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Ghézali G, Ribot J, Curry N, Pillet LE, Boutet-Porretta F, Mozheiko D, Calvo CF, Ezan P, Perfettini I, Lecoin L, Janel S, Zapata J, Escartin C, Etienne-Manneville S, Kaminski CF, Rouach N. Connexin 30 locally controls actin cytoskeleton and mechanical remodeling in motile astrocytes. Glia 2024. [PMID: 38982826 DOI: 10.1002/glia.24590] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 06/04/2024] [Accepted: 06/25/2024] [Indexed: 07/11/2024]
Abstract
During brain maturation, astrocytes establish complex morphologies unveiling intense structural plasticity. Connexin 30 (Cx30), a gap-junction channel-forming protein expressed postnatally, dynamically regulates during development astrocyte morphological properties by controlling ramification and extension of fine processes. However, the underlying mechanisms remain unexplored. Here, we found in vitro that Cx30 interacts with the actin cytoskeleton in astrocytes and inhibits its structural reorganization and dynamics during cell migration. This translates into an alteration of local physical surface properties, as assessed by correlative imaging using stimulated emission depletion (STED) super resolution imaging and atomic force microscopy (AFM). Specifically, Cx30 impaired astrocyte cell surface topology and cortical stiffness in motile astrocytes. As Cx30 alters actin organization, dynamics, and membrane physical properties, we assessed whether it controls astrocyte migration. We found that Cx30 reduced persistence and directionality of migrating astrocytes. Altogether, these data reveal Cx30 as a brake for astrocyte structural and mechanical plasticity.
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Affiliation(s)
- Grégory Ghézali
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
- Doctoral School N° 158, Sorbonne Université, Paris, France
| | - Jérôme Ribot
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
| | - Nathan Curry
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | - Laure-Elise Pillet
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
- Doctoral School N°562, Université Paris Cité, Paris, France
| | - Flora Boutet-Porretta
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
- Doctoral School N° 158, Sorbonne Université, Paris, France
| | - Daria Mozheiko
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
- Doctoral School N° 158, Sorbonne Université, Paris, France
| | - Charles-Félix Calvo
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
| | - Pascal Ezan
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
| | - Isabelle Perfettini
- Institut Pasteur, Université de Paris, CNRS, Cell Polarity, Migration and Cancer Unit, Paris, France
| | - Laure Lecoin
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
| | - Sébastien Janel
- Université de Lille, CNRS, Inserm, CHU Lille, Institut Pasteur de Lille, CIIL - Center for Infection and Immunity of Lille, Lille, France
| | - Jonathan Zapata
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
| | - Carole Escartin
- Université Paris-Saclay, CEA, CNRS, MIRCen, Laboratoire des Maladies Neurodégénératives, Fontenay-aux-Roses, France
| | | | - Clemens F Kaminski
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | - Nathalie Rouach
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
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2
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Yu Y, Zhang J, Zhan Y, Luo G. A novel method for detecting nine hotspot mutations of deafness genes in one tube. Sci Rep 2024; 14:454. [PMID: 38172427 PMCID: PMC10764868 DOI: 10.1038/s41598-023-50928-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Accepted: 12/28/2023] [Indexed: 01/05/2024] Open
Abstract
Deafness is a common sensory disorder. In China, approximately 70% of hereditary deafness originates from four common deafness-causing genes: GJB2, SLC26A4, GJB3, and MT-RNR1. A single-tube rapid detection method based on 2D-PCR technology was established for nine mutation sites in the aforementioned genes, and Sanger sequencing was used to verify its reliability and accuracy. The frequency of hotspot mutations in deafness genes was analysed in 116 deaf students. 2D-PCR identified 27 genotypes of nine loci according to the melting curve of the FAM, HEX, and Alexa568 fluorescence channels. Of the 116 deaf patients, 12.9% (15/116) carried SLC26A4 mutations, including c.919-2A > G and c.2168A > G (allele frequencies, 7.3% and 2.2%, respectively). The positivity rate (29.3%; 34/116) was highest for GJB2 (allele frequency, 15.9% for c.235delC, 6.0% for c.299_300delAT, and 2.6% for c.176-191del16). Sanger sequencing confirmed the consistency of results between the detection methods based on 2D-PCR and DNA sequencing. Common pathogenic mutations in patients with non-syndromic deafness in Changzhou were concentrated in GJB2 (c.235delC, c.299_300delAT, and c.176-191del16) and SLC26A4 (c.919-2A > G and c.2168 A > G). 2D-PCR is an effective method for accurately and rapidly identifying deafness-related genotypes using a single-tube reaction, and is superior to DNA sequencing, which has a high cost and long cycle.
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Affiliation(s)
- Yang Yu
- Comprehensive Laboratory, The Third Affiliated Hospital of Soochow University, Changzhou, 213003, People's Republic of China
| | - Jun Zhang
- Comprehensive Laboratory, The Third Affiliated Hospital of Soochow University, Changzhou, 213003, People's Republic of China
| | - Yuxia Zhan
- Comprehensive Laboratory, The Third Affiliated Hospital of Soochow University, Changzhou, 213003, People's Republic of China
| | - Guanghua Luo
- Comprehensive Laboratory, The Third Affiliated Hospital of Soochow University, Changzhou, 213003, People's Republic of China.
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3
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Tettey-Matey A, Di Pietro C, Donati V, Mammano F, Marazziti D. Generation of Connexin-Expressing Stable Cell Pools. Methods Mol Biol 2024; 2801:147-176. [PMID: 38578420 DOI: 10.1007/978-1-0716-3842-2_12] [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] [Indexed: 04/06/2024]
Abstract
Stable cell pools have the advantage of providing a definite, consistent, and reproducible transmission of a transgene of interest, compared to transient expression from a plasmid transfection. Stably expressing a transgene of interest in cells under induction is a powerful way to (switch on and) study a gene function in both in vitro and in vivo assays. Taking advantage of the ability of lentivirus (LV) to promote transgene delivery, and genomic integration and expression in both dividing and nondividing cells, a doxycycline-inducible transfer vector expressing a bicistronic transgene was developed to study the function of connexins in HeLa DH cells. Here, delving on connexin 32 (Cx32), we report how to use the backbone of this vector as a tool to generate stable pools to study the function of a gene of interest (GOI), especially with assays involving Ca2+ imaging, employing the GCaMP6s indicator. We describe a step-by-step protocol to produce the LV particle by transient transfection and the direct use of the harvested LV stock to generate stable cell pools. We further present step-by-step immunolabeling protocols to characterize the transgene protein expression by confocal microscopy using an antibody that targets an extracellular domain epitope of Cx32 in living cells, and in fixed permeabilized cells using high affinity anti-Cx32 antibodies. Using common molecular biology laboratory techniques, this protocol can be adapted to generate stable pools expressing any transgene of interest, for both in vitro and in vivo functional assays, including molecular, immune, and optical assays.
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Affiliation(s)
- Abraham Tettey-Matey
- Institute of Biochemistry and Cell Biology, Italian National Research Council, Rome, Italy
| | - Chiara Di Pietro
- Institute of Biochemistry and Cell Biology, Italian National Research Council, Rome, Italy
| | - Viola Donati
- Institute of Biochemistry and Cell Biology, Italian National Research Council, Rome, Italy
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Fabio Mammano
- Institute of Biochemistry and Cell Biology, Italian National Research Council, Rome, Italy
- Department of Physics and Astronomy "G. Galilei", University of Padova, Padova, Italy
| | - Daniela Marazziti
- Institute of Biochemistry and Cell Biology, Italian National Research Council, Rome, Italy.
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Lucaciu SA, Leighton SE, Hauser A, Yee R, Laird DW. Diversity in connexin biology. J Biol Chem 2023; 299:105263. [PMID: 37734551 PMCID: PMC10598745 DOI: 10.1016/j.jbc.2023.105263] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 09/08/2023] [Accepted: 09/14/2023] [Indexed: 09/23/2023] Open
Abstract
Over 35 years ago the cell biology community was introduced to connexins as the subunit employed to assemble semicrystalline clusters of intercellular channels that had been well described morphologically as gap junctions. The decade that followed would see knowledge of the unexpectedly large 21-member human connexin family grow to reflect unique and overlapping expression patterns in all organ systems. While connexin biology initially focused on their role in constructing highly regulated intercellular channels, this was destined to change as discoveries revealed that connexin hemichannels at the cell surface had novel roles in many cell types, especially when considering connexin pathologies. Acceptance of connexins as having bifunctional channel properties was initially met with some resistance, which has given way in recent years to the premise that connexins have multifunctional properties. Depending on the connexin isoform and cell of origin, connexins have wide-ranging half-lives that vary from a couple of hours to the life expectancy of the cell. Diversity in connexin channel characteristics and molecular properties were further revealed by X-ray crystallography and single-particle cryo-EM. New avenues have seen connexins or connexin fragments playing roles in cell adhesion, tunneling nanotubes, extracellular vesicles, mitochondrial membranes, transcription regulation, and in other emerging cellular functions. These discoveries were largely linked to Cx43, which is prominent in most human organs. Here, we will review the evolution of knowledge on connexin expression in human adults and more recent evidence linking connexins to a highly diverse array of cellular functions.
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Affiliation(s)
- Sergiu A Lucaciu
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada; Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Stephanie E Leighton
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada
| | - Alexandra Hauser
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada
| | - Ryan Yee
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Dale W Laird
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada; Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
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5
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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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Dydowiczová A, Brózman O, Babica P, Sovadinová I. Improved multiparametric scrape loading-dye transfer assay for a simultaneous high-throughput analysis of gap junctional intercellular communication, cell density and viability. Sci Rep 2020; 10:730. [PMID: 31959888 PMCID: PMC6971000 DOI: 10.1038/s41598-020-57536-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Accepted: 12/31/2019] [Indexed: 12/28/2022] Open
Abstract
Gap junctional intercellular communication (GJIC) is a vital cellular process required for maintenance of tissue homeostasis. In vitro assessment of GJIC represents valuable phenotypic endpoint that could be effectively utilized as an integral component in modern toxicity testing, drug screening or biomedical in vitro research. However, currently available methods for quantifying GJIC with higher-throughputs typically require specialized equipment, proprietary software and/or genetically engineered cell models. To overcome these limitations, we present here an innovative adaptation of traditional, fluorescence microscopy-based scrape loading-dye transfer (SL-DT) assay, which has been optimized to simultaneously evaluate GJIC, cell density and viability. This multiparametric method was demonstrated to be suitable for various multiwell microplate formats, which facilitates an automatized image acquisition. The assay workflow is further assisted by an open source-based software tools for batch image processing, analysis and evaluation of GJIC, cell density and viability. Our results suggest that this approach provides a simple, fast, versatile and cost effective way for in vitro high-throughput assessment of GJIC and other related phenotypic cellular events, which could be included into in vitro screening and assessment of pharmacologically and toxicologically relevant compounds.
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Affiliation(s)
- Aneta Dydowiczová
- Masaryk University, Faculty of Science, RECETOX, Kamenice 5, CZ-62500, Brno, Czech Republic
| | - Ondřej Brózman
- Masaryk University, Faculty of Science, RECETOX, Kamenice 5, CZ-62500, Brno, Czech Republic
| | - Pavel Babica
- Masaryk University, Faculty of Science, RECETOX, Kamenice 5, CZ-62500, Brno, Czech Republic
| | - Iva Sovadinová
- Masaryk University, Faculty of Science, RECETOX, Kamenice 5, CZ-62500, Brno, Czech Republic.
