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Chen H, Li YX, Wong RS, Esseltine JL, Bai D. Genetically engineered human embryonic kidney cells as a novel vehicle for dual patch clamp study of human gap junction channels. Biochem J 2024; 481:741-758. [PMID: 38752978 PMCID: PMC11346430 DOI: 10.1042/bcj20240016] [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: 01/18/2024] [Revised: 04/29/2024] [Accepted: 05/16/2024] [Indexed: 06/11/2024]
Abstract
Mutations in more than half of human connexin genes encoding gap junction (GJ) subunits have been linked to inherited human diseases. Functional studies of human GJ channels are essential for revealing mechanistic insights into the etiology of disease-linked connexin mutants. However, the commonly used Xenopus oocytes, N2A, HeLa, and other model cells for recombinant expression of human connexins have different and significant limitations. Here we developed a human cell line (HEK293) with each of the endogenous connexins (Cx43 and Cx45) knocked out using the CRISPR-Cas9 system. Double knockout HEK293 cells showed no background GJ coupling, were easily transfected with several human connexin genes (such as those encoding Cx46, Cx50, Cx37, Cx45, Cx26, and Cx36) which successfully formed functional GJs and were readily accessible for dual patch clamp analysis. Single knockout Cx43 or Cx45 HEK cell lines could also be used to characterize human GJ channels formed by Cx45 or Cx43, respectively, with an expression level suitable for studying macroscopic and single channel GJ channel properties. A cardiac arrhythmia linked Cx45 mutant R184G failed to form functional GJs in DKO HEK293 cells with impaired localizations. These genetically engineered HEK293 cells are well suited for patch clamp study of human GJ channels.
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Affiliation(s)
- Honghong Chen
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada N6A 5C1
| | - Yi X. Li
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada N6A 5C1
| | - Robert S. Wong
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada N6A 5C1
| | - Jessica L. Esseltine
- Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada A1B 3V6
| | - Donglin Bai
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada N6A 5C1
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2
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Abudara V, Araneda RC, Barrio L, Berthoud VM, Contreras JE, Eugenín E, Lerma J, Orellana JA, Palacios-Prado N, Pérez-Armendariz EM, Retamal MA, Sáez JC. Remembrances of Dr. Michael V.L. Bennett by Iberoamerican Colleagues and Friends. Neuroscience 2024:S0306-4522(24)00021-6. [PMID: 38278514 DOI: 10.1016/j.neuroscience.2024.01.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2024]
Affiliation(s)
- Verónica Abudara
- Facultad de Medicina, Universidad de la República Oriental del Uruguay, Montevideo, Uruguay
| | - Ricardo C Araneda
- Department of Biology, University of Maryland, College Park, MD, United States
| | - Luis Barrio
- Hospital Ramón y Cajal-IRYCIS, Centro de Tecnología Biomédica de la Universidad Politécnica, Madrid, Spain
| | - Viviana M Berthoud
- Department of Pediatrics, University of Chicago, Chicago, IL, United States
| | - Jorge E Contreras
- Department of Physiology and Membrane Biology, University of California-Davis, Davis, CA, United States
| | - Eliseo Eugenín
- Department of Neuroscience, Cell Biology, and Anatomy, The University of Texas Medical Branch, Galveston, TX, United States
| | - Juan Lerma
- Instituto de Neurociencias, CSIC-UMH, San Juan de Alicante, Spain.
| | - Juan A Orellana
- Departamento de Neurología, Escuela de Medicina and Centro Interdisciplinario de Neurociencias, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Nicolás Palacios-Prado
- Instituto de Neurociencias, Centro Interdisciplinario de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
| | - Elia Martha Pérez-Armendariz
- Unidad de Investigación en Medicina Experimental, Laboratorio de Sinapsis Eléctricas, Facultad de Medicina, UNAM, Ciudad de México, México
| | - Mauricio A Retamal
- Universidad del Desarrollo, Programa de Comunicación Celular en Cáncer, Facultad de Medicina Clínica Alemana, Santiago, Chile
| | - Juan C Sáez
- Instituto de Neurociencias, Centro Interdisciplinario de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
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3
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Abrams CK. Mechanisms of Diseases Associated with Mutation in GJC2/Connexin 47. Biomolecules 2023; 13:biom13040712. [PMID: 37189458 DOI: 10.3390/biom13040712] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2023] [Revised: 04/03/2023] [Accepted: 04/04/2023] [Indexed: 05/17/2023] Open
Abstract
Connexins are members of a family of integral membrane proteins that provide a pathway for both electrical and metabolic coupling between cells. Astroglia express connexin 30 (Cx30)-GJB6 and Cx43-GJA1, while oligodendroglia express Cx29/Cx31.3-GJC3, Cx32-GJB1, and Cx47-GJC2. Connexins organize into hexameric hemichannels (homomeric if all subunits are identical or heteromeric if one or more differs). Hemichannels from one cell then form cell-cell channels with a hemichannel from an apposed cell. (These are termed homotypic if the hemichannels are identical and heterotypic if the hemichannels differ). Oligodendrocytes couple to each other through Cx32/Cx32 or Cx47/Cx47 homotypic channels and they couple to astrocytes via Cx32/Cx30 or Cx47/Cx43 heterotypic channels. Astrocytes couple via Cx30/Cx30 and Cx43/Cx43 homotypic channels. Though Cx32 and Cx47 may be expressed in the same cells, all available data suggest that Cx32 and Cx47 cannot interact heteromerically. Animal models wherein one or in some cases two different CNS glial connexins have been deleted have helped to clarify the role of these molecules in CNS function. Mutations in a number of different CNS glial connexin genes cause human disease. Mutations in GJC2 lead to three distinct phenotypes, Pelizaeus Merzbacher like disease, hereditary spastic paraparesis (SPG44) and subclinical leukodystrophy.
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Affiliation(s)
- Charles K Abrams
- Department of Neurology and Rehabilitation, University of Illinois at Chicago College of Medicine, Chicago, IL 60612, USA
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Xu J, Nicholson BJ. Divergence between Hemichannel and Gap Junction Permeabilities of Connexin 30 and 26. Life (Basel) 2023; 13:390. [PMID: 36836746 PMCID: PMC9962233 DOI: 10.3390/life13020390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 01/06/2023] [Accepted: 01/09/2023] [Indexed: 02/04/2023] Open
Abstract
Cx30 has been proposed to play physiological functions in the kidney and cochlea, and this has often been associated with its hemichannel role (deafness mutants frequently affecting hemichannels more than gap junctions), implicated in ATP release. Here, we used heterologous expression systems (Xenopus oocytes and N2A cells) to describe the properties of Cx30 hemichannels, with the objective of better understanding their physiological functions. As previously observed, Cx30 hemichannels gated in response to transmembrane voltage (V0) and extracellular [Ca2+] (pK[Ca2+] of 1.9 μM in the absence of Mg++). They show minimal charge selectivity with respect to small ions (ratio of Na+: K+: Cl- of 1: 0.4: 0.6) and an MW cut-off for Alexa Dyes between 643 (Alex 488) and 820 Da (Alexa 594). However, while cations follow the expected drop in conductance with size (Na+ to TEA+ is 1: 0.3), anions showed an increase, with a ratio of Cl- to gluconate conductance of 1:1.4, suggesting favorable interactions between larger anions and the pore. This was further explored by comparing the permeabilities of both hemichannels and gap junctions to the natural anion (ATP), the release of which has been implicated in Ca++ signaling through hemichannels. We extended this analysis to two closely related connexins co-expressed in the cochlear, Cx26 and Cx30. Cx30 and 26 hemichannels displayed similar permeabilities to ATP, but surprisingly Cx26 gap junctions were six times more permeable than their hemichannels and four times more permeable than Cx30 gap junctions. This suggests a significant physiological difference in the functions of Cx26 and Cx30 gap junctions in organs where they are co-expressed, at least with regard to the distribution of energy resources of the cells. It also demonstrates that the permeability characteristics of hemichannels can significantly diverge from that of their gap junctions for some connexins but not others.
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Affiliation(s)
- Ji Xu
- Department of Pharmacology, Institute of Neuroscience, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou 450001, China
| | - Bruce J. Nicholson
- Department of Biochemistry and Structural Biology, University of Texas Health at San Antonio, San Antonio, TX 78229, USA
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Increased Hemichannel Activity Displayed by a Connexin43 Mutation Causing a Familial Connexinopathy Exhibiting Hypotrichosis with Follicular Keratosis and Hyperostosis. Int J Mol Sci 2023; 24:ijms24032222. [PMID: 36768546 PMCID: PMC9916973 DOI: 10.3390/ijms24032222] [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: 12/19/2022] [Revised: 01/17/2023] [Accepted: 01/18/2023] [Indexed: 01/26/2023] Open
Abstract
Mutations in the GJA1 gene that encodes connexin43 (Cx43) cause several rare genetic disorders, including diseases affecting the epidermis. Here, we examined the in vitro functional consequences of a Cx43 mutation, Cx43-G38E, linked to a novel human phenotype of hypotrichosis, follicular keratosis and hyperostosis. We found that Cx43-G38E was efficiently translated in Xenopus oocytes and localized to gap junction plaques in transfected HeLa cells. Cx43-G38E formed functional gap junction channels with the same efficiency as wild-type Cx43 in Xenopus oocytes, although voltage gating of the gap junction channels was altered. Notably, Cx43-G38E significantly increased membrane current flow through the formation of active hemichannels when compared to wild-type Cx43. These data demonstrate the association of increased hemichannel activity to a connexin mutation linked to a skeletal-cutaneous phenotype, suggesting that augmented hemichannel activity could play a role in skin and skeletal disorders caused by human Cx43 mutations.
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Oliveira MC, Verswyvel H, Smits E, Cordeiro RM, Bogaerts A, Lin A. The pro- and anti-tumoral properties of gap junctions in cancer and their role in therapeutic strategies. Redox Biol 2022; 57:102503. [PMID: 36228438 PMCID: PMC9557036 DOI: 10.1016/j.redox.2022.102503] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 09/06/2022] [Accepted: 10/06/2022] [Indexed: 11/24/2022] Open
Abstract
Gap junctions (GJs), essential structures for cell-cell communication, are made of two hemichannels (commonly called connexons), one on each adjacent cell. Found in almost all cells, GJs play a pivotal role in many physiological and cellular processes, and have even been linked to the progression of diseases, such as cancer. Modulation of GJs is under investigation as a therapeutic strategy to kill tumor cells. Furthermore, GJs have also been studied for their key role in activating anti-cancer immunity and propagating radiation- and oxidative stress-induced cell death to neighboring cells, a process known as the bystander effect. While, gap junction (GJ)-based therapeutic strategies are being developed, one major challenge has been the paradoxical role of GJs in both tumor progression and suppression, based on GJ composition, cancer factors, and tumoral context. Therefore, understanding the mechanisms of action, regulation, and the dual characteristics of GJs in cancer is critical for developing effective therapeutics. In this review, we provide an overview of the current understanding of GJs structure, function, and paradoxical pro- and anti-tumoral role in cancer. We also discuss the treatment strategies to target these GJs properties for anti-cancer responses, via modulation of GJ function.
