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Lucaciu SA, Leighton SE, Hauser A, Yee R, Laird DW. Diversity in connexin biology. J Biol Chem 2023; 299:105263. [PMID: 37734551 PMCID: PMC10598745 DOI: 10.1016/j.jbc.2023.105263] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 09/08/2023] [Accepted: 09/14/2023] [Indexed: 09/23/2023] Open
Abstract
Over 35 years ago the cell biology community was introduced to connexins as the subunit employed to assemble semicrystalline clusters of intercellular channels that had been well described morphologically as gap junctions. The decade that followed would see knowledge of the unexpectedly large 21-member human connexin family grow to reflect unique and overlapping expression patterns in all organ systems. While connexin biology initially focused on their role in constructing highly regulated intercellular channels, this was destined to change as discoveries revealed that connexin hemichannels at the cell surface had novel roles in many cell types, especially when considering connexin pathologies. Acceptance of connexins as having bifunctional channel properties was initially met with some resistance, which has given way in recent years to the premise that connexins have multifunctional properties. Depending on the connexin isoform and cell of origin, connexins have wide-ranging half-lives that vary from a couple of hours to the life expectancy of the cell. Diversity in connexin channel characteristics and molecular properties were further revealed by X-ray crystallography and single-particle cryo-EM. New avenues have seen connexins or connexin fragments playing roles in cell adhesion, tunneling nanotubes, extracellular vesicles, mitochondrial membranes, transcription regulation, and in other emerging cellular functions. These discoveries were largely linked to Cx43, which is prominent in most human organs. Here, we will review the evolution of knowledge on connexin expression in human adults and more recent evidence linking connexins to a highly diverse array of cellular functions.
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Affiliation(s)
- Sergiu A Lucaciu
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada; Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Stephanie E Leighton
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada
| | - Alexandra Hauser
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada
| | - Ryan Yee
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Dale W Laird
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada; Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
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2
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Ngezahayo A, Ruhe FA. Connexins in the development and physiology of stem cells. Tissue Barriers 2021; 9:1949242. [PMID: 34227910 DOI: 10.1080/21688370.2021.1949242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
Connexins (Cxs) form gap junction (GJ) channels linking vertebrate cells. During embryogenesis, Cxs are expressed as early as the 4-8 cell stage. As cells differentiate into pluripotent stem cells (PSCs) and during gastrulation, the Cx expression pattern is adapted. Knockdown of Cx43 and Cx45 does not interfere with embryogenic development until the blastula stage, questioning the role of Cxs in PSC physiology and development. Studies in cultivated and induced PSCs (iPSCs) showed that Cx43 is essential for the maintenance of self-renewal and the expression of pluripotency markers. It was found that the role of Cxs in PSCs is more related to regulation of transcription or cell-cell adherence than to formation of GJ channels. Furthermore, a crucial role of Cxs for the self-renewal and differentiation was shown in cultivated adult mesenchymal stem cells. This review aims to highlight aspects that link Cxs to the function and physiology of stem cell development.
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Affiliation(s)
- Anaclet Ngezahayo
- Dept. Cell Physiology and Biophysics, Institute of Cell Biology and Biophysics, Leibniz University Hannover, Hannover, Germany.,Center for Systems Neuroscience (ZSN), University of Veterinary Medicine Hannover, Hannover, Germany
| | - Frederike A Ruhe
- Dept. Cell Physiology and Biophysics, Institute of Cell Biology and Biophysics, Leibniz University Hannover, Hannover, Germany
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3
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Lag synchronization of coupled time-delayed FitzHugh-Nagumo neural networks via feedback control. Sci Rep 2021; 11:3884. [PMID: 33594138 PMCID: PMC7887243 DOI: 10.1038/s41598-021-82886-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 01/27/2021] [Indexed: 01/31/2023] Open
Abstract
Synchronization plays a significant role in information transfer and decision-making by neurons and brain neural networks. The development of control strategies for synchronizing a network of chaotic neurons with time delays, different direction-dependent coupling (unidirectional and bidirectional), and noise, particularly under external disturbances, is an essential and very challenging task. Researchers have extensively studied the synchronization mechanism of two coupled time-delayed neurons with bidirectional coupling and without incorporating the effect of noise, but not for time-delayed neural networks. To overcome these limitations, this study investigates the synchronization problem in a network of coupled FitzHugh-Nagumo (FHN) neurons by incorporating time delays, different direction-dependent coupling (unidirectional and bidirectional), noise, and ionic and external disturbances in the mathematical models. More specifically, this study investigates the synchronization of time-delayed unidirectional and bidirectional ring-structured FHN neuronal systems with and without external noise. Different gap junctions and delay parameters are used to incorporate time-delay dynamics in both neuronal networks. We also investigate the influence of the time delays between connected neurons on synchronization conditions. Further, to ensure the synchronization of the time-delayed FHN neuronal networks, different adaptive control laws are proposed for both unidirectional and bidirectional neuronal networks. In addition, necessary and sufficient conditions to achieve synchronization are provided by employing the Lyapunov stability theory. The results of numerical simulations conducted for different-sized multiple networks of time-delayed FHN neurons verify the effectiveness of the proposed adaptive control schemes.
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Ishikawa M, Williams G, Forcinito P, Ishikawa M, Petrie RJ, Saito K, Fukumoto S, Yamada Y. Pannexin 3 ER Ca 2+ channel gating is regulated by phosphorylation at the Serine 68 residue in osteoblast differentiation. Sci Rep 2019; 9:18759. [PMID: 31822768 PMCID: PMC6904572 DOI: 10.1038/s41598-019-55371-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Accepted: 11/19/2019] [Indexed: 12/31/2022] Open
Abstract
Pannexin 3 (Panx3) is a regulator of bone formation. Panx3 forms three distinct functional channels: hemichannels, gap junctions, and endoplasmic reticulum (ER) Ca2+ channels. However, the gating mechanisms of the Panx3 channels remain unclear. Here, we show that the Panx3 ER Ca2+ channel is modulated by phosphorylation of the serine 68 residue (Ser68) to promote osteoblast differentiation. Among the 17 candidate phosphorylation sites identified, the mutation of Ser68 to Ala (Ser68Ala) was sufficient to inhibit Panx3-mediated osteoblast differentiation via reduction of Osterix and ALP expression. Using a Ser68 phospho-specific antibody (P-Panx3) revealed Panx3 was phosphorylated in prehypertrophic, hypertrophic chondrocytes, and bone areas of the newborn growth plate. In osteogenic C2C12 cells, P-Panx3 was located on the ER membranes. Importantly, the Ser68Ala mutation only affected Panx3 ER Ca2+ channel function. Ser68 on Panx3 was phosphorylated by ATP stimulation and PI3K/Akt signaling. Finally, real-time FRET imaging and ratio analysis revealed that the Panx3 channel conformation was sensitive to ATP. Together, the phosphorylation of Panx3 at Ser68 is an essential step controlling the gating of the Panx3 ER Ca2+ channel to promote osteogenesis.
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Affiliation(s)
- Masaki Ishikawa
- Operative Dentistry, Tohoku University Graduate School of Dentistry, Sendai, 980-8575, Japan.
| | - Geneva Williams
- Molecular Biology Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Philadelphia, USA
| | - Patricia Forcinito
- Molecular Biology Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Philadelphia, USA
| | - Momoko Ishikawa
- Department of Pediatric Dentistry, Tohoku University Graduate School of Dentistry, Sendai, 980-8576, Japan
| | - Ryan J Petrie
- Department of Biology, Drexel University, Philadelphia, PA, 19104, USA
| | - Kan Saito
- Department of Pediatric Dentistry, Tohoku University Graduate School of Dentistry, Sendai, 980-8576, Japan
| | - Satoshi Fukumoto
- Department of Pediatric Dentistry, Tohoku University Graduate School of Dentistry, Sendai, 980-8576, Japan
| | - Yoshihiko Yamada
- Molecular Biology Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Philadelphia, USA
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Schadzek P, Stahl Y, Preller M, Ngezahayo A. Analysis of the dominant mutation N188T of human connexin46 (hCx46) using concatenation and molecular dynamics simulation. FEBS Open Bio 2019; 9:840-850. [PMID: 31034164 PMCID: PMC6487695 DOI: 10.1002/2211-5463.12624] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 02/06/2019] [Accepted: 02/26/2019] [Indexed: 11/27/2022] Open
Abstract
Connexins (Cx) are proteins that form cell-to-cell gap junction channels. A mutation at position 188 in the second extracellular loop (E2) domain of hCx46 has been linked to an autosomal dominant zonular pulverulent cataract. As it is dominantly inherited, it is possible that the mutant variant affects the co-expressed wild-type Cx and/or its interaction with other cellular components. Here, we proposed to use concatenated hCx46wt-hCx46N188T and hCx46N188T-hCx46wt to analyze how hCx46N188T affected co-expressed hCx46wt to achieve a dominant inheritance. Heterodimer hCx46wt-hCx46N188T formed fewer gap junction plaques compared to homodimer hCx46wt-hCx46wt, while the hCx46N188T-hCx46N188T homodimer formed almost no gap junction plaques. Dye uptake experiments showed that hemichannels of concatenated variants were similar to hemichannels of monomers. Molecular dynamics simulations revealed that for docking, the N188 of a protomer was engaged in hydrogen bonds (HBs) with R180, N189, and D191 of the counterpart protomer of the adjacent hemichannel. T188 suppressed the formation of HBs between protomers. Molecular dynamics simulations of an equimolar hCx46wt/hCx46N188T gap junction channel revealed a reduced number of HBs between protomers, suggesting reduction of gap junction channels between lens fibers co-expressing the variants.
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Affiliation(s)
- Patrik Schadzek
- Institute of Cell Biology and BiophysicsDepartment of Cell Physiology and BiophysicsLeibniz University HannoverGermany
| | - Yannick Stahl
- Institute of Cell Biology and BiophysicsDepartment of Cell Physiology and BiophysicsLeibniz University HannoverGermany
| | - Matthias Preller
- Institute for Biophysical ChemistryHannover Medical School (MHH)Germany
- Centre for Structural Systems Biology, DESY‐CampusHamburgGermany
| | - Anaclet Ngezahayo
- Institute of Cell Biology and BiophysicsDepartment of Cell Physiology and BiophysicsLeibniz University HannoverGermany
- Center for System Neurosciences (ZSN)HannoverGermany
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Kim NK, Santos-Miranda A, Chen H, Aoyama H, Bai D. Heterotypic docking compatibility of human connexin37 with other vascular connexins. J Mol Cell Cardiol 2019; 127:194-203. [PMID: 30594540 DOI: 10.1016/j.yjmcc.2018.12.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Revised: 12/03/2018] [Accepted: 12/26/2018] [Indexed: 01/18/2023]
Abstract
Human vascular connexins (Cx37, Cx40, Cx43, and Cx45) can form various types of gap junction channels to synchronize vasodilation/constriction to control local circulation. Most of our knowledge on heterotypic gap junctions of these vascular connexins was from studies on rodent connexins. In human vasculature, the same four homolog connexins exist, but whether these human connexins can form heterotypic GJs as those of rodents have not been fully studied. Here we used in vitro expression system to study the coupling status and GJ channel properties of human heterotypic Cx37/Cx40, Cx37/Cx43, and Cx37/Cx45 GJs. Our results showed that Cx37/Cx43 and Cx37/Cx45 GJs, but not Cx37/Cx40 GJs, were functional and each with unique rectifying channel properties. The failure of docking between Cx37 and Cx40 could be rescued by designed Cx40 variants. Characterization of the heterotypic Cx37/Cx43 and Cx37/Cx45 GJs may help us in understanding the intercellular communication at the myoendothelial junction.
