-Vilar D, Fernández-Pombo A, Cobelo-Gómez S, Castro AI, Sánchez-Iglesias S. Lipodystrophy-associated progeroid syndromes. Hormones (Athens) 2022; 21:555-571. [PMID: 35835948 DOI: 10.1007/s42000-022-00386-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/13/2022] [Accepted: 06/29/2022] [Indexed: 01/07/2023]
Abstract
With the exception of HIV-associated lipodystrophy, lipodystrophy syndromes are rare conditions characterized by a lack of adipose tissue, which is not generally recovered. As a consequence, an ectopic deposition of lipids frequently occurs, which usually leads to insulin resistance, atherogenic dyslipidemia, and hepatic steatosis. These disorders include certain accelerated aging syndromes or progeroid syndromes. Even though each of them has unique clinical features, most show common clinical characteristics that affect growth, skin and appendages, adipose tissue, muscle, and bone and, in some of them, life expectancy is reduced. Although the molecular bases of these Mendelian disorders are very diverse and not well known, genomic instability is frequent as a consequence of impairment of nuclear organization, chromatin structure, and DNA repair, as well as epigenetic dysregulation and mitochondrial dysfunction. In this review, the main clinical features of the lipodystrophy-associated progeroid syndromes will be described along with their causes and pathogenic mechanisms, and an attempt will be made to identify which of López-Otín's hallmarks of aging are present.
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Affiliation(s)
- David Araújo-Vilar
- UETeM-Molecular Pathology Group, Department of Psychiatry, Radiology, Public Health, Nursing and Medicine (Medicine Area), Center for Research in Molecular Medicine and Chronic Diseases (CIMUS)-IDIS, University of Santiago de Compostela, 15782, Santiago de Compostela, Spain.
- Division of Endocrinology and Nutrition, University Clinical Hospital of Santiago de Compostela, 15706, Santiago de Compostela, Spain.
| | - Antía Fernández-Pombo
- UETeM-Molecular Pathology Group, Department of Psychiatry, Radiology, Public Health, Nursing and Medicine (Medicine Area), Center for Research in Molecular Medicine and Chronic Diseases (CIMUS)-IDIS, University of Santiago de Compostela, 15782, Santiago de Compostela, Spain
- Division of Endocrinology and Nutrition, University Clinical Hospital of Santiago de Compostela, 15706, Santiago de Compostela, Spain
| | - Silvia Cobelo-Gómez
- UETeM-Molecular Pathology Group, Department of Psychiatry, Radiology, Public Health, Nursing and Medicine (Medicine Area), Center for Research in Molecular Medicine and Chronic Diseases (CIMUS)-IDIS, University of Santiago de Compostela, 15782, Santiago de Compostela, Spain
| | - Ana I Castro
- Division of Endocrinology and Nutrition, University Clinical Hospital of Santiago de Compostela, 15706, Santiago de Compostela, Spain
- CIBER Fisiopatología de la Obesidad y la Nutrición (CIBERobn), 28029, Madrid, Spain
| | - Sofía Sánchez-Iglesias
- UETeM-Molecular Pathology Group, Department of Psychiatry, Radiology, Public Health, Nursing and Medicine (Medicine Area), Center for Research in Molecular Medicine and Chronic Diseases (CIMUS)-IDIS, University of Santiago de Compostela, 15782, Santiago de Compostela, Spain
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9
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Kleschevnikov A. GIRK2 Channels in Down Syndrome and Alzheimer's Disease. Curr Alzheimer Res 2022; 19:819-829. [PMID: 36567290 DOI: 10.2174/1567205020666221223122110] [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: 08/13/2022] [Revised: 11/26/2022] [Accepted: 11/29/2022] [Indexed: 12/27/2022]
Abstract
Cognitive impairment in Down syndrome (DS) results from the abnormal expression of hundreds of genes. However, the impact of KCNJ6, a gene located in the middle of the 'Down syndrome critical region' of chromosome 21, seems to stand out. KCNJ6 encodes GIRK2 (KIR3.2) subunits of G protein-gated inwardly rectifying potassium channels, which serve as effectors for GABAB, m2, 5HT1A, A1, and many other postsynaptic metabotropic receptors. GIRK2 subunits are heavily expressed in neocortex, cerebellum, and hippocampus. By controlling resting membrane potential and neuronal excitability, GIRK2 channels may thus affect both synaptic plasticity and stability of neural circuits in the brain regions important for learning and memory. Here, we discuss recent experimental data regarding the role of KCNJ6/GIRK2 in neuronal abnormalities and cognitive impairment in models of DS and Alzheimer's disease (AD). The results compellingly show that signaling through GIRK2 channels is abnormally enhanced in mouse genetic models of Down syndrome and that partial suppression of GIRK2 channels with pharmacological or genetic means can restore synaptic plasticity and improve impaired cognitive functions. On the other hand, signaling through GIRK2 channels is downregulated in AD models, such as models of early amyloidopathy. In these models, reduced GIRK2 channel signaling promotes neuronal hyperactivity, causing excitatory-inhibitory imbalance and neuronal death. Accordingly, activation of GABAB/GIRK2 signaling by GIRK channel activators or GABAB receptor agonists may reduce Aβ-induced hyperactivity and subsequent neuronal death, thereby exerting a neuroprotective effect in models of AD.
