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Beckmann A, Recktenwald J, Ferdinand A, Grißmer A, Meier C. First Responders to Hyperosmotic Stress in Murine Astrocytes: Connexin 43 Gap Junctions Are Subject to an Immediate Ultrastructural Reorganization. BIOLOGY 2021; 10:biology10121307. [PMID: 34943223 PMCID: PMC8698406 DOI: 10.3390/biology10121307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 12/04/2021] [Accepted: 12/06/2021] [Indexed: 11/16/2022]
Abstract
Simple Summary Gap junctions are intercellular channels that provide the means for direct transport of small molecules, ions, and water between connected cells. With these functions, gap junctions are essential for the maintenance of astrocytic homeostasis and of particular importance in the context of pathophysiological disbalances. These include the hyperosmolar hyperglycemic syndrome or the pathology after brain trauma. We demonstrate that short-term hyperosmolarity reduces intercellular communication via gap junctions. These functional changes coincide with the transformation of gap junction ultrastructure as evidenced by freeze-fracture replica immunolabeling and transmission electron microscopy. The hyperosmolarity-induced immediate changes in the ultrastructural assembly of connexons, the protein constituents of gap junction channels, have not been described in astrocytes before and are revealing the coherence of structure and function in gap junctions. Phosphorylation of Connexin 43, the main gap junction protein in astrocytes, at amino acid 368 (Serine) might link the two. Abstract In a short-term model of hyperosmotic stress, primary murine astrocytes were stimulated with a hyperosmolar sucrose solution for five minutes. Astrocytic gap junctions, which are mainly composed of Connexin (Cx) 43, displayed immediate ultrastructural changes, demonstrated by freeze–fracture replica immunogold labeling: their area, perimeter, and distance of intramembrane particles increased, whereas particle numbers per area decreased. Ultrastructural changes were, however, not accompanied by changes in Cx43 mRNA expression. In contrast, transcription of the gap junction regulator zonula occludens (ZO) protein 1 significantly increased, whereas its protein expression was unaffected. Phosphorylation of Serine (S) 368 of the Cx43 C–terminus has previously been associated with gap junction disassembly and reduction in gap junction communication. Hyperosmolar sucrose treatment led to enhanced phosphorylation of Cx43S368 and was accompanied by inhibition of gap junctional intercellular communication, demonstrated by a scrape loading-dye transfer assay. Taken together, Cx43 gap junctions are fast reacting elements in response to hyperosmolar challenges and can therefore be considered as one of the first responders to hyperosmolarity. In this process, phosphorylation of Cx43S368 was associated with disassembly of gap junctions and inhibition of their function. Thus, modulation of the gap junction assembly might represent a target in the treatment of brain edema or trauma.
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Pannese E. Quantitative, structural and molecular changes in neuroglia of aging mammals: A review. Eur J Histochem 2021; 65. [PMID: 34346664 PMCID: PMC8239453 DOI: 10.4081/ejh.2021.3249] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Accepted: 05/27/2021] [Indexed: 01/06/2023] Open
Abstract
The neuroglia of the central and peripheral nervous systems undergo numerous changes during normal aging. Astrocytes become hypertrophic and accumulate intermediate filaments. Oligodendrocytes and Schwann cells undergo alterations that are often accompanied by degenerative changes to the myelin sheath. In microglia, proliferation in response to injury, motility of cell processes, ability to migrate to sites of neural injury, and phagocytic and autophagic capabilities are reduced. In sensory ganglia, the number and extent of gaps between perineuronal satellite cells – that leave the surfaces of sensory ganglion neurons directly exposed to basal lamina – increase significantly. The molecular profiles of neuroglia also change in old age, which, in view of the interactions between neurons and neuroglia, have negative consequences for important physiological processes in the nervous system. Since neuroglia actively participate in numerous nervous system processes, it is likely that not only neurons but also neuroglia will prove to be useful targets for interventions to prevent, reverse or slow the behavioral changes and cognitive decline that often accompany senescence.
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Affiliation(s)
- Ennio Pannese
- Emeritus, Full Professor of Normal Human Anatomy and Neurocytology at the University of Milan.
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Harcha PA, Garcés P, Arredondo C, Fernández G, Sáez JC, van Zundert B. Mast Cell and Astrocyte Hemichannels and Their Role in Alzheimer's Disease, ALS, and Harmful Stress Conditions. Int J Mol Sci 2021; 22:ijms22041924. [PMID: 33672031 PMCID: PMC7919494 DOI: 10.3390/ijms22041924] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2020] [Revised: 02/02/2021] [Accepted: 02/11/2021] [Indexed: 02/07/2023] Open
Abstract
Considered relevant during allergy responses, numerous observations have also identified mast cells (MCs) as critical effectors during the progression and modulation of several neuroinflammatory conditions, including Alzheimer’s disease (AD) and amyotrophic lateral sclerosis (ALS). MC granules contain a plethora of constituents, including growth factors, cytokines, chemokines, and mitogen factors. The release of these bioactive substances from MCs occurs through distinct pathways that are initiated by the activation of specific plasma membrane receptors/channels. Here, we focus on hemichannels (HCs) formed by connexins (Cxs) and pannexins (Panxs) proteins, and we described their contribution to MC degranulation in AD, ALS, and harmful stress conditions. Cx/Panx HCs are also expressed by astrocytes and are likely involved in the release of critical toxic amounts of soluble factors—such as glutamate, adenosine triphosphate (ATP), complement component 3 derivate C3a, tumor necrosis factor (TNFα), apoliprotein E (ApoE), and certain miRNAs—known to play a role in the pathogenesis of AD, ALS, and other neurodegenerative disorders. We propose that blocking HCs on MCs and glial cells offers a promising novel strategy for ameliorating the progression of neurodegenerative diseases by reducing the release of cytokines and other pro-inflammatory compounds.
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Affiliation(s)
- Paloma A. Harcha
- Instituto de Neurociencia, Centro Interdisciplinario de Neurociencia de Valparaíso, Valparaíso 2381850, Chile
- Correspondence: (P.A.H.); (J.C.S.); (B.v.Z.)
| | - Polett Garcés
- Institute of Biomedical Sciences (ICB), Faculty of Medicine & Faculty of Life Sciences, Universidad Andres Bello, Santiago 8370186, Chile; (P.G.); (C.A.); (G.F.)
- CARE Biomedical Research Center, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago 8330005, Chile
| | - Cristian Arredondo
- Institute of Biomedical Sciences (ICB), Faculty of Medicine & Faculty of Life Sciences, Universidad Andres Bello, Santiago 8370186, Chile; (P.G.); (C.A.); (G.F.)
- CARE Biomedical Research Center, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago 8330005, Chile
| | - Germán Fernández
- Institute of Biomedical Sciences (ICB), Faculty of Medicine & Faculty of Life Sciences, Universidad Andres Bello, Santiago 8370186, Chile; (P.G.); (C.A.); (G.F.)
- CARE Biomedical Research Center, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago 8330005, Chile
| | - Juan C. Sáez
- Instituto de Neurociencia, Centro Interdisciplinario de Neurociencia de Valparaíso, Valparaíso 2381850, Chile
- Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago 8331150, Chile
- Correspondence: (P.A.H.); (J.C.S.); (B.v.Z.)
| | - Brigitte van Zundert
- Institute of Biomedical Sciences (ICB), Faculty of Medicine & Faculty of Life Sciences, Universidad Andres Bello, Santiago 8370186, Chile; (P.G.); (C.A.); (G.F.)
- CARE Biomedical Research Center, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago 8330005, Chile
- Department of Neurology, University of Massachusetts Medical School, Worcester, MA 01605, USA
- Correspondence: (P.A.H.); (J.C.S.); (B.v.Z.)
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Sex-related differences in human plasma NAD+/NADH levels depend on age. Biosci Rep 2021; 41:227457. [PMID: 33393613 PMCID: PMC7809543 DOI: 10.1042/bsr20200340] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Revised: 12/22/2020] [Accepted: 12/24/2020] [Indexed: 11/17/2022] Open
Abstract
Nicotinamide adenine dinucleotide (NAD) is a coenzyme in metabolic reactions and cosubstrate in signaling pathways of cells. While the intracellular function of NAD is well described, much less is known about its importance as an extracellular molecule. Moreover, there is only little information about the concentration of extracellular NAD and the ratio between its oxidized (NAD+) and reduced (NADH) form in humans. Therefore, our study aimed at the analysis of total NAD and NAD+/NADH ratio in human plasma depending on sex and age. First, an enzymatic assay was established for detecting NAD+ and NADH in human plasma samples. Then, plasma NAD was analyzed in 205 probands without severe diseases (91 men, 114 women) being 18-83 years old. The total plasma NAD concentration was determined with median 1.34 µM (0.44-2.88 µM) without difference between men and women. Although the amounts of NAD+ and NADH were nearly balanced, women had higher plasma NAD+/NADH ratios than men (median 1.33 vs. 1.09, P<0.001). The sex-related difference in the plasma NAD+/NADH ratio reduces with increasing age, an effect that was more obvious for two parameters of the biological age (skin autofluorescence, brachial-femoral pulse wave velocity (PWV)) than for the chronological age. However, plasma values for total NAD and NAD+/NADH ratio did not generally alter with increasing age. In conclusion, human plasma contains low micromolar concentrations of total NAD with higher NAD+/NADH redox ratios in adult but not older women compared with same-aged men.
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Brancaccio M, Wolfes AC, Ness N. Astrocyte Circadian Timekeeping in Brain Health and Neurodegeneration. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1344:87-110. [PMID: 34773228 DOI: 10.1007/978-3-030-81147-1_6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Marco Brancaccio
- Department of Brain Sciences, Division of Neuroscience, Imperial College London, London, UK.
- UK Dementia Research Institute at Imperial College London, London, UK.
| | - Anne C Wolfes
- Department of Brain Sciences, Division of Neuroscience, Imperial College London, London, UK
- UK Dementia Research Institute at Imperial College London, London, UK
| | - Natalie Ness
- Department of Brain Sciences, Division of Neuroscience, Imperial College London, London, UK
- UK Dementia Research Institute at Imperial College London, London, UK
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Spitale FM, Vicario N, Rosa MD, Tibullo D, Vecchio M, Gulino R, Parenti R. Increased expression of connexin 43 in a mouse model of spinal motoneuronal loss. Aging (Albany NY) 2020; 12:12598-12608. [PMID: 32579130 PMCID: PMC7377853 DOI: 10.18632/aging.103561] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Accepted: 06/05/2020] [Indexed: 12/11/2022]
Abstract
Amyotrophic lateral sclerosis (ALS) is one of the most common motoneuronal disease, characterized by motoneuronal loss and progressive paralysis. Despite research efforts, ALS remains a fatal disease, with a survival of 2-5 years after disease onset. Numerous gene mutations have been correlated with both sporadic (sALS) and familiar forms of the disease, but the pathophysiological mechanisms of ALS onset and progression are still largely uncertain. However, a common profile is emerging in ALS pathological features, including misfolded protein accumulation and a cross-talk between neuroinflammatory and degenerative processes. In particular, astrocytes and microglial cells have been proposed as detrimental influencers of perineuronal microenvironment, and this role may be exerted via gap junctions (GJs)- and hemichannels (HCs)-mediated communications. Herein we investigated the role of the main astroglial GJs-forming connexin, Cx43, in human ALS and the effects of focal spinal cord motoneuronal depletion onto the resident glial cells and Cx43 levels. Our data support the hypothesis that motoneuronal depletion may affect glial activity, which in turn results in reactive Cx43 expression, further promoting neuronal suffering and degeneration.
