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Posukh OL, Maslova EA, Danilchenko VY, Zytsar MV, Orishchenko KE. Functional Consequences of Pathogenic Variants of the GJB2 Gene (Cx26) Localized in Different Cx26 Domains. Biomolecules 2023; 13:1521. [PMID: 37892203 PMCID: PMC10604905 DOI: 10.3390/biom13101521] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 10/08/2023] [Accepted: 10/10/2023] [Indexed: 10/29/2023] Open
Abstract
One of the most common forms of genetic deafness has been predominantly associated with pathogenic variants in the GJB2 gene, encoding transmembrane protein connexin 26 (Cx26). The Cx26 molecule consists of an N-terminal domain (NT), four transmembrane domains (TM1-TM4), two extracellular loops (EL1 and EL2), a cytoplasmic loop, and a C-terminus (CT). Pathogenic variants in the GJB2 gene, resulting in amino acid substitutions scattered across the Cx26 domains, lead to a variety of clinical outcomes, including the most common non-syndromic autosomal recessive deafness (DFNB1A), autosomal dominant deafness (DFNA3A), as well as syndromic forms combining hearing loss and skin disorders. However, for rare and poorly documented variants, information on the mode of inheritance is often lacking. Numerous in vitro studies have been conducted to elucidate the functional consequences of pathogenic GJB2 variants leading to amino acid substitutions in different domains of Cx26 protein. In this work, we summarized all available data on a mode of inheritance of pathogenic GJB2 variants leading to amino acid substitutions and reviewed published information on their functional effects, with an emphasis on their localization in certain Cx26 domains.
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Affiliation(s)
- Olga L. Posukh
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
- Novosibirsk State University, 630090 Novosibirsk, Russia
| | - Ekaterina A. Maslova
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
- Novosibirsk State University, 630090 Novosibirsk, Russia
| | - Valeriia Yu. Danilchenko
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
- Novosibirsk State University, 630090 Novosibirsk, Russia
| | - Marina V. Zytsar
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
| | - Konstantin E. Orishchenko
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
- Novosibirsk State University, 630090 Novosibirsk, Russia
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Abbott AC, García IE, Villanelo F, Flores-Muñoz C, Ceriani R, Maripillán J, Novoa-Molina J, Figueroa-Cares C, Pérez-Acle T, Sáez JC, Sánchez HA, Martínez AD. Expression of KID syndromic mutation Cx26S17F produces hyperactive hemichannels in supporting cells of the organ of Corti. Front Cell Dev Biol 2023; 10:1071202. [PMID: 36699003 PMCID: PMC9868548 DOI: 10.3389/fcell.2022.1071202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2022] [Accepted: 12/15/2022] [Indexed: 01/11/2023] Open
Abstract
Some mutations in gap junction protein Connexin 26 (Cx26) lead to syndromic deafness, where hearing impairment is associated with skin disease, like in Keratitis Ichthyosis Deafness (KID) syndrome. This condition has been linked to hyperactivity of connexin hemichannels but this has never been demonstrated in cochlear tissue. Moreover, some KID mutants, like Cx26S17F, form hyperactive HCs only when co-expressed with other wild-type connexins. In this work, we evaluated the functional consequences of expressing a KID syndromic mutation, Cx26S17F, in the transgenic mouse cochlea and whether co-expression of Cx26S17F and Cx30 leads to the formation of hyperactive HCs. Indeed, we found that cochlear explants from a constitutive knock-in Cx26S17F mouse or conditional in vitro cochlear expression of Cx26S17F produces hyperactive HCs in supporting cells of the organ of Corti. These conditions also produce loss of hair cells stereocilia. In supporting cells, we found high co-localization between Cx26S17F and Cx30. The functional properties of HCs formed in cells co-expressing Cx26S17F and Cx30 were also studied in oocytes and HeLa cells. Under the recording conditions used in this study Cx26S17F did not form functional HCs and GJCs, but cells co-expressing Cx26S17F and Cx30 present hyperactive HCs insensitive to HCs blockers, Ca2+ and La3+, resulting in more Ca2+ influx and cellular damage. Molecular dynamic analysis of putative heteromeric HC formed by Cx26S17F and Cx30 presents alterations in extracellular Ca2+ binding sites. These results support that in KID syndrome, hyperactive HCs are formed by the interaction between Cx26S17F and Cx30 in supporting cells probably causing damage to hair cells associated to deafness.
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Affiliation(s)
- Ana C. Abbott
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile,Facultad de Medicina Veterinaria y Agronomía, Instituto de Ciencias Naturales, Universidad de las Américas, Viña del Mar, Chile
| | - Isaac E. García
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile,Laboratorio de Fisiología Molecular y Biofísica, Facultad de Odontología, Universidad de Valparaíso, Valparaíso, Chile,Centro de Investigaciones en Ciencias Odontológicas y Médicas, CICOM, Universidad de Valparaíso, Valparaíso, Chile
| | - Felipe Villanelo
- Facultad de Ingeniería, Arquitectura y Diseño, Universidad San Sebastián, Santiago, Chile,Computational Biology Lab, Centro Basal Ciencia & Vida, Universidad San Sebastián, Santiago, Chile
| | - Carolina Flores-Muñoz
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Ricardo Ceriani
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile,Escuela de Química y Farmacia, Facultad de Farmacia, Universidad de Valparaíso, Valparaíso, Chile
| | - Jaime Maripillán
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Joel Novoa-Molina
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Cindel Figueroa-Cares
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Tomas Pérez-Acle
- Facultad de Ingeniería, Arquitectura y Diseño, Universidad San Sebastián, Santiago, Chile,Computational Biology Lab, Centro Basal Ciencia & Vida, Universidad San Sebastián, Santiago, Chile
| | - Juan C. Sáez
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Helmuth A. Sánchez
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile,*Correspondence: Helmuth A. Sánchez, ; Agustín D. Martínez,
| | - Agustín D. Martínez
- Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile,*Correspondence: Helmuth A. Sánchez, ; Agustín D. Martínez,
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3
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Liu W, Rask-Andersen H. GJB2 and GJB6 gene transcripts in the human cochlea: A study using RNAscope, confocal, and super-resolution structured illumination microscopy. Front Mol Neurosci 2022; 15:973646. [PMID: 36204137 PMCID: PMC9530750 DOI: 10.3389/fnmol.2022.973646] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Accepted: 08/01/2022] [Indexed: 11/26/2022] Open
Abstract
Background Gap junction (GJ) proteins, connexin26 and 30, are highly prevalent in the human cochlea (HC), where they are involved in transcellular signaling, metabolic supply, and fluid homeostasis. Their genes, GJB2 and GJB6, are both located at the DFNB1 locus on chromosome 13q12. Mutations in GJB2 may cause mild to profound non-syndromic deafness. Here, we analyzed for the first time the various expressions of GJB2 and GJB6 gene transcripts in the different cell networks in the HC using the RNAscope technique. Materials and methods Archival paraformaldehyde-fixed sections of surgically obtained HC were used to label single mRNA oligonucleotides using the sensitive multiplex RNAscope® technique with fluorescent-tagged probes. Positive and negative controls also included the localization of ATP1A1, ATP1A2, and KCNJ10 gene transcripts in order to validate the specificity of labeling. Results Confocal and super-resolution structured illumination microscopy (SR-SIM) detected single gene transcripts as brightly stained puncta. The GJB2 and GJB6 gene transcripts were distributed in the epithelial and connective tissue systems in all three cochlear turns. The largest number of GJB2 and GJB6 gene transcripts was in the outer sulcus, spiral ligament, and stria vascularis (SV). Oligonucleotides were present in the supporting cells of the organ of Corti (OC), spiral limbus fibrocytes, and the floor of the scala vestibuli. Multiplex gene data suggest that cells in the cochlear lateral wall contain either GJB2 or GJB6 gene transcripts or both. The GJB6, but not GJB2, gene transcripts were found in the intermediate cells but none were found in the marginal cells. There were no GJB2 or GJB6 gene transcripts found in the hair cells and only a few in the spiral ganglion cells. Conclusion Both GJB2 and GJB6 mRNA gene transcripts were localized in cells in the adult HC using RNAscope®in situ hybridization (ISH) and high resolution microscopy. Generally, GJB6 dominated over GJB2, except in the basal cells. Results suggest that cells may contain either GJB2 or GJB6 gene transcripts or both. This may be consistent with specialized GJ plaques having separate channel permeability and gating properties. A reduction in the number of GJB2 gene transcripts was found in the basal turn. Such information may be useful for future gene therapy.
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Waissbluth S, Maass JC, Sanchez HA, Martínez AD. Supporting Cells and Their Potential Roles in Cisplatin-Induced Ototoxicity. Front Neurosci 2022; 16:867034. [PMID: 35573297 PMCID: PMC9104564 DOI: 10.3389/fnins.2022.867034] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 04/06/2022] [Indexed: 11/13/2022] Open
Abstract
Cisplatin is a known ototoxic chemotherapy drug, causing irreversible hearing loss. Evidence has shown that cisplatin causes inner ear damage as a result of adduct formation, a proinflammatory environment and the generation of reactive oxygen species within the inner ear. The main cochlear targets for cisplatin are commonly known to be the outer hair cells, the stria vascularis and the spiral ganglion neurons. Further evidence has shown that certain transporters can mediate cisplatin influx into the inner ear cells including organic cation transporter 2 (OCT2) and the copper transporter Ctr1. However, the expression profiles for these transporters within inner ear cells are not consistent in the literature, and expression of OCT2 and Ctr1 has also been observed in supporting cells. Organ of Corti supporting cells are essential for hair cell activity and survival. Special interest has been devoted to gap junction expression by these cells as certain mutations have been linked to hearing loss. Interestingly, cisplatin appears to affect connexin expression in the inner ear. While investigations regarding cisplatin-induced hearing loss have been focused mainly on the known targets previously mentioned, the role of supporting cells for cisplatin-induced ototoxicity has been overlooked. In this mini review, we discuss the implications of supporting cells expressing OCT2 and Ctr1 as well as the potential role of gap junctions in cisplatin-induced cytotoxicity.
