101
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Pogoda K, Kameritsch P, Retamal MA, Vega JL. Regulation of gap junction channels and hemichannels by phosphorylation and redox changes: a revision. BMC Cell Biol 2016; 17 Suppl 1:11. [PMID: 27229925 PMCID: PMC4896245 DOI: 10.1186/s12860-016-0099-3] [Citation(s) in RCA: 108] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Post-translational modifications of connexins play an important role in the regulation of gap junction and hemichannel permeability. The prerequisite for the formation of functional gap junction channels is the assembly of connexin proteins into hemichannels and their insertion into the membrane. Hemichannels can affect cellular processes by enabling the passage of signaling molecules between the intracellular and extracellular space. For the intercellular communication hemichannels from one cell have to dock to its counterparts on the opposing membrane of an adjacent cell to allow the transmission of signals via gap junctions from one cell to the other. The controlled opening of hemichannels and gating properties of complete gap junctions can be regulated via post-translational modifications of connexins. Not only channel gating, but also connexin trafficking and assembly into hemichannels can be affected by post-translational changes. Recent investigations have shown that connexins can be modified by phosphorylation/dephosphorylation, redox-related changes including effects of nitric oxide (NO), hydrogen sulfide (H2S) or carbon monoxide (CO), acetylation, methylation or ubiquitination. Most of the connexin isoforms are known to be phosphorylated, e.g. Cx43, one of the most studied connexin at all, has 21 reported phosphorylation sites. In this review, we provide an overview about the current knowledge and relevant research of responsible kinases, connexin phosphorylation sites and reported effects on gap junction and hemichannel regulation. Regarding the effects of oxidants we discuss the role of NO in different cell types and tissues and recent studies about modifications of connexins by CO and H2S.
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Affiliation(s)
- Kristin Pogoda
- Walter Brendel Centre of Experimental Medicine, Ludwig-Maximilians-Universität München and Munich University Hospital, München, Germany. .,DZHK (German Centre for Cardiovascular Research), partner site Munich Heart Alliance, München, Germany.
| | - Petra Kameritsch
- Walter Brendel Centre of Experimental Medicine, Ludwig-Maximilians-Universität München and Munich University Hospital, München, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Munich Heart Alliance, München, Germany
| | - Mauricio A Retamal
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo, Santiago, Chile
| | - José L Vega
- Experimental Physiology Laboratory (EPhyL), Antofagasta Institute, Universidad de Antofagasta, Antofagasta, Chile
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102
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Cellular uptake of lead in the blood-cerebrospinal fluid barrier: Novel roles of Connexin 43 hemichannel and its down-regulations via Erk phosphorylation. Toxicol Appl Pharmacol 2016; 297:1-11. [DOI: 10.1016/j.taap.2016.02.021] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Revised: 02/24/2016] [Accepted: 02/25/2016] [Indexed: 11/23/2022]
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103
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Connexin 43, breast cancer tumor suppressor: Missed connections? Cancer Lett 2016; 374:117-126. [DOI: 10.1016/j.canlet.2016.02.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Revised: 01/28/2016] [Accepted: 02/03/2016] [Indexed: 12/21/2022]
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104
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Retamal MA, García IE, Pinto BI, Pupo A, Báez D, Stehberg J, Del Rio R, González C. Extracellular Cysteine in Connexins: Role as Redox Sensors. Front Physiol 2016; 7:1. [PMID: 26858649 PMCID: PMC4729916 DOI: 10.3389/fphys.2016.00001] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Accepted: 01/05/2016] [Indexed: 12/11/2022] Open
Abstract
Connexin-based channels comprise hemichannels and gap junction channels. The opening of hemichannels allow for the flux of ions and molecules from the extracellular space into the cell and vice versa. Similarly, the opening of gap junction channels permits the diffusional exchange of ions and molecules between the cytoplasm and contacting cells. The controlled opening of hemichannels has been associated with several physiological cellular processes; thereby unregulated hemichannel activity may induce loss of cellular homeostasis and cell death. Hemichannel activity can be regulated through several mechanisms, such as phosphorylation, divalent cations and changes in membrane potential. Additionally, it was recently postulated that redox molecules could modify hemichannels properties in vitro. However, the molecular mechanism by which redox molecules interact with hemichannels is poorly understood. In this work, we discuss the current knowledge on connexin redox regulation and we propose the hypothesis that extracellular cysteines could be important for sensing changes in redox potential. Future studies on this topic will offer new insight into hemichannel function, thereby expanding the understanding of the contribution of hemichannels to disease progression.
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Affiliation(s)
- Mauricio A Retamal
- Facultad de Medicina, Centro de Fisiología Celular e Integrativa, Clínica Alemana Universidad del Desarrollo Santiago, Chile
| | - Isaac E García
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencias, Universidad de Valparaíso Valparaíso, Chile
| | - Bernardo I Pinto
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencias, Universidad de Valparaíso Valparaíso, Chile
| | - Amaury Pupo
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencias, Universidad de Valparaíso Valparaíso, Chile
| | - David Báez
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencias, Universidad de Valparaíso Valparaíso, Chile
| | - Jimmy Stehberg
- Laboratorio de Neurobiología, Centro de Investigaciones Biomédicas, Universidad Andres Bello Santiago, Chile
| | - Rodrigo Del Rio
- Laboratory of Cardiorespiratory Control, Center for Biomedical Research, Universidad Autónoma de ChileSantiago, Chile; Dirección de Investigación, Universidad Científica del SurLima, Perú
| | - Carlos González
- Facultad de Ciencias, Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto de Neurociencias, Universidad de Valparaíso Valparaíso, Chile
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105
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Del Rio R, Quintanilla RA, Orellana JA, Retamal MA. Neuron-Glia Crosstalk in the Autonomic Nervous System and Its Possible Role in the Progression of Metabolic Syndrome: A New Hypothesis. Front Physiol 2015; 6:350. [PMID: 26648871 PMCID: PMC4664731 DOI: 10.3389/fphys.2015.00350] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Accepted: 11/09/2015] [Indexed: 01/26/2023] Open
Abstract
Metabolic syndrome (MS) is characterized by the following physiological alterations: increase in abdominal fat, insulin resistance, high concentration of triglycerides, low levels of HDL, high blood pressure, and a generalized inflammatory state. One of the pathophysiological hallmarks of this syndrome is the presence of neurohumoral activation, which involve autonomic imbalance associated to hyperactivation of the sympathetic nervous system. Indeed, enhanced sympathetic drive has been linked to the development of endothelial dysfunction, hypertension, stroke, myocardial infarct, and obstructive sleep apnea. Glial cells, the most abundant cells in the central nervous system, control synaptic transmission, and regulate neuronal function by releasing bioactive molecules called gliotransmitters. Recently, a new family of plasma membrane channels called hemichannels has been described to allow the release of gliotransmitters and modulate neuronal firing rate. Moreover, a growing amount of evidence indicates that uncontrolled hemichannel opening could impair glial cell functions, affecting synaptic transmission and neuronal survival. Given that glial cell functions are disturbed in various metabolic diseases, we hypothesize that progression of MS may relies on hemichannel-dependent impairment of glial-to-neuron communication by a mechanism related to dysfunction of inflammatory response and mitochondrial metabolism of glial cells. In this manuscript, we discuss how glial cells may contribute to the enhanced sympathetic drive observed in MS, and shed light about the possible role of hemichannels in this process.
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Affiliation(s)
- Rodrigo Del Rio
- Centro de Investigación Biomédica, Universidad Autónoma de Chile Santiago, Chile ; Dirección de Investigación, Universidad Científica del Sur Lima, Perú
| | | | - Juan A Orellana
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile Santiago, Chile
| | - Mauricio A Retamal
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina. Clínica Alemana Universidad del Desarrollo Santiago, Chile
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106
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Talaverón R, Fernández P, Escamilla R, Pastor AM, Matarredona ER, Sáez JC. Neural progenitor cells isolated from the subventricular zone present hemichannel activity and form functional gap junctions with glial cells. Front Cell Neurosci 2015; 9:411. [PMID: 26528139 PMCID: PMC4602088 DOI: 10.3389/fncel.2015.00411] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2015] [Accepted: 09/25/2015] [Indexed: 01/19/2023] Open
Abstract
The postnatal subventricular zone (SVZ) lining the walls of the lateral ventricles contains neural progenitor cells (NPCs) that generate new olfactory bulb interneurons. Communication via gap junctions between cells in the SVZ is involved in NPC proliferation and in neuroblast migration towards the olfactory bulb. SVZ NPCs can be expanded in vitro in the form of neurospheres that can be used for transplantation purposes after brain injury. We have previously reported that neurosphere-derived NPCs form heterocellular gap junctions with host glial cells when they are implanted after mechanical injury. To analyze functionality of NPC-glial cell gap junctions we performed dye coupling experiments in co-cultures of SVZ NPCs with astrocytes or microglia. Neurosphere-derived cells expressed mRNA for at least the hemichannel/gap junction channel proteins connexin 26 (Cx26), Cx43, Cx45 and pannexin 1 (Panx1). Dye coupling experiments revealed that gap junctional communication occurred among neurosphere cells (incidence of coupling: 100%). Moreover, hemichannel activity was also detected in neurosphere cells as evaluated in time-lapse measurements of ethidium bromide uptake. Heterocellular coupling between NPCs and glial cells was evidenced in co-cultures of neurospheres with astrocytes (incidence of coupling: 91.0 ± 4.7%) or with microglia (incidence of coupling: 71.9 ± 6.7%). Dye coupling in neurospheres and in co-cultures was inhibited by octanol, a gap junction blocker. Altogether, these results suggest the existence of functional hemichannels and gap junction channels in postnatal SVZ neurospheres. In addition, they demonstrate that SVZ-derived NPCs can establish functional gap junctions with astrocytes or microglia. Therefore, cell-cell communication via gap junctions and hemichannels with host glial cells might subserve a role in the functional integration of NPCs after implantation in the damaged brain.
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Affiliation(s)
- Rocío Talaverón
- Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla Sevilla, Spain
| | - Paola Fernández
- Departamento de Fisiología, Pontificia Universidad Católica de Chile, Santiago de Chile, Chile and Instituto Milenio, Centro Interdisciplinario de Neurociencias de Valparaíso Chile
| | - Rosalba Escamilla
- Departamento de Fisiología, Pontificia Universidad Católica de Chile, Santiago de Chile, Chile and Instituto Milenio, Centro Interdisciplinario de Neurociencias de Valparaíso Chile
| | - Angel M Pastor
- Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla Sevilla, Spain
| | | | - Juan C Sáez
- Departamento de Fisiología, Pontificia Universidad Católica de Chile, Santiago de Chile, Chile and Instituto Milenio, Centro Interdisciplinario de Neurociencias de Valparaíso Chile
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107
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Brown IA, McClain JL, Watson RE, Patel BA, Gulbransen BD. Enteric glia mediate neuron death in colitis through purinergic pathways that require connexin-43 and nitric oxide. Cell Mol Gastroenterol Hepatol 2015; 2:77-91. [PMID: 26771001 PMCID: PMC4707972 DOI: 10.1016/j.jcmgh.2015.08.007] [Citation(s) in RCA: 117] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
BACKGROUND AND AIMS The concept of enteric glia as regulators of intestinal homeostasis is slowly gaining acceptance as a central concept in neurogastroenterology. Yet how glia contribute to intestinal disease is still poorly understood. Purines generated during inflammation drive enteric neuron death by activating neuronal P2X7 purine receptors (P2X7R), triggering ATP release via neuronal pannexin-1 channels that subsequently recruits intracellular calcium ([Ca2+]i) responses in the surrounding enteric glia. We tested the hypothesis that the activation of enteric glia contributes to neuron death during inflammation. METHODS We studied neuroinflammation in vivo using the 2,4-dinitrobenzenesulfonic acid model of colitis and in situ using whole-mount preparations of human and mouse intestine. Transgenic mice with a targeted deletion of glial connexin-43 (Cx43) [GFAP∷CreERT2+/-/Cx43f/f ] were used to specifically disrupt glial signaling pathways. Mice deficient in inducible nitric oxide (NO) synthase (iNOS-/-) were used to study NO production. Protein expression and oxidative stress were measured using immunohistochemistry and in situ Ca2+ and NO imaging were used to monitor glial [Ca2+]i and [NO]i. RESULTS Purinergic activation of enteric glia drove [Ca2+]i responses and enteric neuron death through a Cx43-dependent mechanism. Neurotoxic Cx43 activity, driven by NO production from glial iNOS, was required for neuron death. Glial Cx43 opening liberated ATP and Cx43-dependent ATP release was potentiated by NO. CONCLUSIONS Our results show that the activation of glial cells in the context of neuroinflammation kills enteric neurons. Mediators of inflammation that include ATP and NO activate neurotoxic pathways that converge on glial Cx43 hemichannels. The glial response to inflammatory mediators might contribute to the development of motility disorders.