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Affiliation(s)
- Nicholas K Kim
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Artur Santos-Miranda
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Honghong Chen
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Hiroshi Aoyama
- Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan
| | - Donglin Bai
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
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Schadzek P, Hermes D, Stahl Y, Dilger N, Ngezahayo A. Concatenation of Human Connexin26 (hCx26) and Human Connexin46 (hCx46) for the Analysis of Heteromeric Gap Junction Hemichannels and Heterotypic Gap Junction Channels. Int J Mol Sci 2018; 19:E2742. [PMID: 30217016 PMCID: PMC6163895 DOI: 10.3390/ijms19092742] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Revised: 09/10/2018] [Accepted: 09/11/2018] [Indexed: 12/16/2022] Open
Abstract
Gap junction channels and hemichannels formed by concatenated connexins were analyzed. Monomeric (hCx26, hCx46), homodimeric (hCx46-hCx46, hCx26-hCx26), and heterodimeric (hCx26-hCx46, hCx46-hCx26) constructs, coupled to GFP, were expressed in HeLa cells. Confocal microscopy showed that the tandems formed gap junction plaques with a reduced plaque area compared to monomeric hCx26 or hCx46. Dye transfer experiments showed that concatenation allows metabolic transfer. Expressed in Xenopus oocytes, the inside-out patch-clamp configuration showed single channels with a conductance of about 46 pS and 39 pS for hemichannels composed of hCx46 and hCx26 monomers, respectively, when chloride was replaced by gluconate on both membrane sides. The conductance was reduced for hCx46-hCx46 and hCx26-hCx26 homodimers, probably due to the concatenation. Heteromerized hemichannels, depending on the connexin-order, were characterized by substates at 26 pS and 16 pS for hCx46-hCx26 and 31 pS and 20 pS for hCx26-hCx46. Because of the linker between the connexins, the properties of the formed hemichannels and gap junction channels (e.g., single channel conductance) may not represent the properties of hetero-oligomerized channels. However, should the removal of the linker be successful, this method could be used to analyze the electrical and metabolic selectivity of such channels and the physiological consequences for a tissue.
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Affiliation(s)
- Patrik Schadzek
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
| | - Doris Hermes
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
- Department of Clinical Neurophysiology, University of Göttingen, Robert-Koch Str. 40, D-37075 Göttingen, Germany.
| | - Yannick Stahl
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
| | - Nadine Dilger
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
| | - Anaclet Ngezahayo
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
- Zentrum für Systemische Neurowissenschaften Stiftung Tierärztliche Hochschule Hannover, Bünteweg 2, 30559 Hannover, Germany.
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8
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Valdebenito S, Lou E, Baldoni J, Okafo G, Eugenin E. The Novel Roles of Connexin Channels and Tunneling Nanotubes in Cancer Pathogenesis. Int J Mol Sci 2018; 19:E1270. [PMID: 29695070 PMCID: PMC5983846 DOI: 10.3390/ijms19051270] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 04/13/2018] [Accepted: 04/18/2018] [Indexed: 12/28/2022] Open
Abstract
Neoplastic growth and cellular differentiation are critical hallmarks of tumor development. It is well established that cell-to-cell communication between tumor cells and "normal" surrounding cells regulates tumor differentiation and proliferation, aggressiveness, and resistance to treatment. Nevertheless, the mechanisms that result in tumor growth and spread as well as the adaptation of healthy surrounding cells to the tumor environment are poorly understood. A major component of these communication systems is composed of connexin (Cx)-containing channels including gap junctions (GJs), tunneling nanotubes (TNTs), and hemichannels (HCs). There are hundreds of reports about the role of Cx-containing channels in the pathogenesis of cancer, and most of them demonstrate a downregulation of these proteins. Nonetheless, new data demonstrate that a localized communication via Cx-containing GJs, HCs, and TNTs plays a key role in tumor growth, differentiation, and resistance to therapies. Moreover, the type and downstream effects of signals communicated between the different populations of tumor cells are still unknown. However, new approaches such as artificial intelligence (AI) and machine learning (ML) could provide new insights into these signals communicated between connected cells. We propose that the identification and characterization of these new communication systems and their associated signaling could provide new targets to prevent or reduce the devastating consequences of cancer.
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Affiliation(s)
- Silvana Valdebenito
- Public Health Research Institute (PHRI), Newark, NJ 07103, USA.
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers New Jersey Medical School, Rutgers the State University of NJ, Newark, NJ 07103, USA.
| | - Emil Lou
- Department of Medicine, Division of Hematology, Oncology and Transplantation, University of Minnesota, Minneapolis, MN 55455, USA.
| | - John Baldoni
- GlaxoSmithKline, In-Silico Drug Discovery Unit, 1250 South Collegeville Road, Collegeville, PA 19426, USA.
| | - George Okafo
- GlaxoSmithKline, In-Silico Drug Discovery Unit, Stevenage SG1 2NY, UK.
| | - Eliseo Eugenin
- Public Health Research Institute (PHRI), Newark, NJ 07103, USA.
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers New Jersey Medical School, Rutgers the State University of NJ, Newark, NJ 07103, USA.
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Valdebenito S, Barreto A, Eugenin EA. The role of connexin and pannexin containing channels in the innate and acquired immune response. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:154-165. [PMID: 28559189 DOI: 10.1016/j.bbamem.2017.05.015] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Revised: 05/17/2017] [Accepted: 05/25/2017] [Indexed: 12/20/2022]
Abstract
Connexin (Cx) and pannexin (Panx) containing channels - gap junctions (GJs) and hemichannels (HCs) - are present in virtually all cells and tissues. Currently, the role of these channels under physiological conditions is well defined. However, their role in the immune response and pathological conditions has only recently been explored. Data from several laboratories demonstrates that infectious agents, including HIV, have evolved to take advantage of GJs and HCs to improve viral/bacterial replication, enhance inflammation, and help spread toxicity into neighboring areas. In the current review, we discuss the role of Cx and Panx containing channels in immune activation and the pathogenesis of several infectious diseases. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.
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Affiliation(s)
- Silvana Valdebenito
- Public Health Research Institute (PHRI), Newark, NJ, USA; Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers New Jersey Medical School, Rutgers the State University of New Jersey, Newark, NJ, USA
| | - Andrea Barreto
- Public Health Research Institute (PHRI), Newark, NJ, USA; Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers New Jersey Medical School, Rutgers the State University of New Jersey, Newark, NJ, USA
| | - Eliseo A Eugenin
- Public Health Research Institute (PHRI), Newark, NJ, USA; Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers New Jersey Medical School, Rutgers the State University of New Jersey, Newark, NJ, USA.
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Pannexin 3 regulates proliferation and differentiation of odontoblasts via its hemichannel activities. PLoS One 2017; 12:e0177557. [PMID: 28494020 PMCID: PMC5426780 DOI: 10.1371/journal.pone.0177557] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 04/28/2017] [Indexed: 12/25/2022] Open
Abstract
Highly coordinated regulation of cell proliferation and differentiation contributes to the formation of functionally shaped and sized teeth; however, the mechanism underlying the switch from cell cycle exit to cell differentiation during odontogenesis is poorly understood. Recently, we identified pannexin 3 (Panx3) as a member of the pannexin gap junction protein family from tooth germs. The expression of Panx3 was predominately localized in preodontoblasts that arise from dental papilla cells and can differentiate into dentin-secreting odontoblasts. Panx3 also co-localized with p21, a cyclin-dependent kinase inhibitor protein, in preodontoblasts. Panx3 was expressed in primary dental mesenchymal cells and in the mDP dental mesenchymal cell line. Both Panx3 and p21 were induced during the differentiation of mDP cells. Overexpression of Panx3 in mDP cells reduced cell proliferation via up-regulation of p21, but not of p27, and promoted the Bone morphogenetic protein 2 (BMP2)-induced phosphorylation of Smad1/5/8 and the expression of dentin sialophosphoprotein (Dspp), a marker of differentiated odontoblasts. Furthermore, Panx3 released intracellular ATP into the extracellular space through its hemichannel and induced the phosphorylation of AMP-activated protein kinase (AMPK). 5-Aminoimidazole-4-carboxamide-ribonucleoside (AICAR), an activator of AMPK, reduced mDP cell proliferation and induced p21 expression. Conversely, knockdown of endogenous Panx3 by siRNA inhibited AMPK phosphorylation, p21 expression, and the phosphorylation of Smad1/5/8 even in the presence of BMP2. Taken together, our results suggest that Panx3 modulates intracellular ATP levels, resulting in the inhibition of odontoblast proliferation through the AMPK/p21 signaling pathway and promotion of cell differentiation by the BMP/Smad signaling pathway.
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Wong P, Laxton V, Srivastava S, Chan YWF, Tse G. The role of gap junctions in inflammatory and neoplastic disorders (Review). Int J Mol Med 2017; 39:498-506. [PMID: 28098880 PMCID: PMC5360388 DOI: 10.3892/ijmm.2017.2859] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Accepted: 12/23/2016] [Indexed: 12/29/2022] Open
Abstract
Gap junctions are intercellular channels made of connexin proteins, mediating both electrical and biochemical signals between cells. The ability of gap junction proteins to regulate immune responses, cell proliferation, migration, apoptosis and carcinogenesis makes them attractive therapeutic targets for treating inflammatory and neoplastic disorders in different organ systems. Alterations in gap junction profile and expression levels are observed in hyperproliferative skin disorders, lymphatic vessel diseases, inflammatory lung diseases, liver injury and neoplastic disorders. It is now recognized that the therapeutic effects mediated by traditional pharmacological agents are dependent upon gap junction communication and may even act by influencing gap junction expression or function. Novel strategies for modulating the function or expression of connexins, such as the use of synthetic mimetic peptides and siRNA technology are considered.