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Affiliation(s)
- Sofia Waissbluth
- Department of Otolaryngology, Pontificia Universidad Católica de Chile, Santiago, Chile
- *Correspondence: Sofia Waissbluth, ;
| | - Juan Cristóbal Maass
- Department of Otolaryngology, Hospital Clínico de la Universidad de Chile, Santiago, Chile
| | - Helmuth A. Sanchez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
| | - Agustín D. Martínez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
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Liu W, Rask-Andersen H. Na/K-ATPase Gene Expression in the Human Cochlea: A Study Using mRNA in situ Hybridization and Super-Resolution Structured Illumination Microscopy. Front Mol Neurosci 2022; 15:857216. [PMID: 35431803 PMCID: PMC9009265 DOI: 10.3389/fnmol.2022.857216] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Accepted: 02/23/2022] [Indexed: 12/03/2022] Open
Abstract
Background The pervasive Na/K-ATPase pump is highly expressed in the human cochlea and is involved in the generation of the endocochlear potential as well as auditory nerve signaling and relay. Its distribution, molecular organization and gene regulation are essential to establish to better understand inner ear function and disease. Here, we analyzed the expression and distribution of the ATP1A1, ATP1B1, and ATP1A3 gene transcripts encoding the Na/K-ATPase α1, α3, and β1 isoforms in different domains of the human cochlea using RNA in situ hybridization. Materials and Methods Archival paraformaldehyde-fixed sections derived from surgically obtained human cochleae were used to label single mRNA gene transcripts using the highly sensitive multiplex RNAscope® technique. Localization of gene transcripts was performed by super-resolution structured illumination microscopy (SR-SIM) using fluorescent-tagged probes. GJB6 encoding of the protein connexin30 served as an additional control. Results Single mRNA gene transcripts were seen as brightly stained puncta. Positive and negative controls verified the specificity of the labeling. ATP1A1 and ATP1B1 gene transcripts were demonstrated in the organ of Corti, including the hair and supporting cells. In the stria vascularis, these transcripts were solely expressed in the marginal cells. A large number of ATP1B1 gene transcripts were found in the spiral ganglion cell soma, outer sulcus, root cells, and type II fibrocytes. The ATP1B1 and ATP1A3 gene transcripts were rarely detected in axons. Discussion Surgically obtained inner ear tissue can be used to identify single mRNA gene transcripts using high-resolution fluorescence microscopy after prompt formaldehyde fixation and chelate decalcification. A large number of Na/K-ATPase gene transcripts were localized in selected areas of the cochlear wall epithelium, fibrocyte networks, and spiral ganglion, confirming the enzyme’s essential role for human cochlear function.
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Orellana VP, Tittarelli A, Retamal MA. Connexins in melanoma: Potential role of Cx46 in its aggressiveness. Pigment Cell Melanoma Res 2021; 34:853-868. [PMID: 33140904 DOI: 10.1111/pcmr.12945] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 10/20/2020] [Accepted: 10/27/2020] [Indexed: 12/19/2022]
Abstract
Melanoma is the most aggressive skin cancer, and in metastatic advanced states, it is completely refractory to chemotherapy. Therefore, it is relevant to understand the molecular bases that rule their aggressiveness. Connexins (Cxs) are proteins that under normal physiological conditions participate in intercellular communication, via the exchange of signaling molecules between the cytoplasm and extracellular milieu and the exchange of ions/second messengers between the cytoplasm of contacting cells. These proteins have shown important roles in cancer progression, chemo- and radiotherapy resistance, and metastasis. Accordingly, Cx26 and Cx43 seem to play important roles in melanoma progression and metastasis. On the other hand, Cx46 is typically expressed in the eye lens, where it seems to be associated with oxidative stress protection in fiber lens cells. However, in the last decade, Cx46 expression has been associated with breast and brain cancers, due to its role in potentiation of both extracellular vesicle release and cancer stem cell-like properties. In this review, we analyzed a potential role of Cx46 as a new biomarker and therapeutic target in melanoma.
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Affiliation(s)
- Viviana P Orellana
- Universidad del Desarrollo. Centro de Fisiología Celular e Integrativa, Clinica Alemana Facultad de Medicina, Santiago, Chile
- Universidad del Desarrollo. Programa de Comunicación Celular en Cáncer, Clínica Alemana Facultad de Medicina, Santiago, Chile
| | - Andrés Tittarelli
- Programa Institucional de Fomento a la Investigación, Desarrollo e Innovación (PIDi), Universidad Tecnológica Metropolitana (UTEM), Santiago, Chile
| | - Mauricio A Retamal
- Universidad del Desarrollo. Centro de Fisiología Celular e Integrativa, Clinica Alemana Facultad de Medicina, Santiago, Chile
- Universidad del Desarrollo. Programa de Comunicación Celular en Cáncer, Clínica Alemana Facultad de Medicina, Santiago, Chile
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Zhang J, Wang X, Hou Z, Neng L, Cai J, Zhang Y, Shi X. Suppression of Connexin 43 Leads to Strial Vascular Hyper-Permeability, Decrease in Endocochlear Potential, and Mild Hearing Loss. Front Physiol 2020; 11:974. [PMID: 32922309 PMCID: PMC7457066 DOI: 10.3389/fphys.2020.00974] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 07/16/2020] [Indexed: 12/20/2022] Open
Abstract
Objective: Connexin 43 (Cx43) is a protein constituent of gap junctions (GJs) in various barrier cells, especially astrocytes and microglia of the blood-brain-barrier (BBB), where it plays an important role in intercellular communication and regulation of the barrier. Despite the importance of Cx43 in other blood barriers, not much attention has been paid to expression and function of Cx43 in the blood-labyrinth-barrier (BLB) of the stria vascularis in the cochlea. Methods: We used multiple research approaches, including immunocytochemical staining, patch-clamp dye loading technique, real-time quantitative reverse transcription (RT)-PCR, western blot, measurement of endocochlear potential (EP) with an electrode through the scala media, and auditory brainstem response to test hearing function. Results: We found Cx43 expressed in vascular endothelial cells (ECs) and perivascular resident macrophages (PVMs) in the stria vascularis of adult C57BL/6 mouse cochleae. In particular, we found Cx43 expressed in foot processes of PVMs at points of contact with the endothelium. Consistent with Cx43 expression in vivo, we also found Cx43 expressed in EC-EC and EC-PVM interfaces in a co-cultured cell line model. Using a patch-clamp dye loading technique, we demonstrated that Alexa Fluor® 568 dye injected into PVMs diffuses to connected neighboring ECs. The functional coupling between the ECs and PVMs is blocked by 18α-Glycyrrhetinic acid (18α-GA), a GJ blocker. Suppression of Cx43 with small interfering RNA (siRNA) in vivo significantly elevated hearing threshold and caused the EP to drop and the blood barrier to become more permeable. In further study, using in vitro primary EC cell line models, we demonstrated that suppression of Cx43 disrupts intercellular tight junctions (TJs) in the EC monolayer and increases endothelial monolayer permeability. Conculsion: Taken together, these findings underscore the importance of Cx43 expression in the normal ear for maintaining BLB integrity, normal EP, and hearing function.
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Affiliation(s)
- Jinhui Zhang
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States
| | - Xiaohan Wang
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States
- Boston Children’s Hospital, Harvard Medical School, Boston, MA, United States
| | - Zhiqiang Hou
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States
| | - Lingling Neng
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States
| | - Jing Cai
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States
| | - Yunpei Zhang
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States
| | - Xiaorui Shi
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States
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Abitbol J, Beach R, Barr K, Esseltine J, Allman B, Laird D. Cisplatin-induced ototoxicity in organotypic cochlear cultures occurs independent of gap junctional intercellular communication. Cell Death Dis 2020; 11:342. [PMID: 32393745 PMCID: PMC7214471 DOI: 10.1038/s41419-020-2551-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Revised: 04/23/2020] [Accepted: 04/23/2020] [Indexed: 12/11/2022]
Abstract
Cisplatin is a very effective chemotherapeutic, but severe and permanent hearing loss remains a prevalent side effect. The processes underpinning cisplatin-induced ototoxicity are not well understood. Gap junction channels composed of connexin (Cx) subunits allow for the passage of small molecules and ions between contacting neighboring cells. These specialized channels have been postulated to enhance cisplatin-induced cell death by spreading “death signals” throughout the supporting cells of the organ of Corti. This study sought to investigate the role of Cx43 in cisplatin-induced ototoxicity using organotypic cochlear cultures from control and two Cx43-mutant mouse strains harboring either a moderate (Cx43I130T/+) or severe (Cx43G60S/+) reduction of Cx43 function. Cochlear cultures from Cx43-mutant mice with a severe reduction in Cx43-based gap junctional intercellular communication (GJIC) had an enhanced number of hair cells that were positive for cleaved caspase 3, a marker of active apoptosis, after cisplatin treatment. In cisplatin-treated organotypic cochlear cultures, there was a decrease in the co-localization of Cx26 and Cx30 compared with untreated cultures, suggesting that cisplatin causes reorganization of connexin composition in supporting cells. Both Cx26 and Cx30 protein expression as well as GJIC were decreased in organotypic cochlear cultures treated with the gap-junction blocker carbenoxolone. When cisplatin and carbenoxolone were co-administered, there were no differences in hair cell loss compared with cisplatin treatment alone. Using cisplatin-treated control and Cx43-ablated organ of Corti derived HEI-OC1 mouse cells, we found that greatly reducing GJIC led to preferential induction of an ER stress pathway. Taken together, this study strongly suggests that inhibition of GJIC in organ of Corti cells does not lead to differential susceptibility to cisplatin-induced ototoxicity. Although cisplatin causes the same degree of cell death in gap junction competent and incompetent cochlear cells, the engagement of the mitochondrial dysregulation and ER stress differs.
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Affiliation(s)
- Julia Abitbol
- Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5C1, Canada
| | - Rianne Beach
- Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5C1, Canada
| | - Kevin Barr
- Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5C1, Canada
| | - Jessica Esseltine
- Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, NL, A1B 3V6, Canada
| | - Brian Allman
- Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5C1, Canada
| | - Dale Laird
- Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5C1, Canada.
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Beach R, Abitbol JM, Allman BL, Esseltine JL, Shao Q, Laird DW. GJB2 Mutations Linked to Hearing Loss Exhibit Differential Trafficking and Functional Defects as Revealed in Cochlear-Relevant Cells. Front Cell Dev Biol 2020; 8:215. [PMID: 32300592 PMCID: PMC7142214 DOI: 10.3389/fcell.2020.00215] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Accepted: 03/12/2020] [Indexed: 11/13/2022] Open
Abstract
GJB2 gene (that encodes Cx26) mutations are causal of hearing loss highlighting the importance of Cx26-based channel signaling amongst the supporting cells in the organ of Corti. While the majority of these GJB2 mutations are inherited in an autosomal recessive manner, others are inherited in an autosomal dominant manner and lead to syndromic hearing loss as well as skin diseases. To assess if common or divergent mechanisms are at the root of GJB2-linked hearing loss, we expressed several mutants in cochlear-relevant HEI-OC1 cells derived from the developing organ of Corti. Since supporting cells of the mature mammalian organ of Corti have negligible Cx43, but HEI-OC1 cells are rich in Cx43, we first used CRISPR-Cas9 to ablate endogenous Cx43, thus establishing a connexin-deficient platform for controlled reintroduction of hearing-relevant connexins and Cx26 mutants. We found three distinct outcomes and cellular phenotypes when hearing loss-linked Cx26 mutants were expressed in cochlear-relevant cells. The dominant syndromic Cx26 mutant N54K had trafficking defects and did not fully prevent wild-type Cx26 gap junction plaque formation but surprisingly formed gap junctions when co-expressed with Cx30. In contrast, the dominant syndromic S183F mutant formed gap junctions incapable of transferring dye and, as expected, co-localized in the same gap junctions as wild-type Cx26 and Cx30, but also gained the capacity to intermix with Cx43 within gap junctions. Both recessive non-syndromic Cx26 mutants (R32H and R184P) were retained in intracellular vesicles including early endosomes and did not co-localize with Cx30. As might be predicted, none of the Cx26 mutants prevented Cx43 gap junction plaque formation in Cx43-rich HEI-OC1 cells while Cx43-ablation had little effect on the expression of reference genes linked to auditory cell differentiation. We conclude from our studies in cochlear-relevant cells that the selected Cx26 mutants likely evoke hearing loss via three unique connexin defects that are independent of Cx43 status.
