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Wang Q, He R, Chen L, Zhang Q, Shan J, Wang P, Wang X, Zhao Y. MIG-23 is involved in sperm migration by modulating extracellular ATP levels in Ascaris suum. Development 2022; 149:275964. [DOI: 10.1242/dev.200478] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 05/24/2022] [Indexed: 11/20/2022]
Abstract
ABSTRACT
In nematodes, spermiogenesis is a process of sperm activation in which nonmotile spermatids are transformed into crawling spermatozoa. Sperm motility acquisition during this process is essential for successful fertilization, but the underlying mechanisms remain to be clarified. Herein, we have found that extracellular adenosine-5′-triphosphate (ATP) level regulation by MIG-23, which is a homolog of human ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase), was required for major sperm protein (MSP) filament dynamics and sperm motility in the nematode Ascaris suum. During sperm activation, a large amount of ATP was produced in mitochondria and was stored in refringent granules (RGs). Some of the produced ATP was released to the extracellular space through innexin channels. MIG-23 was localized in the sperm plasma membrane and contributed to the ecto-ATPase activity of spermatozoa. Blocking MIG-23 activity resulted in a decrease in the ATP hydrolysis activity of spermatozoa and an increase in the depolymerization rate of MSP filaments in pseudopodia, which eventually affected sperm migration. Overall, our data suggest that MIG-23, which contributes to the ecto-ATPase activity of spermatozoa, regulates sperm migration by modulating extracellular ATP levels.
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Affiliation(s)
- Qiushi Wang
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences 1 , Beijing 100101 , China
| | - Ruijun He
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences 1 , Beijing 100101 , China
| | - Lianwan Chen
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences 1 , Beijing 100101 , China
| | - Qi Zhang
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences 1 , Beijing 100101 , China
- University of Chinese Academy of Sciences 2 , Beijing 100049 , China
| | - Jin Shan
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences 1 , Beijing 100101 , China
- University of Chinese Academy of Sciences 2 , Beijing 100049 , China
| | - Peng Wang
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences 1 , Beijing 100101 , China
- University of Chinese Academy of Sciences 2 , Beijing 100049 , China
| | - Xia Wang
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences 1 , Beijing 100101 , China
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences 3 , Beijing 100101 , China
| | - Yanmei Zhao
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences 1 , Beijing 100101 , China
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Syrjanen J, Michalski K, Kawate T, Furukawa H. On the molecular nature of large-pore channels. J Mol Biol 2021; 433:166994. [PMID: 33865869 PMCID: PMC8409005 DOI: 10.1016/j.jmb.2021.166994] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Revised: 04/08/2021] [Accepted: 04/08/2021] [Indexed: 12/25/2022]
Abstract
Membrane transport is a fundamental means to control basic cellular processes such as apoptosis, inflammation, and neurodegeneration and is mediated by a number of transporters, pumps, and channels. Accumulating evidence over the last half century has shown that a type of so-called "large-pore channel" exists in various tissues and organs in gap-junctional and non-gap-junctional forms in order to flow not only ions but also metabolites such as ATP. They are formed by a number of protein families with little or no evolutionary linkages including connexin, innexin, pannexin, leucine-rich repeat-containing 8 (LRRC8), and calcium homeostasis modulator (CALHM). This review summarizes the history and concept of large-pore channels starting from connexin gap junction channels to the more recent developments in innexin, pannexin, LRRC8, and CALHM. We describe structural and functional features of large-pore channels that are crucial for their diverse functions on the basis of available structures.
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Affiliation(s)
- Johanna Syrjanen
- W.M. Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
| | - Kevin Michalski
- W.M. Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
| | - Toshimitsu Kawate
- Department of Molecular Medicine, Fields of Biochemistry, Molecular, and Cell Biology (BMCB), and Biophysics, Cornell University, Ithaca, NY 14853, USA
| | - Hiro Furukawa
- W.M. Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
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3
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Huang Z, Xie N, Illes P, Di Virgilio F, Ulrich H, Semyanov A, Verkhratsky A, Sperlagh B, Yu SG, Huang C, Tang Y. From purines to purinergic signalling: molecular functions and human diseases. Signal Transduct Target Ther 2021; 6:162. [PMID: 33907179 PMCID: PMC8079716 DOI: 10.1038/s41392-021-00553-z] [Citation(s) in RCA: 172] [Impact Index Per Article: 57.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 01/24/2021] [Accepted: 02/24/2021] [Indexed: 02/06/2023] Open
Abstract
Purines and their derivatives, most notably adenosine and ATP, are the key molecules controlling intracellular energy homoeostasis and nucleotide synthesis. Besides, these purines support, as chemical messengers, purinergic transmission throughout tissues and species. Purines act as endogenous ligands that bind to and activate plasmalemmal purinoceptors, which mediate extracellular communication referred to as "purinergic signalling". Purinergic signalling is cross-linked with other transmitter networks to coordinate numerous aspects of cell behaviour such as proliferation, differentiation, migration, apoptosis and other physiological processes critical for the proper function of organisms. Pathological deregulation of purinergic signalling contributes to various diseases including neurodegeneration, rheumatic immune diseases, inflammation, and cancer. Particularly, gout is one of the most prevalent purine-related disease caused by purine metabolism disorder and consequent hyperuricemia. Compelling evidence indicates that purinoceptors are potential therapeutic targets, with specific purinergic agonists and antagonists demonstrating prominent therapeutic potential. Furthermore, dietary and herbal interventions help to restore and balance purine metabolism, thus addressing the importance of a healthy lifestyle in the prevention and relief of human disorders. Profound understanding of molecular mechanisms of purinergic signalling provides new and exciting insights into the treatment of human diseases.
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Grants
- National Key R&D Program of China (2019YFC1709101,2020YFA0509400, 2020YFC2002705), the National Natural Science Foundation of China (81821002, 81790251, 81373735, 81972665), Guangdong Basic and Applied Basic Research Foundation (2019B030302012), the Project First-Class Disciplines Development of Chengdu University of Traditional Chinese Medicine (CZYHW1901), São Paulo Research Foundation (FAPESP 2018/07366-4), Russian Science Foundation grant 20-14-00241, NSFC-BFBR;and Science and Technology Program of Sichuan Province, China (2019YFH0108)
- National Key R&D Program of China (2020YFA0509400, 2020YFC2002705), the National Natural Science Foundation of China (81821002, 81790251).
- National Key R&D Program of China (2020YFA0509400, 2020YFC2002705), the National Natural Science Foundation of China (81821002, 81790251), Guangdong Basic and Applied Basic Research Foundation (2019B030302012).
- the Project First-Class Disciplines Development of Chengdu University of Traditional Chinese Medicine (CZYHW1901) and Science and Technology Program of Sichuan Province, China (2019YFH0108).
- the Project First-Class Disciplines Development of Chengdu University of Traditional Chinese Medicine (CZYHW1901), and Science and Technology Program of Sichuan Province, China (2019YFH0108).
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Affiliation(s)
- Zhao Huang
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, and West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, China
| | - Na Xie
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, and West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, China
| | - Peter Illes
- International Collaborative Centre on Big Science Plan for Purinergic Signalling, Chengdu University of Traditional Chinese Medicine, Chengdu, China
- Rudolf-Boehm-Institut für Pharmakologie und Toxikologie, Universitaet Leipzig, Leipzig, Germany
| | | | - Henning Ulrich
- International Collaborative Centre on Big Science Plan for Purinergic Signalling, Chengdu University of Traditional Chinese Medicine, Chengdu, China
- Department of Biochemistry, Institute of Chemistry, University of São Paulo, São Paulo, Brazil
| | - Alexey Semyanov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
- Sechenov First Moscow State Medical University, Moscow, Russia
| | - Alexei Verkhratsky
- International Collaborative Centre on Big Science Plan for Purinergic Signalling, Chengdu University of Traditional Chinese Medicine, Chengdu, China
- Sechenov First Moscow State Medical University, Moscow, Russia
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Beata Sperlagh
- Department of Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary
| | - Shu-Guang Yu
- International Collaborative Centre on Big Science Plan for Purinergic Signalling, Chengdu University of Traditional Chinese Medicine, Chengdu, China
- Acupuncture and Chronobiology Key Laboratory of Sichuan Province, Chengdu, China
| | - Canhua Huang
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, and West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, China.
- School of Basic Medical Sciences, Chengdu University of Traditional Chinese Medicine, Chengdu, China.
| | - Yong Tang
- International Collaborative Centre on Big Science Plan for Purinergic Signalling, Chengdu University of Traditional Chinese Medicine, Chengdu, China.
- Acupuncture and Chronobiology Key Laboratory of Sichuan Province, Chengdu, China.
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4
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Mim C, Perkins G, Dahl G. Structure versus function: Are new conformations of pannexin 1 yet to be resolved? J Gen Physiol 2021; 153:211971. [PMID: 33835130 PMCID: PMC8042604 DOI: 10.1085/jgp.202012754] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Pannexin 1 (Panx1) plays a decisive role in multiple physiological and pathological settings, including oxygen delivery to tissues, mucociliary clearance in airways, sepsis, neuropathic pain, and epilepsy. It is widely accepted that Panx1 exerts its role in the context of purinergic signaling by providing a transmembrane pathway for ATP. However, under certain conditions, Panx1 can also act as a highly selective membrane channel for chloride ions without ATP permeability. A recent flurry of publications has provided structural information about the Panx1 channel. However, while these structures are consistent with a chloride selective channel, none show a conformation with strong support for the ATP release function of Panx1. In this Viewpoint, we critically assess the existing evidence for the function and structure of the Panx1 channel and conclude that the structure corresponding to the ATP permeation pathway is yet to be determined. We also list a set of additional topics needing attention and propose ways to attain the large-pore, ATP-permeable conformation of the Panx1 channel.
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Affiliation(s)
- Carsten Mim
- Department of Biomedical Engineering and Health Systems Royal Institute of Technology, Huddinge, Sweden
| | - Guy Perkins
- National Center for Microscopy and Imaging Research, University of California, San Diego School of Medicine, La Jolla, CA
| | - Gerhard Dahl
- Department of Physiology, University of Miami School of Medicine, Miami, FL
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5
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D’Aloia A, Molteni L, Gullo F, Bresciani E, Artusa V, Rizzi L, Ceriani M, Meanti R, Lecchi M, Coco S, Costa B, Torsello A. Palmitoylethanolamide Modulation of Microglia Activation: Characterization of Mechanisms of Action and Implication for Its Neuroprotective Effects. Int J Mol Sci 2021; 22:ijms22063054. [PMID: 33802689 PMCID: PMC8002502 DOI: 10.3390/ijms22063054] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 03/14/2021] [Accepted: 03/15/2021] [Indexed: 12/26/2022] Open
Abstract
Palmitoylethanolamide (PEA) is an endogenous lipid produced on demand by neurons and glial cells that displays neuroprotective properties. It is well known that inflammation and neuronal damage are strictly related processes and that microglia play a pivotal role in their regulation. The aim of the present work was to assess whether PEA could exert its neuroprotective and anti-inflammatory effects through the modulation of microglia reactive phenotypes. In N9 microglial cells, the pre-incubation with PEA blunted the increase of M1 pro-inflammatory markers induced by lipopolysaccharide (LPS), concomitantly increasing those M2 anti-inflammatory markers. Images of microglial cells were processed to obtain a set of morphological parameters that highlighted the ability of PEA to inhibit the LPS-induced M1 polarization and suggested that PEA might induce the anti-inflammatory M2a phenotype. Functionally, PEA prevented Ca2+ transients in both N9 cells and primary microglia and antagonized the neuronal hyperexcitability induced by LPS, as revealed by multi-electrode array (MEA) measurements on primary cortical cultures of neurons, microglia, and astrocyte. Finally, the investigation of the molecular pathway indicated that PEA effects are not mediated by toll-like receptor 4 (TLR4); on the contrary, a partial involvement of cannabinoid type 2 receptor (CB2R) was shown by using a selective receptor inverse agonist.