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7
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Ghézali G, Calvo CF, Pillet LE, Llense F, Ezan P, Pannasch U, Bemelmans AP, Etienne Manneville S, Rouach N. Connexin 30 controls astroglial polarization during postnatal brain development. Development 2018; 145:145/4/dev155275. [PMID: 29475972 PMCID: PMC5869003 DOI: 10.1242/dev.155275] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Accepted: 01/21/2018] [Indexed: 12/26/2022]
Abstract
Astrocytes undergo intense morphological maturation during development, changing from individual sparsely branched cells to polarized and tremendously ramified cells. Connexin 30, an astroglial gap-junction channel-forming protein expressed postnatally, regulates in situ the extension and ramification of astroglial processes. However, the involvement of connexin 30 in astroglial polarization, which is known to control cell morphology, remains unexplored. We found that connexin 30, independently of gap-junction-mediated intercellular biochemical coupling, alters the orientation of astrocyte protrusion, centrosome and Golgi apparatus during polarized migration in an in vitro wound-healing assay. Connexin 30 sets the orientation of astroglial motile protrusions via modulation of the laminin/β1 integrin/Cdc42 polarity pathway. Connexin 30 indeed reduces laminin levels, inhibits the redistribution of the β1-integrin extracellular matrix receptors, and inhibits the recruitment and activation of the small Rho GTPase Cdc42 at the leading edge of migrating astrocytes. In vivo, connexin 30, the expression of which is developmentally regulated, also contributes to the establishment of hippocampal astrocyte polarity during postnatal maturation. This study thus reveals that connexin 30 controls astroglial polarity during development. Summary: Connexin 30 sets the orientation of astroglial motile protrusions during polarized migration in vitro and contributes in vivo to the establishment of hippocampal astrocyte polarity during postnatal maturation.
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Affiliation(s)
- Grégory Ghézali
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS UMR 7241, INSERM U1050, Labex Memolife, PSL Research University, Paris 75005, France.,Doctoral School N°158, Pierre and Marie Curie University, Paris 75005, France
| | - Charles-Félix Calvo
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS UMR 7241, INSERM U1050, Labex Memolife, PSL Research University, Paris 75005, France
| | - Laure-Elise Pillet
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS UMR 7241, INSERM U1050, Labex Memolife, PSL Research University, Paris 75005, France.,Doctoral School N°562, Paris Descartes University, Paris 75006, France
| | - Flora Llense
- Institut Pasteur, CNRS UMR 3691, Cell Polarity, Migration and Cancer Unit, 25 Rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Pascal Ezan
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS UMR 7241, INSERM U1050, Labex Memolife, PSL Research University, Paris 75005, France
| | - Ulrike Pannasch
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS UMR 7241, INSERM U1050, Labex Memolife, PSL Research University, Paris 75005, France
| | - Alexis-Pierre Bemelmans
- Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Département de la Recherche Fondamentale, Institut de biologie François Jacob, MIRCen, and CNRS UMR 9199, Université Paris-Sud, Neurodegenerative Diseases Laboratory, Fontenay-aux-Roses 92260, France
| | - Sandrine Etienne Manneville
- Institut Pasteur, CNRS UMR 3691, Cell Polarity, Migration and Cancer Unit, 25 Rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Nathalie Rouach
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS UMR 7241, INSERM U1050, Labex Memolife, PSL Research University, Paris 75005, France
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8
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Zhao HB. Hypothesis of K +-Recycling Defect Is Not a Primary Deafness Mechanism for Cx26 ( GJB2) Deficiency. Front Mol Neurosci 2017; 10:162. [PMID: 28603488 PMCID: PMC5445178 DOI: 10.3389/fnmol.2017.00162] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Accepted: 05/10/2017] [Indexed: 12/20/2022] Open
Abstract
K+-recycling defect is a long-standing hypothesis for deafness mechanism of Connexin26 (Cx26, GJB2) mutations, which cause the most common hereditary deafness and are responsible for >50% of nonsyndromic hearing loss. The hypothesis states that Cx26 deficiency may disrupt inner ear gap junctions and compromise sinking and recycling of expelled K+ ions after hair cell excitation, causing accumulation of K+-ions in the extracellular space around hair cells producing K+-toxicity, which eventually induces hair cell degeneration and hearing loss. However, this hypothesis has never been directly evidenced, even though it has been widely referred to. Recently, more and more experiments demonstrate that this hypothesis may not be a deafness mechanism underlying Cx26 deficiency. In this review article, we summarized recent advances on the K+-recycling and mechanisms underlying Cx26 deficiency induced hearing loss. The mechanisms underlying K+-sinking, which is the first step for K+-recycling in the cochlea, and Cx26 deficiency induced cochlear developmental disorders, which are responsible for Cx26 deficiency induced congenital deafness and associated with disruption of permeability of inner ear gap junctional channels to miRNAs, are also summarized and discussed.
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Affiliation(s)
- Hong-Bo Zhao
- Department of Otolaryngology, University of Kentucky Medical CenterLexington, KY, United States
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9
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Mondal A, Sachse FB, Moreno AP. Modulation of Asymmetric Flux in Heterotypic Gap Junctions by Pore Shape, Particle Size and Charge. Front Physiol 2017; 8:206. [PMID: 28428758 PMCID: PMC5382223 DOI: 10.3389/fphys.2017.00206] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 03/20/2017] [Indexed: 01/26/2023] Open
Abstract
Gap junction channels play a vital role in intercellular communication by connecting cytoplasm of adjoined cells through arrays of channel-pores formed at the common membrane junction. Their structure and properties vary depending on the connexin isoform(s) involved in forming the full gap junction channel. Lack of information on the molecular structure of gap junction channels has limited the development of computational tools for single channel studies. Currently, we rely on cumbersome experimental techniques that have limited capabilities. We have earlier reported a simplified Brownian dynamics gap junction pore model and demonstrated that variations in pore shape at the single channel level can explain some of the differences in permeability of heterotypic channels observed in in vitro experiments. Based on this computational model, we designed simulations to study the influence of pore shape, particle size and charge in homotypic and heterotypic pores. We simulated dye diffusion under whole cell voltage clamping. Our simulation studies with pore shape variations revealed a pore shape with maximal flux asymmetry in a heterotypic pore. We identified pore shape profiles that match the in silico flux asymmetry results to the in vitro results of homotypic and heterotypic gap junction formed out of Cx43 and Cx45. Our simulation results indicate that the channel's pore-shape established flux asymmetry and that flux asymmetry is primarily regulated by the sizes of the conical and/or cylindrical mouths at each end of the pore. Within the set range of particle size and charge, flux asymmetry was found to be independent of particle size and directly proportional to charge magnitude. While particle charge was vital to creating flux asymmetry, charge magnitude only scaled the observed flux asymmetry. Our studies identified the key factors that help predict asymmetry. Finally, we suggest the role of such flux asymmetry in creating concentration imbalances of messenger molecules in cardiomyocytes. We also assess the potency of fibroblasts in aggravating such imbalances through Cx43-Cx45 heterotypic channels in fibrotic heart tissue.
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Affiliation(s)
- Abhijit Mondal
- Department of Bioengineering, University of UtahSalt Lake City, UT, USA.,Nora Eccles Harrison Cardiovascular Research and Training Institute, University of UtahSalt Lake City, UT, USA
| | - Frank B Sachse
- Department of Bioengineering, University of UtahSalt Lake City, UT, USA.,Nora Eccles Harrison Cardiovascular Research and Training Institute, University of UtahSalt Lake City, UT, USA
| | - Alonso P Moreno
- Department of Bioengineering, University of UtahSalt Lake City, UT, USA.,Nora Eccles Harrison Cardiovascular Research and Training Institute, University of UtahSalt Lake City, UT, USA.,Department of Internal Medicine, Cardiology, University of UtahSalt Lake City, UT, USA
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10
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Ek Vitorín JF, Pontifex TK, Burt JM. Determinants of Cx43 Channel Gating and Permeation: The Amino Terminus. Biophys J 2016; 110:127-40. [PMID: 26745416 DOI: 10.1016/j.bpj.2015.10.054] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Revised: 10/11/2015] [Accepted: 10/30/2015] [Indexed: 11/30/2022] Open
Abstract
Separate connexin domains partake in proposed gating mechanisms of gap junction channels. The amino-terminus (NT) domains, which contribute to voltage sensing, may line the channel's cytoplasmic-facing funnel surface, stabilize the channel's overall structure through interactions with the transmembrane domains and each other, and integrate to form a compound particle to gate the channel closed. Interactions of the carboxyl-terminus (CT) and cytoplasmic loop (CL) domains underlie voltage- and low pH-triggered channel closure. To elucidate potential cooperation of these gating mechanisms, we replaced the Cx43NT with the Cx37NT (chimera Cx43(∗)NT37), leaving the remainder of the Cx43 sequence, including the CT and CL, unchanged. Compared to wild-type Cx43 (Cx43WT), Cx43(∗)NT37 junctions exhibited several functional alterations: extreme resistance to halothane- and acidification-induced uncoupling, absence of voltage-dependent fast inactivation, longer channel open times, larger unitary channel conductances, low junctional dye permeability/permselectivity, and an overall cation selectivity more typical of Cx37WT than Cx43WT junctions. Together, these results suggest a cohesive model of channel function wherein: 1) channel conductance and size selectivity are largely determined by pore diameter, whereas charge selectivity results from the NT domains, and 2) transition between fully open and (multiple) closed states involves global changes in structure of the pore-forming domains transduced by interactions of the pore-forming domains with either the NT, CT, or both, with the NT domains forming the gate of the completely closed channel.
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Affiliation(s)
| | - Tasha K Pontifex
- Department of Physiology, University of Arizona, Tucson, Arizona
| | - Janis M Burt
- Department of Physiology, University of Arizona, Tucson, Arizona
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11
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Gap junction mediated miRNA intercellular transfer and gene regulation: A novel mechanism for intercellular genetic communication. Sci Rep 2016; 6:19884. [PMID: 26814383 PMCID: PMC4728487 DOI: 10.1038/srep19884] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Accepted: 12/21/2015] [Indexed: 12/01/2022] Open
Abstract
Intercellular genetic communication is an essential requirement for coordination of cell proliferation and differentiation and has an important role in many cellular processes. Gap junction channels possess large pore allowing passage of ions and small molecules between cells. MicroRNAs (miRNAs) are small regulatory RNAs that can regulate gene expression broadly. Here, we report that miRNAs can pass through gap junction channels in a connexin-dependent manner. Connexin43 (Cx43) had higher permeability, whereas Cx30 showed little permeability to miRNAs. In the tested connexin cell lines, the permeability to miRNAs demonstrated: Cx43 > Cx26/30 > Cx26 > Cx31 > Cx30 = Cx-null. However, consistent with a uniform structure of miRNAs, there was no significant difference in permeability to different miRNAs. The passage is efficient; the miRNA level in the recipient cells could be up to 30% of the donor level. Moreover, the transferred miRNA is functional and could regulate gene expression in neighboring cells. Connexin mutation and gap junctional blockers could eliminate this miRNA intercellular transfer and gene regulation. These data reveal a novel mechanism for intercellular genetic communication. Given that connexin expression is cell-specific, this connexin-dependent, miRNA intercellular genetic communication may play an important role in synchronizing and coordinating proliferation and differentiation of specific cell types during multicellular organ development.
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12
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Zhu Y, Zong L, Mei L, Zhao HB. Connexin26 gap junction mediates miRNA intercellular genetic communication in the cochlea and is required for inner ear development. Sci Rep 2015; 5:15647. [PMID: 26490746 PMCID: PMC4614881 DOI: 10.1038/srep15647] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2015] [Accepted: 10/01/2015] [Indexed: 11/18/2022] Open
Abstract
Organ development requires well-established intercellular communication to coordinate cell proliferations and differentiations. MicroRNAs (miRNAs) are small, non-coding RNAs that can broadly regulate gene expression and play a critical role in the organ development. In this study, we found that miRNAs could pass through gap junctions between native cochlear supporting cells to play a role in the cochlear development. Connexin26 (Cx26) and Cx30 are predominant isoforms and co-express in the cochlea. Cx26 deficiency but not Cx30 deficiency can cause cochlear developmental disorders. We found that associated with Cx26 deletion induced the cochlear developmental disorders, deletion of Cx26 but not Cx30 disrupted miRNA intercellular transfer in the cochlea, although inner ear gap junctions still retained permeability after deletion of Cx26. Moreover, we found that deletion of Cx26 but not Cx30 reduced miR-96 expression in the cochlea during postnatal development. The reduction is associated with the cochlear tunnel developmental disorder in Cx26 knockout (KO) mice. These data reveal that Cx26-mediated intercellular communication is required for cochlear development and that deficiency of Cx26 can impair miRNA-mediated intercellular genetic communication in the cochlea, which may lead to cochlear developmental disorders and eventually congenital deafness as previously reported.
