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Papin M, Bouchet AM, Chantôme A, Vandier C. Ether-lipids and cellular signaling: A differential role of alkyl- and alkenyl-ether-lipids? Biochimie 2023; 215:50-59. [PMID: 37678745 DOI: 10.1016/j.biochi.2023.09.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 08/17/2023] [Accepted: 09/04/2023] [Indexed: 09/09/2023]
Abstract
Ether-lipids (EL) are specific lipids bearing a characteristic sn-1 ether bond. Depending on the ether or vinyl-ether nature of this bond, they are present as alkyl- or alkenyl-EL, respectively. Among EL, alkenyl-EL, also referred as plasmalogens in the literature, attract most of the scientific interest as they are the predominant EL species in eukaryotic cells, thus less is known about alkyl-EL. EL have been implicated in various signaling pathways and alterations in their quantity are frequently observed in pathologies such as neurodegenerative and cardiovascular diseases or cancer. However, it remains unknown whether both alkyl- and alkenyl-EL play the same roles in these processes. This review summarizes the roles and mechanisms of action of EL in cellular signaling and tries to discriminate between alkyl- and alkenyl-EL. We also focus on the involvement of EL-mediated alterations of cellular signaling in diseases and discuss the potential interest for EL in therapy.
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Affiliation(s)
- Marion Papin
- Nutrition, Croissance, Cancer (N2C) UMR 1069, University of Tours, INSERM, 37000, Tours, France.
| | | | - Aurélie Chantôme
- Nutrition, Croissance, Cancer (N2C) UMR 1069, University of Tours, INSERM, 37000, Tours, France
| | - Christophe Vandier
- Nutrition, Croissance, Cancer (N2C) UMR 1069, University of Tours, INSERM, 37000, Tours, France; Lifesome Therapeutics, López de Hoyos 42, 28006, Madrid, Spain
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2
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Pan K, Garaschuk O. The role of intracellular calcium-store-mediated calcium signals in in vivo sensor and effector functions of microglia. J Physiol 2023; 601:4203-4215. [PMID: 35315518 DOI: 10.1113/jp279521] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 03/09/2022] [Indexed: 11/08/2022] Open
Abstract
Under physiological conditions microglia, the immune sentinels of the brain, constantly monitor their microenvironment. In the case of danger, damage or cell/tissue dyshomeostasis, they react with changes in process motility, polarization, directed process movement, morphology and gene expression profile; release pro- and anti-inflammatory mediators; proliferate; and clean brain parenchyma by means of phagocytosis. Based on recent transcriptomic and in vivo Ca2+ imaging data, we argue that the local cell/tissue dyshomeostasis is sensed by microglia via intracellular Ca2+ signals, many of which are mediated by Ca2+ release from the intracellular Ca2+ stores. These signals encode the strength, duration and spatiotemporal pattern of the stimulus and, at the same time, relay this information further to trigger the respective Ca2+ -dependent effector pathways. We also point to the fact that microglial Ca2+ signalling is sexually dimorphic and undergoes profound changes across the organism's lifespan. Interestingly, the first changes in microglial Ca2+ signalling are visible already in 9- to 11-month-old mice, roughly corresponding to 40-year-old humans.
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Affiliation(s)
- Kuang Pan
- Institute of Physiology, Department of Neurophysiology, Eberhard Karls University of Tübingen, Tübingen, Germany
| | - Olga Garaschuk
- Institute of Physiology, Department of Neurophysiology, Eberhard Karls University of Tübingen, Tübingen, Germany
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3
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Travers JB, Rohan JG, Sahu RP. New Insights Into the Pathologic Roles of the Platelet-Activating Factor System. Front Endocrinol (Lausanne) 2021; 12:624132. [PMID: 33796070 PMCID: PMC8008455 DOI: 10.3389/fendo.2021.624132] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 02/17/2021] [Indexed: 12/15/2022] Open
Abstract
Described almost 50 years ago, the glycerophosphocholine lipid mediator Platelet-activating factor (PAF) has been implicated in many pathologic processes. Indeed, elevated levels of PAF can be measured in response to almost every type of pathology involving inflammation and cell damage/death. In this review, we provide evidence for PAF involvement in pathologic processes, with focus on cancer, the nervous system, and in photobiology. Importantly, recent insights into how PAF can generate and travel via bioactive extracellular vesicles such as microvesicle particles (MVP) are presented. What appears to be emerging from diverse pathologies in different organ systems is a common theme where pro-oxidative stressors generate oxidized glycerophosphocholines with PAF agonistic effects, which then trigger more enzymatic PAF synthesis via the PAF receptor. A downstream consequence of PAF receptor activation is the generation and release of MVP which provide a mechanism to transmit PAF as well as other bioactive agents. The knowledge gaps which when addressed could result in novel therapeutic strategies are also discussed. Taken together, an enhanced understanding of the PAF family of lipid mediators is essential in our improved comprehension of the relationship amongst the diverse cutaneous, cancerous, neurologic and systemic pathologic processes.
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Affiliation(s)
- Jeffrey B. Travers
- Department of Pharmacology & Toxicology, Boonshoft School of Medicine at Wright State University, Dayton, OH, United States
- Department of Dermatology, Boonshoft School of Medicine at Wright State University, Dayton, OH, United States
- Dayton Veterans Administration Medical Center, Dayton, OH, United States
- *Correspondence: Jeffrey B. Travers, ; orcid.org/0000-0001-7232-1039
| | - Joyce G. Rohan
- Naval Medical Research Unit Dayton, Environmental Health Effects Directorate, Wright Patterson Air Force Base, OH, United States
| | - Ravi P. Sahu
- Department of Pharmacology & Toxicology, Boonshoft School of Medicine at Wright State University, Dayton, OH, United States
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4
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Zhang I, Hu H. Store-Operated Calcium Channels in Physiological and Pathological States of the Nervous System. Front Cell Neurosci 2020; 14:600758. [PMID: 33328896 PMCID: PMC7732603 DOI: 10.3389/fncel.2020.600758] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 11/03/2020] [Indexed: 12/13/2022] Open
Abstract
Store-operated calcium channels (SOCs) are widely expressed in excitatory and non-excitatory cells where they mediate significant store-operated calcium entry (SOCE), an important pathway for calcium signaling throughout the body. While the activity of SOCs has been well studied in non-excitable cells, attention has turned to their role in neurons and glia in recent years. In particular, the role of SOCs in the nervous system has been extensively investigated, with links to their dysregulation found in a wide variety of neurological diseases from Alzheimer’s disease (AD) to pain. In this review, we provide an overview of their molecular components, expression, and physiological role in the nervous system and describe how the dysregulation of those roles could potentially lead to various neurological disorders. Although further studies are still needed to understand how SOCs are activated under physiological conditions and how they are linked to pathological states, growing evidence indicates that SOCs are important players in neurological disorders and could be potential new targets for therapies. While the role of SOCE in the nervous system continues to be multifaceted and controversial, the study of SOCs provides a potentially fruitful avenue into better understanding the nervous system and its pathologies.