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Affiliation(s)
- Alessia D’Aloia
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, 20126 Milano, Italy; (A.D.); (F.G.); (V.A.); (M.C.); (M.L.)
| | - Laura Molteni
- School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (L.M.); (E.B.); (L.R.); (R.M.); (S.C.)
| | - Francesca Gullo
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, 20126 Milano, Italy; (A.D.); (F.G.); (V.A.); (M.C.); (M.L.)
| | - Elena Bresciani
- School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (L.M.); (E.B.); (L.R.); (R.M.); (S.C.)
| | - Valentina Artusa
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, 20126 Milano, Italy; (A.D.); (F.G.); (V.A.); (M.C.); (M.L.)
| | - Laura Rizzi
- School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (L.M.); (E.B.); (L.R.); (R.M.); (S.C.)
| | - Michela Ceriani
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, 20126 Milano, Italy; (A.D.); (F.G.); (V.A.); (M.C.); (M.L.)
| | - Ramona Meanti
- School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (L.M.); (E.B.); (L.R.); (R.M.); (S.C.)
| | - Marzia Lecchi
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, 20126 Milano, Italy; (A.D.); (F.G.); (V.A.); (M.C.); (M.L.)
| | - Silvia Coco
- School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (L.M.); (E.B.); (L.R.); (R.M.); (S.C.)
| | - Barbara Costa
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, 20126 Milano, Italy; (A.D.); (F.G.); (V.A.); (M.C.); (M.L.)
- Correspondence: (B.C.); (A.T.)
| | - Antonio Torsello
- School of Medicine and Surgery, University of Milano-Bicocca, 20900 Monza, Italy; (L.M.); (E.B.); (L.R.); (R.M.); (S.C.)
- Correspondence: (B.C.); (A.T.)
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6
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Fernandez-Abascal J, Graziano B, Encalada N, Bianchi L. Glial Chloride Channels in the Function of the Nervous System Across Species. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1349:195-223. [PMID: 35138616 PMCID: PMC11247392 DOI: 10.1007/978-981-16-4254-8_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
In the nervous system, the concentration of Cl- in neurons that express GABA receptors plays a key role in establishing whether these neurons are excitatory, mostly during early development, or inhibitory. Thus, much attention has been dedicated to understanding how neurons regulate their intracellular Cl- concentration. However, regulation of the extracellular Cl- concentration by other cells of the nervous system, including glia and microglia, is as important because it ultimately affects the Cl- equilibrium potential across the neuronal plasma membrane. Moreover, Cl- ions are transported in and out of the cell, via either passive or active transporter systems, as counter ions for K+ whose concentration in the extracellular environment of the nervous system is tightly regulated because it directly affects neuronal excitability. In this book chapter, we report on the Cl- channel types expressed in the various types of glial cells focusing on the role they play in the function of the nervous system in health and disease. Furthermore, we describe the types of stimuli that these channels are activated by, the other solutes that they may transport, and the involvement of these channels in processes such as pH regulation and Regulatory Volume Decrease (RVD). The picture that emerges is one of the glial cells expressing a variety of Cl- channels, encoded by members of different gene families, involved both in short- and long-term regulation of the nervous system function. Finally, we report data on invertebrate model organisms, such as C. elegans and Drosophila, that are revealing important and previously unsuspected functions of some of these channels in the context of living and behaving animals.
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Affiliation(s)
- Jesus Fernandez-Abascal
- Department Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, FL, USA
| | - Bianca Graziano
- Department Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, FL, USA
| | - Nicole Encalada
- Department Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, FL, USA
| | - Laura Bianchi
- Department Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, FL, USA.
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7
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Brief Electrical Stimulation Triggers an Effective Regeneration of Leech CNS. eNeuro 2020; 7:ENEURO.0030-19.2020. [PMID: 32471846 PMCID: PMC7317182 DOI: 10.1523/eneuro.0030-19.2020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 05/05/2020] [Accepted: 05/06/2020] [Indexed: 01/01/2023] Open
Abstract
The search for therapeutic strategies to promote neuronal regeneration following injuries toward functional recovery is of great importance. Brief low-frequency electrical stimulation (ES) has been reported as a useful method to improve neuronal regeneration in different animal models; however, the effect of ES on single neuron behavior has not been shown. Here, we study the effect of brief ES on neuronal regeneration of the CNS of adult medicinal leeches. Studying the regeneration of selected sets of identified neurons allow us to quantify the ES effect per cell type at the single-cell level. Chains of the CNS that were subjected to cut injury were observed for 3 d, and the spontaneous regeneration was compared with the electrically stimulated injured chains. We show that the ES improves the efficiency of regeneration of Retzius cells, as larger masses of the total branching tree traverse the injury site with better directed growth with no effect on the average branching tree length. No antero-posterior polarity was found along regeneration within the leech CNS. Moreover, the microglial cell distribution was examined revealing more microglial cells in proximity to the stimulation site compared with non-stimulated. Our results lay a foundation for future ES-based neuroregenerative therapies.
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8
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Pannexin-1 Channel Regulates ATP Release in Epilepsy. Neurochem Res 2020; 45:965-971. [PMID: 32170674 DOI: 10.1007/s11064-020-02981-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Revised: 01/16/2020] [Accepted: 02/01/2020] [Indexed: 12/28/2022]
Abstract
With the deepening of research on epilepsy in recent decades, great progress has been made in the diagnosis and treatment of the disease. However, the clinical outcome remains unsatisfactory due to the confounding symptoms and complications, as well as complex intrinsic pathogenesis. A better understanding of the pathogenesis of epilepsy should be able to hinder the progress of the disease and improve the therapeutic effectiveness. Since the discovery of pannexin (Panx), unremitting efforts on the study of this gap junction protein family member have revealed its role in participating in the expression of various physiopathological processes. Among them, the activation or inhibition of Panx channel has been shown to regulate the release of adenosine triphosphate (ATP) and other signals, which is very important for the onset and control of nervous system diseases including epilepsy. In this article, we summarize the factors influencing the regulation of Panx channel opening, hoping to find a way to interfere with the activation or inhibition of Panx channel that regulates the signal transduction of ATP and other factors so as to control the progression of epilepsy and improve the quality of life of epileptic patients who fail to respond to the existing medical therapies and those at risk of surgical treatment.
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9
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Segura OM, Abdulnoor L, Hua VV, Solano MJ, Macagno ER, Baker MW. Purinergic modulation of neuronal gap junction circuits in the CNS of the leech. J Neurosci Res 2020; 98:1232-1249. [PMID: 32096570 DOI: 10.1002/jnr.24599] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 01/25/2020] [Accepted: 02/05/2020] [Indexed: 11/08/2022]
Abstract
Gap junctions (GJs) are widely distributed in brains across the animal kingdom. To visualize the GJ- coupled networks of two major mechanosensory neurons in the ganglia of medicinal leeches, we injected these cells with the GJ-permeable tracer Neurobiotin. When diffusion time was limited to only 30 min, tracer coupling was highly variable for both cells, suggesting a possible modulation of GJ permeability. In invertebrates the innexins (homologs of vertebrate pannexins) form the GJs. Because extracellular adenosine triphosphate (ATP) modulates pannexin and leech innexin hemichannel permeability and is released by leech glial cells following injury, we tested the effects of bath application of ATP after the injection of Neurobiotin and observed a significant increase in the number of neurons tracer coupled to the sensory neurons. This effect required the elevation of intracellular Ca2+ and could be produced by bath application of caffeine. Conversely, scavenging endogenous extracellular ATP with the ATPase apyrase decreased the number of coupled cells. ATP also increased electrical conductance and tracer permeability between the bilateral Retzius neurons. This modulatory effect of ATP on GJ coupling was blocked by siRNA knockdown of a P1-like adenosine receptor. Finally, exposure of leech ganglia to extracellular ATP induced a characteristic low frequency (<0.3 Hz) rhythmic bursting activity that was roughly synchronous among multiple neurons, a behavior that was significantly attenuated by the GJ blocker octanol. These findings highlight the mediation by ATP of a robust physiological mechanism for modifying neuronal circuits by rapidly recruiting neurons into active networks and entraining synchronized bursting activity.
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Affiliation(s)
- Oliva Mota Segura
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Lina Abdulnoor
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Vinh-Vincent Hua
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Martha J Solano
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Eduardo R Macagno
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Michael W Baker
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA.,Department of Psychology, Mount Saint Vincent University, Halifax, Nova Scotia, Canada
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10
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Linden J, Koch-Nolte F, Dahl G. Purine Release, Metabolism, and Signaling in the Inflammatory Response. Annu Rev Immunol 2019; 37:325-347. [PMID: 30676821 DOI: 10.1146/annurev-immunol-051116-052406] [Citation(s) in RCA: 208] [Impact Index Per Article: 41.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
ATP, NAD+, and nucleic acids are abundant purines that, in addition to having critical intracellular functions, have evolved extracellular roles as danger signals released in response to cell lysis, apoptosis, degranulation, or membrane pore formation. In general ATP and NAD+ have excitatory and adenosine has anti-inflammatory effects on immune cells. This review focuses on recent advances in our understanding of purine release mechanisms, ectoenzymes that metabolize purines (CD38, CD39, CD73, ENPP1, and ENPP2/autotaxin), and signaling by key P2 purinergic receptors (P2X7, P2Y2, and P2Y12). In addition to metabolizing ATP or NAD+, some purinergic ectoenzymes metabolize other inflammatory modulators, notably lysophosphatidic acid and cyclic GMP-AMP (cGAMP). Also discussed are extracellular signaling effects of NAD+ mediated by ADP-ribosylation, and epigenetic effects of intracellular adenosine mediated by modification of S-adenosylmethionine-dependent DNA methylation.
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Affiliation(s)
- Joel Linden
- Division of Developmental Immunology, La Jolla Institute for Immunology, La Jolla, California 92037, USA; .,Department of Pharmacology, University of California, San Diego, La Jolla, California 92093, USA
| | - Friedrich Koch-Nolte
- Institute of Immunology, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany;
| | - Gerhard Dahl
- Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida 33136, USA;
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11
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Dalgarno R, Leduc-Pessah H, Pilapil A, Kwok CH, Trang T. Intrathecal delivery of a palmitoylated peptide targeting Y382-384 within the P2X7 receptor alleviates neuropathic pain. Mol Pain 2018; 14:1744806918795793. [PMID: 30146934 PMCID: PMC6111392 DOI: 10.1177/1744806918795793] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Pain hypersensitivity resulting from peripheral nerve injury depends on
pathological microglial activation in the dorsal horn of the spinal cord. This
microglial activity is critically modulated by P2X7 receptors (P2X7R) and ATP
stimulation of these receptors produces mechanical allodynia, a defining feature
of neuropathic pain. Peripheral nerve injury increases P2X7R expression and
potentiates its cation channel function in spinal microglia. Here, we report a
means to preferentially block the potentiation of P2X7R function by delivering a
membrane permeant small interfering peptide that targets Y382-384, a
putative tyrosine phosphorylation site within the P2X7R intracellular C-terminal
domain. Intrathecal administration of this palmitoylated peptide
(P2X7R379-389) transiently reversed mechanical allodynia caused
by peripheral nerve injury in both male and female rats. Furthermore, targeting
Y382-384 suppressed P2X7R-mediated release of cytokine tumor
necrosis factor alpha and blocked the adoptive transfer of mechanical allodynia
caused by intrathecal injection of P2X7R-stimulated microglia. Thus,
Y382-384 site-specific modulation of P2X7R is an important
microglial mechanism in neuropathic pain.