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Affiliation(s)
- Rianne Beach
- Department of Anatomy and Cell Biology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada
| | - Julia M. Abitbol
- Department of Anatomy and Cell Biology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada
| | - Brian L. Allman
- Department of Anatomy and Cell Biology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada
| | - Jessica L. Esseltine
- Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John’s, NL, Canada
| | - Qing Shao
- Department of Anatomy and Cell Biology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada
| | - Dale W. Laird
- Department of Anatomy and Cell Biology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada
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Pandya A, O'Brien A, Kovasala M, Bademci G, Tekin M, Arnos KS. Analyses of del(GJB6-D13S1830) and del(GJB6-D13S1834) deletions in a large cohort with hearing loss: Caveats to interpretation of molecular test results in multiplex families. Mol Genet Genomic Med 2020; 8:e1171. [PMID: 32067424 PMCID: PMC7196463 DOI: 10.1002/mgg3.1171] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 01/24/2020] [Accepted: 01/30/2020] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND Mutations involving the closely linked GJB2 and GJB6 at the DFNB1 locus are a common genetic cause of profound congenital hearing loss in many populations. In some deaf GJB2 heterozygotes, a 309 kb deletion involving the GJB6 has been found to be the cause for hearing loss when inherited in trans to a GJB2 mutation. METHODS We screened 2,376 probands from a National DNA Repository of deaf individuals. RESULTS Fifty-two of 318 heterozygous probands with pathogenic GJB2 sequence variants had a GJB6 deletion. Additionally, eight probands had an isolated heterozygous GJB6 deletion that did not explain their hearing loss. In two deaf subjects, including one proband, a homozygous GJB6 deletion was the cause for their hearing loss, a rare occurrence not reported to date. CONCLUSION This study represents the largest US cohort of deaf individuals harboring GJB2 and GJB6 variants, including unique subsets of families with deaf parents. Testing additional members to clarify the phase of GJB2/GJB6 variants in multiplex families was crucial in interpreting clinical significance of the variants in the proband. It highlights the importance of determining the phase of GJB2/GJB6 variants when interpreting molecular test results especially in multiplex families with assortative mating.
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Affiliation(s)
- Arti Pandya
- Department of Pediatrics, Division of Genetics and Metabolism, UNC Chapel Hill, Chapel Hill, NC, USA
| | - Alexander O'Brien
- Department of Pediatrics, Division of Genetics and Metabolism, UNC Chapel Hill, Chapel Hill, NC, USA
| | - Michael Kovasala
- Department of Pediatrics, Division of Genetics and Metabolism, UNC Chapel Hill, Chapel Hill, NC, USA
| | - Guney Bademci
- Dr. John T. Macdonald Foundation Department of Human Genetics, John P. Hussman Institute for Human Genomics, University of Miami, Miami, FL, USA
| | - Mustafa Tekin
- Dr. John T. Macdonald Foundation Department of Human Genetics, John P. Hussman Institute for Human Genomics, University of Miami, Miami, FL, USA
| | - Kathleen S Arnos
- Department of Science, Technology, & Mathematics, Gallaudet University, Washington, DC, USA
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11
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Miwa T, Minoda R, Ishikawa Y, Kajii T, Orita Y, Ohyama T. Role of Dach1 revealed using a novel inner ear-specific Dach1-knockdown mouse model. Biol Open 2019; 8:bio.043612. [PMID: 31405829 PMCID: PMC6737983 DOI: 10.1242/bio.043612] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Dach1 gene is expressed in the inner ear of normal mouse embryos in the area that differentiates into the cochlear stria vascularis (SV). We hypothesised that Dach1 downregulation in the inner ear would lead to SV dysplasia. However, because Dach1 knockout is embryonic lethal in mice, the role of Dach1 in the inner ear is unclear. Here, we established inner ear-specific Dach1-knockdown mice and showed that Dach1 downregulation resulted in hearing loss, reduced endocochlear potential and secondary outer hair cell loss. There were no abnormalities in marginal cells and basal cells in the SV or spiral ligament in inner ear-specific Dach1-knockdown mature mice. However, intermediate cell dysplasia and thinning of the SV were observed. Moreover, dynamic changes in the expression of key genes related to the epithelial-mesenchymal transition were observed in the lateral wall of the cochlear epithelium, which differentiated into the SV in inner ear-specific Dach1-knockdown mice at embryonic stages. In summary, suppression of Dach1 expression in the inner ear caused the epithelial-mesenchymal transition in the lateral wall of cochlear epithelium, resulting in loss of intermediate cells in the SV and SV dysplasia. This article has an associated First Person interview with the first author of the paper. Summary: Inner ear-specific downregulation of Dach1 reveals that the epithelial–mesenchymal transition is crucial for the generation of the stria vascularis.
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Affiliation(s)
- Toru Miwa
- Department of Otolaryngology and Head and Neck Surgery, Graduate of School of Medicine, Kumamoto University, Kumamoto 8608556, Japan .,Otolaryngology-Head and Neck Surgery, JCHO Kumamoto General Hospital, Kumamoto 8668660, Japan
| | - Ryosei Minoda
- Otolaryngology-Head and Neck Surgery, JCHO Kumamoto General Hospital, Kumamoto 8668660, Japan
| | - Yoshihide Ishikawa
- Department of Otolaryngology and Head and Neck Surgery, Graduate of School of Medicine, Kumamoto University, Kumamoto 8608556, Japan
| | - Tomohito Kajii
- Department of Otolaryngology and Head and Neck Surgery, Graduate of School of Medicine, Kumamoto University, Kumamoto 8608556, Japan
| | - Yorihisa Orita
- Department of Otolaryngology and Head and Neck Surgery, Graduate of School of Medicine, Kumamoto University, Kumamoto 8608556, Japan
| | - Takahiro Ohyama
- USC-Tina and Rick Caruso Department of Otolaryngology-Head & Neck Surgery, Zilkha Neurogenetic Institute, USC Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, USA
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12
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Liu W, Luque M, Glueckert R, Danckwardt-Lillieström N, Nordström CK, Schrott-Fischer A, Rask-Andersen H. Expression of Na/K-ATPase subunits in the human cochlea: a confocal and super-resolution microscopy study with special reference to auditory nerve excitation and cochlear implantation. Ups J Med Sci 2019; 124:168-179. [PMID: 31460814 PMCID: PMC6758701 DOI: 10.1080/03009734.2019.1653408] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Background: For the first time the expression of the ion transport protein sodium/potassium-ATPase and its isoforms was analyzed in the human cochlea using light- and confocal microscopy as well as super-resolution structured illumination microscopy. It may increase our understanding of its role in the propagation and processing of action potentials in the human auditory nerve and how electric nerve responses are elicited from auditory prostheses. Material and methods: Archival human cochlear sections were obtained from trans-cochlear surgeries. Antibodies against the Na/K-ATPase β1 isoform together with α1 and α3 were used for immunohistochemistry. An algorithm was applied to assess the expression in various domains. Results: Na/K ATPase β1 subunit was expressed, mostly combined with the α1 isoform. Neurons expressed the β1 subunit combined with α3, while satellite glial cells expressed the α1 isoform without recognized association with β1. Types I and II spiral ganglion neurons and efferent fibers expressed the Na/K-ATPase α3 subunit. Inner hair cells, nerve fibers underneath, and efferent and afferent fibers in the organ of Corti also expressed α1. The highest activity of Na/K-ATPase β1 was at the inner hair cell/nerve junction and spiral prominence. Conclusion: The human auditory nerve displays distinct morphologic features represented in its molecular expression. It was found that electric signals generated via hair cells may not go uninterrupted across the spiral ganglion, but are locally processed. This may be related to particular filtering properties in the human acoustic pathway.
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Affiliation(s)
- Wei Liu
- Department of Surgical Sciences, Section of Otolaryngology, Uppsala University Hospital, Uppsala, Sweden
- Wei Liu
| | - Maria Luque
- Department of Otolaryngology, Medical University of Innsbruck, Innsbruck, Austria
| | - Rudolf Glueckert
- Department of Otolaryngology, Medical University of Innsbruck, Innsbruck, Austria
| | | | - Charlotta Kämpfe Nordström
- Department of Surgical Sciences, Section of Otolaryngology, Uppsala University Hospital, Uppsala, Sweden
| | | | - Helge Rask-Andersen
- Department of Surgical Sciences, Head and Neck Surgery, Section of Otolaryngology, Uppsala University Hospital, Uppsala, Sweden
- CONTACT Helge Rask-Andersen Department of Surgical Sciences, Head and Neck Surgery, Section of Otolaryngology, Uppsala University Hospital, SE-751 85, Uppsala, Sweden
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13
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Mammano F. Inner Ear Connexin Channels: Roles in Development and Maintenance of Cochlear Function. Cold Spring Harb Perspect Med 2019; 9:a033233. [PMID: 30181354 PMCID: PMC6601451 DOI: 10.1101/cshperspect.a033233] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Connexin 26 and connexin 30 are the prevailing isoforms in the epithelial and connective tissue gap junction systems of the developing and mature cochlea. The most frequently encountered variants of the genes that encode these connexins, which are transcriptionally coregulated, determine complete loss of protein function and are the predominant cause of prelingual hereditary deafness. Reducing connexin 26 expression by Cre/loxP recombination in the inner ear of adult mice results in a decreased endocochlear potential, increased hearing thresholds, and loss of >90% of outer hair cells, indicating that this connexin is essential for maintenance of cochlear function. In the developing cochlea, connexins are necessary for intercellular calcium signaling activity. Ribbon synapses and basolateral membrane currents fail to mature in inner hair cells of mice that are born with reduced connexin expression, even though hair cells do not express any connexin. In contrast, pannexin 1, an alternative mediator of intercellular signaling, is dispensable for hearing acquisition and auditory function.
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Affiliation(s)
- Fabio Mammano
- University of Padova, Department of Physics and Astronomy "G. Galilei," Padova 35129, Italy
- CNR Institute of Cell Biology and Neurobiology, Monterotondo 00015, Italy
- Shanghai Institute for Advanced Immunochemical Studies, ShanghaiTech University, Shanghai 201210, China
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14
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Kelly JJ, Abitbol JM, Hulme S, Press ER, Laird DW, Allman BL. The connexin 30 A88V mutant reduces cochlear gap junction expression and confers long-term protection against hearing loss. J Cell Sci 2019; 132:jcs.224097. [PMID: 30559251 DOI: 10.1242/jcs.224097] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Accepted: 12/06/2018] [Indexed: 12/23/2022] Open
Abstract
Mutations in the genes that encode the gap junction proteins connexin 26 (Cx26, encoded by GJB2) and Cx30 (GJB6) are the leading cause of hereditary hearing loss. That said, the Cx30 p.Ala88Val (A88V) mutant causes Clouston syndrome, but not hearing loss. Here, we report that the Cx30-A88V mutant, despite being toxic to inner ear-derived HEI-OC1 cells, conferred remarkable long-term protection against age-related high frequency hearing loss in Cx30A88V/A88V mice. During early development, there were no overt structural differences in the cochlea between genotypes, including a normal complement of hair cells; however, the supporting cell Cx30 gap junction plaques in mutant mice were reduced in size. In adulthood, Cx30A88V/A88V mutant mice had a reduction of cochlear Cx30 mRNA and protein, yet a full complement of hair cells. Conversely, the age-related high frequency hearing loss in Cx30+/+ and Cx30+/A88V mice was due to extensive loss of outer hair cells. Our data suggest that the Cx30-A88V mutant confers long-term hearing protection and prevention of hair cell death, possibly via a feedback mechanism that leads to the reduction of total Cx30 gap junction expression in the cochlea.