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Affiliation(s)
- Isis Zhang
- Department of Anesthesiology, Rutgers New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, United States
| | - Huijuan Hu
- Department of Anesthesiology, Rutgers New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, United States
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5
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Fontaine D, Figiel S, Félix R, Kouba S, Fromont G, Mahéo K, Potier-Cartereau M, Chantôme A, Vandier C. Roles of endogenous ether lipids and associated PUFAs in the regulation of ion channels and their relevance for disease. J Lipid Res 2020; 61:840-858. [PMID: 32265321 PMCID: PMC7269763 DOI: 10.1194/jlr.ra120000634] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 03/29/2020] [Indexed: 12/16/2022] Open
Abstract
Ether lipids (ELs) are lipids characterized by the presence of either an ether linkage (alkyl lipids) or a vinyl ether linkage [i.e., plasmalogens (Pls)] at the sn1 position of the glycerol backbone, and they are enriched in PUFAs at the sn2 position. In this review, we highlight that ELs have various biological functions, act as a reservoir for second messengers (such as PUFAs) and have roles in many diseases. Some of the biological effects of ELs may be associated with their ability to regulate ion channels that control excitation-contraction/secretion/mobility coupling and therefore cell physiology. These channels are embedded in lipid membranes, and lipids can regulate their activities directly or indirectly as second messengers or by incorporating into membranes. Interestingly, ELs and EL-derived PUFAs have been reported to play a key role in several pathologies, including neurological disorders, cardiovascular diseases, and cancers. Investigations leading to a better understanding of their mechanisms of action in pathologies have opened a new field in cancer research. In summary, newly identified lipid regulators of ion channels, such as ELs and PUFAs, may represent valuable targets to improve disease diagnosis and advance the development of new therapeutic strategies for managing a range of diseases and conditions.
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Affiliation(s)
- Delphine Fontaine
- Inserm N2C UMR1069, Université de Tours, F-37032 Tours CEDEX 1, France
| | - Sandy Figiel
- Inserm N2C UMR1069, Université de Tours, F-37032 Tours CEDEX 1, France
| | - Romain Félix
- Inserm N2C UMR1069, Université de Tours, F-37032 Tours CEDEX 1, France
| | - Sana Kouba
- Inserm N2C UMR1069, Université de Tours, F-37032 Tours CEDEX 1, France
| | - Gaëlle Fromont
- Inserm N2C UMR1069, Université de Tours, F-37032 Tours CEDEX 1, France; Department of Pathology, CHRU Bretonneau, F-37044 Tours CEDEX 9, France
| | - Karine Mahéo
- Inserm N2C UMR1069, Université de Tours, F-37032 Tours CEDEX 1, France; Faculté de Pharmacie, Université de Tours, F-37200 Tours, France
| | | | - Aurélie Chantôme
- Inserm N2C UMR1069, Université de Tours, F-37032 Tours CEDEX 1, France; Faculté de Pharmacie, Université de Tours, F-37200 Tours, France
| | - Christophe Vandier
- Inserm N2C UMR1069, Université de Tours, F-37032 Tours CEDEX 1, France. mailto:
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6
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Younger D, Murugan M, Rama Rao KV, Wu LJ, Chandra N. Microglia Receptors in Animal Models of Traumatic Brain Injury. Mol Neurobiol 2018; 56:5202-5228. [DOI: 10.1007/s12035-018-1428-7] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 11/13/2018] [Indexed: 02/07/2023]
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Liu Y, Shields LBE, Gao Z, Wang Y, Zhang YP, Chu T, Zhu Q, Shields CB, Cai J. Current Understanding of Platelet-Activating Factor Signaling in Central Nervous System Diseases. Mol Neurobiol 2016; 54:5563-5572. [PMID: 27613281 DOI: 10.1007/s12035-016-0062-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 08/17/2016] [Indexed: 12/13/2022]
Abstract
Platelet-activating factor (PAF) is a bioactive lipid mediator which serves as a reciprocal messenger between the immune and nervous systems. PAF, a pluripotent inflammatory mediator, is extensively expressed in many cells and tissues and has either beneficial or detrimental effects on the progress of inflammation-related neuropathology. Its wide distribution and various biological functions initiate a cascade of physiological or pathophysiological responses during development or diseases. Current evidence indicates that excess PAF accumulation in CNS diseases exacerbates the inflammatory response and pathological consequences, while application of PAF inhibitors or PAFR antagonists by blocking this signaling pathway significantly reduces inflammation, protects cells, and improves the recovery of neural functions. In this review, we integrate the current findings of PAF signaling in CNS diseases and elucidate topics less appreciated but important on the role of PAF signaling in neurological diseases. We propose that the precise use of PAF inhibitors or PAFR antagonists that target the specific neural cells during the appropriate temporal window may constitute a potential therapy for CNS diseases.