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Affiliation(s)
- Yan Zhu
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536
| | - Liang Zong
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536
| | - Ling Mei
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536
| | - Hong-Bo Zhao
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536
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13
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Wingard JC, Zhao HB. Cellular and Deafness Mechanisms Underlying Connexin Mutation-Induced Hearing Loss - A Common Hereditary Deafness. Front Cell Neurosci 2015; 9:202. [PMID: 26074771 PMCID: PMC4448512 DOI: 10.3389/fncel.2015.00202] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2015] [Accepted: 05/11/2015] [Indexed: 11/30/2022] Open
Abstract
Hearing loss due to mutations in the connexin gene family, which encodes gap junctional proteins, is a common form of hereditary deafness. In particular, connexin 26 (Cx26, GJB2) mutations are responsible for ~50% of non-syndromic hearing loss, which is the highest incidence of genetic disease. In the clinic, Cx26 mutations cause various auditory phenotypes ranging from profound congenital deafness at birth to mild, progressive hearing loss in late childhood. Recent experiments demonstrate that congenital deafness mainly results from cochlear developmental disorders rather than hair cell degeneration and endocochlear potential reduction, while late-onset hearing loss results from reduction of active cochlear amplification, even though cochlear hair cells have no connexin expression. However, there is no apparent, demonstrable relationship between specific changes in connexin (channel) functions and the phenotypes of mutation-induced hearing loss. Moreover, new experiments further demonstrate that the hypothesized K+-recycling disruption is not a principal deafness mechanism for connexin deficiency induced hearing loss. Cx30 (GJB6), Cx29 (GJC3), Cx31 (GJB3), and Cx43 (GJA1) mutations can also cause hearing loss with distinct pathological changes in the cochlea. These new studies provide invaluable information about deafness mechanisms underlying connexin mutation-induced hearing loss and also provide important information for developing new protective and therapeutic strategies for this common deafness. However, the detailed cellular mechanisms underlying these pathological changes remain unclear. Also, little is known about specific mutation-induced pathological changes in vivo and little information is available for humans. Such further studies are urgently required.
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Affiliation(s)
- Jeffrey C Wingard
- Department of Otolaryngology, University of Kentucky Medical Center , Lexington, KY , USA
| | - Hong-Bo Zhao
- Department of Otolaryngology, University of Kentucky Medical Center , Lexington, KY , USA
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14
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Jagger DJ, Forge A. Connexins and gap junctions in the inner ear--it's not just about K⁺ recycling. Cell Tissue Res 2014; 360:633-44. [PMID: 25381570 PMCID: PMC4452565 DOI: 10.1007/s00441-014-2029-z] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Accepted: 10/06/2014] [Indexed: 12/19/2022]
Abstract
Normal development, function and repair of the sensory epithelia in the inner ear are all dependent on gap junctional intercellular communication. Mutations in the connexin genes GJB2 and GJB6 (encoding CX26 and CX30) result in syndromic and non-syndromic deafness via various mechanisms. Clinical vestibular defects, however, are harder to connect with connexin dysfunction. Cx26 and Cx30 proteins are widely expressed in the epithelial and connective tissues of the cochlea, where they may form homomeric or heteromeric gap junction channels in a cell-specific and spatiotemporally complex fashion. Despite the study of mutant channels and animal models for both recessive and dominant autosomal deafness, it is still unclear why gap junctions are essential for auditory function, and why Cx26 and Cx30 do not compensate for each other in vivo. Cx26 appears to be essential for normal development of the auditory sensory epithelium, but may be dispensable during normal hearing. Cx30 appears to be essential for normal repair following sensory cell loss. The specific modes of intercellular signalling mediated by inner ear gap junction channels remain undetermined, but they are hypothesised to play essential roles in the maintenance of ionic and metabolic homeostasis in the inner ear. Recent studies have highlighted involvement of gap junctions in the transfer of essential second messengers between the non-sensory cells, and have proposed roles for hemichannels in normal hearing. Here, we summarise the current knowledge about the molecular and functional properties of inner ear gap junctions, and about tissue pathologies associated with connexin mutations.
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Affiliation(s)
- Daniel J Jagger
- UCL Ear Institute, University College London, 332 Gray's Inn Road, London, WC1X 8EE, UK,
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15
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Li TC, Kuan YH, Ko TY, Li C, Yang JJ. Mechanism of a novel missense mutation, p.V174M, of the human connexin31 (GJB3) in causing nonsyndromic hearing loss. Biochem Cell Biol 2014; 92:251-7. [PMID: 24913888 DOI: 10.1139/bcb-2013-0126] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hearing loss is the most common sensory disorder, worldwide. In a recent study, we have identified a missense mutation, p.V174M, in the connexin 31 encoded by the GJB3 gene, in a patient with nonsyndromic hearing loss. However, the functional change in the CX31V174M mutant remains unknown. This study compared the intracellular distribution and assembly of the mutant CX31V174M with that of the wild-type (WT) CX31 in HeLa cells, and it examined the effect that the mutant protein had on those cells. A fluorescent localization assay of WT CX31 showed the typical punctuate pattern of a gap junction channel between the neighboring expression cells. Conversely, the p.V174M missense mutation resulted in the accumulation of the mutant protein in the lysosomes rather than in the cytoplasmic membrane. Moreover, dye transfer experiments have also demonstrated that the CX31V174M mutant did not form functional gap junction channels, probably due to the incorrect assembly or the altered properties of the CX31 channels. In addition, we found that CX31V174M-transfection can cause cell death by MTT assay. CX31V174M co-expressed with either CX31WT or CX26WT studies, suggested the impairment of the ability of CX26WT proteins to intracellular trafficking and targeting to the plasma membrane, but did not influence the trafficking of CX31WT. Based on these findings, we suggest that the CX31V174M mutant may have an effect on the formation and function of the gap junction, and CX31V174M has a trans-dominant negative effect on the function of wild types CX26. These results provide a novel molecular explanation for the role that GJB3 plays in hearing loss.
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Affiliation(s)
- Tung-Cheng Li
- a Institute of Medicine, Chung Shan Medical University, Taichung, Taiwan
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16
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Chang-Chien J, Yen YC, Chien KH, Li SY, Hsu TC, Yang JJ. The connexin 30.3 of zebrafish homologue of human connexin 26 may play similar role in the inner ear. Hear Res 2014; 313:55-66. [PMID: 24811980 DOI: 10.1016/j.heares.2014.04.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Revised: 04/11/2014] [Accepted: 04/22/2014] [Indexed: 12/24/2022]
Abstract
The intercellular gap junction channels formed by connexins (CXs) are important for recycling potassium ions in the inner ear. CXs are encoded by a family of the CX gene, such as GJB2, and the mechanism leading to mutant connexin-associated diseases, including hearing loss, remains to be elucidated. In this study, using bioinformatics, we found that two zebrafish cx genes, cx27.5 and cx30.3, are likely homologous to human and mouse GJB2. During embryogenesis, zebrafish cx27.5 was rarely expressed at 1.5-3 h post-fertilization (hpf), but a relatively high level of cx27.5 expression was detected from 6 to 96 hpf. However, zebrafish cx30.3 transcripts were hardly detected until 9 hpf. The temporal experiment was conducted in whole larvae. Both cx27.5 and cx30.3 transcripts were revealed significantly in the inner ear by reverse transcription polymerase chain reaction (RT-PCR) and whole-mount in situ hybridization (WISH). In the HeLa cell model, we found that zebrafish Cx27.5 was distributed intracellularly in the cytoplasm, whereas Cx30.3 was localized in the plasma membrane of HeLa cells stably expressing Cx proteins. The expression pattern of zebrafish Cx30.3 in HeLa cells was more similar to that of cells expressing human CX26 than Cx27.5. In addition, we found that Cx30.3 was localized in the cell membrane of hair cells within the inner ear by immunohistochemistry (IHC), suggesting that zebrafish cx30.3 might play an essential role in the development of the inner ear, in the same manner as human GJB2. We then performed morpholino knockdown studies in zebrafish embryos to elucidate the physiological functions of Cx30.3. The zebrafish cx30.3 morphants exhibited wild-type-like and heart edema phenotypes with smaller inner ears at 72 hpf. Based on these results, we suggest that the zebrafish Cx30.3 and mammalian CX26 may play alike roles in the inner ear. Thus, zebrafish can potentially serve as a model for studying hearing loss disorders that result from human CX26 mutations.
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Affiliation(s)
- Ju Chang-Chien
- Department of Biomedical Sciences, Chung Shan Medical University, Taichung, Taiwan; Institute of Microbiology & Immunology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Yung-Chang Yen
- Department of Ophthalmology, CHi-Mei Medical Center, Liou-Ying, Tainan, Taiwan; Department of Nursing, Min Hwei College of Health Care Management, Tainan, Taiwan
| | - Kuo-Hsuan Chien
- Department of Biomedical Sciences, Chung Shan Medical University, Taichung, Taiwan
| | - Shaun-Yow Li
- Department of Biomedical Sciences, Chung Shan Medical University, Taichung, Taiwan
| | - Tsai-Ching Hsu
- Institute of Microbiology & Immunology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan; Clinical Laboratory, Chung Shan Medical University Hospital, Taichung, Taiwan.
| | - Jiann-Jou Yang
- Department of Biomedical Sciences, Chung Shan Medical University, Taichung, Taiwan; Department of Medical Sciences, Chung Shan Medical University Hospital, Taichung, Taiwan.
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17
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Hansen DB, Braunstein TH, Nielsen MS, MacAulay N. Distinct permeation profiles of the connexin 30 and 43 hemichannels. FEBS Lett 2014; 588:1446-57. [PMID: 24503060 DOI: 10.1016/j.febslet.2014.01.036] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 01/23/2014] [Accepted: 01/24/2014] [Indexed: 01/10/2023]
Abstract
Connexin 43 (Cx43) hemichannels may form open channels in the plasma membrane when exposed to specific stimuli, e.g. reduced extracellular concentration of divalent cations, and allow passage of fluorescent molecules and presumably a range of smaller physiologically relevant molecules. However, the permeability profile of Cx43 hemichannels remains unresolved. Exposure of Cx43-expressing Xenopus laevis oocytes to divalent cation free solution induced a gadolinium-sensitive uptake of the fluorescent dye ethidium. In spite thereof, a range of biological molecules smaller than ethidium, such as glutamate, lactate, and glucose, did not permeate the pore whereas ATP did. In contrast, permeability of glutamate, glucose and ATP was observed in oocytes expressing Cx30. Exposure to divalent cation free solutions induced a robust membrane conductance in Cx30-expressing oocytes but none in Cx43-expressing oocytes. C-terminally truncated Cx43 (M257) displayed increased dye uptake and, unlike wild type Cx43 channels, conducted current. Neither Cx30 nor Cx43 acted as water channels in their hemichannel configuration. Our results demonstrate that connexin hemichannels have isoform-specific permeability profiles and that dye uptake cannot be equaled to permeability of smaller physiologically relevant molecules in given settings.