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Affiliation(s)
- Federica Maria Spitale
- Department of Biomedical and Biotechnological Sciences, Section of Physiology, University of Catania, Catania 95123, Italy
| | - Nunzio Vicario
- Department of Biomedical and Biotechnological Sciences, Section of Physiology, University of Catania, Catania 95123, Italy
| | - Michelino Di Rosa
- Department of Biomedical and Biotechnological Sciences, Section of Anatomy, Histology and Movement Sciences, University of Catania, Catania 95123, Italy
| | - Daniele Tibullo
- Department of Biomedical and Biotechnological Sciences, Section of Biochemistry, University of Catania, Catania 95123, Italy
| | - Michele Vecchio
- Department of Biomedical and Biotechnological Sciences, Section of Pharmacology, University of Catania, Catania 95123, Italy.,Rehabilitation Unit, "AOU Policlinico Vittorio Emanuele", University of Catania, Catania 95123, Italy
| | - Rosario Gulino
- Department of Biomedical and Biotechnological Sciences, Section of Physiology, University of Catania, Catania 95123, Italy
| | - Rosalba Parenti
- Department of Biomedical and Biotechnological Sciences, Section of Physiology, University of Catania, Catania 95123, Italy
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Vicario N, Turnaturi R, Spitale FM, Torrisi F, Zappalà A, Gulino R, Pasquinucci L, Chiechio S, Parenti C, Parenti R. Intercellular communication and ion channels in neuropathic pain chronicization. Inflamm Res 2020; 69:841-850. [PMID: 32533221 DOI: 10.1007/s00011-020-01363-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2020] [Revised: 05/13/2020] [Accepted: 05/17/2020] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Neuropathic pain is caused by primary lesion or dysfunction of either peripheral or central nervous system. Due to its complex pathogenesis, often related to a number of comorbidities, such as cancer, neurodegenerative and neurovascular diseases, neuropathic pain still represents an unmet clinical need, lacking long-term effective treatment and complex case-by-case approach. AIM AND METHODS We analyzed the recent literature on the role of selective voltage-sensitive sodium, calcium and potassium permeable channels and non-selective gap junctions (GJs) and hemichannels (HCs) in establishing and maintaining chronic neuropathic conditions. We finally focussed our review on the role of extracellular microenvironment modifications induced by resident glial cells and on the recent advances in cell-to-cell and cell-to-extracellular environment communication in chronic neuropathies. CONCLUSION In this review, we provide an update on the current knowledge of neuropathy chronicization processes with a focus on both neuronal and glial ion channels, as well as on channel-mediated intercellular communication.
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Affiliation(s)
- Nunzio Vicario
- Section of Physiology, Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy
| | - Rita Turnaturi
- Section of Medicinal Chemistry, Department of Drug Sciences, University of Catania, Catania, Italy
| | - Federica Maria Spitale
- Section of Physiology, Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy
| | - Filippo Torrisi
- Section of Physiology, Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy
| | - Agata Zappalà
- Section of Physiology, Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy
| | - Rosario Gulino
- Section of Physiology, Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy
| | - Lorella Pasquinucci
- Section of Medicinal Chemistry, Department of Drug Sciences, University of Catania, Catania, Italy
| | - Santina Chiechio
- Section of Pharmacology, Department of Drug Sciences, University of Catania, Catania, Italy
- Oasi Research Institute IRCCS, Troina, Italy
| | - Carmela Parenti
- Section of Pharmacology, Department of Drug Sciences, University of Catania, Catania, Italy.
| | - Rosalba Parenti
- Section of Physiology, Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy.
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Pestana F, Edwards-Faret G, Belgard TG, Martirosyan A, Holt MG. No Longer Underappreciated: The Emerging Concept of Astrocyte Heterogeneity in Neuroscience. Brain Sci 2020; 10:brainsci10030168. [PMID: 32183137 PMCID: PMC7139801 DOI: 10.3390/brainsci10030168] [Citation(s) in RCA: 59] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 03/02/2020] [Accepted: 03/05/2020] [Indexed: 12/18/2022] Open
Abstract
Astrocytes are ubiquitous in the central nervous system (CNS). These cells possess thousands of individual processes, which extend out into the neuropil, interacting with neurons, other glia and blood vessels. Paralleling the wide diversity of their interactions, astrocytes have been reported to play key roles in supporting CNS structure, metabolism, blood-brain-barrier formation and control of vascular blood flow, axon guidance, synapse formation and modulation of synaptic transmission. Traditionally, astrocytes have been studied as a homogenous group of cells. However, recent studies have uncovered a surprising degree of heterogeneity in their development and function, in both the healthy and diseased brain. A better understanding of astrocyte heterogeneity is urgently needed to understand normal brain function, as well as the role of astrocytes in response to injury and disease.
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Affiliation(s)
- Francisco Pestana
- Laboratory of Glia Biology, VIB-KU Leuven Center for Brain and Disease Research, 3000 Leuven, Belgium;
| | - Gabriela Edwards-Faret
- Laboratory of Neuronal Wiring, VIB-KU Leuven Center for Brain and Disease Research, 3000 Leuven, Belgium;
- Life & Medical Sciences (LIMES) Institute, Faculty of Mathematics and Natural Sciences, University of Bonn, 53115 Bonn, Germany
| | | | - Araks Martirosyan
- Laboratory of Glia Biology, VIB-KU Leuven Center for Brain and Disease Research, 3000 Leuven, Belgium;
- Correspondence: (A.M.); (M.G.H.); Tel.: +32-16-37-31-27 (M.G.H.)
| | - Matthew G. Holt
- Laboratory of Glia Biology, VIB-KU Leuven Center for Brain and Disease Research, 3000 Leuven, Belgium;
- Leuven Brain Institute, KU Leuven, 3000 Leuven, Belgium
- Correspondence: (A.M.); (M.G.H.); Tel.: +32-16-37-31-27 (M.G.H.)
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Kolenicova D, Tureckova J, Pukajova B, Harantova L, Kriska J, Kirdajova D, Vorisek I, Kamenicka M, Valihrach L, Androvic P, Kubista M, Vargova L, Anderova M. High potassium exposure reveals the altered ability of astrocytes to regulate their volume in the aged hippocampus of GFAP/EGFP mice. Neurobiol Aging 2019; 86:162-181. [PMID: 31757575 DOI: 10.1016/j.neurobiolaging.2019.10.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 09/25/2019] [Accepted: 10/16/2019] [Indexed: 10/25/2022]
Abstract
In this study, we focused on age-related changes in astrocyte functioning, predominantly on the ability of astrocytes to regulate their volume in response to a pathological stimulus, namely extracellular 50 mM K+ concentration. The aim of our project was to identify changes in the expression and function of transport proteins in the astrocytic membrane and properties of the extracellular space, triggered by aging. We used three-dimensional confocal morphometry, gene expression profiling, immunohistochemical analysis, and diffusion measurement in the hippocampal slices from 3-, 9-, 12-, and 18-month-old mice, in which astrocytes are visualized by enhanced green fluorescent protein under the control of the promoter for human glial fibrillary acidic protein. Combining a pharmacological approach and the quantification of astrocyte volume changes evoked by hyperkalemia, we found that marked diversity in the extent of astrocyte swelling in the hippocampus during aging is due to the gradually declining participation of Na+-K+-Cl- transporters, glutamate transporters (glutamate aspartate transporter and glutamate transporter 1), and volume-regulated anion channels. Interestingly, there was a redistribution of Na+-K+-Cl- cotransporter and glutamate transporters from astrocytic soma to processes. In addition, immunohistochemical analysis confirmed an age-dependent decrease in the content of Na+-K+-Cl- cotransporter in astrocytes. The overall extracellular volume changes revealed a similar age-dependent diversity during hyperkalemia as observed in astrocytes. In addition, the recovery of the extracellular space was markedly impaired in aged animals.
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Affiliation(s)
- Denisa Kolenicova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic; 2nd Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Jana Tureckova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Barbora Pukajova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Lenka Harantova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Jan Kriska
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic; 2nd Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Denisa Kirdajova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic; 2nd Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Ivan Vorisek
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Monika Kamenicka
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic; 2nd Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Lukas Valihrach
- Laboratory of Gene Expression, Institute of Biotechnology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Peter Androvic
- Laboratory of Gene Expression, Institute of Biotechnology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Mikael Kubista
- Laboratory of Gene Expression, Institute of Biotechnology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Lydia Vargova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic; 2nd Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Miroslava Anderova
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic; 2nd Faculty of Medicine, Charles University, Prague, Czech Republic.
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Wang M, Chen JJ, Huang Q, Su X, Yu YC, Liu LY. Connexin43 in neonatal excitatory neurons is important for short-term motor learning. Brain Res 2019; 1720:146287. [PMID: 31194949 DOI: 10.1016/j.brainres.2019.06.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Revised: 05/29/2019] [Accepted: 06/09/2019] [Indexed: 11/26/2022]
Abstract
In the neocortex, gap junctions are expressed at very early developmental stages, and they are involved in many processes such as neurogenesis, neuronal migration and synapse formation. Connexin43 (Cx43), a gap junction protein, has been found to be abundantly expressed in radial glial cells, excitatory neurons and astrocytes. Although accumulating evidence suggests that Cx43-mediated gap-junctional coupling between astrocytes plays an important role in the central nervous system, the function of Cx43 in early excitatory neurons remains elusive. To investigate the impact of Cx43 deficiency in excitatory neurons at early postnatal stages, we conditionally knocked out Cx43 in excitatory neurons under the Emx1 promoter by tamoxifen induction. We found that deletion of Cx43 around birth did not impair the laminar distribution of excitatory neurons in the neocortex. Moreover, mice with Cx43 deletion during the early postnatal stages had normal anxiety-like behaviors, depression-related behaviors, learning and memory-associated behaviors at adolescent stages. However, Cx43 conditional knockout mice exhibited impaired motor-learning behavior. These results suggested that Cx43 expression in excitatory neurons at early postnatal stages contributes to short-term motor learning capacity.
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Affiliation(s)
- Min Wang
- State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Institutes of Brain Science, Fudan University, Shanghai 200032, China
| | - Jing-Jing Chen
- State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Institutes of Brain Science, Fudan University, Shanghai 200032, China
| | - Qian Huang
- State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Institutes of Brain Science, Fudan University, Shanghai 200032, China
| | - Xin Su
- State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Institutes of Brain Science, Fudan University, Shanghai 200032, China
| | - Yong-Chun Yu
- State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Institutes of Brain Science, Fudan University, Shanghai 200032, China
| | - Lin-Yun Liu
- State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Institutes of Brain Science, Fudan University, Shanghai 200032, China.
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Bronzuoli MR, Facchinetti R, Valenza M, Cassano T, Steardo L, Scuderi C. Astrocyte Function Is Affected by Aging and Not Alzheimer's Disease: A Preliminary Investigation in Hippocampi of 3xTg-AD Mice. Front Pharmacol 2019; 10:644. [PMID: 31244658 PMCID: PMC6562169 DOI: 10.3389/fphar.2019.00644] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 05/17/2019] [Indexed: 01/12/2023] Open
Abstract
Old age is a risk factor for Alzheimer's disease (AD), which is characterized by hippocampal impairment together with substantial changes in glial cell functions. Are these alterations due to the disease progression or are they a consequence of aging? To start addressing this issue, we studied the expression of specific astrocytic and microglial structural and functional proteins in a validated transgenic model of AD (3×Tg-AD). These mice develop both amyloid plaques and neurofibrillary tangles, and initial signs of the AD-like pathology have been documented as early as three months of age. We compared male 3×Tg-AD mice at 6 and 12 months of age with their wild-type age-matched counterparts. We also investigated neurons by examining the expression of both the microtubule-associated protein 2 (MAP2), a neuronal structural protein, and the brain-derived neurotrophic factor (BDNF). The latter is indeed a crucial indicator for synaptic plasticity and neurogenesis/neurodegeneration. Our results show that astrocytes are more susceptible to aging than microglia, regardless of mouse genotype. Moreover, we discovered significant age-dependent alterations in the expression of proteins responsible for astrocyte-astrocyte and astrocyte-neuron communication, as well as a significant age-dependent decline in BDNF expression. Our data promote further research on the unexplored role of astroglia in both physiological and pathological aging.