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Affiliation(s)
- Rebecca Dalgarno
- 1 Department of Comparative Biology & Experimental Medicine, University of Calgary, Calgary, Alberta, Canada.,2 Department of Physiology & Pharmacology, University of Calgary, Calgary, Alberta, Canada.,3 Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada
| | - Heather Leduc-Pessah
- 1 Department of Comparative Biology & Experimental Medicine, University of Calgary, Calgary, Alberta, Canada.,2 Department of Physiology & Pharmacology, University of Calgary, Calgary, Alberta, Canada.,3 Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada
| | - Alexandra Pilapil
- 1 Department of Comparative Biology & Experimental Medicine, University of Calgary, Calgary, Alberta, Canada.,2 Department of Physiology & Pharmacology, University of Calgary, Calgary, Alberta, Canada.,3 Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada
| | - Charlie Ht Kwok
- 1 Department of Comparative Biology & Experimental Medicine, University of Calgary, Calgary, Alberta, Canada.,2 Department of Physiology & Pharmacology, University of Calgary, Calgary, Alberta, Canada.,3 Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada
| | - Tuan Trang
- 1 Department of Comparative Biology & Experimental Medicine, University of Calgary, Calgary, Alberta, Canada.,2 Department of Physiology & Pharmacology, University of Calgary, Calgary, Alberta, Canada.,3 Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada
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12
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Zhang W, Liu MW, Li M, Xiao W, Zhang XW, He HJ, Chen YB, Ding L, Luo KJ. Unexpected link between insect innexins and apoptosis of HeLa cells. ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY 2018; 99:e21473. [PMID: 29862562 DOI: 10.1002/arch.21473] [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: 06/08/2023]
Abstract
Little is known about how mammalian cells respond to the expression of innexins (Inxs), which are known to mediate cell-to-cell communication that causes apoptosis in the cells of the insect Spodoptera litura. The mammalian expression system, p3xFLAG tag protein, containing the CMV promoter, allowed us to construct two C-terminally elongated innexins (Cte-Inxs), SpliInx2 (Inx2-FLAG), and SpliInx3 (Inx3-FLAG), which were predicted to have the same secondary topological structures as the native SpliInx2 and SpliInx3. Here, we found that only the mRNAs of the two Cte-Inxs were expressed under the control of the CMV promoter in HeLa cells. Unexpectedly, mRNA expression of the two Cte-Inxs enhanced apoptosis of HeLa cells. The two Cte-Inx mRNAs were associated with a significant decrease in Akt phosphorylation in HeLa cells undergoing apoptosis. Furthermore, Inx3-FLAG mRNA expression in nonapoptotic HCT116 cells was also associated with a significant decrease in the levels of phosphorylated Akt. Intriguingly, expression of the mRNAs of the two Cte-Inxs did not activate caspase 3, but it markedly reduced Bid levels in HeLa cells undergoing apoptosis. These results suggest that mRNA expression of the two Cte-Inxs may activate a Bid-dependent apoptotic pathway in HeLa cells. Our study demonstrates that invertebrate gap junction mRNAs can function in vertebrate cancer cells as tumor suppressors.
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Affiliation(s)
- Wei Zhang
- School of Life Sciences, Yunnan University, Kunming, P.R. China
- Key Laboratory for Biochemistry and Molecular Biology of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
- Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
| | - Meng-Wei Liu
- School of Life Sciences, Yunnan University, Kunming, P.R. China
- Key Laboratory for Biochemistry and Molecular Biology of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
| | - Ming Li
- School of Life Sciences, Yunnan University, Kunming, P.R. China
- Key Laboratory for Biochemistry and Molecular Biology of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
- Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
| | - Wei Xiao
- School of Life Sciences, Yunnan University, Kunming, P.R. China
| | - Xue-Wen Zhang
- School of Life Sciences, Yunnan University, Kunming, P.R. China
- Key Laboratory for Biochemistry and Molecular Biology of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
- Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
| | - Hao-Juan He
- School of Life Sciences, Yunnan University, Kunming, P.R. China
- Key Laboratory for Biochemistry and Molecular Biology of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
- Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
| | - Ya-Bin Chen
- School of Life Sciences, Yunnan University, Kunming, P.R. China
- Key Laboratory for Biochemistry and Molecular Biology of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
| | - Lei Ding
- School of Life Sciences, Yunnan University, Kunming, P.R. China
- Key Laboratory for Biochemistry and Molecular Biology of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
| | - Kai-Jun Luo
- School of Life Sciences, Yunnan University, Kunming, P.R. China
- Key Laboratory for Biochemistry and Molecular Biology of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
- Key Laboratory for Animal Genetic Diversity and Evolution of High Education in Yunnan Province, Yunnan University, Kunming, P.R. China
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13
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Hatano N, Ohya S, Imaizumi Y, Clark RB, Belke D, Giles WR. ATP increases [Ca 2+ ] i and activates a Ca 2+ -dependent Cl - current in rat ventricular fibroblasts. Exp Physiol 2018; 103:666-682. [PMID: 29493027 DOI: 10.1113/ep086822] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 02/22/2018] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? Although electrophysiological and biophysical characteristics of heart fibroblasts have been studied in detail, their responses to prominent paracrine agents in the myocardium have not been addressed adequately. Our experiments characterize changes in cellular electrophysiology and intracellular calcium in response to ATP. What is the main finding and its importance? In rat ventricular fibroblasts maintained in cell culture, we find that ATP activates a specific subset of Ca2+ -activated Cl- channels as a consequence of binding to P2Y purinoceptors and then activating phospholipase C. This response is not dependent on [Ca2+ ]o but requires an increase in [Ca2+ ]i and is modulated by the type of nucleotide that is the purinergic agonist. ABSTRACT Effects of ATP on enzymatically isolated rat ventricular fibroblasts maintained in short-term (36-72 h) cell culture were examined. Immunocytochemical staining of these cells revealed that a fibroblast, as opposed to a myofibroblast, phenotype was predominant. ATP, ADP or uridine 5'-triphosphate (UTP) all produced large increases in [Ca2+ ]i . Voltage-clamp studies (amphotericin-perforated patch) showed that ATP (1-100 μm) activated an outwardly rectifying current, with a reversal potential very close to the Nernst potential for Cl- . In contrast, ADP was much less effective, and UTP produced no detectable current. The non-selective Cl- channel blockers niflumic acid, DIDS and NPPB (each at 100 μm), blocked the responses to 100 μm ATP. An agonist for P2Y purinoceptors, 2-MTATP, activated a very similar outwardly rectifying C1- current. The P2Y receptor antagonists, suramin and PPADS (100 μm each), significantly inhibited the Cl- current produced by 100 μm ATP. ATP was able to activate this Cl- current when [Ca2+ ]o was removed, but not when [Ca2+ ]i was buffered with BAPTA-AM. In the presence of the phospholipase C inhibitor U73122, this Cl- current could not be activated. PCR analysis revealed strong signals for a number of P2Y purinoceptors and for the Ca2+ -activated Cl- channel, TMEM16F (also denoted ANO6). In summary, these results demonstrate that activation of P2Y receptors by ATP causes a phospholipase C-dependent increase in [Ca2+ ]i , followed by activation of a Ca2+ -dependent Cl- current in rat ventricular fibroblasts.
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Affiliation(s)
- Noriyuki Hatano
- Laboratory of Cellular Pharmacology, School of Pharmacy, Aichi-Gakuin University, Nagoya, Japan
| | - Susumu Ohya
- Department of Pharmacology, Graduate School of Medical Sciences, Nagoya City University, Nagoya, 467-8601, Japan
| | - Yuji Imaizumi
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, 467-8603, Japan
| | - Robert B Clark
- Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
| | - Darrell Belke
- Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
| | - Wayne R Giles
- Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
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14
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Dvoriantchikova G, Pronin A, Kurtenbach S, Toychiev A, Chou TH, Yee CW, Prindeville B, Tayou J, Porciatti V, Sagdullaev BT, Slepak VZ, Shestopalov VI. Pannexin 1 sustains the electrophysiological responsiveness of retinal ganglion cells. Sci Rep 2018; 8:5797. [PMID: 29643381 PMCID: PMC5895610 DOI: 10.1038/s41598-018-23894-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Accepted: 03/20/2018] [Indexed: 12/16/2022] Open
Abstract
Pannexin 1 (Panx1) forms ATP-permeable membrane channels that play a key role in purinergic signaling in the nervous system in both normal and pathological conditions. In the retina, particularly high levels of Panx1 are found in retinal ganglion cells (RGCs), but the normal physiological function in these cells remains unclear. In this study, we used patch clamp recordings in the intact inner retina to show that evoked currents characteristic of Panx1 channel activity were detected only in RGCs, particularly in the OFF-type cells. The analysis of pattern electroretinogram (PERG) recordings indicated that Panx1 contributes to the electrical output of the retina. Consistently, PERG amplitudes were significantly impaired in the eyes with targeted ablation of the Panx1 gene in RGCs. Under ocular hypertension and ischemic conditions, however, high Panx1 activity permeated cell membranes and facilitated the selective loss of RGCs or stably transfected Neuro2A cells. Our results show that high expression of the Panx1 channel in RGCs is essential for visual function in the inner retina but makes these cells highly sensitive to mechanical and ischemic stresses. These findings are relevant to the pathophysiology of retinal disorders induced by increased intraocular pressure, such as glaucoma.
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Affiliation(s)
- Galina Dvoriantchikova
- Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami Miller School of Medicine, 900 NW 10 Ave., Miami, FL, 33136, USA
| | - Alexey Pronin
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, 1600 NW 10th Ave., Miami, FL, 33136, USA
| | - Sarah Kurtenbach
- Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami Miller School of Medicine, 900 NW 10 Ave., Miami, FL, 33136, USA
| | - Abduqodir Toychiev
- Department of Ophthalmology, Weill Cornell Medical College, 156 William St., New York, NY, 10038, USA
| | - Tsung-Han Chou
- Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami Miller School of Medicine, 900 NW 10 Ave., Miami, FL, 33136, USA
| | - Christopher W Yee
- Winifred Masterson Burke Medical Research Institute, New York, 785 Mamaroneck Ave., White Plains, NY, 10605, USA
| | - Breanne Prindeville
- Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami Miller School of Medicine, 900 NW 10 Ave., Miami, FL, 33136, USA
| | - Junior Tayou
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, 1600 NW 10th Ave., Miami, FL, 33136, USA
| | - Vittorio Porciatti
- Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami Miller School of Medicine, 900 NW 10 Ave., Miami, FL, 33136, USA
| | - Botir T Sagdullaev
- Department of Ophthalmology, Weill Cornell Medical College, 156 William St., New York, NY, 10038, USA
- Winifred Masterson Burke Medical Research Institute, New York, 785 Mamaroneck Ave., White Plains, NY, 10605, USA
| | - Vladlen Z Slepak
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, 1600 NW 10th Ave., Miami, FL, 33136, USA
| | - Valery I Shestopalov
- Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami Miller School of Medicine, 900 NW 10 Ave., Miami, FL, 33136, USA.
- Department of Cell Biology, University of Miami Miller School of Medicine, 1600 NW 10th Ave., Miami, FL, 33136, USA.
- Vavilov Institute for General Genetics, Gubkina Str. 3, Russian Academy of Sciences, Moscow, Russia.
- Kharkevich Institute for Information Transmission Problems, Russian Academy of Sciences, Moscow, Russia.