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10
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Chen IS, Eldstrom J, Fedida D, Kubo Y. A novel ion conducting route besides the central pore in an inherited mutant of G-protein-gated inwardly rectifying K + channel. J Physiol 2021; 600:603-622. [PMID: 34881429 DOI: 10.1113/jp282430] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 11/25/2021] [Indexed: 01/21/2023] Open
Abstract
G-protein-gated inwardly rectifying K+ (GIRK; Kir3.x) channels play important physiological roles in various organs. Some of the disease-associated mutations of GIRK channels are known to induce loss of K+ selectivity but their structural changes remain unclear. In this study, we investigated the mechanisms underlying the abnormal ion selectivity of inherited GIRK mutants. By the two-electrode voltage-clamp analysis of GIRK mutants heterologously expressed in Xenopus oocytes, we observed that Kir3.2 G156S permeates Li+ better than Rb+ , while T154del or L173R of Kir3.2 and T158A of Kir3.4 permeate Rb+ better than Li+ , suggesting a unique conformational change in the G156S mutant. Applications of blockers of the selectivity filter (SF) pathway, Ba2+ or Tertiapin-Q (TPN-Q), remarkably increased the Li+ -selectivity of Kir3.2 G156S but did not alter those of the other mutants. In single-channel recordings of Kir3.2 G156S expressed in mouse fibroblasts, two types of events were observed, one attributable to a TPN-Q-sensitive K+ current and the second a TPN-Q-resistant Li+ current. The results show that a novel Li+ -permeable and blocker-resistant pathway exists in G156S in addition to the SF pathway. Mutations in the pore helix, S148F and T151A also induced high Li+ permeation. Our results demonstrate that the mechanism underlying the loss of K+ selectivity of Kir3.2 G156S involves formation of a novel ion permeation pathway besides the SF pathway, which allows permeation of various species of cations. KEY POINTS: G-protein-gated inwardly rectifying K+ (GIRK; Kir3.x) channels play important roles in controlling excitation of cells in various organs, such as the brain and the heart. Some of the disease-associated mutations of GIRK channels are known to induce loss of K+ selectivity but their structural changes remain unclear. In this study, we investigated the mechanisms underlying the abnormal ion selectivity of inherited mutants of Kir3.2 and Kir3.4. Here we show that a novel Na+ , Li+ -permeable and blocker-resistant pathway exists in an inherited mutant, Kir3.2 G156S, in addition to the conventional ion conducting pathway formed by the selectivity filter (SF). Our results demonstrate that the mechanism underlying the loss of K+ selectivity of Kir3.2 G156S involves formation of a novel ion permeation pathway besides the SF pathway, which allows permeation of various species of cations.