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Affiliation(s)
- Maria Rosanna Bronzuoli
- Department of Physiology and Pharmacology "V. Erspamer," Sapienza University of Rome, Rome, Italy
| | - Roberta Facchinetti
- Department of Physiology and Pharmacology "V. Erspamer," Sapienza University of Rome, Rome, Italy
| | - Marta Valenza
- Department of Physiology and Pharmacology "V. Erspamer," Sapienza University of Rome, Rome, Italy.,Epitech Group SpA, Saccolongo, Italy
| | - Tommaso Cassano
- Department of Clinical and Experimental Medicine, University of Foggia, Foggia, Italy
| | - Luca Steardo
- Department of Physiology and Pharmacology "V. Erspamer," Sapienza University of Rome, Rome, Italy
| | - Caterina Scuderi
- Department of Physiology and Pharmacology "V. Erspamer," Sapienza University of Rome, Rome, Italy
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A Computational Model of the Escape Response Latency in the Giant Fiber System of Drosophila melanogaster. eNeuro 2019; 6:eN-NWR-0423-18. [PMID: 31001574 PMCID: PMC6469880 DOI: 10.1523/eneuro.0423-18.2019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 02/22/2019] [Accepted: 03/11/2019] [Indexed: 11/29/2022] Open
Abstract
The giant fiber system (GFS) is a multi-component neuronal pathway mediating rapid escape response in the adult fruit-fly Drosophila melanogaster, usually in the face of a threatening visual stimulus. Two branches of the circuit promote the response by stimulating an escape jump followed by flight initiation. A recent work demonstrated an age-associated decline in the speed of signal propagation through the circuit, measured as the stimulus-to-muscle depolarization response latency. The decline is likely due to the diminishing number of inter-neuronal gap junctions in the GFS of ageing flies. In this work, we presented a realistic conductance-based, computational model of the GFS that recapitulates the experimental results and identifies some of the critical anatomical and physiological components governing the circuit’s response latency. According to our model, anatomical properties of the GFS neurons have a stronger impact on the transmission than neuronal membrane conductance densities. The model provides testable predictions for the effect of experimental interventions on the circuit’s performance in young and ageing flies.
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Susceptibility of the cerebral cortex to spreading depolarization in neurological disease states: The impact of aging. Neurochem Int 2018; 127:125-136. [PMID: 30336178 DOI: 10.1016/j.neuint.2018.10.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2018] [Revised: 10/10/2018] [Accepted: 10/13/2018] [Indexed: 12/17/2022]
Abstract
Secondary injury following acute brain insults significantly contributes to poorer neurological outcome. The spontaneous, recurrent occurrence of spreading depolarization events (SD) has been recognized as a potent secondary injury mechanism in subarachnoid hemorrhage, malignant ischemic stroke and traumatic brain injury. In addition, SD is the underlying mechanism of the aura symptoms of migraineurs. The susceptibility of the nervous tissue to SD is subject to the metabolic status of the tissue, the ionic composition of the extracellular space, and the functional status of ion pumps, voltage-gated and other cation channels, glutamate receptors and excitatory amino acid transporters. All these mechanisms tune the excitability of the nervous tissue. Aging has also been found to alter SD susceptibility, which appears to be highest at young adulthood, and decline over the aging process. The lower susceptibility of the cerebral gray matter to SD in the old brain may be caused by the age-related impairment of mechanisms implicated in ion translocations between the intra- and extracellular compartments, glutamate signaling and surplus potassium and glutamate clearance. Even though the aging nervous tissue is thus less able to sustain SD, the consequences of SD recurrence in the old brain have proven to be graver, possibly leading to accelerated lesion maturation. Taken that recurrent SDs may pose an increased burden in the aging injured brain, the benefit of therapeutic approaches to restrict SD generation and propagation may be particularly relevant for elderly patients.
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Yi C, Teillon J, Koulakoff A, Berry H, Giaume C. Monitoring gap junctional communication in astrocytes from acute adult mouse brain slices using the gap-FRAP technique. J Neurosci Methods 2018; 303:103-113. [PMID: 29551292 DOI: 10.1016/j.jneumeth.2018.03.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Revised: 03/08/2018] [Accepted: 03/08/2018] [Indexed: 01/14/2023]
Abstract
Intercellular communication through gap junction channels plays a key role in cellular homeostasis and in synchronizing physiological functions, a feature that is modified in number of pathological situations. In the brain, astrocytes are the cell population that expresses the highest amount of gap junction proteins, named connexins. Several techniques have been used to assess the level of gap junctional communication in astrocytes, but so far they remain very difficult to apply in adult brain tissue. Here, using specific loading of astrocytes with sulforhodamine 101, we adapted the gap-FRAP (Fluorescence Recovery After Photobleaching) to acute hippocampal slices from 9 month-old adult mice. We show that gap junctional communication monitored in astrocytes with this technique was inhibited either by pharmacological treatment with a gap junctional blocker or in mice lacking the two main astroglial connexins, while a partial inhibition was measured when only one connexin was knocked-out. We validate this approach using a mathematical model of sulforhodamine 101 diffusion in an elementary astroglial network and a quantitative analysis of the exponential fits to the fluorescence recovery curves. Consequently, we consider that the adaptation of the gap-FRAP technique to acute brain slices from adult mice provides an easy going and valuable approach that allows overpassing this age-dependent obstacle and will facilitate the investigation of gap junctional communication in adult healthy or pathological brain.
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Affiliation(s)
- Chenju Yi
- Collège de France, Center for Interdisciplinary Research in Biology (CIRB), Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7241, Institut National de la Santé et de la Recherche Médicale U1050, 75231 Paris Cedex 05, France; University Pierre et Marie Curie, ED, N°158, 75005 Paris, France; MEMOLIFE Laboratory of Excellence and Paris Science Lettre Research University, 75005 Paris, France
| | - Jérémy Teillon
- Collège de France, Center for Interdisciplinary Research in Biology (CIRB), Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7241, Institut National de la Santé et de la Recherche Médicale U1050, 75231 Paris Cedex 05, France; University Pierre et Marie Curie, ED, N°158, 75005 Paris, France; MEMOLIFE Laboratory of Excellence and Paris Science Lettre Research University, 75005 Paris, France
| | - Annette Koulakoff
- Collège de France, Center for Interdisciplinary Research in Biology (CIRB), Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7241, Institut National de la Santé et de la Recherche Médicale U1050, 75231 Paris Cedex 05, France; University Pierre et Marie Curie, ED, N°158, 75005 Paris, France; MEMOLIFE Laboratory of Excellence and Paris Science Lettre Research University, 75005 Paris, France
| | - Hugues Berry
- INRIA, 69603 Villeurbanne, France; University of Lyon, LIRIS UMR5205, 69622 Villeurbanne, France
| | - Christian Giaume
- Collège de France, Center for Interdisciplinary Research in Biology (CIRB), Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7241, Institut National de la Santé et de la Recherche Médicale U1050, 75231 Paris Cedex 05, France; University Pierre et Marie Curie, ED, N°158, 75005 Paris, France; MEMOLIFE Laboratory of Excellence and Paris Science Lettre Research University, 75005 Paris, France.
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Augustin H, McGourty K, Allen MJ, Madem SK, Adcott J, Kerr F, Wong CT, Vincent A, Godenschwege T, Boucrot E, Partridge L. Reduced insulin signaling maintains electrical transmission in a neural circuit in aging flies. PLoS Biol 2017; 15:e2001655. [PMID: 28902870 PMCID: PMC5597081 DOI: 10.1371/journal.pbio.2001655] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Accepted: 08/04/2017] [Indexed: 12/11/2022] Open
Abstract
Lowered insulin/insulin-like growth factor (IGF) signaling (IIS) can extend healthy lifespan in worms, flies, and mice, but it can also have adverse effects (the “insulin paradox”). Chronic, moderately lowered IIS rescues age-related decline in neurotransmission through the Drosophila giant fiber system (GFS), a simple escape response neuronal circuit, by increasing targeting of the gap junctional protein innexin shaking-B to gap junctions (GJs). Endosomal recycling of GJs was also stimulated in cultured human cells when IIS was reduced. Furthermore, increasing the activity of the recycling small guanosine triphosphatases (GTPases) Rab4 or Rab11 was sufficient to maintain GJs upon elevated IIS in cultured human cells and in flies, and to rescue age-related loss of GJs and of GFS function. Lowered IIS thus elevates endosomal recycling of GJs in neurons and other cell types, pointing to a cellular mechanism for therapeutic intervention into aging-related neuronal disorders. Insulin and insulin-like growth factors play an important role in the nervous system development and function. Reduced insulin signaling, however, can improve symptoms of neurodegenerative diseases in different model organisms and protect against age-associated decline in neuronal function extending lifespan. Here, we analyze the effects of genetically attenuated insulin signaling on the escape response pathway in the fruit fly Drosophila melanogaster. This simple neuronal circuit is dominated by electrical synapses composed of the gap junctional shaking-B protein, which allows for the transfer of electrical impulses between cells. Transmission through the circuit is known to slow down with age. We show that this functional decline is prevented by systemic or circuit-specific suppression of insulin signaling due to the preservation of the number of gap junctional proteins in aging animals. Our experiments in a human cell culture system reveal increased membrane targeting of gap junctional proteins via small proteins Rab4 and Rab11 under reduced insulin conditions. We also find that increasing the level of these recycling-mediating proteins in flies preserves the escape response circuit output in old flies and suggests ways of improving the function of neuronal circuits dominated by electrical synapses during aging.
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Affiliation(s)
- Hrvoje Augustin
- Max Planck Institute for Biology of Aging, Köln, Germany
- Institute of Healthy Aging, and Genetics, Evolution, and Environment, University College London, London, United Kingdom
| | - Kieran McGourty
- Department of Structural and Molecular Biology, London, United Kingdom
| | - Marcus J. Allen
- School of Biosciences, University of Kent, Canterbury, Kent, United Kingdom
| | - Sirisha Kudumala Madem
- Department of Biological Sciences, Florida Atlantic University, Jupiter, Florida, United States of America
| | - Jennifer Adcott
- Max Planck Institute for Biology of Aging, Köln, Germany
- Institute of Healthy Aging, and Genetics, Evolution, and Environment, University College London, London, United Kingdom
| | - Fiona Kerr
- Max Planck Institute for Biology of Aging, Köln, Germany
- Institute of Healthy Aging, and Genetics, Evolution, and Environment, University College London, London, United Kingdom
| | - Chi Tung Wong
- Max Planck Institute for Biology of Aging, Köln, Germany
| | - Alec Vincent
- Max Planck Institute for Biology of Aging, Köln, Germany
| | - Tanja Godenschwege
- Department of Biological Sciences, Florida Atlantic University, Jupiter, Florida, United States of America
| | - Emmanuel Boucrot
- Department of Structural and Molecular Biology, London, United Kingdom
| | - Linda Partridge
- Max Planck Institute for Biology of Aging, Köln, Germany
- Institute of Healthy Aging, and Genetics, Evolution, and Environment, University College London, London, United Kingdom
- * E-mail:
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16
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Wilhelm I, Nyúl-Tóth Á, Kozma M, Farkas AE, Krizbai IA. Role of pattern recognition receptors of the neurovascular unit in inflamm-aging. Am J Physiol Heart Circ Physiol 2017; 313:H1000-H1012. [PMID: 28801521 DOI: 10.1152/ajpheart.00106.2017] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 08/09/2017] [Accepted: 08/09/2017] [Indexed: 01/18/2023]
Abstract
Aging is associated with chronic inflammation partly mediated by increased levels of damage-associated molecular patterns, which activate pattern recognition receptors (PRRs) of the innate immune system. Furthermore, many aging-related disorders are associated with inflammation. PRRs, such as Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-like receptors (NLRs), are expressed not only in cells of the innate immune system but also in other cells, including cells of the neurovascular unit and cerebral vasculature forming the blood-brain barrier. In this review, we summarize our present knowledge about the relationship between activation of PRRs expressed by cells of the neurovascular unit-blood-brain barrier, chronic inflammation, and aging-related pathologies of the brain. The most important damage-associated molecular pattern-sensing PRRs in the brain are TLR2, TLR4, and NLR family pyrin domain-containing protein-1 and pyrin domain-containing protein-3, which are activated during physiological and pathological aging in microglia, neurons, astrocytes, and possibly endothelial cells and pericytes.