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Affiliation(s)
- Isola A.M. Brown
- Department of Physiology, Michigan State University, East Lansing, Michigan
- Pharmacology and Toxicology Program, Michigan State University, East Lansing, Michigan
| | | | - Ralph E. Watson
- Department of Medicine, Michigan State University, East Lansing, Michigan
| | - Bhavik A. Patel
- School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, United Kingdom
| | - Brian D. Gulbransen
- Department of Physiology, Michigan State University, East Lansing, Michigan
- Neuroscience Program, Michigan State University, East Lansing, Michigan
- Correspondence Address correspondence to: Brian D. Gulbransen, PhD, Department of Physiology, Michigan State University, 567 Wilson Road, East Lansing, Michigan 48824. fax: (517) 355-5125.Department of PhysiologyMichigan State University567 Wilson RoadEast LansingMichigan 48824
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108
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Intracellular Cleavage of the Cx43 C-Terminal Domain by Matrix-Metalloproteases: A Novel Contributor to Inflammation? Mediators Inflamm 2015; 2015:257471. [PMID: 26424967 PMCID: PMC4573893 DOI: 10.1155/2015/257471] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2015] [Accepted: 08/13/2015] [Indexed: 01/11/2023] Open
Abstract
The coordination of tissue function is mediated by gap junctions (GJs) that enable direct cell-cell transfer of metabolic and electric signals. GJs are formed by connexin (Cx) proteins of which Cx43 is most widespread in the human body. Beyond its role in direct intercellular communication, Cx43 also forms nonjunctional hemichannels (HCs) in the plasma membrane that mediate the release of paracrine signaling molecules in the extracellular environment. Both HC and GJ channel function are regulated by protein-protein interactions and posttranslational modifications that predominantly take place in the C-terminal domain of Cx43. Matrix metalloproteases (MMPs) are a major group of zinc-dependent proteases, known to regulate not only extracellular matrix remodeling, but also processing of intracellular proteins. Together with Cx43 channels, both GJs and HCs, MMPs contribute to acute inflammation and a small number of studies reports on an MMP-Cx43 link. Here, we build further on these reports and present a novel hypothesis that describes proteolytic cleavage of the Cx43 C-terminal domain by MMPs and explores possibilities of how such cleavage events may affect Cx43 channel function. Finally, we set out how aberrant channel function resulting from cleavage can contribute to the acute inflammatory response during tissue injury.
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109
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Retamal MA, Reyes EP, García IE, Pinto B, Martínez AD, González C. Diseases associated with leaky hemichannels. Front Cell Neurosci 2015; 9:267. [PMID: 26283912 PMCID: PMC4515567 DOI: 10.3389/fncel.2015.00267] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Accepted: 06/29/2015] [Indexed: 01/10/2023] Open
Abstract
Hemichannels (HCs) and gap junction channels (GJCs) formed by protein subunits called connexins (Cxs) are major pathways for intercellular communication. While HCs connect the intracellular compartment with the extracellular milieu, GJCs allow the interchange of molecules between cytoplasm of two contacting cells. Under physiological conditions, HCs are mostly closed, but they can open under certain stimuli allowing the release of autocrine and paracrine molecules. Moreover, some pathological conditions, like ischemia or other inflammation conditions, significantly increase HCs activity. In addition, some mutations in Cx genes associated with human diseases, such as deafness or cataracts, lead to the formation of more active HCs or “leaky HCs.” In this article we will revise cellular and molecular mechanisms underlying the appearance of leaky HCs, and the consequences of their expression in different cellular systems and animal models, in seeking a common pattern or pathological mechanism of disease.
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Affiliation(s)
- Mauricio A Retamal
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile
| | - Edison P Reyes
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile ; Centro de Investigación Biomédica, Universidad Autónoma de Chile Santiago, Chile
| | - Isaac E García
- Centro Interdisciplinario de Neurociencia de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso Valparaíso, Chile
| | - Bernardo Pinto
- Centro Interdisciplinario de Neurociencia de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso Valparaíso, Chile
| | - Agustín D Martínez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso Valparaíso, Chile
| | - Carlos González
- Centro Interdisciplinario de Neurociencia de Valparaíso, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso Valparaíso, Chile
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110
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Meigh L, Cook D, Zhang J, Dale N. Rational design of new NO and redox sensitivity into connexin26 hemichannels. Open Biol 2015; 5:140208. [PMID: 25673329 PMCID: PMC4345282 DOI: 10.1098/rsob.140208] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
CO2 directly opens hemichannels of connexin26 (Cx26) by carbamylating K125, thereby allowing salt bridge formation with R104 of the neighbouring subunit in the connexin hexamer. The formation of the inter-subunit carbamate bridges within the hexameric hemichannel traps it in the open state. Here, we use insights derived from this model to test whether the range of agonists capable of opening Cx26 can be extended by promoting the formation of analogous inter-subunit bridges via different mechanisms. The mutation K125C gives potential for nitrosylation on Cys125 and formation of an SNO bridge to R104 of the neighbouring subunit. Unlike wild-type Cx26 hemichannels, which are insensitive to NO and NO2−, hemichannels comprising Cx26K125C can be opened by NO2− and NO donors. However, NO2− was unable to modulate the doubly mutated (K125C, R104A) hemichannels, indicating that an inter-subunit bridge between C125 and R104 is required for the opening action of NO2−. In a further test, we introduced two mutations into Cx26, K125C and R104C, to allow disulfide bridge formation across the inter-subunit boundary. These doubly mutated hemichannels open in response to changes in intracellular redox potential.
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Affiliation(s)
- Louise Meigh
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
| | - Daniel Cook
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
| | - Jie Zhang
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
| | - Nicholas Dale
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
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111
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Avendaño BC, Montero TD, Chávez CE, von Bernhardi R, Orellana JA. Prenatal exposure to inflammatory conditions increases Cx43 and Panx1 unopposed channel opening and activation of astrocytes in the offspring effect on neuronal survival. Glia 2015; 63:2058-2072. [PMID: 26096155 DOI: 10.1002/glia.22877] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Accepted: 06/04/2015] [Indexed: 12/17/2022]
Abstract
Several epidemiological studies indicate that children born from mothers exposed to infections during gestation, have an increased risk to develop neurological disorders, including schizophrenia, autism and cerebral palsy. Given that it is unknown if astrocytes and their crosstalk with neurons participate in the above mentioned brain pathologies, the aim of this work was to address if astroglial paracrine signaling mediated by Cx43 and Panx1 unopposed channels could be affected in the offspring of LPS-exposed dams during pregnancy. Ethidium uptake experiments showed that prenatal LPS-exposure increases the activity of astroglial Cx43 and Panx1 unopposed channels in the offspring. Induction of unopposed channel opening by prenatal LPS exposure depended on intracellular Ca2+ levels, cytokine production and activation of p38 MAP kinase/iNOS pathway. Biochemical assays and Fura-2AM/DAF-FM time-lapse fluorescence images revealed that astrocytes from the offspring of LPS-exposed dams displayed increased spontaneous Ca2+ dynamics and NO production, whereas iNOS levels and release of IL-1β/TNF-α were also increased. Interestingly, we found that prenatal LPS exposure enhanced the release of ATP through astroglial Cx43 and Panx1 unopposed channels in the offspring, resulting in an increased neuronal death mediated by the activation of neuronal P2X7 receptors and Panx1 channels. Altogether, this evidence suggests that astroglial Cx43 and Panx1 unopposed channel opening induced by prenatal LPS exposure depended on the inflammatory activation profile and the activation pattern of astrocytes. The understanding of the mechanism underlying astrocyte-neuron crosstalk could contribute to the development of new strategies to ameliorate the brain abnormalities induced in the offspring by prenatal inflammation. GLIA 2015;63:2058-2072.
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Affiliation(s)
- Beatriz C Avendaño
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Trinidad D Montero
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Carolina E Chávez
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Rommy von Bernhardi
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Juan A Orellana
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
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112
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Retamal MA, León-Paravic CG, Ezquer M, Ezquer F, Rio RD, Pupo A, Martínez AD, González C. Carbon monoxide: A new player in the redox regulation of connexin hemichannels. IUBMB Life 2015; 67:428-37. [DOI: 10.1002/iub.1388] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 05/05/2015] [Indexed: 01/23/2023]
Affiliation(s)
- Mauricio A. Retamal
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina; Clínica Alemana Universidad del Desarrollo; Santiago Chile
| | - Carmen G. León-Paravic
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina; Clínica Alemana Universidad del Desarrollo; Santiago Chile
| | - Marcelo Ezquer
- Centro de Medicina Regenerativa, Facultad de Medicina; Clínica Alemana Universidad del Desarrollo; Santiago Chile
| | - Fernando Ezquer
- Centro de Medicina Regenerativa, Facultad de Medicina; Clínica Alemana Universidad del Desarrollo; Santiago Chile
| | - Rodrigo Del Rio
- Centro de Investigación Biomédica; Universidad Autónoma de Chile; Santiago Chile
| | - Amaury Pupo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias; Instituto de Neurociencia; Universidad de Valparaíso; Valparaíso Chile
| | - Agustín D. Martínez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias; Instituto de Neurociencia; Universidad de Valparaíso; Valparaíso Chile
| | - Carlos González
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias; Instituto de Neurociencia; Universidad de Valparaíso; Valparaíso Chile
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113
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Fontes JD, Ramsey J, Polk JM, Koop A, Denisova JV, Belousov AB. Death of Neurons following Injury Requires Conductive Neuronal Gap Junction Channels but Not a Specific Connexin. PLoS One 2015; 10:e0125395. [PMID: 26017008 PMCID: PMC4446213 DOI: 10.1371/journal.pone.0125395] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Accepted: 03/24/2015] [Indexed: 01/01/2023] Open
Abstract
Pharmacological blockade or genetic knockout of neuronal connexin 36 (Cx36)-containing gap junctions reduces neuronal death caused by ischemia, traumatic brain injury and NMDA receptor (NMDAR)-mediated excitotoxicity. However, whether Cx36 gap junctions contribute to neuronal death via channel-dependent or channel-independent mechanism remains an open question. To address this, we manipulated connexin protein expression via lentiviral transduction of mouse neuronal cortical cultures and analyzed neuronal death twenty-four hours following administration of NMDA (a model of NMDAR excitotoxicity) or oxygen-glucose deprivation (a model of ischemic injury). In cultures prepared from wild-type mice, over-expression and knockdown of Cx36-containing gap junctions augmented and prevented, respectively, neuronal death from NMDAR-mediated excitotoxicity and ischemia. In cultures obtained form from Cx36 knockout mice, re-expression of functional gap junction channels, containing either neuronal Cx36 or non-neuronal Cx43 or Cx31, resulted in increased neuronal death following insult. In contrast, the expression of communication-deficient gap junctions (containing mutated connexins) did not have this effect. Finally, the absence of ethidium bromide uptake in non-transduced wild-type neurons two hours following NMDAR excitotoxicity or ischemia suggested the absence of active endogenous hemichannels in those neurons. Taken together, these results suggest a role for neuronal gap junctions in cell death via a connexin type-independent mechanism that likely relies on channel activities of gap junctional complexes among neurons. A possible contribution of gap junction channel-permeable death signals in neuronal death is discussed.