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Affiliation(s)
- Yulong Liu
- Department of Orthopedic Surgery, China-Japan Union Hospital of Jilin University, Changchun, 130033, People's Republic of China
- Department of Pediatrics, University of Louisville School of Medicine, 570 S. Preston Street, Donald Baxter Building, Suite 321B, Louisville, KY, 40202, USA
| | - Lisa B E Shields
- Norton Neuroscience Institute, Norton Healthcare, Louisville, KY, 40202, USA
| | - Zhongwen Gao
- Department of Orthopedic Surgery, China-Japan Union Hospital of Jilin University, Changchun, 130033, People's Republic of China
- Department of Pediatrics, University of Louisville School of Medicine, 570 S. Preston Street, Donald Baxter Building, Suite 321B, Louisville, KY, 40202, USA
| | - Yuanyi Wang
- Department of Pediatrics, University of Louisville School of Medicine, 570 S. Preston Street, Donald Baxter Building, Suite 321B, Louisville, KY, 40202, USA
- Department of Spine Surgery, First Hospital of Jilin University, Changchun, 130021, People's Republic of China
| | - Yi Ping Zhang
- Norton Neuroscience Institute, Norton Healthcare, Louisville, KY, 40202, USA
| | - Tianci Chu
- Department of Pediatrics, University of Louisville School of Medicine, 570 S. Preston Street, Donald Baxter Building, Suite 321B, Louisville, KY, 40202, USA
| | - Qingsan Zhu
- Department of Orthopedic Surgery, China-Japan Union Hospital of Jilin University, Changchun, 130033, People's Republic of China.
| | | | - Jun Cai
- Department of Pediatrics, University of Louisville School of Medicine, 570 S. Preston Street, Donald Baxter Building, Suite 321B, Louisville, KY, 40202, USA.
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8
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Park JH, Kim JN, Jang BC, Im SS, Song DK, Bae JH. Glucosamine suppresses platelet-activating factor-induced activation of microglia through inhibition of store-operated calcium influx. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2016; 42:1-8. [PMID: 26745504 DOI: 10.1016/j.etap.2015.12.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 12/17/2015] [Accepted: 12/19/2015] [Indexed: 06/05/2023]
Abstract
Microglia activation and subsequent release of inflammatory mediators are implicated in the pathophysiology of neurodegenerative diseases. Platelet-activating factor (PAF), a potent lipid mediator synthesized by microglia, is known to stimulate microglia functional responses. In this study, we determined that endogenous PAF exert autocrine effects on microglia activation, as well as the underlying mechanism involved. We also investigated the effect of D-glucosamine (GlcN) on PAF-induced cellular activation in human HMO6 microglial cells. PAF induced sustained intracellular Ca(2+) ([Ca(2+)]i) increase through store-operated Ca(2+) channels (SOC) and reactive oxygen species (ROS) generation. PAF also induced pro-inflammatory markers through NFκB/COX-2 signaling. GlcN significantly inhibited PAF-induced Ca(2+) influx and ROS generation without significant cytotoxicity. GlcN downregulated excessive expression of pro-inflammatory markers and promoted filopodia formation through NFκB/COX-2 inhibition in PAF-stimulated HMO6 cells. Taken together, these data suggest that GlcN may offer substantial therapeutic potential for treating inflammatory and neurodegenerative diseases accompanied by microglial activation.
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Affiliation(s)
- Jae-Hyung Park
- Department of Physiology, Keimyung University School of Medicine, Daegu, South Korea
| | - Jeong-Nam Kim
- Department of Physiology, Keimyung University School of Medicine, Daegu, South Korea
| | - Byeong-Churl Jang
- Department of Molecular Medicine, Keimyung University School of Medicine, Daegu, South Korea
| | - Seung-Soon Im
- Department of Physiology, Keimyung University School of Medicine, Daegu, South Korea
| | - Dae-Kyu Song
- Department of Physiology, Keimyung University School of Medicine, Daegu, South Korea
| | - Jae-Hoon Bae
- Department of Physiology, Keimyung University School of Medicine, Daegu, South Korea.
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9
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Sharma P, Ping L. Calcium ion influx in microglial cells: physiological and therapeutic significance. J Neurosci Res 2014; 92:409-23. [PMID: 24464907 DOI: 10.1002/jnr.23344] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 11/09/2013] [Accepted: 11/12/2013] [Indexed: 01/16/2023]
Abstract
Microglial cells, the immunocompetent cells of the central nervous system (CNS), exhibit a resting phenotype under healthy conditions. In response to injury, however, they transform into an activated state, which is a hallmark feature of many CNS diseases. Factors or agents released from the neurons, blood vessels, and/or astrocytes could activate these cells, leading to their functional and structural modifications. Microglial cells are well equipped to sense environmental changes within the brain under both physiological and pathological conditions. Entry of calcium ions (Ca(2+)) plays a critical role in the process of microglial transformation; several channels and receptors have been identified on the surface of microglial cells. These include store-operated channel, Orai1, and its sensor protein, stromal interaction molecule 1 (STIM1), in microglial cells, and their functions are modulated under pathological stimulations. Transient receptor potential (TRP) channels and voltage- and ligand-gated channels (ionotropic and metabotropic receptors) are also responsible for Ca(2+) influx into the microglial cells. An elevation of intracellular Ca(2+) concentration subsequently regulates microglial cell functions by activating a diverse array of Ca(2+)-sensitive signaling cascades. Perturbed Ca(2+) homeostasis contributes to the progression of a number of CNS disorders. Thus, regulation of Ca(2+) entry into microglial cells could be a pharmacological target for several CNS-related pathological conditions. This Review addresses the recent insights into microglial cell Ca(2+) influx mechanisms, their roles in the regulation of functions, and alterations of Ca(2+) entry in specific CNS disorders.