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Affiliation(s)
- Imola Wilhelm
- Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary; and .,Institute of Life Sciences, Vasile Goldiş Western University of Arad, Arad, Romania
| | - Ádám Nyúl-Tóth
- Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary; and
| | - Mihály Kozma
- Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary; and
| | - Attila E Farkas
- Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary; and
| | - István A Krizbai
- Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary; and.,Institute of Life Sciences, Vasile Goldiş Western University of Arad, Arad, Romania
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17
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Yi C, Ezan P, Fernández P, Schmitt J, Sáez JC, Giaume C, Koulakoff A. Inhibition of glial hemichannels by boldine treatment reduces neuronal suffering in a murine model of Alzheimer's disease. Glia 2017; 65:1607-1625. [PMID: 28703353 DOI: 10.1002/glia.23182] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 05/04/2017] [Accepted: 05/30/2017] [Indexed: 01/06/2023]
Abstract
The contribution of reactive gliosis to the pathological phenotype of Alzheimer's disease (AD) opened the way for therapeutic strategies targeting glial cells instead of neurons. In such context, connexin hemichannels were proposed recently as potential targets since neuronal suffering is alleviated when connexin expression is genetically suppressed in astrocytes of a murine model of AD. Here, we show that boldine, an alkaloid from the boldo tree, inhibited hemichannel activity in astrocytes and microglia without affecting gap junctional communication in culture and acute hippocampal slices. Long-term oral administration of boldine in AD mice prevented the increase in glial hemichannel activity, astrocytic Ca2+ signal, ATP and glutamate release and alleviated hippocampal neuronal suffering. These findings highlight the important pathological role of hemichannels in AD mice. The neuroprotective effect of boldine treatment might provide the basis for future pharmacological strategies that target glial hemichannels to reduce neuronal damage in neurodegenerative diseases.
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Affiliation(s)
- Chenju Yi
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, PSL Research University, Paris, 75005, France
| | - Pascal Ezan
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, PSL Research University, Paris, 75005, France
| | - Paola Fernández
- Departamento de Fisiología, Pontificia Universidad Católica de Chile, Santiago, Chile.,Centro Interdisciplinario de Neurociencias de Valparaíso, Valparaíso, Chile
| | - Julien Schmitt
- Sorbonne Universités, UPMC Univ Paris 06, INSERM, CNRS, Neurosciences Paris Seine, Institut de Biologie Paris Seine (NPS-IBPS), Cerebellum Navigation and Memory team (CeZaMe), Paris, 75005, France
| | - Juan C Sáez
- Departamento de Fisiología, Pontificia Universidad Católica de Chile, Santiago, Chile.,Centro Interdisciplinario de Neurociencias de Valparaíso, Valparaíso, Chile
| | - Christian Giaume
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, PSL Research University, Paris, 75005, France
| | - Annette Koulakoff
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, PSL Research University, Paris, 75005, France
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18
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Cai W, Zhang K, Li P, Zhu L, Xu J, Yang B, Hu X, Lu Z, Chen J. Dysfunction of the neurovascular unit in ischemic stroke and neurodegenerative diseases: An aging effect. Ageing Res Rev 2017; 34:77-87. [PMID: 27697546 PMCID: PMC5384332 DOI: 10.1016/j.arr.2016.09.006] [Citation(s) in RCA: 177] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Revised: 08/15/2016] [Accepted: 09/26/2016] [Indexed: 12/23/2022]
Abstract
Current understanding on the mechanisms of brain injury and neurodegeneration highlights an appreciation of multicellular interactions within the neurovascular unit (NVU), which include the evolution of blood-brain barrier (BBB) damage, neuronal cell death or degeneration, glial reaction, and immune cell infiltration. Aging is an important factor that influences the integrity of the NVU. The age-related physiological or pathological changes in the cellular components of the NVU have been shown to increase the vulnerability of the NVU to ischemia/reperfusion injury or neurodegeneration, and to result in deteriorated brain damage. This review describes the impacts of aging on each NVU component and discusses the mechanisms by which aging increases NVU sensitivity to stroke and neurodegenerative diseases. Prophylactic or therapeutic perspectives that may delay or diminish aging and thus prevent the incidence of these neurological disorders will also be reviewed.
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Affiliation(s)
- Wei Cai
- Geriatric Research, Education and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA; Department of Neurology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510630, China; Pittsburgh Institute of Brain Disorders and Recovery, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Kai Zhang
- Geriatric Research, Education and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA; Pittsburgh Institute of Brain Disorders and Recovery, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Peiying Li
- Department of Anesthesiology, Renji Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200127, China; Pittsburgh Institute of Brain Disorders and Recovery, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Ling Zhu
- Geriatric Research, Education and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA; Department of Anesthesiology, Renji Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200127, China; Pittsburgh Institute of Brain Disorders and Recovery, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Jing Xu
- Geriatric Research, Education and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA; Pittsburgh Institute of Brain Disorders and Recovery, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Boyu Yang
- Geriatric Research, Education and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA; Pittsburgh Institute of Brain Disorders and Recovery, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Xiaoming Hu
- Geriatric Research, Education and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA; Pittsburgh Institute of Brain Disorders and Recovery, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Zhengqi Lu
- Department of Neurology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510630, China.
| | - Jun Chen
- Geriatric Research, Education and Clinical Center, Veterans Affairs Pittsburgh Health Care System, Pittsburgh, PA 15261, USA; Pittsburgh Institute of Brain Disorders and Recovery, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
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Astroglial connexin43 contributes to neuronal suffering in a mouse model of Alzheimer's disease. Cell Death Differ 2016; 23:1691-701. [PMID: 27391799 DOI: 10.1038/cdd.2016.63] [Citation(s) in RCA: 86] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Revised: 05/19/2016] [Accepted: 05/25/2016] [Indexed: 01/15/2023] Open
Abstract
In Alzheimer's disease (AD), astrocyte properties are modified but their involvement in this pathology is only beginning to be appreciated. The expression of connexins, proteins forming gap junction channels and hemichannels, is increased in astrocytes contacting amyloid plaques in brains of AD patients and APP/PS1 mice. The consequences on their channel functions was investigated in a murine model of familial AD, the APPswe/PS1dE9 mice. Whereas gap junctional communication was not affected, we revealed that hemichannels were activated in astrocytes of acute hippocampal slices containing Aβ plaques. Such hemichannel activity was detected in all astrocytes, whatever their distance from amyloid plaques, but with an enhanced activity in the reactive astrocytes contacting amyloid plaques. Connexin43 was the main hemichannel contributor, however, a minor pannexin1 component was also identified in the subpopulation of reactive astrocytes in direct contact with plaques. Distinct regulatory pathways are involved in connexin and pannexin hemichannel activation. Inflammation triggered pannexin hemichannel activity, whereas connexin43 hemichannels were activated by the increase in resting calcium level of astrocytes. Importantly, hemichannel activation led to the release of ATP and glutamate that contributed to maintain a high calcium level in astrocytes placing them in the center of a vicious circle. The astroglial targeted connexin43 gene knocking-out in APPswe/PS1dE9 mice allowed to diminish gliotransmitter release and to alleviate neuronal damages, reducing oxidative stress and neuritic dystrophies in hippocampal neurons associated to plaques. Altogether, these data highlight the importance of astroglial hemichannels in AD and suggest that blocking astroglial hemichannel activity in astrocytes could represent an alternative therapeutic strategy in AD.
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20
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Almad AA, Doreswamy A, Gross SK, Richard JP, Huo Y, Haughey N, Maragakis NJ. Connexin 43 in astrocytes contributes to motor neuron toxicity in amyotrophic lateral sclerosis. Glia 2016; 64:1154-69. [PMID: 27083773 DOI: 10.1002/glia.22989] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Revised: 03/09/2016] [Accepted: 03/30/2016] [Indexed: 11/09/2022]
Abstract
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive loss of motor neurons in the CNS. Astrocytes play a critical role in disease progression of ALS. Astrocytes are interconnected through a family of gap junction proteins known as connexins (Cx). Cx43 is a major astrocyte connexin conducting crucial homeostatic functions in the CNS. Under pathological conditions, connexin expression and functions are altered. Here we report that an abnormal increase in Cx43 expression serves as one of the mechanisms for astrocyte-mediated toxicity in ALS. We observed a progressive increase in Cx43 expression in the SOD1(G93A) mouse model of ALS during the disease course. Notably, this increase in Cx43 was also detected in the motor cortex and spinal cord of ALS patients. Astrocytes isolated from SOD1(G93A) mice as well as human induced pluripotent stem cell (iPSC)-derived astrocytes showed an increase in Cx43 protein, which was found to be an endogenous phenomenon independent of neuronal co-culture. Increased Cx43 expression led to important functional consequences when tested in SOD1(G93A) astrocytes when compared to control astrocytes over-expressing wild-type SOD1 (SOD1(WT) ). We observed SOD1(G93A) astrocytes exhibited enhanced gap junction coupling, increased hemichannel-mediated activity, and elevated intracellular calcium levels. Finally, we tested the impact of increased expression of Cx43 on MN survival and observed that use of both a pan Cx43 blocker and Cx43 hemichannel blocker conferred neuroprotection to MNs cultured with SOD1(G93A) astrocytes. These novel findings show a previously unrecognized role of Cx43 in ALS-related motor neuron loss. GLIA 2016;64:1154-1169.
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Affiliation(s)
- Akshata A Almad
- Department of Neurology, Johns Hopkins University, School of Medicine, Baltimore, Maryland
| | - Arpitha Doreswamy
- Department of Neurology, Johns Hopkins University, School of Medicine, Baltimore, Maryland
| | - Sarah K Gross
- Department of Neurology, Johns Hopkins University, School of Medicine, Baltimore, Maryland
| | - Jean-Philippe Richard
- Department of Neurology, Johns Hopkins University, School of Medicine, Baltimore, Maryland
| | - Yuqing Huo
- Department of Neurology, Johns Hopkins University, School of Medicine, Baltimore, Maryland
| | - Norman Haughey
- Department of Neurology, Johns Hopkins University, School of Medicine, Baltimore, Maryland
| | - Nicholas J Maragakis
- Department of Neurology, Johns Hopkins University, School of Medicine, Baltimore, Maryland
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21
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Freitas-Andrade M, Naus CC. Astrocytes in neuroprotection and neurodegeneration: The role of connexin43 and pannexin1. Neuroscience 2015; 323:207-21. [PMID: 25913636 DOI: 10.1016/j.neuroscience.2015.04.035] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Revised: 04/13/2015] [Accepted: 04/15/2015] [Indexed: 12/26/2022]
Abstract
The World Health Organization has predicted that by 2040 neurodegenerative diseases will overtake cancer to become the world's second leading cause of death after cardiovascular disease. This has sparked the development of several European and American brain research initiatives focusing on elucidating the underlying cellular and molecular mechanisms of neurodegenerative diseases. Connexin (Cx) and pannexin (Panx) membrane channel proteins are conduits through which neuronal, glial, and vascular tissues interact. In the brain, this interaction is highly critical for homeostasis and brain repair after injury. Understanding the molecular mechanisms by which these membrane channels function, in health and disease, might be particularly influential in establishing conceptual frameworks to develop new therapeutics against Cx and Panx channels. This review focuses on current insights and emerging concepts, particularly the impact of connexin43 and pannexin1, under neuroprotective and neurodegenerative conditions within the context of astrocytes.
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Affiliation(s)
- M Freitas-Andrade
- Department of Cellular and Physiological Sciences, The Life Science Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - C C Naus
- Department of Cellular and Physiological Sciences, The Life Science Institute, University of British Columbia, Vancouver, British Columbia, Canada.