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Affiliation(s)
- Joseph D. Fontes
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas, United States of America
| | - Jon Ramsey
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas, United States of America
| | - Jeremy M Polk
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas, United States of America
| | - Andre Koop
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas, United States of America
| | - Janna V. Denisova
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas, United States of America
| | - Andrei B. Belousov
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas, United States of America
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Ye XY, Jiang QH, Hong T, Zhang ZY, Yang RJ, Huang JQ, Hu K, Peng YP. Altered expression of connexin43 and phosphorylation connexin43 in glioma tumors. INTERNATIONAL JOURNAL OF CLINICAL AND EXPERIMENTAL PATHOLOGY 2015; 8:4296-4306. [PMID: 26191122 PMCID: PMC4502994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 01/24/2015] [Accepted: 04/18/2015] [Indexed: 06/04/2023]
Abstract
In this study, we aim to evaluate the connexin (Cx43) and phosphorylation Cx43 (p-Cx43) expression of human glioma tumors and correlate their expression with degrees of malignancy and proliferation, apoptosis, and migration activity of tumors. Cx43 and p-Cx43 expression were examined by Western blot analysis and immunohistochemical staining. The U251 cell viability was measured by MTT analysis. The apoptosis and migration were also evaluated by flow cytometric analysis and fluoroblok transwell chambers, respectively. We found that the Cx43 expression were significantly downregulated in in malignant glioma (WHO grade III and IV), compared to the malignant glioma (WHO grade I and II) and the p-Cx43 expression levels of malignant glioma (WHO grade III and IV) were significantly increased (P<0.05), compared to the malignant glioma (WHO grade I and II) at immunohistochemical analysis. After treatment of cells with a specific inhibitor of PKC, MAPK, and PTK inhibitors, the cell viability and migration were significantly decreased, while the apoptosis was slightly induced. In conclusion, the Cx43 expression level is inversely correlated with the tumor grade and proliferation and migration activity of tumor. Higher p-Cx43 expression level in high tumor grade suggests that a complex mechanism is involved in the suppression of tumor growth by connexins.
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Affiliation(s)
- Xin-Yun Ye
- Department of Neurosurgery, Nanfang Hospital, Southern Medical UniversityGuangzhou 510515, Guangdong, China
- Department of Neurosurgery, Ganzhou People’s HospitalGanzhou 341000, Jiangxi, China
| | - Qiu-Hua Jiang
- Department of Neurosurgery, Ganzhou People’s HospitalGanzhou 341000, Jiangxi, China
| | - Tao Hong
- Department of Neurosurgery, The First Affiliated Hospital of Nanchang UniversityNanchang 330006, Jiangxi, China
| | - Zhen-Yu Zhang
- Department of Neurosurgery, Ganzhou People’s HospitalGanzhou 341000, Jiangxi, China
| | - Rui-Jin Yang
- Department of Neurosurgery, Ganzhou People’s HospitalGanzhou 341000, Jiangxi, China
| | - Jin-Qing Huang
- Department of Neurosurgery, Ganzhou People’s HospitalGanzhou 341000, Jiangxi, China
| | - Kun Hu
- Department of Neurosurgery, Ganzhou People’s HospitalGanzhou 341000, Jiangxi, China
| | - Yu-Ping Peng
- Department of Neurosurgery, Nanfang Hospital, Southern Medical UniversityGuangzhou 510515, Guangdong, China
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Le Gal L, Alonso F, Mazzolai L, Meda P, Haefliger JA. Interplay between connexin40 and nitric oxide signaling during hypertension. Hypertension 2015; 65:910-5. [PMID: 25712722 DOI: 10.1161/hypertensionaha.114.04775] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Connexins (Cxs) and endothelial nitric oxide synthase (eNOS) contribute to the adaptation of endothelial and smooth muscle cells to hemodynamic changes. To decipher the in vivo interplay between these proteins, we studied Cx40-null mice, a model of renin-dependent hypertension which displays an altered endothelium-dependent relaxation of the aorta because of reduced eNOS levels. These mice, which were either untreated or subjected to the 1-kidney, 1-clip (1K1C) procedure, a model of volume-dependent hypertension, were compared with control mice submitted to either the 1K1C or the 2-kidney, 1-clip (2K1C) procedure, a model of renin-dependent hypertension. All operated mice became hypertensive and featured hypertrophy and altered Cx expression of the aorta. The combination of volume- and renin-dependent hypertension in Cx40-/- 1K1C mice raised blood pressure and cardiac weight index. Under these conditions, all aortas showed increased levels of Cx40 in endothelial cells and of both Cx37 and Cx45 in smooth muscle cells. In the wild-type 1K1C mice, the interactions between Cx40 and Cx37 with eNOS were enhanced, resulting in increased NO release. The Cx40-eNOS interaction could not be observed in mice lacking Cx40, which also featured decreased levels of eNOS. In these animals, the volume overload caused by the 1K1C procedure resulted in increased phosphorylation of eNOS and in a higher NO release. The findings provide evidence that Cx40 and Cx37 play an in vivo role in the regulation of eNOS.
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Affiliation(s)
- Loïc Le Gal
- From the Departments of Medicine (L.L.G., F.A., J.-A.H.) and Angiology (L.M.), Centre Hospitalier Universitaire Vaudois, University of Lausanne, Lausanne, Switzerland; and Department of Cell Physiology and Metabolism, University of Geneva, Medical Center, Geneva, Switzerland (P.M.)
| | - Florian Alonso
- From the Departments of Medicine (L.L.G., F.A., J.-A.H.) and Angiology (L.M.), Centre Hospitalier Universitaire Vaudois, University of Lausanne, Lausanne, Switzerland; and Department of Cell Physiology and Metabolism, University of Geneva, Medical Center, Geneva, Switzerland (P.M.)
| | - Lucia Mazzolai
- From the Departments of Medicine (L.L.G., F.A., J.-A.H.) and Angiology (L.M.), Centre Hospitalier Universitaire Vaudois, University of Lausanne, Lausanne, Switzerland; and Department of Cell Physiology and Metabolism, University of Geneva, Medical Center, Geneva, Switzerland (P.M.)
| | - Paolo Meda
- From the Departments of Medicine (L.L.G., F.A., J.-A.H.) and Angiology (L.M.), Centre Hospitalier Universitaire Vaudois, University of Lausanne, Lausanne, Switzerland; and Department of Cell Physiology and Metabolism, University of Geneva, Medical Center, Geneva, Switzerland (P.M.)
| | - Jacques-Antoine Haefliger
- From the Departments of Medicine (L.L.G., F.A., J.-A.H.) and Angiology (L.M.), Centre Hospitalier Universitaire Vaudois, University of Lausanne, Lausanne, Switzerland; and Department of Cell Physiology and Metabolism, University of Geneva, Medical Center, Geneva, Switzerland (P.M.).
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Salas D, Puebla C, Lampe PD, Lavandero S, Sáez JC. Role of Akt and Ca2+ on cell permeabilization via connexin43 hemichannels induced by metabolic inhibition. Biochim Biophys Acta Mol Basis Dis 2015; 1852:1268-77. [PMID: 25779082 DOI: 10.1016/j.bbadis.2015.03.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 02/25/2015] [Accepted: 03/06/2015] [Indexed: 10/23/2022]
Abstract
Connexin hemichannels are regulated under physiological and pathological conditions. Metabolic inhibition, a model of ischemia, promotes surface hemichannel activation associated, in part, with increased surface hemichannel levels, but little is known about its underlying mechanism. Here, we investigated the role of Akt on the connexin43 hemichannel's response induced by metabolic inhibition. In HeLa cells stably transfected with rat connexin43 fused to EGFP (HeLa43 cells), metabolic inhibition induced a transient Akt activation necessary to increase the amount of surface connexin43. The increase in levels of surface connexin43 was also found to depend on an intracellular Ca2+ signal increase that was partially mediated by Akt activation. However, the metabolic inhibition-induced Akt activation was not significantly affected by intracellular Ca2+ chelation. The Akt-dependent increase in connexin43 hemichannel activity in HeLa43 cells also occurred after oxygen-glucose deprivation, another ischemia-like condition, and in cultured cortical astrocytes (endogenous connexin43 expression system) under metabolic inhibition. Since opening of hemichannels has been shown to accelerate cell death, inhibition of Akt-dependent phosphorylation of connexin43 hemichannels could reduce cell death induced by ischemia/reperfusion.
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Affiliation(s)
- Daniela Salas
- Advanced Center for Chronic Diseases (ACCDIS) & Centro Estudios Moleculares de la Célula (CMEC), Facultad Ciencias Químicas y Farmacéuticas & Facultad Medicina, Universidad de Chile, Santiago, Chile; Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile.
| | - Carlos Puebla
- Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Paul D Lampe
- Translational Research Program, Human Biology and Public Health Sciences Divisions, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA
| | - Sergio Lavandero
- Advanced Center for Chronic Diseases (ACCDIS) & Centro Estudios Moleculares de la Célula (CMEC), Facultad Ciencias Químicas y Farmacéuticas & Facultad Medicina, Universidad de Chile, Santiago, Chile
| | - Juan C Sáez
- Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile; Instituto Milenio, Centro Interdisciplinario de Neurociencias de Valparaíso, Valparaíso, Chile.
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Muñoz MF, Puebla M, Figueroa XF. Control of the neurovascular coupling by nitric oxide-dependent regulation of astrocytic Ca(2+) signaling. Front Cell Neurosci 2015; 9:59. [PMID: 25805969 PMCID: PMC4354411 DOI: 10.3389/fncel.2015.00059] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 02/07/2015] [Indexed: 12/28/2022] Open
Abstract
Neuronal activity must be tightly coordinated with blood flow to keep proper brain function, which is achieved by a mechanism known as neurovascular coupling. Then, an increase in synaptic activity leads to a dilation of local parenchymal arterioles that matches the enhanced metabolic demand. Neurovascular coupling is orchestrated by astrocytes. These glial cells are located between neurons and the microvasculature, with the astrocytic endfeet ensheathing the vessels, which allows fine intercellular communication. The neurotransmitters released during neuronal activity reach astrocytic receptors and trigger a Ca2+ signaling that propagates to the endfeet, activating the release of vasoactive factors and arteriolar dilation. The astrocyte Ca2+ signaling is coordinated by gap junction channels and hemichannels formed by connexins (Cx43 and Cx30) and channels formed by pannexins (Panx-1). The neuronal activity-initiated Ca2+ waves are propagated among neighboring astrocytes directly via gap junctions or through ATP release via connexin hemichannels or pannexin channels. In addition, Ca2+ entry via connexin hemichannels or pannexin channels may participate in the regulation of the astrocyte signaling-mediated neurovascular coupling. Interestingly, nitric oxide (NO) can activate connexin hemichannel by S-nitrosylation and the Ca2+-dependent NO-synthesizing enzymes endothelial NO synthase (eNOS) and neuronal NOS (nNOS) are expressed in astrocytes. Therefore, the astrocytic Ca2+ signaling triggered in neurovascular coupling may activate NO production, which, in turn, may lead to Ca2+ influx through hemichannel activation. Furthermore, NO release from the hemichannels located at astrocytic endfeet may contribute to the vasodilation of parenchymal arterioles. In this review, we discuss the mechanisms involved in the regulation of the astrocytic Ca2+ signaling that mediates neurovascular coupling, with a special emphasis in the possible participation of NO in this process.