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15
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Yin X, Feng L, Ma D, Yin P, Wang X, Hou S, Hao Y, Zhang J, Xin M, Feng J. Roles of astrocytic connexin-43, hemichannels, and gap junctions in oxygen-glucose deprivation/reperfusion injury induced neuroinflammation and the possible regulatory mechanisms of salvianolic acid B and carbenoxolone. J Neuroinflammation 2018; 15:97. [PMID: 29587860 PMCID: PMC5872583 DOI: 10.1186/s12974-018-1127-3] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Accepted: 03/12/2018] [Indexed: 02/07/2023] Open
Abstract
Background Glia-mediated neuroinflammation is related to brain injury exacerbation after cerebral ischemia/reperfusion (I/R) injury. Astrocytic hemichannels or gap junctions, which were mainly formed by connexin-43, have been implicated in I/R damage. However, the exact roles of astrocytic hemichannels and gap junction in neuroinflammatory responses induced by I/R injury remain unknown. Methods Primary cultured astrocytes were subjected to OGD/R injury, an in vitro model of I/R injury. Salvianolic acid B (SalB) or carbenoxolone (CBX) were applied for those astrocytes. Besides, Cx43 mimetic peptides Gap19 or Gap26 were also applied during OGD/R injury; Cx43 protein levels were determined by western blot and cytoimmunofluorescene staining, hemichannel activities by Ethidium bromide uptake and ATP concentration detection, and gap junction intercellular communication (GJIC) permeability by parachute assay. Further, astrocyte-conditioned medium (ACM) was collected and incubated with microglia. Meanwhile, ATP or apyrase were applied to explore the role of ATP during OGD/R injury. Microglial activation, M1/M2 phenotypes, and M1/M2-related cytokines were detected. Also, microglia-conditioned medium (MEM) was collected and incubated with astrocytes to further investigate its influence on astrocytic hemichannel activity and GJIC permeability. Lastly, effects of ACM and MCM on neuronal viability were detected by flow cytometry. Results We found that OGD/R induced abnormally opened hemichannels with increased ATP release and EtBr uptake but reduced GJIC permeability. WB tests showed decreased astrocytic plasma membrane’s Cx43, while showing an increase in cytoplasma. Treating OGD/R-injured microglia with ATP or OGD/R-ACM induced further microglial activation and secondary pro-inflammatory cytokine release, with the M1 phenotype predominating. Conversely, astrocytes incubated with OGD/R-MCM exhibited increased hemichannel opening but reduced GJIC coupling. Both SalB and CBX inhibited abnormal astrocytic hemichannel opening and ATP release and switched the activated microglial phenotype from M1 to M2, thus providing effective neuroprotection. Application of Gap19 or Gap26 showed similar results with CBX. We also found that OGD/R injury caused both plasma membrane p-Cx43(Ser265) and p-Src(Tyr416) significantly upregulated; application of SalB may be inhibiting Src kinase and attenuating Cx43 internalization. Meanwhile, CBX treatment induced obviously downregulation of p-Cx43(Ser368) and p-PKC(Ser729) protein levels in plasma membrane. Conclusions We propose a vicious cycle exists between astrocytic hemichannel and microglial activation after OGD/R injury, which would aggravate neuroinflammatory responses and neuronal damage. Astrocytic Cx43, hemichannels, and GJIC play critical roles in OGD/R injury-induced neuroinflammatory responses; treatment differentially targeting astrocytic Cx43, hemichannels, and GJIC may provide novel avenues for therapeutics during cerebral I/R injury. Electronic supplementary material The online version of this article (10.1186/s12974-018-1127-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Xiang Yin
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China
| | - Liangshu Feng
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China
| | - Di Ma
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China
| | - Ping Yin
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China
| | - Xinyu Wang
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China
| | - Shuai Hou
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China
| | - Yulei Hao
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China
| | - Jingdian Zhang
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China
| | - Meiying Xin
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China
| | - Jiachun Feng
- Department of Neurology and Neuroscience Center, the First Hospital of Jilin University, Changchun, Jilin Province, 130021, People's Republic of China.
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16
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Plattner H, Verkhratsky A. Inseparable tandem: evolution chooses ATP and Ca2+ to control life, death and cellular signalling. Philos Trans R Soc Lond B Biol Sci 2017; 371:rstb.2015.0419. [PMID: 27377729 DOI: 10.1098/rstb.2015.0419] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/29/2016] [Indexed: 01/01/2023] Open
Abstract
From the very dawn of biological evolution, ATP was selected as a multipurpose energy-storing molecule. Metabolism of ATP required intracellular free Ca(2+) to be set at exceedingly low concentrations, which in turn provided the background for the role of Ca(2+) as a universal signalling molecule. The early-eukaryote life forms also evolved functional compartmentalization and vesicle trafficking, which used Ca(2+) as a universal signalling ion; similarly, Ca(2+) is needed for regulation of ciliary and flagellar beat, amoeboid movement, intracellular transport, as well as of numerous metabolic processes. Thus, during evolution, exploitation of atmospheric oxygen and increasingly efficient ATP production via oxidative phosphorylation by bacterial endosymbionts were a first step for the emergence of complex eukaryotic cells. Simultaneously, Ca(2+) started to be exploited for short-range signalling, despite restrictions by the preset phosphate-based energy metabolism, when both phosphates and Ca(2+) interfere with each other because of the low solubility of calcium phosphates. The need to keep cytosolic Ca(2+) low forced cells to restrict Ca(2+) signals in space and time and to develop energetically favourable Ca(2+) signalling and Ca(2+) microdomains. These steps in tandem dominated further evolution. The ATP molecule (often released by Ca(2+)-regulated exocytosis) rapidly grew to be the universal chemical messenger for intercellular communication; ATP effects are mediated by an extended family of purinoceptors often linked to Ca(2+) signalling. Similar to atmospheric oxygen, Ca(2+) must have been reverted from a deleterious agent to a most useful (intra- and extracellular) signalling molecule. Invention of intracellular trafficking further increased the role for Ca(2+) homeostasis that became critical for regulation of cell survival and cell death. Several mutually interdependent effects of Ca(2+) and ATP have been exploited in evolution, thus turning an originally unholy alliance into a fascinating success story.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'.
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Affiliation(s)
- Helmut Plattner
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany
| | - Alexei Verkhratsky
- Faculty of Biological Sciences, University of Manchester, Manchester M13 9PT, UK Achucarro Center for Neuroscience, IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain Department of Neurosciences, University of the Basque Country UPV/EHU and CIBERNED, Leioa, Spain University of Nizhny Novgorod, Nizhny Novgorod 603022, Russia
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17
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Jiang P, Xing F, Guo B, Yang J, Li Z, Wei W, Hu F, Lee I, Zhang X, Pan L, Xu J. Nucleotide transmitters ATP and ADP mediate intercellular calcium wave communication via P2Y12/13 receptors among BV-2 microglia. PLoS One 2017; 12:e0183114. [PMID: 28800362 PMCID: PMC5553643 DOI: 10.1371/journal.pone.0183114] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 07/28/2017] [Indexed: 12/24/2022] Open
Abstract
Nerve injury is accompanied by a liberation of diverse nucleotides, some of which act as ‘find/eat-me’ signals in mediating neuron-glial interplay. Intercellular Ca2+ wave (ICW) communication is the main approach by which glial cells interact and coordinate with each other to execute immune defense. However, the detailed mechanisms on how these nucleotides participate in ICW communication remain largely unclear. In the present work, we employed a mechanical stimulus to an individual BV-2 microglia to simulate localized injury. Remarkable ICW propagation was observed no matter whether calcium was in the environment or not. Apyrase (ATP/ADP-hydrolyzing enzyme), suramin (broad-spectrum P2 receptor antagonist), 2-APB (IP3 receptor blocker) and thapsigargin (endoplasmic reticulum calcium pump inhibitor) potently inhibited these ICWs, respectively, indicating the dependence of nucleotide signals and P2Y receptors. Then, we detected the involvement of five naturally occurring nucleotides (ATP, ADP, UTP, UDP and UDP-glucose) by desensitizing receptors. Results showed that desensitization with ATP and ADP could block ICW propagation in a dose-dependent manner, whereas other nucleotides had little effect. Meanwhile, the expression of P2Y receptors in BV-2 microglia was identified and their contributions were analyzed, from which we suggested P2Y12/13 receptors activation mostly contributed to ICWs. Besides, we estimated that extracellular ATP and ADP concentration sensed by BV-2 microglia was about 0.3 μM during ICWs by analyzing calcium dynamic characteristics. Taken together, these results demonstrated that the nucleotides ATP and ADP were predominant signal transmitters in mechanical stimulation-induced ICW communication through acting on P2Y12/13 receptors in BV-2 microglia.
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Affiliation(s)
- Pengchong Jiang
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
| | - Fulin Xing
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
| | - Bu Guo
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
| | - Jianyu Yang
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
| | - Zheming Li
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
| | - Wei Wei
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
| | - Fen Hu
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
| | - Imshik Lee
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
| | - Xinzheng Zhang
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi, China
| | - Leiting Pan
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
- The 2011 Project Collaborative Innovation Center for Biological Therapy, Nankai University, Tianjin, China
- * E-mail:
| | - Jingjun Xu
- The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, TEDA Institute of Applied Physics and School of Physics, Nankai University, Tianjin, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi, China
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18
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Baker MW, Macagno ER. Gap junction proteins and the wiring (Rewiring) of neuronal circuits. Dev Neurobiol 2017; 77:575-586. [PMID: 27512961 DOI: 10.1002/dneu.22429] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Revised: 08/01/2016] [Accepted: 08/08/2016] [Indexed: 11/11/2022]
Abstract
The unique morphology and pattern of synaptic connections made by a neuron during development arise in part by an extended period of growth in which cell-cell interactions help to sculpt the arbor into its final shape, size, and participation in different synaptic networks. Recent experiments highlight a guiding role played by gap junction proteins in controlling this process. Ectopic and overexpression studies in invertebrates have revealed that the selective expression of distinct gap junction genes in neurons and glial cells is sufficient to establish selective new connections in the central nervous systems of the leech (Firme et al. [2012]: J Neurosci 32:14265-14270), the nematode (Rabinowitch et al. [2014]: Nat Commun 5:4442), and the fruit fly (Pézier et al., 2016: PLoS One 11:e0152211). We present here an overview of this work and suggest that gap junction proteins, in addition to their synaptic/communicative functions, have an instructive role as recognition and adhesion factors. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 575-586, 2017.
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Affiliation(s)
- Michael W Baker
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, 92093
| | - Eduardo R Macagno
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, 92093
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19
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Gajardo-Gómez R, Labra VC, Orellana JA. Connexins and Pannexins: New Insights into Microglial Functions and Dysfunctions. Front Mol Neurosci 2016; 9:86. [PMID: 27713688 PMCID: PMC5031785 DOI: 10.3389/fnmol.2016.00086] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 09/05/2016] [Indexed: 12/11/2022] Open
Abstract
Under physiological conditions, microglia adopt a resting phenotype associated with the production of anti-inflammatory and neurotrophic factors. In response to a wide variety of insults, these cells shift to an activated phenotype that is necessary for the proper restoration of brain homeostasis. However, when the intensity of a threat is relatively high, microglial activation worsens the progression of damage rather than providing protection, with potentially significant consequences for neuronal survival. Coordinated interactions among microglia and other brain cells, including astrocytes and neurons, are critical for the development of timely and optimal inflammatory responses in the brain parenchyma. Tissue synchronization is in part mediated by connexins and pannexins, which are protein families that form different plasma membrane channels to communicate with neighboring cells. Gap junction channels (which are exclusively formed by connexins in vertebrates) connect the cytoplasm of contacting cells to coordinate electrical and metabolic coupling. Hemichannels (HCs) and pannexons (which are formed by connexins and pannexins, respectively) communicate the intra- and extracellular compartments and serve as diffusion pathways for the exchange of ions and small molecules. In this review article, we discuss the available evidence concerning the functional expression and regulation of connexin- and pannexin-based channels in microglia and their contributions to microglial function and dysfunction. Specifically, we focus on the possible implications of these channels in microglia-to-microglia, microglia-to-astrocyte and neuron-to-microglia interactions in the inflamed brain.
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Affiliation(s)
- Rosario Gajardo-Gómez
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile Santiago, Chile
| | - Valeria C Labra
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile Santiago, Chile
| | - Juan A Orellana
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile Santiago, Chile
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20
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Dahl G. ATP release through pannexon channels. Philos Trans R Soc Lond B Biol Sci 2016; 370:rstb.2014.0191. [PMID: 26009770 DOI: 10.1098/rstb.2014.0191] [Citation(s) in RCA: 170] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Extracellular adenosine triphosphate (ATP) serves as a signal for diverse physiological functions, including spread of calcium waves between astrocytes, control of vascular oxygen supply and control of ciliary beat in the airways. ATP can be released from cells by various mechanisms. This review focuses on channel-mediated ATP release and its main enabler, Pannexin1 (Panx1). Six subunits of Panx1 form a plasma membrane channel termed 'pannexon'. Depending on the mode of stimulation, the pannexon has large conductance (500 pS) and unselective permeability to molecules less than 1.5 kD or is a small (50 pS), chloride-selective channel. Most physiological and pathological stimuli induce the large channel conformation, whereas the small conformation so far has only been observed with exclusive voltage activation of the channel. The interaction between pannexons and ATP is intimate. The pannexon is not only the conduit for ATP, permitting ATP efflux from cells down its concentration gradient, but the pannexon is also modulated by ATP. The channel can be activated by ATP through both ionotropic P2X as well as metabotropic P2Y purinergic receptors. In the absence of a control mechanism, this positive feedback loop would lead to cell death owing to the linkage of purinergic receptors with apoptotic processes. A control mechanism preventing excessive activation of the purinergic receptors is provided by ATP binding (with low affinity) to the Panx1 protein and gating the channel shut.