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Affiliation(s)
- Maria C Oliveira
- Plasma Lab for Applications in Sustainability and Medicine-Antwerp (PLASMANT), Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium; Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Avenida dos Estados 5001, CEP 09210-580, Santo André, SP, Brazil.
| | - Hanne Verswyvel
- Plasma Lab for Applications in Sustainability and Medicine-Antwerp (PLASMANT), Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium; Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Universiteitsplein 1, B-2610, Antwerp, Belgium
| | - Evelien Smits
- Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Universiteitsplein 1, B-2610, Antwerp, Belgium
| | - Rodrigo M Cordeiro
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Avenida dos Estados 5001, CEP 09210-580, Santo André, SP, Brazil
| | - Annemie Bogaerts
- Plasma Lab for Applications in Sustainability and Medicine-Antwerp (PLASMANT), Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
| | - Abraham Lin
- Plasma Lab for Applications in Sustainability and Medicine-Antwerp (PLASMANT), Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium; Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Universiteitsplein 1, B-2610, Antwerp, Belgium
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Function and Plasticity of Electrical Synapses in the Mammalian Brain: Role of Non-Junctional Mechanisms. BIOLOGY 2022; 11:biology11010081. [PMID: 35053079 PMCID: PMC8773336 DOI: 10.3390/biology11010081] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Revised: 12/30/2021] [Accepted: 12/31/2021] [Indexed: 01/27/2023]
Abstract
Simple Summary Relevant brain functions, such as perception, organization of behavior, and cognitive processes, are the outcome of information processing by neural circuits. Within these circuits, communication between neurons mainly relies on two modalities of synaptic transmission: chemical and electrical. Moreover, changes in the strength of these connections, aka synaptic plasticity, are believed to underlie processes of learning and memory, and its dysfunction has been suggested to underlie a variety of neurological disorders. While the relevance of chemical transmission and its plastic changes are known in great detail, analogous mechanisms and functional impact of their electrical counterparts were only recently acknowledged. In this article, we review the basic physical principles behind electrical transmission between neurons, the plethora of functional operations supported by this modality of neuron-to-neuron communication, as well as the basic principles of plasticity at these synapses. Abstract Electrical transmission between neurons is largely mediated by gap junctions. These junctions allow the direct flow of electric current between neurons, and in mammals, they are mostly composed of the protein connexin36. Circuits of electrically coupled neurons are widespread in these animals. Plus, experimental and theoretical evidence supports the notion that, beyond synchronicity, these circuits are able to perform sophisticated operations such as lateral excitation and inhibition, noise reduction, as well as the ability to selectively respond upon coincident excitatory inputs. Although once considered stereotyped and unmodifiable, we now know that electrical synapses are subject to modulation and, by reconfiguring neural circuits, these modulations can alter relevant operations. The strength of electrical synapses depends on the gap junction resistance, as well as on its functional interaction with the electrophysiological properties of coupled neurons. In particular, voltage and ligand gated channels of the non-synaptic membrane critically determine the efficacy of transmission at these contacts. Consistently, modulatory actions on these channels have been shown to represent relevant mechanisms of plasticity of electrical synaptic transmission. Here, we review recent evidence on the regulation of electrical synapses of mammals, the underlying molecular mechanisms, and the possible ways in which they affect circuit function.
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Abrams CK, Flores-Obando RE, Dungan GD, Cherepanova E, Freidin MM. Investigating oligodendrocyte connexins: Heteromeric interactions between Cx32 and mutant or wild-type forms of Cx47 do not contribute to or modulate gap junction function. Glia 2021; 69:1882-1896. [PMID: 33835612 DOI: 10.1002/glia.23999] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 03/16/2021] [Accepted: 03/17/2021] [Indexed: 11/11/2022]
Abstract
Oligodendrocytes express two gap junction forming connexins, connexin 32 (Cx32) and Cx47; therefore, formation of heteromeric channels containing both Cx47 and Cx32 monomers might occur. Mutations in Cx47 cause both Pelizaeus-Merzbacher-like disease Type 1 (PMLD1) and hereditary spastic paraparesis Type 44 (SPG44) and heteromer formation between these mutants and Cx32 may contribute to the pathogenesis of these disorders. Here, we utilized electrophysiological and antibody-based techniques to examine this possibility. When cells expressing both Cx32 and Cx47 were paired with cells expressing either Cx32 or Cx47, properties were indistinguishable from those produced by cells expressing homotypic Cx32 or Cx47 channels. Similarly, pairing cells expressing both Cx32 and Cx47 with cells expressing Cx30 or Cx43 produced channels indistinguishable from heterotypic Cx32/Cx30 or Cx47/Cx43 channels, respectively. The same assessments were performed on cells expressing Cx32 and four mutant forms of Cx47 (p.I33M associated with SPG44 or p.P87S, p.Y269D or p.M283T associated with PMLD1). None of these mutants showed a functional effect on Cx32. Immunostained cells co-expressing Cx32WT (wild type) and Cx47WT showed a Pearson correlation coefficient close to zero, suggesting that any overlap was due to chance. p.Y269D showed a statistically significant negative correlation with Cx32, suggesting that Cx32 and this mutant overlap less than expected by chance. Co-immunoprecipitation of Cx32 with Cx47WT and mutants show only very low levels of co-immunoprecipitated protein. Overall, our data suggest that interactions between PMLD1 or SPG44 mutants and Cx32 gap junctions do not contribute to the pathogenesis of these disorders.
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Affiliation(s)
- Charles K Abrams
- Department of Neurology and Rehabilitation, University of Illinois at Chicago College of Medicine, Chicago, Illinois, USA
- Department of Neurology, SUNY Downstate Medical Center, Brooklyn, New York, USA
| | | | - Gabriel D Dungan
- Department of Neurology and Rehabilitation, University of Illinois at Chicago College of Medicine, Chicago, Illinois, USA
| | - Elina Cherepanova
- Department of Neurology, SUNY Downstate Medical Center, Brooklyn, New York, USA
| | - Mona M Freidin
- Department of Neurology and Rehabilitation, University of Illinois at Chicago College of Medicine, Chicago, Illinois, USA
- Department of Neurology, SUNY Downstate Medical Center, Brooklyn, New York, USA
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Miniou P, Fontes M. Therapeutic Development in Charcot Marie Tooth Type 1 Disease. Int J Mol Sci 2021; 22:ijms22136755. [PMID: 34201736 PMCID: PMC8268813 DOI: 10.3390/ijms22136755] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Revised: 06/11/2021] [Accepted: 06/15/2021] [Indexed: 01/04/2023] Open
Abstract
Charcot–Marie–Tooth disease (CMT) is the most frequent hereditary peripheral neuropathies. It is subdivided in two main groups, demyelinating (CMT1) and axonal (CMT2). CMT1 forms are the most frequent. The goal of this review is to present published data on 1—cellular and animal models having opened new potential therapeutic approaches. 2—exploration of these tracks, including clinical trials. The first conclusion is the great increase of publications on CMT1 subtypes since 2000. We discussed two points that should be considered in the therapeutic development toward a regulatory-approved therapy to be proposed to patients. The first point concerns long term safety if treatments will be a long-term process. The second point relates to the evaluation of treatment efficiency. Degradation of CMT clinical phenotype is not linear and progressive.
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Affiliation(s)
- Pierre Miniou
- InFlectis BioScience SAS, 21 Rue La Noue Bras de Fer, 44200 Nantes, France;
| | - Michel Fontes
- Centre de recherche en CardioVasculaire et Nutrition, Aix-Marseille Université, INRA 1260—INSERM 1263, 13005 Marseille, France
- Repositioning SAS, 8 Rue Napoleon, 20210 Calenzana, France
- Correspondence:
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Squecco R, Pierucci F, Idrizaj E, Frati A, Lenci E, Vicenti C, Iachini MC, Martinesi M, Garella R, Baccari MC, Francini F, Meacci E. Ceramide/protein phosphatase 2A axis is engaged in gap junction impairment elicited by PCB153 in liver stem-like progenitor cells. Mol Cell Biochem 2021; 476:3111-3126. [PMID: 33837873 PMCID: PMC8263450 DOI: 10.1007/s11010-021-04135-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 03/11/2021] [Indexed: 12/22/2022]
Abstract
The widespread environmental pollutant 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) is a non-dioxin-like toxicant. It is a potential carcinogen compound able to induce gap junction (GJ) intercellular communication impairment, probably the first non-genomic event leading to tumor promotion. Although PCBs have been known for many years, the molecular mode of PCB153 action is still unclear. Recent studies from our research group have shown that the toxicant elicits a transient modulation of connexin (Cx) 43-formed GJs in hepatic stem-like WB-F344 cells involving sphingosine 1-phosphate (S1P) path. Taking into account that other strictly related bioactive sphingolipids, such as ceramide (Cer), may have different effects from S1P, here we aim to clarify the signaling paths engaged by PCB153 in the control of GJs, focusing primarily on the role of Cer. Accordingly, we have achieved a combined biomolecular and electrophysiological analysis of GJs in cultured WB-F344 cells treated with PCB153 at different time points. We have found that the toxicant elicited a time-dependent regulation of GJs formed by different Cx isoforms, through a transient modulation of Cer/Cer kinase (CerK) axis and, in turn, of protein phosphatase 2A (PP2A). Our new findings demonstrate the existence of a specific molecular mechanism downstream to Cer, which distinctly affects the voltage-dependent and -independent GJs in liver stem-like cells, and open new opportunities for the identification of additional potential targets of these environmental toxicants.
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Affiliation(s)
- Roberta Squecco
- Department of Experimental and Clinical Medicine, Section of Physiological Sciences, University of Florence, Viale GB Morgagni 63, 50134, Florence, Italy
| | - Federica Pierucci
- Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy
| | - Eglantina Idrizaj
- Department of Experimental and Clinical Medicine, Section of Physiological Sciences, University of Florence, Viale GB Morgagni 63, 50134, Florence, Italy
| | - Alessia Frati
- Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy
| | - Elena Lenci
- Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy
| | - Catia Vicenti
- Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy
| | - Maria Chiara Iachini
- Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy
| | - Maria Martinesi
- Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy
| | - Rachele Garella
- Department of Experimental and Clinical Medicine, Section of Physiological Sciences, University of Florence, Viale GB Morgagni 63, 50134, Florence, Italy
| | - Maria Caterina Baccari
- Department of Experimental and Clinical Medicine, Section of Physiological Sciences, University of Florence, Viale GB Morgagni 63, 50134, Florence, Italy
| | - Fabio Francini
- Department of Experimental and Clinical Medicine, Section of Physiological Sciences, University of Florence, Viale GB Morgagni 63, 50134, Florence, Italy
| | - Elisabetta Meacci
- Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy.
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Wang Q, Liu S. Analysis of Hemichannels and Gap Junctions: Application and Extension of the Passive Transmembrane Ion Transport Model. Front Cell Neurosci 2021; 15:596953. [PMID: 33897368 PMCID: PMC8058385 DOI: 10.3389/fncel.2021.596953] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Accepted: 02/15/2021] [Indexed: 02/02/2023] Open
Abstract
Electrical synaptic transmission is an essential form of interneuronal communication which is mediated by gap junctions that permit ion flow. Three gene families (connexins, innexins, and pannexins) have evolved to form gap junctional channels. Each gap junctional channel is formed by the docking of the hemichannel of one cell with the corresponding hemichannel of an adjacent cell. To date, there has been a lack of study models to describe this structure in detail. In this study, we demonstrate that numerical simulations suggest that the passive transmembrane ion transport model, based on the generality of ion channels, also applies to hemichannels in non-junctional plasma membranes. On this basis, we established a gap junctional channel model, which describes hemichannels' docking. We simulated homotypic and heterotypic gap junctions formed by connexins, innexins, and pannexins. Based on the numerical results and our theoretical model, we discussed the physiology of hemichannels and gap junctions, including ion blockage of hemichannels, voltage gating of gap junctions, and asymmetry and delay of electrical synaptic transmission, for which the numerical simulations are first comprehensively realized.
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Affiliation(s)
- Qiqian Wang
- School of Mathematics, South China University of Technology, Guangzhou, China
| | - Shenquan Liu
- School of Mathematics, South China University of Technology, Guangzhou, China
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12
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Zanotto FM, Steinbock O. Asymmetric synchronization in lattices of pinned spiral waves. Phys Rev E 2021; 103:022213. [PMID: 33736004 DOI: 10.1103/physreve.103.022213] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2020] [Accepted: 02/03/2021] [Indexed: 11/07/2022]
Abstract
Networks of coupled oscillators show a wealth of fascinating dynamics and are capable of storing and processing information. In biological and social networks, the coupling is often asymmetric. We use the chirality of rotating spiral waves to introduce this asymmetry in an excitable reaction-diffusion model. The individual vortices are pinned to unexcitable disks and arranged at a constant spacing L along straight lines or simple geometric patterns. In the case of periodic boundaries or pinning disks arranged along the edge of a closed shape, small L values lead to synchronization via repeated wave collisions. The rate of synchronization as a function of L shows a single maximum and is determined by the dispersion behavior of a continuous wave train traveling along the system boundary. For finite systems, spirals are affected by their upstream neighbor, and a single dominant spiral exists along each chain. Specific initial conditions can decouple neighboring vortices even for small L values. We also present a time-delay differential equation that reproduces the phase dynamics in periodic systems.
