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Guidolin D, Tortorella C, De Caro R, Agnati LF. A Self-Similarity Logic May Shape the Organization of the Nervous System. ADVANCES IN NEUROBIOLOGY 2024; 36:203-225. [PMID: 38468034 DOI: 10.1007/978-3-031-47606-8_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/13/2024]
Abstract
From the morphological point of view, the nervous system exhibits a fractal, self-similar geometry at various levels of observations, from single cells up to cell networks. From the functional point of view, it is characterized by a hierarchical organization in which self-similar structures (networks) of different miniaturizations are nested within each other. In particular, neuronal networks, interconnected to form neuronal systems, are formed by neurons, which operate thanks to their molecular networks, mainly having proteins as components that via protein-protein interactions can be assembled in multimeric complexes working as micro-devices. On this basis, the term "self-similarity logic" was introduced to describe a nested organization where, at the various levels, almost the same rules (logic) to perform operations are used. Self-similarity and self-similarity logic both appear to be intimately linked to the biophysical evidence for the nervous system being a pattern-forming system that can flexibly switch from one coherent state to another. Thus, they can represent the key concepts to describe its complexity and its concerted, holistic behavior.
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Affiliation(s)
- Diego Guidolin
- Department of Neuroscience, University of Padova, Padova, Italy.
| | | | | | - Luigi F Agnati
- Department of Biomedical Sciences, University of Modena and Reggio Emilia, Modena, Italy
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2
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Cai M, Zhang Y, Chen S, Wu Z, Zhu L. The past, present, and future of research on neuroinflammation-induced mild cognitive impairment: A bibliometric analysis. Front Aging Neurosci 2022; 14:968444. [PMID: 35966781 PMCID: PMC9372471 DOI: 10.3389/fnagi.2022.968444] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 07/08/2022] [Indexed: 11/29/2022] Open
Abstract
Background Mild cognitive impairment (MCI) is a precursor to dementia, and neuroinflammation in the brain is thought to be one of the main pathogenic mechanisms of MCI. However, the underlying neurobiological mechanisms have not been fully explored. The purpose of this study was to establish a visual model map of the articles in the field of neuroinflammation-induced MCI over the past 11 years to reveal the research hotspots and predict the future development trends in this field, which will help to promote the research and development for MCI. Methods The “neuroinflammation” and “mild cognitive impairment” were used as search terms, and literature about neuroinflammation-induced MCI published between 2011 and 2021 was collected from the Web of Science. CiteSpace and VOSviewer were used to create visual model maps, and assess collaboration among different authors, countries, and institutions. Finally, the current research hotspots and future research directions were analyzed by using high-frequency keywords analysis and co-cited reference burst analysis. Results A total of 226 articles were retrieved. The number of publications in neuroinflammation-induced MCI shows an upward trend. Since 2018, the number of papers published in this field has increased significantly, with an average of more than 100 published each year. The United States had the highest literature production and the number of cited journals in this research area, and the National Institute on Aging was the most productive research institution. Brooks D.J. and Heneka M.T. had the highest number of publications and had the highest frequency of co-citations. The co-cited references revealed the evolution of the research themes, and the current studies are mainly focused on the effects of various metabolites on the control of microglial activation. “Cerebrospinal fluid,” “mouse model,” “tau,” “microglial activation,” “astrocytes,” and “TREM2” were the current high-frequency and emerging keywords. Conclusion Research on neuroinflammation-induced MCI is burgeoning, and the close collaboration with different nations and institutions need to be further strengthened. Current research hotspots are focused on the effects of various metabolites on microglia activation. Future studies should focus on how to regulate the phenotypes of microglia and astrocyte to reduce neuroinflammation and treat MCI.
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Affiliation(s)
- Ming Cai
- College of Rehabilitation Sciences, Shanghai University of Medicine and Health Sciences, Shanghai, China
| | - Yuanqi Zhang
- School of Sports Sciences, Qufu Normal University, Qufu, China
| | - Si Chen
- School of Sports Sciences, Qufu Normal University, Qufu, China
| | - Zhan Wu
- The Affiliated High School of Qufu Normal University, Qufu, China
| | - Lei Zhu
- School of Sports Sciences, Qufu Normal University, Qufu, China
- *Correspondence: Lei Zhu,
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3
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Liu LR, Liu JC, Bao JS, Bai QQ, Wang GQ. Interaction of Microglia and Astrocytes in the Neurovascular Unit. Front Immunol 2020; 11:1024. [PMID: 32733433 PMCID: PMC7362712 DOI: 10.3389/fimmu.2020.01024] [Citation(s) in RCA: 246] [Impact Index Per Article: 61.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Accepted: 04/28/2020] [Indexed: 12/27/2022] Open
Abstract
The interaction between microglia and astrocytes significantly influences neuroinflammation. Microglia/astrocytes, part of the neurovascular unit (NVU), are activated by various brain insults. The local extracellular and intracellular signals determine their characteristics and switch of phenotypes. Microglia and astrocytes are activated into two polarization states: the pro-inflammatory phenotype (M1 and A1) and the anti-inflammatory phenotype (M2 and A2). During neuroinflammation, induced by stroke or lipopolysaccharides, microglia are more sensitive to pathogens, or damage; they are thus initially activated into the M1 phenotype and produce common inflammatory signals such as IL-1 and TNF-α to trigger reactive astrocytes into the A1 phenotype. These inflammatory signals can be amplified not only by the self-feedback loop of microglial activation but also by the unique anatomy structure of astrocytes. As the pathology further progresses, resulting in local environmental changes, M1-like microglia switch to the M2 phenotype, and M2 crosstalk with A2. While astrocytes communicate simultaneously with neurons and blood vessels to maintain the function of neurons and the blood-brain barrier (BBB), their subtle changes may be identified and responded by astrocytes, and possibly transferred to microglia. Although both microglia and astrocytes have different functional characteristics, they can achieve immune "optimization" through their mutual communication and cooperation in the NVU and build a cascaded immune network of amplification.