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Affiliation(s)
- I-Shan Chen
- Division of Biophysics and Neurobiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Japan.,Department of Physiological Sciences, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Japan.,Department of Pharmacology, School of Medicine, Wakayama Medical University, Wakayama, Japan
| | - Jodene Eldstrom
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - David Fedida
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Yoshihiro Kubo
- Division of Biophysics and Neurobiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Japan.,Department of Physiological Sciences, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Japan
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11
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Structural insights into GIRK2 channel modulation by cholesterol and PIP 2. Cell Rep 2021; 36:109619. [PMID: 34433062 PMCID: PMC8436891 DOI: 10.1016/j.celrep.2021.109619] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2021] [Revised: 05/10/2021] [Accepted: 08/05/2021] [Indexed: 12/28/2022] Open
Abstract
G-protein-gated inwardly rectifying potassium (GIRK) channels are important for determining neuronal excitability. In addition to G proteins, GIRK channels are potentiated by membrane cholesterol, which is elevated in the brains of people with neurodegenerative diseases such as Alzheimer’s dementia and Parkinson’s disease. The structural mechanism of cholesterol modulation of GIRK channels is not well understood. In this study, we present cryo-electron microscopy (cryoEM) structures of GIRK2 in the presence and absence of the cholesterol analog cholesteryl hemisuccinate (CHS) and phosphatidylinositol 4,5-bisphosphate (PIP2). The structures reveal that CHS binds near PIP2 in lipid-facing hydrophobic pockets of the transmembrane domain. Our structural analysis suggests that CHS stabilizes PIP2 interaction with the channel and promotes engagement of the cytoplasmic domain onto the transmembrane region. Mutagenesis of one of the CHS binding pockets eliminates cholesterol-dependent potentiation of GIRK2. Elucidating the structural mechanisms underlying cholesterol modulation of GIRK2 channels could facilitate the development of therapeutics for treating neurological diseases. Ion channels are important in determining neuronal excitability. Elevated cholesterol levels found in some neurodegenerative diseases can affect the function of ion channels. Mathiharan et al. take a structural and functional approach to identifying physical sites for cholesterol, and they provide details on how cholesterol potentiates ion channel activity.
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12
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Abstract
K+ channels enable potassium to flow across the membrane with great selectivity. There are four K+ channel families: voltage-gated K (Kv), calcium-activated (KCa), inwardly rectifying K (Kir), and two-pore domain potassium (K2P) channels. All four K+ channels are formed by subunits assembling into a classic tetrameric (4x1P = 4P for the Kv, KCa, and Kir channels) or tetramer-like (2x2P = 4P for the K2P channels) architecture. These subunits can either be the same (homomers) or different (heteromers), conferring great diversity to these channels. They share a highly conserved selectivity filter within the pore but show different gating mechanisms adapted for their function. K+ channels play essential roles in controlling neuronal excitability by shaping action potentials, influencing the resting membrane potential, and responding to diverse physicochemical stimuli, such as a voltage change (Kv), intracellular calcium oscillations (KCa), cellular mediators (Kir), or temperature (K2P).
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13
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van Karnebeek CD, Blydt-Hansen I, Matthews AM, Avramovic V, Price M, Drogemoller B, Shyr C, Lee J, Mwenifumbo J, Ghani A, Stockler S, Friedman JM, Lehman A, Ross CJ, Wasserman WW, Tarailo-Graovac M, Horvath GA. Secondary biogenic amine deficiencies: genetic etiology, therapeutic interventions, and clinical effects. Neurogenetics 2021; 22:251-262. [PMID: 34213677 DOI: 10.1007/s10048-021-00652-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 06/08/2021] [Indexed: 11/25/2022]
Abstract
Monoamine neurotransmitter disorders present predominantly with neurologic features, including dystonic or dyskinetic cerebral palsy and movement disorders. Genetic conditions that lead to secondary defects in the synthesis, catabolism, transport, and metabolism of biogenic amines can lead to neurotransmitter abnormalities, which can present with similar features. Eleven patients with secondary neurotransmitter abnormalities were enrolled between 2011 and 2015. All patients underwent research-based whole exome and/or whole genome sequencing (WES/WGS). A trial of treatment with levodopa/carbidopa and 5-hydroxytryptophan was initiated. In six families with abnormal neurotransmitter profiles and neurological phenotypes, variants in known disease-causing genes (KCNJ6, SCN2A, CSTB in 2 siblings, NRNX1, KIF1A and PAK3) were identified, while one patient had a variant of uncertain significance in a candidate gene (DLG4) that may explain her phenotype. In 3 patients, no compelling candidate genes were identified. A trial of neurotransmitter replacement therapy led to improvement in motor and behavioral symptoms in all but two patients. The patient with KCNJ6 variant did not respond to L-dopa therapy, but rather experienced increased dyskinetic movements even at low dose of medication. The patient's symptoms harboring the NRNX1 deletion remained unaltered. This study demonstrates the utility of genome-wide sequencing in further understanding the etiology and pathophysiology of neurometabolic conditions, and the potential of secondary neurotransmitter deficiencies to serve as novel therapeutic targets. As there was a largely favorable response to therapy in our case series, a careful trial of neurotransmitter replacement therapy should be considered in patients with cerebrospinal fluid (CSF) monoamines below reference range.