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Affiliation(s)
- John J Kelly
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario N6A 5C1, Canada
| | - Julia M Abitbol
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario N6A 5C1, Canada
| | - Stephanie Hulme
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario N6A 5C1, Canada
| | - Eric R Press
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario N6A 5C1, Canada
| | - Dale W Laird
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario N6A 5C1, Canada
| | - Brian L Allman
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario N6A 5C1, Canada
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15
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del Castillo FJ, del Castillo I. DFNB1 Non-syndromic Hearing Impairment: Diversity of Mutations and Associated Phenotypes. Front Mol Neurosci 2017; 10:428. [PMID: 29311818 PMCID: PMC5743749 DOI: 10.3389/fnmol.2017.00428] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 12/07/2017] [Indexed: 02/02/2023] Open
Abstract
The inner ear is a very complex sensory organ whose development and function depend on finely balanced interactions among diverse cell types. The many different kinds of inner ear supporting cells play the essential roles of providing physical and physiological support to sensory hair cells and of maintaining cochlear homeostasis. Appropriately enough, the gene most commonly mutated among subjects with hereditary hearing impairment (HI), GJB2, encodes the connexin-26 (Cx26) gap-junction channel protein that underlies both intercellular communication among supporting cells and homeostasis of the cochlear fluids, endolymph and perilymph. GJB2 lies at the DFNB1 locus on 13q12. The specific kind of HI associated with this locus is caused by recessively-inherited mutations that inactivate the two alleles of the GJB2 gene, either in homozygous or compound heterozygous states. We describe the many diverse classes of genetic alterations that result in DFNB1 HI, such as large deletions that either destroy the GJB2 gene or remove a regulatory element essential for GJB2 expression, point mutations that interfere with promoter function or splicing, and small insertions or deletions and nucleotide substitutions that target the GJB2 coding sequence. We focus on how these alterations disrupt GJB2 and Cx26 functions and on their different effects on cochlear development and physiology. We finally discuss the diversity of clinical features of DFNB1 HI as regards severity, age of onset, inner ear malformations and vestibular dysfunction, highlighting the areas where future research should be concentrated.
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Affiliation(s)
- Francisco J. del Castillo
- Servicio de Genética, Hospital Universitario Ramón y Cajal, IRYCIS, Madrid, Spain
- Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Madrid, Spain
| | - Ignacio del Castillo
- Servicio de Genética, Hospital Universitario Ramón y Cajal, IRYCIS, Madrid, Spain
- Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Madrid, Spain
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16
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Chen L, Su D, Li S, Guan L, Shi C, Li D, Hu S, Ma X. The connexin 46 mutant (V44M) impairs gap junction function causing congenital cataract. J Genet 2017; 96:969-976. [PMID: 29321356 DOI: 10.1007/s12041-017-0861-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Connexin 46 (Cx46) is important for gap junction channels formation which plays crucial role in the preservation of lens homeostasis and transparency. Previously, we have identified a missense mutation (p.V44M) of Cx46 in a congenital cataract family. This study aims at dissecting the potential pathogenesis of the causative mutant of cataract. Plasmids carrying wild-type (wt) and mutant (V44M) of Cx46 were constructed and expressed in Hela cells respectively.Western blotting and fluorescence microscopy were applied to analyse the expression and subcellular localization of recombinant proteins, respectively. Scrape loading dye transfer experiment was performed to detect the transfer capability of gap junction channels among cells expressed V44Mmutant. The results demonstrated that in transfected Hela cells, both wt-Cx46 and Cx46 V44M were localized abundantly in the plasma membrane. No significant difference was found between the protein expressions of the two types of Cx46. The fluorescent localization assay revealed the plaque formation, significantly reduced in the cells expressing Cx46 V44M. Immunoblotting analysis demonstrated that formation of Triton X-100 insoluble complex decreased obviously in mutant Cx46. Additionally, the scrape-loading dye-transfer experiment showed a lower dye diffusion distance of Cx46 V44M cells, which indicates that the gap junction intercellular communication activity was aberrant. Human Cx46 V44M mutant causing cataracts result in abnormally decreased formation of gap junction plaques and impaired gap junction channel function.
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Affiliation(s)
- Lijuan Chen
- Department of Ophthalmology, Hongqi Hospital of Mudanjiang Medical College, Mudanjiang 157000, Heilongjiang Province, People's Republic of China.
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17
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Liu W, Schrott-Fischer A, Glueckert R, Benav H, Rask-Andersen H. The Human "Cochlear Battery" - Claudin-11 Barrier and Ion Transport Proteins in the Lateral Wall of the Cochlea. Front Mol Neurosci 2017; 10:239. [PMID: 28848383 PMCID: PMC5554435 DOI: 10.3389/fnmol.2017.00239] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Accepted: 07/14/2017] [Indexed: 11/21/2022] Open
Abstract
Background: The cochlea produces an electric field potential essential for hair cell transduction and hearing. This biological “battery” is situated in the lateral wall of the cochlea and contains molecular machinery that secretes and recycles K+ ions. Its functioning depends on junctional proteins that restrict the para-cellular escape of ions. The tight junction protein Claudin-11 has been found to be one of the major constituents of this barrier that maintains ion gradients (Gow et al., 2004; Kitajiri et al., 2004a). We are the first to elucidate the human Claudin-11 framework and the associated ion transport machinery using super-resolution fluorescence illumination microscopy (SR-SIM). Methods: Archival cochleae obtained during meningioma surgery were used for SR-SIM together with transmission electron microscopy after ethical consent. Results: Claudin-11-expressing cells formed parallel tight junction lamellae that insulated the epithelial syncytium of the stria vascularis and extended to the suprastrial region. Intercellular gap junctions were found between the barrier cells and fibrocytes. Conclusion: Transmission electron microscopy, confocal microscopy and SR-SIM revealed exclusive cell specialization in the various subdomains of the lateral wall of the human cochlea. The Claudin-11-expressing cells exhibited both conductor and isolator characteristics, and these micro-porous separators may selectively mediate the movement of charged units to the intrastrial space in a manner that is analogous to a conventional electrochemical “battery.” The function and relevance of this battery for the development of inner ear disease are discussed.
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Affiliation(s)
- Wei Liu
- Department of Surgical Sciences, Section of Otolaryngology, Uppsala University HospitalUppsala, Sweden
| | | | - Rudolf Glueckert
- Department of Otolaryngology, Medical University of InnsbruckInnsbruck, Austria
| | | | - Helge Rask-Andersen
- Department of Surgical Sciences, Head and Neck Surgery, Section of Otolaryngology, Uppsala University HospitalUppsala, Sweden
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18
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In vivo genetic manipulation of inner ear connexin expression by bovine adeno-associated viral vectors. Sci Rep 2017; 7:6567. [PMID: 28779115 PMCID: PMC5544751 DOI: 10.1038/s41598-017-06759-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 06/19/2017] [Indexed: 01/03/2023] Open
Abstract
We have previously shown that in vitro transduction with bovine adeno–associated viral (BAAV) vectors restores connexin expression and rescues gap junction coupling in cochlear organotypic cultures from connexin–deficient mice that are models DFNB1 nonsyndromic hearing loss and deafness. The aims of this study were to manipulate inner ear connexin expression in vivo using BAAV vectors, and to identify the optimal route of vector delivery. Injection of a BAAV vector encoding a bacterial Cre recombinase via canalostomy in adult mice with floxed connexin 26 (Cx26) alleles promoted Cre/LoxP recombination, resulting in decreased Cx26 expression, decreased endocochlear potential, increased hearing thresholds, and extensive loss of outer hair cells. Injection of a BAAV vector encoding GFP-tagged Cx30 via canalostomy in P4 mice lacking connexin 30 (Cx30) promoted formation of Cx30 gap junctions at points of contacts between adjacent non-sensory cells of the cochlear sensory epithelium. Levels of exogenous Cx30 decayed over time, but were still detectable four weeks after canalostomy. Our results suggest that persistence of BAAV-mediated gene replacement in the cochlea is limited by the extensive remodeling of the organ of Corti throughout postnatal development and associated loss of non-sensory cells.
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19
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Pshennikova VG, Barashkov NA, Solovyev AV, Romanov GP, Diakonov EE, Sazonov NN, Morozov IV, Bondar AA, Posukh OL, Dzhemileva LU, Khusnutdinova EK, Tomsky MI, Fedorova SA. Analysis of GJB6 (Сx30) and GJB3 (Сx31) genes in deaf patients with monoallelic mutations in GJB2 (Сx26) gene in the Sakha Republic (Yakutia). RUSS J GENET+ 2017. [DOI: 10.1134/s1022795417030103] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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20
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Super-resolution structured illumination fluorescence microscopy of the lateral wall of the cochlea: the Connexin26/30 proteins are separately expressed in man. Cell Tissue Res 2016; 365:13-27. [DOI: 10.1007/s00441-016-2359-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 01/07/2016] [Indexed: 10/22/2022]
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21
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Lee MY, Takada T, Takada Y, Kappy MD, Beyer LA, Swiderski DL, Godin AL, Brewer S, King WM, Raphael Y. Mice with conditional deletion of Cx26 exhibit no vestibular phenotype despite secondary loss of Cx30 in the vestibular end organs. Hear Res 2015; 328:102-12. [PMID: 26232528 DOI: 10.1016/j.heares.2015.07.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2015] [Revised: 07/22/2015] [Accepted: 07/23/2015] [Indexed: 01/19/2023]
Abstract
Connexins are components of gap junctions which facilitate transfer of small molecules between cells. One member of the connexin family, Connexin 26 (Cx26), is prevalent in gap junctions in sensory epithelia of the inner ear. Mutations of GJB2, the gene encoding Cx26, cause significant hearing loss in humans. The vestibular system, however, does not usually show significant functional deficits in humans with this mutation. Mouse models for loss of Cx26 function demonstrate hearing loss and cochlear pathology but the extent of vestibular dysfunction and organ pathology are less well characterized. To understand the vestibular effects of Cx26 mutations, we evaluated vestibular function and histology of the vestibular sensory epithelia in a conditional knockout (CKO) mouse with Cx26 loss of function. Transgenic C57BL/6 mice, in which cre-Sox10 drives excision of the Cx26 gene from non-sensory cells flanking the sensory epithelium of the inner ear (Gjb2-CKO), were compared to age-matched wild types. Animals were sacrificed at ages between 4 and 40 weeks and their cochlear and vestibular sensory organs harvested for histological examination. Cx26 immunoreactivity was prominent in the peripheral vestibular system and the cochlea of wild type mice, but absent in the Gjb2-CKO specimens. The hair cell population in the cochleae of the Gjb2-CKO mice was severely depleted but in the vestibular organs it was intact, despite absence of Cx26 expression. The vestibular organs appeared normal at the latest time point examined, 40 weeks. To determine whether compensation by another connexin explains survival of the normal vestibular sensory epithelium, we evaluated the presence of Cx30 in the Gjb2-CKO mouse. We found that Cx30 labeling was normal in the cochlea, but it was decreased or absent in the vestibular system. The vestibular phenotype of the mutants was not different from wild-types as determined by time on the rotarod, head stability tests and physiological responses to vestibular stimulation. Thus presence of Cx30 in the cochlea does not compensate for Cx26 loss, and the absence of both connexins from vestibular sensory epithelia is no more injurious than the absence of one of them. Further studies to uncover the physiological foundation for this difference between the cochlea and the vestibular organs may help in designing treatments for GJB2 mutations.