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Affiliation(s)
- Daniel Bloch Hansen
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Thomas Hartig Braunstein
- Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Morten Schak Nielsen
- Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Nanna MacAulay
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
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18
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Ceriani F, Mammano F. A rapid and sensitive assay of intercellular coupling by voltage imaging of gap junction networks. Cell Commun Signal 2013; 11:78. [PMID: 24144139 PMCID: PMC3819673 DOI: 10.1186/1478-811x-11-78] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 10/01/2013] [Indexed: 12/16/2022] Open
Abstract
Background A variety of mechanisms that govern connexin channel gating and permeability regulate coupling in gap junction networks. Mutations in connexin genes have been linked to several pathologies, including cardiovascular anomalies, peripheral neuropathy, skin disorders, cataracts and deafness. Gap junction coupling and its patho–physiological alterations are commonly assayed by microinjection experiments with fluorescent tracers, which typically require several minutes to allow dye transfer to a limited number of cells. Comparable or longer time intervals are required by fluorescence recovery after photobleaching experiments. Paired electrophysiological recordings have excellent time resolution but provide extremely limited spatial information regarding network connectivity. Results Here, we developed a rapid and sensitive method to assay gap junction communication using a combination of single cell electrophysiology, large–scale optical recordings and a digital phase–sensitive detector to extract signals with a known frequency from Vf2.1.Cl, a novel fluorescent sensor of plasma membrane potential. Tests performed in HeLa cell cultures confirmed that suitably encoded Vf2.1.Cl signals remained confined within the network of cells visibly interconnected by fluorescently tagged gap junction channels. We used this method to visualize instantly intercellular connectivity over the whole field of view (hundreds of cells) in cochlear organotypic cultures from postnatal mice. A simple resistive network model reproduced accurately the spatial dependence of the electrical signals throughout the cellular network. Our data suggest that each pair of cochlear non−sensory cells of the lesser epithelial ridge is coupled by ~1500 gap junction channels, on average. Junctional conductance was reduced by 14% in cochlear cultures harboring the T5M mutation of connexin30, which induces a moderate hearing loss in connexin30T5M/T5M knock–in mice, and by 91% in cultures from connexin30−/− mice, which are profoundly deaf. Conclusions Our methodology allows greater sensitivity (defined as the minimum magnitude of input signal required to produce a specified output signal having a specified signal−to−noise ratio) and better time resolution compared to classical tracer–based techniques. It permitted us to dynamically visualize intercellular connectivity down to the 10th order in non−sensory cell networks of the developing cochlea. We believe that our approach is of general interest and can be seamlessly extended to a variety of biological systems, as well as to other connexin−related disease conditions.
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Affiliation(s)
| | - Fabio Mammano
- Dipartimento di Fisica e Astronomia "G, Galilei", Università di Padova, Padova 35131, Italy.
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19
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A novel, highly sensitive method for assessing gap junctional coupling. J Neurosci Methods 2013; 220:18-23. [PMID: 23958747 DOI: 10.1016/j.jneumeth.2013.08.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 08/02/2013] [Accepted: 08/05/2013] [Indexed: 11/20/2022]
Abstract
To assess gap junctional intercellular communication we have developed a tracer-based methodology which is both highly sensitive and potentially adaptable for in vivo measurements. We found that injection of serotonin revealed significantly more intercellular communication than that injection of the most permeant synthetic tracer currently in use, neurobiotin. Furthermore, mechanical tracer loading steps can be replaced by transfection with human serotonin transporter and the inclusion of serotonin in the medium. Tracer and transporter are detected using immunocytochemical techniques and the presence of cells that are tracer-positive but transporter-negative indicates junctional communication. Tracer loading in vivo using transgenesis, electroporation or viral transduction to direct expression of transporter should be more easily accomplished than with mechanical loading methods.
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20
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Wan CK, Shaikh SB, Green CR, Nicholson LFB. Comparison of bidirectional and bicistronic inducible systems for coexpression of connexin genes and fluorescent reporters. Anal Biochem 2012; 431:90-5. [PMID: 22929700 DOI: 10.1016/j.ab.2012.08.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2012] [Revised: 08/17/2012] [Accepted: 08/18/2012] [Indexed: 11/18/2022]
Abstract
Gene expression studies often require inducible coexpression of both a gene of interest and a reporter gene. Fusion of fluorescent reporters can, however, modify protein structure and function. We have generated inducible expression systems for two connexin genes: Cx30 and Cx43. It has been reported recently that reporter fusion to connexins can modify their function. Therefore, we compared two methods of independent reporter coexpression and examined colocalization with induced connexin expression. Identical levels of connexin expression were observed for both the bidirectional and bicistronic expression systems. In contrast, however, reporter gene expression by the bidirectional promoter provided brighter average fluorescent pixel intensity than expression of a reporter gene in a bicistronic transcript. Moreover, as a result of this difference in reporter expression, bidirectional expression systems provided equal or better colocalization between the connexins and reporter gene fluorescence. The results of our study indicate that bidirectional reporter expression provides a robust indicator of transfection and gene expression and, therefore, may favor the use of bidirectional over bicistronic reporters in the design of expression systems where the gene of interest, such as a connexin gene, contains translational motifs or long intronic regions.
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Affiliation(s)
- Carthur K Wan
- Department of Anatomy with Radiology and Centre for Brain Research, Faculty of Medical and Health Sciences, University of Auckland, Auckland 92-019, New Zealand.
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21
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Xu J, Nicholson BJ. The role of connexins in ear and skin physiology - functional insights from disease-associated mutations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:167-78. [PMID: 22796187 DOI: 10.1016/j.bbamem.2012.06.024] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2012] [Revised: 06/23/2012] [Accepted: 06/29/2012] [Indexed: 12/20/2022]
Abstract
Defects in several different connexins have been associated with several different diseases. The most common of these is deafness, where a few mutations in connexin (Cx) 26 have been found to contribute to over 50% of the incidence of non-syndromic deafness in different human populations. Other mutations in Cx26 or Cx30 have also been associated with various skin phenotypes linked to deafness (palmoplanta keratoderma, Bart-Pumphrey syndrome, Vohwinkel syndrome, keratitis-ichthyosis-deafness syndrome, etc.). The large array of disease mutants offers unique opportunities to gain insights into the underlying function of gap junction proteins and their channels in the normal and pathogenic physiologies of the cochlea and epidermis. This review focuses on those mutants where the impact on channel function has been assessed, and correlated with the disease phenotype, or organ function in knock-out mouse models. These approaches have provided evidence supporting a role of gap junctions and hemichannels in K(+) removal and recycling in the ear, as well as possible roles for nutrient passage, in the cochlea. In contrast, increases in hemichannel opening leading to increased cell death, were associated with several keratitis-ichthyosis-deafness syndrome skin disease/hearing mutants. In addition to providing clues for therapeutic strategies, these findings allow us to better understand the specific functions of connexin channels that are important for normal tissue function. This article is part of a Special Issue entitled: The communicating junctions, roles and dysfunctions.
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Affiliation(s)
- Ji Xu
- Department of Physiology, University of California, Los Angeles, CA 90095, USA
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22
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Wang X, Xu X, Ma M, Zhou W, Wang Y, Yang L. pH-dependent channel gating in connexin26 hemichannels involves conformational changes in N-terminus. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:1148-57. [PMID: 22285739 DOI: 10.1016/j.bbamem.2011.12.027] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Revised: 12/23/2011] [Accepted: 12/27/2011] [Indexed: 10/14/2022]
Abstract
Connexin (Cx) hemichannels controlling an exchange of ions and metabolites between the cytoplasm and extracellular milieu can be modulated by the variation of intracellular pH during physiological and pathological conditions. To address the mechanism by which the pH exerts its effect on hemichannels, we have performed two 100-ns molecular dynamics simulations of the Cx26 channel in both acidic and neutral states. The results show that: 1) transmembrane domains undergo clockwise motions around the pore axis under both acidic and neutral conditions, while extracellular segments keep stable. 2) Under neutral condition, Cx26 has a tightly closed configuration that occurs through the assembly of N-terminal helix (NTH) region. This shows a constriction formed by the interhelical interactions of Asp2 and Met1 from neighboring NTH, which shapes the narrowest segment (pore radius<2Å) of the pore, preventing the passage of ions from the extracellular side. This indicates that Asp2 may act as a channel gate. 3) Under the acidic condition, the constriction is relieved by the protonation of Asp2 causing interruption of interhelical interactions, Cx26 has a flexibly opening pore (pore radius>4.5Å) around NTH region, allowing the passage of chloride ions unimpeded by the side-chain Asp2. While in the extracellular part two chloride ions interact with the side-chain Lys41 from three subunits. Finally, we provide a plausible mechanism of pH-dependent gating of hemichannel that involves protonation of the aspartic residues, suggesting that the pH sensitivity of hemichannel permeability is a sophisticated mechanism for cell regulating ion permeation.
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Affiliation(s)
- Xia Wang
- Center of Bioinformatics, Northwest A&F University, Yangling, Shaanxi, 712100, China
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23
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Plazzo AP, De Franceschi N, Da Broi F, Zonta F, Sanasi MF, Filippini F, Mongillo M. Bioinformatic and mutational analysis of channelrhodopsin-2 protein cation-conducting pathway. J Biol Chem 2011; 287:4818-25. [PMID: 22139833 DOI: 10.1074/jbc.m111.326207] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Channelrhodopsin-2 (ChR2) is a light-gated cation channel widely used as a biotechnological tool to control membrane depolarization in various cell types and tissues. Although several ChR2 variants with modified properties have been generated, the structural determinants of the protein function are largely unresolved. We used bioinformatic modeling of the ChR2 structure to identify the putative cationic pathway within the channel, which is formed by a system of inner cavities that are uniquely present in this microbial rhodopsin. Site-directed mutagenesis combined with patch clamp analysis in HeLa cells was used to determine key residues involved in ChR2 conductance and selectivity. Among them, Gln-56 is important for ion conductance, whereas Ser-63, Thr-250, and Asn-258 are previously unrecognized residues involved in ion selectivity and photocurrent kinetics. This study widens the current structural information on ChR2 and can assist in the design of new improved variants for specific biological applications.
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Affiliation(s)
- Anna Pia Plazzo
- Department of Biomedical Sciences, University of Padova, viale Colombo 3, 35100 Padova, Italy
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24
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Liang WG, Su CC, Nian JH, Chiang AS, Li SY, Yang JJ. Human connexin30.2/31.3 (GJC3) does not form functional gap junction channels but causes enhanced ATP release in HeLa cells. Cell Biochem Biophys 2011; 61:189-97. [PMID: 21480002 DOI: 10.1007/s12013-011-9188-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Gap junctional intercellular communication has numerous functions, each of which meets the particular needs of organs, tissues, or groups of cells. Connexins (CXs) are homologous four-transmembrane-domain proteins that are the major components of gap junctions. CX30.2/CX31.3 (GJC3) is a relatively new member of the CX protein family. Until now, however, the functional characteristics of CX30.2/CX31.3 have been unclear. To elucidate the properties of CX30.2/CX31.3 channels, their subcellular localization in HeLa cells, their effectiveness in dye transfer, and function on channels were investigated. In the immunofluorescent assay, cells that express CX30.2/CX31.3-GFP exhibited continuous fluorescence along the apposed cell membranes, rather than punctated fluorescence in contacting membranes between two cells. Surprisingly, dyes that can be capable of being permeated by CX26 GJ, according to a scrape loading dye transfer assay in previous studies, are impermeated by CX30.2/CX31.3 GJ, suggesting a difference between the characteristics of CX30.2/CX31.3 GJ and CX26 GJ. Furthermore, a significant amount of ATP was released from the HeLa cells that stably expressed CX30.2/CX31.3, in a medium with low calcium ion concentration, suggesting a hemichannel-based function for CX30.2/CX31.3. Based on these findings, we suggest that CX30.2/CX31.3 shares functional properties with pannexin (hemi) channels rather than gap junction channels of other CXs.