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Affiliation(s)
- Clara D van Karnebeek
- BC Children's Hospital Research Institute, Vancouver, BC, Canada.,Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada.,Department of Pediatrics, Amsterdam University Medical Centre, Amsterdam, the Netherlands.,Department of Pediatrics, Radboud University Medical Center, Nijmegen, the Netherlands.,United for Metabolic Diseases', Amsterdam, the Netherlands
| | | | - Allison M Matthews
- BC Children's Hospital Research Institute, Vancouver, BC, Canada.,Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada.,Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada
| | - Vladimir Avramovic
- Department of Biochemistry, Molecular Biology, and Medical Genetics, Cumming School of Medicine, Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada
| | - Magda Price
- BC Children's Hospital Research Institute, Vancouver, BC, Canada.,Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada.,Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada
| | | | - Casper Shyr
- BC Children's Hospital Research Institute, Vancouver, BC, Canada
| | - Jessica Lee
- BC Children's Hospital Research Institute, Vancouver, BC, Canada
| | - Jill Mwenifumbo
- Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada
| | - Aisha Ghani
- BC Children's Hospital Research Institute, Vancouver, BC, Canada
| | - Sylvia Stockler
- BC Children's Hospital Research Institute, Vancouver, BC, Canada.,Department of Pediatrics, University of British Columbia, Vancouver, BC, Canada
| | - Jan M Friedman
- BC Children's Hospital Research Institute, Vancouver, BC, Canada.,Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada
| | - Anna Lehman
- Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada.,Adult Metabolic Diseases Clinic, Vancouver General Hospital, Vancouver, Canada
| | | | - Colin J Ross
- BC Children's Hospital Research Institute, Vancouver, BC, Canada.,Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Wyeth W Wasserman
- BC Children's Hospital Research Institute, Vancouver, BC, Canada.,Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada.,Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada
| | - Maja Tarailo-Graovac
- Department of Biochemistry, Molecular Biology, and Medical Genetics, Cumming School of Medicine, Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada.
| | - Gabriella A Horvath
- Department of Pediatrics, University of British Columbia, Vancouver, BC, Canada. .,Adult Metabolic Diseases Clinic, Vancouver General Hospital, Vancouver, Canada. .,Biochemical Genetics, BC Children's Hospital, 4480 Oak Street, Vancouver, BC, V6H 3V4, Canada.
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14
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Identification of a G-Protein-Independent Activator of GIRK Channels. Cell Rep 2021; 31:107770. [PMID: 32553165 DOI: 10.1016/j.celrep.2020.107770] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Revised: 03/24/2020] [Accepted: 05/22/2020] [Indexed: 12/18/2022] Open
Abstract
G-protein-gated inwardly rectifying K+ (GIRK) channels are essential effectors of inhibitory neurotransmission in the brain. GIRK channels have been implicated in diseases with abnormal neuronal excitability, including epilepsy and addiction. GIRK channels are tetramers composed of either the same subunit (e.g., homotetramers) or different subunits (e.g., heterotetramers). Compounds that specifically target subsets of GIRK channels in vivo are lacking. Previous studies have shown that alcohol directly activates GIRK channels through a hydrophobic pocket located in the cytoplasmic domain of the channel. Here, we report the identification and functional characterization of a GIRK1-selective activator, termed GiGA1, that targets the alcohol pocket. GiGA1 activates GIRK1/GIRK2 both in vitro and in vivo and, in turn, mitigates the effects of a convulsant in an acute epilepsy mouse model. These results shed light on the structure-based development of subunit-specific GIRK modulators that could provide potential treatments for brain disorders.
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15
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Zhao Y, Gameiro-Ros I, Glaaser IW, Slesinger PA. Advances in Targeting GIRK Channels in Disease. Trends Pharmacol Sci 2021; 42:203-215. [PMID: 33468322 DOI: 10.1016/j.tips.2020.12.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 11/30/2020] [Accepted: 12/11/2020] [Indexed: 12/12/2022]
Abstract
G protein-gated inwardly rectifying potassium (GIRK) channels are essential regulators of cell excitability in the brain. While they are implicated in a variety of neurological diseases in both human and animal model studies, their therapeutic potential has been largely untapped. Here, we review recent advances in the development of small molecule compounds that specifically modulate GIRK channels and compare them with first-generation compounds that exhibit off-target activity. We describe the method of discovery of these small molecule modulators, their chemical features, and their effects in vivo. These studies provide a promising outlook on the future development of subunit-specific GIRK modulators to regulate neuronal excitability in a brain region-specific manner.