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Affiliation(s)
- Franco M Zanotto
- Florida State University, Department of Chemistry and Biochemistry, Tallahassee, Florida 32306-4390, USA
| | - Oliver Steinbock
- Florida State University, Department of Chemistry and Biochemistry, Tallahassee, Florida 32306-4390, USA
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Nielsen BS, Zonta F, Farkas T, Litman T, Nielsen MS, MacAulay N. Structural determinants underlying permeant discrimination of the Cx43 hemichannel. J Biol Chem 2019; 294:16789-16803. [PMID: 31554662 DOI: 10.1074/jbc.ra119.007732] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Revised: 09/24/2019] [Indexed: 02/03/2023] Open
Abstract
Connexin (Cx) gap junction channels comprise two hemichannels in neighboring cells, and their permeability is well-described, but permeabilities of the single Cx hemichannel remain largely unresolved. Moreover, determination of isoform-specific Cx hemichannel permeability is challenging because of concurrent expression of other channels with similar permeability profiles and inhibitor sensitivities. The mammalian Cx hemichannels Cx30 and Cx43 are gated by extracellular divalent cations, removal of which promotes fluorescent dye uptake in both channels but atomic ion conductance only through Cx30. To determine the molecular determinants of this difference, here we employed chimeras and mutagenesis of predicted pore-lining residues in Cx43. We expressed the mutated channels in Xenopus laevis oocytes to avoid background activity of alternative channels. Oocytes expressing a Cx43 hemichannel chimera containing the N terminus or the first extracellular loop from Cx30 displayed ethidium uptake and, unlike WT Cx43, ion conduction, an observation further supported by molecular dynamics simulations. Additional C-terminal truncation of the chimeric Cx43 hemichannel elicited an even greater ion conductance with a magnitude closer to that of Cx30. The inhibitory profile for the connexin hemichannels depended on the permeant, with conventional connexin hemichannel inhibitors having a higher potency toward the ion conductance pathway than toward fluorescent dye uptake. Our results demonstrate a permeant-dependent, isoform-specific inhibition of connexin hemichannels. They further reveal that the outer segments of the pore-lining region, including the N terminus and the first extracellular loop, together with the C terminus preclude ion conductance of the open Cx43 hemichannel.
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Affiliation(s)
- Brian Skriver Nielsen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Francesco Zonta
- Shanghai Institute for Advanced Immunochemical Studies, ShanghaiTech University, Shanghai 201210, China
| | - Thomas Farkas
- Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Thomas Litman
- Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Morten Schak Nielsen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Nanna MacAulay
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
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14
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Mammano F. Inner Ear Connexin Channels: Roles in Development and Maintenance of Cochlear Function. Cold Spring Harb Perspect Med 2019; 9:a033233. [PMID: 30181354 PMCID: PMC6601451 DOI: 10.1101/cshperspect.a033233] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Connexin 26 and connexin 30 are the prevailing isoforms in the epithelial and connective tissue gap junction systems of the developing and mature cochlea. The most frequently encountered variants of the genes that encode these connexins, which are transcriptionally coregulated, determine complete loss of protein function and are the predominant cause of prelingual hereditary deafness. Reducing connexin 26 expression by Cre/loxP recombination in the inner ear of adult mice results in a decreased endocochlear potential, increased hearing thresholds, and loss of >90% of outer hair cells, indicating that this connexin is essential for maintenance of cochlear function. In the developing cochlea, connexins are necessary for intercellular calcium signaling activity. Ribbon synapses and basolateral membrane currents fail to mature in inner hair cells of mice that are born with reduced connexin expression, even though hair cells do not express any connexin. In contrast, pannexin 1, an alternative mediator of intercellular signaling, is dispensable for hearing acquisition and auditory function.
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Affiliation(s)
- Fabio Mammano
- University of Padova, Department of Physics and Astronomy "G. Galilei," Padova 35129, Italy
- CNR Institute of Cell Biology and Neurobiology, Monterotondo 00015, Italy
- Shanghai Institute for Advanced Immunochemical Studies, ShanghaiTech University, Shanghai 201210, China
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15
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Connexin43 mutations linked to skin disease have augmented hemichannel activity. Sci Rep 2019; 9:19. [PMID: 30631135 PMCID: PMC6328547 DOI: 10.1038/s41598-018-37221-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Accepted: 12/04/2018] [Indexed: 01/22/2023] Open
Abstract
Mutations in the gene (GJA1) encoding connexin43 (Cx43) are responsible for several rare genetic disorders, including non-syndromic skin-limited diseases. Here we used two different functional expression systems to characterize three Cx43 mutations linked to palmoplantar keratoderma and congenital alopecia-1, erythrokeratodermia variabilis et progressiva, or inflammatory linear verrucous epidermal nevus. In HeLa cells and Xenopus oocytes, we show that Cx43-G8V, Cx43-A44V and Cx43-E227D all formed functional gap junction channels with the same efficiency as wild-type Cx43, with normal voltage gating and a unitary conductance of ~110 pS. In HeLa cells, all three mutations also localized to regions of cell-cell contact and displayed a punctate staining pattern. In addition, we show that Cx43-G8V, Cx43-A44V and Cx43-E227D significantly increase membrane current flow through formation of active hemichannels, a novel activity that was not displayed by wild-type Cx43. The increased membrane current was inhibited by either 2 mM calcium, or 5 µM gadolinium, mediated by hemichannels with a unitary conductance of ~250 pS, and was not due to elevated mutant protein expression. The three Cx43 mutations all showed the same gain of function activity, suggesting that augmented hemichannel activity could play a role in skin-limited diseases caused by human Cx43 mutations.
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16
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Abstract
As the physiology of synapses began to be explored in the 1950s, it became clear that electrical communication between neurons could not always be explained by chemical transmission. Instead, careful studies pointed to a direct intercellular pathway of current flow and to the anatomical structure that was (eventually) called the gap junction. The mechanism of intercellular current flow was simple compared with chemical transmission, but the consequences of electrical signaling in excitable tissues were not. With the recognition that channels were a means of passive ion movement across membranes, the character and behavior of gap junction channels came under scrutiny. It became evident that these gated channels mediated intercellular transfer of small molecules as well as atomic ions, thereby mediating chemical, as well as electrical, signaling. Members of the responsible protein family in vertebrates-connexins-were cloned and their channels studied by many of the increasingly biophysical techniques that were being applied to other channels. As described here, much of the evolution of the field, from electrical coupling to channel structure-function, has appeared in the pages of the Journal of General Physiology.
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Affiliation(s)
- Andrew L Harris
- Department of Pharmacology, Physiology, and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ
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17
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Youssefian L, Vahidnezhad H, Saeidian AH, Mahmoudi H, Karamzadeh R, Kariminejad A, Huang J, Li L, Jannace TF, Fortina P, Zeinali S, White TW, Uitto J. A novel autosomal recessive GJB2-associated disorder: Ichthyosis follicularis, bilateral severe sensorineural hearing loss, and punctate palmoplantar keratoderma. Hum Mutat 2018; 40:217-229. [PMID: 30431684 DOI: 10.1002/humu.23686] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 10/26/2018] [Accepted: 10/30/2018] [Indexed: 11/07/2022]
Abstract
Ichthyosis follicularis, a distinct cutaneous entity reported in combination with atrichia, and photophobia has been associated with mutations in MBTPS2. We sought the genetic cause of a novel syndrome of ichthyosis follicularis, bilateral severe sensorineural hearing loss and punctate palmoplantar keratoderma in two families. We performed whole exome sequencing on three patients from two families. The pathogenicity and consequences of mutations were studied in the Xenopus oocyte expression system and by molecular modeling analysis. Compound heterozygous mutations in the GJB2 gene were discovered: a pathogenic c.526A>G; p.Asn176Asp, and a common frameshift mutation, c.35delG; p.Gly12Valfs*2. The p.Asn176Asp missense mutation was demonstrated to significantly reduce the cell-cell gap junction channel activity and increase the nonjunctional hemichannel activity in the Xenopus oocyte expression system. Molecular modeling analyses of the mutant Cx26 protein revealed significant changes in the structural characteristics and electrostatic potential of the Cx26, either in hemichannel or gap junction conformation. Thus, association of a new syndrome of an autosomal recessive disorder of ichthyosis follicularis, bilateral severe sensorineural hearing loss and punctate palmoplantar keratoderma with mutations in GJB2, expands the phenotypic spectrum of the GJB2-associated disorders. The findings attest to the complexity of the clinical consequences of different mutations in GJB2.
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Affiliation(s)
- Leila Youssefian
- Department of Dermatology and Cutaneous Biology, Sidney Kimmel Medical College, Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA, USA
- Department of Medical Genetics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
- Genetics, Genomics and Cancer Biology PhD Program, Thomas Jefferson University, Philadelphia, PA, USA
| | - Hassan Vahidnezhad
- Department of Dermatology and Cutaneous Biology, Sidney Kimmel Medical College, Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA, USA
- Biotechnology Research Center, Department of Molecular Medicine, Pasteur Institute of Iran, Tehran, Iran
| | - Amir Hossein Saeidian
- Department of Dermatology and Cutaneous Biology, Sidney Kimmel Medical College, Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA, USA
- Genetics, Genomics and Cancer Biology PhD Program, Thomas Jefferson University, Philadelphia, PA, USA
| | - Hamidreza Mahmoudi
- Department of Dermatology, Razi Hospital, Tehran University of Medical Sciences, Tehran, Iran
| | - Razieh Karamzadeh
- Department of Stem Cells and Developmental Biology, Cell Science Research Center, Royan Institute for Stem Cell Biology and Technology, ACECR, Tehran, Iran
| | | | - Jianhe Huang
- Department of Dermatology and Cutaneous Biology, Sidney Kimmel Medical College, Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA, USA
| | - Leping Li
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA
| | - Thomas F Jannace
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA
| | - Paolo Fortina
- Department of Cancer Biology, Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA
- Department of Molecular Medicine, Sapienza University, Rome, Italy
| | - Sirous Zeinali
- Biotechnology Research Center, Department of Molecular Medicine, Pasteur Institute of Iran, Tehran, Iran
| | - Thomas W White
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA
| | - Jouni Uitto
- Department of Dermatology and Cutaneous Biology, Sidney Kimmel Medical College, Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA, USA
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18
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Faber DS, Pereda AE. Two Forms of Electrical Transmission Between Neurons. Front Mol Neurosci 2018; 11:427. [PMID: 30534051 PMCID: PMC6276723 DOI: 10.3389/fnmol.2018.00427] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Accepted: 11/05/2018] [Indexed: 12/30/2022] Open
Abstract
Electrical signaling is a cardinal feature of the nervous system and endows it with the capability of quickly reacting to changes in the environment. Although synaptic communication between nerve cells is perceived to be mainly chemically mediated, electrical synaptic interactions also occur. Two different strategies are responsible for electrical communication between neurons. One is the consequence of low resistance intercellular pathways, called "gap junctions", for the spread of electrical currents between the interior of two cells. The second occurs in the absence of cell-to-cell contacts and is a consequence of the extracellular electrical fields generated by the electrical activity of neurons. Here, we place present notions about electrical transmission in a historical perspective and contrast the contributions of the two different forms of electrical communication to brain function.