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Affiliation(s)
- Li-Rong Liu
- Shanxi Medical University, Taiyuan, China.,People's Hospital of Yaodu District, Linfen, China
| | - Jia-Chen Liu
- Xiangya Medical College, Central South University, Changsha, China
| | | | | | - Gai-Qing Wang
- Shanxi Medical University, Taiyuan, China.,SanYa Central Hospital, The Third People's Hospital of HaiNan Province, SanYa, China
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Beiersdorfer A, Scheller A, Kirchhoff F, Lohr C. Panglial gap junctions between astrocytes and olfactory ensheathing cells mediate transmission of Ca 2+ transients and neurovascular coupling. Glia 2019; 67:1385-1400. [PMID: 30883940 DOI: 10.1002/glia.23613] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Revised: 02/22/2019] [Accepted: 02/25/2019] [Indexed: 12/13/2022]
Abstract
Astrocytes are arranged in highly organized gap junction-coupled networks, communicating via the propagation of Ca2+ waves. Astrocytes are gap junction-coupled not only to neighboring astrocytes, but also to oligodendrocytes, forming so-called panglial syncytia. It is not known, however, whether glial cells in panglial syncytia transmit information using Ca2+ signaling. We used confocal Ca2+ imaging to study intercellular communication between astrocytes and olfactory ensheathing glial cells (OECs) in in-toto preparations of the mouse olfactory bulb. Our results demonstrate that Ca2+ transients in juxtaglomerular astrocytes, evoked by local photolysis of "caged" ATP and "caged" tACPD, led to subsequent Ca2+ responses in OECs. This transmission of Ca2+ responses from astrocytes to OECs persisted in the presence of neuronal inhibition, but was absent when gap junctional coupling was suppressed with carbenoxolone. When Ca2+ transients were directly evoked in OECs by puff application of DHPG, they resulted in delayed Ca2+ responses in juxtaglomerular astrocytes, indicating that panglial transmission of Ca2+ signals occurred in a bidirectional manner. In addition, panglial transmission of Ca2+ signals from astrocytes to OECs resulted in vasoconstriction of OEC-associated blood vessels in the olfactory nerve layer. Our results demonstrate functional transmission of Ca2+ signals between different classes of glial cells within gap junction-coupled panglial networks and the resulting regulation of blood vessel diameter in the olfactory bulb.
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Affiliation(s)
| | - Anja Scheller
- Molecular Physiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), University of Saarland, Homburg, Germany
| | - Frank Kirchhoff
- Molecular Physiology, Center for Integrative Physiology and Molecular Medicine (CIPMM), University of Saarland, Homburg, Germany
| | - Christian Lohr
- Division of Neurophysiology, University of Hamburg, Hamburg, Germany
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5
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Lallouette J, De Pittà M, Berry H. Astrocyte Networks and Intercellular Calcium Propagation. SPRINGER SERIES IN COMPUTATIONAL NEUROSCIENCE 2019. [DOI: 10.1007/978-3-030-00817-8_7] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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6
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Charvériat M, Naus CC, Leybaert L, Sáez JC, Giaume C. Connexin-Dependent Neuroglial Networking as a New Therapeutic Target. Front Cell Neurosci 2017; 11:174. [PMID: 28694772 PMCID: PMC5483454 DOI: 10.3389/fncel.2017.00174] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2017] [Accepted: 06/08/2017] [Indexed: 12/12/2022] Open
Abstract
Astrocytes and neurons dynamically interact during physiological processes, and it is now widely accepted that they are both organized in plastic and tightly regulated networks. Astrocytes are connected through connexin-based gap junction channels, with brain region specificities, and those networks modulate neuronal activities, such as those involved in sleep-wake cycle, cognitive, or sensory functions. Additionally, astrocyte domains have been involved in neurogenesis and neuronal differentiation during development; they participate in the “tripartite synapse” with both pre-synaptic and post-synaptic neurons by tuning down or up neuronal activities through the control of neuronal synaptic strength. Connexin-based hemichannels are also involved in those regulations of neuronal activities, however, this feature will not be considered in the present review. Furthermore, neuronal processes, transmitting electrical signals to chemical synapses, stringently control astroglial connexin expression, and channel functions. Long-range energy trafficking toward neurons through connexin-coupled astrocytes and plasticity of those networks are hence largely dependent on neuronal activity. Such reciprocal interactions between neurons and astrocyte networks involve neurotransmitters, cytokines, endogenous lipids, and peptides released by neurons but also other brain cell types, including microglial and endothelial cells. Over the past 10 years, knowledge about neuroglial interactions has widened and now includes effects of CNS-targeting drugs such as antidepressants, antipsychotics, psychostimulants, or sedatives drugs as potential modulators of connexin function and thus astrocyte networking activity. In physiological situations, neuroglial networking is consequently resulting from a two-way interaction between astrocyte gap junction-mediated networks and those made by neurons. As both cell types are modulated by CNS drugs we postulate that neuroglial networking may emerge as new therapeutic targets in neurological and psychiatric disorders.