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Affiliation(s)
- Gerhard Dahl
- School of Medicine, University of Miami, 1600 NW 10th Avenue, Miami, FL 33136, USA
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Wang SP, Chen FY, Dong LX, Zhang YQ, Chen HY, Qiao K, Wang KJ. A novel innexin2 forming membrane hemichannel exhibits immune responses and cell apoptosis in Scylla paramamosain. FISH & SHELLFISH IMMUNOLOGY 2015; 47:485-499. [PMID: 26384843 DOI: 10.1016/j.fsi.2015.09.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Revised: 09/06/2015] [Accepted: 09/14/2015] [Indexed: 06/05/2023]
Abstract
Innexins are a class of transmembrane proteins that are important for embryonic development, morphogenesis and electrical synapse formation. In the present study, a novel innexin2 gene from Scylla paramamosain was named Sp-inx2 and characterized. The complete cDNA and genomic DNA sequences of Sp-inx2 were revealed. Sp-inx2 mRNA transcripts were distributed in various tissues of S. paramamosain and were most abundant in the hemocytes. The Sp-inx2 was significantly upregulated in hemocyte, gill and hepatopancreas tissues with the challenge of either Vibrio alginolyticus, Vibrio parahaemolyticus or lipopolysaccharides (LPSs) when analyzed at 3 and 6 h using quantitative real-time PCR, suggesting that it could activate an immune response against the challenge of LPSs or Vibrio species. Using the chemical inhibitors carbenoxolone and probenecid, the absorption of the fluorescent dye Lucifer yellow decreased in the primary cultured hemocytes of crabs, thus confirming that hemichannels composed of Sp-inx2 existed in the crab hemocytes. With LPS stimulation, the level of mRNA transcripts and protein expression of Sp-inx2 in the same cultured hemocytes gradually increased from 6 to 48 h, while the activity of hemichannels was down-regulated at 6 and 12 h, demonstrating that LPSs could modulate the absorption activity of hemichannels in addition to its upregulation of Sp-inx2 gene expression. Furthermore, the dye uptake rate in HeLa cells in which Sp-inx2 was ectopically expressed increased dramatically but the increase was significantly down-regulated with the addition of 50 μg mL(-1) LPS, suggesting that the LPS stimulation could effectively reduce the activity of hemichannels. Interestingly, with the ectopic expression of Sp-inx2 in HeLa and EPC cells, apoptosis spontaneously occurred in both cultured cell lines when detected using TUNEL assay. In summary, a new Sp-inx2 gene was first characterized in a marine animal S. paramamosain and it had a function associated with immune response and cell apoptosis.
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Affiliation(s)
- Shu-Ping Wang
- State Key Laboratory of Marine Environmental Science, College of Ocean & Earth Science, Xiamen University, Xiamen, Fujian, PR China
| | - Fang-Yi Chen
- State Key Laboratory of Marine Environmental Science, College of Ocean & Earth Science, Xiamen University, Xiamen, Fujian, PR China; Fujian Collaborative Innovation Center for Exploitation and Utilization of Marine Biological Resources, Xiamen University, Xiamen, Fujian, PR China; Fujian Engineering Laboratory of Marine Bioproducts and Technology, Xiamen University, Xiamen, Fujian, PR China
| | - Li-Xia Dong
- State Key Laboratory of Marine Environmental Science, College of Ocean & Earth Science, Xiamen University, Xiamen, Fujian, PR China
| | - Ya-Qun Zhang
- State Key Laboratory of Marine Environmental Science, College of Ocean & Earth Science, Xiamen University, Xiamen, Fujian, PR China
| | - Hui-Yun Chen
- State Key Laboratory of Marine Environmental Science, College of Ocean & Earth Science, Xiamen University, Xiamen, Fujian, PR China; Fujian Collaborative Innovation Center for Exploitation and Utilization of Marine Biological Resources, Xiamen University, Xiamen, Fujian, PR China; Fujian Engineering Laboratory of Marine Bioproducts and Technology, Xiamen University, Xiamen, Fujian, PR China
| | - Kun Qiao
- State Key Laboratory of Marine Environmental Science, College of Ocean & Earth Science, Xiamen University, Xiamen, Fujian, PR China
| | - Ke-Jian Wang
- State Key Laboratory of Marine Environmental Science, College of Ocean & Earth Science, Xiamen University, Xiamen, Fujian, PR China; Fujian Collaborative Innovation Center for Exploitation and Utilization of Marine Biological Resources, Xiamen University, Xiamen, Fujian, PR China; Fujian Engineering Laboratory of Marine Bioproducts and Technology, Xiamen University, Xiamen, Fujian, PR China.
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Decrock E, De Bock M, Wang N, Bultynck G, Giaume C, Naus CC, Green CR, Leybaert L. Connexin and pannexin signaling pathways, an architectural blueprint for CNS physiology and pathology? Cell Mol Life Sci 2015; 72:2823-51. [PMID: 26118660 PMCID: PMC11113968 DOI: 10.1007/s00018-015-1962-7] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Accepted: 06/11/2015] [Indexed: 02/06/2023]
Abstract
The central nervous system (CNS) is composed of a highly heterogeneous population of cells. Dynamic interactions between different compartments (neuronal, glial, and vascular systems) drive CNS function and allow to integrate and process information as well as to respond accordingly. Communication within this functional unit, coined the neuro-glio-vascular unit (NGVU), typically relies on two main mechanisms: direct cell-cell coupling via gap junction channels (GJCs) and paracrine communication via the extracellular compartment, two routes to which channels composed of transmembrane connexin (Cx) or pannexin (Panx) proteins can contribute. Multiple isoforms of both protein families are present in the CNS and each CNS cell type is characterized by a unique Cx/Panx portfolio. Over the last two decades, research has uncovered a multilevel platform via which Cxs and Panxs can influence different cellular functions within a tissue: (1) Cx GJCs enable a direct cell-cell communication of small molecules, (2) Cx hemichannels and Panx channels can contribute to autocrine/paracrine signaling pathways, and (3) different structural domains of these proteins allow for channel-independent functions, such as cell-cell adhesion, interactions with the cytoskeleton, and the activation of intracellular signaling pathways. In this paper, we discuss current knowledge on their multifaceted contribution to brain development and to specific processes in the NGVU, including synaptic transmission and plasticity, glial signaling, vasomotor control, and blood-brain barrier integrity in the mature CNS. By highlighting both physiological and pathological conditions, it becomes evident that Cxs and Panxs can play a dual role in the CNS and that an accurate fine-tuning of each signaling mechanism is crucial for normal CNS physiology.
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Affiliation(s)
- Elke Decrock
- Physiology Group, Department of Basic Medical Sciences, Ghent University, De Pintelaan 185 (Block B, 3rd floor), 9000 Ghent, Belgium
| | - Marijke De Bock
- Physiology Group, Department of Basic Medical Sciences, Ghent University, De Pintelaan 185 (Block B, 3rd floor), 9000 Ghent, Belgium
| | - Nan Wang
- Physiology Group, Department of Basic Medical Sciences, Ghent University, De Pintelaan 185 (Block B, 3rd floor), 9000 Ghent, Belgium
| | - Geert Bultynck
- Laboratory of Molecular and Cellular Signalling, Department of Cellular and Molecular Medicine, KU Leuven, Louvain, Belgium
| | - 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
| | - Christian C. Naus
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC V6T 1Z3 Canada
| | - Colin R. Green
- Department of Ophthalmology, The University of Auckland, Auckland, New Zealand
| | - Luc Leybaert
- Physiology Group, Department of Basic Medical Sciences, Ghent University, De Pintelaan 185 (Block B, 3rd floor), 9000 Ghent, Belgium
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Montero TD, Orellana JA. Hemichannels: new pathways for gliotransmitter release. Neuroscience 2014; 286:45-59. [PMID: 25475761 DOI: 10.1016/j.neuroscience.2014.11.048] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Revised: 10/14/2014] [Accepted: 11/20/2014] [Indexed: 01/16/2023]
Abstract
Growing evidence suggests that glial cells express virtually all known types of neurotransmitter receptors, enabling them to sense neuronal activity and microenvironment changes by responding locally via the Ca(2+)-dependent release of bioactive molecules, known as "gliotransmitters". Several mechanisms of gliotransmitter release have been documented. One of these mechanisms involves the opening of plasma membrane channels, known as hemichannels. These channels are composed of six protein subunits consisting of connexins or pannexins, two highly conserved protein families encoded by 21 or 3 genes, respectively, in humans. Most data indicate that under physiological conditions, glial cell hemichannels have low activity, but this activity is sufficient to ensure the release of relevant quantities of gliotransmitters to the extracellular milieu, including ATP, glutamate, adenosine and glutathione. Nevertheless, it has been suggested that dysregulations of hemichannel properties could be critical in the beginning and during the maintenance of homeostatic imbalances observed in several brain diseases. In this study, we review the current knowledge on the hemichannel-dependent release of gliotransmitters in the physiology and pathophysiology of the CNS.
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Affiliation(s)
- T D Montero
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - J A Orellana
- Departamento de Neurología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
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Palacios-Prado N, Huetteroth W, Pereda AE. Hemichannel composition and electrical synaptic transmission: molecular diversity and its implications for electrical rectification. Front Cell Neurosci 2014; 8:324. [PMID: 25360082 PMCID: PMC4197764 DOI: 10.3389/fncel.2014.00324] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Accepted: 09/26/2014] [Indexed: 11/29/2022] Open
Abstract
Unapposed hemichannels (HCs) formed by hexamers of gap junction proteins are now known to be involved in various cellular processes under both physiological and pathological conditions. On the other hand, less is known regarding how differences in the molecular composition of HCs impact electrical synaptic transmission between neurons when they form intercellular heterotypic gap junctions (GJs). Here we review data indicating that molecular differences between apposed HCs at electrical synapses are generally associated with rectification of electrical transmission. Furthermore, this association has been observed at both innexin and connexin (Cx) based electrical synapses. We discuss the possible molecular mechanisms underlying electrical rectification, as well as the potential contribution of intracellular soluble factors to this phenomenon. We conclude that asymmetries in molecular composition and sensitivity to cellular factors of each contributing hemichannel can profoundly influence the transmission of electrical signals, endowing electrical synapses with more complex functional properties.
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Affiliation(s)
- Nicolás Palacios-Prado
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine Bronx, NY, USA ; Marine Biological Laboratory, Woods Hole Massachusetts, MA, USA
| | - Wolf Huetteroth
- Marine Biological Laboratory, Woods Hole Massachusetts, MA, USA ; Department of Neurobiology, University of Konstanz Konstanz, Germany
| | - Alberto E Pereda
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine Bronx, NY, USA ; Marine Biological Laboratory, Woods Hole Massachusetts, MA, USA
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25
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Sangaletti R, Dahl G, Bianchi L. Mechanosensitive unpaired innexin channels in C. elegans touch neurons. Am J Physiol Cell Physiol 2014; 307:C966-77. [PMID: 25252948 DOI: 10.1152/ajpcell.00246.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Invertebrate innexin proteins share sequence homology with vertebrate pannexins and general membrane topology with both pannexins and connexins. While connexins form gap junctions that mediate intercellular communication, pannexins are thought to function exclusively as plasma membrane channels permeable to both ions and small molecules. Undoubtedly, certain innexins function as gap junction proteins. However, due to sequence similarity to pannexins, it was postulated that innexins also function as plasma membrane channels. Indeed, some of the leech innexins were found to mediate ATP release as unpaired membrane channels with shared pharmacology to pannexin channels. We show here that Caenorhabditis elegans touch-sensing neurons express a mechanically gated innexin channel with a conductance of ∼1 nS and voltage-dependent and K(+)-selective subconductance state. We also show that C. elegans touch neurons take up ethidium bromide through a mechanism that is activated and blocked by innexin activating stimuli and inhibitors, respectively. Finally, we present evidence that touch neurons' innexins are required for cell death induced by chemical ischemia. Our work demonstrates that innexins function as plasma membrane channels in native C. elegans neurons, where they may play a role in pathological cell death.