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Affiliation(s)
- Donald S. Faber
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, NY, United States
- Marine Biological Laboratory, Woods Hole, MA, United States
| | - Alberto E. Pereda
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, NY, United States
- Marine Biological Laboratory, Woods Hole, MA, United States
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19
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Fasciani I, Pluta P, González-Nieto D, Martínez-Montero P, Molano J, Paíno CL, Millet O, Barrio LC. Directional coupling of oligodendrocyte connexin-47 and astrocyte connexin-43 gap junctions. Glia 2018; 66:2340-2352. [PMID: 30144323 DOI: 10.1002/glia.23471] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Revised: 05/21/2018] [Accepted: 05/22/2018] [Indexed: 12/15/2022]
Abstract
Intercellular communication via gap junction channels between oligodendrocytes and between astrocytes as well as between these cell types is essential to maintain the integrity of myelin in the central nervous system. Oligodendrocyte gap junction connexin-47 (Cx47) is a key element in this crosstalk and indeed, mutations in human Cx47 cause severe myelin disorders. However, the permeation properties of channels of Cx47 alone and in heterotypic combination with astrocyte Cx43 remain unclear. We show here that Cx47 contains three extra residues at 5' amino-terminus that play a critical role in the channel pore structure and account for relative low ionic conductivity, cationic permselectivity and voltage-gating properties of oligodendrocyte-oligodendrocyte Cx47 channels. Regarding oligodendrocyte-astrocyte coupling, heterotypic channels formed by Cx47 with Cx43 exhibit ionic and chemical rectification, which creates a directional diffusion barrier for the movement of ions and larger negatively charged molecules from cells expressing Cx47 to those with Cx43. The restrictive permeability of Cx47 channels and the diffusion barrier of Cx47-Cx43 channels was abolished by a mutation associated with leukodystrophy, the Cx47P90S, suggesting a novel pathogenic mechanism underlying myelin disorders that involves alterations in the panglial permeation.
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Affiliation(s)
- Ilaria Fasciani
- Unit of Experimental Neurology and Neurobiology, "Ramón y Cajal" Hospital-IRYCIS, Carretera de Colmenar km 9, Madrid, 28034, Spain
| | - Paula Pluta
- Structural Biology Unit of CIC bioGUNE, Bizkaia Technology Park, Building 800, Derio, 48160, Spain
| | - Daniel González-Nieto
- Biomedical Research Networking Center in Bioengineering Biomaterials and Nanomedicine (CIBER-BBN), 28040 Madrid, and Center for Biomedical Technology, Universidad Politécnica de Madrid, Campus de Montegancedo S/N, Pozuelo de Alarcón, Madrid, 28223, Spain
| | - Paloma Martínez-Montero
- Unit of Molecular Genetics-INGEMM, Hospital "La Paz"-IDIPAZ, Paseo de la Castellana 261, 28046-Madrid, Spain
| | - Jesús Molano
- Unit of Molecular Genetics-INGEMM, Hospital "La Paz"-IDIPAZ, Paseo de la Castellana 261, 28046-Madrid, Spain
| | - Carlos L Paíno
- Unit of Experimental Neurology and Neurobiology, "Ramón y Cajal" Hospital-IRYCIS, Carretera de Colmenar km 9, Madrid, 28034, Spain
| | - Oscar Millet
- Structural Biology Unit of CIC bioGUNE, Bizkaia Technology Park, Building 800, Derio, 48160, Spain
| | - Luis C Barrio
- Unit of Experimental Neurology and Neurobiology, "Ramón y Cajal" Hospital-IRYCIS, Carretera de Colmenar km 9, Madrid, 28034, Spain
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20
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Jabeen S, Thirumalai V. The interplay between electrical and chemical synaptogenesis. J Neurophysiol 2018; 120:1914-1922. [PMID: 30067121 PMCID: PMC6230774 DOI: 10.1152/jn.00398.2018] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Neurons communicate with each other via electrical or chemical synaptic connections. The pattern and strength of connections between neurons are critical for generating appropriate output. What mechanisms govern the formation of electrical and/or chemical synapses between two neurons? Recent studies indicate that common molecular players could regulate the formation of both of these classes of synapses. In addition, electrical and chemical synapses can mutually coregulate each other’s formation. Electrical activity, generated spontaneously by the nervous system or initiated from sensory experience, plays an important role in this process, leading to the selection of appropriate connections and the elimination of inappropriate ones. In this review, we discuss recent studies that shed light on the formation and developmental interactions of chemical and electrical synapses.
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Affiliation(s)
- Shaista Jabeen
- National Centre for Biological Sciences, Tata Institute for Fundamental Research , Bangalore , India.,Manipal Academy of Higher Education, Madhav Nagar, Manipal , India
| | - Vatsala Thirumalai
- National Centre for Biological Sciences, Tata Institute for Fundamental Research , Bangalore , India
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21
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Hu Z, Riquelme MA, Wang B, Bugay V, Brenner R, Gu S, Jiang JX. Cataract-associated connexin 46 mutation alters its interaction with calmodulin and function of hemichannels. J Biol Chem 2018; 293:2573-2585. [PMID: 29298900 PMCID: PMC5818178 DOI: 10.1074/jbc.ra117.001348] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Revised: 12/29/2017] [Indexed: 11/06/2022] Open
Abstract
Connexin channels help maintain eye lens homeostasis and transparency. The G143R missense substitution in connexin (Cx) 46 is associated with congenital Coppock cataracts; however, the underlying molecular mechanism is largely unknown. Here, we report that compared with WT Cx46, the G143R substitution abolishes hemichannel conductance in Xenopus oocytes and in HeLa cells. Moreover, this substitution is dominant-negative and inhibits conductance of WT Cx46. CD analysis indicated that the substitution greatly reduces the α-helical structure of the intracellular Cx46 loop domain. Protein pulldown assays and isothermal titration calorimetry revealed that this Cx46 domain directly interacts with calmodulin (CaM) in a Ca2+-dependent fashion, an observation confirmed by immunofluorescent co-localization of Cx46 with CaM. Interestingly, the G143R substitution enhanced the Cx46-CaM interaction and attenuated its abolishment by Ca2+ depletion. Moreover, Cx46 increased dye influx, and the G143R substitution augmented this effect. Inhibition of Ca2+-mediated CaM activation blocked hemichannel permeability. The membrane potential plays a crucial role in Cx46 membrane permeability. We found that the activity of hemichannels is detectable under rest and hyperpolarization conditions but is eliminated with depolarization. These results suggested that the G143R substitution impairs voltage-dependent electrical conductance and alters membrane permeability mediated by Cx46 hemichannels. The latter likely is caused by the substitution-induced structural changes of the intracellular loop domain associated with the increased interaction with CaM and reduced Ca2+ sensitivity. The data suggest that the G143R-induced enhancement of the CaM-Cx46 interaction results in altered hemichannel activities and might be related to cataract formation.
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Affiliation(s)
- Zhengping Hu
- From the Departments of Biochemistry and Structural Biology and
- the Second Xiangya Hospital, Central South University, Changsha 410011, China
| | | | - Bin Wang
- Cellular and Integrative Physiology, University of Texas Health Science Center, San Antonio, Texas 78229 and
| | - Vladislav Bugay
- Cellular and Integrative Physiology, University of Texas Health Science Center, San Antonio, Texas 78229 and
| | - Robert Brenner
- Cellular and Integrative Physiology, University of Texas Health Science Center, San Antonio, Texas 78229 and
| | - Sumin Gu
- From the Departments of Biochemistry and Structural Biology and
| | - Jean X Jiang
- From the Departments of Biochemistry and Structural Biology and
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22
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Bai D, Yue B, Aoyama H. Crucial motifs and residues in the extracellular loops influence the formation and specificity of connexin docking. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:9-21. [PMID: 28693896 DOI: 10.1016/j.bbamem.2017.07.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 06/25/2017] [Accepted: 07/03/2017] [Indexed: 12/19/2022]
Abstract
Most of the early studies on gap junction (GJ) channel function and docking compatibility were on rodent connexins, while recent research on GJ channels gradually shifted from rodent to human connexins largely due to the fact that mutations in many human connexin genes are found to associate with inherited human diseases. The studies on human connexins have revealed some key differences from those found in rodents, calling for a comprehensive characterization of human GJ channels. Functional studies revealed that docking and formation of functional GJ channels between two hemichannels are possible only between docking-compatible connexins. Two groups of docking-compatible rodent connexins have been identified. Compatibility is believed to be due to their amino acid residue differences at the extracellular loop domains (E1 and E2). Sequence alignment of the E1 and E2 domains of all connexins known to make GJs revealed that they are highly conserved and show high sequence identity with human Cx26, which is the only connexin with near atomic resolution GJ structure. We hypothesize that different connexins have a similar structure as that of Cx26 at the E1 and E2 domains and use the corresponding residues in their E1 and E2 domains for docking. Based on the Cx26 GJ structure and sequence analysis of well-studied connexins, we propose that the E1-E1 docking interactions are staggered with each E1 interacting with two E1s on the docked connexon. The putative E1 docking residues are conserved in both docking-compatible and -incompatible connexins, indicating that E1 does not likely serve a role in docking compatibility. However, in the case of E2-E2 docking interactions, the putative docking residues are only conserved within the docking-compatible connexins, suggesting the E2 is likely to serve the function of docking compatibility. Docking compatibility studies on human connexins have attracted a lot of attention due to the fact that putative docking residues are mutational hotspots for several connexin-linked human diseases. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.
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Affiliation(s)
- Donglin Bai
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
| | - Benny Yue
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Hiroshi Aoyama
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
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23
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Komarova YA, Kruse K, Mehta D, Malik AB. Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability. Circ Res 2017; 120:179-206. [PMID: 28057793 DOI: 10.1161/circresaha.116.306534] [Citation(s) in RCA: 303] [Impact Index Per Article: 43.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2016] [Revised: 10/04/2016] [Accepted: 10/06/2016] [Indexed: 12/31/2022]
Abstract
The monolayer of endothelial cells lining the vessel wall forms a semipermeable barrier (in all tissue except the relatively impermeable blood-brain and inner retinal barriers) that regulates tissue-fluid homeostasis, transport of nutrients, and migration of blood cells across the barrier. Permeability of the endothelial barrier is primarily regulated by a protein complex called adherens junctions. Adherens junctions are not static structures; they are continuously remodeled in response to mechanical and chemical cues in both physiological and pathological settings. Here, we discuss recent insights into the post-translational modifications of junctional proteins and signaling pathways regulating plasticity of adherens junctions and endothelial permeability. We also discuss in the context of what is already known and newly defined signaling pathways that mediate endothelial barrier leakiness (hyperpermeability) that are important in the pathogenesis of cardiovascular and lung diseases and vascular inflammation.
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Affiliation(s)
- Yulia A Komarova
- From the Department of Pharmacology and the Center for Lung and Vascular Biology, University of Illinois College of Medicine, Chicago
| | - Kevin Kruse
- From the Department of Pharmacology and the Center for Lung and Vascular Biology, University of Illinois College of Medicine, Chicago
| | - Dolly Mehta
- From the Department of Pharmacology and the Center for Lung and Vascular Biology, University of Illinois College of Medicine, Chicago
| | - Asrar B Malik
- From the Department of Pharmacology and the Center for Lung and Vascular Biology, University of Illinois College of Medicine, Chicago.
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24
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Bargiello TA, Oh S, Tang Q, Bargiello NK, Dowd TL, Kwon T. Gating of Connexin Channels by transjunctional-voltage: Conformations and models of open and closed states. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:22-39. [PMID: 28476631 DOI: 10.1016/j.bbamem.2017.04.028] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Revised: 04/26/2017] [Accepted: 04/28/2017] [Indexed: 11/18/2022]
Abstract
Voltage is an important physiologic regulator of channels formed by the connexin gene family. Connexins are unique among ion channels in that both plasma membrane inserted hemichannels (undocked hemichannels) and intercellular channels (aggregates of which form gap junctions) have important physiological roles. The hemichannel is the fundamental unit of gap junction voltage-gating. Each hemichannel displays two distinct voltage-gating mechanisms that are primarily sensitive to a voltage gradient formed along the length of the channel pore (the transjunctional voltage) rather than sensitivity to the absolute membrane potential (Vm or Vi-o). These transjunctional voltage dependent processes have been termed Vj- or fast-gating and loop- or slow-gating. Understanding the mechanism of voltage-gating, defined as the sequence of voltage-driven transitions that connect open and closed states, first and foremost requires atomic resolution models of the end states. Although ion channels formed by connexins were among the first to be characterized structurally by electron microscopy and x-ray diffraction in the early 1980's, subsequent progress has been slow. Much of the current understanding of the structure-function relations of connexin channels is based on two crystal structures of Cx26 gap junction channels. Refinement of crystal structure by all-atom molecular dynamics and incorporation of charge changing protein modifications has resulted in an atomic model of the open state that arguably corresponds to the physiologic open state. Obtaining validated atomic models of voltage-dependent closed states is more challenging, as there are currently no methods to solve protein structure while a stable voltage gradient is applied across the length of an oriented channel. It is widely believed that the best approach to solve the atomic structure of a voltage-gated closed ion channel is to apply different but complementary experimental and computational methods and to use the resulting information to derive a consensus atomic structure that is then subjected to rigorous validation. In this paper, we summarize our efforts to obtain and validate atomic models of the open and voltage-driven closed states of undocked connexin hemichannels. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.