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Affiliation(s)
| | - Christian C Naus
- Department of Cellular and Physiological Science, Life Science Institute, University of British ColumbiaVancouver, BC, Canada
| | - Luc Leybaert
- Physiology Group, Department of Basic Medical Sciences, Faculty of Medicine and Health Sciences, Ghent UniversityGhent, Belgium
| | - Juan C Sáez
- Departamento de Fisiología, Pontificia Universidad Católica de ChileSantiago, Chile.,Centro Interdisciplinario de Neurociencias de Valparaíso, Instituto MilenioValparaíso, Chile
| | - Christian Giaume
- Center of Interdisciplinary Research in Biology, Collège de FranceParis, France
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Shtrahman E, Maruyama D, Olariu E, Fink C, Zochowski M. Understanding spatial and temporal patterning of astrocyte calcium transients via interactions between network transport and extracellular diffusion. Phys Biol 2017; 14:016001. [PMID: 28004641 PMCID: PMC5333993 DOI: 10.1088/1478-3975/aa5565] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Astrocytes form interconnected networks in the brain and communicate via calcium signaling. We investigate how modes of coupling between astrocytes influence the spatio-temporal patterns of calcium signaling within astrocyte networks and specifically how these network interactions promote coordination within this group of cells. To investigate these complex phenomena, we study reduced cultured networks of astrocytes and neurons. We image the spatial temporal patterns of astrocyte calcium activity and quantify how perturbing the coupling between astrocytes influences astrocyte activity patterns. To gain insight into the pattern formation observed in these cultured networks, we compare the experimentally observed calcium activity patterns to the patterns produced by a reduced computational model, where we represent astrocytes as simple units that integrate input through two mechanisms: gap junction coupling (network transport) and chemical release (extracellular diffusion). We examine the activity patterns in the simulated astrocyte network and their dependence upon these two coupling mechanisms. We find that gap junctions and extracellular chemical release interact in astrocyte networks to modulate the spatiotemporal patterns of their calcium dynamics. We show agreement between the computational and experimental findings, which suggests that the complex global patterns can be understood as a result of simple local coupling mechanisms.
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Affiliation(s)
- E. Shtrahman
- Applied Physics Program, University of Michigan – Ann Arbor 48109, USA
| | - D. Maruyama
- Department of Physics, University of Michigan - Ann Arbor 48109, USA
| | - E. Olariu
- Department of Physics, University of Michigan - Ann Arbor 48109, USA
| | - C.G. Fink
- Department of Physics, Ohio Wesleyan University -- Delaware 43015, USA
- Neuroscience Program, Ohio Wesleyan University -- Delaware 43015, USA
| | - M. Zochowski
- Department of Physics, University of Michigan - Ann Arbor 48109, USA
- Biophysics Program, University of Michigan - Ann Arbor 48109, USA
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8
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Petit JM, Magistretti P. Regulation of neuron–astrocyte metabolic coupling across the sleep–wake cycle. Neuroscience 2016; 323:135-56. [DOI: 10.1016/j.neuroscience.2015.12.007] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Revised: 12/01/2015] [Accepted: 12/04/2015] [Indexed: 11/30/2022]
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9
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Hu X, Yuan Y, Wang D, Su Z. Heterogeneous astrocytes: Active players in CNS. Brain Res Bull 2016; 125:1-18. [PMID: 27021168 DOI: 10.1016/j.brainresbull.2016.03.017] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Revised: 03/22/2016] [Accepted: 03/24/2016] [Indexed: 12/12/2022]
Abstract
Astrocytes, the predominant cell type that are broadly distributed in the brain and spinal cord, play key roles in maintaining homeostasis of the central nerve system (CNS) in physiological and pathological conditions. Increasing evidence indicates that astrocytes are a complex colony with heterogeneity on morphology, gene expression, function and many other aspects depending on their spatio-temporal distribution and activation level. In pathological conditions, astrocytes differentially respond to all kinds of insults, including injury and disease, and participate in the neuropathological process. Based on current studies, we here give an overview of the roles of heterogeneous astrocytes in CNS, especially in neuropathologies, which focuses on biological and functional diversity of astrocytes. We propose that a precise understanding of the heterogeneous astrocytes is critical to unlocking the secrets about pathogenesis and treatment of the mazy CNS.
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Affiliation(s)
- Xin Hu
- Institute of Neuroscience and Key Laboratory of Molecular Neurobiology of Ministry of Education, Second Military Medical University, Shanghai, China
| | - Yimin Yuan
- Institute of Neuroscience and Key Laboratory of Molecular Neurobiology of Ministry of Education, Second Military Medical University, Shanghai, China
| | - Dan Wang
- Institute of Neuroscience and Key Laboratory of Molecular Neurobiology of Ministry of Education, Second Military Medical University, Shanghai, China
| | - Zhida Su
- Institute of Neuroscience and Key Laboratory of Molecular Neurobiology of Ministry of Education, Second Military Medical University, Shanghai, China.