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Affiliation(s)
- Pui Wong
- School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, SAR, P.R. China
| | - Victoria Laxton
- Intensive Care Department, Royal Brompton and Harefield NHS Foundation Trust, London SW3 6NP
| | | | - Yin Wah Fiona Chan
- School of Biological Sciences, University of Cambridge, Cambridge CB2 1AG, UK
| | - Gary Tse
- Department of Medicine and Therapeutics
- Li Ka Shing Institute of Health Sciences, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, SAR, P.R. China
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12
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Snipas M, Kraujalis T, Paulauskas N, Maciunas K, Bukauskas FF. Stochastic Model of Gap Junctions Exhibiting Rectification and Multiple Closed States of Slow Gates. Biophys J 2016; 110:1322-33. [PMID: 27028642 DOI: 10.1016/j.bpj.2016.01.035] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Revised: 01/03/2016] [Accepted: 01/27/2016] [Indexed: 12/26/2022] Open
Abstract
Gap-junction (GJ) channels formed from connexin (Cx) proteins provide direct pathways for electrical and metabolic cell-cell communication. Earlier, we developed a stochastic 16-state model (S16SM) of voltage gating of the GJ channel containing two pairs of fast and slow gates, each operating between open (o) and closed (c) states. However, experimental data suggest that gates may in fact contain two or more closed states. We developed a model in which the slow gate operates according to a linear reaction scheme, o↔c1↔c2, where c1 and c2 are initial-closed and deep-closed states that both close the channel fully, whereas the fast gate operates between the open state and the closed state and exhibits a residual conductance. Thus, we developed a stochastic 36-state model (S36SM) of GJ channel gating that is sensitive to transjunctional voltage (Vj). To accelerate simulation and eliminate noise in simulated junctional conductance (gj) records, we transformed an S36SM into a Markov chain 36-state model (MC36SM) of GJ channel gating. This model provides an explanation for well-established experimental data, such as delayed gj recovery after Vj gating, hysteresis of gj-Vj dependence, and the low ratio of functional channels to the total number of GJ channels clustered in junctional plaques, and it has the potential to describe chemically mediated gating, which cannot be reflected using an S16SM. The MC36SM, when combined with global optimization algorithms, can be used for automated estimation of gating parameters including probabilities of c1↔c2 transitions from experimental gj-time and gj-Vj dependencies.
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Affiliation(s)
- Mindaugas Snipas
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania; Department of Mathematical Modelling, Kaunas University of Technology, Kaunas, Lithuania
| | - Tadas Kraujalis
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Nerijus Paulauskas
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Kestutis Maciunas
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Feliksas F Bukauskas
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania; Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, New York.
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Wong P, Tan T, Chan C, Laxton V, Chan YWF, Liu T, Wong WT, Tse G. The Role of Connexins in Wound Healing and Repair: Novel Therapeutic Approaches. Front Physiol 2016; 7:596. [PMID: 27999549 PMCID: PMC5138227 DOI: 10.3389/fphys.2016.00596] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 11/16/2016] [Indexed: 12/26/2022] Open
Abstract
Gap junctions are intercellular proteins responsible for mediating both electrical and biochemical coupling through the exchange of ions, second messengers and small metabolites. They consist of two connexons, with (one) connexon supplied by each cell. A connexon is a hexamer of connexins and currently more than 20 connexin isoforms have been described in the literature thus far. Connexins have a short half-life, and therefore gap junction remodeling constantly occurs with a high turnover rate. Post-translational modification, such as phosphorylation, can modify their channel activities. In this article, the roles of connexins in wound healing and repair are reviewed. Novel strategies for modulating the function or expression of connexins, such as the use of antisense technology, synthetic mimetic peptides and bioactive materials for the treatment of skin wounds, diabetic and pressure ulcers as well as cornea wounds, are considered.
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Affiliation(s)
- Pui Wong
- Li Ka Shing Faculty of Medicine, School of Biomedical Sciences, University of Hong Kong Hong Kong, Hong Kong
| | - Teresa Tan
- Department of Surgery, Faculty of Medicine, Chinese University of Hong Kong Hong Kong, Hong Kong
| | - Catherine Chan
- Department of Surgery, Faculty of Medicine, Chinese University of Hong Kong Hong Kong, Hong Kong
| | - Victoria Laxton
- Intensive Care Department, Royal Brompton and Harefield NHS Foundation Trust London, UK
| | - Yin Wah Fiona Chan
- Department of Psychology, School of Biological Sciences, University of Cambridge Cambridge, UK
| | - Tong Liu
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University Tianjin, China
| | - Wing Tak Wong
- School of Life Sciences, Chinese University of Hong Kong Hong Kong, Hong Kong
| | - Gary Tse
- Department of Medicine and Therapeutics, Faculty of Medicine, Chinese University of Hong KongHong Kong, Hong Kong; Faculty of Medicine, Li Ka Shing Institute of Health Sciences, Chinese University of Hong KongHong Kong, Hong Kong
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14
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A Langevin model of physical forces in cell volume fluctuations. J Biomech 2016; 49:1286-1289. [DOI: 10.1016/j.jbiomech.2015.12.051] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Revised: 10/30/2015] [Accepted: 12/30/2015] [Indexed: 11/17/2022]
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15
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Huang SF, Zhang JQ, Wang MS. Response Ability to External Signal Enhanced by Biological Spatial Configuration in Coupled Hindmarsh-Rose Neural System. CHINESE J CHEM PHYS 2016. [DOI: 10.1063/1674-0068/29/cjcp1505088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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16
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Schadzek P, Schlingmann B, Schaarschmidt F, Lindner J, Koval M, Heisterkamp A, Preller M, Ngezahayo A. The cataract related mutation N188T in human connexin46 (hCx46) revealed a critical role for residue N188 in the docking process of gap junction channels. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1858:57-66. [PMID: 26449341 DOI: 10.1016/j.bbamem.2015.10.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Revised: 09/28/2015] [Accepted: 10/01/2015] [Indexed: 12/16/2022]
Abstract
The mutation N188T in human connexin46 (hCx46) correlates with a congenital nuclear pulverulent cataract. This mutation is in the second extracellular loop, a domain involved in docking of gap junction hemichannels. To analyze the functional consequences of this mutation, we expressed hCx46N188T and the wild type (hCx46wt) in Xenopus oocytes and HeLa cells. In Xenopus oocytes, hemichannels formed by hCx46wt and hCx46N188T had similar electrical properties. Additionally, a Ca(2+) and La(3+) sensitive current was observed in HeLa cells expressing eGFP-labeled hCx46wt or eGFP-labeled hCx46N188T. These results suggest that the N188T mutation did not alter apparent expression and the membrane targeting of the protein. Cells expressing hCx46wt-eGFP formed gap junction plaques, but plaques formed by hCx46N188T were extremely rare. A reduced plaque formation was also found in cells cotransfected with hCx46N188T-eGFP and mCherry-labeled hCx46wt as well as in cocultured cells expressing hCx46N188T-eGFP and hCx46wt-mCherry. Dye transfer experiments in cells expressing hCx46N188T revealed a lower transfer rate than cells expressing hCx46wt. We postulate that the N188T mutation affects intercellular connexon docking. This hypothesis is supported by molecular modeling of hCx46 using the crystal structure of hCx26 as a template. The model indicated that N188 is important for hemichannel docking through formation of hydrogen bonds with the residues R180, T189 and D191 of the opposing hCx46. The results suggest that the N188T mutation hinders the docking of the connexons to form gap junction channels. Moreover, the finding that a glutamine substitution (hCx46N188Q) could not rescue the docking emphasizes the specific role of N188.
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Affiliation(s)
- Patrik Schadzek
- Institute of Biophysics, Leibniz University Hannover, Germany
| | - Barbara Schlingmann
- Institute of Biophysics, Leibniz University Hannover, Germany; Division of Pulmonary, Allergy and Critical Care and Sleep Medicine, Department of Medicine and Department of Cell Biology, Emory School of Medicine, Atlanta, GA, USA
| | | | - Julia Lindner
- Institute of Biophysics, Leibniz University Hannover, Germany
| | - Michael Koval
- Division of Pulmonary, Allergy and Critical Care and Sleep Medicine, Department of Medicine and Department of Cell Biology, Emory School of Medicine, Atlanta, GA, USA; Department of Cell Biology, Emory University, Atlanta, GA, USA
| | | | - Matthias Preller
- Institute for Biophysical Chemistry, Hannover Medical School (MHH), Hannover, Germany; Center for Structural Systems Biology, German Electron Synchrotron (DESY), Hamburg, Germany.
| | - Anaclet Ngezahayo
- Institute of Biophysics, Leibniz University Hannover, Germany; Center for System Neurosciences (ZSN), Hannover, Germany.
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17
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Cell Volume Fluctuations in MDCK Monolayers. Biophys J 2015; 108:247-50. [PMID: 25606673 DOI: 10.1016/j.bpj.2014.11.1856] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Revised: 11/07/2014] [Accepted: 11/14/2014] [Indexed: 12/13/2022] Open
Abstract
Cells moving collectively in tissues constitute a form of active matter, in which collective motion depends strongly on driven fluctuations at the single-cell scale. Fluctuations in cell area and number density are often seen in monolayers, yet their role in collective migration is not known. Here we study density fluctuations at the single- and multicell level, finding that single-cell volumes oscillate with a timescale of 4 h and an amplitude of 20%; the timescale and amplitude are found to depend on cytoskeletal activity. At the multicellular scale, density fluctuations violate the central limit theorem, highlighting the role of nonequilibrium driving forces in multicellular density fluctuations.
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18
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Buzsáki G. Hippocampal sharp wave-ripple: A cognitive biomarker for episodic memory and planning. Hippocampus 2015; 25:1073-188. [PMID: 26135716 PMCID: PMC4648295 DOI: 10.1002/hipo.22488] [Citation(s) in RCA: 914] [Impact Index Per Article: 101.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 06/30/2015] [Indexed: 12/23/2022]
Abstract
Sharp wave ripples (SPW-Rs) represent the most synchronous population pattern in the mammalian brain. Their excitatory output affects a wide area of the cortex and several subcortical nuclei. SPW-Rs occur during "off-line" states of the brain, associated with consummatory behaviors and non-REM sleep, and are influenced by numerous neurotransmitters and neuromodulators. They arise from the excitatory recurrent system of the CA3 region and the SPW-induced excitation brings about a fast network oscillation (ripple) in CA1. The spike content of SPW-Rs is temporally and spatially coordinated by a consortium of interneurons to replay fragments of waking neuronal sequences in a compressed format. SPW-Rs assist in transferring this compressed hippocampal representation to distributed circuits to support memory consolidation; selective disruption of SPW-Rs interferes with memory. Recently acquired and pre-existing information are combined during SPW-R replay to influence decisions, plan actions and, potentially, allow for creative thoughts. In addition to the widely studied contribution to memory, SPW-Rs may also affect endocrine function via activation of hypothalamic circuits. Alteration of the physiological mechanisms supporting SPW-Rs leads to their pathological conversion, "p-ripples," which are a marker of epileptogenic tissue and can be observed in rodent models of schizophrenia and Alzheimer's Disease. Mechanisms for SPW-R genesis and function are discussed in this review.