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Affiliation(s)
- Thaddeus A Bargiello
- Dominic P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, United States.
| | - Seunghoon Oh
- Department of Physiology, College of Medicine, Dankook University, Cheonan, Republic of Korea
| | - Qingxiu Tang
- Dominic P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, United States
| | - Nicholas K Bargiello
- Dominic P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, United States
| | - Terry L Dowd
- Department of Chemistry, Brooklyn College, Brooklyn, NY 11210, United States
| | - Taekyung Kwon
- Dominic P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, United States
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25
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Skerrett IM, Williams JB. A structural and functional comparison of gap junction channels composed of connexins and innexins. Dev Neurobiol 2017; 77:522-547. [PMID: 27582044 PMCID: PMC5412853 DOI: 10.1002/dneu.22447] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 08/12/2016] [Accepted: 08/30/2016] [Indexed: 02/03/2023]
Abstract
Methods such as electron microscopy and electrophysiology led to the understanding that gap junctions were dense arrays of channels connecting the intracellular environments within almost all animal tissues. The characteristics of gap junctions were remarkably similar in preparations from phylogenetically diverse animals such as cnidarians and chordates. Although few studies directly compared them, minor differences were noted between gap junctions of vertebrates and invertebrates. For instance, a slightly wider gap was noted between cells of invertebrates and the spacing between invertebrate channels was generally greater. Connexins were identified as the structural component of vertebrate junctions in the 1980s and innexins as the structural component of pre-chordate junctions in the 1990s. Despite a lack of similarity in gene sequence, connexins and innexins are remarkably similar. Innexins and connexins have the same membrane topology and form intercellular channels that play a variety of tissue- and temporally specific roles. Both protein types oligomerize to form large aqueous channels that allow the passage of ions and small metabolites and are regulated by factors such as pH, calcium, and voltage. Much more is currently known about the structure, function, and structure-function relationships of connexins. However, the innexin field is expanding. Greater knowledge of innexin channels will permit more detailed comparisons with their connexin-based counterparts, and provide insight into the ubiquitous yet specific roles of gap junctions. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 522-547, 2017.
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Affiliation(s)
- I Martha Skerrett
- Biology Department, SUNY Buffalo State, 1300 Elmwood Ave, Buffalo, New York, 14222
| | - Jamal B Williams
- Biology Department, SUNY Buffalo State, 1300 Elmwood Ave, Buffalo, New York, 14222
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Nielsen BS, Hansen DB, Ransom BR, Nielsen MS, MacAulay N. Connexin Hemichannels in Astrocytes: An Assessment of Controversies Regarding Their Functional Characteristics. Neurochem Res 2017; 42:2537-2550. [DOI: 10.1007/s11064-017-2243-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 03/17/2017] [Accepted: 03/17/2017] [Indexed: 12/19/2022]
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Connexin26 Mutations Causing Palmoplantar Keratoderma and Deafness Interact with Connexin43, Modifying Gap Junction and Hemichannel Properties. J Invest Dermatol 2016; 136:225-235. [PMID: 26763442 PMCID: PMC4731051 DOI: 10.1038/jid.2015.389] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Revised: 09/03/2015] [Accepted: 09/21/2015] [Indexed: 12/23/2022]
Abstract
Mutations in GJB2 (Cx26) cause either deafness, or deafness associated with skin diseases. That different disorders can be caused by distinct mutations within the same gene suggests that unique channel activities are influenced by each class of mutation. We have examined the functional characteristics of two human mutations, Cx26-H73R and Cx26-S183F, causing palmoplantar keratoderma (PPK) and deafness. Both failed to form gap junction channels or hemichannels when expressed alone. Co-expression of the mutants with wild-type Cx43 showed a trans-dominant inhibition of Cx43 gap junction channels, without reductions in Cx43 protein synthesis. In addition, the presence of mutant Cx26 shifted Cx43 channel gating and kinetics towards a more Cx26-like behavior. Co-immunoprecipitation showed Cx43 being pulled down more efficiently with mutant Cx26, than wild-type, confirming the enhanced formation of heteromeric connexons. Finally, the formation of heteromeric connexons resulted in significantly increased Cx43 hemichannel activity in the presence of Cx26 mutants. These findings suggest a common mechanism whereby Cx26 mutations causing PPK and deafness trans-dominantly influence multiple functions of wild-type Cx43. They also implicate a role for aberrant hemichannel activity in the pathogenesis of PPK, and further highlight an emerging role for Cx43 in genetic skin diseases.
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Zolnik TA, Connors BW. Electrical synapses and the development of inhibitory circuits in the thalamus. J Physiol 2016; 594:2579-92. [PMID: 26864476 PMCID: PMC4865577 DOI: 10.1113/jp271880] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Accepted: 02/05/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The thalamus is a structure critical for information processing and transfer to the cortex. Thalamic reticular neurons are inhibitory cells interconnected by electrical synapses, most of which require the gap junction protein connexin36 (Cx36). We investigated whether electrical synapses play a role in the maturation of thalamic networks by studying neurons in mice with and without Cx36. When Cx36 was deleted, inhibitory synapses were more numerous, although both divergent inhibitory connectivity and dendritic complexity were reduced. Surprisingly, we observed non-Cx36-dependent electrical synapses with unusual biophysical properties interconnecting some reticular neurons in mice lacking Cx36. The results of the present study suggest an important role for Cx36-dependent electrical synapses in the development of thalamic circuits. ABSTRACT Neurons within the mature thalamic reticular nucleus (TRN) powerfully inhibit ventrobasal (VB) thalamic relay neurons via GABAergic synapses. TRN neurons are also coupled to one another by electrical synapses that depend strongly on the gap junction protein connexin36 (Cx36). Electrical synapses in the TRN precede the postnatal development of TRN-to-VB inhibition. We investigated how the deletion of Cx36 affects the maturation of TRN and VB neurons, electrical coupling and GABAergic synapses by studying wild-type (WT) and Cx36 knockout (KO) mice. The incidence and strength of electrical coupling in TRN was sharply reduced, but not abolished, in KO mice. Surprisingly, electrical synapses between Cx36-KO neurons had faster voltage-dependent decay kinetics and conductance asymmetry (rectification) than did electrical synapses between WT neurons. The properties of TRN-mediated inhibition in VB also depended on the Cx36 genotype. Deletion of Cx36 increased the frequency and shifted the amplitude distributions of miniature IPSCs, whereas the paired-pulse ratio of evoked IPSCs was unaffected, suggesting that the absence of Cx36 led to an increase in GABAergic synaptic contacts. VB neurons from Cx36-KO mice also tended to have simpler dendritic trees and fewer divergent inputs from the TRN compared to WT cells. The findings obtained in the present study suggest that proper development of thalamic inhibitory circuitry, neuronal morphology, TRN cell function and electrical coupling requires Cx36. In the absence of Cx36, some TRN neurons express asymmetric electrical coupling mediated by other unidentified connexin subtypes.
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Affiliation(s)
- Timothy A Zolnik
- Department of Neuroscience, Division of Biology & Medicine, Brown University, Providence, RI, USA
- Charité Universitätsmedizin Berlin, Berlin, Germany
| | - Barry W Connors
- Department of Neuroscience, Division of Biology & Medicine, Brown University, Providence, RI, USA
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Pinto BI, García IE, Pupo A, Retamal MA, Martínez AD, Latorre R, González C. Charged Residues at the First Transmembrane Region Contribute to the Voltage Dependence of the Slow Gate of Connexins. J Biol Chem 2016; 291:15740-52. [PMID: 27143357 DOI: 10.1074/jbc.m115.709402] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Indexed: 12/17/2022] Open
Abstract
Connexins (Cxs) are a family of membrane-spanning proteins that form gap junction channels and hemichannels. Connexin-based channels exhibit two distinct voltage-dependent gating mechanisms termed slow and fast gating. Residues located at the C terminus of the first transmembrane segment (TM-1) are important structural components of the slow gate. Here, we determined the role of the charged residues at the end of TM-1 in voltage sensing in Cx26, Cx46, and Cx50. Conductance/voltage curves obtained from tail currents together with kinetics analysis reveal that the fast and slow gates of Cx26 involves the movement of two and four charges across the electric field, respectively. Primary sequence alignment of different Cxs shows the presence of well conserved glutamate residues in the C terminus of TM-1; only Cx26 contains a lysine in that position (lysine 41). Neutralization of lysine 41 in Cx26 increases the voltage dependence of the slow gate. Swapping of lysine 41 with glutamate 42 maintains the voltage dependence. In Cx46, neutralization of negative charges or addition of a positive charge in the Cx26 equivalent region reduced the slow gate voltage dependence. In Cx50, the addition of a glutamate in the same region decreased the voltage dependence, and the neutralization of a negative charge increased it. These results indicate that the charges at the end of TM-1 are part of the slow gate voltage sensor in Cxs. The fact that Cx42, which has no charge in this region, still presents voltage-dependent slow gating suggests that charges still unidentified also contribute to the slow gate voltage sensitivity.
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Affiliation(s)
- Bernardo I Pinto
- From the Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso 2360102 and
| | - Isaac E García
- From the Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso 2360102 and
| | - Amaury Pupo
- From the Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso 2360102 and
| | - Mauricio A Retamal
- the Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo, Santiago 7710162, Chile
| | - Agustín D Martínez
- From the Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso 2360102 and
| | - Ramón Latorre
- From the Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso 2360102 and
| | - Carlos González
- From the Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso 2360102 and
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Watanabe M, Sawada R, Aramaki T, Skerrett IM, Kondo S. The Physiological Characterization of Connexin41.8 and Connexin39.4, Which Are Involved in the Striped Pattern Formation of Zebrafish. J Biol Chem 2016; 291:1053-63. [PMID: 26598520 PMCID: PMC4714190 DOI: 10.1074/jbc.m115.673129] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Revised: 11/02/2015] [Indexed: 11/06/2022] Open
Abstract
The zebrafish has a striped skin pattern on its body, and Connexin41.8 (Cx41.8) and Cx39.4 are involved in striped pattern formation. Mutations in these connexins change the striped pattern to a spot or labyrinth pattern. In this study, we characterized Cx41.8 and Cx39.4 after expression in Xenopus oocytes. In addition, we analyzed Cx41.8 mutants Cx41.8I203F and Cx41.8M7, which caused spot or labyrinth skin patterns, respectively, in transgenic zebrafish. In the electrophysiological analysis, the gap junctions formed by Cx41.8 and Cx39.4 showed distinct sensitivity to transjunctional voltage. Analysis of non-junctional (hemichannel) currents revealed a large voltage-dependent current in Cx39.4-expressing oocytes that was absent in cells expressing Cx41.8. Junctional currents induced by both Cx41.8 and Cx39.4 were reduced by co-expression of Cx41.8I203F and abolished by co-expression of Cx41.8M7. In the transgenic experiment, Cx41.8I203F partially rescued the Cx41.8 null mutant phenotype, whereas Cx41.8M7 failed to rescue the null mutant, and it elicited a more severe phenotype than the Cx41.8 null mutant, as evidenced by a smaller spot pattern. Our results provide evidence that gap junctions formed by Cx41.8 play an important role in stripe/spot patterning and suggest that mutations in Cx41.8 can effect patterning by way of reduced function (I203F) and dominant negative effects (M7). Our results suggest that functional differences in Cx41.8 and Cx39.4 relate to spot or labyrinth mutant phenotypes and also provide evidence that these two connexins interact in vivo and in vitro.