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Affiliation(s)
- Rachele Sangaletti
- Department of Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, Florida
| | - Gerhard Dahl
- Department of Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, Florida
| | - Laura Bianchi
- Department of Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, Florida
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26
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Toll-like receptor-triggered calcium mobilization protects mice against bacterial infection through extracellular ATP release. Infect Immun 2014; 82:5076-85. [PMID: 25245808 DOI: 10.1128/iai.02546-14] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Extracellular ATP (eATP), released as a "danger signal" by injured or stressed cells, plays an important role in the regulation of immune responses, but the relationship between ATP release and innate immune responses is still uncertain. In this study, we demonstrated that ATP was released through Toll-like receptor (TLR)-associated signaling in both Escherichia coli-infected mice and lipopolysaccharide (LPS)- or Pam3CSK4-treated macrophages. This ATP release could be blocked completely only by N-ethylmaleimide (NEM), not by carbenoxolone (CBX), flufenamic acid (FFA), or probenecid, suggesting the key role of exocytosis in this process. Furthermore, LPS-induced ATP release could also be reduced dramatically through suppressing calcium mobilization by use of U73122, caffeine, and thapsigargin (TG). In addition, the secretion of interleukin-1β (IL-1β) and CCL-2 was enhanced significantly by ATP, in a time- and dose-dependent manner. Meanwhile, macrophage-mediated phagocytosis of bacteria was also promoted significantly by ATP stimulation. Furthermore, extracellular ATP reduced the number of invading bacteria and protected mice from peritonitis by activating purinergic receptors. Mechanistically, phosphorylation of AKT and ERK was overtly increased by ATP in antibacterial immune responses. Accordingly, if we blocked the P2X- and P2Y-associated signaling pathway by using suramin and pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid), tetrasodium salt (PPADS), the ATP-enhanced immune response was restrained significantly. Taken together, our findings reveal an internal relationship between danger signals and TLR signaling in innate immune responses, which suggests a potential therapeutic significance of calcium mobilization-mediated ATP release in infectious diseases.
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Verkhratsky A, Burnstock G. Biology of purinergic signalling: its ancient evolutionary roots, its omnipresence and its multiple functional significance. Bioessays 2014; 36:697-705. [PMID: 24782352 DOI: 10.1002/bies.201400024] [Citation(s) in RCA: 116] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The purinergic signalling system, which utilises ATP, related nucleotides and adenosine as transmitter molecules, appeared very early in evolution: release mechanisms and ATP-degrading enzymes are operative in bacteria, and the first specific receptors are present in single cell eukaryotic protozoa and algae. Further evolution of the purinergic signalling system resulted in the development of multiple classes of purinoceptors, several pathways for release of nucleotides and adenosine, and a system of ectonucleotidases controlling extracellular levels of purinergic transmitters. The purinergic signalling system is expressed in virtually all types of tissues and cells, where it mediates numerous physiological reactions and contributes to pathological responses in a variety of diseases.
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Affiliation(s)
- Alexei Verkhratsky
- School of Biological Sciences, The University of Manchester, Manchester, UK; Achucarro Center for Neuroscience, IKERBASQUE, Basque Foundation for Science, Bilbao, Spain; University of Nizhny Novgorod, Nizhny Novgorod, Russia
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Drago F, Sautière PE, Le Marrec-Croq F, Accorsi A, Van Camp C, Salzet M, Lefebvre C, Vizioli J. Microglia of medicinal leech (Hirudo medicinalis) express a specific activation marker homologous to vertebrate ionized calcium-binding adapter molecule 1 (Iba1/alias aif-1). Dev Neurobiol 2014; 74:987-1001. [PMID: 24723370 DOI: 10.1002/dneu.22179] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Accepted: 04/07/2014] [Indexed: 01/13/2023]
Abstract
The Ionized calcium-Binding Adapter molecule 1 (Iba1), also known as Allograft Inflammatory Factor 1 (AIF-1), is a 17 kDa cytokine-inducible protein, produced by activated macrophages during chronic transplant rejection and inflammatory reactions in Vertebrates. In mammalian central nervous system (CNS), Iba1 is a sensitive marker associated with activated macrophages/microglia and is upregulated following neuronal death or brain lesions. The medicinal leech Hirudo medicinalis is able to regenerate its CNS after injury, leading to a complete functional repair. Similar to Vertebrates, leech neuroinflammatory processes are linked to microglia activation and recruitment at the lesion site. We identified a gene, named Hmiba1, coding a 17.8 kDa protein showing high similarity with Vertebrate AIF-1. The present work constitutes the first report on an Iba1 protein in the nervous system of an invertebrate. Immunochemistry and gene expression analyses showed that HmIba1, like its mammalian counterpart, is modulated in leech CNS by mechanical injury or chemical stimuli (ATP). We presently demonstrate that most of leech microglial cells migrating and accumulating at the lesion site specifically expressed the activation marker HmIba1. While the functional role of Iba1, whatever species, is still unclear in reactive microglia, this molecule appeared as a good selective marker of activated cells in leech and presents an interesting tool to investigate the functions of these cells during nerve repair events.
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Affiliation(s)
- Francesco Drago
- Université Lille 1, Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée, EA4550, Villeneuve d'Ascq, 59655, France
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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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Le Marrec-Croq F, Bocquet-Garcon A, Vizioli J, Vancamp C, Drago F, Franck J, Wisztorski M, Salzet M, Sautiere PE, Lefebvre C. Calreticulin contributes to C1q-dependent recruitment of microglia in the leech Hirudo medicinalis following a CNS injury. Med Sci Monit 2014; 20:644-53. [PMID: 24747831 PMCID: PMC3999160 DOI: 10.12659/msm.890091] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Background The medicinal leech is considered as a complementary and appropriate model to study immune functions in the central nervous system (CNS). In a context in which an injured leech’s CNS can naturally restore normal synaptic connections, the accumulation of microglia (immune cells of the CNS that are exclusively resident in leeches) has been shown to be essential at the lesion to engage the axonal sprouting. HmC1q (Hm for Hirudo medicinalis) possesses chemotactic properties that are important in the microglial cell recruitment by recognizing at least a C1q binding protein (HmC1qBP alias gC1qR). Material/Methods Recombinant forms of C1q were used in affinity purification and in vitro chemotaxis assays. Anti-calreticulin antibodies were used to neutralize C1q-mediated chemotaxis and locate the production of calreticulin in leech CNS. Results A newly characterized leech calreticulin (HmCalR) has been shown to interact with C1q and participate to the HmC1q-dependent microglia accumulation. HmCalR, which has been detected in only some microglial cells, is consequently a second binding protein for HmC1q, allowing the chemoattraction of resident microglia in the nerve repair process. Conclusions These data give new insight into calreticulin/C1q interaction in an immune function of neuroprotection, suggesting another molecular target to use in investigation of microglia reactivity in a model of CNS injury.
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Affiliation(s)
- Francoise Le Marrec-Croq
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
| | - Annelise Bocquet-Garcon
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
| | - Jacopo Vizioli
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
| | - Christelle Vancamp
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
| | - Francesco Drago
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
| | - Julien Franck
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
| | - Maxence Wisztorski
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
| | - Michel Salzet
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
| | - Pierre-Eric Sautiere
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
| | - Christophe Lefebvre
- Laboratoire de Spectrométrie de Masse Biologique Fondamentale et Appliquée - EA4550, Université Lille Nord de France, University of Lille 1, Villeneuve d'Ascq, France
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31
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Innexin and pannexin channels and their signaling. FEBS Lett 2014; 588:1396-402. [PMID: 24632288 DOI: 10.1016/j.febslet.2014.03.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Accepted: 03/06/2014] [Indexed: 01/24/2023]
Abstract
Innexins are bifunctional membrane proteins in invertebrates, forming gap junctions as well as non-junctional membrane channels (innexons). Their vertebrate analogues, the pannexins, have not only lost the ability to form gap junctions but are also prevented from it by glycosylation. Pannexins appear to form only non-junctional membrane channels (pannexons). The membrane channels formed by pannexins and innexins are similar in their biophysical and pharmacological properties. Innexons and pannexons are permeable to ATP, are present in glial cells, and are involved in activation of microglia by calcium waves in glia. Directional movement and accumulation of microglia following nerve injury, which has been studied in the leech which has unusually large glial cells, involves at least 3 signals: ATP is the "go" signal, NO is the "where" signal and arachidonic acid is a "stop" signal.
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Baker MW, Macagno ER. Control of neuronal morphology and connectivity: Emerging developmental roles for gap junctional proteins. FEBS Lett 2014; 588:1470-9. [DOI: 10.1016/j.febslet.2014.02.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 02/10/2014] [Accepted: 02/12/2014] [Indexed: 11/25/2022]
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Maslieieva V, Thompson RJ. A critical role for pannexin-1 in activation of innate immune cells of the choroid plexus. Channels (Austin) 2014; 8:131-41. [PMID: 24418937 PMCID: PMC4048302 DOI: 10.4161/chan.27653] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Epiplexus cells are a population of innate immune cells in the choroid plexus of the brain ventricles. They are thought to contribute to the immune component of the blood-cerebrospinal-fluid-barrier (BCSFB). Here we have developed a novel technique for studying epiplexus cells in acutely isolated, live and intact choroid plexus. We show that epiplexus cells are potently activated by exogenous ATP, increasing their motility within the tissue. This ATP-induced chemokinesis required activation of pannexin-1 channels, which are expressed by the epithelial cells of the choroid plexus and not the epiplexus cells themselves. Furthermore, ATP acts at least in part through the P2X4 ionotropic purinergic receptor. Thus, the resident immune cells of the choroid plexus appear to be in communication with the epithelial cells through pannexin-1 channels.
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Affiliation(s)
- Valentyna Maslieieva
- Hotchkiss Brain Institute; Department of Cell Biology and Anatomy; University of Calgary; Calgary, AB Canada
| | - Roger J Thompson
- Hotchkiss Brain Institute; Department of Cell Biology and Anatomy; University of Calgary; Calgary, AB Canada
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Appikatla S, Bessert D, Lee I, Hüttemann M, Mullins C, Somayajulu-Nitu M, Yao F, Skoff RP. Insertion of proteolipid protein into oligodendrocyte mitochondria regulates extracellular pH and adenosine triphosphate. Glia 2013; 62:356-73. [PMID: 24382809 DOI: 10.1002/glia.22591] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Revised: 10/04/2013] [Accepted: 10/07/2013] [Indexed: 11/08/2022]
Abstract
Proteolipid protein (PLP) and DM20, the most abundant myelin proteins, are coded by the human PLP1 and non-human Plp1 PLP gene. Mutations in the PLP1 gene cause Pelizaeus-Merzbacher disease (PMD) with duplications of the native PLP1 gene accounting for 70% of PLP1 mutations. Humans with PLP1 duplications and mice with extra Plp1 copies have extensive neuronal degeneration. The mechanism that causes neuronal degeneration is unknown. We show that native PLP traffics to mitochondria when the gene is duplicated in mice and in humans. This report is the first demonstration of a specific cellular defect in brains of PMD patients; it validates rodent models as ideal models to study PMD. Insertion of nuclear-encoded mitochondrial proteins requires specific import pathways; we show that specific cysteine motifs, part of the Mia40/Erv1 mitochondrial import pathway, are present in PLP and are required for its insertion into mitochondria. Insertion of native PLP into mitochondria of transfected cells acidifies media, partially due to increased lactate; it also increases adenosine triphosphate (ATP) in the media. The same abnormalities are found in the extracellular space of mouse brains with extra copies of Plp1. These physiological abnormalities are preventable by mutations in PLP cysteine motifs, a hallmark of the Mia40/Erv1 pathway. Increased extracellular ATP and acidosis lead to neuronal degeneration. Our findings may be the mechanism by which microglia are activated and proinflammatory molecules are upregulated in Plp1 transgenic mice (Tatar et al. (2010) ASN Neuro 2:art:e00043). Manipulation of this metabolic pathway may restore normal metabolism and provide therapy for PMD patients.