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10
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Sajja VSSS, Hlavac N, VandeVord PJ. Role of Glia in Memory Deficits Following Traumatic Brain Injury: Biomarkers of Glia Dysfunction. Front Integr Neurosci 2016; 10:7. [PMID: 26973475 PMCID: PMC4770450 DOI: 10.3389/fnint.2016.00007] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Accepted: 02/05/2016] [Indexed: 12/15/2022] Open
Abstract
Historically, glial cells have been recognized as a structural component of the brain. However, it has become clear that glial cells are intimately involved in the complexities of neural networks and memory formations. Astrocytes, microglia, and oligodendrocytes have dynamic responsibilities which substantially impact neuronal function and activities. Moreover, the importance of glia following brain injury has come to the forefront in discussions to improve axonal regeneration and functional recovery. The numerous activities of glia following injury can either promote recovery or underlie the pathobiology of memory deficits. This review outlines the pathological states of glial cells which evolve from their positive supporting roles to those which disrupt synaptic function and neuroplasticity following injury. Evidence suggests that glial cells interact extensively with neurons both chemically and physically, reinforcing their role as pivotal for higher brain functions such as learning and memory. Collectively, this mini review surveys investigations of how glial dysfunction following brain injury can alter mechanisms of synaptic plasticity and how this may be related to an increased risk for persistent memory deficits. We also include recent findings, that demonstrate new molecular avenues for clinical biomarker discovery.
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Affiliation(s)
- Venkata S S S Sajja
- Cellular Imaging Section and Vascular Biology Program, Department of Radiology and Radiological Science, Institute for Cell Engineering, Johns Hopkins University School of Medicine Baltimore, MA, USA
| | - Nora Hlavac
- Department of Biomedical Engineering and Mechanics, Virginia Tech University Blacksburg, VA, USA
| | - Pamela J VandeVord
- Department of Biomedical Engineering and Mechanics, Virginia Tech University Blacksburg, VA, USA
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11
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Hamelin S, Depaulis A. Revisiting hippocampal sclerosis in mesial temporal lobe epilepsy according to the "two-hit" hypothesis. Rev Neurol (Paris) 2015; 171:227-35. [PMID: 25748332 DOI: 10.1016/j.neurol.2015.01.560] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2014] [Accepted: 01/20/2015] [Indexed: 12/28/2022]
Abstract
Hippocampal sclerosis (HS) is the most common neuropathological pattern observed in pharmacoresistant epilepsy and represents a critical feature in mesial temporal lobe epilepsy syndrome. However, its pathophysiological mechanisms and neuropathological consequences on seizures remain mostly unresolved. The new international classification of hippocampal sclerosis aims at standardizing its description to allow comparisons between different clinical studies. However, several aspects are not considered in this classification (granule cell dispersion, sprouting, glial modifications…). In this chapter, we discuss these different features associated with hippocampal sclerosis in perspective with the "two-hit" hypothesis and propose mechanisms that could be involved in the modulation of some specific neuropathological aspects like early life stress, hyperthermic seizures, brain lesions or hormonal modifications.
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Affiliation(s)
- S Hamelin
- Inserm, U836, université Joseph-Fourier, dite Santé, bâtiment Edmond-J.-Safra, chemin Fortuné-Ferrini, 38706 La Tronche cedex, France; University Grenoble-Alpes, Grenoble institut des neurosciences, chemin Fortuné-Ferrini, 38700 La Tronche, France; Hôpital Pierre-Oudot, 30, avenue du Médipôle, BP 40348, 38302 Bourgoin-Jallieu cedex, France.
| | - A Depaulis
- Inserm, U836, université Joseph-Fourier, dite Santé, bâtiment Edmond-J.-Safra, chemin Fortuné-Ferrini, 38706 La Tronche cedex, France; University Grenoble-Alpes, Grenoble institut des neurosciences, chemin Fortuné-Ferrini, 38700 La Tronche, France; CHU de Grenoble, avenue Maquis-du-Grésivaudan, 38700 La Tronche, France
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12
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Naskar K, Stern JE. A functional coupling between extrasynaptic NMDA receptors and A-type K+ channels under astrocyte control regulates hypothalamic neurosecretory neuronal activity. J Physiol 2014; 592:2813-27. [PMID: 24835172 DOI: 10.1113/jphysiol.2014.270793] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Neuronal activity is controlled by a fine-tuned balance between intrinsic properties and extrinsic synaptic inputs. Moreover, neighbouring astrocytes are now recognized to influence a wide spectrum of neuronal functions. Yet, how these three key factors act in concert to modulate and fine-tune neuronal output is not well understood. Here, we show that in rat hypothalamic magnocellular neurosecretory cells (MNCs), glutamate NMDA receptors (NMDARs) are negatively coupled to the transient, voltage-gated A-type K(+) current (IA). We found that activation of NMDARs by extracellular glutamate levels influenced by astrocyte glutamate transporters resulted in a significant inhibition of IA. The NMDAR-IA functional coupling resulted from activation of extrasynaptic NMDARs, was calcium- and protein kinase C-dependent, and involved enhanced steady-state, voltage-dependent inactivation of IA. The NMDAR-IA coupling diminished the latency to the first evoked spike in response to membrane depolarization and increased the total number of evoked action potentials, thus strengthening the neuronal input/output function. Finally, we found a blunted NMDA-mediated inhibition of IA in dehydrated rats. Together, our findings support a novel signalling mechanism that involves a functional coupling between extrasynaptic NMDARs and A-type K(+) channels, which is influenced by local astrocytes. We show this signalling complex to play an important role in modulating hypothalamic neuronal excitability, which may contribute to adaptive responses during a sustained osmotic challenge such as dehydration.