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Affiliation(s)
- Purnima Sharma
- All India Institute of Medical Sciences-Physiology, Basni Industrial Area Phase II Jodhpur, Rajasthan, India
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10
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Verkhratsky A, Parpura V. Store-operated calcium entry in neuroglia. Neurosci Bull 2013; 30:125-33. [PMID: 23677809 DOI: 10.1007/s12264-013-1343-x] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2013] [Accepted: 02/14/2013] [Indexed: 11/30/2022] Open
Abstract
Neuroglial cells are homeostatic neural cells. Generally, they are electrically non-excitable and their activation is associated with the generation of complex intracellular Ca(2+) signals that define the "Ca(2+) excitability" of glia. In mammalian glial cells the major source of Ca(2+) for this excitability is the lumen of the endoplasmic reticulum (ER), which is ultimately (re)filled from the extracellular space. This occurs via store-operated Ca(2+) entry (SOCE) which is supported by a specific signaling system connecting the ER with plasmalemmal Ca(2+) entry. Here, emptying of the ER Ca(2+) store is necessary and sufficient for the activation of SOCE, and without Ca(2+) influx via SOCE the ER store cannot be refilled. The molecular arrangements underlying SOCE are relatively complex and include plasmalemmal channels, ER Ca(2+) sensors, such as stromal interaction molecule, and possibly ER Ca(2+) pumps (of the SERCA type). There are at least two sets of plasmalemmal channels mediating SOCE, the Ca(2+)-release activated channels, Orai, and transient receptor potential (TRP) channels. The molecular identity of neuroglial SOCE has not been yet identified unequivocally. However, it seems that Orai is predominantly expressed in microglia, whereas astrocytes and oligodendrocytes rely more on TRP channels to produce SOCE. In physiological conditions the SOCE pathway is instrumental for the sustained phase of the Ca(2+) signal observed following stimulation of metabotropic receptors on glial cells.
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Affiliation(s)
- Alexei Verkhratsky
- Faculty of Life Sciences, The University of Manchester, Manchester, M13 9PT, UK,
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Brawek B, Garaschuk O. Microglial calcium signaling in the adult, aged and diseased brain. Cell Calcium 2013; 53:159-69. [PMID: 23395344 DOI: 10.1016/j.ceca.2012.12.003] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Accepted: 12/10/2012] [Indexed: 10/27/2022]
Abstract
Microglial cells are the resident immune cells of the CNS. They mediate innate immune response of the brain to injury, inflammation and neurodegenerative diseases. Apart from their role in disease they are critically involved in the development and plasticity-driven reorganization of neuronal networks and the homeostatic maintenance of brain tissue. Accumulating in vitro evidence suggests that executive functions of microglia are coupled to the intracellular Ca(2+) signaling of these cells. So far, however, very little is known about microglial Ca(2+) signaling in situ or in vivo, both in the healthy and in the diseased brain. Here, we summarize the recent in vivo/in situ findings and compare the properties of surveillant microglia in these preparations with those of microglia in vitro. The data suggest that surveillant microglia rarely show spontaneous Ca(2+) transients, express fewer functional receptors directly coupled to changes in the intracellular free Ca(2+) concentration on their surface, but vividly respond with Ca(2+) transients to cell or tissue damage in their microenvironment. Interestingly, some of these properties microglia share with monocytes engrafting in the brain under pathological conditions.
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Affiliation(s)
- Bianca Brawek
- Institute of Physiology II, Eberhard Karls University of Tuebingen, Keplerstr. 15, 72074 Tuebingen, Germany
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12
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Abstract
Microglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia." Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments.
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Weinstein JR, Swarts S, Bishop C, Hanisch UK, Möller T. Lipopolysaccharide is a frequent and significant contaminant in microglia-activating factors. Glia 2008; 56:16-26. [PMID: 17910052 PMCID: PMC2926344 DOI: 10.1002/glia.20585] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Lipopolysaccharide (LPS/endotoxin) is a potent immunologic stimulant. Many commercial-grade reagents used in research are not screened for LPS contamination. LPS induces a wide spectrum of proinflammatory responses in microglia, the immune cells of the brain. Recent studies have demonstrated that a broad range of endogenous factors including plasma-derived proteins and bioactive phospholipids can also activate microglia. However, few of these studies have reported either the LPS levels found in the preparations used or the effect of LPS inhibitors such as polymyxin B (PMX) on factor-induced responses. Here, we used the Limulus amoebocyte lysate assay to screen a broad range of commercial- and pharmaceutical-grade proteins, peptides, lipids, and inhibitors commonly used in microglia research for contamination with LPS. We then characterized the ability of PMX to alter a representative set of factor-induced microglial activation parameters including surface antigen expression, metabolic activity/proliferation, and NO/cytokine/chemokine release in both the N9 microglial cell line and primary microglia. Significant levels of LPS contamination were detected in a number of commercial-grade plasma/serum- and nonplasma/serum-derived proteins, phospholipids, and synthetic peptide preparations, but not in pharmaceutical-grade recombinant proteins or pharmacological inhibitors. PMX had a significant inhibitory effect on the microglia-activating potential of a number of commercial-, but not pharmaceutical-grade, protein preparations. Novel PMX-resistant responses to alpha(2)-macroglobulin and albumin were incidentally observed. Our results indicate that LPS is a frequent and significant contaminant in commercial-grade preparations of previously reported microglia-activating factors. Careful attention to LPS levels and appropriate controls are necessary for future studies in the neuroinflammation field.
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Affiliation(s)
- Jonathan R Weinstein
- Department of Neurology, School of Medicine, University of Washington, Seattle, Washington 98195, USA.
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14
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Abstract
In this review we summarize mechanisms of Ca(2+) signaling in microglial cells and the impact of Ca(2+) signaling and Ca(2+) levels on microglial function. So far, Ca(2+) signaling has been only characterized in cultured microglia and thus these data refer rather to activated microglia as observed in pathology when compared with the resting form found under physiological conditions. Purinergic receptors are the most prominently expressed ligand-gated Ca(2+)-permeable channels in microglia and control several microglial functions such as cytokine release in a Ca(2+)-dependent fashion. A large variety of metabotropic receptors are linked to Ca(2+) release from intracellular stores. Depletion of these intracellular stores triggers a capacitative Ca(2+) entry. While microglia are already in an activated state in culture, they can be further activated, for example, by exposure to bacterial endotoxin. This activation leads to a chronic increase of [Ca(2+)](i) and this Ca(2+) increase is a prerequisite for the release of nitric oxide and cytokines. Moreover, several factors (TNFalpha, IL-1beta, and IFN-gamma) regulate resting [Ca(2+)](i) levels.