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Affiliation(s)
- Sunita Appikatla
- Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, Michigan
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Abstract
Oppositely directed projections of some homologous neurons in the developing CNS of the medicinal leech (Hirudo verbana), such as the AP cells, undergo a form of contact-dependent homolog avoidance. Embryonic APs extend axons within the connective nerve toward adjacent ganglia, in which they meet and form gap junctions (GJs) with the oppositely directed axons of their segmental homologs, stop growing, and are later permanently retracted (Wolszon et al., 1994a,b). However, early deletion of an AP neuron leads to resumed growth and permanent maintenance of the projections of neighboring APs. Here we test the hypothesis that a GJ-based signaling mechanism is responsible for this instance of homolog avoidance. We demonstrate that selective knockdown of GJ gene Hve-inx1 expression in single embryonic APs, by expressing a short-hairpin interfering RNA, leads to continued growth of the projections of the cell toward, into, and beyond adjacent ganglia. Moreover, the projections of the APs in adjacent ganglia also resume growth, mimicking their responses to cell deletion. Continued growth was also observed when two different INX1 mutant transgenes that abolish dye coupling between APs were expressed. These include a mutant transgene that effectively downregulates all GJ plaques that include the INX1 protein and a closed channel INX1 mutant that retains the adhesive cellular binding characteristic of INX1 GJs but not the open channel pore function. Our results add GJ intercellular communication to the list of molecular signaling mechanisms that can act as mediators of growth-inhibiting cell-cell interactions that define the topography of neuronal arbors.
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Holcroft CE, Jackson WD, Lin WH, Bassiri K, Baines RA, Phelan P. Innexins Ogre and Inx2 are required in glial cells for normal postembryonic development of the Drosophila central nervous system. J Cell Sci 2013; 126:3823-34. [PMID: 23813964 DOI: 10.1242/jcs.117994] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Innexins are one of two gene families that have evolved to permit neighbouring cells in multicellular systems to communicate directly. Innexins are found in prechordates and persist in small numbers in chordates as divergent sequences termed pannexins. Connexins are functionally analogous proteins exclusive to chordates. Members of these two families of proteins form intercellular channels, assemblies of which constitute gap junctions. Each intercellular channel is a composite of two hemichannels, one from each of two apposed cells. Hemichannels dock in the extracellular space to form a complete channel with a central aqueous pore that regulates the cell-cell exchange of ions and small signalling molecules. Hemichannels can also act independently by releasing paracrine signalling molecules. optic ganglion reduced (ogre) is a member of the Drosophila innexin family, originally identified as a gene essential for postembryonic neurogenesis. Here we demonstrate, by heterologous expression in paired Xenopus oocytes, that Ogre alone does not form homotypic gap-junction channels; however, co-expression of Ogre with Innexin2 (Inx2) induces formation of functional channels with properties distinct from Inx2 homotypic channels. In the Drosophila larval central nervous system, we find that Inx2 partially colocalises with Ogre in proliferative neuroepithelia and in glial cells. Downregulation of either ogre or inx2 selectively in glia, by targeted expression of RNA interference transgenes, leads to a significant reduction in the size of the larval nervous system and behavioural defects in surviving adults. We conclude that these innexins are crucially required in glial cells for normal postembryonic development of the central nervous system.
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The leech nervous system: a valuable model to study the microglia involvement in regenerative processes. Clin Dev Immunol 2013; 2013:274019. [PMID: 23878582 PMCID: PMC3710617 DOI: 10.1155/2013/274019] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2013] [Accepted: 06/07/2013] [Indexed: 11/25/2022]
Abstract
Microglia are intrinsic components of the central nervous system (CNS). During pathologies in mammals, inflammatory processes implicate the resident microglia and the infiltration of blood cells including macrophages. Functions of microglia appear to be complex as they exhibit both neuroprotective and neurotoxic effects during neuropathological conditions in vivo and in vitro. The medicinal leech Hirudo medicinalis is a well-known model in neurobiology due to its ability to naturally repair its CNS following injury. Considering the low infiltration of blood cells in this process, the leech CNS is studied to specify the activation mechanisms of only resident microglial cells. The microglia recruitment is known to be essential for the usual sprouting of injured axons and does not require any other glial cells. The present review will describe the questions which are addressed to understand the nerve repair. They will discuss the implication of leech factors in the microglial accumulation, the identification of nerve cells producing these molecules, and the study of different microglial subsets. Those questions aim to better understand the mechanisms of microglial cell recruitment and their crosstalk with damaged neurons. The study of this dialog is necessary to elucidate the balance of the inflammation leading to the leech CNS repair.
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Samuels SE, Lipitz JB, Wang J, Dahl G, Muller KJ. Arachidonic acid closes innexin/pannexin channels and thereby inhibits microglia cell movement to a nerve injury. Dev Neurobiol 2013; 73:621-31. [PMID: 23650255 DOI: 10.1002/dneu.22088] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 04/24/2013] [Accepted: 04/26/2013] [Indexed: 01/04/2023]
Abstract
Pannexons are membrane channels formed by pannexins and are permeable to ATP. They have been implicated in various physiological and pathophysiological processes. Innexins, the invertebrate homologues of the pannexins, form innexons. Nerve injury induces calcium waves in glial cells, releasing ATP through glial pannexon/innexon channels. The ATP then activates microglia. More slowly, injury releases arachidonic acid (ArA). The present experiments show that ArA itself reduced the macroscopic membrane currents of innexin- and of pannexin-injected oocytes; ArA also blocked K(+) -induced release of ATP. In leeches, whose large glial cells have been favorable for studying control of microglia migration, ArA blocked glial dye-release and, evidently, ATP-release. A physiological consequence in the leech was block of microglial migration to nerve injuries. Exogenous ATP (100 µM) reversed the effect, for ATP causes activation and movement of microglia after nerve injury, but nitric oxide directs microglia to the lesion. It was not excluded that metabolites of ArA may also inhibit the channels. But for all these effects, ArA and its non-metabolizable analog eicosatetraynoic acid (ETYA) were indistinguishable. Therefore, ArA itself is an endogenous regulator of pannexons and innexons. ArA thus blocks release of ATP from glia after nerve injury and thereby, at least in leeches, stops microglia at lesions.
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Affiliation(s)
- Stuart E Samuels
- Neuroscience Program, University of Miami, Miami, Florida, 33136, USA
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Yazdani N, Firme CP, Macagno ER, Baker MW. Expression of a dominant negative mutant innexin in identified neurons and glial cells reveals selective interactions among gap junctional proteins. Dev Neurobiol 2013; 73:571-86. [DOI: 10.1002/dneu.22082] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2013] [Revised: 02/25/2013] [Accepted: 02/26/2013] [Indexed: 11/12/2022]
Affiliation(s)
- Neema Yazdani
- Section of Cell and Developmental Biology; University of California; San Diego La Jolla; California; 92093
| | - Constantine P. Firme
- Section of Cell and Developmental Biology; University of California; San Diego La Jolla; California; 92093
| | - Eduardo R. Macagno
- Section of Cell and Developmental Biology; University of California; San Diego La Jolla; California; 92093
| | - Michael W. Baker
- Section of Cell and Developmental Biology; University of California; San Diego La Jolla; California; 92093
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40
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Arafah K, Croix D, Vizioli J, Desmons A, Fournier I, Salzet M. Involvement of nitric oxide through endocannabinoids release in microglia activation during the course of CNS regeneration in the medicinal leech. Glia 2013; 61:636-49. [DOI: 10.1002/glia.22462] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Accepted: 12/17/2012] [Indexed: 11/06/2022]
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Ectopic expression of select innexins in individual central neurons couples them to pre-existing neuronal or glial networks that express the same innexin. J Neurosci 2013; 32:14265-70. [PMID: 23055495 DOI: 10.1523/jneurosci.2693-12.2012] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Fifteen of the 21 innexin (Inx) genes (Hve-inx) found in the genome of the medicinal leech, Hirudo verbana, are expressed in the CNS (Kandarian et al., 2012). Two are expressed pan-neuronally, while the others are restricted in their expression to small numbers of cells, in some cases reflecting the membership of known networks of electrically coupled and dye-coupled neurons or glial cells. We report here that when Hve-inx genes characteristic of discrete coupled networks were expressed ectopically in neurons known not to express them, the experimental cells were found to become dye coupled with the other cells in that network. Hve-inx6 is normally expressed by only three neurons in each ganglion, which form strongly dye-coupled electrical connections with each other [Shortening-Coupling interneuron (S-CI) network] (Muller and Scott, 1981; Dykes and Macagno, 2006). But when Hve-inx6 was ectopically expressed in a variety of central embryonic neurons, those cells became dye coupled with the S-CI network. Similarly, Hve-inx2 is normally uniquely expressed by the ganglion's large glial cells, but when it was ectopically expressed in different central neurons, they became dye coupled to the glial cells. In contrast, overexpression of the pan-neuronal Inx genes Hve-inx1 and Hve-inx14 did not yield any novel instances of dye coupling to pre-existent neuronal networks. These results reveal that expression of certain innexins is sufficient to couple individual neurons to pre-existing networks in the CNS. We propose that a primary determinant of selective neuronal connectivity and circuit formation in the leech is the surface expression of unique subsets of gap junctional proteins.
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42
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Dahl G, Keane RW. Pannexin: from discovery to bedside in 11±4 years? Brain Res 2012; 1487:150-9. [PMID: 22771709 PMCID: PMC3590907 DOI: 10.1016/j.brainres.2012.04.058] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Revised: 03/29/2012] [Accepted: 04/11/2012] [Indexed: 12/22/2022]
Abstract
Pannexin1 (Panx1) originally was discovered as a gap junction related protein. However, rather than forming the cell-to-cell channels of gap junctions, Panx1 forms a mechanosensitive and highly ATP permeable channel in the cell membrane allowing the exchange of molecules between the cytoplasm and the extracellular space. The list of arguments for Panx1 representing the major ATP release channel includes: (1) Panx1 is expressed in (all?) cells releasing ATP in a non-vesicular fashion, such as erythrocytes; (2) in cells with polar release of ATP, Panx1 is expressed at the ATP release site, such as the apical membrane in airway epithelial cells; (3) the pharmacology of Panx1 channels matches that of ATP release; (4) mutation of Panx1 in strategic positions in the protein modifies ATP release; and (5) knockdown or knockout of Panx1 attenuates or abolishes ATP release. Panx1, in association with the purinergic receptor P2X7, is involved in the innate immune response and in apoptotic/pyroptotic cell death. Inflammatory processes are responsible for amplification of the primary lesion in CNS trauma and stroke. Panx1, as an early signal event and as a signal amplifier in these processes, is an obvious target for the prevention of secondary cell death due to inflammasome activity. Since Panx1 inhibitors such as probenecid are already clinically tested in different settings they should be considered for therapy in stroke and CNS trauma.
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Affiliation(s)
- Gerhard Dahl
- Department of Physiology and Biophysics, University of Miami, School of Medicine, PO Box 016430, Miami, FL 33101, USA.
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43
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Chen P, Chen P, Feng X, Du W, Liu BF. Analysis of intercellular communication by flexible hydrodynamic gating on a microfluidic chip. Anal Bioanal Chem 2012; 405:307-14. [PMID: 23052886 DOI: 10.1007/s00216-012-6447-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Revised: 08/31/2012] [Accepted: 09/21/2012] [Indexed: 01/09/2023]
Abstract
Intercellular Ca(2+) waves are propagation of Ca(2+) transients among cells that could be initiated by chemical stimulation. Current methods for analyzing intercellular Ca(2+) waves are difficult to realize localized chemical stimulations upon the target cell without interfering with adjacent contacting cells. In this paper, a simple and flexible microfluidic method was developed for investigating the intercellular communication of Ca(2+) signals. A cross-patterned microfluidic chip was designed and fabricated with polydimethylsiloxane as the structural material. Localized chemical stimulation was achieved by a new strategy based on hydrodynamic gating technique. Clusters of target cells were seeded at the location within 300 μm downstream of the intersection of the cross-shaped microchannel. Confined lateral molecular diffusion largely minimized the interference from diffusion-induced stimulation of adjacent cells. Localized stimulation of the target cell with adenosine 5'-triphosphate successfully induced the propagation of intercellular Ca(2+) waves among a population of adjacent contacting cells. Further inhibition studies verified that the propagation of calcium signals among NIH-3 T3 cells was dependent on direct cytosolic transfer via gap junctions. The developed microfluidic method provides a versatile platform for investigating the dynamics of intercellular communications.