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Affiliation(s)
- Min Young Lee
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA
| | - Tomoko Takada
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA
| | - Yohei Takada
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA
| | - Michelle D Kappy
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA
| | - Lisa A Beyer
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA
| | - Donald L Swiderski
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA
| | - Ashley L Godin
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA
| | - Shannon Brewer
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA
| | - W Michael King
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA
| | - Yehoash Raphael
- Kresge Hearing Research Institute, Department of Otolaryngology - Head and Neck Surgery, University of Michigan, 1150 West. Medical Center Dr., Ann Arbor, MI 48109-5648, USA.
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22
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Kelly JJ, Shao Q, Jagger DJ, Laird DW. Cx30 exhibits unique characteristics including a long half-life when assembled into gap junctions. J Cell Sci 2015; 128:3947-60. [DOI: 10.1242/jcs.174698] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 09/08/2015] [Indexed: 01/04/2023] Open
Abstract
In the present study we investigated the life-cycle, trafficking, assembly and cell surface dynamics of a poorly characterized connexin family member, connexin 30 (Cx30), which plays a critical role in skin health and hearing. Unexpectedly, Cx30 localization at the cell surface and gap junctional intercellular communication was not affected by prolonged treatments with the ER-Golgi transport inhibitor brefeldin-A or the protein synthesis inhibitor cycloheximide, whereas Cx43 was rapidly cleared. Fluorescent recovery after photobleaching revealed that Cx30 plaques were rebuilt from the outer edges in keeping with older channels residing in the inner core of the plaque. Expression of a dominant-negative form of Sar1 GTPase led to the accumulation of Cx30 within the ER in contrast to a report that Cx30 traffics via a Golgi-independent pathway. Co-expression of Cx30 with Cx43 revealed that these connexins segregate into distinct domains within common gap junction plaques suggesting their assembly is governed by different mechanisms. In summary, Cx30 was found to be an unusually stable, long-lived connexin (half-life >12 hrs), which may underlie its specific role in the epidermis and cochlea.
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Affiliation(s)
- John J. Kelly
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada
| | - Qing Shao
- Department of Anatomy and Cell Biology, 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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23
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Spontaneous regeneration of cochlear supporting cells after neonatal ablation ensures hearing in the adult mouse. Proc Natl Acad Sci U S A 2014; 111:16919-24. [PMID: 25385613 DOI: 10.1073/pnas.1408064111] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Supporting cells in the cochlea play critical roles in the development, maintenance, and function of sensory hair cells and auditory neurons. Although the loss of hair cells or auditory neurons results in sensorineural hearing loss, the consequence of supporting cell loss on auditory function is largely unknown. In this study, we specifically ablated inner border cells (IBCs) and inner phalangeal cells (IPhCs), the two types of supporting cells surrounding inner hair cells (IHCs) in mice in vivo. We demonstrate that the organ of Corti has the intrinsic capacity to replenish IBCs/IPhCs effectively during early postnatal development. Repopulation depends on the presence of hair cells and cells within the greater epithelial ridge and is independent of cell proliferation. This plastic response in the neonatal cochlea preserves neuronal survival, afferent innervation, and hearing sensitivity in adult mice. In contrast, the capacity for IBC/IPhC regeneration is lost in the mature organ of Corti, and consequently IHC survival and hearing sensitivity are impaired significantly, demonstrating that there is a critical period for the regeneration of cochlear supporting cells. Our findings indicate that the quiescent neonatal organ of Corti can replenish specific supporting cells completely after loss in vivo to guarantee mature hearing function.
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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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25
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Meigh L, Greenhalgh SA, Rodgers TL, Cann MJ, Roper DI, Dale N. CO₂directly modulates connexin 26 by formation of carbamate bridges between subunits. eLife 2013; 2:e01213. [PMID: 24220509 PMCID: PMC3821526 DOI: 10.7554/elife.01213] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Homeostatic regulation of the partial pressure of CO2 (PCO2) is vital for life. Sensing of pH has been proposed as a sufficient proxy for determination of PCO2 and direct CO2-sensing largely discounted. Here we show that connexin 26 (Cx26) hemichannels, causally linked to respiratory chemosensitivity, are directly modulated by CO2. A ‘carbamylation motif’, present in CO2-sensitive connexins (Cx26, Cx30, Cx32) but absent from a CO2-insensitive connexin (Cx31), comprises Lys125 and four further amino acids that orient Lys125 towards Arg104 of the adjacent subunit of the connexin hexamer. Introducing the carbamylation motif into Cx31 created a mutant hemichannel (mCx31) that was opened by increases in PCO2. Mutation of the carbamylation motif in Cx26 and mCx31 destroyed CO2 sensitivity. Course-grained computational modelling of Cx26 demonstrated that the proposed carbamate bridge between Lys125 and Arg104 biases the hemichannel to the open state. Carbamylation of Cx26 introduces a new transduction principle for physiological sensing of CO2. DOI:http://dx.doi.org/10.7554/eLife.01213.001 A number of gaseous molecules, including nitric oxide and carbon monoxide, play important roles in many cellular processes by acting as signalling molecules. Surprisingly, however, it has long been assumed that carbon dioxide – a gaseous molecule that is produced during cellular metabolism – is not a signalling molecule. Controlling the concentration of carbon dioxide (CO2) in a biological system is essential to sustain life, and it was thought that the body used pH – which is the concentration of hydrogen ions – as a proxy for the level of CO2. The concentration of CO2 is related to pH because CO2 reacts with water to form carbonic acid, which quickly breaks down to form hydrogen ions and bicarbonate ions. This close relationship has led many researchers to equate pH-sensing with CO2-sensing, and to suggest that a physiological receptor for CO2 does not exist. Recent research into structures called connexin hemichannels has challenged this view. Researchers found that when pH levels were held constant, increasing the level of CO2 caused the structures to open up, suggesting that CO2 could be directly detected by the hemichannels. Each hemichannel contains six connexin subunits, but the details of how the CO2 molecules interact with the individual connexin subunits to open up the hemichannels remained mysterious. Now Meigh et al. show that CO2 molecules bind to a specific amino acid (lysine) at a particular place (residue 125) in one of the connexin subunits to form a carbamate group. This group then interacts with the amino acid (arginine) at residue 104 in a neighbouring connexin subunit to form a carbamate bridge between the two subunits. This leads to structural changes that cause the gap junction hemichannels to open and release signals that can activate other cells. Since connexin hemichannels are found throughout the human body, these results suggest that CO2 might act as a signalling molecule in processes as diverse as the control of blood flow, breathing, hearing and reproduction. DOI:http://dx.doi.org/10.7554/eLife.01213.002
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Affiliation(s)
- Louise Meigh
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
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Axelsen LN, Calloe K, Holstein-Rathlou NH, Nielsen MS. Managing the complexity of communication: regulation of gap junctions by post-translational modification. Front Pharmacol 2013; 4:130. [PMID: 24155720 PMCID: PMC3804956 DOI: 10.3389/fphar.2013.00130] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Accepted: 09/30/2013] [Indexed: 12/21/2022] Open
Abstract
Gap junctions are comprised of connexins that form cell-to-cell channels which couple neighboring cells to accommodate the exchange of information. The need for communication does, however, change over time and therefore must be tightly controlled. Although the regulation of connexin protein expression by transcription and translation is of great importance, the trafficking, channel activity and degradation are also under tight control. The function of connexins can be regulated by several post translational modifications, which affect numerous parameters; including number of channels, open probability, single channel conductance or selectivity. The most extensively investigated post translational modifications are phosphorylations, which have been documented in all mammalian connexins. Besides phosphorylations, some connexins are known to be ubiquitinated, SUMOylated, nitrosylated, hydroxylated, acetylated, methylated, and γ-carboxyglutamated. The aim of the present review is to summarize our current knowledge of post translational regulation of the connexin family of proteins.
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Affiliation(s)
- Lene N Axelsen
- Department of Biomedical Sciences and The Danish National Research Foundation Centre for Cardiac Arrhythmia, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
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Dash-Wagh S, Jacob S, Lindberg S, Fridberger A, Langel U, Ulfendahl M. Intracellular Delivery of Short Interfering RNA in Rat Organ of Corti Using a Cell-penetrating Peptide PepFect6. MOLECULAR THERAPY. NUCLEIC ACIDS 2012; 1:e61. [PMID: 23232329 PMCID: PMC3528302 DOI: 10.1038/mtna.2012.50] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
RNA interference (RNAi) using short interfering RNA (siRNA) is an attractive therapeutic approach for treatment of dominant-negative mutations. Some rare missense dominant-negative mutations lead to congenital-hearing impairments. A variety of viral vectors have been tested with variable efficacy for modulating gene expression in inner ear. However, there is concern regarding their safety for clinical use. Here, we report a novel cell-penetrating peptide (CPP)-based nonviral approach for delivering siRNA into inner ear tissue using organotypic cultures as model system. PepFect6 (PF6), a variant of stearyl-TP10, was specially designed for improved delivery of siRNA by facilitating endosomal release. We show that PF6 was internalized by all cells without inducing cytotoxicity in cochlear cultures. PF6/siRNA nanoparticles lead to knockdown of target genes, a housekeeping gene and supporting cell-specific connexin 26. Interestingly, application of PF6/connexin 26 siRNA exhibited knockdown of both connexin 26 and 30 mRNA and their absence led to impaired intercellular communication as demonstrated by reduced transfer of calcein among the PF6/connexin 26-siRNA–treated cells. Thus, we conclude that PF6 is an efficient nonviral vector for delivery of siRNA, which can be applied as a tool for the development of siRNA-based therapeutic applications for hearing impairments.