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Affiliation(s)
- Katrin Färber
- Cellular Neuroscience, Max-Delbrueck-Center for Molecular Medicine, Robert-Rössle-Straβe 10, 13092 Berlin, Germany
| | - Helmut Kettenmann
- Cellular Neuroscience, Max-Delbrueck-Center for Molecular Medicine, Robert-Rössle-Straβe 10, 13092 Berlin, Germany
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McLarnon JG, Choi HB, Lue LF, Walker DG, Kim SU. Perturbations in calcium-mediated signal transduction in microglia from Alzheimer's disease patients. J Neurosci Res 2005; 81:426-35. [PMID: 15948178 DOI: 10.1002/jnr.20487] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Calcium-sensitive fluorescence microscopy has been used to study Ca2+-dependent signal transduction pathways in microglia obtained from Alzheimer's disease (AD) patients and non-demented (ND) individuals. Data were obtained from nine AD cases and seven ND individuals and included basal levels of intracellular Ca2+ [Ca2+]i, peak amplitudes (Delta[Ca2+]i) and time courses of adenosine triphosphate (ATP) responses and amplitudes of an initial transient response and a subsequent second component of Ca2+ influx through store-operated channels (SOC) induced by platelet-activating factor (PAF). Overall, AD microglia were characterized by significantly higher (20%) basal Ca2+ [Ca2+]i relative to ND cells. The Delta[Ca2+]i of ATP and initial phase of PAF responses, which reflect rapid depletion of Ca2+ from endoplasmic reticulum stores, were reduced by respective values of 63% and 59% in AD cells relative to amplitudes recorded from ND microglia. Additionally, AD microglia showed diminished amplitudes (reduction of 61%) of SOC-mediated Ca2+ entry induced by PAF and prolonged time courses (increase of 60%) of ATP responses with respect to ND microglia. We have generally replicated these results with exposure of human fetal microglia to beta amyloid (5 microM Abeta1-42 applied for 24 hr). Overall, these data indicate significant abnormalities are present in Ca2+-mediated signal transduction in microglia isolated from AD patients.
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Affiliation(s)
- James G McLarnon
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
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16
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Sattayaprasert P, Choi HB, Chongthammakun S, McLarnon JG. Platelet-activating factor enhancement of calcium influx and interleukin-6 expression, but not production, in human microglia. J Neuroinflammation 2005; 2:11. [PMID: 15833109 PMCID: PMC1097754 DOI: 10.1186/1742-2094-2-11] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2005] [Accepted: 04/15/2005] [Indexed: 11/10/2022] Open
Abstract
Calcium-sensitive fluorescence microscopy and molecular biology analysis have been used to study the effects of platelet-activating factor (PAF) on intracellular calcium [Ca2+]i and IL-6 expression in human microglia. PAF (applied acutely at 100 nM) elicited a biphasic response in [Ca2+]i consisting of an initial rapid increase of [Ca2+]i due to release from internal stores, followed by a sustained influx. The latter phase of the [Ca2+]i increase was blocked by SKF96365, a non-selective store-operated channel (SOC) inhibitor. RT-PCR analysis showed PAF treatment of microglia induced expression of the pro-inflammatory cytokine IL-6 in a time-dependent manner which was blocked in the presence of SKF96365. However, ELISA assay showed no production of IL-6 was elicited at any time point (1–24 h) for microglial exposures to PAF. These findings suggest that PAF stimulation of human microglia induces expression, but not production, of IL-6 and that SOC-mediated [Ca2+]i influx contributes to the enhanced expression of the cytokine.
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Affiliation(s)
- Prasongchai Sattayaprasert
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
- Department of Anatomy, Mahidol University, Bangkok, Thailand
| | - Hyun B Choi
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
- Division of Neurology, Department of Medicine, University of British Columbia, Canada
| | | | - James G McLarnon
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
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17
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Ranasinghe S, Bolsover S. Microglial Calcium Responses to Platelet-Activating Factor are Inhibited by Analogue CAS 99103-16-9 and Dihydropyridine PCA 4248 but Not by Ginkgolide A. ACTA ACUST UNITED AC 2004; 95:87-91. [PMID: 15379786 DOI: 10.1111/j.1742-7843.2004.950208.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Calcium signals evoked in N9 microglial cells were monitored using the calcium indicator dye Fluo-4 in a fluorescence imaging plate reader. Platelet activating factor in the range 100 nM to 20 microM elicited graded calcium responses. The analogue CAS 99103-16-9 inhibited the evoked calcium rise with an apparent KB of 1.3 +/- 0.4 microM. The dihydropyridine PCA 4248 inhibited the evoked calcium rise with an apparent KB of 1.2 +/- 0.2 microM. Ginkgolide A at concentrations up to 18 microM had no effect on the evoked calcium rise. While CAS 99103-16-9 and PCA 4248 appear to be simple competitive inhibitors of platelet-activating factor responses, the efficacy of ginkgolide in more complex pharmacological situations may result from an action at a site other than the platelet-activating factor receptor.