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Affiliation(s)
- Krishna Naskar
- Department of Physiology, Medical College of Georgia, Georgia Regents University, Augusta, GA, 30912, USA
| | - Javier E Stern
- Department of Physiology, Medical College of Georgia, Georgia Regents University, Augusta, GA, 30912, USA
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De Bock M, Decrock E, Wang N, Bol M, Vinken M, Bultynck G, Leybaert L. The dual face of connexin-based astroglial Ca(2+) communication: a key player in brain physiology and a prime target in pathology. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:2211-32. [PMID: 24768716 DOI: 10.1016/j.bbamcr.2014.04.016] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Revised: 04/11/2014] [Accepted: 04/12/2014] [Indexed: 12/21/2022]
Abstract
For decades, studies have been focusing on the neuronal abnormalities that accompany neurodegenerative disorders. Yet, glial cells are emerging as important players in numerous neurological diseases. Astrocytes, the main type of glia in the central nervous system , form extensive networks that physically and functionally connect neuronal synapses with cerebral blood vessels. Normal brain functioning strictly depends on highly specialized cellular cross-talk between these different partners to which Ca(2+), as a signaling ion, largely contributes. Altered intracellular Ca(2+) levels are associated with neurodegenerative disorders and play a crucial role in the glial responses to injury. Intracellular Ca(2+) increases in single astrocytes can be propagated toward neighboring cells as intercellular Ca(2+) waves, thereby recruiting a larger group of cells. Intercellular Ca(2+) wave propagation depends on two, parallel, connexin (Cx) channel-based mechanisms: i) the diffusion of inositol 1,4,5-trisphosphate through gap junction channels that directly connect the cytoplasm of neighboring cells, and ii) the release of paracrine messengers such as glutamate and ATP through hemichannels ('half of a gap junction channel'). This review gives an overview of the current knowledge on Cx-mediated Ca(2+) communication among astrocytes as well as between astrocytes and other brain cell types in physiology and pathology, with a focus on the processes of neurodegeneration and reactive gliosis. Research on Cx-mediated astroglial Ca(2+) communication may ultimately shed light on the development of targeted therapies for neurodegenerative disorders in which astrocytes participate. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.
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Affiliation(s)
- Marijke De Bock
- Department of Basic Medical Sciences, Physiology group, Faculty of Medicine and Health Sciences, Ghent University, B-9000 Ghent, Belgium
| | - Elke Decrock
- Department of Basic Medical Sciences, Physiology group, Faculty of Medicine and Health Sciences, Ghent University, B-9000 Ghent, Belgium.
| | - Nan Wang
- Department of Basic Medical Sciences, Physiology group, Faculty of Medicine and Health Sciences, Ghent University, B-9000 Ghent, Belgium
| | - Mélissa Bol
- Department of Basic Medical Sciences, Physiology group, Faculty of Medicine and Health Sciences, Ghent University, B-9000 Ghent, Belgium
| | - Mathieu Vinken
- Department of Toxicology, Center for Pharmaceutical Research, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, B-1090 Brussels, Belgium
| | - Geert Bultynck
- Department of Cellular and Molecular Medicine, Laboratory of Molecular and Cellular Signalling, KULeuven, Campus Gasthuisberg O/N-I bus 802, B-3000 Leuven, Belgium
| | - Luc Leybaert
- Department of Basic Medical Sciences, Physiology group, Faculty of Medicine and Health Sciences, Ghent University, B-9000 Ghent, Belgium
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A new angle on blood-CNS interfaces: A role for connexins? FEBS Lett 2014; 588:1259-70. [DOI: 10.1016/j.febslet.2014.02.060] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 02/27/2014] [Accepted: 02/28/2014] [Indexed: 12/12/2022]
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15
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Zhang X, Wang J, Qian W, Zhao J, Sun L, Qian Y, Xiao H. Dexmedetomidine Inhibits Tumor Necrosis Factor-Alpha and Interleukin 6 in Lipopolysaccharide-Stimulated Astrocytes by Suppression of c-Jun N-Terminal Kinases. Inflammation 2014; 37:942-9. [DOI: 10.1007/s10753-014-9814-4] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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16
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Orellana JA, Sáez JC, Bennett MVL, Berman JW, Morgello S, Eugenin EA. HIV increases the release of dickkopf-1 protein from human astrocytes by a Cx43 hemichannel-dependent mechanism. J Neurochem 2013; 128:752-63. [PMID: 24134157 DOI: 10.1111/jnc.12492] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2013] [Revised: 09/27/2013] [Accepted: 10/11/2013] [Indexed: 11/26/2022]
Abstract
Human immunodeficiency virus-1 (HIV) is a public health issue and a major complication of the disease is NeuroAIDS. In vivo, microglia/macrophages are the main cells infected. However, a low but significant number of HIV-infected astrocytes has also been detected, but their role in the pathogenesis of NeuroAIDS is not well understood. Our previous data indicate that gap junction channels amplify toxicity from few HIV-infected into uninfected astrocytes. Now, we demonstrated that HIV infection of astrocytes results in the opening of connexin43 hemichannels (HCs). HIV-induced opening of connexin43 HCs resulted in dysregulated secretion of dickkopf-1 protein (DKK1, a soluble wnt pathway inhibitor). Treatment of mixed cultures of neurons and astrocytes with DKK1, in the absence of HIV infection, resulted in the collapse of neuronal processes. HIV infection of mixed cultures of human neurons and astrocytes also resulted in the collapse of neuronal processes through a DKK1-dependent mechanism. In addition, dysregulated DKK1 expression in astrocytes was observed in human brain tissue sections of individuals with HIV encephalitis as compared to tissue sections from uninfected individuals. Thus, we demonstrated that HIV infection of astrocytes induces dysregulation of DKK1 by a HC-dependent mechanism that contributes to the brain pathogenesis observed in HIV-infected individuals. Our studies demonstrated that HIV infection of astrocytes, despite minimal replication and a low number of infected cells, induces dysregulation of DKK1 secretion by a Cx43 hemichannel (HC)-dependent mechanism. Enhanced DKK1 secretion in response to HIV infection of glial cells compromised formation and stability of neuronal processes, similar to the synaptic compromise observed in HIV-infected individuals. In addition, analysis of human brain tissue sections obtained from encephalitic individuals also shows enhanced expression of DKK1 in astrocytes. Our data provide a novel mechanism by which HIV infection of glial cells participate in the pathogenesis of brain dysfunction observed in HIV-infected individuals. LRP5 = Low-density lipoprotein receptor-related protein 5.