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Affiliation(s)
- György Buzsáki
- The Neuroscience Institute, School of Medicine and Center for Neural Science, New York University, New York, New York
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Kurata S, Goto T, K. Gunjigake K, Kataoka S, N. Kuroishi K, Ono K, Toyono T, Kobayashi S, Yamaguchi K. Nerve Growth Factor Involves Mutual Interaction between Neurons and Satellite Glial Cells in the Rat Trigeminal Ganglion. Acta Histochem Cytochem 2013; 46:65-73. [PMID: 23720605 PMCID: PMC3661776 DOI: 10.1267/ahc.13003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2013] [Accepted: 03/07/2013] [Indexed: 12/24/2022] Open
Abstract
Nerve growth factor (NGF) plays a critical role in the trigeminal ganglion (TG) following peripheral nerve damage in the oral region. Although neurons in the TG are surrounded by satellite glial cells (SGCs) that passively support neural function, little is known regarding NGF expression and its interactions with TG neurons and SGCs. This study was performed to examine the expression of NGF in TG neurons and SGCs with nerve damage by experimental tooth movement. An elastic band was inserted between the first and second upper molars of rats. The TG was removed at 0–7 days after tooth movement. Using in situ hybridization, NGF mRNA was expressed in both neurons and SGCs. Immunostaining for NGF demonstrated that during tooth movement the number of NGF-immunoreactive SGCs increased significantly as compared with baseline and reached maximum levels at day 3. Furthermore, the administration of the gap junction inhibitor carbenoxolone at the TG during tooth movement significantly decreased the number of NGF-immunoreactive SGCs. These results suggested that peripheral nerve damage may induce signal transduction from neurons to SGCs via gap junctions, inducing NGF expression in SGCs around neurons, and released NGF may be involved in the restoration of damaged neurons.
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Affiliation(s)
- Sayaka Kurata
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University
| | | | - Kaori K. Gunjigake
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University
| | | | - Kayoko N. Kuroishi
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University
| | - Kentaro Ono
- Division of Physiology, Kyushu Dental University
| | - Takashi Toyono
- Division of Oral Histology and Neurobiology, Kyushu Dental University
| | | | - Kazunori Yamaguchi
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University
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20
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Völgyi B, Kovács-Oller T, Atlasz T, Wilhelm M, Gábriel R. Gap junctional coupling in the vertebrate retina: variations on one theme? Prog Retin Eye Res 2013; 34:1-18. [PMID: 23313713 DOI: 10.1016/j.preteyeres.2012.12.002] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Revised: 12/18/2012] [Accepted: 12/28/2012] [Indexed: 10/27/2022]
Abstract
Gap junctions connect cells in the bodies of all multicellular organisms, forming either homologous or heterologous (i.e. established between identical or different cell types, respectively) cell-to-cell contacts by utilizing identical (homotypic) or different (heterotypic) connexin protein subunits. Gap junctions in the nervous system serve electrical signaling between neurons, thus they are also called electrical synapses. Such electrical synapses are particularly abundant in the vertebrate retina where they are specialized to form links between neurons as well as glial cells. In this article, we summarize recent findings on retinal cell-to-cell coupling in different vertebrates and identify general features in the light of the evergrowing body of data. In particular, we describe and discuss tracer coupling patterns, connexin proteins, junctional conductances and modulatory processes. This multispecies comparison serves to point out that most features are remarkably conserved across the vertebrate classes, including (i) the cell types connected via electrical synapses; (ii) the connexin makeup and the conductance of each cell-to-cell contact; (iii) the probable function of each gap junction in retinal circuitry; (iv) the fact that gap junctions underlie both electrical and/or tracer coupling between glial cells. These pan-vertebrate features thus demonstrate that retinal gap junctions have changed little during the over 500 million years of vertebrate evolution. Therefore, the fundamental architecture of electrically coupled retinal circuits seems as old as the retina itself, indicating that gap junctions deeply incorporated in retinal wiring from the very beginning of the eye formation of vertebrates. In addition to hard wiring provided by fast synaptic transmitter-releasing neurons and soft wiring contributed by peptidergic, aminergic and purinergic systems, electrical coupling may serve as the 'skeleton' of lateral processing, enabling important functions such as signal averaging and synchronization.
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Affiliation(s)
- Béla Völgyi
- Department of Ophthalmology, School of Medicine, New York University, 550 First Avenue, MSB 149, New York, NY 10016, USA.
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Paulauskas N, Pranevicius H, Mockus J, Bukauskas FF. Stochastic 16-state model of voltage gating of gap-junction channels enclosing fast and slow gates. Biophys J 2012; 102:2471-80. [PMID: 22713562 DOI: 10.1016/j.bpj.2012.04.038] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Revised: 04/23/2012] [Accepted: 04/25/2012] [Indexed: 11/25/2022] Open
Abstract
Gap-junction (GJ) channels formed of connexin (Cx) proteins provide a direct pathway for electrical and metabolic cell-cell interaction. Each hemichannel in the GJ channel contains fast and slow gates that are sensitive to transjunctional voltage (Vj). We developed a stochastic 16-state model (S16SM) that details the operation of two fast and two slow gates in series to describe the gating properties of homotypic and heterotypic GJ channels. The operation of each gate depends on the fraction of Vj that falls across the gate (VG), which varies depending on the states of three other gates in series, as well as on parameters of the fast and slow gates characterizing 1), the steepness of each gate's open probability on VG; 2), the voltage at which the open probability of each gate equals 0.5; 3), the gating polarity; and 4), the unitary conductances of the gates and their rectification depending on VG. S16SM allows for the simulation of junctional current dynamics and the dependence of steady-state junctional conductance (gj,ss) on Vj. We combined global coordinate optimization algorithms with S16SM to evaluate the gating parameters of fast and slow gates from experimentally measured gj,ss-Vj dependencies in cells expressing different Cx isoforms and forming homotypic and/or heterotypic GJ channels.
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Affiliation(s)
- Nerijus Paulauskas
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, New York, USA
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22
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Bukauskas FF. Neurons and β-cells of the pancreas express connexin36, forming gap junction channels that exhibit strong cationic selectivity. J Membr Biol 2012; 245:243-53. [PMID: 22752717 PMCID: PMC3626077 DOI: 10.1007/s00232-012-9445-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Accepted: 06/01/2012] [Indexed: 01/30/2023]
Abstract
We examined the permeability of connexin36 (Cx36) homotypic gap junction (GJ) channels, expressed in neurons and β-cells of the pancreas, to dyes differing in molecular mass and net charge. Experiments were performed in HeLa cells stably expressing Cx36 tagged with EGFP by combining a dual whole-cell voltage clamp and fluorescence imaging. To assess the permeability of the single GJ channel (P(γ)), we used a dual-mode excitation of fluorescent dyes that allowed us to measure cell-to-cell dye transfer at levels not resolvable using whole-field excitation solely. We demonstrate that P(γ) of Cx36 for cationic dyes (EAM-1⁺ and EAM-2⁺) is ~10-fold higher than that for an anionic dye of the same net charge and similar molecular mass, Alexa fluor-350 (AFl-350⁻). In addition, P(γ) for Lucifer yellow (LY²⁻) is approximately fourfold smaller than that for AFl-350⁻, which suggests that the higher negativity of LY²⁻ significantly reduces permeability. The P(γ) of Cx36 for AFl-350 is approximately 358, 138, 23 and four times smaller than the P(γ)s of Cx43, Cx40, Cx45, and Cx57, respectively. In contrast, it is 6.5-fold higher than the P(γ) of mCx30.2, which exhibits a smaller single-channel conductance. Thus, Cx36 GJs are highly cation-selective and should exhibit relatively low permeability to numerous vital negatively charged metabolites and high permeability to K⁺, a major charge carrier in cell-cell communication.
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Affiliation(s)
- Feliksas F Bukauskas
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
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23
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Kremmyda LS, Tvrzicka E, Stankova B, Zak A. Fatty acids as biocompounds: their role in human metabolism, health and disease: a review. part 2: fatty acid physiological roles and applications in human health and disease. Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub 2012; 155:195-218. [PMID: 22286806 DOI: 10.5507/bp.2011.052] [Citation(s) in RCA: 112] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
BACKGROUND This is the second of two review parts aiming at describing the major physiological roles of fatty acids, as well as their applications in specific conditions related to human health. RESULTS The review included the current literature published in Pubmed up to March 2011. In humans, fatty acids are a principle energy substrate and structural components of cell membranes (phospholipids) and second messengers. Fatty acids are also ligands of nuclear receptors affecting gene expression. Longer-chain (LC) polyunsaturated fatty acids (PUFA), including eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid are precursors of lipid mediators such as eicosanoids (prostaglandins, leukotrienes, thromboxanes), resolvins and neuroprotectins. Lipid mediators produced by EPA and DHA (LC n-3 PUFA; mainly found in oily fish) are considered as inflammation-resolving, and thus, fish oil has been characterised as antiinflammatory. Recommendations for EPA plus DHA intake from oily fish vary between 250-450 mg/day. Dietary reference values for fat vary between nutrition bodies, but mainly agree on a low total and saturated fat intake. The existing literature supports the protective effects of LC n-3 PUFA (as opposed to n-6 PUFA and saturated fat) in maternal and offspring health, cardiovascular health, insulin sensitivity, the metabolic syndrome, cancer, critically ill patients, and immune system disorders. CONCLUSION Fatty acids are involved in multiple pathways and play a major role in health. Further investigation and a nutrigenomics approach to the effects of these biocompounds on health and disease development are imperative and highlight the importance of environmental modifications on disease outcome.