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Affiliation(s)
- Saman Ranasinghe
- Department of Physiology, University College London, Gower Street, London WC1E 6BT, U.K
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18
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Tanaka S, Koike T. Selective inflammatory stimulations enhance release of microglial response factor (MRF)-1 from cultured microglia. Glia 2002; 40:360-71. [PMID: 12420315 DOI: 10.1002/glia.10142] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The mrf-1 gene has been isolated from microglia exposed to cultured cerebellar granule neurons undergoing apoptosis. We have shown that mrf-1 is upregulated in response to neuronal death and degeneration both in vitro and in vivo. However, the exact role of MRF-1 remains unknown. Here we show that MRF-1 is released from cultured rat microglia, and its release is greatly enhanced under inflammatory conditions. When microglia were treated with ATP, the amount of MRF-1 that was released increased 10-fold compared to the basal level of release. Enhanced MRF-1 release was induced within 10 min and peaked within 1 h; after approximately 4 h, the MRF-1 release had returned to normal. MRF-1 release was stimulated by 2-methyl-thio-ATP (five-fold) and a P2X(7) selective agonist, 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (ten-fold). Moreover, the ATP-stimulated MRF-1 release was inhibited by a P2X(7) selective antagonist, oxidized ATP (oATP), and also under a Ca(2+)-free condition. These results indicate that the effects of ATP are dependent on Ca(2+) influx through P2X(7) receptors. MRF-1 release was enhanced by Ca(2+)-ionophore A23187 (sixfold), thapsigargin (threefold); however, it was not enhanced by glutamate or lipopolysaccharide. Moreover, a platelet-activating factor enhanced microglial MRF-1 release in a dose-dependent manner. We also showed that a conditioned medium from cerebellar granule neurons undergoing apoptosis markedly increased MRF-1 release from microglia; that effect was significantly inhibited by oATP. These results indicate that selective inflammatory stimulations, including ATP and PAF, enhance MRF-1 release from microglia through a Ca(2+)-dependent mechanism and suggest that MRF-1 may play a role in cell-cell interactions under inflammatory conditions.
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Affiliation(s)
- Shuuitsu Tanaka
- Molecular Neurobiology Laboratory, Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
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19
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Abstract
Receptor-mediated Ca(2+) signals are a common signal transduction mechanism in all living cells, including microglia. Recent years have brought major advances in our understanding of microglial Ca(2+) signaling. More than 20 receptor/ligand interactions leading to Ca(2+) signals in microglia have been described so far, and it seems that this is just the beginning. The literature has grown rapidly during the past few years, especially in regard to chemokine and ATP/UTP receptor signaling. This article presents a brief overview of the basics of Ca(2+) signaling, reviews the current literature on microglial Ca(2+) signaling, and discusses the current challenges and possible future directions of this emerging field.
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Affiliation(s)
- Thomas Möller
- Department of Neurology, Box 356465, 1959 NE Pacific St., University of Washington, Seattle, WA 98195
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20
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Franciosi S, Choi HB, Kim SU, McLarnon JG. Interferon-gamma acutely induces calcium influx in human microglia. J Neurosci Res 2002; 69:607-13. [PMID: 12210826 DOI: 10.1002/jnr.10331] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The acute actions of the cytokine, interferon-gamma (IFN-gamma), on intracellular calcium [Ca(2+)](i) levels in human microglia were investigated. In the presence of a calcium-containing physiological solution (Ca(2+)-PSS), IFN-gamma caused a progressive increase in [Ca(2+)](i) to a plateau level with a mean rate of increase of 0.81 +/- 0.17 nM/s and mean amplitude of 102 +/- 12 nM (n = 67 cells). Washout of the cytokine did not alter the plateau established with IFN-gamma in Ca(2+)-PSS; however, introduction of a Ca(2+)-free PSS diminished [Ca(2+)](i) to baseline levels. The decrease in [Ca(2+)](i) with Ca(2+)-free PSS would indicate that the response to IFN-gamma was mediated by an influx pathway. This result was confirmed in separate experiments showing the lack of an induced change in [Ca(2+)](i) with IFN-gamma applied in Ca(2+)-free PSS. The increase in [Ca(2+)](i) induced in Ca(2+)-PSS was reduced to near baseline levels when the external solution contained low Cl(-) in the maintained presence of IFN-gamma suggesting that cellular depolarization inhibited the cytokine mediated entry pathway. The compound SKF96365, which blocks store operated influx of Ca(2+) in human microglia, was ineffective in altering the increase in [Ca(2+)](i), however, La(3+) completely inhibited the Ca(2+) response induced by IFN-gamma. Whole-cell patch clamp studies showed no effect of IFN-gamma to alter outward currents and inward rectifier K(+) currents. The influx of Ca(2+) may serve a signaling role in microglia linking IFN-gamma to functional responses of the cells to infiltrating T lymphocytes into the central nervous system (CNS) during inflammatory processes.
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Affiliation(s)
- Sonia Franciosi
- Department of Pharmacology, University of British Columbia, Vancouver, British Columbia, Canada
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21
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Abstract
Microglia, residential macrophages in the central nervous system, can release a variety of factors including cytokines, chemokines, etc. to regulate the communication among neuronal and other types of glial cells. Microglia play immunological roles in mechanisms underlying the phagocytosis of invading microorganisms and removal of dead or damaged cells. When microglia are hyperactivated due to a certain pathological imbalance, they may cause neuronal degeneration. Pathological activation of microglia has been reported in a wide range of conditions such as cerebral ischemia, Alzheimer's disease, prion diseases, multiple sclerosis, AIDS dementia, and others. Nearly 5000 papers on microglia can be retrieved on the Web site PubMed at present (November 2001) and half of them were published within the past 5 years. Although it is not possible to read each paper in detail, as many factors as possible affecting microglial functions in in vitro culture systems are presented in this review. The factors are separated into "activators" and "inhibitors," although it is difficult to classify many of them. An overview on these factors may help in the development of a new strategy for the treatment of various neurodegenerative diseases.
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Affiliation(s)
- Yoichi Nakamura
- Laboratory of Integrative Physiology in Veterinary Sciences, Osaka Prefecture University; Sakai, Japan.