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Affiliation(s)
- Juan Andres Orellana
- Public Health Research Institute (PHRI), Rutgers New Jersey Medical School, Rutgers The State University of New Jersey, Newark, New Jersey, USA
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17
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De Bock M, Kerrebrouck M, Wang N, Leybaert L. Neurological manifestations of oculodentodigital dysplasia: a Cx43 channelopathy of the central nervous system? Front Pharmacol 2013; 4:120. [PMID: 24133447 PMCID: PMC3783840 DOI: 10.3389/fphar.2013.00120] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Accepted: 09/02/2013] [Indexed: 12/30/2022] Open
Abstract
The coordination of tissue function is mediated by gap junctions (GJs) that enable direct cell–cell transfer of metabolic and electric signals. GJs are formed by connexins of which Cx43 is most widespread in the human body. In the brain, Cx43 GJs are mostly found in astroglia where they coordinate the propagation of Ca2+ waves, spatial K+ buffering, and distribution of glucose. Beyond its role in direct intercellular communication, Cx43 also forms unapposed, non-junctional hemichannels in the plasma membrane of glial cells. These allow the passage of several neuro- and gliotransmitters that may, combined with downstream paracrine signaling, complement direct GJ communication among glial cells and sustain glial-neuronal signaling. Mutations in the GJA1 gene encoding Cx43 have been identified in a rare, mostly autosomal dominant syndrome called oculodentodigital dysplasia (ODDD). ODDD patients display a pleiotropic phenotype reflected by eye, hand, teeth, and foot abnormalities, as well as craniofacial and bone malformations. Remarkably, neurological symptoms such as dysarthria, neurogenic bladder (manifested as urinary incontinence), spasticity or muscle weakness, ataxia, and epilepsy are other prominent features observed in ODDD patients. Over 10 mutations detected in patients diagnosed with neurological disorders are associated with altered functionality of Cx43 GJs/hemichannels, but the link between ODDD-related abnormal channel activities and neurologic phenotype is still elusive. Here, we present an overview on the nature of the mutants conveying structural and functional changes of Cx43 channels and discuss available evidence for aberrant Cx43 GJ and hemichannel function. In a final step, we examine the possibilities of how channel dysfunction may lead to some of the neurological manifestations of ODDD.
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Affiliation(s)
- Marijke De Bock
- Physiology Group, Department of Basic Medical Sciences, Ghent University Ghent, Belgium
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18
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Agnati LF, Guidolin D, Battistin L, Pagnoni G, Fuxe K. The neurobiology of imagination: possible role of interaction-dominant dynamics and default mode network. Front Psychol 2013; 4:296. [PMID: 23745117 PMCID: PMC3662866 DOI: 10.3389/fpsyg.2013.00296] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 05/07/2013] [Indexed: 11/29/2022] Open
Abstract
This work aims at presenting some hypotheses about the potential neurobiological substrate of imagery and imagination. For the present purposes, we will define imagery as the production of mental images associated with previous percepts, and imagination as the faculty of forming mental images of a novel character relating to something that has never been actually experienced by the subject but at a great extent emerges from his inner world. The two processes appear intimately related and imagery can arguably be considered as one of the main components of imagination. In this proposal, we argue that exaptation and redeployment, two basic concepts capturing important aspects of the evolution of biological structures and functions (Anderson, 2007), could also be useful in explaining imagery and imagination. As far as imagery is concerned it is proposed that neural structures originally implicated in performing certain functions, e.g., motor actions, can be reused for the imagery of the virtual execution of that function. As far as imagination is concerned we speculate that it can be the result of a “tinkering” that combines and modifies stored perceptual information and concepts leading to the creation of novel “mental objects” that are shaped by the subject peculiar inner world. Hence it is related to his self-awareness. The neurobiological substrate of the tinkering process could be found in a hierarchical model of the brain characterized by a multiplicity of functional modules (FMs) that can be assembled according to different spatial and temporal scales. Thus, it is surmised that a possible mechanism for the emergence of imagination could be represented by modulatory mechanisms controlling the perviousness of “modifiers” along the communication channels within and between FMs leading to their dynamically reassembling into novel configurations.