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Affiliation(s)
- Manuel F Muñoz
- Facultad de Ciencias Biológicas, Departamento de Fisiología, Pontificia Universidad Católica de Chile Santiago, Chile
| | - Mariela Puebla
- Facultad de Ciencias Biológicas, Departamento de Fisiología, Pontificia Universidad Católica de Chile Santiago, Chile
| | - Xavier F Figueroa
- Facultad de Ciencias Biológicas, Departamento de Fisiología, Pontificia Universidad Católica de Chile Santiago, Chile
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Rovegno M, Soto PA, Sáez PJ, Naus CC, Sáez JC, von Bernhardi R. Connexin43 hemichannels mediate secondary cellular damage spread from the trauma zone to distal zones in astrocyte monolayers. Glia 2015; 63:1185-99. [PMID: 25731866 DOI: 10.1002/glia.22808] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Accepted: 02/05/2015] [Indexed: 11/11/2022]
Abstract
The mechanism of secondary damage spread after brain trauma remains unsolved. In this work, we redirected the attention to astrocytic communication pathways. Using an in vitro trauma model that consists of a scratch injury applied to an astrocyte monolayer, we found a significant and transient induction of connexin43 (Cx43) hemichannel activity in regions distal from the injury, which was maximal ∼1 h after scratch. Two connexin hemichannel blockers, La(3+) and the peptide Gap26, abolished the increased activity, which was also absent in Cx43 KO astrocytes. In addition, the scratch-induced increase of hemichannel activity was prevented by inhibition of P2 purinergic receptors. Changes in hemichannel activity took place with a particular spatial distribution, with cells located at ∼17 mm away from the scratch presenting the highest activity (dye uptake). In contrast, the functional state of gap junction channels (dye coupling) was not significantly affected. Cx43 hemichannel activity was also enhanced by the acute extracellular application of 60 mM K(+) . The increase in hemichannel activity was associated with an increment in apoptotic cells at 24 h after scratch that was totally prevented by Gap26 peptide. These findings suggest that Cx43 hemichannels could be a new approach to prevent or reduce the secondary cell damage of brain trauma.
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Affiliation(s)
- Maximiliano Rovegno
- Laboratorio de Neurociencias, Departamento de Neurología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile; Departamento de Medicina Intensiva, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
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Kaneko Y, Tachikawa M, Akaogi R, Fujimoto K, Ishibashi M, Uchida Y, Couraud PO, Ohtsuki S, Hosoya KI, Terasaki T. Contribution of pannexin 1 and connexin 43 hemichannels to extracellular calcium-dependent transport dynamics in human blood-brain barrier endothelial cells. J Pharmacol Exp Ther 2015; 353:192-200. [PMID: 25670633 DOI: 10.1124/jpet.114.220210] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Dysregulation of blood-brain barrier (BBB) transport function is thought to exacerbate neuronal damage in acute ischemic stroke. The purpose of this study was to clarify the characteristics of pannexin (Px) and/or connexin (Cx) hemichannel(s)-mediated transport of organic anions and cations in human BBB endothelial cell line hCMEC/D3 and to identify inhibitors of hemichannel opening in hCMEC/D3 cells in the absence of extracellular Ca(2+), a condition mimicking acute ischemic stroke. In the absence of extracellular Ca(2+), the cells showed increased uptake and efflux transport of organic ionic fluorescent dyes. Classic hemichannel inhibitors markedly inhibited the enhanced uptake and efflux. Quantitative targeted absolute proteomics confirmed Px1 and Cx43 protein expression in plasma membrane of hCMEC/D3 cells. Knockdown of Px1 and Cx43 with the small interfering RNAs significantly inhibited the enhanced uptake and efflux of organic anionic and cationic fluorescent dyes. Clinically used cilnidipine and progesterone, which have neuroprotective effects in animal ischemia models, were identified as inhibitors of hemichannel opening. These findings suggest that altered transport dynamics at the human BBB in the absence of extracellular Ca(2+) is at least partly attributable to opening of Px1 and Cx43 hemichannels. Therefore, we speculate that Px1 and Cx43 may be potential drug targets to ameliorate BBB transport dysregulation during acute ischemia.
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Affiliation(s)
- Yosuke Kaneko
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
| | - Masanori Tachikawa
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
| | - Ryo Akaogi
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
| | - Kazuhisa Fujimoto
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
| | - Megumi Ishibashi
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
| | - Yasuo Uchida
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
| | - Pierre-Olivier Couraud
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
| | - Sumio Ohtsuki
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
| | - Ken-ichi Hosoya
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
| | - Tetsuya Terasaki
- Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan (Y.K., M.T., R.A., Y.U., T.T.); Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan (K.F., M.I.); INSERM, U1016, Institut Cochin and CNRS, UMR8104, and Université Paris Descartes, Paris, France (P.-O.C.); Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan (S.O.); and Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (K.H.)
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Kirca M, Kleinbongard P, Soetkamp D, Heger J, Csonka C, Ferdinandy P, Schulz R. Interaction between connexin 43 and nitric oxide synthase in mice heart mitochondria. J Cell Mol Med 2015; 19:815-25. [PMID: 25678382 PMCID: PMC4395196 DOI: 10.1111/jcmm.12499] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2014] [Accepted: 10/22/2014] [Indexed: 01/07/2023] Open
Abstract
Connexin 43 (Cx43), which is highly expressed in the heart and especially in cardiomyocytes, interferes with the expression of nitric oxide synthase (NOS) isoforms. Conversely, Cx43 gene expression is down-regulated by nitric oxide derived from the inducible NOS. Thus, a complex interplay between Cx43 and NOS expression appears to exist. As cardiac mitochondria are supposed to contain a NOS, we now investigated the expression of NOS isoforms and the nitric oxide production rate in isolated mitochondria of wild-type and Cx43-deficient (Cx43(Cre-ER(T)/fl) ) mice hearts. Mitochondria were isolated from hearts using differential centrifugation and purified via Percoll gradient ultracentrifugation. Isolated mitochondria were stained with an antibody against the mitochondrial marker protein adenine-nucleotide-translocator (ANT) in combination with either a neuronal NOS (nNOS) or an inducible NOS (iNOS) antibody and analysed using confocal laser scanning microscopy. The nitric oxide formation was quantified in purified mitochondria using the oxyhaemoglobin assay. Co-localization of predominantly nNOS (nNOS: 93 ± 4.1%; iNOS: 24.6 ± 7.5%) with ANT was detected in isolated mitochondria of wild-type mice. In contrast, iNOS expression was increased in Cx43(Cre-ER(T)/fl) mitochondria (iNOS: 90.7 ± 3.2%; nNOS: 53.8 ± 17.5%). The mitochondrial nitric oxide formation was reduced in Cx43(Cre-ER(T)/fl) mitochondria (0.14 ± 0.02 nmol/min./mg protein) in comparison to wild-type mitochondria (0.24 ± 0.02 nmol/min./mg). These are the first data demonstrating, that a reduced mitochondrial Cx43 content is associated with a switch of the mitochondrial NOS isoform and the respective mitochondrial rate of nitric oxide formation.
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Affiliation(s)
- Mücella Kirca
- Physiologisches Institut, Justus-Liebig-Universität, Giessen, Germany; Institute for Pathophysiology, West German Heart and Vascular Center, University Schhool of Medicine Essen, Essen, Germany
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121
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Hills CE, Price GW, Squires PE. Mind the gap: connexins and cell-cell communication in the diabetic kidney. Diabetologia 2015; 58:233-41. [PMID: 25358446 DOI: 10.1007/s00125-014-3427-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Accepted: 09/25/2014] [Indexed: 10/24/2022]
Abstract
Connexins, assembled as a hexameric connexon, form a transmembrane hemichannel that provides a conduit for paracrine signalling of small molecules and ions to regulate the activity and function of adjacent cells. When hemichannels align and associate with similar channels on opposing cells, they form a continuous aqueous pore or gap junction, allowing the direct transmission of metabolic and electrical signals between coupled cells. Regulation of gap junction synthesis and channel activity is critical for cell function, and a number of diseases can be attributed to changes in the expression/function of these important proteins. Diabetic nephropathy is associated with several complex metabolic and inflammatory responses characterised by defects at the molecular, cellular and tissue level. In both type 1 and type 2 diabetes, glycaemic injury of the kidney is the leading cause of end-stage renal failure, a consequence of multiple aetiologies, including increased deposition of extracellular matrix, glomerular hyperfiltration, albuminuria and tubulointerstitial fibrosis. In diabetic nephropathy, loss of connexin mediated cell-cell communication within the nephron may represent an early sign of disease; however, our current knowledge of the role of connexins in the diabetic kidney is sparse. This review highlights recent evidence demonstrating that maintenance of connexin-mediated cell-cell communication could benefit region-specific renal function in diabetic nephropathy and suggests that these proteins should be viewed as a tantalising novel target for therapeutic intervention.
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Affiliation(s)
- Claire E Hills
- School of Life Sciences, University of Lincoln, Brayford Pool, Lincoln, LN6 7TS, UK,
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Tonkin RS, Mao Y, O'Carroll SJ, Nicholson LFB, Green CR, Gorrie CA, Moalem-Taylor G. Gap junction proteins and their role in spinal cord injury. Front Mol Neurosci 2015; 7:102. [PMID: 25610368 PMCID: PMC4285056 DOI: 10.3389/fnmol.2014.00102] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Accepted: 12/12/2014] [Indexed: 12/25/2022] Open
Abstract
Gap junctions are specialized intercellular communication channels that are formed by two hexameric connexin hemichannels, one provided by each of the two adjacent cells. Gap junctions and hemichannels play an important role in regulating cellular metabolism, signaling, and functions in both normal and pathological conditions. Following spinal cord injury (SCI), there is damage and disturbance to the neuronal elements of the spinal cord including severing of axon tracts and rapid cell death. The initial mechanical disruption is followed by multiple secondary cascades that cause further tissue loss and dysfunction. Recent studies have implicated connexin proteins as playing a critical role in the secondary phase of SCI by propagating death signals through extensive glial networks. In this review, we bring together past and current studies to outline the distribution, changes and roles of various connexins found in neurons and glial cells, before and in response to SCI. We discuss the contribution of pathologically activated connexin proteins, in particular connexin 43, to functional recovery and neuropathic pain, as well as providing an update on potential connexin specific pharmacological agents to treat SCI.
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Affiliation(s)
- Ryan S Tonkin
- School of Medical Sciences, Faculty of Medicine, University of New South Wales Sydney, NSW, Australia
| | - Yilin Mao
- School of Medical and Molecular Bioscience, Faculty of Science, University of Technology Sydney, NSW, Australia
| | - Simon J O'Carroll
- Department of Anatomy with Radiology and Centre for Brain Research, Faculty of Medical and Health Sciences, University of Auckland Auckland, New Zealand
| | - Louise F B Nicholson
- Department of Anatomy with Radiology and Centre for Brain Research, Faculty of Medical and Health Sciences, University of Auckland Auckland, New Zealand
| | - Colin R Green
- Department of Ophthalmology, Faculty of Medical and Health Sciences, University of Auckland Auckland, New Zealand
| | - Catherine A Gorrie
- School of Medical and Molecular Bioscience, Faculty of Science, University of Technology Sydney, NSW, Australia
| | - Gila Moalem-Taylor
- School of Medical Sciences, Faculty of Medicine, University of New South Wales Sydney, NSW, Australia
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León-Paravic CG, Figueroa VA, Guzmán DJ, Valderrama CF, Vallejos AA, Fiori MC, Altenberg GA, Reuss L, Retamal MA. Carbon monoxide (CO) is a novel inhibitor of connexin hemichannels. J Biol Chem 2014; 289:36150-7. [PMID: 25384983 PMCID: PMC4276878 DOI: 10.1074/jbc.m114.602243] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Revised: 11/07/2014] [Indexed: 12/13/2022] Open
Abstract
Hemichannels (HCs) are hexamers of connexins that can form gap-junction channels at points of cell contacts or "free HCs" at non-contacting regions. HCs are involved in paracrine and autocrine cell signaling, and under pathological conditions may induce and/or accelerate cell death. Therefore, studies of HC regulation are of great significance. Nitric oxide affects the activity of Cx43 and Cx46 HCs, whereas carbon monoxide (CO), another gaseous transmitter, modulates the activity of several ion channels, but its effect on HCs has not been explored. We studied the effect of CO donors (CORMs) on Cx46 HCs expressed in Xenopus laevis oocytes using two-electrode voltage clamp and on Cx43 and Cx46 expressed in HeLa cells using a dye-uptake technique. CORM-2 inhibited Cx46 HC currents in a concentration-dependent manner. The C-terminal domain and intracellular Cys were not necessary for the inhibition. The effect of CORM-2 was not prevented by guanylyl-cyclase, protein kinase G, or thioredoxin inhibitors, and was not due to endocytosis of HCs. However, the effect of CORM-2 was reversed by reducing agents that act extracellularly. Additionally, CO inhibited dye uptake of HeLa cells expressing Cx43 or Cx46, and MCF-7 cells, which endogenously express Cx43 and Cx46. Because CORM-2 carbonylates Cx46 in vitro and induces conformational changes, a direct effect of that CO on Cx46 is possible. The inhibition of HCs could help to understand some of the biological actions of CO in physiological and pathological conditions.