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22
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Martínez AD, Eugenín EA, Brañes MC, Bennett MVL, Sáez JC. Identification of second messengers that induce expression of functional gap junctions in microglia cultured from newborn rats. Brain Res 2002; 943:191-201. [PMID: 12101041 DOI: 10.1016/s0006-8993(02)02621-5] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The effect of several second messengers on the functional expression of gap junctions was investigated in primary cultures of newborn rat microglia. As previously reported, microglia cultured under resting conditions expressed low levels of the gap junction protein connexin 43, and exhibited little dye coupling. After treatment with 4bromo-A23187, a Ca(2+) ionophore, the incidence of dye coupling between microglia increased progressively over a 12-h period. Dye coupling was markedly reduced by gap junction blockers. Induction of dye coupling by 4bromo-A23187 was prevented by the addition of a synthetic peptide with the same sequence as a region of the extracellular loop 1 of connexin 43 (residues 53-66). The increase in dye coupling induced by 4bromo-A23187 was associated with increased connexin 43 mRNA and protein levels. Treatment of microglia with phorbol 12-myristate 13-acetate, an activator of protein kinase C, did not promote gap junctional communication in untreated microglia and reversed 4bromo-A23187-induced dye coupling. Thus, gap junctional communication between microglia can be regulated oppositely by calcium- and protein kinase C-dependent pathways. Activators of cGMP-dependent protein kinase (8bromo-cGMP) or protein kinase A (8bromo-cAMP) had no effect on untreated microglia or on 4bromo-A23187-induced dye coupling. Differential regulation of gap junctions by intracellular calcium concentration and protein kinase C activity may help to explain how various stimuli evoke differences in microglia responses, such as synthesis and secretion of cytokines and proteases.
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Affiliation(s)
- Agustín D Martínez
- Departamento de Ciencias Fisiológicas, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
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23
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Khoo C, Helm J, Choi HB, Kim SU, McLarnon JG. Inhibition of store-operated Ca(2+) influx by acidic extracellular pH in cultured human microglia. Glia 2001; 36:22-30. [PMID: 11571781 DOI: 10.1002/glia.1092] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The effects of extracellular acidification on Ca(2+)-dependent signaling pathways in human microglia were investigated using Ca(2+)-sensitive fluorescence microscopy. Adenosine triphosphate (ATP) was used to elicit Ca(2+) responses primarily dependent on the depletion of intracellular endoplasmic reticulum (ER) stores, while platelet-activating factor (PAF) was used to elicit responses primarily dependent on store-operated channel (SOC) influx of Ca(2+). The duration of transient responses induced by ATP was not significantly different in standard physiological pH 7.4 (mean duration 30.2 +/- 2.5 s) or acidified pH 6.2 (mean duration 31.7 +/- 2.8 s) extracellular solutions. However, the time course of the PAF response at pH 7.4 was significantly reduced by 87% with external pH at 6.2. These results suggest that acidification of extracellular solutions inhibits SOC entry of Ca(2+) with little or no effect on depletion of ER stores. Changes of extracellular pH over the range from 8.6 to 6.2 during the development of a sustained SOC influx induced by PAF resulted in instantaneous modulation of SOC amplitude indicating a rapidly reversible effect of pH on this Ca(2+) pathway. Whole-cell patch clamp recordings showed external acidification blocked depolarization-activated outward K(+) current indicating cellular depolarization may be involved in the acid pH inhibition. Since SOC mediated influx of Ca(2+) is strongly modulated by membrane potential, the electrophysiological data suggest that acidification may act to inhibit SOC by cellular depolarization. These results suggest that acidification observed during cerebral ischemia may alter microglial responses and functions.
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Affiliation(s)
- C Khoo
- Department of Pharmacology & Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
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24
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McLarnon JG, Franciosi S, Wang X, Bae JH, Choi HB, Kim SU. Acute actions of tumor necrosis factor-alpha on intracellular Ca(2+) and K(+) currents in human microglia. Neuroscience 2001; 104:1175-84. [PMID: 11457600 DOI: 10.1016/s0306-4522(01)00119-1] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The effects of acute application of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFalpha) on levels of intracellular Ca(2+) ([Ca(2+)]i) and on whole-cell outward and inward K(+) currents were studied in cultured human microglia. TNFalpha elicited a linear increase in [Ca(2+)]i to a plateau level in microglia bathed in either standard physiological saline solution or Ca(2+)-free physiological saline solution. The rate of increase of [Ca(2+)]i or the level of [Ca(2+)]i attained was not significantly altered in the absence of external Ca(2+) indicating that Ca(2+) influx did not contribute appreciably to the cytokine-induced rise in [Ca(2+)]i. This point was directly confirmed using Mn(2+) quenching where no change in signal fluorescence was observed with TNFalpha treatment of microglia in Ca(2+)-free physiological saline solution. The rate of increase of [Ca(2+)]i induced by TNFalpha in Ca(2+)-free physiological saline solution was not altered by prior application of ATP to deplete inositol triphosphate stores indicating that these stores did not contribute to the cytokine response. In whole-cell patch clamp recordings, the acute treatment of human microglia with TNFalpha led to the expression of an outward K(+) current in one-third (14 of 41) of cells. This current was activated at potentials positive to -30 mV, showed rapid kinetics of activation with no evident inactivation and had an I-V relation exhibiting outward rectification. Analysis of tail currents showed reversal of the outward K(+) current near -70 mV and tetraethylammonium (10 mM) inhibited the outward K(+) current to 24% of control level. Acute application of TNFalpha had no effect to alter inward rectifier currents generated from voltage ramps. The signaling pathways involving TNFalpha modulation of [Ca(2+)]i and K(+) channels in human microglia may contribute to functional and pathological actions of the cytokine in the brain.
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Affiliation(s)
- J G McLarnon
- Department of Pharmacology and Therapeutics, Faculty of Medicine, The University of British Columbia, Vancouver, BC, Canada V6T 1Z3.
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25
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Abstract
Inflammatory events in the CNS are associated with injuries as well as with well-known chronic degenerative diseases, such as Multiple Sclerosis, Parkinson's, or Alzheimer's disease. Compared to inflammation in peripheral tissues, inflammation in brain appears to follow distinct pathways and time-courses, which likely has to do with a relatively strong immunosuppression in that organ. For this reason, it is of great importance to get insights into the molecular mechanism governing immune reactions in brain tissue. This task is hard to achieve in vivo, but can be approached by studying the major cell type responsible for brain inflammation, the microglia, in culture. Since these cells are the only professional antigen-presenting cells resident in brain parenchyma, molecular mechanisms of antigen presentation are being discussed first. After covering the expression and regulation of anti- and proinflammatory cytokines, induction and regulation of two key enzymes and their products-COX-2 and iNOS-are summarized. Possibly, pivotal molecular targets for drug therapies of brain disorders will be discovered in intracellular signaling pathways leading to activation of transcription factors. Finally, the impact of growth factors, of neurotrophins in particular, is highlighted. It is concluded that the presently available data on the molecular level is far from being statisfying, but that only from better insights into molecular events will we obtain the information required for more specific therapies.