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22
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McClain J, Grubišić V, Fried D, Gomez-Suarez RA, Leinninger GM, Sévigny J, Parpura V, Gulbransen BD. Ca2+ responses in enteric glia are mediated by connexin-43 hemichannels and modulate colonic transit in mice. Gastroenterology 2014; 146:497-507.e1. [PMID: 24211490 PMCID: PMC3935238 DOI: 10.1053/j.gastro.2013.10.061] [Citation(s) in RCA: 148] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Revised: 10/18/2013] [Accepted: 10/30/2013] [Indexed: 12/17/2022]
Abstract
BACKGROUND & AIMS In the enteric nervous system, neurotransmitters initiate changes in calcium (Ca(2+) responses) in glia, but it is not clear how this process affects intestinal function. We investigated whether Ca(2+)-mediated responses in enteric glia are required to maintain gastrointestinal function. METHODS We used in situ Ca(2+) imaging to monitor glial Ca(2+) responses, which were manipulated with pharmacologic agents or via glia-specific disruption of the gene encoding connexin-43 (Cx43) (hGFAP::CreER(T2+/-)/Cx43(f/f) mice). Gastrointestinal function was assessed based on pellet output, total gut transit, colonic bead expulsion, and muscle tension recordings. Proteins were localized and quantified by immunohistochemistry, immunoblot, and reverse transcription polymerase chain reaction analyses. RESULTS Ca(2+) responses in enteric glia of mice were mediated by Cx43 hemichannels. Cx43 immunoreactivity was confined to enteric glia within the myenteric plexus of the mouse colon; the Cx43 inhibitors carbenoxolone and 43Gap26 inhibited the ability of enteric glia to propagate Ca(2+) responses. In vivo attenuation of Ca(2+) responses in the enteric glial network slowed gut transit overall and delayed colonic transit--these changes are also observed during normal aging. Altered motility with increasing age was associated with reduced glial Ca(2+)-mediated responses and changes in glial expression of Cx43 messenger RNA and protein. CONCLUSIONS Ca(2+)-mediated responses in enteric glia regulate gastrointestinal function in mice. Altered intercellular signaling between enteric glia and neurons might contribute to motility disorders.
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Affiliation(s)
- Jonathon McClain
- Neuroscience Program and Department of Physiology, Michigan State University, 567 Wilson Road, East Lansing, MI, 48824 USA
| | - Vladimir Grubišić
- Department of Neurobiology, Center for Glial Biology in Medicine, Atomic Force Microscopy and Nanotechnology Laboratories, Civitan International Research Center, Evelyn F. McKnight Brain Institute, University of Alabama, Birmingham, AL 35294, USA
| | - David Fried
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824
| | - Roberto A Gomez-Suarez
- Department of Neurobiology, Center for Glial Biology in Medicine, Atomic Force Microscopy and Nanotechnology Laboratories, Civitan International Research Center, Evelyn F. McKnight Brain Institute, University of Alabama, Birmingham, AL 35294, USA.,Department of Pediatrics Division of Pediatric Gastroenterology Hepatology And Nutrition at Nemours Chlidren's Hospital. Orlando, FL 32827, USA
| | - Gina M Leinninger
- Neuroscience Program and Department of Physiology, Michigan State University, 567 Wilson Road, East Lansing, MI, 48824 USA
| | - Jean Sévigny
- Département de microbiologie-infectiologie et d'immunologie, Faculté de Médecine, Université Laval, Québec, QC, Canada.,Centre de recherche du CHU de Québec, Québec, QC, G1V 4G2 Canada
| | - Vladimir Parpura
- Department of Neurobiology, Center for Glial Biology in Medicine, Atomic Force Microscopy and Nanotechnology Laboratories, Civitan International Research Center, Evelyn F. McKnight Brain Institute, University of Alabama, Birmingham, AL 35294, USA.,Department of Biotechnology, University of Rijeka, 51000 Rijeka, Croatia
| | - Brian D Gulbransen
- Neuroscience Program and Department of Physiology, Michigan State University, 567 Wilson Road, East Lansing, MI, 48824 USA
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Mansour H, McColm JR, Cole L, Weible M, Korlimbinis A, Chan-Ling T. Connexin 30 expression and frequency of connexin heterogeneity in astrocyte gap junction plaques increase with age in the rat retina. PLoS One 2013; 8:e57038. [PMID: 23516399 PMCID: PMC3597639 DOI: 10.1371/journal.pone.0057038] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2012] [Accepted: 01/16/2013] [Indexed: 11/24/2022] Open
Abstract
We investigated age-associated changes in retinal astrocyte connexins (Cx) by assaying Cx numbers, plaque sizes, protein expression levels and heterogeneity of gap junctions utilizing six-marker immunohistochemistry (IHC). We compared Wistar rat retinal wholemounts in animals aged 3 (young adult), 9 (middle-aged) and 22 months (aged). We determined that retinal astrocytes have gap junctions composed of Cx26, -30, -43 and -45. Cx30 was consistently elevated at 22 months compared to younger ages both when associated with parenchymal astrocytes and vascular-associated astrocytes. Not only was the absolute number of Cx30 plaques significantly higher (P<0.05) but the size of the plaques was significantly larger at 22 months compared to younger ages (p<0.05). With age, Cx26 increased significantly initially, but returned to basal levels; whereas Cx43 expression remained low and stable with age. Evidence that astrocytes alter connexin compositions of gap junctions was demonstrated by the significant increase in the number of Cx26/Cx45 gap junctions with age. We also found gap junctions comprised of 1, 2, 3 or 4 Cx proteins suggesting that retinal astrocytes use various connexin protein combinations in their gap junctions during development and aging. These data provides new insight into the dynamic and extensive Cx network utilized by retinal astrocytes for communication within both the parenchyma and vasculature for the maintenance of normal retinal physiology with age. This characterisation of the changes in astrocytic gap junctional communication with age in the CNS is crucial to the understanding of physiological aging and age-related neurodegenerative diseases.
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Affiliation(s)
- Hussein Mansour
- Department of Anatomy, School of Medical Sciences and Bosch Institute, University of Sydney, New South Wales, Australia
| | - Janet R. McColm
- Department of Anatomy, School of Medical Sciences and Bosch Institute, University of Sydney, New South Wales, Australia
| | - Louise Cole
- Advanced Microscopy Facility, School of Medical Sciences, Bosch Institute, University of Sydney, New South Wales, Australia
| | - Michael Weible
- Department of Anatomy, School of Medical Sciences and Bosch Institute, University of Sydney, New South Wales, Australia
| | - Anastasia Korlimbinis
- Department of Anatomy, School of Medical Sciences and Bosch Institute, University of Sydney, New South Wales, Australia
| | - Tailoi Chan-Ling
- Department of Anatomy, School of Medical Sciences and Bosch Institute, University of Sydney, New South Wales, Australia
- * E-mail:
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Theis M, Giaume C. Connexin-based intercellular communication and astrocyte heterogeneity. Brain Res 2012; 1487:88-98. [PMID: 22789907 DOI: 10.1016/j.brainres.2012.06.045] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Revised: 06/10/2012] [Accepted: 06/13/2012] [Indexed: 12/21/2022]
Abstract
This review gives an overview of the current knowledge on connexin-mediated communication in astrocytes, covering gap junction and hemichannel functions mediated by connexins. Astroglia is the main brain cell type that expresses the largest amount of connexin and exhibits high level of gap junctional communication compared to neurons and oligodendrocytes. However, in certain developmental and regional situations, astrocytes are also coupled with oligodendrocytes and neurons. This heterotypic coupling is infrequent and minor in terms of extent of the coupling area, which does not mean that it is not important in terms of cell interaction. Here, we present an update on heterogeneity of connexin expression and function at the molecular, subcellular, cellular and networking levels. Interestingly, while astrocytes were initially considered as a homogenous population, there is now increasing evidence for morphological, developmental, molecular and physiological heterogeneity of astrocytes. Consequently, the specificity of gap junction channel- and hemichannel-mediated communication, which tends to synchronize cell populations, is also a parameter to take into account when neuroglial interactions are investigated. This article is part of a Special Issue entitled Electrical Synapses.
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Affiliation(s)
- Martin Theis
- Institute of Cellular Neurosciences, Medical Faculty, University of Bonn, Sigmund-Freud-Straße 25, D-53105 Bonn, Germany.
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25
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Naiki-Ito A, Kato H, Asamoto M, Naiki T, Shirai T. Age-dependent carcinogenic susceptibility in rat liver is related to potential of gap junctional intercellular communication. Toxicol Pathol 2012; 40:715-21. [PMID: 22569583 DOI: 10.1177/0192623312441402] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Connexin 32 (Cx32) is a major gap junction protein in the liver. The authors previously demonstrated that transgenic rats carrying a dominant negative mutant of Cx32 (Cx32ΔTg) have much decreased capacity for gap junctional intercellular communication (GJIC) and increased susceptibility to diethylnitrosamine (DEN)-induced hepatocarcinogenesis as compared to littermate wild-type (wt) rats. To evaluate the age-dependent susceptibility to DEN-induced hepatocarcinogenesis and alteration of GJIC function, male Cx32ΔTg and wt rats at 10, 30, or 85 weeks old were given a single intraperitoneal administration of DEN (40 mg/rat) and sacrificed 12 weeks later. The number and area of glutathione S-transferase placental form (GST-P)-positive preneoplastic foci were significantly increased in the liver of 10- and 30-wk-old Cx32ΔTg rats compared with age-matched wt. However, in the 85-wk-old rats, both Cx32ΔTg and wt rats had similarly large number and area of GST-P-positive foci, and the difference was not significant. Interestingly, function of hepatic GJIC was reduced and protein and mRNA expression of Cx32 were decreased with aging in wt rats. These results suggest that a decline of hepatic intercellular communication through gap junction results in increased susceptibility to DEN-induced hepatocarcinogenesis in aged rats.
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Affiliation(s)
- Aya Naiki-Ito
- Department of Experimental Pathology and Tumor Biology, Nagoya City University Graduate School of Medical Sciences, Mizuho-ku, Nagoya, Japan.
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Scemes E, Spray DC. Extracellular K⁺ and astrocyte signaling via connexin and pannexin channels. Neurochem Res 2012; 37:2310-6. [PMID: 22481627 DOI: 10.1007/s11064-012-0759-4] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2012] [Revised: 03/09/2012] [Accepted: 03/21/2012] [Indexed: 10/28/2022]
Abstract
Astrocytes utilize two major pathways to achieve long distance intercellular communication. One pathway involves direct gap junction mediated signal transmission and the other consists of release of ATP through pannexin channels and excitation of purinergic receptors on nearby cells. Elevated extracellular potassium to levels occurring around hyperactive neurons affects both gap junction and pannexin1 channels. The action on Cx43 gap junctions is to increase intercellular coupling for a period that long outlasts the stimulus. This long term increase in coupling, termed "LINC", is mediated through calcium and calmodulin dependent activation of calmodulin dependent kinase (CaMK). Pannexin1 can be activated by elevations in extracellular potassium through a mechanism that is quite different. In this case, potassium shifts activation potentials to more physiological range, thereby allowing channel opening at resting or slightly depolarized potentials. Enhanced activity of both these channel types by elevations in extracellular potassium of the magnitude occurring during periods of high neuronal activity likely has profound effects on intercellular signaling among astrocytes in the nervous system.
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Affiliation(s)
- Eliana Scemes
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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27
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Giaume C, Orellana JA, Abudara V, Sáez JC. Connexin-based channels in astrocytes: how to study their properties. Methods Mol Biol 2012; 814:283-303. [PMID: 22144314 DOI: 10.1007/978-1-61779-452-0_19] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
A typical feature of astrocytes is their high level of connexin expression. These membrane proteins constitute the molecular basis of two types of channels: gap junction channels that allow direct cytoplasm-to-cytoplasm communication and hemichannels that provide a pathway for exchanges between the intra- and extracellular media. An unusual property of these channels is their permeability for ions but also for small signaling molecules. They support intercellular communication that contribute to dynamic neuroglial interaction and interplay with neuronal activity and survival. Here, we describe multiple techniques based either on electrophysiological approaches or the monitoring of dye intercellular diffusion and uptake that permits an investigation of the properties of gap junction channels and hemichannels, respectively. These techniques are applied in astrocyte studies using in vitro models, mainly primary cultures and acute brain slices.