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Affiliation(s)
- Carmen G León-Paravic
- From the Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo, Santiago, Chile 7690000 and
| | - Vania A Figueroa
- From the Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo, Santiago, Chile 7690000 and
| | - Diego J Guzmán
- From the Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo, Santiago, Chile 7690000 and
| | - Carlos F Valderrama
- From the Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo, Santiago, Chile 7690000 and
| | - Antonio A Vallejos
- From the Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo, Santiago, Chile 7690000 and
| | - Mariana C Fiori
- the Department of Cell Physiology and Molecular Biophysics, and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
| | - Guillermo A Altenberg
- the Department of Cell Physiology and Molecular Biophysics, and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
| | - Luis Reuss
- the Department of Cell Physiology and Molecular Biophysics, and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
| | - Mauricio A Retamal
- From the Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo, Santiago, Chile 7690000 and the Department of Cell Physiology and Molecular Biophysics, and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
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124
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Meckes B, Ambrosi C, Barnard H, Arce FT, Sosinsky GE, Lal R. Atomic force microscopy shows connexin26 hemichannel clustering in purified membrane fragments. Biochemistry 2014; 53:7407-14. [PMID: 25365227 PMCID: PMC4255643 DOI: 10.1021/bi501265p] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
![]()
Connexin
proteins form hexameric assemblies known as hemichannels.
When docked to form gap junction (GJ) channels, hemichannels play
a critical role in cell–cell communication and cellular homeostasis,
but often are functional entities on their own in unapposed cell membranes.
Defects in the Connexin26 (Cx26) gene are the major cause of hereditary
deafness arising from dysfunctional hemichannels in the cochlea. Structural
studies of Cx26 hemichannels properly trafficked and inserted in plasma
membranes, including their clustering that forms a plaque-like feature
in whole gap junctions, are limited. We used atomic force microscopy
(AFM) to study the surface topography of Cx26 hemichannels using two
different membrane preparations. Rat Cx26 containing appended carboxy
terminal V5 and hexahistidine tags were expressed in baculovirus/Sf9
cell systems. The expressed Cx26 proteins form hemichannels in situ
in Sf9 cells that were then purified either as (1) Sf9 membrane fragments
containing Cx26 hemichannels or (2) solubilized hemichannels. The
latter were subsequently reconstituted in liposomes. AFM images of
purified membrane fragments showed clusters of protein macromolecular
structures in the membrane that at higher magnification corresponded
to Cx26 hemichannels. Hemichannels reconstituted into DOPC bilayers
displayed two populations of channel heights likely resulting from
differences in orientations of inserted hemichannels. Hemichannels
in the protein rich portions of purified membranes also showed a reduced
channel height above the bilayer compared to membranes with reconstituted
hemichannels perhaps due to reduced AFM probe access to the lipid
bilayer. These preparations of purified membranes enriched for connexin
hemichannels that have been properly trafficked and inserted in membranes
provide a platform for high-resolution AFM imaging of the structure,
interconnexon interactions, and cooperativity of properly trafficked
and inserted noncrystalline connexin hemichannels.
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Affiliation(s)
- Brian Meckes
- Department of Bioengineering, ‡National Center for Microscopy and Imaging Research, §Department of Aerospace and Mechanical Engineering, ∥Department of Neurosciences, and ⊥Materials Science Program, University of California San Diego , 9500 Gillman Drive, La Jolla, California 92093, United States
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125
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Soetkamp D, Nguyen TT, Menazza S, Hirschhäuser C, Hendgen-Cotta UB, Rassaf T, Schlüter KD, Boengler K, Murphy E, Schulz R. S-nitrosation of mitochondrial connexin 43 regulates mitochondrial function. Basic Res Cardiol 2014; 109:433. [PMID: 25115184 PMCID: PMC4168224 DOI: 10.1007/s00395-014-0433-x] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 08/05/2014] [Accepted: 08/06/2014] [Indexed: 01/31/2023]
Abstract
S-nitrosation (SNO) of connexin 43 (Cx43)-formed channels modifies dye uptake in astrocytes and gap junctional communication in endothelial cells. Apart from forming channels at the plasma membrane of several cell types, Cx43 is also located at the inner membrane of myocardial subsarcolemmal mitochondria (SSM), but not in interfibrillar mitochondria (IFM). The absence or pharmacological blockade of mitochondrial Cx43 (mtCx43) reduces dye and potassium uptake. Lack of mtCx43 is associated with loss of endogenous cardioprotection by ischemic preconditioning (IPC), which is mediated by formation of reactive oxygen species (ROS). Whether or not mitochondrial Lucifer Yellow (LY), ion uptake, or ROS generation are affected by SNO of mtCx43 and whether or not cardioprotective interventions affect SNO of mtCx43 remains unknown. In SSM from rat hearts, application of NO donors (48 nmol to 1 mmol) increased LY uptake (0.5 mmol SNAP 38.4 ± 7.1 %, p < 0.05; 1 mmol GSNO 28.1 ± 7.4 %, p < 0.05) and the refilling rate of potassium (SNAP 227.9 ± 30.1 %, p < 0.05; GSNO 122.6 ± 28.1 %, p < 0.05). These effects were absent following blockade of Cx43 hemichannels by carbenoxolone as well as in IFM lacking Cx43. Unlike potassium, the sodium permeability was not affected by application of NO. Furthermore, mitochondrial ROS formation was increased following NO application compared to control SSM (0.5 mmol SNAP 22.9 ± 1.8 %, p < 0.05; 1 mmol GSNO 40.6 ± 7.1 %, p < 0.05), but decreased in NO treated IFM compared to control (0.5 mmol SNAP 14.4 ± 4 %, p < 0.05; 1 mmol GSNO 13.8 ± 4 %, p < 0.05). NO donor administration to isolated SSM increased SNO of mtCx43 by 109.2 ± 15.8 %. Nitrite application (48 nmol) to mice was also associated with elevated SNO of mtCx43 by 59.3 ± 18.2 % (p < 0.05). IPC by four cycles of 5 min of ischemia and 5 min of reperfusion increased SNO of mtCx43 by 41.6 ± 1.7 % (p < 0.05) when compared to control perfused rat hearts. These data suggest that SNO of mtCx43 increases mitochondrial permeability, especially for potassium and leads to increased ROS formation. The increased amount of SNO mtCx43 by IPC or nitrite administration may link NO and Cx43 in the signal transduction cascade of cardioprotective interventions.
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Affiliation(s)
- Daniel Soetkamp
- Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
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126
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O'Carroll SJ, Becker DL, Davidson JO, Gunn AJ, Nicholson LFB, Green CR. The use of connexin-based therapeutic approaches to target inflammatory diseases. Methods Mol Biol 2014; 1037:519-46. [PMID: 24029957 DOI: 10.1007/978-1-62703-505-7_31] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Alterations in Connexin43 (Cx43) expression levels have been shown to play a role in inflammatory processes including skin wounding and neuroinflammation. Cx43 protein levels increase following a skin wound and can inhibit wound healing. Increased Cx43 has been observed following stroke, epilepsy, ischemia, optic nerve damage, and spinal cord injury with gap junctional communication and hemichannel opening leading to increased secondary damage via the inflammatory response. Connexin43 modulation has been identified as a potential target for protection and repair in neuroinflammation and skin wound repair. This review describes the use of a Cx43 specific antisense oligonucleotide (Cx43 AsODN) and peptide mimetics of the connexin extracellular loop domain to modulate Cx43 expression and/or function in inflammatory disorders of the skin and central nervous system. An overview of the role of connexin43 in inflammatory conditions, how antisense and peptide have allowed us to elucidate the role of Cx43 in these diseases, create models of diseases to test interventions and their potential for use clinically or in current clinical trials is presented. Antisense oligonucleotides are applied topically and have been used to improve wound healing following skin injury. They have also been used to develop ex vivo models of neuroinflammatory diseases that will allow testing of intervention strategies. The connexin mimetic peptides have shown potential in a number of neuroinflammatory disorders in ex vivo models as well as in vivo when delivered directly to the injury site or when delivered systemically.
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Affiliation(s)
- Simon J O'Carroll
- Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
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127
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Orellana JA, Stehberg J. Hemichannels: new roles in astroglial function. Front Physiol 2014; 5:193. [PMID: 24987373 PMCID: PMC4060415 DOI: 10.3389/fphys.2014.00193] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Accepted: 05/07/2014] [Indexed: 01/16/2023] Open
Abstract
The role of astrocytes in brain function has evolved over the last decade, from support cells to active participants in the neuronal synapse through the release of "gliotransmitters."Astrocytes express receptors for most neurotransmitters and respond to them through Ca(2+) intracellular oscillations and propagation of intercellular Ca(2+) waves. While such waves are able to propagate among neighboring astrocytes through gap junctions, thereby activating several astrocytes simultaneously, they can also trigger the release of gliotransmitters, including glutamate, d-serine, glycine, ATP, adenosine, or GABA. There are several mechanisms by which gliotransmitter release occurs, including functional hemichannels. These gliotransmitters can activate neighboring astrocytes and participate in the propagation of intercellular Ca(2+) waves, or activate pre- and post-synaptic receptors, including NMDA, AMPA, and purinergic receptors. In consequence, hemichannels could play a pivotal role in astrocyte-to-astrocyte communication and astrocyte-to-neuron cross-talk. Recent evidence suggests that astroglial hemichannels are involved in higher brain functions including memory and glucose sensing. The present review will focus on the role of hemichannels in astrocyte-to-astrocyte and astrocyte-to neuron communication and in brain physiology.
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Affiliation(s)
- Juan A Orellana
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile Santiago, Chile
| | - Jimmy Stehberg
- Laboratorio de Neurobiología, Centro de Investigaciones Médicas, Facultad de Ciencias Biológicas and Facultad de Medicina, Universidad Andrés Bello Santiago, Chile
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128
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Carette D, Gilleron J, Chevallier D, Segretain D, Pointis G. Connexin a check-point component of cell apoptosis in normal and physiopathological conditions. Biochimie 2014; 101:1-9. [DOI: 10.1016/j.biochi.2013.11.015] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Accepted: 11/18/2013] [Indexed: 12/16/2022]
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129
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Gebicke-Haerter PJ. Engram formation in psychiatric disorders. Front Neurosci 2014; 8:118. [PMID: 24904262 PMCID: PMC4036307 DOI: 10.3389/fnins.2014.00118] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Accepted: 05/02/2014] [Indexed: 01/17/2023] Open
Abstract
Environmental factors substantially influence beginning and progression of mental illness, reinforcing or reducing the consequences of genetic vulnerability. Often initiated by early traumatic events, “engrams” or memories are formed that may give rise to a slow and subtle progression of psychiatric disorders. The large delay between beginning and time of onset (diagnosis) may be explained by efficient compensatory mechanisms observed in brain metabolism that use optional pathways in highly redundant molecular interactions. To this end, research has to deal with mechanisms of learning and long-term memory formation, which involves (a) epigenetic changes, (b) altered neuronal activities, and (c) changes in neuron-glia communication. On the epigenetic level, apparently DNA-methylations are more stable than histone modifications, although both closely interact. Neuronal activities basically deliver digital information, which clearly can serve as basis for memory formation (LTP). However, research in this respect has long time neglected the importance of glia. They are more actively involved in the control of neuronal activities than thought before. They can both reinforce and inhibit neuronal activities by transducing neuronal information from frequency-encoded to amplitude and frequency-modulated calcium wave patterns spreading in the glial syncytium by use of gap junctions. In this way, they serve integrative functions. In conclusion, we are dealing with two concepts of encoding information that mutually control each other and synergize: a digital (neuronal) and a wave-like (glial) computing, forming neuron-glia functional units with inbuilt feedback loops to maintain balance of excitation and inhibition. To better understand mental illness, we have to gain more insight into the dynamics of adverse environmental impact on those cellular and molecular systems. This report summarizes existing knowledge and draws some outline about further research in molecular psychiatry.