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Ishikawa M, Iwamoto T, Nakamura T, Doyle A, Fukumoto S, Yamada Y. Pannexin 3 functions as an ER Ca(2+) channel, hemichannel, and gap junction to promote osteoblast differentiation. ACTA ACUST UNITED AC 2011; 193:1257-74. [PMID: 21690309 PMCID: PMC3216329 DOI: 10.1083/jcb.201101050] [Citation(s) in RCA: 169] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Pannexin 3 functions as an essential protein for Ca2+ and ATP transport and cell–cell communication during osteoblast differentiation The pannexin proteins represent a new gap junction family. However, the cellular functions of pannexins remain largely unknown. Here, we demonstrate that pannexin 3 (Panx3) promotes differentiation of osteoblasts and ex vivo growth of metatarsals. Panx3 expression was induced during osteogenic differentiation of C2C12 cells and primary calvarial cells, and suppression of this endogenous expression inhibited differentiation. Panx3 functioned as a unique Ca2+ channel in the endoplasmic reticulum (ER), which was activated by purinergic receptor/phosphoinositide 3-kinase (PI3K)/Akt signaling, followed by activation of calmodulin signaling for differentiation. Panx3 also formed hemichannels that allowed release of ATP into the extracellular space and activation of purinergic receptors with the subsequent activation of PI3K–Akt signaling. Panx3 also formed gap junctions and propagated Ca2+ waves between cells. Blocking the Panx3 Ca2+ channel and gap junction activities inhibited osteoblast differentiation. Thus, Panx3 appears to be a new regulator that promotes osteoblast differentiation by functioning as an ER Ca2+ channel and a hemichannel, and by forming gap junctions.
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Affiliation(s)
- Masaki Ishikawa
- Laboratory of Cell and Developmental Biology, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
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Gao J, Sun X, Moore LC, White TW, Brink PR, Mathias RT. Lens intracellular hydrostatic pressure is generated by the circulation of sodium and modulated by gap junction coupling. J Gen Physiol 2011; 137:507-20. [PMID: 21624945 PMCID: PMC3105514 DOI: 10.1085/jgp.201010538] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Accepted: 05/13/2011] [Indexed: 11/30/2022] Open
Abstract
We recently modeled fluid flow through gap junction channels coupling the pigmented and nonpigmented layers of the ciliary body. The model suggested the channels could transport the secretion of aqueous humor, but flow would be driven by hydrostatic pressure rather than osmosis. The pressure required to drive fluid through a single layer of gap junctions might be just a few mmHg and difficult to measure. In the lens, however, there is a circulation of Na(+) that may be coupled to intracellular fluid flow. Based on this hypothesis, the fluid would cross hundreds of layers of gap junctions, and this might require a large hydrostatic gradient. Therefore, we measured hydrostatic pressure as a function of distance from the center of the lens using an intracellular microelectrode-based pressure-sensing system. In wild-type mouse lenses, intracellular pressure varied from ∼330 mmHg at the center to zero at the surface. We have several knockout/knock-in mouse models with differing levels of expression of gap junction channels coupling lens fiber cells. Intracellular hydrostatic pressure in lenses from these mouse models varied inversely with the number of channels. When the lens' circulation of Na(+) was either blocked or reduced, intracellular hydrostatic pressure in central fiber cells was either eliminated or reduced proportionally. These data are consistent with our hypotheses: fluid circulates through the lens; the intracellular leg of fluid circulation is through gap junction channels and is driven by hydrostatic pressure; and the fluid flow is generated by membrane transport of sodium.
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Affiliation(s)
- Junyuan Gao
- Department of Physiology and Biophysics, SUNY at Stony Brook, NY 11794, USA
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Dahm L, Klugmann F, Gonzalez-Algaba A, Reuss B. Tamoxifen and raloxifene modulate gap junction coupling during early phases of retinoic acid-dependent neuronal differentiation of NTera2/D1 cells. Cell Biol Toxicol 2010; 26:579-91. [PMID: 20437090 PMCID: PMC2959160 DOI: 10.1007/s10565-010-9165-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Accepted: 04/12/2010] [Indexed: 01/21/2023]
Abstract
Gap junctions (GJ) represent a cellular communication system known to influence neuronal differentiation and survival. To assess a putative role of this system for neural effects of tamoxifen (TAM) and raloxifene (RAL), we used the human teratocarcinoma cell line NTera2/D1, retinoic acid (RA)-dependent neuronal differentiation of which is regulated by gap junctions formed of connexin43 (Cx43). As demonstrated by Western blot analysis, concentrations above 1 µmol/l for TAM, and 0.1 µmol/l for RAL lead to a temporary time- and concentration-dependent increase in Cx43 immunoreactivity, which reached a peak for TAM after 1 day and for RAL after 2 days. Immunocytochemical stainings revealed the increase in Cx43 immunoreactivity to result from an accumulation in intracellular compartments such as the Golgi apparatus or lysosomes. In addition, TAM and RAL were able to prevent the RA-dependent decrease of Cx43 immunoreactivity in NTera2/D1 cells, normally observed during neuronal differentiation. This suggested a suppression of neuronal differentiation to result from these substances. According to this, treatment of NTera2/D1 cells with 10 µmol/l TAM or RAL during weeks 1 and 2 of a 6 weeks RA-driven differentiation schedule impaired, whereas treatment during weeks 5 and 6 did not impair, neuronal differentiation of these cells. Modulation of GJ coupling between NTera2/D1 cells by TAM and RAL seems therefore to perturb early neuronal differentiation, whereas differentiated neurons in the mature brain seem to be not affected. These effects could be of importance for actions of TAM and RAL on early embryonic steps of nervous system formation.
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Affiliation(s)
- Liane Dahm
- Center for Anatomy-Neuroanatomy, University of Göttingen, Kreuzbergring 36, 37075, Göttingen, Germany
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Paulauskas N, Pranevicius M, Pranevicius H, Bukauskas FF. A stochastic four-state model of contingent gating of gap junction channels containing two "fast" gates sensitive to transjunctional voltage. Biophys J 2009; 96:3936-48. [PMID: 19450466 DOI: 10.1016/j.bpj.2009.01.059] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2008] [Revised: 12/29/2008] [Accepted: 01/14/2009] [Indexed: 11/30/2022] Open
Abstract
Connexins, a family of membrane proteins, form gap junction (GJ) channels that provide a direct pathway for electrical and metabolic signaling between cells. We developed a stochastic four-state model describing gating properties of homotypic and heterotypic GJ channels each composed of two hemichannels (connexons). GJ channel contain two "fast" gates (one per hemichannel) oriented opposite in respect to applied transjunctional voltage (V(j)). The model uses a formal scheme of peace-linear aggregate and accounts for voltage distribution inside the pore of the channel depending on the state, unitary conductances and gating properties of each hemichannel. We assume that each hemichannel can be in the open state with conductance gamma(h,o) and in the residual state with conductance gamma(h,res), and that both gamma(h,o) and gamma(h,res) rectifies. Gates can exhibit the same or different gating polarities. Gating of each hemichannel is determined by the fraction of V(j) that falls across the hemichannel, and takes into account contingent gating when gating of one hemichannel depends on the state of apposed hemichannel. At the single-channel level, the model revealed the relationship between unitary conductances of hemichannels and GJ channels and how this relationship is affected by gamma(h,o) and gamma(h,res) rectification. Simulation of junctions containing up to several thousands of homotypic or heterotypic GJs has been used to reproduce experimentally measured macroscopic junctional current and V(j)-dependent gating of GJs formed from different connexin isoforms. V(j)-gating was simulated by imitating several frequently used experimental protocols: 1), consecutive V(j) steps rising in amplitude, 2), slowly rising V(j) ramps, and 3), series of V(j) steps of high frequency. The model was used to predict V(j)-gating of heterotypic GJs from characteristics of corresponding homotypic channels. The model allowed us to identify the parameters of V(j)-gates under which small changes in the difference of holding potentials between cells forming heterotypic junctions effectively modulates cell-to-cell signaling from bidirectional to unidirectional. The proposed model can also be used to simulate gating properties of unapposed hemichannels.
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Affiliation(s)
- Nerijus Paulauskas
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, The Bronx, New York, USA
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Donnell P, Baigent SA, Banaji M. Monotone dynamics of two cells dynamically coupled by a voltage-dependent gap junction. J Theor Biol 2009; 261:120-5. [PMID: 19627994 DOI: 10.1016/j.jtbi.2009.07.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Revised: 07/07/2009] [Accepted: 07/08/2009] [Indexed: 11/17/2022]
Abstract
We introduce and analyse a simple model for two non-excitable cells that are dynamically coupled by a gap junction, a plaque of aqueous channels that electrically couple the cells. The gap junction channels have a low and high conductance state, and the transition rates between these states are voltage-dependent. We show that the number and stability of steady states of the system has a simple relationship with the determinant of the Jacobian matrix. For the case that channel opening rates decrease with increasing trans-junctional voltage, and closing rates increase with increasing trans-junctional voltage, we show that the system is monotone, with tridiagonal Jacobian matrix, and hence every initial condition evolves to a steady state, but that there may be multiple steady states.
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Affiliation(s)
- Peter Donnell
- Department of Medical Physics and Bioengineering, UCL, Gower Street, London WC1E 6BT, UK.
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29
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Dobrowolski R, Hertig G, Lechner H, Worsdorfer P, Wulf V, Dicke N, Eckert D, Bauer R, Schorle H, Willecke K. Loss of connexin43-mediated gap junctional coupling in the mesenchyme of limb buds leads to altered expression of morphogens in mice. Hum Mol Genet 2009; 18:2899-911. [DOI: 10.1093/hmg/ddp227] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
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30
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Rossello RA, Kohn DH. Gap junction intercellular communication: a review of a potential platform to modulate craniofacial tissue engineering. J Biomed Mater Res B Appl Biomater 2009; 88:509-18. [PMID: 18481782 DOI: 10.1002/jbm.b.31127] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Defects in craniofacial tissues, resulting from trauma, congenital abnormalities, oncologic resection or progressive deforming diseases, may result in aesthetic deformity, pain and reduced function. Restoring the structure, function and aesthetics of craniofacial tissues represents a substantial clinical problem in need of new solutions. More biologically-interactive biomaterials could potentially improve the treatment of craniofacial defects, and an understanding of developmental processes may help identify strategies and materials that can be used in tissue engineering. One such strategy that can potentially advance tissue engineering is cell-cell communication. Gap junction intercellular communication is the most direct way of achieving such signaling. Gap junction communication through connexin-mediated junctions, in particular connexin 43 (Cx43), plays a major role bone development. Given the important role of Cx43 in controlling development and differentiation, especially in bone cells, controlling the expression of Cx43 may provide control over cell-to-cell communication and may help overcome some of the challenges in craniofacial tissue engineering. Following a review of gap junctions in bone cells, the ability to enhance cell-cell communication and osteogenic differentiation via control of gap junctions is discussed, as is the potential utility of this approach in craniofacial tissue engineering.