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Affiliation(s)
- Masakatsu Watanabe
- From the Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan,
| | - Risa Sawada
- From the Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Toshihiro Aramaki
- From the Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - I Martha Skerrett
- the Biology Department, Buffalo State College, Buffalo, New York, 14222, and
| | - Shigeru Kondo
- From the Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan, CREST, Japan Science and Technology Agency, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
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Veenstra RD. Establishment of the Dual Whole Cell Recording Patch Clamp Configuration for the Measurement of Gap Junction Conductance. Methods Mol Biol 2016; 1437:213-231. [PMID: 27207298 DOI: 10.1007/978-1-4939-3664-9_16] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The development of the patch clamp technique has enabled investigators to directly measure gap junction conductance between isolated pairs of small cells with resolution to the single channel level. The dual patch clamp recording technique requires specialized equipment and the acquired skill to reliably establish gigaohm seals and the whole cell recording configuration with high efficiency. This chapter describes the equipment needed and methods required to achieve accurate measurement of macroscopic and single gap junction channel conductances. Inherent limitations with the dual whole cell recording technique and methods to correct for series access resistance errors are defined as well as basic procedures to determine the essential electrical parameters necessary to evaluate the accuracy of gap junction conductance measurements using this approach.
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Affiliation(s)
- Richard D Veenstra
- Department of Pharmacology, SUNY Upstate Medical University, 3162 Weiskotten Hall, 766 Irving Ave., Syracuse, NY, 13210, USA.
- Department Cell and Developmental Biology, SUNY Upstate Medical University, 3162 Weiskotten Hall, 766 Irving Ave., Syracuse, NY, 13210, USA.
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32
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Abrams CK, Freidin M. GJB1-associated X-linked Charcot-Marie-Tooth disease, a disorder affecting the central and peripheral nervous systems. Cell Tissue Res 2015; 360:659-73. [PMID: 25370202 DOI: 10.1007/s00441-014-2014-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Accepted: 09/22/2014] [Indexed: 11/24/2022]
Abstract
Charcot-Marie-Tooth disease (CMT) is a group of inherited diseases characterized by exclusive or predominant involvement of the peripheral nervous system. Mutations in GJB1, the gene encoding Connexin 32 (Cx32), a gap-junction channel forming protein, cause the most common X-linked form of CMT, CMT1X. Cx32 is expressed in Schwann cells and oligodendrocytes, the myelinating glia of the peripheral and central nervous systems, respectively. Thus, patients with CMT1X have both central and peripheral nervous system manifestations. Study of the genetics of CMT1X and the phenotypes of patients with this disorder suggest that the peripheral manifestations of CMT1X are likely to be due to loss of function, while in the CNS gain of function may contribute. Mice with targeted ablation of Gjb1 develop a peripheral neuropathy similar to that seen in patients with CMT1X, supporting loss of function as a mechanism for the peripheral manifestations of this disorder. Possible roles for Cx32 include the establishment of a reflexive gap junction pathway in the peripheral and central nervous system and of a panglial syncitium in the central nervous system.
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Affiliation(s)
- Charles K Abrams
- Departments of Neurology and Physiology & Pharmacology, State University of New York, Brooklyn, NY, 11203, USA,
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33
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Sevetson J, Haas JS. Asymmetry and modulation of spike timing in electrically coupled neurons. J Neurophysiol 2015; 113:1743-51. [DOI: 10.1152/jn.00843.2014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Electrical coupling mediates interactions between neurons of the thalamic reticular nucleus (TRN), which play a critical role in regulating thalamocortical and corticothalamic communication by inhibiting thalamic relay cells. Accumulating evidence has shown that asymmetry of electrical synapses is a fundamental and dynamic property, but the effect of asymmetry on coupled networks is unexplored. Recording from patched pairs in rat brain slices, we investigate asymmetry in the subthreshold regime and show that electrical synapses can exert powerful effects on the spike times of coupled neighbors. Electrical synaptic signaling modulates spike timing by 10–20 ms, in an effect that also exhibits asymmetry. Furthermore, we show through modeling that coupling asymmetry expands the set of outputs for pairs of coupled neurons through enhanced regions of synchrony and reversals of spike order. These results highlight the power and specificity of signaling exerted by electrical synapses, which contribute to information flow across the brain.
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Affiliation(s)
- Jessica Sevetson
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania
| | - Julie S. Haas
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania
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34
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Keratitis-ichthyosis-deafness syndrome-associated Cx26 mutants produce nonfunctional gap junctions but hyperactive hemichannels when co-expressed with wild type Cx43. J Invest Dermatol 2015; 135:1338-1347. [PMID: 25625422 PMCID: PMC4801018 DOI: 10.1038/jid.2015.20] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Revised: 01/13/2015] [Accepted: 01/14/2015] [Indexed: 11/09/2022]
Abstract
Mutations in Cx26 gene are found in most cases of human genetic deafness. Some mutations produce syndromic deafness associated with skin disorders, like the Keratitis-Ichthyosis-Deafness syndrome (KID). Because in the human skin connexin 26 (Cx26) is co-expressed with other connexins, like Cx43 and Cx30, and as the KID syndrome is inherited as autosomal dominant condition, it is possible that KID mutations change the way Cx26 interacts with other co-expressed connexins. Indeed, some Cx26 syndromic mutations showed gap junction dominant negative effect when co-expressed with wild-type connexins, including Cx26 and Cx43. The nature of these interactions and the consequences on hemichannels and gap junction channel (GJC) functions remain unknown. In this study, we demonstrate that syndromic mutations, at the N terminus segment of Cx26, change connexin oligomerization compatibility, allowing aberrant interactions with Cx43. Strikingly, heteromeric oligomer formed by Cx43/Cx26 (syndromic mutants) shows exacerbated hemichannel activity but nonfunctional GJCs; this also occurs for those Cx26 KID mutants that do not show functional homomeric hemichannels. Heterologous expression of these hyperactive heteromeric hemichannels increases cell membrane permeability, favoring ATP release and Ca(2+) overload. The functional paradox produced by oligomerization of Cx43 and Cx26 KID mutants could underlie the severe syndromic phenotype in human skin.
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35
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Abstract
Voltage is an important parameter that regulates the conductance of both intercellular and plasma membrane channels (undocked hemichannels) formed by the 21 members of the mammalian connexin gene family. Connexin channels display two forms of voltage-dependence, rectification of ionic currents and voltage-dependent gating. Ionic rectification results either from asymmetries in the distribution of fixed charges due to heterotypic pairing of different hemichannels, or by channel block, arising from differences in the concentrations of divalent cations on opposite sides of the junctional plaque. This rectification likely underpins the electrical rectification observed in some electrical synapses. Both intercellular and undocked hemichannels also display two distinct forms of voltage-dependent gating, termed Vj (fast)-gating and loop (slow)-gating. This review summarizes our current understanding of the molecular determinants and mechanisms underlying these conformational changes derived from experimental, molecular-genetic, structural, and computational approaches.
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Affiliation(s)
- Seunghoon Oh
- Department of Physiology, College of Medicine, Dankook University, Cheonan, Korea
| | - Thaddeus A Bargiello
- Dominic P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, USA.
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36
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Palacios-Prado N, Huetteroth W, Pereda AE. Hemichannel composition and electrical synaptic transmission: molecular diversity and its implications for electrical rectification. Front Cell Neurosci 2014; 8:324. [PMID: 25360082 PMCID: PMC4197764 DOI: 10.3389/fncel.2014.00324] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Accepted: 09/26/2014] [Indexed: 11/29/2022] Open
Abstract
Unapposed hemichannels (HCs) formed by hexamers of gap junction proteins are now known to be involved in various cellular processes under both physiological and pathological conditions. On the other hand, less is known regarding how differences in the molecular composition of HCs impact electrical synaptic transmission between neurons when they form intercellular heterotypic gap junctions (GJs). Here we review data indicating that molecular differences between apposed HCs at electrical synapses are generally associated with rectification of electrical transmission. Furthermore, this association has been observed at both innexin and connexin (Cx) based electrical synapses. We discuss the possible molecular mechanisms underlying electrical rectification, as well as the potential contribution of intracellular soluble factors to this phenomenon. We conclude that asymmetries in molecular composition and sensitivity to cellular factors of each contributing hemichannel can profoundly influence the transmission of electrical signals, endowing electrical synapses with more complex functional properties.
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Affiliation(s)
- Nicolás Palacios-Prado
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine Bronx, NY, USA ; Marine Biological Laboratory, Woods Hole Massachusetts, MA, USA
| | - Wolf Huetteroth
- Marine Biological Laboratory, Woods Hole Massachusetts, MA, USA ; Department of Neurobiology, University of Konstanz Konstanz, Germany
| | - Alberto E Pereda
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine Bronx, NY, USA ; Marine Biological Laboratory, Woods Hole Massachusetts, MA, USA
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37
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Levit NA, Sellitto C, Wang HZ, Li L, Srinivas M, Brink PR, White TW. Aberrant connexin26 hemichannels underlying keratitis-ichthyosis-deafness syndrome are potently inhibited by mefloquine. J Invest Dermatol 2014; 135:1033-1042. [PMID: 25229253 PMCID: PMC4363291 DOI: 10.1038/jid.2014.408] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 08/02/2014] [Accepted: 09/04/2014] [Indexed: 11/27/2022]
Abstract
Keratitis-ichthyosis-deafness (KID) syndrome is an ectodermal dysplasia caused by dominant mutations of connexin26 (Cx26). Loss of Cx26 function causes non-syndromic sensorineural deafness, without consequence in the epidermis. Functional analyses have revealed that a majority of KID-causing mutations confer a novel expansion of hemichannel activity, mediated by connexin channels in a non-junctional configuration. Inappropriate Cx26 hemichannel opening is hypothesized to compromise keratinocyte integrity and epidermal homeostasis. Pharmacological modulators of Cx26 are needed to assess the pathomechanistic involvement of hemichannels in the development of hyperkeratosis in KID syndrome. We have used electrophysiological assays to evaluate small molecule analogs of quinine for suppressive effects on aberrant hemichannel currents elicited by KID mutations. Here, we show that mefloquine inhibits several mutant hemichannel forms implicated in KID syndrome when expressed in Xenopus laevis oocytes (IC50≈16µM), using an extracellular divalent cation, zinc (Zn++), as a non-specific positive control for comparison (IC50≈3µM). Furthermore, we used freshly isolated transgenic keratinocytes to show that micromolar concentrations of mefloquine attenuated increased macroscopic membrane currents in primary mouse keratinocytes expressing human Cx26-G45E, a mutation causing a lethal form of KID syndrome.
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Affiliation(s)
- Noah A Levit
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, USA
| | - Caterina Sellitto
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, USA
| | - Hong-Zhan Wang
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, USA
| | - Leping Li
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, USA
| | - Miduturu Srinivas
- Department of Biological and Vision Sciences, SUNY College of Optometry, New York, USA
| | - Peter R Brink
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, USA
| | - Thomas W White
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, USA.