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Affiliation(s)
- Yulin Zhao
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Isabel Gameiro-Ros
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Ian W Glaaser
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Paul A Slesinger
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.
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16
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"Electrifying dysmorphology": Potassium channelopathies causing dysmorphic syndromes. ADVANCES IN GENETICS 2020; 105:137-174. [PMID: 32560786 DOI: 10.1016/bs.adgen.2020.03.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Potassium channels are a heterogeneous group of membrane-bound proteins, whose functions support a diverse range of biological processes. Genetic disorders arising from mutations in potassium channels are classically recognized by symptoms arising from acute channel dysfunction, such as periodic paralysis, ataxia, seizures, or cardiac conduction abnormalities, often in a patient with otherwise normal examination findings. In this chapter, we review a distinct subgroup of rare potassium channelopathies whose presentations are instead suggestive of a developmental disorder, with features including intellectual disability, craniofacial dysmorphism or other physical anomalies. Known conditions within this subgroup are: Andersen-Tawil syndrome, Birk-Barel syndrome, Cantú syndrome, Keppen-Lubinsky syndrome, Temple-Baraitser syndrome, Zimmerman-Laband syndrome and a very similar disorder called Bauer-Tartaglia or FHEIG syndrome. Ion channelopathies are unlikely to be routinely considered in the differential diagnosis of children presenting with developmental concerns, and so detailed description and photographs of the clinical phenotype are provided to aid recognition. For several of these disorders, functional characterization of the genetic mutations responsible has led to identification of candidate therapies, including drugs already commonly used for other indications, which adds further impetus to their prompt recognition. Together, these cases illustrate the potential for mechanistic insights gained from genetic diagnosis to drive translational work toward targeted, disease-modifying therapies for rare disorders.
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17
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Zangerl-Plessl EM, Qile M, Bloothooft M, Stary-Weinzinger A, van der Heyden MAG. Disease Associated Mutations in K IR Proteins Linked to Aberrant Inward Rectifier Channel Trafficking. Biomolecules 2019; 9:biom9110650. [PMID: 31731488 PMCID: PMC6920955 DOI: 10.3390/biom9110650] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Revised: 10/22/2019] [Accepted: 10/23/2019] [Indexed: 12/28/2022] Open
Abstract
The ubiquitously expressed family of inward rectifier potassium (KIR) channels, encoded by KCNJ genes, is primarily involved in cell excitability and potassium homeostasis. Channel mutations associate with a variety of severe human diseases and syndromes, affecting many organ systems including the central and peripheral neural system, heart, kidney, pancreas, and skeletal muscle. A number of mutations associate with altered ion channel expression at the plasma membrane, which might result from defective channel trafficking. Trafficking involves cellular processes that transport ion channels to and from their place of function. By alignment of all KIR channels, and depicting the trafficking associated mutations, three mutational hotspots were identified. One localized in the transmembrane-domain 1 and immediately adjacent sequences, one was found in the G-loop and Golgi-export domain, and the third one was detected at the immunoglobulin-like domain. Surprisingly, only few mutations were observed in experimentally determined Endoplasmic Reticulum (ER)exit-, export-, or ER-retention motifs. Structural mapping of the trafficking defect causing mutations provided a 3D framework, which indicates that trafficking deficient mutations form clusters. These “mutation clusters” affect trafficking by different mechanisms, including protein stability.
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Affiliation(s)
- Eva-Maria Zangerl-Plessl
- Department of Pharmacology and Toxicology, University of Vienna, 1090 Vienna, Austria; (E.-M.Z.-P.); (A.S.-W.)
| | - Muge Qile
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, 3584 CM Utrecht, The Netherlands; (M.Q.); (M.B.)
| | - Meye Bloothooft
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, 3584 CM Utrecht, The Netherlands; (M.Q.); (M.B.)
| | - Anna Stary-Weinzinger
- Department of Pharmacology and Toxicology, University of Vienna, 1090 Vienna, Austria; (E.-M.Z.-P.); (A.S.-W.)
| | - Marcel A. G. van der Heyden
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, 3584 CM Utrecht, The Netherlands; (M.Q.); (M.B.)
- Correspondence: ; Tel.: +31-887558901
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