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Affiliation(s)
- Suvarna Dash-Wagh
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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Iossa S, Marciano E, Franzé A. GJB2 Gene Mutations in Syndromic Skin Diseases with Sensorineural Hearing Loss. Curr Genomics 2012; 12:475-785. [PMID: 22547955 PMCID: PMC3219843 DOI: 10.2174/138920211797904098] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2011] [Revised: 07/27/2011] [Accepted: 08/10/2011] [Indexed: 01/10/2023] Open
Abstract
The GJB2 gene is located on chromosome 13q12 and it encodes the connexin 26, a transmembrane protein involved in cell-cell attachment of almost all tissues. GJB2 mutations cause autosomal recessive (DFNB1) and sometimes dominant (DFNA3) non-syndromic sensorineural hearing loss. Moreover, it has been demonstrated that connexins are involved in regulation of growth and differentiation of epidermis and, in fact, GJB2 mutations have also been identified in syndromic disorders with hearing loss associated with various skin disease phenotypes. GJB2 mutations associated with skin disease are, in general, transmitted with a dominant inheritance pattern. Nonsyndromic deafness is caused prevalently by a loss-of-function, while literature evidences suggest for syndromic deafness a mechanism based on gain-of-function. The spectrum of skin manifestations associated with some mutations seems to have a very high phenotypic variability. Why some mutations can lead to widely varying cutaneous manifestations is poorly understood and in particular, the reason why the skin disease-deafness phenotypes differ from each other thus remains unclear. This review provides an overview of recent findings concerning pathogenesis of syndromic deafness imputable to GJB2 mutations with an emphasis on relevant clinical genotype-phenotype correlations. After describing connexin 26 fundamental characteristics, the most relevant and recent information about its known mutations involved in the syndromic forms causing hearing loss and skin problems are summarized. The possible effects of the mutations on channel expression and function are discussed.
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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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30
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Ceriani F, Mammano F. Calcium signaling in the cochlea - Molecular mechanisms and physiopathological implications. Cell Commun Signal 2012; 10:20. [PMID: 22788415 PMCID: PMC3408374 DOI: 10.1186/1478-811x-10-20] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Accepted: 07/12/2012] [Indexed: 12/20/2022] Open
Abstract
Calcium ions (Ca2+) regulate numerous and diverse aspects of cochlear and vestibular physiology. This review focuses on the Ca2+ control of mechanotransduction and synaptic transmission in sensory hair cells, as well as on Ca2+ signalling in non-sensory cells of the developing cochlea.
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Affiliation(s)
- Federico Ceriani
- Dipartimento di Fisica e Astronomia "G, Galilei", Università di Padova, 35131, Padova, Italy.
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31
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Jagger DJ, Nevill G, Forge A. The Membrane Properties of Cochlear Root Cells are Consistent with Roles in Potassium Recirculation and Spatial Buffering. J Assoc Res Otolaryngol 2010; 11:435-48. [PMID: 20393778 DOI: 10.1007/s10162-010-0218-3] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Accepted: 03/24/2010] [Indexed: 11/27/2022] Open
Abstract
Auditory transduction, amplification, and hair cell survival depend on the regulation of extracellular [K(+)] in the cochlea. K(+) is removed from the vicinity of sensory hair cells by epithelial cells, and may be distributed through the epithelial cell syncytium, reminiscent of "spatial buffering" in glia. Hypothetically, K(+) is then transferred from the epithelial syncytium into the connective tissue syncytium within the cochlear lateral wall, enabling recirculation of K(+) back into endolymph. This may involve secretion of K(+) from epithelial root cells, and its re-uptake via transporters into spiral ligament fibrocytes. The molecular basis of this secretion is not known. Using a combination of approaches we demonstrated that the resting conductance in guinea pig root cells was dominated by K(+) channels, most likely composed of the Kir4.1 subunit. Dye injections revealed extensive intercellular gap junctional coupling, and delineated the root cell processes that penetrated the spiral ligament. Following uncoupling using 1-octanol, individual cells had Ba(2+)-sensitive weakly rectifying currents. In the basal (high-frequency encoding) cochlear region K(+) loads are predicted to be the highest, and root cells in this region had the largest surface area and the highest current density, consistent with their role in K(+) secretion. Kir4.1 was localized within root cells by immunofluorescence, and specifically to root cell process membranes by immunogold labeling. These results support a role for root cells in cochlear K(+) regulation, and suggest that channels composed of Kir4.1 subunits may mediate K(+) secretion from the epithelial gap junction network.
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Affiliation(s)
- Daniel J Jagger
- Centre for Auditory Research, UCL Ear Institute, University College London, 332 Gray's Inn Road, London, WC1X 8EE UK
| | - Graham Nevill
- Centre for Auditory Research, UCL Ear Institute, University College London, 332 Gray's Inn Road, London, WC1X 8EE UK
| | - Andrew Forge
- Centre for Auditory Research, UCL Ear Institute, University College London, 332 Gray's Inn Road, London, WC1X 8EE UK
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Wilch E, Azaiez H, Fisher RA, Elfenbein J, Murgia A, Birkenhäger R, Bolz H, Da Silva-Costa SM, Del Castillo I, Haaf T, Hoefsloot L, Kremer H, Kubisch C, Le Marechal C, Pandya A, Sartorato EL, Schneider E, Van Camp G, Wuyts W, Smith RJH, Friderici KH. A novel DFNB1 deletion allele supports the existence of a distant cis-regulatory region that controls GJB2 and GJB6 expression. Clin Genet 2010; 78:267-74. [PMID: 20236118 DOI: 10.1111/j.1399-0004.2010.01387.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Eleven affected members of a large German-American family segregating recessively inherited, congenital, non-syndromic sensorineural hearing loss (SNHL) were found to be homozygous for the common 35delG mutation of GJB2, the gene encoding the gap junction protein Connexin 26. Surprisingly, four additional family members with bilateral profound SNHL carried only a single 35delG mutation. Previously, we demonstrated reduced expression of both GJB2 and GJB6 mRNA from the allele carried in trans with that bearing the 35delG mutation in these four persons. Using array comparative genome hybridization (array CGH), we have now identified on this allele a deletion of 131.4 kb whose proximal breakpoint lies more than 100 kb upstream of the transcriptional start sites of GJB2 and GJB6. This deletion, del(chr13:19,837,344-19,968,698), segregates as a completely penetrant DFNB1 allele in this family. It is not present in 528 persons with SNHL and monoallelic mutation of GJB2 or GJB6, and we have not identified any other candidate pathogenic copy number variation by arrayCGH in a subset of 10 such persons. Characterization of distant GJB2/GJB6 cis-regulatory regions evidenced by this allele may be required to find the 'missing' DFNB1 mutations that are believed to exist.
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Affiliation(s)
- E Wilch
- Genetics Program, Michigan State University, East Lansing, MI 48824, USA
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Nemoto-Hasebe I, Akiyama M, Kudo S, Ishiko A, Tanaka A, Arita K, Shimizu H. Novel mutation p.Gly59Arg inGJB6encoding connexin 30 underlies palmoplantar keratoderma with pseudoainhum, knuckle pads and hearing loss. Br J Dermatol 2009; 161:452-5. [DOI: 10.1111/j.1365-2133.2009.09137.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Sargiannidou I, Vavlitou N, Aristodemou S, Hadjisavvas A, Kyriacou K, Scherer SS, Kleopa KA. Connexin32 mutations cause loss of function in Schwann cells and oligodendrocytes leading to PNS and CNS myelination defects. J Neurosci 2009; 29:4736-49. [PMID: 19369543 PMCID: PMC2721059 DOI: 10.1523/jneurosci.0325-09.2009] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2009] [Revised: 02/23/2009] [Accepted: 03/05/2009] [Indexed: 11/21/2022] Open
Abstract
The gap junction (GJ) protein connexin32 (Cx32) is expressed by myelinating Schwann cells and oligodendrocytes and is mutated in X-linked Charcot-Marie-Tooth disease. In addition to a demyelinating peripheral neuropathy, some Cx32 mutants are associated with transient or chronic CNS phenotypes. To investigate the molecular basis of these phenotypes, we generated transgenic mice expressing the T55I or the R75W mutation and an IRES-EGFP, driven by the mouse Cnp promoter. The transgene was expressed in oligodendrocytes throughout the CNS and in Schwann cells. Both the T55I and the R75W mutants were localized in the perinuclear cytoplasm, did not form GJ plaques, and did not alter the expression or localization of two other oligodendrocytic GJ proteins, Cx47 and Cx29, or the expression of Cx29 in Schwann cells. On wild type background, the expression of endogenous mCx32 was unaffected by the T55I mutant, but was partly impaired by R75W. Transgenic mice with the R75W mutation and all mutant animals with Gjb1-null background developed a progressive demyelinating peripheral neuropathy along with CNS myelination defects. These findings suggest that Cx32 mutations result in loss of function in myelinated cells without trans-dominant effects on other GJ proteins. Loss of Cx32 function alone in the CNS causes myelination defects.
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Affiliation(s)
| | | | - Sophia Aristodemou
- Department of Molecular Pathology and Electron Microscopy, The Cyprus Institute of Neurology and Genetics, 1683 Nicosia, Cyprus, and
| | - Andreas Hadjisavvas
- Department of Molecular Pathology and Electron Microscopy, The Cyprus Institute of Neurology and Genetics, 1683 Nicosia, Cyprus, and
| | - Kyriacos Kyriacou
- Department of Molecular Pathology and Electron Microscopy, The Cyprus Institute of Neurology and Genetics, 1683 Nicosia, Cyprus, and
| | - Steven S. Scherer
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
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Hoang Dinh E, Ahmad S, Chang Q, Tang W, Stong B, Lin X. Diverse deafness mechanisms of connexin mutations revealed by studies using in vitro approaches and mouse models. Brain Res 2009; 1277:52-69. [PMID: 19230829 DOI: 10.1016/j.brainres.2009.02.008] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2009] [Revised: 02/01/2009] [Accepted: 02/04/2009] [Indexed: 12/12/2022]
Abstract
Mutations in connexins (Cxs), the constitutive protein subunits of gap junction (GJ) intercellular channels, are one of the most common human genetic defects that cause severe prelingual non-syndromic hearing impairments. Many subtypes of Cxs (e.g., Cxs 26, 29, 30, 31, 43) and pannexins (Panxs) are expressed in the cochlea where they contribute to the formation of a GJ-based intercellular communication network. Cx26 and Cx30 are the predominant cochlear Cxs and they co-assemble in most GJ plaques to form hybrid GJs. The cellular localization of specific Cx subtypes provides a basis for understanding the molecular structure of GJs and hemichannels in the cochlea. Information about the interactions among the various co-assembled Cx partners is critical to appreciate the functional consequences of various types of genetic mutations. In vitro studies of reconstituted GJs in cell lines have yielded surprisingly heterogeneous mechanisms of dysfunction caused by various Cx mutations. Availability of multiple lines of Cx-mutant mouse models has provided some insight into the pathogenesis processes in the cochlea of deaf mice. Here we summarize recent advances in understanding the structure and function of cochlear GJs and give a critical review of current findings obtained from both in vitro studies and mouse models on the mechanisms of Cx mutations that lead to cell death in the cochlea and hearing loss.