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Affiliation(s)
- Christian Giaume
- CIRB, CNRS UMR7241/INSERM U1050 Collège de France, Paris, France.
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28
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Unger T, Bette S, Zhang J, Theis M, Engele J. Connexin-deficiency affects expression levels of glial glutamate transporters within the cerebrum. Neurosci Lett 2011; 506:12-6. [PMID: 22037505 DOI: 10.1016/j.neulet.2011.10.032] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Revised: 10/12/2011] [Accepted: 10/16/2011] [Indexed: 11/17/2022]
Abstract
The glial glutamate transporter subtypes, GLT-1/EAAT-2 and GLAST/EAAT-1 clear the bulk of extracellular glutamate and are severely dysregulated in various acute and chronic brain diseases. Despite the previous identification of several extracellular factors modulating glial glutamate transporter expression, our knowledge of the regulatory network controlling glial glutamate transport in health and disease still remains incomplete. In studies with cultured cortical astrocytes, we previously obtained evidence that glial glutamate transporter expression is also affected by gap junctions/connexins. To assess whether gap junctions would likewise control the in vivo expression of glial glutamate transporters, we have now assessed their expression levels in brains of conditional Cx43 knockout mice, total Cx30 knockouts, as well as Cx43/Cx30 double knockouts. We found that either knocking out Cx30, Cx43, or both increases GLT-1/EAAT-2 protein levels in the cerebral cortex to a similar extent. By contrast, GLAST/EAAT-1 protein levels maximally increased in cerebral cortices of Cx30/Cx43 double knockouts, implying that gap junctions differentially affect the expression of GLT-1/EAAT-2 and GLAST/EAAT-1. Quantitative PCR analysis further revealed that increases in glial glutamate transporter expression are brought about by transcriptional and translational/posttranslational processes. Moreover, GLT-1/EAAT-2- and GLAST/EAAT-1 protein levels remained unchanged in the hippocampi of Cx43/Cx30 double knockouts when compared to Cx43fl/fl controls, indicating brain region-specific effects of gap junctions on glial glutamate transport. Since astrocytic gap junction coupling is affected in various forms of brain injuries, our findings point to gap junctions/connexins as important regulators of glial glutamate turnover in the diseased cerebral cortex.
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Affiliation(s)
- Tina Unger
- Institute of Anatomy, University of Leipzig, Medical Faculty, Liebigstr. 13, 04103 Leipzig, Germany
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29
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Glial connexin expression and function in the context of Alzheimer's disease. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:2048-57. [PMID: 22008509 DOI: 10.1016/j.bbamem.2011.10.001] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2011] [Revised: 09/20/2011] [Accepted: 10/03/2011] [Indexed: 01/26/2023]
Abstract
A hallmark of neurodegenerative diseases is the reactive gliosis characterized by a phenotypic change in astrocytes and microglia. This glial response is associated with modifications in the expression and function of connexins (Cxs), the proteins forming gap junction channels and hemichannels. Increased Cx expression is detected in most reactive astrocytes located at amyloid plaques, the histopathological lesions typically present in the brain of Alzheimer's patients and animal models of the disease. The activity of Cx channels analyzed in vivo as well as in vitro after treatment with the amyloid β peptide is also modified and, in particular, hemichannel activation may contribute to neuronal damage. In this review, we summarize and discuss recent data that suggest glial Cx channels participate in the neurodegenerative process of Alzheimer's disease. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.
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30
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Giaume C, Liu X. From a glial syncytium to a more restricted and specific glial networking. ACTA ACUST UNITED AC 2011; 106:34-9. [PMID: 21979115 DOI: 10.1016/j.jphysparis.2011.09.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Revised: 08/26/2011] [Accepted: 09/02/2011] [Indexed: 02/03/2023]
Abstract
In the brain, glia represents the cell population that expresses the highest level of connexins, the membrane protein constituents of gap junction channels and hemichannels. This statement has initially led to propose the existence of a glial syncytium. Since then, functional studies have established that connexin channel-mediated communication between glial cells was more restricted and plastic that primarily thought. In particular, this is the case for astrocytes that form functional networks of communicating cells. Altogether these findings lead to reconsider the interaction between neurons and glia that should not be solely studied at the single cell level but also at a more integrated level as the interplay between neuronal circuits and glial networks.
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Affiliation(s)
- Christian Giaume
- CIRB, CNRS UMR UMR7241/INSERM U1050, MEMOLIFE Laboratory of Excellence and Paris Science Lettre, Collège de France, University Pierre et Marie Curie, ED, N°158, 11 Place Marcelin Berthelot, 75005 Paris, France.
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31
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Homkajorn B, Sims N, Muyderman H. Connexin 43 regulates astrocytic migration and proliferation in response to injury. Neurosci Lett 2010; 486:197-201. [DOI: 10.1016/j.neulet.2010.09.051] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2010] [Revised: 09/15/2010] [Accepted: 09/16/2010] [Indexed: 11/16/2022]
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32
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Giaume C, Koulakoff A, Roux L, Holcman D, Rouach N. Astroglial networks: a step further in neuroglial and gliovascular interactions. Nat Rev Neurosci 2010; 11:87-99. [DOI: 10.1038/nrn2757] [Citation(s) in RCA: 562] [Impact Index Per Article: 40.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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33
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Young NJ, Becker DL, Fleck RA, Goodship AE, Patterson-Kane JC. Maturational alterations in gap junction expression and associated collagen synthesis in response to tendon function. Matrix Biol 2009; 28:311-23. [PMID: 19481603 DOI: 10.1016/j.matbio.2009.05.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2008] [Revised: 04/15/2009] [Accepted: 05/21/2009] [Indexed: 11/18/2022]
Abstract
Energy-storing tendons including the equine superficial digital flexor tendon (SDFT) contribute to energetic efficiency of locomotion at high-speed gaits, but consequently operate close to their physiological strain limits. Significant evidence of exercise-induced microdamage has been found in the SDFT which appears not to exhibit functional adaptation; the degenerative changes have not been repaired by the tendon fibroblasts (tenocytes), and are proposed to accumulate and predispose the tendon to rupture during normal athletic activity. The anatomically opposing common digital extensor tendon (CDET) functions only to position the digit, experiencing significantly lower levels of strain and is rarely damaged by exercise. A number of studies have indicated that tenocytes in the adult SDFT are less active in collagen synthesis and turnover than those in the immature SDFT or the CDET. Gap junction intercellular communication (GJIC) is known to be necessary for strain-induced collagen synthesis by tenocytes. We postulate therefore that expression of GJ proteins connexin 43 and 32 (Cx43; Cx32), GJIC and associated collagen expression levels are high in the SDFT and CDET of immature horses, when the SDFT in particular grows significantly in cross-sectional area, but reduce significantly during maturation in the energy-storing tendon only. The hypothesis was tested using tissue from the SDFT and CDET of foetuses, foals, and young adult Thoroughbred horses. Cellularity and the total area of both Cx43 and Cx32 plaques/mm(2) of tissue reduced significantly with maturation in each tendon. However, the total Cx43 plaque area per tenocyte significantly increased in the adult CDET. Evidence of recent collagen synthesis in the form of levels of neutral salt-soluble collagen, and collagen type I mRNA was significantly less in the adult compared with the immature SDFT; procollagen type I amino-propeptide (PINP) and procollagen type III amino-propeptide (PIIINP) levels per mm(2) of tissue and PINP expression per tenocyte also decreased with maturation in the SDFT. In the CDET PINP and PIIINP expression per tenocyte increased in the adult, and exceeded those in the adult SDFT. The level of PINP per mm(2) was greater in the adult CDET than in the SDFT despite the higher cellularity of the latter tendon. In the adult SDFT, levels of PIIINP were greater than those of PINP, suggesting relatively greater synthesis of a weaker form of collagen previously associated with microdamage. Tenocytes in monolayers showed differences in Cx43 and Cx32 expression compared with those in tissue, however there were age- and tendon-specific phenotypic differences, with a longer time for 50% recovery of fluorescence after photobleaching in adult SDFT cells compared with those from the CDET and immature SDFT. As cellularity reduces following growth in the SDFT, a failure of the remaining tenocytes to show a compensatory increase in GJ expression and collagen synthesis may explain why cell populations are not able to respond to exercise and to repair microdamage in some adult athletes. Enhancing GJIC in mature energy-storing tendons could provide a strategy to increase the cellular synthetic and reparative capacity.
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Affiliation(s)
- N J Young
- Department of Veterinary Clinical Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hertfordshire AL9 7TA, United Kingdom.
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34
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Meme W, Vandecasteele M, Giaume C, Venance L. Electrical coupling between hippocampal astrocytes in rat brain slices. Neurosci Res 2009; 63:236-43. [PMID: 19167439 DOI: 10.1016/j.neures.2008.12.008] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2008] [Revised: 12/22/2008] [Accepted: 12/25/2008] [Indexed: 11/28/2022]
Abstract
Gap junctions in astrocytes play a crucial role in intercellular communication by supporting both biochemical and electrical coupling between adjacent cells. Despite the critical role of electrical coupling in the network organization of these glial cells, the electrophysiological properties of gap junctions have been characterized in cultures while no direct evidence has been sought in situ. In the present study, gap-junctional currents were investigated using simultaneous dual whole-cell patch-clamp recordings between astrocytes from rat hippocampal slices. Bidirectional electrotonic coupling was observed in 82% of the cell pairs with an average coupling coefficient of 5.1%. Double patch-clamp analysis indicated that junctional currents were independent of the transjunctional voltage over a range from -100 to +110 mV. Interestingly, astrocytic electrical coupling displayed weak low-pass filtering properties compared to neuronal electrical synapses. Finally, during uncoupling processes triggered by either the gap-junction inhibitor carbenoxolone or endothelin-1, an increase in the input resistance in the injected cell paralleled the decrease in the coupling coefficient. Altogether, these results demonstrate that hippocampal astrocytes are electrically coupled through gap-junction channels characterized by properties that are distinct from those of electrical synapses between neurons. In addition, gap-junctional communication is efficiently regulated by endogenous compounds. This is taken to represent a mode of communication that may have important implications for the functional role of astrocyte networks in situ.
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Affiliation(s)
- William Meme
- Laboratoire de Neurobiologie, Université d'Orléans, BP 6759, 45067 Orléans Cedex 2, France
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35
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Shao M, Gottesman-Davis A, Popratiloff A, Peusner KD. Dye coupling in developing vestibular nuclei. J Neurosci Res 2008; 86:832-44. [PMID: 17941057 DOI: 10.1002/jnr.21541] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The chick tangential nucleus is a major vestibular nucleus whose principal cells participate in the vestibular reflexes. During development, most mature vestibular nucleus neurons must acquire repetitive firing of action potentials on depolarization and spontaneous spike activity to process signals effectively. In the chicken, these properties emerge gradually in the embryo, starting the week before (E13, E16) and continuing through the first week after hatching (H7). Since gap junction-mediated cell coupling may influence the emergence of neuronal excitability, we investigated whether neuron-neuron and neuron-glia coupling are present in this morphologically distinctive vestibular nucleus during the period for establishing signal processing. In brain slices, principal cells were injected with biocytin in the whole-cell configuration and visualized via confocal imaging at E13, E16, and H7. The incidence of dye coupling between the injected principal cell and neurons was 42% at E13, 75% at E16, and 7% at H7, whereas the incidence of dye coupling with glia was 100% at both embryonic ages but decreased to 27% by H7. For each injected principal cell at E13, one coupled neuron and 35 coupled glia were detected, whereas three coupled neurons and 12 coupled glia were observed at E16, and few if any coupled neurons and glia were detected at H7. These results suggest that neuron-neuron and neuron-glia coupling are developmentally regulated and present before, but not after, the onset of mature signal processing by these neurons. Thus, transient neuron-neuron and neuron-glia coupling may both play roles in establishing excitability in vestibular nucleus neurons during development.