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Affiliation(s)
- Peng Chen
- Britton Chance Center for Biomedical Photonics at Wuhan National Laboratory for Optoelectronics-Hubei Bioinformatics, Systems Biology Theme, Department of Biomedical Engineering, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China
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44
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Sieger D, Peri F. Animal models for studying microglia: The first, the popular, and the new. Glia 2012; 61:3-9. [DOI: 10.1002/glia.22385] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Accepted: 06/15/2012] [Indexed: 11/06/2022]
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45
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Bennett MVL, Garré JM, Orellana JA, Bukauskas FF, Nedergaard M, Sáez JC. Connexin and pannexin hemichannels in inflammatory responses of glia and neurons. Brain Res 2012; 1487:3-15. [PMID: 22975435 DOI: 10.1016/j.brainres.2012.08.042] [Citation(s) in RCA: 162] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Revised: 08/11/2012] [Accepted: 08/22/2012] [Indexed: 11/17/2022]
Abstract
Mammals express ∼20 different connexins, the main gap junction forming proteins in mammals, and 3 pannexins, homologs of innexins, the main gap junction forming proteins in invertebrates. In both classes of gap junction, each channel is formed by two hemichannels, one contributed by each of the coupled cells. There is now general, if not universal, agreement that hemichannels of both classes can open in response to various physiological and pathological stimuli when they are not apposed to another hemichannels and face the external milieu. Connexin (and likely pannexin) hemichannel permeability is consistent with that of the cell-cell channels and open hemichannels can be a release site for relatively large molecules such as ATP and glutamate, which can serve as transmitters between cells. Here we describe three experimental paradigms in which connexin and pannexin hemichannel signaling occurs. (1) In cultures of spinal astrocytes FGF-1 causes the release of ATP, and ATP causes opening of pannexin hemichannels, which then release further ATP. Subsequently, several hours later, connexin hemichannels are also opened by an unknown mechanism. Release of ATP appears to become self sustaining through action of P2X7 receptors to open pannexin hemichannels and then connexin hemichannels, both of which are ATP permeable. (2) Spinal cord injury by dropping a small weight on the exposed cord is followed by release of ATP in the region surrounding the primary lesion. This release is greatly reduced in a mouse in which Cx43 is knocked down in the astrocytes. Application of FGF-1 causes a similar release of ATP in the uninjured spinal cord, and an inhibitor of the FGF-1 receptor, PD173074, inhibits both FGF-1 and injury-induced release. Reduction in ATP release is associated with reduced inflammation and less secondary expansion of the lesion. (3) Cortical astrocytes in culture are permeabilized by hypoxia, and this effect is increased by high or zero glucose. The mechanism of permeabilization is opening of Cx43 hemichannels, which can lead to cell death. Activated microglia secrete TNF-α and IL-1β, which open connexin hemichannels in astrocytes. Astrocytes release ATP and glutamate which can kill neurons in co-culture through activation of neuronal pannexin hemichannels. These studies implicate two kinds of gap junction hemichannel in inflammatory responses and cell death. This article is part of a Special Issue entitled Electrical Synapses.
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Affiliation(s)
- Michael V L Bennett
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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46
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Corriden R, Insel PA. New insights regarding the regulation of chemotaxis by nucleotides, adenosine, and their receptors. Purinergic Signal 2012; 8:587-98. [PMID: 22528684 PMCID: PMC3360098 DOI: 10.1007/s11302-012-9311-x] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Accepted: 01/05/2012] [Indexed: 12/23/2022] Open
Abstract
The directional movement of cells can be regulated by ATP, certain other nucleotides (e.g., ADP, UTP), and adenosine. Such regulation occurs for cells that are "professional phagocytes" (e.g., neutrophils, macrophages, certain lymphocytes, and microglia) and that undergo directional migration and subsequent phagocytosis. Numerous other cell types (e.g., fibroblasts, endothelial cells, neurons, and keratinocytes) also change motility and migration in response to ATP, other nucleotides, and adenosine. In this article, we review how nucleotides and adenosine modulate chemotaxis and motility and highlight the importance of nucleotide- and adenosine-regulated cell migration in several cell types: neutrophils, microglia, endothelial cells, and cancer cells. We also discuss difficulties in conducting experiments and drawing conclusions regarding the ability of nucleotides and adenosine to modulate the migration of professional and non-professional phagocytes.
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Affiliation(s)
- Ross Corriden
- Institute of Cell Signalling, University of Nottingham, Nottingham, UK
| | - Paul A. Insel
- Departments of Pharmacology and Medicine, University of California, San Diego, CA USA
- Department of Pharmacology, University of California San Diego, 9500 Gilman Drive, Mail code 0636, La Jolla, CA 92093 USA
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47
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Brites D. The evolving landscape of neurotoxicity by unconjugated bilirubin: role of glial cells and inflammation. Front Pharmacol 2012; 3:88. [PMID: 22661946 PMCID: PMC3361682 DOI: 10.3389/fphar.2012.00088] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2012] [Accepted: 04/23/2012] [Indexed: 12/13/2022] Open
Abstract
Unconjugated hyperbilirubinemia is a common condition in the first week of postnatal life. Although generally harmless, some neonates may develop very high levels of unconjugated bilirubin (UCB), which may surpass the protective mechanisms of the brain in preventing UCB accumulation. In this case, both short-term and long-term neurodevelopmental disabilities, such as acute and chronic UCB encephalopathy, known as kernicterus, or more subtle alterations defined as bilirubin-induced neurological dysfunction (BIND) may be produced. There is a tremendous variability in babies' vulnerability toward UCB for reasons not yet explained, but preterm birth, sepsis, hypoxia, and hemolytic disease are comprised as risk factors. Therefore, UCB levels and neurological abnormalities are not strictly correlated. Even nowadays, the mechanisms of UCB neurotoxicity are still unclear, as are specific biomarkers, and little is known about lasting sequelae attributable to hyperbilirubinemia. On autopsy, UCB was shown to be within neurons, neuronal processes, and microglia, and to produce loss of neurons, demyelination, and gliosis. In isolated cell cultures, UCB was shown to impair neuronal arborization and to induce the release of pro-inflammatory cytokines from microglia and astrocytes. However, cell dependent sensitivity to UCB toxicity and the role of each nerve cell type remains not fully understood. This review provides a comprehensive insight into cell susceptibilities and molecular targets of UCB in neurons, astrocytes, and oligodendrocytes, and on phenotypic and functional responses of microglia to UCB. Interplay among glia elements and cross-talk with neurons, with a special emphasis in the UCB-induced immunostimulation, and the role of sepsis in BIND pathogenesis are highlighted. New and interesting data on the anti-inflammatory and antioxidant activities of different pharmacological agents are also presented, as novel and promising additional therapeutic approaches to BIND.
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Affiliation(s)
- Dora Brites
- Neuron Glia Biology in Health and Disease Unit, Research Institute for Medicines and Pharmaceutical Sciences, Faculty of Pharmacy, University of Lisbon Lisbon, Portugal
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48
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Kim HJ, Ajit D, Peterson TS, Wang Y, Camden JM, Gibson Wood W, Sun GY, Erb L, Petris M, Weisman GA. Nucleotides released from Aβ₁₋₄₂ -treated microglial cells increase cell migration and Aβ₁₋₄₂ uptake through P2Y₂ receptor activation. J Neurochem 2012; 121:228-38. [PMID: 22353164 DOI: 10.1111/j.1471-4159.2012.07700.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Amyloid β-protein (Aβ) deposits in brains of Alzheimer's disease patients generate proinflammatory cytokines and chemokines that recruit microglial cells to phagocytose Aβ. Nucleotides released from apoptotic cells activate P2Y(2) receptors (P2Y(2) Rs) in macrophages to promote clearance of dead cells. In this study, we investigated the role of P2Y(2) Rs in the phagocytosis and clearance of Aβ. Treatment of mouse primary microglial cells with fibrillar (fAβ(1-42) ) and oligomeric (oAβ(1-42) ) Aβ(1-42) aggregation solutions caused a rapid release of ATP (maximum after 10 min). Furthermore, fAβ(1-42) and oAβ(1-42) treatment for 24 h caused an increase in P2Y(2) R gene expression. Treatment with fAβ(1-42) and oAβ(1-42) aggregation solutions increased the motility of neighboring microglial cells, a response inhibited by pre-treatment with apyrase, an enzyme that hydrolyzes nucleotides. The P2Y(2) R agonists ATP and UTP caused significant uptake of Aβ(1-42) by microglial cells within 30 min, which reached a maximum within 1 h, but did not increase Aβ(1-42) uptake by primary microglial cells isolated from P2Y(2) R(-/-) mice. Inhibitors of α(v) integrins, Src and Rac decreased UTP-induced Aβ(1-42) uptake, suggesting that these previously identified components of the P2Y(2) R signaling pathway play a role in Aβ phagocytosis by microglial cells. Finally, we found that UTP treatment enhances Aβ(1-42) degradation by microglial cells, but not in cells isolated from P2Y(2) R(-/-) mice. Taken together, our findings suggest that P2Y(2) Rs can activate microglial cells to enhance Aβ clearance and highlight the P2Y(2) R as a therapeutic target in Alzheimer's disease.
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Affiliation(s)
- Hye Jung Kim
- Department of Biochemistry, University of Missouri, Columbia, Missouri, USA
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49
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Sun J, Zheng Y, Feng X, Du W, Liu BF. Analysis of intercellular calcium signaling using microfluidic adjustable laminar flow for localized chemical stimulation. Anal Chim Acta 2012; 721:104-9. [PMID: 22405307 DOI: 10.1016/j.aca.2012.01.053] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2011] [Revised: 01/20/2012] [Accepted: 01/26/2012] [Indexed: 01/09/2023]
Abstract
The propagation of intercellular calcium signals provides a mechanism to coordinate cell population activity, which is essential for regulating cell behavior and organ development. However, existing analytical methods are difficult to realize localized chemical stimulation of a single cell among a population of cells that are in close contact with one another for studying the propagation of calcium wave. In this work, a microfluidic method is presented for the analysis of contact-dependent propagation of intercellular calcium wave induced by extracellular ATP using multiple laminar flows. Adjacent cells were seeded ∼300 μm downstream the intersection of a Y-shaped microchannel with negative pressure pulses. Consequently, the lateral diffusion distance of the chemical at cell locations was limited to ∼26 μm with a total flow rate of 20 μL min(-1), which prevented the interference of diffusion-induced cellular responses. Localized stimulation of the target cell with ATP induced the propagation of intercellular calcium wave among the cell population. In addition, studies on the spread of intercellular calcium wave under octanol inhibition allowed us to characterize the gap junction mediated cell-cell communication. Thus, this novel device will provide a versatile platform for intercellular signal transduction studies and high throughput drug screening.
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Affiliation(s)
- Jian Sun
- Britton Chance Center for Biomedical Photonics at Wuhan National Laboratory for Optoelectronics-Hubei Bioinformatics, Department of Systems Biology, College of Life Science and Technology, Huazhong University of Science and Technology, People's Republic of China
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Regulation of microglia by ionotropic glutamatergic and GABAergic neurotransmission. ACTA ACUST UNITED AC 2011; 7:41-6. [PMID: 22166726 DOI: 10.1017/s1740925x11000123] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Recent studies have indicated that constitutive functions of microglia in the healthy adult central nervous system (CNS) involve immune surveillance, synapse maintenance and trophic support. These functions have been related to the ramified structure of 'resting' microglia and the prominent motility in their processes that provide extensive coverage of the entire extracellular milleu. In this review, we examine how external signals, and in particular, ionotropic neurotransmission, regulate features of microglial morphology and process motility. Current findings indicate that microglial physiology in the healthy CNS is constitutively and reciprocally regulated by endogenous ionotropic glutamatergic and GABAergic neurotransmission. These influences do not act directly on microglial cells but indirectly via the activity-dependent release of ATP, likely through a mechanism involving pannexin channels. Microglia in the 'resting' state are not only dynamically active, but also constantly engaged in ongoing communication with neuronal and macroglial components of the CNS in a functionally relevant way.
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