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Affiliation(s)
- Wei-Guang Liang
- Department of BioMedical Sciences, Chung Shan Medical University, Taichung, Taiwan, Republic of China
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25
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A dominant connexin43 mutant does not have dominant effects on gap junction coupling in astrocytes. ACTA ACUST UNITED AC 2011; 6:213-23. [PMID: 21375791 DOI: 10.1017/s1740925x11000019] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Dominant mutations in GJA1, the gene encoding the gap junction protein connexin43 (Cx43), cause oculodentodigital dysplasia (ODDD), a syndrome affecting multiple tissues, including the central nervous system (CNS). We investigated the effects of the G60S mutant, which causes a similar, dominant phenotype in mice (Gja1(Jrt/+)). Astrocytes in acute brain slices from Gja1(Jrt/+) mice transfer sulforhodamine-B comparably to that in their wild-type (WT) littermates. Further, astrocytes and cardiomyocytes cultured from Gja1(Jrt/+) mice showed a comparable transfer of lucifer yellow to those from WT mice. In transfected cells, the G60S mutant formed gap junction (GJ) plaques but not functional channels. In co-transfected cells, the G60S mutant co-immunoprecipitated with WT Cx43, but did not diminish GJ coupling as measured by dual patch clamp. Thus, whereas G60S has dominant effects, it did not appreciably reduce GJ coupling.
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26
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Magnotti LM, Goodenough DA, Paul DL. Functional heterotypic interactions between astrocyte and oligodendrocyte connexins. Glia 2011; 59:26-34. [PMID: 21046554 DOI: 10.1002/glia.21073] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Human genetic diseases and mouse knockouts illustrate that the maintenance of central nervous system myelin requires connexin expression by both astrocytes and oligodendrocytes. Because these cell types express nonoverlapping sets of connexins, the intercellular channels formed between them must be asymmetric with regard to connexin content, defined as heterotypic. Here, we show that oligodendrocyte Cx47 can form heterotypic channels with astrocyte Cx43 or Cx30 but not Cx26, whereas oligodendrocyte Cx32 can functionally interact with astrocyte Cx30 or Cx26 but not Cx43. Thus, as many as four types of intercellular channels could be formed between astrocytes and oligodendrocytes.
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Affiliation(s)
- Laura M Magnotti
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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Schütz M, Scimemi P, Majumder P, De Siati RD, Crispino G, Rodriguez L, Bortolozzi M, Santarelli R, Seydel A, Sonntag S, Ingham N, Steel KP, Willecke K, Mammano F. The human deafness-associated connexin 30 T5M mutation causes mild hearing loss and reduces biochemical coupling among cochlear non-sensory cells in knock-in mice. Hum Mol Genet 2010; 19:4759-73. [PMID: 20858605 PMCID: PMC2989887 DOI: 10.1093/hmg/ddq402] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 08/18/2010] [Accepted: 09/14/2010] [Indexed: 12/11/2022] Open
Abstract
Mutations in the GJB2 and GJB6 genes, respectively, coding for connexin26 (Cx26) and connexin30 (Cx30) proteins, are the most common cause for prelingual non-syndromic deafness in humans. In the inner ear, Cx26 and Cx30 are expressed in different non-sensory cell types, where they largely co-localize and may form heteromeric gap junction channels. Here, we describe the generation and characterization of a mouse model for human bilateral middle/high-frequency hearing loss based on the substitution of an evolutionarily conserved threonine by a methionine residue at position 5 near the N-terminus of Cx30 (Cx30T5M). The mutation was inserted in the mouse genome by homologous recombination in mouse embryonic stem cells. Expression of the mutated Cx30T5M protein in these transgenic mice is under the control of the endogenous Cx30 promoter and was analysed via activation of the lacZ reporter gene. When probed by auditory brainstem recordings, Cx30(T5M/T5M) mice exhibited a mild, but significant increase in their hearing thresholds of about 15 dB at all frequencies. Immunolabelling with antibodies to Cx26 or Cx30 suggested normal location of these proteins in the adult inner ear, but western blot analysis showed significantly down-regulated the expression levels of Cx26 and Cx30. In the developing cochlea, electrical coupling, probed by dual patch-clamp recordings, was normal. However, transfer of the fluorescent tracer calcein between cochlear non-sensory cells was reduced, as was intercellular Ca(2+) signalling due to spontaneous ATP release from connexin hemichannels. Our findings link hearing loss to decreased biochemical coupling due to the point-mutated Cx30 in mice.
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Affiliation(s)
- Melanie Schütz
- Institut fuer Genetik, Rheinische Friedrich-Wilhelms-Universitaet Bonn, Roemerstrasse 164, D-53117 Bonn, Germany
| | - Pietro Scimemi
- Dipartimento di Specialità Medico Chirurgiche, Università di Padova, via Giustiniani 2, 35129 Padova, Italy
- Servizio di Audiologia, Ospedale ‘Ca’ Foncello’, Treviso, Italy
| | - Paromita Majumder
- Istituto Veneto di Medicina Molecolare, Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
| | - Romolo Daniele De Siati
- Dipartimento di Specialità Medico Chirurgiche, Università di Padova, via Giustiniani 2, 35129 Padova, Italy
- Servizio di Audiologia, Ospedale ‘Ca’ Foncello’, Treviso, Italy
| | - Giulia Crispino
- Istituto Veneto di Medicina Molecolare, Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
| | - Laura Rodriguez
- Istituto Veneto di Medicina Molecolare, Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
| | - Mario Bortolozzi
- Istituto Veneto di Medicina Molecolare, Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
- Dipartimento di Fisica ‘G. Galilei’, Università di Padova, 35131 Padova, Italy
- Istituto CNR di Neuroscienze, Padova, Italy and
| | - Rosamaria Santarelli
- Dipartimento di Specialità Medico Chirurgiche, Università di Padova, via Giustiniani 2, 35129 Padova, Italy
- Servizio di Audiologia, Ospedale ‘Ca’ Foncello’, Treviso, Italy
| | - Anke Seydel
- Istituto Veneto di Medicina Molecolare, Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
| | - Stephan Sonntag
- Institut fuer Genetik, Rheinische Friedrich-Wilhelms-Universitaet Bonn, Roemerstrasse 164, D-53117 Bonn, Germany
| | - Neil Ingham
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, UK
| | - Karen P. Steel
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, UK
| | - Klaus Willecke
- Institut fuer Genetik, Rheinische Friedrich-Wilhelms-Universitaet Bonn, Roemerstrasse 164, D-53117 Bonn, Germany
| | - Fabio Mammano
- Istituto Veneto di Medicina Molecolare, Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
- Dipartimento di Fisica ‘G. Galilei’, Università di Padova, 35131 Padova, Italy
- Istituto CNR di Neuroscienze, Padova, Italy and
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Su CC, Li SY, Su MC, Chen WC, Yang JJ. Mutation R184Q of connexin 26 in hearing loss patients has a dominant-negative effect on connexin 26 and connexin 30. Eur J Hum Genet 2010; 18:1061-4. [PMID: 20442751 DOI: 10.1038/ejhg.2010.50] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Hearing impairment is the most common sensory disorder worldwide. In a recent study, the authors have shown that a heterozygous missense mutation, p.R184Q, in the connexin 26 (Cx26) is causally related to hearing loss. However, the functional change in the Cx26R184Q mutant remains unknown. This study compared the intracellular distribution and assembly of mutant Cx26R184Q with that of the wild-type (WT) Cx26 and Cx30WT in tet-on HeLa cells and the effect that the mutant protein had on those cells. Fluorescent localization assay of WT Cx26 showed the typical punctuate pattern of gap junction channel between neighboring expression cells. Conversely, the p.R184Q missense mutation resulted in accumulation of the Cx26 mutant protein in the Golgi apparatus rather than in the cytoplasmic membrane. Cx26R184Q coexpressed with either Cx26WT or Cx30WT showed perinuclear localization by bidirectional tet-on expression system, suggesting the impairment of the ability of both WT proteins to intracellular trafficking and targeting to the plasma membrane. Therefore, we proposed that Cx26R184Q has a dominant-negative effect on the function of WT Cx26 and Cx30.
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Dominant connexin26 mutants associated with human hearing loss have trans-dominant effects on connexin30. Neurobiol Dis 2010; 38:226-36. [PMID: 20096356 DOI: 10.1016/j.nbd.2010.01.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Revised: 11/27/2009] [Accepted: 01/12/2010] [Indexed: 11/23/2022] Open
Abstract
Dominant mutations in GJB2, the gene encoding the human gap junction protein connexin26 (Cx26), cause hearing loss. We investigated whether dominant Cx26 mutants interact directly with Cx30. HeLa cells stably expressing nine dominant Cx26 mutants, six associated with non-syndromic hearing loss (W44C, W44S, R143Q, D179N, R184Q and C202F) and three associated with hearing loss and palmoplantar keratoderma (G59A, R75Q and R75W), individually or together with Cx30, were analyzed by immunocytochemistry, co-immunoprecipitation, and functional assays (scrape-loading and/or fluorescence recovery after photobleaching). When expressed alone, all mutants formed gap junction plaques, but with impaired intercellular dye transfer. When expressed with Cx30, all mutants co-localized and co-immunoprecipitated with Cx30, indicating they likely co-assembled into heteromers. Furthermore, 8/9 Cx26 mutants inhibited the transfer of neurobiotin or calcein, indicating that these Cx26 mutants have trans-dominant effects on Cx30, an effect that may contribute to the pathogenesis of hearing loss.
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30
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A novel mutation in the connexin 29 gene may contribute to nonsyndromic hearing loss. Hum Genet 2009; 127:191-9. [DOI: 10.1007/s00439-009-0758-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2009] [Accepted: 10/17/2009] [Indexed: 10/20/2022]
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Gap junctions and connexins in the inner ear: their roles in homeostasis and deafness. Curr Opin Otolaryngol Head Neck Surg 2009; 16:452-7. [PMID: 18797288 DOI: 10.1097/moo.0b013e32830e20b0] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
PURPOSE OF REVIEW Mutations in GJB2 and GJB6, the genes encoding the gap-junction proteins connexin 26 and connexin 30, are the most common cause of autosomal recessive nonsyndromic deafness in many populations across the world. In this review, we discuss current ideas about the roles of gap junctions in the inner ear and the implications of connexin mutations on auditory function. RECENT FINDINGS In recent years, a complex picture of the roles of gap junctions in cochlear physiology emerged. Rather than being mere conduits for the circulation of potassium ions in the inner ear, gap junctions have been implicated in intercellular signaling among nonsensory cells and may be involved in the maintenance of the endothelial barrier in the stria vascularis. Studies of mutant channels and mouse models for connexin-related deafness have provided valuable insights into some of the mechanisms by which connexin dysfunction causes cochlear degeneration. They have also identified potential therapeutic interventions for specific connexin mutations, such as the restoration of normal connexin 26 protein levels in GJB6-associated deafness. SUMMARY Despite recent advances, a better understanding of the complexity of gap-junctional communication in the inner ear and the structure-function relationships of connexin proteins is required for the development of mechanism-based treatments of connexin-associated hearing loss.