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Affiliation(s)
- Ricardo A Rossello
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2099, USA
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31
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Ron A, Fishelson N, Croitoriu N, Benayahu D, Shacham-Diamand Y. Theoretical examination of aggregation effect on the dielectric characteristics of spherical cellular suspension. Biophys Chem 2009; 140:39-50. [DOI: 10.1016/j.bpc.2008.11.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2008] [Accepted: 11/16/2008] [Indexed: 11/30/2022]
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32
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Dodd R, Peracchia C, Stolady D, Török K. Calmodulin association with connexin32-derived peptides suggests trans-domain interaction in chemical gating of gap junction channels. J Biol Chem 2008; 283:26911-20. [PMID: 18676375 PMCID: PMC2555998 DOI: 10.1074/jbc.m801434200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Revised: 07/14/2008] [Indexed: 12/30/2022] Open
Abstract
Calmodulin plays a key role in the chemical gating of gap junction channels. Two calmodulin-binding regions have previously been identified in connexin32 gap junction protein, one in the N-terminal and another in the C-terminal cytoplasmic tail of the molecule. The aim of this study was to better understand how calmodulin interacts with the connexin32-binding domains. Lobe-specific interactions of calmodulin with connexin32 peptides were studied by stopped flow kinetics, using Ca(2+) binding-deficient mutants. Peptides corresponding to the N-terminal tail (residues 1-22) of connexin32 engaged both the N- and C-terminal lobes (N- and C-lobes) of calmodulin, binding with higher affinity to the C-lobe of calmodulin (Ca(2+) dissociation rate constants k(3,4), 1.7+/-0.5 s(-1)) than to the N-lobe (k(1,2), 10.8+/-1.3 s(-1)). In contrast, peptides representing the C-terminal tail domain (residues 208-227) of connexin32 bound either the C- or the N-lobe but only one calmodulin lobe at a time (k(3,4), 2.6+/-0.1 s(-1) or k(1), 13.8+/-0.5 s(-1) and k(2), 1000 s(-1)). The calmodulin-binding domains of the N- and C-terminal tails of connexin32 were best defined as residues 1-21 and 216-227, respectively. Our data, showing separate functions of the N- and C-lobes of calmodulin in the interactions with connexin32, suggest trans-domain or trans-subunit bridging by calmodulin as a possible mechanism of gap junction gating.
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Affiliation(s)
- Ryan Dodd
- Division of Basic Medical Sciences, St George's, University of London, London, SW17 0RE United Kingdom
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33
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Mi LY, Ettenson DS, Edelman ER. Phospholipase C-delta extends intercellular signalling range and responses to injury-released growth factors in non-excitable cells. Cell Prolif 2008; 41:671-90. [PMID: 18616695 DOI: 10.1111/j.1365-2184.2008.00544.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
OBJECTIVES Intercellular communication in non-excitable cells is restricted to a limited range close to the signal source. Here, we have examined whether modification of the intracellular microenvironment could prolong the spatial proposition of signal generation and could increase cell proliferation. MATERIAL AND METHODS Mathematical models and experimental studies of endothelial repair after controlled mechanical injury were used. The models predict the diffusion range of injury-released growth factors and identify important parameters involved in a signalling regenerative mode. Transfected human umbilical vein endothelial cells (HUVECs) were used to validate model results, by examining intercellular calcium signalling range, cell proliferation and wound healing rate. RESULTS The models predict that growth factors have a limited capacity of extracellular diffusion and that intercellular signals are specially sensitive to cell phospholipase C-delta (PLCdelta) levels. As basal PLCdelta levels are increased by transfection, a significantly increased intercellular calcium range, enhanced cell proliferation, and faster wound healing rate were observed. CONCLUSION Our in silico and in vitro studies demonstrated that non-excitable endothelial cells respond to stimuli in a complex manner, in which intercellular communication is controlled by physicochemical properties of the stimulus and by the cell microenvironment. Such findings may have profound implications for our understanding of the tight nature of autocrine cell growth control, compensation to stress states and response to altered microenvironment, under pathological conditions.
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Affiliation(s)
- L Y Mi
- Harvard-MIT Division of Health Science and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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34
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Dobrowolski R, Sasse P, Schrickel JW, Watkins M, Kim JS, Rackauskas M, Troatz C, Ghanem A, Tiemann K, Degen J, Bukauskas FF, Civitelli R, Lewalter T, Fleischmann BK, Willecke K. The conditional connexin43G138R mouse mutant represents a new model of hereditary oculodentodigital dysplasia in humans. Hum Mol Genet 2007; 17:539-54. [PMID: 18003637 DOI: 10.1093/hmg/ddm329] [Citation(s) in RCA: 136] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Oculodentodigital dysplasia (ODDD) is a dominant negatively inherited disorder with variable but characteristic anomalies of the fingers and toes, eyes, face and teeth, which are caused by mutations in the connexin 43 (Cx43) gene. All mutations analyzed so far have a negative influence on the conductance through gap junctional channels and hemichannels, as well as trafficking of Cx43 protein in transfected cells. In this study, we inserted the human Cx43G138R point mutation into the mouse Cx43 gene and generated mice conditionally expressing this mutation. All ODDD phenotypic manifestations observed in humans, including syndactyly and enamel hypoplasia as well as craniofacial, bone and heart anomalies, were also observed with significant penetrance in Cx43G138R mice. When this mutation was specifically expressed in cardiomyocytes, characteristic alterations in the electrocardiogram and spontaneous arrhythmias were recorded. In vitro studies with Cx43G138R-expressing cells revealed loss of the Cx43 P2 phosphorylation state, which was also absent in the mutated hearts. This loss has previously been associated with gap junctional dysfunction and increased cellular ATP release. The Cx43G138R mutated mice show significantly increased arrhythmogeneity ex vivo in Langendorff experiments with explanted hearts and in vivo in particular under hypoxic conditions. Our results suggest that the increased activity of ATP-releasing channels in Cx43G138R mutated cardiomyocytes may further reduce the already decreased gap junctional communication and thus aggravate arrhythmogenesis in the mouse mutant.
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35
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Regulation of ion channels and arrhythmias in the ischemic heart. J Electrocardiol 2007; 40:S37-41. [DOI: 10.1016/j.jelectrocard.2007.05.020] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Accepted: 05/14/2007] [Indexed: 02/06/2023]
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36
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37
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Dobrowolski R, Sommershof A, Willecke K. Some oculodentodigital dysplasia-associated Cx43 mutations cause increased hemichannel activity in addition to deficient gap junction channels. J Membr Biol 2007; 219:9-17. [PMID: 17687502 DOI: 10.1007/s00232-007-9055-7] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2007] [Accepted: 06/11/2007] [Indexed: 11/26/2022]
Abstract
Oculodentodigital dysplasia (ODDD) is a dominantly inherited human disorder associated with different symptoms like craniofacial anomalies, syndactyly and heart dysfunction. ODDD is caused by mutations in the GJA1 gene encoding the gap junction protein connexin43 (Cx43). Here, we have characterized four Cx43 mutations (I31M, G138R, G143S and H194P) after stable expression in HeLa cells. In patients, the I31M and G138R mutations showed all phenotypic characteristics of ODDD, whereas G143S did not result in facial abnormalities and H194P mutated patients exhibited no syndactylies. In transfected HeLa cells, these mutations led to lack of the P2 phosphorylation state of the Cx43 protein, complete inhibition of gap junctional coupling measured by neurobiotin transfer and increased hemichannel activity. In addition, altered trafficking and delayed degradation were found in these mutants by immunofluorescence and pulse-chase analyses. In G138R and G143S mutants, the increased hemichannel activity correlated with an increased half-time of the Cx43 protein. However, the I31M mutated protein showed no extended half-time. Thus, the increased hemichannel activity may be directly caused by an altered conformation of the mutated channel forming protein. We hypothesize that increased hemichannel activity may aggravate the phenotypic abnormalities in ODDD patients who are deficient in Cx43 gap junction channels.
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Affiliation(s)
- Radoslaw Dobrowolski
- Institute of Genetics, University of Bonn, Roemerstrasse 164, 53117, Bonn, Germany
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38
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Jiang W, Xiangyang F, Feng D. Chaotic Synchronization of Multi-neurons in External Electrical Stimulation. CONFERENCE PROCEEDINGS : ... ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL CONFERENCE 2007; 2005:2103-6. [PMID: 17282643 DOI: 10.1109/iembs.2005.1616874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The synchronization of n(n≥3) neurons coupled with gap junction in external electrical stimulation is investigated. In this paper, the coupled model is established on the basis of nonlinear cable model, and then the relation of coupling strength of the gap junction and the synchronization is discussed in detail. The sufficient condition of complete synchronization is attained from rigorously mathematical derivation. The synchronizations of periodic neurons and chaotic neurons are studied respectively.
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Affiliation(s)
- Wang Jiang
- School of Electrical and Automation Eng., Tianjin University, Tianjin 300072, China. (e-mail: )
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39
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Abstract
Evaluation of the human genome suggests that all members of the connexin family of gap-junction proteins have now been successfully identified. This large and diverse family of proteins facilitates a number of vital cellular functions coupled with their roles, which range from the intercellular propagation of electrical signals to the selective intercellular passage of small regulatory molecules. Importantly, the extent of gap-junctional intercellular communication is under the direct control of regulatory events associated with channel assembly and turnover, as the vast majority of connexins have remarkably short half-lives of only a few hours. Since most cell types express multiple members of the connexin family, compensatory mechanisms exist to salvage tissue function in cases when one connexin is mutated or lost. However, numerous studies of the last decade have revealed that mutations in connexin genes can also lead to severe and debilitating diseases. In many cases, single point mutations lead to dramatic effects on connexin trafficking, assembly and channel function. This review will assess the current understanding of wild-type and selected disease-linked mutant connexin transport through the secretory pathway, gap-junction assembly at the cell surface, internalization and degradation.
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Affiliation(s)
- Dale W Laird
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada N6A 5C1.