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Affiliation(s)
- M Shao
- Department of Anatomy and Regenerative Biology, George Washington University Medical Center, Washington, DC 20037, USA
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36
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Mennecier G, Derangeon M, Coronas V, Hervé JC, Mesnil M. Aberrant expression and localization of connexin43 and connexin30 in a rat glioma cell line. Mol Carcinog 2008; 47:391-401. [DOI: 10.1002/mc.20393] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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37
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Stanley RL, Fleck RA, Becker DL, Goodship AE, Ralphs JR, Patterson-Kane JC. Gap junction protein expression and cellularity: comparison of immature and adult equine digital tendons. J Anat 2007; 211:325-34. [PMID: 17848160 PMCID: PMC2375813 DOI: 10.1111/j.1469-7580.2007.00781.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/07/2007] [Indexed: 11/30/2022] Open
Abstract
Injury to the energy-storing superficial digital flexor tendon is common in equine athletes and is age-related. Tenocytes in the superficial digital flexor tendon of adult horses appear to have limited ability to respond adaptively to exercise or prevent the accumulation of strain-induced microdamage. It has been suggested that conditioning exercise should be introduced during the growth period, when tenocytes may be more responsive to increased quantities or intensities of mechanical strain. Tenocytes are linked into networks by gap junctions that allow coordination of synthetic activity and facilitate strain-induced collagen synthesis. We hypothesised that there are reductions in cellular expression of the gap junction proteins connexin (Cx) 43 and 32 during maturation and ageing of the superficial digital flexor tendon that do not occur in the non-injury-prone common digital extensor tendon. Cryosections from the superficial digital flexor tendon and common digital extensor tendon of 5 fetuses, 5 foals (1-6 months), 5 young adults (2-7 years) and 5 old horses (18-33 years) were immunofluorescently labelled and quantitative confocal laser microscopy was performed. Expression of Cx43 and Cx32 protein per tenocyte was significantly higher in the fetal group compared with all other age groups in both tendons. The density of tenocytes was found to be highest in immature tissue. Higher levels of cellularity and connexin protein expression in immature tendons are likely to relate to requirements for tissue remodelling and growth. However, if further studies demonstrate that this correlates with greater gap junctional communication efficiency and synthetic responsiveness to mechanical strain in immature compared with adult tendons, it could support the concept of early introduction of controlled exercise as a means of increasing resistance to later injury.
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Affiliation(s)
- Rachael L Stanley
- Department of Pathology and Infectious Diseases, Royal Veterinary College, Hatfield, Hertfordshire, UK.
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38
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Zündorf G, Kahlert S, Reiser G. Gap-junction blocker carbenoxolone differentially enhances NMDA-induced cell death in hippocampal neurons and astrocytes in co-culture. J Neurochem 2007; 102:508-21. [PMID: 17403140 DOI: 10.1111/j.1471-4159.2007.04509.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The beneficial or detrimental role of gap junction communication in the pathophysiology of brain injury is still controversial. We used co-cultures of hippocampal astrocytes and neurons, where we identified homocellular astrocyte-astrocyte and heterocellular astrocyte-neuron coupling by fluorescence recovery after photobleaching, which was decreased by the gap junction blocker carbenoxolone (CBX). In these cultures, we determined the cell type-specific effects of CBX on the excitotoxic damage caused by N-methyl-D-aspartate (NMDA). We determined in both astrocytes and neurons the influence of CBX, alone or together with NMDA challenge, on cytotoxicity using propidium iodide labeling. CBX alone was not cytotoxic, but CBX treatment differentially accelerated the NMDA-induced cell death in both astrocytes and neurons. In addition, we measured mitochondrial potential using rhodamine 123, membrane potential using the oxonol dye bis(1,3-diethylthiobarbituric acid)trimethine oxonol, cytosolic Ca(2+) level using fura-2, and formation of reactive oxygen species (ROS) using dihydroethidium. CBX alone induced neither an intracellular Ca(2+) rise nor a membrane depolarization. However, CBX elicited a mitochondrial depolarization in both astrocytes and neurons and increased the ROS formation in neurons. In contrast, NMDA caused a membrane depolarization in neurons, coinciding with intracellular Ca(2+) rise, but neither mitochondrial depolarization nor ROS production seem to be involved in NMDA-mediated cytotoxicity. Pre-treatment with CBX accelerated the NMDA-induced membrane depolarization and prevented the repolarization of neurons after the NMDA challenge. We hypothesize that these effects are possibly mediated via blockage of gap junctions, and might be involved in the mechanism of CBX-induced acceleration of excitotoxic cell death, whereas the CBX-induced mitochondrial depolarization and ROS formation are not responsible for the increase in cytotoxicity. We conclude that both in astrocytes and neurons gap junctions provide protection against NMDA-induced cytotoxicity.
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Affiliation(s)
- Gregor Zündorf
- Institut für Neurobiochemie, Medizinische Fakultät, Otto-von-Guericke-Universität Magdeburg, Leipziger Strasse, Magdeburg, Germany
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39
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Abbaci M, Barberi-Heyob M, Stines JR, Blondel W, Dumas D, Guillemin F, Didelon J. Gap junctional intercellular communication capacity by gap-FRAP technique: A comparative study. Biotechnol J 2007; 2:50-61. [PMID: 17225250 DOI: 10.1002/biot.200600092] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Gap junctions play an important role in vital functions, including the regulation of cell growth and cell differentiation. Connexins 43 (Cx43) are the most widely expressed gap junction proteins. Cellular localization of phosphorylated Cx43 has been implicated in the capacity of gap junctional intercellular communication (GJIC). To follow the functionality of GJIC of different cell types, in monolayer cultures, characterized by different patterns of phosphorylated Cx43, we used a fluorescence recovery after photobleaching (FRAP) technique, and compared two tracers, 5(6)-carboxyfluorescein diacetate (CFDA) and calcein acetoxymethylester (AM). The GJIC capacity was quantified by estimating fluorescence redistribution parameters. The functionality of GJIC was in relation with the staining localization of phosphorylated Cx43 to the cell-cell contact areas, corresponding to gap junctions between contacting cells. GJIC involvement in fluorescence restitution after photobleaching was checked by a gap junction channel inhibition assay. We demonstrated that the choice of the dye did not significantly influence the fluorescence recovery percentages despite a cell line-dependent CFDA release, whereas it had an important impact on fluorescence kinetic profiles. This study reinforces the interest of the gap-FRAP approach to quantify modifications in the functionality of gap junctions and, above all, argues about the limits of CFDA for 3-D future approaches.
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Affiliation(s)
- Muriel Abbaci
- Faculté de Médecine, Nancy University, Vandoeuvre-les-Nancy, France
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Delayed neurodegeneration and early astrogliosis after excitotoxicity to the aged brain. Exp Gerontol 2006; 42:343-54. [PMID: 17126514 DOI: 10.1016/j.exger.2006.10.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2006] [Revised: 09/14/2006] [Accepted: 10/10/2006] [Indexed: 11/29/2022]
Abstract
Excitotoxicity is well recognised as a mechanism underlying neuronal cell death in several brain injuries. To investigate age-dependent differences in neurodegeneration, edema formation and astrogliosis, intrastriatal N-methyl-d-aspartate injections were performed in young (3 months) and aged (22-24 months) male Wistar rats. Animals were sacrificed at different times between 12h and 14 days post-lesion (DPL) and cryostat sections were processed for Toluidine blue, Fluoro-Jade B staining, NeuN and GFAP immunohistochemistry. Our results show that both size of tissue injury and edema were reduced in the old subjects only up to 1DPL, correlating with a slower progression of neurodegeneration with peak numbers of degenerating neurons at 3DPL in the aged, contrasting with maximum neurodegeneration at 1DPL in the young. However, old animals showed an earlier onset of astroglial response, seen at 1DPL, and a larger area of astrogliosis at all time-points studied, including a greater glial scar. In conclusion, after excitotoxic striatal damage, progression of neurodegeneration is delayed in the aged but the astroglial response is earlier and exacerbated. Our results emphasize the importance of using aged animals and several survival times for the study of acute age-related brain insults.
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41
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Fukaya T, Gondaira T, Kashiyae Y, Kotani S, Ishikura Y, Fujikawa S, Kiso Y, Sakakibara M. Arachidonic acid preserves hippocampal neuron membrane fluidity in senescent rats. Neurobiol Aging 2006; 28:1179-86. [PMID: 16790296 DOI: 10.1016/j.neurobiolaging.2006.05.023] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2005] [Revised: 03/29/2006] [Accepted: 05/22/2006] [Indexed: 10/24/2022]
Abstract
Previous studies indicate that long-term dietary supplementation with arachidonic acid (AA) in 20-month-old rats (OA) effectively restores performance in a memory task and the induction of long-term potentiation in the hippocampus to the level of young control animals (YC). The present study examined protein mobility using the live cell imaging technique "Fluorescent Recovery After Photobleaching (FRAP)" in YC, old control (OC) and OA neurons in hippocampal slice preparations. Three measures; mobile fraction (M(f)), diffusion constant (D) and time constant (tau), were estimated among YC, OC and OA. Each of these parameters was significantly different between OC and YC, suggesting that membrane fluidity is lower in OC than in YC. In contrast, D and tau were comparable in OA and YC, indicating that hippocampal neuronal membranes supplemented with AA were more fluid than those in OC, whereas the fraction of diffusible protein in the bleached region remained smaller than in YC. Long-term administration of AA to senescent rats might help to preserve membrane fluidity and maintain hippocampal plasticity.
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Affiliation(s)
- Taisuke Fukaya
- Graduate School of High-Technology for Human Welfare, Tokai University, Numazu 410-0321, Shizuoka, Japan
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42
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Zhang X, Chen X, Wu D, Liu W, Wang J, Feng Z, Cai G, Fu B, Hong Q, Du J. Downregulation of connexin 43 expression by high glucose induces senescence in glomerular mesangial cells. J Am Soc Nephrol 2006; 17:1532-42. [PMID: 16675599 DOI: 10.1681/asn.2005070776] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Connexin 43 (Cx43) plays an important role in cell differentiation and growth control, but whether it can be regulated by high glucose and whether it can mediate in glomerular mesangial cells (GMC) the phenotype alterations that are induced by high glucose still remain to be explored. In this study, RNA interference and gene transfer techniques were used to knock down and overexpress Cx43 gene in rat GMC to determine the contribution of Cx43 to GMC senescence that was induced by high glucose. The results show that high glucose (30 mM) not only downregulated Cx43 mRNA and protein expression (P<0.05) but also increased the percentage of senescence-associated beta-galactosidase (SA-beta-gal) stained cells and expression of p21cip1 and p27kip1 (P<0.05), indicating that high glucose promoted rat GMC senescence. Knocking down Cx43 gene expression significantly increased the percentage of SA-beta-gal stained cells and p27kip1 and p21cip1 expression in GMC (P<0.05), whereas overexpression of Cx43 significantly decreased the percentage of SA-beta-gal stained cells (P<0.05). These results demonstrate for the first time that downregulation of Cx43 expression by high glucose promotes the senescence of GMC, which may be involved in the pathogenesis of diabetic nephropathy.
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Affiliation(s)
- Xiaojie Zhang
- Department of Nephrology, Kidney Center and Key Lab of PLA, General Hospital of PLA, 28 Fuxing Road, Beijing 100853, People's Republic of China
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43
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May CA, Mittag T. Optic nerve degeneration in the DBA/2NNia mouse: is the lamina cribrosa important in the development of glaucomatous optic neuropathy? Acta Neuropathol 2006; 111:158-67. [PMID: 16453144 DOI: 10.1007/s00401-005-0011-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Revised: 09/14/2005] [Accepted: 09/25/2005] [Indexed: 10/25/2022]
Abstract
To study optic nerve (ON) degeneration in the DBA/2NNia (DBA) mouse, a species lacking a lamina cribrosa and a model for secondary angle-closure glaucoma, serial semi- and ultra-thin sectioning of the myelinated ON and of the ON head was performed and sections evaluated qualitatively and quantitatively by light and electron microscopy. Immunohistochemistry was performed using antibodies against collagen type I, III, VI, laminin, and connexin43. The major finding on the myelinated ON was a significant decrease in cross section area during ON degeneration which was paralleled by a loss of axons and an increase in microglia. The number of astrocytes and blood vessels did not change. The major findings on the ON papilla were that ON heads with only mild degeneration showed a pronounced focal degeneration around the central retinal artery. In more severely degenerated ON, newly formed bundles of collagen type VI were located between astrocyte processes within the ON head. In a species that has no lamina cribrosa, DBA mice can develop typical signs of glaucomatous optic neuropathy. The entrance of the central retinal vessels into the ONH seems to be a preferentially vulnerable region for axon loss in this mouse model. In addition, astrocytes in the ON head form extracellular material similar to that found in human glaucomatous eyes.