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Affiliation(s)
- P J Gebicke-Haerter
- Department of Psychopharmacology, Central Institute for Mental Health, Mannheim, Germany.
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26
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McLarnon JG, Helm J, Goghari V, Franciosi S, Choi HB, Nagai A, Kim SU. Anion channels modulate store-operated calcium influx in human microglia. Cell Calcium 2000; 28:261-8. [PMID: 11032781 DOI: 10.1054/ceca.2000.0150] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Recent work from this laboratory has demonstrated that purinergic-mediated depolarization of human microglia inhibited a store-operated pathway for entry of Ca2+. We have used Fura-2 spectrofluorometry to investigate the effects on store-operated Ca2+ influx induced by replacement of NaCl with Na-gluconate in extracellular solutions. Three separate procedures were used to activate store-operated channels. Platelet activating factor (PAF) was used to generate a sustained influx of Ca2+ in standard physiological saline solution (PSS). The magnitude of this response was depressed by 70% after replacement of PSS with low Cl- PSS. A second procedure used ATP, initially applied in Ca2+-free PSS solution to deplete intracellular stores. The subsequent perfusion of PSS solution containing Ca2+ resulted in a large and sustained entry of Ca2+, which was inhibited by 75% with low Cl- PSS. The SERCA inhibitor cyclopiazonic acid (CPA) was used to directly deplete stores in zero-Ca2+ PSS. Following the introduction of PSS containing Ca2+, a maintained stores-operated influx of Ca2+ was evident which was inhibited by 77% in the presence of the low Cl- PSS. Ca2+ influx was linearly reduced with cell depolarization in elevated K+ (7.5 to 35 mM) suggesting that changes in external Cl- were manifest as altered electrical driving force for Ca2+ entry. However, 50 mM external KCl effectively eliminated divalent entry which may indicate inactivation of this pathway with high magnitudes of depolarization. Patch clamp studies showed low Cl-PSS to cause depolarizing shifts in both holding currents and reversal potentials of currents activated with voltage ramps. The results demonstrate that Cl- channels play an important role in regulating store-operated entry of Ca2+ in human microglia.
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Affiliation(s)
- J G McLarnon
- Department of Pharmacology and Therapeutics, Faculty of Medicine, The University of British Columbia, Vancouver, British Columbia, Canada.
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27
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Wang X, Kim SU, van Breemen C, McLarnon JG. Activation of purinergic P2X receptors inhibits P2Y-mediated Ca2+ influx in human microglia. Cell Calcium 2000; 27:205-12. [PMID: 10858666 DOI: 10.1054/ceca.2000.0110] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Purinoceptor (P2X and P2Y) mediated Ca2+ signaling in cultured human microglia was studied using Ca2+ sensitive fluorescence microscopy. ATP (at 100 microM) induced a transient increase in [Ca2+]i in both normal and Ca(2+)-free solution suggesting a primary contribution by release from intracellular stores. This conclusion was further supported by the failure of ATP to cause a divalent cationic influx in Mn2+ quenching experiments. However, when fluorescence quenching was repeated after removal of extracellular Na+, ATP induced a large influx of Mn2+, indicating that inward Na+ current through a non-selective P2X-coupled channel may normally suppress divalent cation influx. Inhibition of Mn2+ entry was also found when microglia were depolarized using elevated external K+ in Na(+)-free solutions. The possibility of P2X inhibition of Ca2+ influx was then investigated by minimizing P2X contributions of purinergic responses using either the specific P2Y agonist, ADP-beta-S in the absence of ATP or using ATP combined with PPADS, a specific inhibitor of P2X receptors. In quenching studies both procedures resulted in large increases in Mn2+ influx in contrast to the lack of effect observed with ATP. In addition, perfusion of either ATP plus PPADS or ADP-beta-S alone caused a significantly enhanced duration (about 200%) of the [Ca2+]i response relative to that induced by ATP. These results show that depolarization induced by P2X-mediated Na+ influx inhibits store-operated Ca2+ entry resulting from P2Y activation, thereby modulating purinergic signaling in human microglia.
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Affiliation(s)
- X Wang
- Department of Pharmacology, University of British Columbia, Vancouver, Canada
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28
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Goghari V, Franciosi S, Kim SU, Lee YB, McLarnon JG. Acute application of interleukin-1beta induces Ca(2+) responses in human microglia. Neurosci Lett 2000; 281:83-6. [PMID: 10704748 DOI: 10.1016/s0304-3940(00)00824-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The effects of the pro-inflammatory cytokine interleukin-1-beta (IL-1beta) on levels of intracellular calcium [Ca(2+)](i) in cultured human microglia have been studied using the fluorescent Ca(2+) indicator fura-2. IL-1beta (2 ng/ml) caused a slow, progressive increase in [Ca(2+)](i) in standard Ca(2+)-containing physiological solution (PSS). A similar effect was observed in separate studies using Ca(2+)-free PSS, however, the mean rate of increase was significantly lower than that measured with PSS. Similar results were obtained in a separate protocol, where cells were exposed to both IL-1beta in Ca(2+)-free PSS and PSS. The slope of the IL-1beta induced increase of [Ca(2+)](i) in Ca(2+)-free PSS was not altered when adenosine triphosphate was added prior to application of the cytokine. These results suggest that IL-1beta-induced responses in human microglia involve both a Ca(2+) entry pathway and a mechanism of intracellular increase other than from IP(3)-sensitive stores.
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Affiliation(s)
- V Goghari
- Department of Pharmacology and Therapeutics, Faculty of Medicine, The University of British Columbia, 2176 Health Sciences Mall, Vancouver, Canada
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