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Anselmi F, Hernandez VH, Crispino G, Seydel A, Ortolano S, Roper SD, Kessaris N, Richardson W, Rickheit G, Filippov MA, Monyer H, Mammano F. ATP release through connexin hemichannels and gap junction transfer of second messengers propagate Ca2+ signals across the inner ear. Proc Natl Acad Sci U S A 2008; 105:18770-5. [PMID: 19047635 PMCID: PMC2596208 DOI: 10.1073/pnas.0800793105] [Citation(s) in RCA: 262] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2008] [Indexed: 11/18/2022] Open
Abstract
Extracellular ATP controls various signaling systems including propagation of intercellular Ca(2+) signals (ICS). Connexin hemichannels, P2x7 receptors (P2x7Rs), pannexin channels, anion channels, vesicles, and transporters are putative conduits for ATP release, but their involvement in ICS remains controversial. We investigated ICS in cochlear organotypic cultures, in which ATP acts as an IP(3)-generating agonist and evokes Ca(2+) responses that have been linked to noise-induced hearing loss and development of hair cell-afferent synapses. Focal delivery of ATP or photostimulation with caged IP(3) elicited Ca(2+) responses that spread radially to several orders of unstimulated cells. Furthermore, we recorded robust Ca(2+) signals from an ATP biosensor apposed to supporting cells outside the photostimulated area in WT cultures. ICS propagated normally in cultures lacking either P2x7R or pannexin-1 (Px1), as well as in WT cultures exposed to blockers of anion channels. By contrast, Ca(2+) responses failed to propagate in cultures with defective expression of connexin 26 (Cx26) or Cx30. A companion paper demonstrates that, if expression of either Cx26 or Cx30 is blocked, expression of the other is markedly down-regulated in the outer sulcus. Lanthanum, a connexin hemichannel blocker that does not affect gap junction (GJ) channels when applied extracellularly, limited the propagation of Ca(2+) responses to cells adjacent to the photostimulated area. Our results demonstrate that these connexins play a dual crucial role in inner ear Ca(2+) signaling: as hemichannels, they promote ATP release, sustaining long-range ICS propagation; as GJ channels, they allow diffusion of Ca(2+)-mobilizing second messengers across coupled cells.
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Affiliation(s)
- Fabio Anselmi
- Foundation for Advanced Biomedical Research, Venetian Institute of Molecular Medicine, 35129 Padua, Italy
| | - Victor H. Hernandez
- Foundation for Advanced Biomedical Research, Venetian Institute of Molecular Medicine, 35129 Padua, Italy
| | - Giulia Crispino
- Foundation for Advanced Biomedical Research, Venetian Institute of Molecular Medicine, 35129 Padua, Italy
| | - Anke Seydel
- Foundation for Advanced Biomedical Research, Venetian Institute of Molecular Medicine, 35129 Padua, Italy
| | - Saida Ortolano
- Foundation for Advanced Biomedical Research, Venetian Institute of Molecular Medicine, 35129 Padua, Italy
- Department of Physics “G. Galilei,” University of Padua, 35129 Padua, Italy
| | - Stephen D. Roper
- Department of Physiology and Biophysics and Program in Neurosciences, Miller School of Medicine, University of Miami, Miami, FL 33136
| | - Nicoletta Kessaris
- Wolfson Institute for Biomedical Research and Department of Biology, University College London, London WC1E 6BT, United Kingdom
| | - William Richardson
- Wolfson Institute for Biomedical Research and Department of Biology, University College London, London WC1E 6BT, United Kingdom
| | - Gesa Rickheit
- Leibniz-Institut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), D-13125 Berlin, Germany; and
| | - Mikhail A. Filippov
- Department of Clinical Neurobiology, University Hospital of Neurology, Heidelberg, Germany
| | - Hannah Monyer
- Department of Clinical Neurobiology, University Hospital of Neurology, Heidelberg, Germany
| | - Fabio Mammano
- Foundation for Advanced Biomedical Research, Venetian Institute of Molecular Medicine, 35129 Padua, Italy
- Department of Physics “G. Galilei,” University of Padua, 35129 Padua, Italy
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Meşe G, Valiunas V, Brink PR, White TW. Connexin26 deafness associated mutations show altered permeability to large cationic molecules. Am J Physiol Cell Physiol 2008; 295:C966-74. [PMID: 18684989 DOI: 10.1152/ajpcell.00008.2008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Intercellular communication is important for cochlear homeostasis because connexin26 (Cx26) mutations are the leading cause of hereditary deafness. Gap junctions formed by different connexins have unique selectivity to large molecules, so compensating for the loss of one isoform can be challenging in the case of disease causing mutations. We compared the properties of Cx26 mutants T8M and N206S with wild-type channels in transfected cells using dual whole cell voltage clamp and dye flux experiments. Wild-type and mutant channels demonstrated comparable ionic coupling, and their average unitary conductance was approximately 106 and approximately 60 pS in 120 mM K(+)-aspartate(-) and TEA(+)-aspartate(-) solution, respectively, documenting their equivalent permeability to K(+) and TEA(+). Comparison of cAMP, Lucifer Yellow (LY), and ethidium bromide (EtBr) transfer revealed differences in selectivity for larger anionic and cationic tracers. cAMP and LY permeability to wild-type and mutant channels was similar, whereas the transfer of EtBr through mutant channels was greatly reduced compared with wild-type junctions. Altered permeability of Cx26 to large cationic molecules suggests an essential role for biochemical coupling in cochlear homeostasis.
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Affiliation(s)
- Gülistan Meşe
- Graduate Program in Genetics, State University of New York, Stony Brook, New York 11794-8661, USA
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34
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Ahn M, Lee J, Gustafsson A, Enriquez A, Lancaster E, Sul JY, Haydon PG, Paul DL, Huang Y, Abrams CK, Scherer SS. Cx29 and Cx32, two connexins expressed by myelinating glia, do not interact and are functionally distinct. J Neurosci Res 2008; 86:992-1006. [PMID: 17972320 PMCID: PMC2663799 DOI: 10.1002/jnr.21561] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
In rodents, oligodendrocytes and myelinating Schwann cells express connexin32 (Cx32) and Cx29, which have different localizations in the two cell types. We show here that, in contrast to Cx32, Cx29 does not form gap junction plaques or functional gap junctions in transfected cells. Furthermore, when expressed together, Cx29 and Cx32 are not colocalized and do not coimmunoprecipitate. To determine the structural basis of their divergent behavior, we generated a series of chimeric Cx32-Cx29 proteins by exchanging their intracellular loops and/or their C-terminal cytoplasmic tails. Although some chimerae reach the cell membrane, others appear to be largely localized intracellularly; none form gap junction plaques or functional gap junctions. Substituting the C-terminus or the intracellular loop and the C-terminus of Cx32 with those of Cx29 does not disrupt their colocalization or coimmunoprecipitation with Cx32. Substituting the C-terminus of Cx29 with that of Cx32 does not disrupt the coimmunoprecipitation or the colocalization with Cx29, whereas substituting both the intracellular loop and the C-terminus of Cx32 with those of Cx29 diminishes the coimmunoprecipitation with Cx29. Conversely, the Cx32 chimera that contains the intracellular loop of Cx29 coimmunoprecipitates with Cx29, indicating that the intracellular loop participates in Cx29-Cx29 interactions. These data indicate that homomeric interactions of Cx29 and especially Cx32 largely require other domains: the N-terminus, transmembrane domains, and extracellular loops. Substituting the intracellular loop and/or tail of Cx32 with those of Cx29 appears to prevent Cx32 from forming functional gap junctions.
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Affiliation(s)
- Meejin Ahn
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - Jonathan Lee
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - Andreas Gustafsson
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - Alan Enriquez
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - Eric Lancaster
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - Jai-Yoon Sul
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - Philip G. Haydon
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - David L. Paul
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts
| | - Yan Huang
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| | - Charles K. Abrams
- Department of Neurology, SUNY Downstate Medical Center, Brooklyn, New York
| | - Steven S. Scherer
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
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Clair C, Combettes L, Pierre F, Sansonetti P, Tran Van Nhieu G. Extracellular-loop peptide antibodies reveal a predominant hemichannel organization of connexins in polarized intestinal cells. Exp Cell Res 2008; 314:1250-65. [PMID: 18267319 DOI: 10.1016/j.yexcr.2007.12.021] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2007] [Revised: 11/19/2007] [Accepted: 12/20/2007] [Indexed: 01/18/2023]
Abstract
Shigella, the causative agent of bacillary dysentery, invades colonic epithelial cells to elicit an intense inflammatory reaction leading to destruction of the mucosa. ATP-dependent paracrine signalling induced by connexin (Cx) hemichannel opening was previously shown to favor Shigella flexneri invasion and dissemination in transfectants of HeLa cells [G. Tran Van Nhieu, C. Clair, R. Bruzzone, M. Mesnil, P. Sansonetti and L. Combettes. (2003). Connexin-dependent intercellular communication increases invasion and dissemination of Shigella in epithelial cells. Nat. Cell Biol. 5, 720-726.]. However, although Cxs have been described in polarized epithelial cells, little is known about their structural organization and the role of hemichannels during S. flexneri invasion. We show here that polarized Caco-2/TC7 cells express significant amounts of Cx26, Cx32 and Cx43, but that unexpectedly, cell-cell coupling assessed by dye-transfer experiments is inefficient. Consistent with a predominant Cx organization in hemichannels, dye loading induced by low calcium was readily observed, with preferential loading at the basolateral side. Antibodies (Abs) against connexin extracellular loop peptides (CELAbs) demonstrated the importance of hemichannel signalling since they inhibited dye uptake at low calcium and at physiological calcium concentrations during S. flexneri invasion. Importantly, CELAbs allowed the visualization of hemichannels at the surface of epithelial cells, as structures distinct from gap intercellular junctions.
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Affiliation(s)
- Caroline Clair
- Unité de Pathogénie Microbienne Moléculaire, Institut Pasteur, Paris Cedex 15, France
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36
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Orthmann-Murphy JL, Freidin M, Fischer E, Scherer SS, Abrams CK. Two distinct heterotypic channels mediate gap junction coupling between astrocyte and oligodendrocyte connexins. J Neurosci 2007; 27:13949-57. [PMID: 18094232 PMCID: PMC6673504 DOI: 10.1523/jneurosci.3395-07.2007] [Citation(s) in RCA: 139] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2007] [Revised: 10/11/2007] [Accepted: 10/22/2007] [Indexed: 12/23/2022] Open
Abstract
Genetic diseases demonstrate that the normal function of CNS myelin depends on connexin32 (Cx32) and Cx47, gap junction (GJ) proteins expressed by oligodendrocytes. GJs couple oligodendrocytes and astrocytes (O/A channels) as well as astrocytes themselves (A/A channels). Because astrocytes express different connexins (Cx30 and Cx43), O/A channels must be heterotypic, whereas A/A channels may be homotypic or heterotypic. Using electrophysiological and immunocytochemical approaches, we found that Cx47/Cx43 and Cx32/Cx30 efficiently formed functional channels, but other potential heterotypic O/A and A/A pairs did not. These results suggest that Cx30/Cx30 and Cx43/Cx43 channels mediate A/A coupling, and Cx47/Cx43 and Cx32/Cx30 channels mediate O/A coupling. Furthermore, Cx47/Cx43 and Cx32/Cx30 channels have distinct macroscopic and single-channel properties and different dye permeabilities. Finally, Cx47 mutants that cause Pelizaeus-Merzbacher-like disease do not efficiently form functional channels with Cx43, indicating that disrupted Cx47/Cx43 channels cause this disease.
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Affiliation(s)
- Jennifer L Orthmann-Murphy
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6077, USA.
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37
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Yum SW, Zhang J, Valiunas V, Kanaporis G, Brink PR, White TW, Scherer SS. Human connexin26 and connexin30 form functional heteromeric and heterotypic channels. Am J Physiol Cell Physiol 2007; 293:C1032-48. [PMID: 17615163 DOI: 10.1152/ajpcell.00011.2007] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mutations in GJB2 and GJB6, the genes that encode the human gap junction proteins connexin26 (Cx26) and connexin30 (Cx30), respectively, cause hearing loss. Cx26 and Cx30 are both expressed in the cochlea, leading to the potential formation of heteromeric hemichannels and heterotypic gap junction channels. To investigate their interactions, we expressed human Cx26 and Cx30 individually or together in HeLa cells. When they were expressed together, Cx26 and Cx30 appeared to interact directly (by their colocalization in gap junction plaques, by coimmunoprecipitation, and by fluorescence resonance energy transfer). Scrape-loading cells that express either Cx26 or Cx30 demonstrated that Cx26 homotypic channels robustly transferred both cationic and anionic tracers, whereas Cx30 homotypic channels transferred cationic but not anionic tracers. Cells expressing both Cx26 and Cx30 also transferred both cationic and anionic tracers by scrape loading, and the rate of calcein (an anionic tracer) transfer was intermediate between their homotypic counterparts by fluorescence recovery after photobleaching. Fluorescence recovery after photobleaching also showed that Cx26 and Cx30 form functional heterotypic channels, allowing the transfer of calcein, which did not pass the homotypic Cx30 channels. Electrophysiological recordings of cell pairs expressing different combinations of Cx26 and/or Cx30 demonstrated unique gating properties of cell pairs expressing both Cx26 and Cx30. These results indicate that Cx26 and Cx30 form functional heteromeric and heterotypic channels, whose biophysical properties and permeabilities are different from their homotypic counterparts.