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Affiliation(s)
- Emilie Hoang Dinh
- Department of Otolaryngology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322-3030, USA
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36
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Martínez AD, Acuña R, Figueroa V, Maripillan J, Nicholson B. Gap-junction channels dysfunction in deafness and hearing loss. Antioxid Redox Signal 2009; 11:309-22. [PMID: 18837651 PMCID: PMC2673109 DOI: 10.1089/ars.2008.2138] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Gap-junction channels connect the cytoplasm of adjacent cells, allowing the diffusion of ions and small metabolites. They are formed at the appositional plasma membranes by a family of related proteins named connexins. Mutations in connexins 26, 31, 30, 32, and 43 have been associated with nonsyndromic or syndromic deafness. The majority of these mutations are inherited in an autosomal recessive manner, but a few of them have been associated with dominantly inherited hearing loss. Mutations in the connexin26 gene (GJB2) are the most common cause of genetic deafness. This review summarizes the most relevant and recent information about different mutations in connexin genes found in human patients, with emphasis on GJB2. The possible effects of the mutations on channel expression and function are discussed, in addition to their possible physiologic consequences for inner ear physiology. Finally, we propose that connexin channels (gap junctions and hemichannels) may be targets for age-related hearing loss induced by oxidative damage.
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Affiliation(s)
- Agustín D Martínez
- Centro de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile.
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Ortolano S, Di Pasquale G, Crispino G, Anselmi F, Mammano F, Chiorini JA. Coordinated control of connexin 26 and connexin 30 at the regulatory and functional level in the inner ear. Proc Natl Acad Sci U S A 2008; 105:18776-81. [PMID: 19047647 PMCID: PMC2596232 DOI: 10.1073/pnas.0800831105] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [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
Connexin 26 (Cx26) and connexin 30 (Cx30) are encoded by two genes (GJB2 and GJB6, respectively) that are found within 50 kb in the same complex deafness locus, DFNB1. Immunocytochemistry and quantitative PCR analysis of Cx30 KO mouse cultures revealed that Cx26 is downregulated at the protein level and at the mRNA level in nonsensory cells located between outer hair cells and the stria vascularis. To explore connexin coregulation, we manipulated gene expression using the bovine adeno-associated virus. Overexpression of Cx30 in the Cx30 KO mouse by transduction with bovine adeno-associated virus restored Cx26 expression, permitted the formation of functional gap junction channels, and rescued propagating Ca(2+) signals. Ablation of Cx26 by transduction of Cx26(loxP/loxP) cultures with a Cre recombinase vector caused concurrent downregulation of Cx30 and impaired intercellular communication. The coordinated regulation of Cx26 and Cx30 expression appears to occur as a result of signaling through PLC and the NF-kappaB pathway, because activation of IP(3)-mediated Ca(2+) responses by stimulation of P2Y receptors for 20 min with 20 nM ATP increased the levels of Cx26 transcripts in Cx30 KO cultures. This effect was inhibited by expressing a stable form of the IkappaB repressor protein that prevents activation/translocation of NF-kappaB. Thus, our data reveal a Ca(2+)-dependent control in the expression of inner ear connexins implicated in hereditary deafness as well as insight into the hitherto unexplained observation that some deafness-associated DFNB1 alleles are characterized by hereditable reduction of both GJB2 and GJB6 expression.
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Affiliation(s)
- Saida Ortolano
- Venetian Institute of Molecular Medicine, Foundation for Advanced Biomedical Research, 35129 Padua, Italy
- Department of Physics “G.Galilei,” University of Padua, 35129 Padua, Italy; and
| | - Giovanni Di Pasquale
- Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892
| | - Giulia Crispino
- Venetian Institute of Molecular Medicine, Foundation for Advanced Biomedical Research, 35129 Padua, Italy
| | - Fabio Anselmi
- Venetian Institute of Molecular Medicine, Foundation for Advanced Biomedical Research, 35129 Padua, Italy
| | - Fabio Mammano
- Venetian Institute of Molecular Medicine, Foundation for Advanced Biomedical Research, 35129 Padua, Italy
- Department of Physics “G.Galilei,” University of Padua, 35129 Padua, Italy; and
| | - John A. Chiorini
- Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892
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38
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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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39
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Regulation of connexons composed of human connexin26 (hCx26) by temperature. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1206-12. [DOI: 10.1016/j.bbamem.2008.01.016] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2007] [Revised: 01/10/2008] [Accepted: 01/25/2008] [Indexed: 11/18/2022]
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40
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Trowe MO, Maier H, Schweizer M, Kispert A. Deafness in mice lacking the T-box transcription factor Tbx18 in otic fibrocytes. Development 2008; 135:1725-34. [PMID: 18353863 DOI: 10.1242/dev.014043] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In the cochlea, fibrocytes play important physiological roles, including the maintenance of the ionic composition of the endolymph. Human deafness upon fibrocyte alterations witnesses their crucial role for hearing. We demonstrate that differentiation of otic fibrocytes requires the T-box transcription factor gene Tbx18. Tbx18 expression during inner ear development is restricted to the sub-region of otic mesenchyme that is fated to differentiate into fibrocytes. We rescued the somitic defect that underlies the perinatal lethality of Tbx18-mutant mice by a transgenic approach, and measured auditory brainstem responses. Adult Tbx18-deficient mice showed profound deafness and a complete disruption of the endocochlear potential that is essential for the transduction of sound by sensory hair cells. The differentiation of otic fibrocytes of the spiral ligament was severely compromised. Tissue architecture of the stria vascularis of the lateral wall was disrupted, exhibiting an almost complete absence of the basal cell layer, and a reduction and changes of intermediate and marginal cells, respectively. Stria vascularis defects resulted from the failure of Tbx18-mutant otic fibrocytes to generate the basal cell layer by a mesenchymal-epithelial transition. Defects in otic fibrocyte differentiation may be subordinate to a primary role of Tbx18 in early compartmentalization of the otic mesenchyme, as lineage restriction and boundary formation between otic fibrocytes and the surrounding otic capsule were severely affected in the mutant. Our study sheds light on the genetic control of patterning and differentiation of the otic mesenchyme, uncovers distinct steps of stria vascularis formation and illuminates the importance of non-epithelially-derived otic cell types for normal hearing and the etiology of deafness.
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Affiliation(s)
- Mark-Oliver Trowe
- Institut für Molekularbiologie, Medizinische Hochschule Hannover, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
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41
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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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42
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Wilch E, Zhu M, Burkhart KB, Regier M, Elfenbein JL, Fisher RA, Friderici KH. Expression of GJB2 and GJB6 is reduced in a novel DFNB1 allele. Am J Hum Genet 2006; 79:174-9. [PMID: 16773579 PMCID: PMC1474119 DOI: 10.1086/505333] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2006] [Accepted: 04/20/2006] [Indexed: 11/04/2022] Open
Abstract
In a large kindred of German descent, we found a novel allele that segregates with deafness when present in trans with the 35delG allele of GJB2. Qualitative polymerase chain reaction-based allele-specific expression assays showed that expression of both GJB2 and GJB6 from the novel allele is dramatically reduced. This is the first evidence of a deafness-associated regulatory mutation of GJB2 and of potential coregulation of GJB2 and GJB6.
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Affiliation(s)
- Ellen Wilch
- Genetics Program, Michigan State University, East Lansing, 48824, USA
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43
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Nickel R, Becker D, Forge A. Molecular and functional characterization of gap junctions in the avian inner ear. J Neurosci 2006; 26:6190-9. [PMID: 16763027 PMCID: PMC6675194 DOI: 10.1523/jneurosci.1116-06.2006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2006] [Revised: 04/12/2006] [Accepted: 04/27/2006] [Indexed: 11/21/2022] Open
Abstract
To analyze the fundamental role of gap junctions in the vertebrate inner ear, we examined molecular and functional characteristics of gap junctional communication (GJC) in the auditory and vestibular system of the chicken. By screening inner ear tissues for connexin isoforms using degenerate reverse transcription-PCR, we identified, in addition to chicken Cx43 (cCx43) and the inner-ear-specific cCx30, an as yet uncharacterized connexin predicted to be the ortholog of the mammalian Cx26. In situ hybridization indicated that cCx30 and cCx26 transcripts were both widely expressed in the cochlear duct and utricle in an overlapping pattern, suggesting coexpression of these isoforms similar to that in the mammalian inner ear. Immunohistochemistry demonstrated that cCx43 was present in gap junctions connecting supporting cells of the basilar papilla, in which its immunofluorescence colocalized with that of cCx30. However, cCx43 was absent from supporting cell gap junctions of the utricular macula. This variation in the molecular composition of gap junction plaques coincided with differences in the functional properties of GJC between the auditory and vestibular sensory epithelia. Fluorescence recovery after photobleaching, adapted to examine the diffusion of calcein in inner ear explants, revealed asymmetric communication pathways among supporting cells in the basilar papilla but not in the utricular macula. This study supports the hypothesis that the coexpression of Cx26/Cx30 is unique to gap junctions in the vertebrate inner ear. Furthermore, it demonstrates asymmetric GJC within the supporting cell population of the auditory sensory epithelium, which might mediate potassium cycling and/or intercellular signaling.
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Affiliation(s)
- Regina Nickel
- Centre for Auditory Research, The Ear Institute, University College London, London WC1X 8EE, United Kingdom.
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44
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Tang W, Zhang Y, Chang Q, Ahmad S, Dahlke I, Yi H, Chen P, Paul DL, Lin X. Connexin29 is highly expressed in cochlear Schwann cells, and it is required for the normal development and function of the auditory nerve of mice. J Neurosci 2006; 26:1991-9. [PMID: 16481432 PMCID: PMC6674919 DOI: 10.1523/jneurosci.5055-05.2006] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Connexins (Cxs) are a family of protein subunits constituting gap junctions, which facilitate exchanges of molecules important for cellular signaling and metabolic activities intercellularly or between different regions of the cytoplasm in the same cells. Mutations in Cxs are the major cause of nonsyndromic childhood deafness, which are mostly found in Cx26 and Cx30 expressed in cochlear supporting cells and fibrocytes. So far, little is known about the functional contribution of Cxs in other types of cochlear cells. Here, we show that Cx29 was highly expressed in the cochlea. The developmental expression time course of Cx29 was similar to that of a myelin marker [myelin associate glycoprotein (MAG)]. Immunolabeling identified Cx29 exclusively in the Schwann cells myelinating the soma and fiber of spiral ganglion (SG) neurons. The absence of the Cx29 gene in mice (Cx29(-/-) mice), with a penetrance of approximately 50%, caused a delay in the maturation of hearing thresholds, an early loss of high-frequency sensitivities, a prolongation in latency and distortion in the wave I of the auditory brainstem responses, and elevated sensitivity to noise damages. The morphology of sensory hair cells and otoacoustic emissions that depend on the integrity of hair cells were normal in Cx29(-/-) mice. In contrast, decreases in MAG expression and severe demyelination at the soma of SG neurons were found in Cx29(-/-) mice. Our findings demonstrated the requirement of Cx29 for normal cochlear functions and suggest that Cx29 is a new candidate gene for studying the auditory neuropathy.