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40
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Chen Z, Evans WH, Pflugfelder SC, Li DQ. Gap junction protein connexin 43 serves as a negative marker for a stem cell-containing population of human limbal epithelial cells. Stem Cells 2006; 24:1265-73. [PMID: 16424398 PMCID: PMC2906383 DOI: 10.1634/stemcells.2005-0363] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
This study evaluated whether the gap junction protein connexin (Cx) 43 could serve as a negative cell surface marker for human corneal epithelial stem cells. Cx43 expression was evaluated in corneo-limbal tissue and primary limbal epithelial cultures. Immunofluorescent staining and laser scanning confocal microscopy showed that Cx43 was strongly expressed in the corneal and limbal suprabasal epithelial cells, but the basal cells of the limbal epithelium were negative. Cx43 antibody stained mainly large cells but not small cells in primary limbal epithelial cultures. As determined by semiquantitative reverse transcription polymerase chain reaction (PCR) and real-time PCR, Cx43 mRNA was more abundant in the corneal than limbal epithelia, and it was expressed in higher levels in mature limbal epithelial cultures. Using GAP11, a rabbit polyclonal antibody against the Cx32 extracellular loop 2 (151-187), a sequence that is highly homologous in Cx43, the Cx43(dim) and Cx43(bright) cells were selected from primary limbal epithelial cultures by fluorescence-activated cell sorting and were evaluated for stem cell properties. These Cx43(dim) and Cx43(bright) cells were confirmed by their expression levels of Cx43 protein and mRNA. The Cx43(dim) cells were found to contain higher percentages of slow-cycling bromodeoxyuridine (BrdU)-label retaining cells and the cells that were positive for stem cell-associated markers p63, ABCG2, and integrin beta1 and negative for differentiation markers K3 and involucrin. The Cx43(dim) cells possessed a greater proliferative potential than Cx43(bright) cells and nonfractionated cells as evaluated by BrdU incorporation, colony-forming efficiency, and growth capacity. Our findings suggest that human limbal basal cells do not express connexin 43, which could serve as a negative cell surface marker for the stem cell-containing population of human limbal epithelial cells.
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Affiliation(s)
- Zhuo Chen
- Ocular Surface Center, Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA
| | - W. Howard Evans
- Department of Medical Biochemistry and Immunology, Cardiff University Medical School and The Wales Heart Research Institute, Cardiff, Wales, United Kingdom
| | - Stephen C. Pflugfelder
- Ocular Surface Center, Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA
| | - De-Quan Li
- Ocular Surface Center, Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA
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41
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Jin C, Martyn KD, Kurata WE, Warn-Cramer BJ, Lau AF. Connexin43 PDZ2 binding domain mutants create functional gap junctions and exhibit altered phosphorylation. ACTA ACUST UNITED AC 2005; 11:67-87. [PMID: 16247852 PMCID: PMC2880920 DOI: 10.1080/15419060490951781] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Connexin43 (Cx43) is the most abundantly expressed gap junction protein. The C-terminal tail of Cx43 is important for regulation of gap junctions via phosphorylation of specific tyrosine and serine residues and through interactions with cellular proteins. The C-terminus of Cx43 has been shown to interact with the PDZ2 domain of the tight and adherens junction associated zona occludens 1 (ZO-1) protein. Analysis of the PDZ2 binding domain of Cx43 indicated that positions -3 and -2, and the final hydrophobic amino acid at the C-terminus, are critical for ZO-1 binding. In addition, the C-termini of connexins 40 and 45, but not Cx32, interacted with ZO-1. To evaluate the functional significance of the Cx43-ZO-1 interaction, Cx43 wild type (Cx43wt) and mutants lacking either the C-terminal hydrophobic isoleucine (Cx43deltaI382) or the last five amino acids (Cx43delta378-382), required for ZO-1 binding in vitro, were introduced into a Cx43-deficient MDCK cell line. In vitro binding studies and coimmunoprecipitation assays indicated that these Cx43 mutants failed to interact with ZO-1. Confocal and deconvolution microscopy revealed that a fraction of Cx43wt colocalized with ZO-1 at the plasma membrane. A similar colocalization pattern was observed for the Cx43deltaI382 and Cx43 delta378-382 mutants, which were translocated to the plasma membrane and formed functional gap junction channels. The wt and mutant Cx43 appeared to have similar turnover rates. However, the P2 and P3 phosphoisoforms of the Cx43 mutants were significantly reduced compared to Cx43wt. These studies indicated that the interaction of Cx43 with ZO-1 may contribute to the regulation of Cx43 phosphorylation.
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Affiliation(s)
- Chengshi Jin
- Molecular Carcinogenesis Section, University of Hawaii, Honolulu, Hawaii, USA
- Department of Cell and Molecular Biology, John Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA
| | - Kendra D. Martyn
- Molecular Carcinogenesis Section, University of Hawaii, Honolulu, Hawaii, USA
- Natural Products and Cancer Biology Program, Cancer Research Center, University of Hawaii, Honolulu, Hawaii, USA
| | - Wendy E. Kurata
- Molecular Carcinogenesis Section, University of Hawaii, Honolulu, Hawaii, USA
| | - Bonnie J. Warn-Cramer
- Natural Products and Cancer Biology Program, Cancer Research Center, University of Hawaii, Honolulu, Hawaii, USA
| | - Alan F. Lau
- Molecular Carcinogenesis Section, University of Hawaii, Honolulu, Hawaii, USA
- Department of Cell and Molecular Biology, John Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA
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42
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Kameritsch P, Khandoga N, Nagel W, Hundhausen C, Lidington D, Pohl U. Nitric oxide specifically reduces the permeability of Cx37-containing gap junctions to small molecules. J Cell Physiol 2005; 203:233-42. [PMID: 15481066 DOI: 10.1002/jcp.20218] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Gap junction intercellular communication (GJIC) plays a significant role in the vascular system. Regulation of GJIC is a dynamic process, with alterations in connexin (Cx) protein expression and post-translational modification as contributing mechanisms. We hypothesized that the endothelial autacoid nitric oxide (NO) would reduce dye coupling in human umbilical vein endothelial cells (HUVECs). In our subsequent experiments, we sought to isolate the specific Cx isoform(s) targeted by NO or NO-activated signaling pathways. Since HUVEC cells variably express three Cx (Cx37, Cx40, and Cx43), this latter aim required the use of transfected HeLa cells (HeLaCx37, HeLaCx43), which do not express Cx proteins in their wild type form. Dye coupling was measured by injecting fluorescent dye (e.g., Alexa Fluor 488) into a single cell and determining the number of stained adjacent cells. Application of the NO donor SNAP (2 microM, 20 min) reduced dye coupling in HUVEC by 30%. In HeLa cells, SNAP did not reduce dye transfer of cells expressing Cx43, but decreased the dye transfer from Cx37-expressing cells to Cx43-expressing cells by 76%. The effect of SNAP on dye coupling was not mediated via cGMP. In contrast to its effect on dye coupling, SNAP had no effect on electrical coupling, measured by a double patch clamp in whole cell mode. Our results demonstrate that NO inhibits the intercellular transfer of small molecules by a specific influence on Cx37, suggesting a potential role of NO in controlling certain aspects of vascular GJIC.
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Affiliation(s)
- Petra Kameritsch
- Institute of Physiology, Ludwig-Maximilians-University Munich, Schillerstr, Munich, Germany.
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43
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Vogalis F, Hegg CC, Lucero MT. Electrical coupling in sustentacular cells of the mouse olfactory epithelium. J Neurophysiol 2005; 94:1001-12. [PMID: 15788515 DOI: 10.1152/jn.01299.2004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Sustentacular cells (SCs) line the apical surface of the olfactory epithelium (OE) and provide trophic, metabolic, and mechanical support for olfactory receptor neurons. Morphological studies have suggested that SCs possess gap junctions, although physiological evidence for gap junctional communication in mammalian SCs is lacking. In the present study we investigated whether coupling exists between SCs situated in tissue slices of OE from neonatal (P0-P4) mice. Using whole cell and cell-attached patch recordings from SCs, we demonstrate that SCs are electrically coupled by junctional resistances on the order of 300 M(omega). Under whole cell recording conditions, Alexa 488 added to the pipette solution failed to reveal dye coupling between SCs. Electrical coupling was deduced from the biexponential decay of capacitive currents recorded from SCs and from the bell-shaped voltage dependency of a P2Y-receptor-activated current, both of which were abolished by 18beta-glycyrrhetinic acid (20-50 microM), a blocker of gap junctions. These data provide strong evidence for functional coupling between SCs, the physiological importance of which is discussed.
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Affiliation(s)
- Fivos Vogalis
- Department of Physical Exercise and Sport Science and Division of Neurophysiology, Salt Lake City, UT 84108-1297, USA
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44
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Contreras JE, Sánchez HA, Véliz LP, Bukauskas FF, Bennett MV, Sáez JC. Role of connexin-based gap junction channels and hemichannels in ischemia-induced cell death in nervous tissue. ACTA ACUST UNITED AC 2005; 47:290-303. [PMID: 15572178 PMCID: PMC3651737 DOI: 10.1016/j.brainresrev.2004.08.002] [Citation(s) in RCA: 182] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/27/2004] [Indexed: 01/24/2023]
Abstract
Gap junction channels and hemichannels formed of connexin subunits are found in most cell types in vertebrates. Gap junctions connect cells via channels not open to the extracellular space and permit the passage of ions and molecules of approximately 1 kDa. Single connexin hemichannels, which are connexin hexamers, are present in the surface membrane before docking with a hemichannel in an apposed membrane. Because of their high conductance and permeability in cell-cell channels, it had been thought that connexin hemichannels remained closed until docking to form a cell-cell channel. Now it is clear that at least some hemichannels can open to allow passage of molecules between the cytoplasm and extracellular space. Here we review evidence that gap junction channels may allow intercellular diffusion of necrotic or apoptotic signals, but may also allow diffusion of ions and substances from healthy to injured cells, thereby contributing to cell survival. Moreover, opening of gap junction hemichannels may exacerbate cell injury or mediate paracrine or autocrine signaling. In addition to the cell specific features of an ischemic insult, propagation of cell damage and death within affected tissues may be affected by expression and regulation of gap junction channels and hemichannels formed by connexins.
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Affiliation(s)
- Jorge E. Contreras
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Chile
| | - Helmuth A. Sánchez
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Chile
- Corresponding author. Tel.: +56 2 6862860; fax: +56 2 2225515. (H.A. Sánchez)
| | - Loreto P. Véliz
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Chile
| | | | - Michael V.L. Bennett
- Department of Neurosciences, Albert Einstein College of Medicine, Bronx, NY, USA
| | - Juan C. Sáez
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Chile
- Department of Neurosciences, Albert Einstein College of Medicine, Bronx, NY, USA
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45
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Hunter AW, Jourdan J, Gourdie RG. Fusion of GFP to the carboxyl terminus of connexin43 increases gap junction size in HeLa cells. ACTA ACUST UNITED AC 2004; 10:211-4. [PMID: 14681018 DOI: 10.1080/cac.10.4-6.211.214] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
The pattern of gap junctional coupling between cells is thought to be important for the proper function of many types of tissues. At present, little is known about the molecular mechanisms that control the size and distribution of gap junctions. We addressed this issue by expressing connexin43 (Cx43) constructs in HeLa cells, a connexin-deficient cell line. HeLa cells expressing exogenously introduced wild-type Cx43 formed small, punctate gap junctions. By contrast, cells expressing Cx43-GFP formed large, sheet-like gap junctions. These results suggest that the GFP tag, which is fused to the carboxyl terminus of Cx43, alters gap junction size by masking the carboxyl terminal amino acids of Cx43 that comprise a zonula occludins-1 (ZO-1) binding site. We are currently testing this hypothesis using deletion and dominant-negative constructs that directly target the interaction between Cx43 and ZO-1.
