151
|
Holmgaard K, Aalkjaer C, Lambert JDC, Bek T. ATP-induced relaxation of porcine retinal arterioles depends on the perivascular retinal tissue and acts via an adenosine receptor. Curr Eye Res 2007; 32:353-9. [PMID: 17453957 DOI: 10.1080/02713680701229646] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
PURPOSE Purinergic compounds and cyclooxygenase inhibitors are involved in the tone regulation of isolated retinal arterioles in vitro, but it is unknown whether the perivascular retinal tissue influences these effects. METHODS Adenosine-and ATP-induced vasodilation of porcine retinal arterioles was studied in a wire myograph before and after removal of the perivascular tissue. RESULTS Both adenosine and ATP caused relaxation of the studied arterioles. This effect depended on the perivascular tissue and could be blocked by antagonists but was unaffected by ibuprofen. CONCLUSIONS The relaxation of porcine retinal arterioles induced by purinergic compounds is modulated by the perivascular retinal tissue.
Collapse
Affiliation(s)
- Kim Holmgaard
- Department of Ophthalmology, Arhus University Hospital, Arhus, Denmark.
| | | | | | | |
Collapse
|
152
|
Pangršič T, Potokar M, Stenovec M, Kreft M, Fabbretti E, Nistri A, Pryazhnikov E, Khiroug L, Giniatullin R, Zorec R. Exocytotic release of ATP from cultured astrocytes. J Biol Chem 2007; 282:28749-28758. [PMID: 17627942 DOI: 10.1074/jbc.m700290200] [Citation(s) in RCA: 190] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Astrocytes appear to communicate with each other as well as with neurons via ATP. However, the mechanisms of ATP release are controversial. To explore whether stimuli that increase [Ca(2+)](i) also trigger vesicular ATP release from astrocytes, we labeled ATP-containing vesicles with the fluorescent dye quinacrine, which exhibited a significant co-localization with atrial natriuretic peptide. The confocal microscopy study revealed that quinacrine-loaded vesicles displayed mainly non-directional spontaneous mobility with relatively short track lengths and small maximal displacements, whereas 4% of vesicles exhibited directional mobility. After ionomycin stimulation only non-directional vesicle mobility could be observed, indicating that an increase in [Ca(2+)](i) attenuated vesicle mobility. Total internal reflection fluorescence (TIRF) imaging in combination with epifluorescence showed that a high percentage of fluorescently labeled vesicles underwent fusion with the plasma membrane after stimulation with glutamate or ionomycin and that this event was Ca(2+)-dependent. This was confirmed by patch-clamp studies on HEK-293T cells transfected with P2X(3) receptor, used as sniffers for ATP release from astrocytes. Glutamate stimulation of astrocytes was followed by an increase in the incidence of small transient inward currents in sniffers, reminiscent of postsynaptic quantal events observed at synapses. Their incidence was highly dependent on extracellular Ca(2+). Collectively, these findings indicate that glutamate-stimulated ATP release from astrocytes was most likely exocytotic and that after stimulation the fraction of quinacrine-loaded vesicles, spontaneously exhibiting directional mobility, disappeared.
Collapse
Affiliation(s)
- Tina Pangršič
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, SI-1000 Ljubljana, Slovenia; Celica Biomedical Center, Proletarska cesta 4, SI-1000 Ljubljana, Slovenia
| | - Maja Potokar
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, SI-1000 Ljubljana, Slovenia; Celica Biomedical Center, Proletarska cesta 4, SI-1000 Ljubljana, Slovenia
| | - Matjaž Stenovec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, SI-1000 Ljubljana, Slovenia; Celica Biomedical Center, Proletarska cesta 4, SI-1000 Ljubljana, Slovenia
| | - Marko Kreft
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, SI-1000 Ljubljana, Slovenia; Celica Biomedical Center, Proletarska cesta 4, SI-1000 Ljubljana, Slovenia
| | - Elsa Fabbretti
- Neurobiology Sector, International School for Advanced Studies (SISSA), Via Beirut 2-4, 34014 Trieste, Italy
| | - Andrea Nistri
- Neurobiology Sector, International School for Advanced Studies (SISSA), Via Beirut 2-4, 34014 Trieste, Italy
| | - Evgeny Pryazhnikov
- Neuroscience Center, University of Helsinki, PO Box 56 (Viikinkaari 4), FIN-00014 Helsinki, Finland
| | - Leonard Khiroug
- Neuroscience Center, University of Helsinki, PO Box 56 (Viikinkaari 4), FIN-00014 Helsinki, Finland
| | - Rashid Giniatullin
- Neurobiology Sector, International School for Advanced Studies (SISSA), Via Beirut 2-4, 34014 Trieste, Italy
| | - Robert Zorec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, SI-1000 Ljubljana, Slovenia; Celica Biomedical Center, Proletarska cesta 4, SI-1000 Ljubljana, Slovenia.