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45
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Jagger DJ, Forge A. Compartmentalized and signal-selective gap junctional coupling in the hearing cochlea. J Neurosci 2006; 26:1260-8. [PMID: 16436613 PMCID: PMC6674557 DOI: 10.1523/jneurosci.4278-05.2006] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Gap junctional intercellular communication (GJIC) plays a major role in cochlear function. Recent evidence suggests that connexin 26 (Cx26) and Cx30 are the major constituent proteins of cochlear gap junction channels, possibly in a unique heteromeric configuration. We investigated the functional and structural properties of native cochlear gap junctions in rats, from birth to the onset of hearing [postnatal day 12 (P12)]. Confocal immunofluorescence revealed increasing Cx26 and Cx30 expression from P0 to P12. Functional GJIC was assessed by coinjection of Lucifer yellow (LY) and Neurobiotin (NBN) during whole-cell recordings in cochlear slices. At P0, there was restricted dye transfer between supporting cells around outer hair cells. Transfer was more extensive between supporting cells around inner hair cells. At P8, there was extensive transfer of both dyes between all supporting cell types. By P12, LY no longer transferred between the supporting cells immediately adjacent to hair cells but still transferred between more peripheral cells. NBN transferred freely, but it did not transfer between inner and outer pillar cells. Freeze fracture further demonstrated decreasing GJIC between inner and outer pillar cells around the onset of hearing. These data are supportive of the appearance of signal-selective gap junctions around the onset of hearing, with specific properties required to support auditory function. Furthermore, they suggest that separate medial and lateral buffering compartments exist in the hearing cochlea, which are individually dedicated to the homeostasis of inner hair cells and outer hair cells.
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MESH Headings
- Animals
- Cell Communication/physiology
- Coloring Agents/analysis
- Connexin 26
- Connexin 30
- Connexins/biosynthesis
- Connexins/genetics
- Connexins/physiology
- Fluorescein-5-isothiocyanate/analysis
- Freeze Fracturing
- Gap Junctions/physiology
- Gene Expression
- Hair Cells, Auditory, Inner/metabolism
- Hair Cells, Auditory, Inner/physiology
- Hair Cells, Auditory, Inner/ultrastructure
- Hair Cells, Auditory, Outer/metabolism
- Hair Cells, Auditory, Outer/physiology
- Hair Cells, Auditory, Outer/ultrastructure
- Hearing/physiology
- Microinjections
- Microscopy, Confocal
- Organ of Corti/growth & development
- Organ of Corti/physiology
- Organ of Corti/ultrastructure
- Patch-Clamp Techniques
- Rats
- Rats, Sprague-Dawley
- Rhodamines/analysis
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Affiliation(s)
- Daniel J Jagger
- Centre for Auditory Research, UCL Ear Institute, University College London, London WC1X 8EE, United Kingdom.
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46
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Zhang Y, Tang W, Ahmad S, Sipp JA, Chen P, Lin X. Gap junction-mediated intercellular biochemical coupling in cochlear supporting cells is required for normal cochlear functions. Proc Natl Acad Sci U S A 2005; 102:15201-6. [PMID: 16217030 PMCID: PMC1257692 DOI: 10.1073/pnas.0501859102] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Dysfunction of gap junctions (GJs) caused by mutations in connexin26 (Cx26) and Cx30 accounts for nearly half of all cases of hereditary nonsyndromic deafness cases. Although it is widely held that GJs connecting supporting cells in the organ of Corti mainly provide ionic pathways for rapid removal of K+ around the base of hair cells, the function of GJs in the cochlea remains unknown. Here we show that GJs were not assembled in the supporting cells of the organ of Corti until 3 days after birth in mice and then gradually matured to connect supporting cells before the onset of hearing. In organotypic cochlear cultures that were confirmed to express GJs, GJs mediated the propagation of intracellular Ca2+ concentration waves in supporting cells by allowing intercellular diffusion of inositol 1,4,5-trisphosphate. We found that a subset of structurally mild Cx26 mutations located at the second transmembrane region (V84L, V95M, and A88S) and a Cx30 mutation located at the first cytoplasmic segment (T5M) specifically affect the intercellular exchange of larger molecules but leave the ionic permeability intact. Our results indicated that Cx26 and Cx30 mutations that are linked to sensorineural deafness retained ionic coupling but were deficient in biochemical permeability. Therefore, GJ-mediated intercellular exchange of biochemically important molecules is required for normal cochlear functions.
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Affiliation(s)
- Yanping Zhang
- Department of Otolaryngology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322-3030, USA
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47
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Thomas T, Jordan K, Simek J, Shao Q, Jedeszko C, Walton P, Laird DW. Mechanisms of Cx43 and Cx26 transport to the plasma membrane and gap junction regeneration. J Cell Sci 2005; 118:4451-62. [PMID: 16159960 DOI: 10.1242/jcs.02569] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previous reports have suggested that Cx26 exhibits unique intracellular transport pathways en route to the cell surface compared with other members of the connexin family. To directly examine and compare nascent and steady-state delivery of Cx43 and Cx26 to the plasma membrane and gap junction biogenesis we expressed fluorescent-protein-tagged Cx43 and Cx26 in BICR-M1Rk and NRK cells. Static and time-lapse imaging revealed that both connexins were routed through the Golgi apparatus prior to being transported to the cell surface, a process inhibited in the presence of brefeldin A (BFA) or the expression of a dominant-negative form of Sar1 GTPase. During recovery from BFA, time-lapse imaging of nascent connexin Golgi-to-plasma membrane delivery revealed many dynamic post-Golgi carriers (PGCs) originating from the distal side of the Golgi apparatus consisting of heterogeneous vesicles and long, tubular-like extensions. Vesicles and tubular extensions were also observed in HBL-100 cells expressing a human, disease-linked, Golgi-localized Cx26 mutant, D66H-GFP. A diffuse cell surface rim of fluorescent-protein-tagged wild-type connexins was observed prior to the appearance of punctate gap junctions, which suggests that random fusion of PGCs occurred with the plasma membrane followed by lateral diffusion of connexins into clusters. Fluorescence recovery after photobleaching studies revealed that Cx26-YFP was more mobile within gap junction plaques compared with Cx43-GFP. Intriguingly, Cx43-GFP delivery and gap junction regeneration was inhibited by BFA and nocodazole, whereas Cx26-GFP delivery was prevented by BFA but not nocodazole. Collectively, these studies suggest that during gap junction biogenesis two phylogenetically distinct members of the connexin family, Cx43 and Cx26, share common secretory pathways, types of transport intermediates and turnover dynamics but differ in their microtubule-dependence and mobility within the plasma membrane, which might reflect differences in binding to protein scaffolds.
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Affiliation(s)
- Tamsin Thomas
- Department of Anatomy and Cell Biology, University of Western Ontario, Dental Science Building, Rm. 00077, London, Ontario, Canada N6A 5C1
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48
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Beltramello M, Piazza V, Bukauskas FF, Pozzan T, Mammano F. Impaired permeability to Ins(1,4,5)P3 in a mutant connexin underlies recessive hereditary deafness. Nat Cell Biol 2004; 7:63-9. [PMID: 15592461 DOI: 10.1038/ncb1205] [Citation(s) in RCA: 200] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2004] [Accepted: 11/08/2004] [Indexed: 01/21/2023]
Abstract
Connexins are membrane proteins that assemble into gap-junction channels and are responsible for direct, electrical and metabolic coupling between connected cells. Here we describe an investigation of the properties of a recombinantly expressed recessive mutant of connexin 26 (Cx26), the V84L mutant, associated with deafness. Unlike other Cx26 mutations, V84L affects neither intracellular sorting nor electrical coupling, but specifically reduces permeability to the Ca(2+)-mobilizing messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P(3)). Both the permeability to Lucifer Yellow and the unitary channel conductance of V84L-mutant channels are indistinguishable from those of the wild-type Cx26. Injection of Ins(1,4,5)P(3) into supporting cells of the rat organ of Corti, which abundantly express Cx26, ensues in a regenerative wave of Ca(2+) throughout the tissue. Blocking the gap junction communication abolishes wave propagation. We propose that the V84L mutation reduces metabolic coupling mediated by Ins(1,4,5)P(3) to an extent sufficient to impair the propagation of Ca(2+) waves and the formation of a functional syncytium. Our data provide the first demonstration of a specific defect of metabolic coupling and offer a mechanistic explanation for the pathogenesis of an inherited human disease.
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MESH Headings
- Animals
- Animals, Newborn
- Biological Transport, Active/genetics
- Calcium/metabolism
- Calcium Signaling/drug effects
- Calcium Signaling/genetics
- Cell Communication/drug effects
- Cell Communication/genetics
- Cell Membrane Permeability/genetics
- Connexin 26
- Connexins/genetics
- Connexins/metabolism
- Deafness/congenital
- Deafness/genetics
- Deafness/physiopathology
- Gap Junctions/genetics
- Gap Junctions/metabolism
- Genes, Recessive/genetics
- Hair Cells, Auditory/drug effects
- Hair Cells, Auditory/metabolism
- Humans
- Inositol 1,4,5-Trisphosphate/metabolism
- Inositol 1,4,5-Trisphosphate/pharmacology
- Labyrinth Supporting Cells/drug effects
- Labyrinth Supporting Cells/metabolism
- Membrane Potentials/drug effects
- Membrane Potentials/genetics
- Mutation/genetics
- Organ Culture Techniques
- Organ of Corti/cytology
- Organ of Corti/metabolism
- Organ of Corti/physiopathology
- Rats
- Rats, Sprague-Dawley
- Second Messenger Systems/genetics
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49
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Richard G, Brown N, Ishida-Yamamoto A, Krol A. Expanding The Phenotypic Spectrum of Cx26 Disorders: Bart–Pumphrey Syndrome is Caused by a Novel Missense Mutation in GJB2. J Invest Dermatol 2004; 123:856-63. [PMID: 15482471 DOI: 10.1111/j.0022-202x.2004.23470.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bart-Pumphrey syndrome (BPS) is an autosomal dominant disorder characterized by sensorineural hearing loss, palmoplantar keratoderma, knuckle pads, and leukonychia, which show considerable phenotypic variability. The clinical features partially overlap with Vohwinkel syndrome and Keratitis-Ichthyosis-Deafness syndrome, both disorders caused by dominant mutations in the GJB2 gene encoding the gap junction protein connexin-26, suggesting an etiological relationship. We report here a novel GJB2 mutation N54K segregating in a family with BPS, which was not detected in 110 control individuals of Northern European ancestry. This non-conservative missense mutation lies within a cluster of pathogenic GJB2 mutations affecting the evolutionary conserved first extracellular loop of Cx26 important for docking of connexin hemichannels and voltage gating. Immunostaining of Cx26 in lesional palmar and knuckle skin was weak or absent, although its adnexal expression appeared normal and the punctate membrane staining of Cx26 and other epidermal connexins was not altered. Nevertheless, the widespread immunostaining of Cx30 throughout the spinous cell layers suggested a compensatory overexpression. Our results emphasize that pleiotropic GJB2 mutations are responsible for at least 5 overlapping dermatological disorders associated with syndromic hearing loss and cover a wide range of severity and organ involvement.
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Affiliation(s)
- Gabriele Richard
- Department of Dermatology and Cutaneous Biology, and Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
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