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Affiliation(s)
- Peter J Gebicke-Haerter
- Medical Faculty Mannheim, Central Institute of Mental Health, Institute of Psychopharmacology, Heidelberg University Mannheim, Germany ; Progrs. de Farmacología y Inmunología, Facultad de Medicina, Universidad de Chile Santiago, Chile
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130
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Reyes EP, Cerpa V, Corvalán L, Retamal MA. Cxs and Panx- hemichannels in peripheral and central chemosensing in mammals. Front Cell Neurosci 2014; 8:123. [PMID: 24847209 PMCID: PMC4023181 DOI: 10.3389/fncel.2014.00123] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Accepted: 04/18/2014] [Indexed: 01/08/2023] Open
Abstract
Connexins (Cxs) and Pannexins (Panx) form hemichannels at the plasma membrane of animals. Despite their low open probability under physiological conditions, these hemichannels release signaling molecules (i.e., ATP, Glutamate, PGE2) to the extracellular space, thus subserving several important physiological processes. Oxygen and CO2 sensing are fundamental to the normal functioning of vertebrate organisms. Fluctuations in blood PO2, PCO2 and pH are sensed at the carotid bifurcations of adult mammals by glomus cells of the carotid bodies. Likewise, changes in pH and/or PCO2 of cerebrospinal fluid are sensed by central chemoreceptors, a group of specialized neurones distributed in the ventrolateral medulla (VLM), raphe nuclei, and some other brainstem areas. After many years of research, the molecular mechanisms involved in chemosensing process are not completely understood. This manuscript will review data regarding relationships between chemosensitive cells and the expression of channels formed by Cxs and Panx, with special emphasis on hemichannels.
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Affiliation(s)
- Edison Pablo Reyes
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile ; Dirección de Investigación, Universidad Autónoma de Chile Santiago, Chile
| | - Verónica Cerpa
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile
| | - Liliana Corvalán
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile
| | - Mauricio Antonio Retamal
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina, Clínica Alemana Universidad del Desarrollo Santiago, Chile
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131
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Billaud M, Lohman AW, Johnstone SR, Biwer LA, Mutchler S, Isakson BE. Regulation of cellular communication by signaling microdomains in the blood vessel wall. Pharmacol Rev 2014; 66:513-69. [PMID: 24671377 DOI: 10.1124/pr.112.007351] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
It has become increasingly clear that the accumulation of proteins in specific regions of the plasma membrane can facilitate cellular communication. These regions, termed signaling microdomains, are found throughout the blood vessel wall where cellular communication, both within and between cell types, must be tightly regulated to maintain proper vascular function. We will define a cellular signaling microdomain and apply this definition to the plethora of means by which cellular communication has been hypothesized to occur in the blood vessel wall. To that end, we make a case for three broad areas of cellular communication where signaling microdomains could play an important role: 1) paracrine release of free radicals and gaseous molecules such as nitric oxide and reactive oxygen species; 2) role of ion channels including gap junctions and potassium channels, especially those associated with the endothelium-derived hyperpolarization mediated signaling, and lastly, 3) mechanism of exocytosis that has considerable oversight by signaling microdomains, especially those associated with the release of von Willebrand factor. When summed, we believe that it is clear that the organization and regulation of signaling microdomains is an essential component to vessel wall function.
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Affiliation(s)
- Marie Billaud
- Dept. of Molecular Physiology and Biophysics, University of Virginia School of Medicine, PO Box 801394, Charlottesville, VA 22902.
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132
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Ramachandran S, Arce FT, Patel NR, Quist AP, Cohen DA, Lal R. Structure and permeability of ion-channels by integrated AFM and waveguide TIRF microscopy. Sci Rep 2014; 4:4424. [PMID: 24651823 PMCID: PMC3961736 DOI: 10.1038/srep04424] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Accepted: 03/03/2014] [Indexed: 11/09/2022] Open
Abstract
Membrane ion channels regulate key cellular functions and their activity is dependent on their 3D structure. Atomic force microscopy (AFM) images 3D structure of membrane channels placed on a solid substrate. Solid substrate prevents molecular transport through ion channels thus hindering any direct structure-function relationship analysis. Here we designed a ~70 nm nanopore to suspend a membrane, allowing fluidic access to both sides. We used these nanopores with AFM and total internal reflection fluorescence microscopy (TIRFM) for high resolution imaging and molecular transport measurement. Significantly, membranes over the nanopore were stable for repeated AFM imaging. We studied structure-activity relationship of gap junction hemichannels reconstituted in lipid bilayers. Individual hemichannels in the membrane overlying the nanopore were resolved and transport of hemichannel-permeant LY dye was visualized when the hemichannel was opened by lowering calcium in the medium. This integrated technique will allow direct structure-permeability relationship of many ion channels and receptors.
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Affiliation(s)
- Srinivasan Ramachandran
- 1] Department of Bioengineering; Department of Mechanical & Aerospace Engineering, University of California San Diego, La Jolla, CA 92093 [2]
| | - Fernando Teran Arce
- 1] Department of Bioengineering; Department of Mechanical & Aerospace Engineering, University of California San Diego, La Jolla, CA 92093 [2]
| | - Nirav R Patel
- Department of Bioengineering; Department of Mechanical & Aerospace Engineering, University of California San Diego, La Jolla, CA 92093
| | - Arjan P Quist
- RC Nano Corporation, 2210 Midwest Road, Oak Brook, IL 60523, USA. Current Address: Innovation and New Ventures Office, Northwestern University, 1800 Sherman Ave., Evanston IL 60201
| | - Daniel A Cohen
- Department of Materials, University of California Santa Barbara, CA 93106
| | - Ratnesh Lal
- Department of Bioengineering; Department of Mechanical & Aerospace Engineering, University of California San Diego, La Jolla, CA 92093
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133
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Sáez JC, Leybaert L. Hunting for connexin hemichannels. FEBS Lett 2014; 588:1205-11. [PMID: 24631534 DOI: 10.1016/j.febslet.2014.03.004] [Citation(s) in RCA: 143] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Revised: 03/01/2014] [Accepted: 03/03/2014] [Indexed: 10/25/2022]
Abstract
Connexin hemichannels (connexons) are building blocks of gap junctions but also function as free unapposed channels, which has become an active field of research. Defining functions of hemichannels and their involvement in any biological event requires ruling out possible participation of other channels that share biophysical and regulatory properties, for example pannexins, CALHM1 and P2X receptors. The lack of specific inhibitors for these channels has become an obstacle in elucidating the role of connexin hemichannels. Several experimental approaches are now available to identify hemichannels at the cell surface and to characterize their electrophysiological, permeability and regulatory properties. The use of connexin knockout/knockdown, and the development of peptides that target intracellular connexin domains and specific antibodies directed to extracellular domains have helped to dissect the role of hemichannels in endogenously expressing systems. Moreover, studies of connexin mutants in exogenous expression systems have provided convincing evidence on hemichannels in the pathogenesis of several human genetic diseases. We here present a brief overview of connexin hemichannels as functional channels and itemize a list of aspects to consider when concluding on their involvement.
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Affiliation(s)
- Juan C Sáez
- Departamento de Fisiología, Pontificia Universidad Católica de Chile, Santiago and Instituto Milenio, Centro Interdisciplinario de Neurociencias de Valparaíso, Valparaíso, Chile.
| | - Luc Leybaert
- Physiology Group, Department of Basic Medical Sciences, Faculty of Medicine and Health Sciences, Ghent University, De Pintelaan 185 (Block B - Rm 031), 9000 Ghent, Belgium.
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134
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A new angle on blood-CNS interfaces: A role for connexins? FEBS Lett 2014; 588:1259-70. [DOI: 10.1016/j.febslet.2014.02.060] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 02/27/2014] [Accepted: 02/28/2014] [Indexed: 12/12/2022]
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135
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Ma Y, Cao W, Wang L, Jiang J, Nie H, Wang B, Wei X, Ying W. Basal CD38/cyclic ADP-ribose-dependent signaling mediates ATP release and survival of microglia by modulating connexin 43 hemichannels. Glia 2014; 62:943-55. [PMID: 24578339 DOI: 10.1002/glia.22651] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2013] [Revised: 02/04/2014] [Accepted: 02/05/2014] [Indexed: 02/06/2023]
Abstract
It is necessary to investigate the mechanisms underlying ATP release from neural cells, because extracellular ATP plays multiple important biological roles in the brain. CD38 is an ectoenzyme that consumes NAD(+) to produce cyclic ADP-ribose (cADPR), a potent agonist of ryanodine receptors. Our previous study showed that CD38 reductions led to microglial apoptosis. In this study, we used both murine microglial BV2 cells and primary microglial cultures as cellular models to test our hypothesis that basal CD38/cyclic ADP-ribose (CD38/cADPR)-dependent signaling plays a key role in ATP release, which mediates basal survival of microglia. We found that inhibition of CD38/cADPR-dependent signaling by CD38 silencing or 8-Bromo-cADPR, a ryanodine receptor antagonist, produced significant ATP release from BV2 microglia. Cx43 small interfering RNA and Cx43 hemichannel blocker 18-α-glycyrrhetinic acid completely prevented the CD38 silencing or 8-Bromo-cADPR-induced ATP release. Prevention of the ATP release could also be due to P2X7 receptor antagonists. Our study has further suggested a key role of ATP release in the microglial apoptosis induced by decreased CD38/cADPR-dependent signaling. In addition, by using primary microglial cultures, we found that 8-Bromo-cADPR also induced significant ATP release, which could be attenuated by 18-α-glycyrrhetinic acid. 8-Bromo-cADPR was also found to induce death of primary microglial cultures. In conclusion, our results have suggested novel roles of basal activation of CD38/cADPR-dependent signaling in mediating microglial functions and survival: It mediates ATP release from microglia by modulating Cx43 hemichannels, which can significantly affect microglial survival.
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Affiliation(s)
- Yingxin Ma
- Med-X Research Institute and School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, 200030, People's Republic of China
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136
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Fiori MC, Reuss L, Cuello LG, Altenberg GA. Functional analysis and regulation of purified connexin hemichannels. Front Physiol 2014; 5:71. [PMID: 24611052 PMCID: PMC3933781 DOI: 10.3389/fphys.2014.00071] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Accepted: 02/06/2014] [Indexed: 01/08/2023] Open
Abstract
Gap-junction channels (GJCs) are aqueous channels that communicate adjacent cells. They are formed by head-to-head association of two hemichannels (HCs), one from each of the adjacent cells. Functional HCs are connexin hexamers composed of one or more connexin isoforms. Deafness is the most frequent sensineural disorder, and mutations of Cx26 are the most common cause of genetic deafness. Cx43 is the most ubiquitous connexin, expressed in many organs, tissues, and cell types, including heart, brain, and kidney. Alterations in its expression and function play important roles in the pathophysiology of very frequent medical problems such as those related to cardiac and brain ischemia. There is extensive information on the relationship between phosphorylation and Cx43 targeting, location, and function from experiments in cells and organs in normal and pathological conditions. However, the molecular mechanisms of Cx43 regulation by phosphorylation are hard to tackle in complex systems. Here, we present the use of purified HCs as a model for functional and structural studies. Cx26 and Cx43 are the only isoforms that have been purified, reconstituted, and subjected to functional and structural analysis. Purified Cx26 and Cx43 HCs have properties compatible with those demonstrated in cells, and present methodologies for the functional analysis of purified HCs reconstituted in liposomes. We show that phosphorylation of serine 368 by PKC produces a partial closure of the Cx43 HCs, changing solute selectivity. We also present evidence that the effect of phosphorylation is highly cooperative, requiring modification of several connexin subunits, and that phosphorylation of serine 368 elicits conformational changes in the purified HCs. The use of purified HCs is starting to provide critical data to understand the regulation of HCs at the molecular level.