| |
Collapse
|
153
|
Ho WSC, van den Pol AN. Bystander attenuation of neuronal and astrocyte intercellular communication by murine cytomegalovirus infection of glia. J Virol 2007; 81:7286-92. [PMID: 17459923 PMCID: PMC1933277 DOI: 10.1128/jvi.02501-06] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2006] [Accepted: 04/18/2007] [Indexed: 11/20/2022] Open
Abstract
Astrocytes are the first cells infected by murine cytomegalovirus (MCMV) in primary cultures of brain. These cells play key roles in intercellular signaling and neuronal development, and they modulate synaptic activity within the nervous system. Using ratiometric fura-2 digital calcium imaging of >8,000 neurons and glia, we found that MCMV-infected astrocytes showed an increase in intracellular basal calcium levels and an enhanced response to neuroactive substances, including glutamate and ATP, and to high potassium levels. Cultured neurons with no sign of MCMV infection showed attenuated synaptic signaling after infection of the underlying astrocyte substrate, and intercellular communication between astrocytes with no sign of infection was reduced by the presence of infected glia. These bystander effects would tend to cause further deterioration of cellular communication in the brain in addition to the problems caused by the loss of directly infected cells.
Collapse
Affiliation(s)
- Winson S C Ho
- Department of Neurosurgery, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06520, USA
| | | |
Collapse
|
154
|
Ikeda H, Tsuda M, Inoue K, Murase K. Long-term potentiation of neuronal excitation by neuron-glia interactions in the rat spinal dorsal horn. Eur J Neurosci 2007; 25:1297-306. [PMID: 17425556 DOI: 10.1111/j.1460-9568.2007.05386.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
By imaging neuronal excitation in rat spinal cord slices with a voltage-sensitive dye, we examined the role of glial cells in the P2X receptor agonist alphabeta-methylene ATP (alphabetameATP)-triggered long-term potentiation (LTP) in the dorsal horn. Bath application of alphabetameATP potentiated neuronal excitation in the superficial dorsal horn. The potentiation was inhibited in the presence of the P2X receptor antagonists TNP-ATP, PPADS and A-317491, and was not induced in slices taken from rats neonatally treated with capsaicin. These results suggest that alphabetameATP acts on P2X receptors, possibly P2X(3) and/or P2X(2/3), in capsaicin-sensitive primary afferent terminals. Furthermore, the potentiation was inhibited by treatment with the glial metabolism inhibitor monofluoroacetic acid. Results obtained with the p38 mitogen-activated protein kinase (p38 MAPK) inhibitor SB203580, tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-6, and antibodies to TNF-alpha and IL-6, as well as by double immunolabelling of activated p38 MAPK with markers of astrocytes and microglia, demonstrated that alphabetameATP activated p38 MAPK in astrocytes, and that the presence of proinflammatory cytokines and p38 MAPK activation were necessary for the induction of alphabetameATP-triggered LTP. These findings indicate that glial cells contribute to the alphabetameATP-induced LTP, which might be part of a cellular mechanism for the induction of persistent pain.
Collapse
Affiliation(s)
- Hiroshi Ikeda
- Department of Human and Artificial Intelligence Systems, Graduate School of Engineering, and Research and Education Program for Life Science, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507, Japan.
| | | | | | | |
Collapse
|
155
|
STRIEDINGER KATHARINE, MEDA PAOLO, SCEMES ELIANA. Exocytosis of ATP from astrocyte progenitors modulates spontaneous Ca2+ oscillations and cell migration. Glia 2007; 55:652-62. [PMID: 17309060 PMCID: PMC2617704 DOI: 10.1002/glia.20494] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In the mature central nervous system (CNS) regulated secretion of ATP from astrocytes is thought to play a significant role in cell signaling. Whether such a mechanism is also operative in the developing nervous system and, if so, during which stage of development, has not been investigated. We have tackled this question using cells derived from reconstituted neurospheres, as well as brain explants of embryonic mice. Here, we show that in both models of neural cell development, astrocyte progenitors are competent for the regulated secretion of ATP-containing vesicles. We further document that this secretion is dependent on cytosolic Ca(2+) and the v-SNARE system, and takes place by exocytosis. Interference with ATP secretion alters spontaneous Ca(2+) oscillations and migration of neural progenitors. These data indicate that astrocyte progenitors acquire early in development the competence for regulated secretion of ATP, and that this event is implicated in the regulation of at least two cell functions, which are critical for the proper morphogenesis and functional maturation of the CNS.