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Pizarro-Delgado J, Fasciani I, Temperan A, Romero M, González-Nieto D, Alonso-Magdalena P, Nualart-Marti A, Estil'les E, Paul DL, Martín-del-Río R, Montanya E, Solsona C, Nadal A, Barrio LC, Tamarit-Rodríguez J. Inhibition of connexin 36 hemichannels by glucose contributes to the stimulation of insulin secretion. Am J Physiol Endocrinol Metab 2014; 306:E1354-66. [PMID: 24735890 DOI: 10.1152/ajpendo.00358.2013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The existence of functional connexin36 (Cx36) hemichannels in β-cells was investigated in pancreatic islets of rat and wild-type (Cx36(+/+)), monoallelic (Cx36(+/-)), and biallelic (Cx36(-/-)) knockout mice. Hemichannel opening by KCl depolarization was studied by measuring ATP release and changes of intracellular ATP (ADP). Cx36(+/+) islets lost ATP after depolarization with 70 mM KCl at 5 mM glucose; ATP loss was prevented by 8 and 20 mM glucose or 50 μM mefloquine (connexin inhibitor). ATP content was higher in Cx36(-/-) than Cx36(+/+) islets and was not decreased by KCl depolarization; Cx36(+/-) islets showed values between that of control and homozygous islets. Five minimolar extracellular ATP increased ATP content and ATP/ADP ratio and induced a biphasic insulin secretion in depolarized Cx36(+/+) and Cx36(+/-) but not Cx36(-/-) islets. Cx36 hemichannels expressed in oocytes opened upon depolarization of membrane potential, and their activation was inhibited by mefloquine and glucose (IC₅₀ ∼8 mM). It is postulated that glucose-induced inhibition of Cx36 hemichannels in islet β-cells might avoid depolarization-induced ATP loss, allowing an optimum increase of the ATP/ADP ratio by sugar metabolism and a biphasic stimulation of insulin secretion. Gradual suppression of glucose-induced insulin release in Cx36(+/-) and Cx36(-/-) islets confirms that Cx36 gap junction channels are necessary for a full secretory stimulation and might account for the glucose intolerance observed in mice with defective Cx36 expression. Mefloquine targeting of Cx36 on both gap junctions and hemichannels also suppresses glucose-stimulated secretion. By contrast, glucose stimulation of insulin secretion requires Cx36 hemichannels' closure but keeping gap junction channels opened.
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Affiliation(s)
| | - Ilaria Fasciani
- Research Department, "Ramón y Cajal" Hospital-IRYCIS, Madrid, Spain
| | - Ana Temperan
- Research Department, "Ramón y Cajal" Hospital-IRYCIS, Madrid, Spain
| | - María Romero
- Research Department, "Ramón y Cajal" Hospital-IRYCIS, Madrid, Spain
| | | | - Paloma Alonso-Magdalena
- Institute of Bioengineering and CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Miguel Hernández University, Elche, Spain
| | - Anna Nualart-Marti
- Department of Pathology and Experimental Therapeutics, Faculty of Medicine - Campus Bellvitge, University of Barcelona, Hospitalet del Llobregat, Barcelona, Spain; IDIBELL, Institut d'Investigació Biomèdica de Bellvitge, Hospitalet del Llobregat, Barcelona, Spain
| | - Elisabet Estil'les
- CIBERDEM, Barcelona, Spain; Department of Clinical Sciences, University of Barcelona, Feixa Llarga s/n, L'Hospitalet de Llobregat, Barcelona, Spain; and
| | - David L Paul
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts
| | | | - Eduard Montanya
- CIBERDEM, Barcelona, Spain; Department of Clinical Sciences, University of Barcelona, Feixa Llarga s/n, L'Hospitalet de Llobregat, Barcelona, Spain; and Endocrine Unit, Hospital Universitari Bellvitge-IDIBELL, Barcelona, Spain
| | - Carles Solsona
- Department of Pathology and Experimental Therapeutics, Faculty of Medicine - Campus Bellvitge, University of Barcelona, Hospitalet del Llobregat, Barcelona, Spain; IDIBELL, Institut d'Investigació Biomèdica de Bellvitge, Hospitalet del Llobregat, Barcelona, Spain
| | - Angel Nadal
- Institute of Bioengineering and CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Miguel Hernández University, Elche, Spain
| | | | - J Tamarit-Rodríguez
- Biochemistry Department, Medical School, Complutense University, Madrid, Spain;
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39
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Extracellular domains play different roles in gap junction formation and docking compatibility. Biochem J 2014; 458:1-10. [PMID: 24438327 DOI: 10.1042/bj20131162] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
GJ (gap junction) channels mediate direct intercellular communication and play an important role in many physiological processes. Six connexins oligomerize to form a hemichannel and two hemichannels dock together end-to-end to form a GJ channel. Connexin extracellular domains (E1 and E2) have been shown to be important for the docking, but the molecular mechanisms behind the docking and formation of GJ channels are not clear. Recent developments in atomic GJ structure and functional studies on a series of connexin mutants revealed that E1 and E2 are likely to play different roles in the docking. Non-covalent interactions at the docking interface, including hydrogen bonds, are predicted to form between interdocked extracellular domains. Protein sequence alignment analysis on the docking compatible/incompatible connexins indicate that the E1 domain is important for the formation of the GJ channel and the E2 domain is important in the docking compatibility in heterotypic channels. Interestingly, the hydrogen-bond forming or equivalent residues in both E1 and E2 domains are mutational hot spots for connexin-linked human diseases. Understanding the molecular mechanisms of GJ docking can assist us to develop novel strategies in rescuing the disease-linked connexin mutants.
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40
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Electrical synapses and their functional interactions with chemical synapses. Nat Rev Neurosci 2014; 15:250-63. [PMID: 24619342 DOI: 10.1038/nrn3708] [Citation(s) in RCA: 308] [Impact Index Per Article: 30.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Brain function relies on the ability of neurons to communicate with each other. Interneuronal communication primarily takes place at synapses, where information from one neuron is rapidly conveyed to a second neuron. There are two main modalities of synaptic transmission: chemical and electrical. Far from functioning independently and serving unrelated functions, mounting evidence indicates that these two modalities of synaptic transmission closely interact, both during development and in the adult brain. Rather than conceiving synaptic transmission as either chemical or electrical, this article emphasizes the notion that synaptic transmission is both chemical and electrical, and that interactions between these two forms of interneuronal communication might be required for normal brain development and function.
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41
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Patel D, Zhang X, Veenstra RD. Connexin hemichannel and pannexin channel electrophysiology: how do they differ? FEBS Lett 2014; 588:1372-8. [PMID: 24434538 DOI: 10.1016/j.febslet.2013.12.023] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Revised: 12/20/2013] [Accepted: 12/30/2013] [Indexed: 12/21/2022]
Abstract
Connexin hemichannels are postulated to form a cell permeabilization pore for the uptake of fluorescent dyes and release of cellular ATP. Connexin hemichannel activity is enhanced by low external [Ca(2+)]o, membrane depolarization, metabolic inhibition, and some disease-causing gain-of-function connexin mutations. This paper briefly reviews the electrophysiological channel conductance, permeability, and pharmacology properties of connexin hemichannels, pannexin 1 channels, and purinergic P2X7 receptor channels as studied in exogenous expression systems including Xenopus oocytes and mammalian cell lines such as HEK293 cells. Overlapping pharmacological inhibitory and channel conductance and permeability profiles makes distinguishing between these channel types sometimes difficult. Selective pharmacology for Cx43 hemichannels (Gap19 peptide), probenecid or FD&C Blue #1 (Brilliant Blue FCF, BB FCF) for Panx1, and A740003, A438079, or oxidized ATP (oATP) for P2X7 channels may be the best way to distinguish between these three cell permeabilizing channel types. Endogenous connexin, pannexin, and P2X7 expression should be considered when performing exogenous cellular expression channel studies. Cell pair electrophysiological assays permit the relative assessment of the connexin hemichannel/gap junction channel ratio not often considered when performing isolated cell hemichannel studies.
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Affiliation(s)
- Dakshesh Patel
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY 13210, United States
| | - Xian Zhang
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY 13210, United States
| | - Richard D Veenstra
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY 13210, United States.
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42
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Xin L, Bai D. Functional roles of the amino terminal domain in determining biophysical properties of Cx50 gap junction channels. Front Physiol 2013; 4:373. [PMID: 24385969 PMCID: PMC3866381 DOI: 10.3389/fphys.2013.00373] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Accepted: 11/29/2013] [Indexed: 01/13/2023] Open
Abstract
Communication through gap junction channels is essential for synchronized and coordinated cellular activities. The gap junction channel pore size, its switch control for opening/closing, and the modulations by chemicals can be different depending on the connexin subtypes that compose the channel. Recent structural and functional studies provide compelling evidence that the amino terminal (NT) domains of several connexins line the pore of gap junction channels and play an important role in single channel conductance (γ j ) and transjunctional voltage-dependent gating (V j -gating). This article reviews recent studies conducted on a series of mutations/chimeras in the NT domain of connexin50 (Cx50). Functional examination of the gap junction channels formed by these mutants/chimeras shows the net charge number at the NT domain to be an important factor in γ j and in V j -gating. Furthermore, with an increase in the net negative charge at the NT domain, we observed an increase in the γ j as well as changes in the parameters of the Boltzmann fit of the normalized steady-state conductance and V j relationship. Our data are consistent with a structural model where the NT domain of Cx50 lines the gap junction pore and plays an important role in sensing V j and in the subsequent conformational changes leading to gating, as well as in limiting the rate of ion permeation.
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Affiliation(s)
- Li Xin
- Department of Physiology and Pharmacology, The University of Western Ontario London, ON, Canada
| | - Donglin Bai
- Department of Physiology and Pharmacology, The University of Western Ontario London, ON, Canada
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43
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Nielsen MS, Axelsen LN, Sorgen PL, Verma V, Delmar M, Holstein-Rathlou NH. Gap junctions. Compr Physiol 2013; 2:1981-2035. [PMID: 23723031 DOI: 10.1002/cphy.c110051] [Citation(s) in RCA: 298] [Impact Index Per Article: 27.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Gap junctions are essential to the function of multicellular animals, which require a high degree of coordination between cells. In vertebrates, gap junctions comprise connexins and currently 21 connexins are known in humans. The functions of gap junctions are highly diverse and include exchange of metabolites and electrical signals between cells, as well as functions, which are apparently unrelated to intercellular communication. Given the diversity of gap junction physiology, regulation of gap junction activity is complex. The structure of the various connexins is known to some extent; and structural rearrangements and intramolecular interactions are important for regulation of channel function. Intercellular coupling is further regulated by the number and activity of channels present in gap junctional plaques. The number of connexins in cell-cell channels is regulated by controlling transcription, translation, trafficking, and degradation; and all of these processes are under strict control. Once in the membrane, channel activity is determined by the conductive properties of the connexin involved, which can be regulated by voltage and chemical gating, as well as a large number of posttranslational modifications. The aim of the present article is to review our current knowledge on the structure, regulation, function, and pharmacology of gap junctions. This will be supported by examples of how different connexins and their regulation act in concert to achieve appropriate physiological control, and how disturbances of connexin function can lead to disease.
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Affiliation(s)
- Morten Schak Nielsen
- Department of Biomedical Sciences and The Danish National Research Foundation Centre for Cardiac Arrhythmia, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
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44
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Nualart-Marti A, del Molino EM, Grandes X, Bahima L, Martin-Satué M, Puchal R, Fasciani I, González-Nieto D, Ziganshin B, Llobet A, Barrio LC, Solsona C. Role of connexin 32 hemichannels in the release of ATP from peripheral nerves. Glia 2013; 61:1976-89. [PMID: 24123415 DOI: 10.1002/glia.22568] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Revised: 08/02/2013] [Accepted: 08/05/2013] [Indexed: 11/12/2022]
Abstract
Extracellular purines elicit strong signals in the nervous system. Adenosine-5'-triphosphate (ATP) does not spontaneously cross the plasma membrane, and nervous cells secrete ATP by exocytosis or through plasma membrane proteins such as connexin hemichannels. Using a combination of imaging, luminescence and electrophysiological techniques, we explored the possibility that Connexin 32 (Cx32), expressed in Schwann cells (SCs) myelinating the peripheral nervous system could be an important source of ATP in peripheral nerves. We triggered the release of ATP in vivo from mice sciatic nerves by electrical stimulation and from cultured SCs by high extracellular potassium concentration-evoked depolarization. No ATP was detected in the extracellular media after treatment of the sciatic nerve with Octanol or Carbenoxolone, and ATP release was significantly inhibited after silencing Cx32 from SCs cultures. We investigated the permeability of Cx32 to ATP by expressing Cx32 hemichannels in Xenopus laevis oocytes. We found that ATP release is coupled to the inward tail current generated after the activation of Cx32 hemichannels by depolarization pulses, and it is sensitive to low extracellular calcium concentrations. Moreover, we found altered ATP release in mutated Cx32 hemichannels related to the X-linked form of Charcot-Marie-Tooth disease, suggesting that purinergic-mediated signaling in peripheral nerves could underlie the physiopathology of this neuropathy.