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Affiliation(s)
- Mariana C Fiori
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center Lubbock, TX, USA
| | - Luis Reuss
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center Lubbock, TX, USA
| | - Luis G Cuello
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center Lubbock, TX, USA
| | - Guillermo A Altenberg
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center Lubbock, TX, USA
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137
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Retamal MA. Connexin and Pannexin hemichannels are regulated by redox potential. Front Physiol 2014; 5:80. [PMID: 24611056 PMCID: PMC3933782 DOI: 10.3389/fphys.2014.00080] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 02/08/2014] [Indexed: 01/28/2023] Open
Abstract
Connexins (Cxs) and Pannexins (Panxs) are two non-related protein families, having both the property to form hemichannels at the plasma membrane. There are 21 genes coding for different Cx based proteins and only 3 for Panx. Under physiological conditions, these hemichannels (Cxs and Panxs) present a low open probability, but when open, they allow the release of signaling molecules to the extracellular space. However, under pathological conditions, these hemichannels increase their open probability, inducing important lysis of metabolites, and ionic imbalance, which in turn induce the massive entry of Ca+2 to the cell. Actually, it is well recognized that Cxs and Panxs based channels play an important role in several diseases and -in many cases- this is associated with an aberrant hemichannel opening. Hemichannel opening and closing are controlled by a plethora of signaling including changes of the voltage plasma membrane, protein-protein interactions, and several posttranslational modifications, including protein cleavage, phosphorylation, glycosylation, hydroxylation and S-nitrosylation, among others. In particular, it has been recently shown that the cellular redox status modulates the opening/closing and permeability of at least Cx43, Cx46, and Panx1 hemichannels. Thus, for example, the gaseous transmitter nitric oxide (NO) can induce the S-nitrosylation of these proteins modulating in turn several of their properties. The reason is that the redox status of a cell is fundamental to set their response to the environment and also plays an important role in several pathologies. In this review, I will discuss how NO and other molecules associated with redox signaling modulate Cxs and Panx hemichannels properties.
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Affiliation(s)
- Mauricio A Retamal
- Facultad de Medicina Clínica Alemana, Centro de Fisiología Celular e Integrativa, Universidad del Desarrollo Santiago, Chile
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138
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Baker MW, Macagno ER. Control of neuronal morphology and connectivity: Emerging developmental roles for gap junctional proteins. FEBS Lett 2014; 588:1470-9. [DOI: 10.1016/j.febslet.2014.02.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 02/10/2014] [Accepted: 02/12/2014] [Indexed: 11/25/2022]
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139
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Abstract
The normal function and survival of cells in the avascular lens is facilitated by intercellular communication through an extensive network of gap junctions formed predominantly by three connexins (Cx43, Cx46, and Cx50). In expression systems, these connexins can all induce hemichannel currents, but other lens proteins (e.g., pannexin1) can also induce similar currents. Hemichannel currents have been detected in isolated lens fiber cells. These hemichannels may make significant contributions to normal lens physiology and pathophysiology. Studies of some connexin mutants linked to congenital cataracts have implicated hemichannels with aberrant voltage-dependent gating or modulation by divalent cations in disease pathogenesis. Hemichannels may also contribute to age- and disease-related cataracts.
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Affiliation(s)
- Eric C Beyer
- Department of Pediatrics, University of Chicago Chicago, IL, USA
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140
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Penuela S, Simek J, Thompson RJ. Regulation of pannexin channels by post-translational modifications. FEBS Lett 2014; 588:1411-5. [PMID: 24486011 DOI: 10.1016/j.febslet.2014.01.028] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Revised: 01/16/2014] [Accepted: 01/19/2014] [Indexed: 01/25/2023]
Abstract
The large-pore channels formed by the pannexin family of proteins have been implicated in many physiological and pathophysiological functions, mainly through their ATP release function. However, a tight regulation of channel opening is necessary to modulate their function in vivo. Post-translational modifications have been postulated as some of the regulating mechanisms for Panx1, while Panx2 and Panx3 have not been as well characterized. Positive regulators include caspase cleavage to open Panx1 channels in apoptotic cells, and activation by Src family kinases via ionotropic receptors in neurons and macrophages. S-nitrosylation of cysteines has been shown to both inhibit and activate the Panx1 channel in different cell types. All three pannexins are N-glycosylated but to different levels of modification. Their diverse glycosylation appears to regulate cellular localization, intermixing, and may restrict their ability to function as inter-cellular channels. It is clear that our understanding of pannexin post-translational modification and their role in channel function regulation is still in its infancy even a decade after their discovery.
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Affiliation(s)
- Silvia Penuela
- Department of Anatomy and Cell Biology, University of Western Ontario, London, ON N6A5C1, Canada.
| | - Jamie Simek
- Department of Physiology and Pharmacology, University of Western Ontario, London, ON N6A5C1, Canada
| | - Roger J Thompson
- Hotchkiss Brain Institute and Department of Cell Biology and Anatomy, University of Calgary, Calgary, AB T2N 4N1, Canada
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141
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Patel D, Zhang X, Veenstra RD. Connexin hemichannel and pannexin channel electrophysiology: how do they differ? FEBS Lett 2014; 588:1372-8. [PMID: 24434538 DOI: 10.1016/j.febslet.2013.12.023] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Revised: 12/20/2013] [Accepted: 12/30/2013] [Indexed: 12/21/2022]
Abstract
Connexin hemichannels are postulated to form a cell permeabilization pore for the uptake of fluorescent dyes and release of cellular ATP. Connexin hemichannel activity is enhanced by low external [Ca(2+)]o, membrane depolarization, metabolic inhibition, and some disease-causing gain-of-function connexin mutations. This paper briefly reviews the electrophysiological channel conductance, permeability, and pharmacology properties of connexin hemichannels, pannexin 1 channels, and purinergic P2X7 receptor channels as studied in exogenous expression systems including Xenopus oocytes and mammalian cell lines such as HEK293 cells. Overlapping pharmacological inhibitory and channel conductance and permeability profiles makes distinguishing between these channel types sometimes difficult. Selective pharmacology for Cx43 hemichannels (Gap19 peptide), probenecid or FD&C Blue #1 (Brilliant Blue FCF, BB FCF) for Panx1, and A740003, A438079, or oxidized ATP (oATP) for P2X7 channels may be the best way to distinguish between these three cell permeabilizing channel types. Endogenous connexin, pannexin, and P2X7 expression should be considered when performing exogenous cellular expression channel studies. Cell pair electrophysiological assays permit the relative assessment of the connexin hemichannel/gap junction channel ratio not often considered when performing isolated cell hemichannel studies.
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Affiliation(s)
- Dakshesh Patel
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY 13210, United States
| | - Xian Zhang
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY 13210, United States
| | - Richard D Veenstra
- Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY 13210, United States.
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142
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Berthoud VM, Minogue PJ, Osmolak P, Snabb JI, Beyer EC. Roles and regulation of lens epithelial cell connexins. FEBS Lett 2014; 588:1297-303. [PMID: 24434541 DOI: 10.1016/j.febslet.2013.12.024] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 12/19/2013] [Accepted: 12/30/2013] [Indexed: 11/27/2022]
Abstract
The avascular lens of the eye is covered anteriorly by an epithelium containing nucleated, metabolically active cells. This epithelium contains the first lens cells to encounter noxious external stimuli and cells that can develop compensatory or protective responses. Lens epithelial cells express the gap junction proteins, connexin43 (Cx43) and connexin50 (Cx50). Cx43 and Cx50 form gap junction channels and hemichannels with different properties. Although they may form heteromeric hemichannels, Cx43 and Cx50 probably do not form heterotypic channels in the lens. Cx50 channels make their greatest contribution to intercellular communication during the early postnatal period; subsequently, Cx43 becomes the predominant connexin supporting intercellular communication. Although epithelial Cx43 appears dispensable for lens development, Cx50 is critical for epithelial cell proliferation and differentiation. Cx43 and Cx50 hemichannels and gap junction channels are regulated by multiple different agents. Lens epithelial cell connexins contribute to both normal lens physiology and pathology.
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Affiliation(s)
- Viviana M Berthoud
- Department of Pediatrics and Pritzker School of Medicine, University of Chicago, Chicago, IL 60637, United States.
| | - Peter J Minogue
- Department of Pediatrics and Pritzker School of Medicine, University of Chicago, Chicago, IL 60637, United States
| | - Patricia Osmolak
- Department of Pediatrics and Pritzker School of Medicine, University of Chicago, Chicago, IL 60637, United States
| | - Joseph I Snabb
- Department of Pediatrics and Pritzker School of Medicine, University of Chicago, Chicago, IL 60637, United States
| | - Eric C Beyer
- Department of Pediatrics and Pritzker School of Medicine, University of Chicago, Chicago, IL 60637, United States
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143
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Nielsen MS, Axelsen LN, Sorgen PL, Verma V, Delmar M, Holstein-Rathlou NH. Gap junctions. Compr Physiol 2013; 2:1981-2035. [PMID: 23723031 DOI: 10.1002/cphy.c110051] [Citation(s) in RCA: 289] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Gap junctions are essential to the function of multicellular animals, which require a high degree of coordination between cells. In vertebrates, gap junctions comprise connexins and currently 21 connexins are known in humans. The functions of gap junctions are highly diverse and include exchange of metabolites and electrical signals between cells, as well as functions, which are apparently unrelated to intercellular communication. Given the diversity of gap junction physiology, regulation of gap junction activity is complex. The structure of the various connexins is known to some extent; and structural rearrangements and intramolecular interactions are important for regulation of channel function. Intercellular coupling is further regulated by the number and activity of channels present in gap junctional plaques. The number of connexins in cell-cell channels is regulated by controlling transcription, translation, trafficking, and degradation; and all of these processes are under strict control. Once in the membrane, channel activity is determined by the conductive properties of the connexin involved, which can be regulated by voltage and chemical gating, as well as a large number of posttranslational modifications. The aim of the present article is to review our current knowledge on the structure, regulation, function, and pharmacology of gap junctions. This will be supported by examples of how different connexins and their regulation act in concert to achieve appropriate physiological control, and how disturbances of connexin function can lead to disease.
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Affiliation(s)
- Morten Schak Nielsen
- Department of Biomedical Sciences and The Danish National Research Foundation Centre for Cardiac Arrhythmia, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
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144
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Le HT, Sin WC, Lozinsky S, Bechberger J, Vega JL, Guo XQ, Sáez JC, Naus CC. Gap junction intercellular communication mediated by connexin43 in astrocytes is essential for their resistance to oxidative stress. J Biol Chem 2013; 289:1345-54. [PMID: 24302722 DOI: 10.1074/jbc.m113.508390] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Oxidative stress induced by reactive oxygen species (ROS) is associated with various neurological disorders including aging, neurodegenerative diseases, as well as traumatic and ischemic insults. Astrocytes have an important role in the anti-oxidative defense in the brain. The gap junction protein connexin43 (Cx43) forms intercellular channels as well as hemichannels in astrocytes. In the present study, we investigated the contribution of Cx43 to astrocytic death induced by the ROS hydrogen peroxide (H2O2) and the mechanism by which Cx43 exerts its effects. Lack of Cx43 expression or blockage of Cx43 channels resulted in increased ROS-induced astrocytic death, supporting a cell protective effect of functional Cx43 channels. H2O2 transiently increased hemichannel activity, but reduced gap junction intercellular communication (GJIC). GJIC in wild-type astrocytes recovered after 7 h, but was absent in Cx43 knock-out astrocytes. Blockage of Cx43 hemichannels incompletely inhibited H2O2-induced hemichannel activity, indicating the presence of other hemichannel proteins. Panx1, which is predicted to be a major hemichannel contributor in astrocytes, did not appear to have any cell protective effect from H2O2 insults. Our data suggest that GJIC is important for Cx43-mediated ROS resistance. In contrast to hypoxia/reoxygenation, H2O2 treatment decreased the ratio of the hypophosphorylated isoform to total Cx43 level. Cx43 has been reported to promote astrocytic death induced by hypoxia/reoxygenation. We therefore speculate the increase in Cx43 dephosphorylation may account for the facilitation of astrocytic death. Our findings suggest that the role of Cx43 in response to cellular stress is dependent on the activation of signaling pathways leading to alteration of Cx43 phosphorylation states.