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Affiliation(s)
- Andrew W Hunter
- Department of Cell Biology and Anatomy, Medical University of South Carolina, SC 29425, USA.
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46
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Curti S, Pereda AE. Voltage-dependent enhancement of electrical coupling by a subthreshold sodium current. J Neurosci 2004; 24:3999-4010. [PMID: 15102915 PMCID: PMC6729423 DOI: 10.1523/jneurosci.0077-04.2004] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Voltage-dependent changes in electrical coupling are often attributed to a direct effect on the properties of gap junction channels. Identifiable auditory afferents terminate as mixed (electrical and chemical) synapses on the distal portion of the lateral dendrite of the goldfish Mauthner cells, a pair of large reticulospinal neurons involved in the organization of sensory-evoked escape responses. At these afferents, the amplitude of the coupling potential produced by the retrograde spread of signals from the postsynaptic Mauthner cell is dramatically enhanced by depolarization of the presynaptic terminal. We demonstrate here that this voltage-dependent enhancement of electrical coupling does not represent a property of the junctions themselves but the activation of a subthreshold sodium current present at presynaptic terminals that acts to amplify the synaptic response. We also provide evidence that this amplification operates under physiological conditions, enhancing synaptic communication from the Mauthner cells to the auditory afferents where electrical and geometrical properties of the coupled cells are unfavorable for retrograde transmission. Retrograde electrical communication at these afferents may play an important functional role by promoting cooperativity between afferents and enhancing transmitter release. Thus, the efficacy of an electrical synapse can be dynamically modulated in a voltage-dependent manner by properties of the nonjunctional membrane. Finally, asymmetric amplification of electrical coupling by intrinsic membrane properties, as at the synapses between auditory afferents and the Mauthner cell, may ensure efficient communication between neuronal processes of dissimilar size and shape, promoting neuronal synchronization.
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Affiliation(s)
- Sebastián Curti
- Department of Neuroscience, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York 10461, USA
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De Blasio BF, Iversen JG, Røttingen JA. Intercellular calcium signalling in cultured renal epithelia: a theoretical study of synchronization mode and pacemaker activity. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2004; 33:657-70. [PMID: 15565440 DOI: 10.1007/s00249-004-0409-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2003] [Revised: 02/24/2004] [Accepted: 04/05/2004] [Indexed: 11/27/2022]
Abstract
We investigate a two-dimensional lattice model representation of intercellular Ca2+ signalling in a population of epithelial cells coupled by gap junctions. The model is based on and compared with Ca2+ imaging data from globally bradykinin-stimulated MDCK-I (Madin-Darby canine kidney)-I cell layers. We study large-scale synchronization of relevance to our laboratory experiments. The system is found to express a wealth of dynamics, including quasiperiodic, chaotic and multiply-periodic behaviour for intermediate couplings. We take a particular interest in understanding the role of "pacemaker cells" in the synchronization process. It has been hypothesized that a few highly hormone-sensitive cells control the collective frequency of oscillation, which is close to the natural frequencies (without coupling) of these cells. The model behaviour is consistent with the conjectures of the pacemaker cell hypothesis near the critical coupling where the cells lock onto a single frequency. However, the simulations predict that the frequency in globally connected systems decreases with increasing coupling. It is found that a pacemaker is not defined by its natural frequency alone, but that other intrinsic or local factors must be considered. Inclusion of partly sensitized cells that do not oscillate autonomously in the cell layer increases the coupling necessary for global synchronization. For not excessively high coupling, these cells oscillate irregularly and with distinctive lower frequencies. In summary, the present study shows that the frequency of synchronized oscillations is not dictated by one or few fast-responding cells. The collective frequency is the result of a two-way communication between the phase-advanced pacemaker and its environment.
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48
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Asklund T, Appelskog IB, Ammerpohl O, Ekström TJ, Almqvist PM. Histone deacetylase inhibitor 4-phenylbutyrate modulates glial fibrillary acidic protein and connexin 43 expression, and enhances gap-junction communication, in human glioblastoma cells. Eur J Cancer 2004; 40:1073-81. [PMID: 15093585 DOI: 10.1016/j.ejca.2003.11.034] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2003] [Accepted: 11/17/2003] [Indexed: 11/21/2022]
Abstract
Human glioblastoma cell cultures were established and the expression of glial fibrillary acidic protein (GFAP) and the gap-junction protein connexin 43 (Cx43) was confirmed by Western blot. Following treatment with 4-phenylbutyrate (4-PB), increased concentrations of non-phosphorylated GFAP were seen, while phosphorylated isoforms remained intact. Immunocytochemical staining of glioblastoma cells revealed an intracellular redistribution of GFAP. In addition to cytoplasmic immunostaining, GFAP immunoreactivity was also associated with the nucleus and/or the nuclear membrane. Phosphorylated and non-phosphorylated Cx43 proteins were increased 2- to 5-fold following 4-PB treatment, and were redistributed to areas of the cell surface, participating in cell-to-cell contacts. In addition, functional gap-junction coupling was amplified, as indicated by increased fluorescent dye transfer, and elevated levels of Cx43 protein were detected in parallel with enhanced gap-junction communication. Induced cell differentiation, with improved functional coupling of tumour cells, may be of importance for therapeutic strategies involving intercellular transport of low molecular-weight compounds.
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Affiliation(s)
- T Asklund
- Department of Clinical Neuroscience, Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden
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49
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Kalvelyte A, Imbrasaite A, Bukauskiene A, Verselis VK, Bukauskas FF. Connexins and apoptotic transformation. Biochem Pharmacol 2003; 66:1661-72. [PMID: 14555247 PMCID: PMC3689318 DOI: 10.1016/s0006-2952(03)00540-9] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We examined the influence of connexin (Cx) expression on the development of apoptosis in HeLa parental cells (coupling deficient cell line) and HeLa cells expressing wild-type Cx43 and Cxs fused with enhanced green fluorescent protein (EGFP). EGFP was attached to the C-terminus of Cx32 and Cx43, Cx32-EGFP and Cx43-EGFP, respectively, and to the N-terminus of Cx32, EGFP-Cx32. All fusion proteins assembled into junctional plaques (JPs) at areas of cell-cell contact, but only the C-terminal fusion proteins formed functional gap junction (GJ) channels as well as hemichannels. In each cell line, apoptosis was induced by treatment with various agents including anisomycin, camptothecin, cis-platinum, colchicine, cycloheximide, etoposide, staurosporin and taxol. Using fluorescence microscopy, time-lapse imaging and dual whole-cell voltage clamp techniques, we correlated the changes in functional properties of GJ channels and Cx distribution with the progression of apoptosis based on cells' labeling with acridine orange and ethidium bromide (EB). The early phase of apoptosis (a viable apoptotic (VA) state) was characterized by shrinkage of the cells and by increased internalization of JPs accompanied by decreased cell-cell coupling. The apoptotic reagents had no direct effect on electrical cell-cell coupling. Transformation from a VA to a nonviable apoptotic (NVA) state was faster in HeLa cells expressing Cx43 or Cx43-EGFP than in HeLa parental cells. The potent GJ uncoupler, octanol, slowed the transition of HelaCx43-EGFP cells into a NVA state. In the absence of apoptotic reagents, the rate of EB uptake was higher in HeLaCx43-EGFP than in HeLa parental cells consistent with the presence of open Cx43-EGFP hemichannels. However, in both cell lines the rate of EB uptake decreased proportionally during the development of apoptosis suggesting that membrane permeability ascribed to Cx hemichannels is reduced. Cells expressing Cx32-EGFP and EGFP-Cx32 demonstrate the same apoptotic patterns as HeLaCx43-EGFP and HeLa parental cells, respectively. Intracellular levels of ATP in HeLaCx43-EGFP cells were substantially lower than in HeLa parental cells, and ATP added to the medium abolished the accelerated transition from a VA to a NVA state in HeLaCx43-EGFP cells. In summary, Cx32 or Cx43 accelerates transformation of cells into a NVA state or secondary necrosis and this depends on the ability of Cxs to form functional GJ channels and hemichannels.
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Affiliation(s)
- Audrone Kalvelyte
- Laboratory of Developmental Biology, Institute of Biochemistry, 12
Mokslininku Str., LT-2600 Vilnius, Lithuania
| | - Ausra Imbrasaite
- Laboratory of Developmental Biology, Institute of Biochemistry, 12
Mokslininku Str., LT-2600 Vilnius, Lithuania
| | - Angele Bukauskiene
- Department of Neuroscience, Albert Einstein College of Medicine, 1300
Morris Park Avenue, New York, NY 10461, USA
| | - Vytas K. Verselis
- Department of Neuroscience, Albert Einstein College of Medicine, 1300
Morris Park Avenue, New York, NY 10461, USA
| | - Feliksas F. Bukauskas
- Department of Neuroscience, Albert Einstein College of Medicine, 1300
Morris Park Avenue, New York, NY 10461, USA
- Corresponding author. Tel.: +1-718-430-4130; fax:
+1-718-430-8944. (F.F. Bukauskas)
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Saez JC, Berthoud VM, Branes MC, Martinez AD, Beyer EC. Plasma membrane channels formed by connexins: their regulation and functions. Physiol Rev 2003; 83:1359-400. [PMID: 14506308 DOI: 10.1152/physrev.00007.2003] [Citation(s) in RCA: 867] [Impact Index Per Article: 41.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Members of the connexin gene family are integral membrane proteins that form hexamers called connexons. Most cells express two or more connexins. Open connexons found at the nonjunctional plasma membrane connect the cell interior with the extracellular milieu. They have been implicated in physiological functions including paracrine intercellular signaling and in induction of cell death under pathological conditions. Gap junction channels are formed by docking of two connexons and are found at cell-cell appositions. Gap junction channels are responsible for direct intercellular transfer of ions and small molecules including propagation of inositol trisphosphate-dependent calcium waves. They are involved in coordinating the electrical and metabolic responses of heterogeneous cells. New approaches have expanded our knowledge of channel structure and connexin biochemistry (e.g., protein trafficking/assembly, phosphorylation, and interactions with other connexins or other proteins). The physiological role of gap junctions in several tissues has been elucidated by the discovery of mutant connexins associated with genetic diseases and by the generation of mice with targeted ablation of specific connexin genes. The observed phenotypes range from specific tissue dysfunction to embryonic lethality.
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Affiliation(s)
- Juan C Saez
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile.
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