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Affiliation(s)
- Sabrina W Yum
- Section of Neurology, St. Christopher's Hospital for Children, Erie Ave. at Front St., Philadelphia, PA 19134, USA.
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38
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Locke D, Jamieson S, Stein T, Liu J, Hodgins MB, Harris AL, Gusterson B. Nature of Cx30-containing channels in the adult mouse mammary gland. Cell Tissue Res 2007; 328:97-107. [PMID: 17120054 DOI: 10.1007/s00441-006-0301-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2006] [Accepted: 07/12/2006] [Indexed: 10/23/2022]
Abstract
Oligonucleotide microarray analysis uniquely shows that several members of the connexin family of gap junction proteins are expressed by the epithelium during mouse mammary gland development. Connexin 26 (Cx26) is present throughout pregnancy and lactation, is then undetectable shortly after weaning, but reappears during involution. Additionally, Cx30 is abundant in late-pregnant and early lactating gland epithelium. From mid-pregnancy into early lactation, Cx26 and Cx30 co-localize in junctional plaques between epithelial cells, forming hemichannels of mixed connexin content. Microarray analysis also shows Cx32 is developmentally restricted to parturition, suggesting that specific modification of gap junction channel composition and/or intercellular communication pathways occurs at parturition. Specifically, heteromeric channels of all pairwise combinations are formed when these connexins are expressed within the same cells. Of these hemichannels, Cx26/Cx32 pores are increasingly sensitive to closure by taurine (an osmolyte implicated in milk protein synthesis) with increasing Cx26 content. In contrast, physiological taurine concentrations have no effect on Cx26/Cx30 and Cx30/Cx32 channel activity. Such changes in connexin expression and channel composition and their chemical modulation are discussed in relation to the various stages of mammary gland development in the adult mouse.
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Affiliation(s)
- Darren Locke
- Department of Pharmacology and Physiology, New Jersey Medical School, UMDNJ, Newark, NJ 07103, USA.
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Hernandez VH, Bortolozzi M, Pertegato V, Beltramello M, Giarin M, Zaccolo M, Pantano S, Mammano F. Unitary permeability of gap junction channels to second messengers measured by FRET microscopy. Nat Methods 2007; 4:353-8. [PMID: 17351620 DOI: 10.1038/nmeth1031] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2007] [Accepted: 02/22/2007] [Indexed: 11/08/2022]
Abstract
Gap junction channels assembled from connexin protein subunits mediate intercellular transfer of ions and metabolites. Impaired channel function is implicated in several hereditary human diseases. In particular, defective permeation of cAMP or inositol-1,4,5-trisphosphate (InsP(3)) through connexin channels is associated with peripheral neuropathies and deafness, respectively. Here we present a method to estimate the permeability of single gap junction channels to second messengers. Using HeLa cells that overexpressed wild-type human connexin 26 (HCx26wt) as a model system, we combined measurements of junctional conductance and fluorescence resonance energy transfer (FRET) emission ratio of biosensors selective for cAMP and InsP(3). The unitary permeabilities to cAMP (47 x 10(-3) +/- 15 x 10(-3) microm(3)/s) and InsP(3) (60 x 10(-3) +/- 12 x 10(-3) microm(3)/s) were similar, but substantially larger than the unitary permeability to lucifer yellow (LY; 7 +/- 3 x 10(-3) microm(3)/s), an exogenous tracer. This method permits quantification of defects of metabolic coupling and can be used to investigate interdependence of intercellular diffusion and cross-talk between diverse signaling pathways.
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Affiliation(s)
- Victor H Hernandez
- Istituto Veneto di Medicina Molecolare, Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
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40
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González D, Gómez-Hernández JM, Barrio LC. Species specificity of mammalian connexin-26 to form open voltage-gated hemichannels. FASEB J 2006; 20:2329-38. [PMID: 17077310 DOI: 10.1096/fj.06-5828com] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Mutations of connexin-26 (Cx26) cause nonsyndromic hearing loss and other syndromes affecting ectoderm-derived tissues. While the exact mechanisms underlying these diseases remain elusive, Cx's are generally considered to mediate cell-to-cell communication by forming gap junction channels. We show here that unlike rat Cx26, human and sheep Cx26 form voltage-gated hemichannels when expressed in oocytes and Neuro2A cells. A single evolutionary amino acidic change at position 159 of the rodent protein, the replacement of aspartic acid with asparagine in the human and sheep proteins, accounts for this species specificity. At the resting potential and in normal millimolar extracellular calcium, open human Cx26 hemichannels can be detected both electrophysiologically and by dye uptake, although they did not affect cell viability. These hemichannels opened at approximately -50 mV and their activation increased by depolarization until they inactivate at positive membrane potentials. Single-channel analysis revealed that activation and inactivation involved two distinct voltage gating mechanisms and that the fully open hemichannel displays a conductance twice that of the intercellular channel. The existence of a hemichannel that opens under physiological control of the membrane potential may have important implications for the normal and pathological activity of Cx26 in humans, particularly with respect to hearing and the epidermis.
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Affiliation(s)
- Daniel González
- Unit of Experimental Neurology, Research Department, Ramón y Cajal Hospital, Madrid, Spain
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41
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Zhao HB, Yu N. Distinct and gradient distributions of connexin26 and connexin30 in the cochlear sensory epithelium of guinea pigs. J Comp Neurol 2006; 499:506-18. [PMID: 16998915 PMCID: PMC2553046 DOI: 10.1002/cne.21113] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Connexin26 (Cx26) and Cx30 are predominant isoforms of gap junction channels in the cochlea and play a critical role in hearing. In this study, the cellular distributions of Cx26 and Cx30 in the cochlear sensory epithelium of guinea pigs were examined by immunofluorescent staining and confocal microscopy in whole mounts of the cochlear sensory epithelium and dissociated cell preparations. The expression of Cx26 and Cx30 demonstrated a longitudinal gradient distribution in the epithelium and was reduced threefold from the cochlear apex to base. The reduction was more pronounced in the Deiters cells and pillar cells than in the Hensen cells. Cx26 was expressed in all types of supporting cells, but little Cx30 labeling was seen in the Hensen cells. Cx26 expression in the Hensen cells was concentrated mainly in the second and third rows, forming a distinct band along the sensory epithelium at its outer region. In the dissociated Deiters cells and pillar cells, Cx30 showed dense labeling at the cell bodies and processes in the reticular lamina. Cx26 labeling largely overlapped that of Cx30 in these regions. Cx26 and Cx30 were also coexpressed in the gap junctional plaques between Claudius cells. Neither Cx26 nor Cx30 labeling was seen in the hair cells and spiral ganglion neurons. These observations demonstrate that Cx26 and Cx30 have a longitudinal gradient distribution and distinct cellular expression in the auditory sensory epithelium. This further supports our previous reports that Cx26 and Cx30 can solely and concertedly perform different functions in the cochlea.
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Affiliation(s)
- Hong-Bo Zhao
- Department of Surgery-Otolaryngology, University of Kentucky Medical Center, Lexington, Kentucky 40536, USA.
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42
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Deng Y, Chen Y, Reuss L, Altenberg GA. Mutations of connexin 26 at position 75 and dominant deafness: essential role of arginine for the generation of functional gap-junctional channels. Hear Res 2006; 220:87-94. [PMID: 16945493 DOI: 10.1016/j.heares.2006.07.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Revised: 07/11/2006] [Accepted: 07/13/2006] [Indexed: 11/27/2022]
Abstract
Gap-junctional channels are large intercellular aqueous pores formed by head-to-head association of two gap-junctional hemichannels (connexin hexamers), one from each of the adjacent cells. The mechano-transduction of sound waves into electrical impulses occurs in the cochlea, which houses the organ of Corti. Hereditary deafness is frequent and mutations of connexin 26, the predominant connexin of the cochlea, are its most frequent cause. Mutations of R75 cause deafness and disrupt gap-junctional communication. Here, we determined the effects of substitutions of R75 with different residues (alanine, asparagine, aspartic acid, lysine, phenylalanine, tyrosine or tryptophan) on formation of gap-junctional channels and hemichannels. We show that connexin 26 R75 is essential for the formation of gap-junctional channels. Substitution of R75 with aromatic residues yields functional hemichannels that display altered voltage dependence, whereas substitution with other residues yields non-functional hemichannels. The expression of R75 mutants has a dominant negative effect on gap-junctional communication mediated by wild-type connexin 26, independently of the ability of the mutants to form functional gap-junctional hemichannels. Our results show that the arginine located at position 75 of connexin 26 is essential for function, and cannot be replaced by other residues.
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Affiliation(s)
- Yanqin Deng
- Department of Neuroscience and Cell Biology, and the Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555-0437, United States
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Bicego M, Beltramello M, Melchionda S, Carella M, Piazza V, Zelante L, Bukauskas FF, Arslan E, Cama E, Pantano S, Bruzzone R, D’Andrea P, Mammano F. Pathogenetic role of the deafness-related M34T mutation of Cx26. Hum Mol Genet 2006; 15:2569-87. [PMID: 16849369 PMCID: PMC2829448 DOI: 10.1093/hmg/ddl184] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Mutations in the GJB2 gene, which encodes the gap junction protein connexin26 (Cx26), are the major cause of genetic non-syndromic hearing loss. The role of the allelic variant M34T in causing hereditary deafness remains controversial. By combining genetic, clinical, biochemical, electrophysiological and structural modeling studies, we have re-assessed the pathogenetic role of the M34T mutation. Genetic and audiological data indicate that the majority of heterozygous carriers and all five compound heterozygotes exhibited an impaired auditory function. Functional expression in transiently transfected HeLa cells showed that, although M34T was correctly synthesized and targeted to the plasma membrane, it inefficiently formed intercellular channels that displayed an abnormal electrical behavior and retained only 11% of the unitary conductance of the wild-type protein (HCx26wt). Moreover, M34T channels failed to support the intercellular diffusion of Lucifer Yellow and the spreading of mechanically induced intercellular Ca2+ waves. When co-expressed together with HCx26wt, M34T exerted dominant-negative effects on cell-cell coupling. Our findings are consistent with a structural model, predicting that the mutation leads to a constriction of the channel pore. These data support the view that M34T is a pathological variant of Cx26 associated with hearing impairment.