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44
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Huang TY, Hanani M, Ledda M, De Palo S, Pannese E. Aging is associated with an increase in dye coupling and in gap junction number in satellite glial cells of murine dorsal root ganglia. Neuroscience 2006; 137:1185-92. [PMID: 16326013 DOI: 10.1016/j.neuroscience.2005.10.020] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Revised: 09/25/2005] [Accepted: 10/17/2005] [Indexed: 12/20/2022]
Abstract
Glial cells in both central and peripheral nervous systems are connected by gap junctions, which allow electrical and metabolic coupling between them. In spite of the great current interest in aging of the nervous system, the effect of aging on glial cell coupling received little attention. We examined coupling between satellite glial cells in murine dorsal root ganglia using the dye coupling technique and electron microscopy. We studied mice at ages of postnatal 90-730 days. Dye coupling incidence between satellite glial cells associated with a single neuron increased from 24.2% at postnatal day 90 to 50.5% at postnatal day 730. Dye coupling between satellite glial cells that are in contact with two or more neurons increased from 2.7% at postnatal day 90 to 18.6% at postnatal day 730 (P<0.05). Examination of the ganglia with the electron microscope showed that the number of gap junctions per 100 microm2 of surface area of satellite glial cells increased from 0.22 at postnatal day 90 to 1.56 at postnatal day 730 (P<0.01). The mean length of individual gap junctions did not change with age. These results provide strong evidence for an increase of functional coupling between satellite glial cells during life. This increase is apparently due to an increase in the total area of the system of gap junctions connecting these cells.
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Affiliation(s)
- T Y Huang
- Laboratory of Experimental Surgery, Hebrew University-Hadassah Medical School, Mount Scopus, Jerusalem 91240, Israel
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45
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Martinelli C, Sartori P, De Palo S, Ledda M, Pannese E. Increase in number of the gap junctions between satellite neuroglial cells during lifetime: an ultrastructural study in rabbit spinal ganglia from youth to extremely advanced age. Brain Res Bull 2005; 67:19-23. [PMID: 16140158 DOI: 10.1016/j.brainresbull.2005.05.021] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2005] [Revised: 05/02/2005] [Accepted: 05/05/2005] [Indexed: 10/25/2022]
Abstract
This study investigated quantitative aspects of the gap junctions between satellite neuroglial cells that envelope the spinal ganglion neurons in rabbits aged 1 year (young), 3.6 years (adult), 6.7 years (old), and 8.8 years (very old). Both the total number of gap junctions present in 30,000 microm2 of surface area occupied by perineuronal satellite cells, and the density of these junctions increased throughout life, including the extremely advanced age. By contrast, the mean length of individual gap junctions did not change with age. Thus, the junctional system which provides morphological support for the metabolic cooperation between satellite cells in rabbit spinal ganglia becomes more extensive as the age of the animal increases. These results support the hypothesis that the gap junctions between perineuronal satellite cells are involved in the spatial buffering of extracellular K+ and in neuroprotection.
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Affiliation(s)
- C Martinelli
- Institute of Histology, Embryology and Neurocytology, University of Milan, Via Mangiagalli 14, I-20133 Milan, Italy
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46
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Patel BA, Arundell M, Allen MC, Gard P, O'Hare D, Parker K, Yeoman MS. Changes in the properties of the modulatory cerebral giant cells contribute to aging in the feeding system of Lymnaea. Neurobiol Aging 2005; 27:1892-901. [PMID: 16289475 DOI: 10.1016/j.neurobiolaging.2005.09.041] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Revised: 09/14/2005] [Accepted: 09/29/2005] [Indexed: 10/25/2022]
Abstract
This study examined whether electrophysiological changes in the endogenous properties and connectivity of the modulatory serotonergic cerebral giant cells (CGCs) contributed to the age-related changes in feeding behavior of the pond snail, Lymnaea. With increasing age there was a decrease in spontaneous CGC firing rates and decreased excitability of the CGCs to both chemosensory stimulation (0.05M sucrose applied to the lips) and direct intracellular current injection. These changes could be accounted for by a decrease in the input resistance of the neuron and an increase in the amplitude and the duration of the after-hyperpolarization. Decreases were also seen in the % of CGC pairs that were electrically coupled causing asynchronous firing. Together these changes would tend to reduce the ability of the CGCs to gate and control the frequency of the feeding behavior. Part of the ability of the CGCs to gate and frequency control the feeding network is to provide a background level of excitation to the feeding motor neurons. Recordings from B1 and B4 motor neurons showed an age-related hyperpolarization of the resting membrane potential consistent with a deficit in CGC function. Increases were seen in the strength of the evoked CGC-->B1 connection, however, this increase failed to compensate for the deficits in CGC excitability. In summary, age-related changes in the properties of the CGCs were consistent with them contributing to the age-related changes in feeding behavior seen in Lymnaea.
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Affiliation(s)
- B A Patel
- Physiological Flow Studies Group, School of Bioengineering, Imperial College, Prince Consort Road, London, SW7 2AZ, UK
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47
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Binder DK, Papadopoulos MC, Haggie PM, Verkman AS. In vivo measurement of brain extracellular space diffusion by cortical surface photobleaching. J Neurosci 2005; 24:8049-56. [PMID: 15371505 PMCID: PMC6729785 DOI: 10.1523/jneurosci.2294-04.2004] [Citation(s) in RCA: 151] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Molecular diffusion in the brain extracellular space (ECS) is an important determinant of neural function. We developed a brain surface photobleaching method to measure the diffusion of fluorescently labeled macromolecules in the ECS of the cerebral cortex. The ECS in mouse brain was labeled by exposure of the intact dura to fluorescein-dextrans (M(r) 4, 70, and 500 kDa). Fluorescein-dextran diffusion, detected by fluorescence recovery after laser-induced cortical photobleaching using confocal optics, was slowed approximately threefold in the brain ECS relative to solution. Cytotoxic brain edema (produced by water intoxication) or seizure activity (produced by convulsants) slowed diffusion by >10-fold and created dead-space microdomains in which free diffusion was prevented. The hindrance to diffusion was greater for the larger fluorescein-dextrans. Interestingly, slowed ECS diffusion preceded electroencephalographic seizure activity. In contrast to the slowed diffusion produced by brain edema and seizure activity, diffusion in the ECS was faster in mice lacking aquaporin-4 (AQP4), an astroglial water channel that facilitates fluid movement between cells and the ECS. Our results establish a minimally invasive method to quantify diffusion in the brain ECS in vivo, revealing stimulus-induced changes in molecular diffusion in the ECS with unprecedented spatial and temporal resolution. The in vivo mouse data provide evidence for: (1) dead-space ECS microdomains after brain swelling; (2) slowed molecular diffusion in the ECS as an early predictor of impending seizure activity; and (3) a novel role for AQP4 as a regulator of brain ECS.
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Affiliation(s)
- Devin K Binder
- Department of Medicine, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, California 94143-0521, USA
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48
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Söhl G, Odermatt B, Maxeiner S, Degen J, Willecke K. New insights into the expression and function of neural connexins with transgenic mouse mutants. ACTA ACUST UNITED AC 2005; 47:245-59. [PMID: 15572175 DOI: 10.1016/j.brainresrev.2004.05.006] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/27/2004] [Indexed: 10/26/2022]
Abstract
Gap junctions represent direct intercellular conduits between contacting cells. The subunit proteins of these conduits are called connexins. To date, 20 and 21 connexin genes have been described in the mouse and human genome, respectively, many of them represent sequence-orthologous pairs. Targeted deletion of connexin genes in the mouse genome opened new insights into the biological function of these channel forming proteins, which, in some cases, could be correlated to phenotypic abnormalities in humans, suffering from inherited diseases caused by mutations in the corresponding orthologous connexin gene. Replacing the connexin coding DNA by an appropriate reporter gene has clarified in several cases its cell type specific expression in mouse brain. Various studies demonstrated that connexin36 is mainly expressed in interneurons of retina and brain. Targeted deletion of connexin36 evoked a loss of electrical signal transduction and interferes with synchrony which probably leads to defects in visual transmission and memory. Deletion of connexin43 in astrocytes of mouse brain resulted in increased spreading depression consistent with the notion of altered "spatial buffering" of K(+) ions and glutamate secreted by active neurons. General connexin30-deficiency led to hearing impairment and apoptosis of hair cells, similar to that observed in mice with cochlea specific deletion of connexin26. Reporter gene expression in connexin30-deficient mice indicated that astrocytes in certain brain regions and leptomeningeal as well as ependymal cells are labelled. Reporter gene expression in connexin45- and connexin47-deficient mice was used to reassign connexin45 expression to certain CNS neurons and connexin47 expression to oligodendrocytes.
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Affiliation(s)
- Goran Söhl
- Institut für Genetik, Abteilung Molekulargenetik, Universität Bonn, Römerstr. 164, 53117 Bonn, Germany
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49
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Abstract
I start out with the hypothesis that the basic symptoms of schizophrenia are caused by a loss of self-boundaries. Phenomenologically, schizophrenic symptoms are based on the inability of the brain to delimit conceptual boundaries. At the cellular level in the brain, I have in previous work attributed a spatio-temporal boundary setting function to the glial cells such that glial cells determine the grouping of neurons into functional units. Mutations in genes that result in non-splicing of introns can produce aberrant versions of neurotransmitter receptors that lack protein domains encoded by entire exons and can also have protein sequence encoded by introns that have not been properly spliced out. I propose that such "chimeric" receptors are generated in glial cells and that they cannot interact properly with their cognate neurotransmitters. The glia will then lose their inhibitory function with respect to the information processing within neuronal networks. The loss of glial boundary-setting may result in a 'borderless' generalization of information processing such that the structuring of the brain in functional domains is almost completely lost. This loss of glial boundary setting could be an explanation of the loss of self-boundaries in schizophrenia.
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Affiliation(s)
- B J Mitterauer
- Institute of Forensic Neuropsychiatry and Gotthard Günther Archives, University of Salzburg, Ignaz-Harrer-Strasse 79, A-5020 Salzburg, Austria.
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50
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Rouach N, Koulakoff A, Giaume C. Neurons set the tone of gap junctional communication in astrocytic networks. Neurochem Int 2004; 45:265-72. [PMID: 15145542 DOI: 10.1016/j.neuint.2003.07.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2003] [Accepted: 07/31/2003] [Indexed: 11/20/2022]
Abstract
A number of studies have contributed to demonstrate that neurons and astrocytes tightly and actively interact. Indeed, the presence of astrocytes in neuronal cultures increases the number of synapses and their efficiency, and thanks to enzymatic and uptake processes, astrocytes play a role in neuroprotection. A typical feature of astrocytes is that they establish cell-cell communication in vitro, as well as in situ, through intercellular channels forming specialized membrane areas defined as gap junctions. These channels are composed of junctional proteins termed connexins (Cxs): in astrocytes connexin 43 (Cx43) and 30 (Cx30) have been shown to prevail. Several recent works indicate that gap junctional communication (GJC) and/or connexin expression in astrocytes are controlled by neurons. Altogether, these observations lead to the concept that neuronal and astrocytic networks interact through mutual setting of their respective mode of communication and that astrocyte gap junctions represent a target in neuroglial interaction.
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Affiliation(s)
- Nathalie Rouach
- INSERM U114, Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France
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