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19
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Topology Drives Calcium Wave Propagation in 3D Astrocyte Networks. PROCEEDINGS OF THE EUROPEAN CONFERENCE ON COMPLEX SYSTEMS 2012 2013. [DOI: 10.1007/978-3-319-00395-5_56] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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20
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Min R, Santello M, Nevian T. The computational power of astrocyte mediated synaptic plasticity. Front Comput Neurosci 2012; 6:93. [PMID: 23125832 PMCID: PMC3485583 DOI: 10.3389/fncom.2012.00093] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Accepted: 10/15/2012] [Indexed: 12/05/2022] Open
Abstract
Research in the last two decades has made clear that astrocytes play a crucial role in the brain beyond their functions in energy metabolism and homeostasis. Many studies have shown that astrocytes can dynamically modulate neuronal excitability and synaptic plasticity, and might participate in higher brain functions like learning and memory. With the plethora of astrocyte mediated signaling processes described in the literature today, the current challenge is to identify, which of these processes happen under what physiological condition, and how this shapes information processing and, ultimately, behavior. To answer these questions will require a combination of advanced physiological, genetical, and behavioral experiments. Additionally, mathematical modeling will prove crucial for testing predictions on the possible functions of astrocytes in neuronal networks, and to generate novel ideas as to how astrocytes can contribute to the complexity of the brain. Here, we aim to provide an outline of how astrocytes can interact with neurons. We do this by reviewing recent experimental literature on astrocyte-neuron interactions, discussing the dynamic effects of astrocytes on neuronal excitability and short- and long-term synaptic plasticity. Finally, we will outline the potential computational functions that astrocyte-neuron interactions can serve in the brain. We will discuss how astrocytes could govern metaplasticity in the brain, how they might organize the clustering of synaptic inputs, and how they could function as memory elements for neuronal activity. We conclude that astrocytes can enhance the computational power of neuronal networks in previously unexpected ways.
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Affiliation(s)
- Rogier Min
- Department of Physiology, University of Berne Berne, Switzerland
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21
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Armato U, Bonafini C, Chakravarthy B, Pacchiana R, Chiarini A, Whitfield JF, Dal Prà I. The calcium-sensing receptor: a novel Alzheimer's disease crucial target? J Neurol Sci 2012; 322:137-40. [PMID: 22841885 DOI: 10.1016/j.jns.2012.07.031] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Revised: 05/28/2012] [Accepted: 07/11/2012] [Indexed: 01/09/2023]
Abstract
Alzheimer's disease (AD) is the most common human neurodegenerative ailment, the most prevalent (>95%) late-onset type of which has a still uncertain etiology. The progressive decline of cognitive functions, dementia, and physical disabilities of AD is caused by synaptic losses that progressively disconnect key neuronal networks in crucial brain areas, like the hippocampus and temporoparietal cortex, and critically impair language, sensory processing, memory, and conscious thought. AD's two main hallmarks are fibrillar amyloid-β (fAβ) plaques in extracellular spaces and intracellular accumulation of fAβ peptides and neurofibrillary tangles (NFTs). It is still undecided whether either or both these AD hallmarks cause or result from the disease. Recently, the dysregulation of calcium homeostasis has been advanced as a novel cause of AD. In this case, a suitable candidate of AD driver would be the Aβ peptides-binding/activated calcium-sensing receptor (CaSR), whose intracellular signalling is triggered by Aβ peptides. In this review, we briefly discuss CaSR's roles in normal adult human astrocytes (NAHAs) and their possible impacts on AD.
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Affiliation(s)
- Ubaldo Armato
- Histology and Embryology Unit, Department of Life and Reproduction Sciences, University of Verona Medical School, Verona, Venetia, Italy.
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22
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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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23
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Gap junction proteins on the move: connexins, the cytoskeleton and migration. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:94-108. [PMID: 22613178 DOI: 10.1016/j.bbamem.2012.05.014] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2012] [Revised: 04/25/2012] [Accepted: 05/04/2012] [Indexed: 01/08/2023]
Abstract
Connexin43 (Cx43) has roles in cell-cell communication as well as channel independent roles in regulating motility and migration. Loss of function approaches to decrease Cx43 protein levels in neural cells result in reduced migration of neurons during cortical development in mice and impaired glioma tumor cell migration. In other cell types, correlations between Cx43 expression and cell morphology, adhesion, motility and migration have been noted. In this review we will discuss the common themes that have been revealed by a detailed comparison of the published results of neuronal cells with that of other cell types. In brief, these comparisons clearly show differences in the stability and directionality of protrusions, polarity of movement, and migration, depending on whether a) residual Cx43 levels remain after siRNA or shRNA knockdown, b) Cx43 protein levels are not detectable as in cells from Cx43(-/-) knockout mice or in cells that normally have no endogenous Cx43 expression, c) gain-of-function approaches are used to express Cx43 in cells that have no endogenous Cx43 and, d) Cx43 is over-expressed in cells that already have low endogenous Cx43 protein levels. What is clear from our comparisons is that Cx43 expression influences the adhesiveness of cells and the directionality of cellular processes. These observations are discussed in light of the ability of cells to rearrange their cytoskeleton and move in an organized manner. This article is part of a Special Issue entitled: The Communicating junctions, roles and dysfunctions.
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Wang F, Smith NA, Xu Q, Fujita T, Baba A, Matsuda T, Takano T, Bekar L, Nedergaard M. Astrocytes modulate neural network activity by Ca²+-dependent uptake of extracellular K+. Sci Signal 2012; 5:ra26. [PMID: 22472648 DOI: 10.1126/scisignal.2002334] [Citation(s) in RCA: 204] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Astrocytes are electrically nonexcitable cells that display increases in cytosolic calcium ion (Ca²+) in response to various neurotransmitters and neuromodulators. However, the physiological role of astrocytic Ca²+ signaling remains controversial. We show here that astrocytic Ca²+ signaling ex vivo and in vivo stimulated the Na+,K+-ATPase (Na+- and K+-dependent adenosine triphosphatase), leading to a transient decrease in the extracellular potassium ion (K+) concentration. This in turn led to neuronal hyperpolarization and suppressed baseline excitatory synaptic activity, detected as a reduced frequency of excitatory postsynaptic currents. Synaptic failures decreased in parallel, leading to an increase in synaptic fidelity. The net result was that astrocytes, through active uptake of K+, improved the signal-to-noise ratio of synaptic transmission. Active control of the extracellular K+ concentration thus provides astrocytes with a simple yet powerful mechanism to rapidly modulate network activity.