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Affiliation(s)
- Hoa T Le
- From the Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, V6T 1Z3 Canada
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145
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Khanna A, Kahle KT, Walcott BP, Gerzanich V, Simard JM. Disruption of ion homeostasis in the neurogliovascular unit underlies the pathogenesis of ischemic cerebral edema. Transl Stroke Res 2013; 5:3-16. [PMID: 24323726 DOI: 10.1007/s12975-013-0307-9] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Revised: 10/22/2013] [Accepted: 11/06/2013] [Indexed: 02/06/2023]
Abstract
Cerebral edema is a major cause of morbidity and mortality following ischemic stroke, but its underlying molecular pathophysiology is incompletely understood. Recent data have revealed the importance of ion flux via channels and transporters expressed in the neurogliovascular unit in the development of ischemia-triggered cytotoxic edema, vasogenic edema, and hemorrhagic conversion. Disruption of homeostatic mechanisms governing cell volume regulation and epithelial/endothelial ion transport due to ischemia-associated energy failure results in the thermodynamically driven re-equilibration of solutes and water across the CSF-blood and blood-brain barriers that ultimately increases the brain's extravascular volume. Additionally, hypoxia, inflammation, and other stress-triggered increases in the functional expression of ion channels and transporters normally expressed at low levels in the neurogliovascular unit cause disruptions in ion homeostasis that contribute to ischemic cerebral edema. Here, we review the pathophysiological significance of several molecular mediators of ion transport expressed in the neurogliovascular unit, including targets of existing FDA-approved drugs, which might be potential nodes for therapeutic intervention.
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146
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Axelsen LN, Calloe K, Holstein-Rathlou NH, Nielsen MS. Managing the complexity of communication: regulation of gap junctions by post-translational modification. Front Pharmacol 2013; 4:130. [PMID: 24155720 PMCID: PMC3804956 DOI: 10.3389/fphar.2013.00130] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Accepted: 09/30/2013] [Indexed: 12/21/2022] Open
Abstract
Gap junctions are comprised of connexins that form cell-to-cell channels which couple neighboring cells to accommodate the exchange of information. The need for communication does, however, change over time and therefore must be tightly controlled. Although the regulation of connexin protein expression by transcription and translation is of great importance, the trafficking, channel activity and degradation are also under tight control. The function of connexins can be regulated by several post translational modifications, which affect numerous parameters; including number of channels, open probability, single channel conductance or selectivity. The most extensively investigated post translational modifications are phosphorylations, which have been documented in all mammalian connexins. Besides phosphorylations, some connexins are known to be ubiquitinated, SUMOylated, nitrosylated, hydroxylated, acetylated, methylated, and γ-carboxyglutamated. The aim of the present review is to summarize our current knowledge of post translational regulation of the connexin family of proteins.
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Affiliation(s)
- Lene N Axelsen
- Department of Biomedical Sciences and The Danish National Research Foundation Centre for Cardiac Arrhythmia, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
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147
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De Bock M, Kerrebrouck M, Wang N, Leybaert L. Neurological manifestations of oculodentodigital dysplasia: a Cx43 channelopathy of the central nervous system? Front Pharmacol 2013; 4:120. [PMID: 24133447 PMCID: PMC3783840 DOI: 10.3389/fphar.2013.00120] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Accepted: 09/02/2013] [Indexed: 12/30/2022] Open
Abstract
The coordination of tissue function is mediated by gap junctions (GJs) that enable direct cell–cell transfer of metabolic and electric signals. GJs are formed by connexins of which Cx43 is most widespread in the human body. In the brain, Cx43 GJs are mostly found in astroglia where they coordinate the propagation of Ca2+ waves, spatial K+ buffering, and distribution of glucose. Beyond its role in direct intercellular communication, Cx43 also forms unapposed, non-junctional hemichannels in the plasma membrane of glial cells. These allow the passage of several neuro- and gliotransmitters that may, combined with downstream paracrine signaling, complement direct GJ communication among glial cells and sustain glial-neuronal signaling. Mutations in the GJA1 gene encoding Cx43 have been identified in a rare, mostly autosomal dominant syndrome called oculodentodigital dysplasia (ODDD). ODDD patients display a pleiotropic phenotype reflected by eye, hand, teeth, and foot abnormalities, as well as craniofacial and bone malformations. Remarkably, neurological symptoms such as dysarthria, neurogenic bladder (manifested as urinary incontinence), spasticity or muscle weakness, ataxia, and epilepsy are other prominent features observed in ODDD patients. Over 10 mutations detected in patients diagnosed with neurological disorders are associated with altered functionality of Cx43 GJs/hemichannels, but the link between ODDD-related abnormal channel activities and neurologic phenotype is still elusive. Here, we present an overview on the nature of the mutants conveying structural and functional changes of Cx43 channels and discuss available evidence for aberrant Cx43 GJ and hemichannel function. In a final step, we examine the possibilities of how channel dysfunction may lead to some of the neurological manifestations of ODDD.
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Affiliation(s)
- Marijke De Bock
- Physiology Group, Department of Basic Medical Sciences, Ghent University Ghent, Belgium
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148
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Liu T, Li M, Zhang Y, Pang Z, Xiao W, Yang Y, Luo K. A role for Innexin2 and Innexin3 proteins from Spodoptera litura in apoptosis. PLoS One 2013; 8:e70456. [PMID: 23936205 PMCID: PMC3728205 DOI: 10.1371/journal.pone.0070456] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Accepted: 06/18/2013] [Indexed: 12/31/2022] Open
Abstract
Gap junctions formed by two hemichannels from two neighboring cells are cell-to-cell communication channels; hemichannels are communication channels between intracellular and extracellular environments. Hemichannels are hexameric proteins formed by connexins, pannexins, innexins and vinnexins. Innexin-hemichannels (innexons) exist in the lepidopteran cell surface, but their component innexins and functions have not been reported. Recent studies by others have demonstrated that hemichannels, connexons and pannexons from vertebrates serve as regulators of apoptosis via inactivating the PI3K/Akt signaling pathway. Here, the apoptogenic properties of innexons are demonstrated using two innexin cDNAs, Spli-inx2 and Spli-inx3, which were isolated from hemocytes of lepidopteran Spodoptera litura. Alignment analysis revealed that these two genes belong to a conserved innexin family, as they contain the insect signature YYQWV motif at the beginning of the second transmembrane domain. Immunofluorescence showed that two fusion proteins, Inx2-V5 and Inx3-V5, were localized predominantly in the cell membrane, cytoplasm and also nuclei. Ectopic expression in Sf9 cells and over-expression of Inx2 and Inx3 in Spli221 cells promoted apoptosis. In the Spli221 cells, apoptotic cells presented remarkable membrane blebbing. This study also showed that Sf9 and Spli221 cells undergo low level apoptosis under normal culture conditions, but not Hi5 cells. In Hi5 stable cell lines, biotinylation was used to isolate surface proteins and confirm Inx2 and Inx3 localization in the cell membrane and also further data showed that Hi5 cells may activate the PI3K signaling pathway via phosphorylating molecular Akt downstream. This result suggests that innexon-promoted apoptosis may be involving the PI3K/Akt signaling pathway. These findings will facilitate further examinations of the apoptotic regulation by the PI3K/Akt signaling pathway and comparative studies of innexons, connexons, pannexons, and vinnexons.
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Affiliation(s)
- Tian Liu
- School of Life Sciences, Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, Yunnan, P. R. China
| | - Ming Li
- School of Life Sciences, Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, Yunnan, P. R. China
| | - Yan Zhang
- School of Life Sciences, Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, Yunnan, P. R. China
| | - Zunyu Pang
- School of Life Sciences, Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, Yunnan, P. R. China
| | - Wei Xiao
- School of Life Sciences, Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, Yunnan, P. R. China
| | - Yang Yang
- School of Life Sciences, Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, Yunnan, P. R. China
| | - Kaijun Luo
- School of Life Sciences, Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, Yunnan, P. R. China
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149
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D'hondt C, Iyyathurai J, Vinken M, Rogiers V, Leybaert L, Himpens B, Bultynck G. Regulation of connexin- and pannexin-based channels by post-translational modifications. Biol Cell 2013; 105:373-98. [PMID: 23718186 DOI: 10.1111/boc.201200096] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Accepted: 05/24/2013] [Indexed: 12/28/2022]
Abstract
Connexin (Cx) and pannexin (Panx) proteins form large conductance channels, which function as regulators of communication between neighbouring cells via gap junctions and/or hemichannels. Intercellular communication is essential to coordinate cellular responses in tissues and organs, thereby fulfilling an essential role in the spreading of signalling, survival and death processes. The functional properties of gap junctions and hemichannels are modulated by different physiological and pathophysiological stimuli. At the molecular level, Cxs and Panxs function as multi-protein channel complexes, regulating their channel localisation and activity. In addition to this, gap junctional channels and hemichannels are modulated by different post-translational modifications (PTMs), including phosphorylation, glycosylation, proteolysis, N-acetylation, S-nitrosylation, ubiquitination, lipidation, hydroxylation, methylation and deamidation. These PTMs influence almost all aspects of communicating junctional channels in normal cell biology and pathophysiology. In this review, we will provide a systematic overview of PTMs of communicating junction proteins and discuss their effects on Cx and Panx-channel activity and localisation.
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Affiliation(s)
- Catheleyne D'hondt
- Laboratory of Molecular and Cellular Signalling, Department Cellular and Molecular Medicine, KU Leuven, Campus Gasthuisberg O/N 1, BE-3000, Leuven, Belgium.
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150
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Kar R, Riquelme MA, Werner S, Jiang JX. Connexin 43 channels protect osteocytes against oxidative stress-induced cell death. J Bone Miner Res 2013; 28:1611-21. [PMID: 23456878 PMCID: PMC3688648 DOI: 10.1002/jbmr.1917] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Revised: 02/11/2012] [Accepted: 02/19/2013] [Indexed: 11/11/2022]
Abstract
The increased osteocyte death by oxidative stress (OS) during aging is a major cause contributing to the impairment of bone quality and bone loss. However, the underlying molecular mechanism is largely unknown. Here, we show that H₂O₂ induced cell death of primary osteocytes and osteocytic MLO-Y4 cells, and also caused dose-dependent decreased expression of gap junction and hemichannel-forming connexin 43 (Cx43). The decrease of Cx43 expression was also demonstrated with the treatment of other oxidants, rotenone and menadione. Antioxidant reversed the effects of oxidants on Cx43 expression and osteocyte cell death. Cx43 protein was also much lower in the osteocytes from 20-month-old as opposed to the 5-week-old or 20-week old mice. Dye transfer assay showed that H₂O₂ reduced the gap junction intercellular communication (GJIC). In contrast to the effect on GJIC, there was a dose-dependent increase of hemichannel function by H₂O₂, which was correlated with the increased cell surface expression of Cx43. Cx43(E2) antibody, an antibody that specifically blocks Cx43 hemichannel activity but not gap junctions, completely blocked dye uptake induced by H₂O₂ and further exacerbated H₂O₂-induced osteocytic cell death. In addition, knockdown of Cx43 expression by small interfering RNA (siRNA) increased the susceptibility of the cells to OS-induced death. Together, our study provides a novel cell protective mechanism mediated by osteocytic Cx43 channels against OS.
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Affiliation(s)
- Rekha Kar
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas
| | - Manuel A. Riquelme
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas
| | - Sherry Werner
- Department of Pathology, University of Texas Health Science Center, San Antonio, Texas
| | - Jean X. Jiang
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas
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