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Affiliation(s)
- Anna Nualart-Marti
- Department of Pathology and Experimental Therapeutics, Faculty of Medicine-Campus Bellvitge, University of Barcelona, Hospitalet del Llobregat, Barcelona, Spain; Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), Hospitalet del Llobregat, Barcelona, Spain
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45
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Abstract
Realization of a functional artificial cell, the so-called protocell, is a major challenge posed by synthetic biology. A subsequent goal is to use the protocellular units for the bottom-up assembly of prototissues. There is, however, a looming chasm in our knowledge between protocells and prototissues. In the present paper, we give a brief overview of the work on protocells to date, followed by a discussion on the rational design of key structural elements specific to linking two protocellular bilayers. We propose that designing synthetic parts capable of simultaneous insertion into two bilayers may be crucial in the hierarchical assembly of protocells into a functional prototissue.
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46
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Kwon T, Dowd T, Bargiello T. The carboxyl terminal residues 220-283 are not required for voltage gating of a chimeric connexin32 hemichannel. Biophys J 2013; 105:1376-82. [PMID: 24047988 PMCID: PMC3785884 DOI: 10.1016/j.bpj.2013.08.015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 08/10/2013] [Accepted: 08/12/2013] [Indexed: 11/30/2022] Open
Abstract
Connexin hemichannels display two distinct forms of voltage-dependent gating, corresponding to the operation of Vj- or fast gates and loop- or slow gates. The carboxyl terminus (CT) of connexin 32 has been reported to be required for the operation of the Vj (fast) gates, but this conclusion was inferred from the loss of a fast kinetic component in macroscopic currents of CT-truncated intercellular channels elicited by transjunctional voltage. Such inferences are complicated by presence of both fast and slow gates in each hemichannel and the serial head-to-head arrangement of these gates in the intercellular channel. Examination of voltage gating in undocked hemichannels and Vj gate polarity reversal by a negative charge substitution (N2E) in the amino terminal domain allow unequivocal separation of the two gating processes in a Cx32 chimera (Cx32(∗)43E1). This chimera expresses currents as an undocked hemichannel in Xenopus oocytes and provides a model system to study the molecular determinants and mechanisms of Cx32 voltage gating. Here, we demonstrate that both Vj- and loop gates are operational in a truncation mutation that removes all but the first four CT residues (ACAR(219)) of the Cx32(∗)43E1 hemichannel. We conclude that an operational Cx32 Vj (fast) gate does not require CT residues 220-283, as reported previously by others.
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Affiliation(s)
- Taekyung Kwon
- Dominic P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
| | - Terry L. Dowd
- Department of Chemistry, Brooklyn College of the City University of New York, Brooklyn, New York
| | - Thaddeus A. Bargiello
- Dominic P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
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47
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Rash JR, Curti S, Vanderpool KGV, Kamasawa N, Nannapaneni S, Palacios-Prado N, Flores CE, Yasumura T, O’Brien J, Lynn BD, Bukauskas F, Nagy JI, Pereda AE. Molecular and functional asymmetry at a vertebrate electrical synapse. Neuron 2013; 79:957-69. [PMID: 24012008 PMCID: PMC4020187 DOI: 10.1016/j.neuron.2013.06.037] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/13/2013] [Indexed: 12/20/2022]
Abstract
Electrical synapses are abundant in the vertebrate brain, but their functional and molecular complexities are still poorly understood. We report here that electrical synapses between auditory afferents and goldfish Mauthner cells are constructed by apposition of hemichannels formed by two homologs of mammalian connexin 36 (Cx36) and that, while Cx35 is restricted to presynaptic hemiplaques, Cx34.7 is restricted to postsynaptic hemiplaques, forming heterotypic junctions. This molecular asymmetry is associated with rectification of electrical transmission that may act to promote cooperativity between auditory afferents. Our data suggest that, in similarity to pre- and postsynaptic sites at chemical synapses, one side in electrical synapses should not necessarily be considered the mirror image of the other. While asymmetry based on the presence of two Cx36 homologs is restricted to teleost fish, it might also be based on differences in posttranslational modifications of individual connexins or in the complement of gap junction-associated proteins.
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Affiliation(s)
- John R. Rash
- Department of Biomedical Sciences and Program in Molecular, Cellular and Integrative Neurosciences, Colorado State University, Fort Collins, Colorado
| | - Sebastian Curti
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
- Laboratorio de Neurofisiología Celular, Departamento de Fisiología, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay
| | - Kimberly G. V. Vanderpool
- Department of Biomedical Sciences and Program in Molecular, Cellular and Integrative Neurosciences, Colorado State University, Fort Collins, Colorado
| | | | - Srikant Nannapaneni
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
| | - Nicolas Palacios-Prado
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
| | - Carmen E. Flores
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
| | - Thomas Yasumura
- Department of Biomedical Sciences and Program in Molecular, Cellular and Integrative Neurosciences, Colorado State University, Fort Collins, Colorado
| | - John O’Brien
- University of Texas Health Science Center, Houston, Texas, USA
| | - Bruce D. Lynn
- Department of Physiology, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Feliksas Bukauskas
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
| | - James I. Nagy
- Department of Physiology, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Alberto E. Pereda
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
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48
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Gong XQ, Nakagawa S, Tsukihara T, Bai D. A mechanism of gap junction docking revealed by functional rescue of a human-disease-linked connexin mutant. J Cell Sci 2013; 126:3113-20. [PMID: 23687377 DOI: 10.1242/jcs.123430] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Gap junctions are unique intercellular channels formed by the proper docking of two hemichannels from adjacent cells. Each hemichannel is a hexamer of connexins (Cxs) - the gap junction subunits, which are encoded by 21 homologous genes in the human genome. The docking of two hemichannels to form a functional gap junction channel is only possible between compatible Cxs, but the underlying molecular mechanism is unclear. On the basis of the crystal structure of the Cx26 gap junction, we developed homology models for homotypic and heterotypic channels from Cx32 and/or Cx26; these models predict six hydrogen bonds at the docking interface of each pair of the second extracellular domain (E2). A Cx32 mutation N175H and a human-disease-linked mutant N175D were predicted to lose the majority of the hydrogen bonds at the E2 docking-interface; experimentally both mutations failed to form morphological and functional gap junctions. To restore the lost hydrogen bonds, two complementary Cx26 mutants - K168V and K168A were designed to pair with the Cx32 mutants. When docked with Cx26K168V or K168A, the Cx32N175H mutant was successfully rescued morphologically and functionally in forming gap junction channels, but not Cx32 mutant N175Y. By testing more homotypic and heterotypic Cx32 and/or Cx26 mutant combinations, it is revealed that a minimum of four hydrogen bonds at each E2-docking interface are required for proper docking and functional channel formation between Cx26 and Cx32 hemichannels. Interestingly, the disease-linked Cx32N175D could be rescued by Cx26D179N, which restored five hydrogen bonds at the E2-docking interface. Our findings not only provide a mechanism for gap junction docking for Cx26 and Cx32 hemichannels, but also a potential therapeutic strategy for gap junction channelopathies.
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Affiliation(s)
- Xiang-Qun Gong
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada N6A 5C1
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49
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Fasciani I, Temperán A, Pérez-Atencio LF, Escudero A, Martínez-Montero P, Molano J, Gómez-Hernández JM, Paino CL, González-Nieto D, Barrio LC. Regulation of connexin hemichannel activity by membrane potential and the extracellular calcium in health and disease. Neuropharmacology 2013; 75:479-90. [PMID: 23587648 DOI: 10.1016/j.neuropharm.2013.03.040] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Revised: 03/26/2013] [Accepted: 03/27/2013] [Indexed: 10/27/2022]
Abstract
Connexins are thought to solely mediate cell-to-cell communication by forming gap junction channels composed of two membrane-spanning hemichannels positioned end-to-end. However, many if not all connexin isoforms also form functional hemichannels (i.e., the precursors of complete channels) that mediate the rapid exchange of ions, second messengers and metabolites between the cell interior and the interstitial space. Electrical and molecular signaling via connexin hemichannels is now widely recognized to be important in many physiological scenarios and pathological conditions. Indeed, mutations in connexins that alter hemichannel function have been implicated in several diseases. Here, we present a comprehensive overview of how hemichannel activity is tightly regulated by membrane potential and the external calcium concentration. In addition, we discuss the genetic mutations known to alter hemichannel function and their deleterious effects, of which a better understanding is necessary to develop novel therapeutic approaches for diseases caused by hemichannel dysfunction. This article is part of the Special Issue Section entitled 'Current Pharmacology of Gap Junction Channels and Hemichannels'.
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Affiliation(s)
- Ilaria Fasciani
- Unit of Experimental Neurology-Neurobiology, "Ramón y Cajal" Hospital (IRYCIS), Madrid, Spain
| | - Ana Temperán
- Unit of Experimental Neurology-Neurobiology, "Ramón y Cajal" Hospital (IRYCIS), Madrid, Spain
| | - Leonel F Pérez-Atencio
- Unit of Experimental Neurology-Neurobiology, "Ramón y Cajal" Hospital (IRYCIS), Madrid, Spain
| | - Adela Escudero
- Unit of Experimental Neurology-Neurobiology, "Ramón y Cajal" Hospital (IRYCIS), Madrid, Spain; Unit of Molecular Genetics-INGEM, Hospital La Paz (IDIPAZ), Madrid, Spain
| | | | - Jesús Molano
- Unit of Molecular Genetics-INGEM, Hospital La Paz (IDIPAZ), Madrid, Spain
| | - Juan M Gómez-Hernández
- Unit of Experimental Neurology-Neurobiology, "Ramón y Cajal" Hospital (IRYCIS), Madrid, Spain
| | - Carlos L Paino
- Unit of Experimental Neurology-Neurobiology, "Ramón y Cajal" Hospital (IRYCIS), Madrid, Spain
| | - Daniel González-Nieto
- Unit of Experimental Neurology-Neurobiology, "Ramón y Cajal" Hospital (IRYCIS), Madrid, Spain; Center for Biomedical Technology, Universidad Politécnica de Madrid, Spain
| | - Luis C Barrio
- Unit of Experimental Neurology-Neurobiology, "Ramón y Cajal" Hospital (IRYCIS), Madrid, Spain.
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50
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Mhaske PV, Levit NA, Li L, Wang HZ, Lee JR, Shuja Z, Brink PR, White TW. The human Cx26-D50A and Cx26-A88V mutations causing keratitis-ichthyosis-deafness syndrome display increased hemichannel activity. Am J Physiol Cell Physiol 2013; 304:C1150-8. [PMID: 23447037 DOI: 10.1152/ajpcell.00374.2012] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Mutations in the human gene encoding connexin 26 (Cx26 or GJB2) cause either nonsyndromic deafness or syndromic deafness associated with skin diseases. That distinct clinical disorders can be caused by different mutations within the same gene suggests that different channel activities influence the ear and skin. Here we use three different expression systems to examine the functional characteristics of two Cx26 mutations causing either mild (Cx26-D50A) or lethal (Cx26-A88V) keratitis-ichthyosis-deafness (KID) syndrome. In either cRNA-injected Xenopus oocytes, transfected HeLa cells, or transfected primary human keratinocytes, we show that both Cx26-D50A and Cx26-A88V form active hemichannels that significantly increase membrane current flow compared with wild-type Cx26. This increased membrane current accelerated cell death in low extracellular calcium solutions and was not due to increased mutant protein expression. Elevated mutant hemichannel currents could be blocked by increased extracellular calcium concentration. These results show that these two mutations exhibit a shared gain of functional activity and support the hypothesis that increased hemichannel activity is a common feature of human Cx26 mutations responsible for KID syndrome.
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Affiliation(s)
- Pallavi V Mhaske
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794, USA
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