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Affiliation(s)
- Fushun Wang
- Division of Glia Disease and Therapeutics, Center for Translational Neuromedicine, Department of Neurosurgery, University of Rochester Medical School, Rochester, NY 14640, USA
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25
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Abstract
Astroglial cells, due to their passive electrical properties, were long considered subservient to neurons and to merely provide the framework and metabolic support of the brain. Although astrocytes do play such structural and housekeeping roles in the brain, these glial cells also contribute to the brain's computational power and behavioural output. These more active functions are endowed by the Ca2+-based excitability displayed by astrocytes. An increase in cytosolic Ca2+ levels in astrocytes can lead to the release of signalling molecules, a process termed gliotransmission, via the process of regulated exocytosis. Dynamic components of astrocytic exocytosis include the vesicular-plasma membrane secretory machinery, as well as the vesicular traffic, which is governed not only by general cytoskeletal elements but also by astrocyte-specific IFs (intermediate filaments). Gliotransmitters released into the ECS (extracellular space) can exert their actions on neighbouring neurons, to modulate synaptic transmission and plasticity, and to affect behaviour by modulating the sleep homoeostat. Besides these novel physiological roles, astrocytic Ca2+ dynamics, Ca2+-dependent gliotransmission and astrocyte–neuron signalling have been also implicated in brain disorders, such as epilepsy. The aim of this review is to highlight the newer findings concerning Ca2+ signalling in astrocytes and exocytotic gliotransmission. For this we report on Ca2+ sources and sinks that are necessary and sufficient for regulating the exocytotic release of gliotransmitters and discuss secretory machinery, secretory vesicles and vesicle mobility regulation. Finally, we consider the exocytotic gliotransmission in the modulation of synaptic transmission and plasticity, as well as the astrocytic contribution to sleep behaviour and epilepsy.
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26
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Guidolin D, Albertin G, Guescini M, Fuxe K, Agnati L. Central Nervous System and Computation. QUARTERLY REVIEW OF BIOLOGY 2011; 86:265-85. [DOI: 10.1086/662456] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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Gankam Kengne F, Nicaise C, Soupart A, Boom A, Schiettecatte J, Pochet R, Brion JP, Decaux G. Astrocytes are an early target in osmotic demyelination syndrome. J Am Soc Nephrol 2011; 22:1834-45. [PMID: 21885671 DOI: 10.1681/asn.2010111127] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Abrupt osmotic changes during rapid correction of chronic hyponatremia result in demyelinative brain lesions, but the sequence of events linking rapid osmotic changes to myelin loss is not yet understood. Here, in a rat model of osmotic demyelination syndrome, we found that massive astrocyte death occurred after rapid correction of hyponatremia, delineating the regions of future myelin loss. Astrocyte death caused a disruption of the astrocyte-oligodendrocyte network, rapidly upregulated inflammatory cytokines genes, and increased serum S100B, which predicted clinical manifestations and outcome of osmotic demyelination. These results support a model for the pathophysiology of osmotic brain injury in which rapid correction of hyponatremia triggers apoptosis in astrocytes followed by a loss of trophic communication between astrocytes and oligodendrocytes, secondary inflammation, microglial activation, and finally demyelination.
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Affiliation(s)
- Fabrice Gankam Kengne
- Erasme University Hospital, Department of General Internal Medicine, Research Unit on Hydromineral Metabolism, Faculty of Medicine, Université Libre de Bruxelles, Brussels, Belgium.
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28
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Bernal GM, Peterson DA. Phenotypic and gene expression modification with normal brain aging in GFAP-positive astrocytes and neural stem cells. Aging Cell 2011; 10:466-82. [PMID: 21385309 DOI: 10.1111/j.1474-9726.2011.00694.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Astrocytes secrete growth factors that are both neuroprotective and supportive for the local environment. Identified by glial fibrillary acidic protein (GFAP) expression, astrocytes exhibit heterogeneity in morphology and in the expression of phenotypic markers and growth factors throughout different adult brain regions. In adult neurogenic niches, astrocytes secrete vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2) within the neurogenic niche and are also a source of special GFAP-positive multipotent neural stem cells (NSCs). Normal aging is accompanied by a decline in CNS function and reduced neurogenesis. We asked whether a decreased availability of astrocyte-derived factors may contribute to the age-related decline in neurogenesis. Determining alterations of astrocytic activity in the aging brain is crucial for understanding CNS homeostasis in aging and for assessing appropriate therapeutic targets for an aging population. We found region-specific alterations in the gene expression of GFAP, VEGF, and FGF-2 and their receptors in the aged brain corresponding to changes in astrocytic reactivity, supporting astrocytic heterogeneity and demonstrating a differential aging effect. We found that GFAP-positive NSCs uniquely coexpress both VEGF and its key mitotic receptor Flk-1 in both young and aged hippocampus, indicating a possible autocrine/paracrine signaling mechanism. VEGF expression is lost once NSCs commit to a neuronal fate, but Flk-1-mediated sensitivity to VEGF signaling is maintained. We propose that age-related astrocytic changes result in reduced VEGF and FGF-2 signaling, which in turn limits NSC and progenitor cell maintenance and contributes to decreased neurogenesis.
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Affiliation(s)
- Giovanna M Bernal
- Department of Neuroscience, The Chicago Medical School, Rosalind Franklin University of Medicine and Science, IL 60647, USA
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