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Affiliation(s)
- Massimiliano Bicego
- Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, University of Trieste, 34127 Trieste, Italy
| | - Martina Beltramello
- Istituto Veneto di Medicina Molecolare (VIMM), Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
| | - Salvatore Melchionda
- Servizio di Genetica Medica, IRCCS-Ospedale Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Massimo Carella
- Servizio di Genetica Medica, IRCCS-Ospedale Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Valeria Piazza
- Istituto Veneto di Medicina Molecolare (VIMM), Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
| | - Leopoldo Zelante
- Servizio di Genetica Medica, IRCCS-Ospedale Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Feliksas F. Bukauskas
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Edoardo Arslan
- Servizio di Audiologia e Foniatria, University of Padova, 35128 Padova, Italy
| | - Elona Cama
- Servizio di Audiologia e Foniatria, University of Padova, 35128 Padova, Italy
| | - Sergio Pantano
- Istituto Veneto di Medicina Molecolare (VIMM), Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
- Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (CNISM)
| | - Roberto Bruzzone
- Département de Neuroscience, Institut Pasteur, 75015 Paris, France
- To whom correspondence should be addressed at: Département de Neuroscience, Institut Pasteur, 25, rue du Dr Roux, 75015 Paris, France. Tel: +33 140613436; Fax: +33 140613421;
| | - Paola D’Andrea
- Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, University of Trieste, 34127 Trieste, Italy
| | - Fabio Mammano
- Istituto Veneto di Medicina Molecolare (VIMM), Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova, Italy
- Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (CNISM)
- Dipartimento di Fisica ‘G.Galilei’, Università di Padova, 35131 Padova, Italy
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Gemel J, Lin X, Veenstra RD, Beyer EC. N-terminal residues in Cx43 and Cx40 determine physiological properties of gap junction channels, but do not influence heteromeric assembly with each other or with Cx26. J Cell Sci 2006; 119:2258-68. [PMID: 16723732 PMCID: PMC3237058 DOI: 10.1242/jcs.02953] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The cytoplasmic N-terminal domain in the connexins (Cx) has been implicated in determining several properties including connexin hetero-oligomerization, channel gating and regulation by polyamines. To elucidate the roles of potentially crucial amino acids, we produced site-directed mutants of connexins Cx40 and Cx43 (Cx40E12S,E13G and Cx43D12S,K13G) in which the charged amino acids at positions 12 and 13 were replaced with serine and glycine as found in Cx32. HeLa, N2a and HEK293 cells were transfected and studied by immunochemistry and double whole-cell patch clamping. Immunoblotting confirmed production of the mutant proteins, and immuno-fluorescence localized them to punctuate distributions along appositional membranes. Cx40E12S,E13G and Cx43D12S,K13G formed homotypic gap junction channels that allowed intercellular passage of Lucifer Yellow and electrical current, but these channels exhibited negligible voltage-dependent gating properties. Unlike wild-type Cx40, Cx40E12S,E13G channels were insensitive to block by 2 mM spermine. Affinity purification of material solubilized by Triton X-100 from cells co-expressing mutant Cx43 or mutant Cx40 with wild-type Cx40, Cx43 or Cx26 showed that introducing the mutations did not affect the compatibility or incompatibility of these proteins for heteromeric mixing. Co-expression of Cx40E12S,E13G with wild-type Cx40 or Cx43 dramatically reduced voltage-dependent gating. Thus, whereas the charged amino acids at positions 12 and 13 of Cx40 or Cx43 are not required for gap junction assembly or the compatibility of oligomerization with each other or with Cx26, they strongly influence several physiological properties including those of heteromeric channels.
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Affiliation(s)
- Joanna Gemel
- Department of Pediatrics, Section of Hematology/Oncology and Stem Cell Transplantation, University of Chicago, Chicago MC4060, 5841 S. Maryland Ave, Chicago, IL 60637-1470, USA
| | - Xianming Lin
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY 13210, USA
| | - Richard D. Veenstra
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY 13210, USA
| | - Eric C. Beyer
- Department of Pediatrics, Section of Hematology/Oncology and Stem Cell Transplantation, University of Chicago, Chicago MC4060, 5841 S. Maryland Ave, Chicago, IL 60637-1470, USA
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Bicego M, Morassutto S, Hernandez VH, Morgutti M, Mammano F, D'Andrea P, Bruzzone R. Selective defects in channel permeability associated with Cx32 mutations causing X-linked Charcot-Marie-Tooth disease. Neurobiol Dis 2006; 21:607-17. [PMID: 16442804 DOI: 10.1016/j.nbd.2005.09.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2005] [Revised: 09/04/2005] [Accepted: 09/09/2005] [Indexed: 11/17/2022] Open
Abstract
The X-linked form of Charcot-Marie-Tooth disease (CMTX) is caused by mutations in connexin32 (Cx32), a gap junction protein expressed by Schwann cells where it forms reflexive channels that allow the passage of ions and signaling molecules across the myelin sheath. Although most mutations result in loss of function, several studies have reported that some retain the ability to form homotypic intercellular channels. To gain insight into the molecular defect of three functional CMTX variants, S26L, Delta111-116 and R220stop, we have used several fluorescent tracers of different size and ionic charge to compare their permeation properties to those of wild-type Cx32. Although all mutations allowed the passage of the dye with the smallest molecular mass, they exhibited a clear reduction in the permeability of either one or all of the probes with respect to wild-type channels, as assessed by the percentage of injections showing dye coupling. These data reveal that a lower size cutoff distinguishes these functional CMTX variants from wild-type channels and suggest that this defect may be of pathophysiological relevance.
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Affiliation(s)
- Massimiliano Bicego
- Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, University of Trieste, via Licio Giorgieri 1, 34127 Trieste, Italy
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46
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Abstract
Gap junctions play a critical role in hearing and mutations in connexin genes cause a high incidence of human deafness. Pathogenesis mainly occurs in the cochlea, where gap junctions form extensive networks between non-sensory cells that can be divided into two independent gap junction systems, the epithelial cell gap junction system and the connective tissue cell gap junction system. At least four different connexins have been reported to be present in the mammalian inner ear, and gap junctions are thought to provide a route for recycling potassium ions that pass through the sensory cells during the mechanosensory transduction process back to the endolymph. Here we review the cochlear gap junction networks and their hypothesized role in potassium ion recycling mechanism, pharmacological and physiological gating of cochlear connexins, animal models harboring connexin mutations and functional studies of mutant channels that cause human deafness. These studies elucidate gap junction functions in the cochlea and also provide insight for understanding the pathogenesis of this common hereditary deafness induced by connexin mutations.
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Affiliation(s)
- H.-B. Zhao
- Department of Surgery-Otolaryngology, University of Kentucky Medical Center, Lexington, KY, USA
| | - T. Kikuchi
- Department of Otolaryngology-Head and Neck Surgery, Tohoku University Graduate School of Medicine, Sendai, Japan
| | - A. Ngezahayo
- Institute of Biophysics, University of Hannover, Hannover, Germany
| | - T.W. White
- Department of Physiology and Biophysics, State University of New York, Stony Brook, NY, USA
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47
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Zhao P, Li W, Dong YM, Zhu D, Qu AL, Xu T, Wu ZX. Kir6.2DeltaC26 channel traffics to plasma membrane by constitutive exocytosis. Acta Biochim Biophys Sin (Shanghai) 2006; 38:136-41. [PMID: 16474905 DOI: 10.1111/j.1745-7270.2006.00132.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Adenosine triphosphate (ATP)-sensitive K+ (KATP) channels regulate many cellular functions by coupling the metabolic state of the cell to the changes in membrane potential. Truncation of C-terminal 26 amino acid residues of Kir6.2 protein (Kir6.2DeltaC26) deletes its endoplasmic reticulum retention signal, allowing functional expression of Kir6.2 in the absence of sulfonylurea receptor subunit. pEGFP-Kir6.2DeltaC26 and pKir6.2DeltaC26-IRES2-EGFP expression plasmids were constructed and transfected into HEK293 cells. We identified that Kir6.2DeltaC26 was localized on the plasma membrane and trafficked to the plasmalemma by means of constitutive exocytosis of Kir6.2DeltaC26 transport vesicles, using epi-fluorescence and total internal reflection fluorescence microscopy. Our electrophysiological data showed that Kir6.2DeltaC26 alone expressed KATP currents, whereas EGFP-Kir6.2DeltaC26 fusion protein displayed no KATP channel activity.
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Affiliation(s)
- Ping Zhao
- Institute of Biophysics and Biochemistry, Huazhong University of Science and Technology, Wuhan 430074, China
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48
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Melchionda S, Bicego M, Marciano E, Franzè A, Morgutti M, Bortone G, Zelante L, Carella M, D'Andrea P. Functional characterization of a novel Cx26 (T55N) mutation associated to non-syndromic hearing loss. Biochem Biophys Res Commun 2005; 337:799-805. [PMID: 16226720 DOI: 10.1016/j.bbrc.2005.09.116] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2005] [Accepted: 09/11/2005] [Indexed: 11/20/2022]
Abstract
Mutations of the GJB2 gene, encoding connexin 26, are the most common cause of hereditary congenital hearing loss in many countries and account for up to 50% of cases of autosomal-recessive non-syndromic deafness. By contrast, only a few GJB2 mutations have been reported to cause an autosomal-dominant form of non-syndromic deafness. Here, we report a family from Southern Italy affected by non-syndromic autosomal dominant post-lingual hearing loss, due to a novel missense mutation in the GJB2 gene, a threonine to asparagine amino acid substitution at codon 55 (T55N). Functional studies indicated that the mutation T55N produces a protein that, although expressed to levels similar to those of the wt counterpart, is deeply impaired in its intracellular trafficking and fails to reach the plasma membrane. The mutation T55N is located at the apex of the first extracellular loop of the protein, a region suggested to play a role in protein targeting and a site for other two mutations, G59A and D66H, causing dominant forms of deafness.
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Affiliation(s)
- Salvatore Melchionda
- Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, University of Trieste, Trieste, Italy
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49
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Piazza V, Beltramello M, Menniti M, Colao E, Malatesta P, Argento R, Chiarella G, Gallo LV, Catalano M, Perrotti N, Mammano F, Cassandro E. Functional analysis of R75Q mutation in the gene coding for Connexin 26 identified in a family with nonsyndromic hearing loss. Clin Genet 2005; 68:161-6. [PMID: 15996214 DOI: 10.1111/j.1399-0004.2005.00468.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Mutations in the gene (GJB2) coding for Connexin 26 (Cx26) are responsible for genetic forms of sensorineural hearing loss. This article describes a family characterized by congenital profound hearing loss, inherited in an autosomal dominant fashion and associated to a R75Q substitution in Cx26. Cell transfection and fluorescence imaging, dye transfer experiments and dual patch clamp recording showed that the mutant completely prevents the formation of functional channels despite assembling into junctional plaques, in communication incompetent HeLa cells. The disease is not associated with palmar and plantar keratosis in any of the family members, suggesting that R75Q substitution is not sufficient for the development of the complete syndromic phenotype. The association of palmar and plantar keratosis with profound hearing loss may be dependent on genetic background, requiring a functional interaction between the mutated Cx26 and other epidermally expressed connexins.
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Affiliation(s)
- V Piazza
- Venetian Institute of Molecular Medicine, Padua, Italy
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50
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Chen Y, Deng Y, Bao X, Reuss L, Altenberg GA. Mechanism of the defect in gap-junctional communication by expression of a connexin 26 mutant associated with dominant deafness. FASEB J 2005; 19:1516-8. [PMID: 16009703 DOI: 10.1096/fj.04-3491fje] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Gap-junctional channels (connexin oligomers) are large-diameter aqueous pores formed by head-to-head association of two gap-junctional hemichannels, one from each of the adjacent cells. Profound hearing loss of genetic origin is common, and mutations of connexin 26 (Cx26) are the most frequent cause of this disorder. The Cx26 R75W mutant has been associated with disruption of cell-to-cell communication and profound hearing loss, but the mechanism of the gap-junctional defect is unknown. Here, we show that Cx26 R75W forms gap-junctional hemichannels that display altered voltage dependency and reduced permeability, and which cannot form functional gap-junctional channels between neighboring cells. The R75W phenotype is dominant at the gap-junction channel but not at the hemichannel level. Therefore, the absence of gap-junctional communication caused by R75W expression is due to defective gap-junction formation by functional hemichannels.
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Affiliation(s)
- Y Chen
- Department of Neuroscience and Cell Biology, and Membrane Protein Laboratory of the Sealy Center for Structural Biology, The University of Texas Medical Branch Galveston, Texas 77555-0437, USA
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