Collapse
Affiliation(s)
| | - PAOLO MEDA
- Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - ELIANA SCEMES
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
- Correspondence to: Eliana Scemes, Department of Neuroscience, Kennedy Center, Room no. 203, Albert Einstein College of Medicine, 1410 Pelham Parkway South, Bronx, NY 10461, USA. E-mail:
| |
Collapse
|
156
|
Dupont G, Combettes L, Leybaert L. Calcium Dynamics: Spatio‐Temporal Organization from the Subcellular to the Organ Level. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 261:193-245. [PMID: 17560283 DOI: 10.1016/s0074-7696(07)61005-5] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
Many essential physiological processes are controlled by calcium. To ensure reliability and specificity, calcium signals are highly organized in time and space in the form of oscillations and waves. Interesting findings have been obtained at various scales, ranging from the stochastic opening of a single calcium channel to the intercellular calcium wave spreading through an entire organ. A detailed understanding of calcium dynamics thus requires a link between observations at different scales. It appears that some regulations such as calcium-induced calcium release or PLC activation by calcium, as well as the weak diffusibility of calcium ions play a role at all levels of organization in most cell types. To comprehend how calcium waves spread from one cell to another, specific gap-junctional coupling and paracrine signaling must also be taken into account. On the basis of a pluridisciplinar approach ranging from physics to physiology, a unified description of calcium dynamics is emerging, which could help understanding how such a small ion can mediate so many vital functions in living systems.
Collapse
Affiliation(s)
- Geneviève Dupont
- Theoretical Chronobiology Unit, Université Libre de Bruxelles, Faculté des Sciences, 1050 Brussels, Belgium
| | | | | |
Collapse
|
157
|
Werry EL, Liu GJ, Bennett MR. Glutamate-stimulated ATP release from spinal cord astrocytes is potentiated by substance P. J Neurochem 2006; 99:924-36. [PMID: 17076659 DOI: 10.1111/j.1471-4159.2006.04133.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
ATP has recently emerged as a key molecule mediating pathological pain. The aim of this study was to examine whether spinal cord astrocytes could be a source of ATP in response to the nociceptive neurotransmitters glutamate and substance P. Glutamate stimulated ATP release from these astrocytes and this release was greatly potentiated by substance P, even though substance P alone did not elicit ATP release. Substance P also potentiated glutamate-induced inward currents, but did not cause such currents alone. When glutamate was applied alone it acted exclusively through alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionate receptors to stimulate Ca(2+) influx-dependent ATP release. However, when substance P was co-applied with glutamate, ATP release could be elicited by activation of NMDA and metabotropic glutamate receptors. Activation of neurokinin receptor subtypes, protein kinase C and phospholipases A(2), C and D were needed for substance P to bring about its effects. These results suggest that astrocytes may be a major source of ATP in the spinal cord on activation of nerve fibres that release substance P and glutamate.
Collapse
Affiliation(s)
- Eryn L Werry
- Neurobiology Laboratory, Discipline of Physiology, Bosch Institute, University of Sydney, New South Wales, Australia
| | | | | |
Collapse
|
158
|
Abstract
Among seven members of P2X ionotropic receptors activated by extracellular ATP, the P2X(7) subtype is unique in that it can function as a cation channel, a nonselective pore, or even a signaling complex coupled with multiple downstream components. Several roles of P2X(7) receptors have been described in CNS cells in the past decade, including release of cytokines and transmitters, modulation of presynaptic transmitter release, and activation of multiple signaling pathways. The finding that P2X(7) pores may directly mediate efflux of cytosolic glutamate, GABA, and ATP in glial cells is particularly interesting, as it provides a novel mechanism of glial transmitter release that may play important roles not only in physiological intercellular communication but also in pathological neural injury.
Collapse
Affiliation(s)
- Shumin Duan
- Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Joseph T Neary
- Research Service, Miami VA Medical Center, Departments of Pathology, Biochemistry and Molecular Biology, and Neuroscience Program, University of Miami School of Medicine, Miami, Florida
| |
Collapse
|
159
|
Abstract
Several lines of evidence indicate that the elaborated calcium signals and the occurrence of calcium waves in astrocytes provide these cells with a specific form of excitability. The identification of the cellular and molecular steps involved in the triggering and transmission of Ca(2+) waves between astrocytes resulted in the identification of two pathways mediating this form of intercellular communication. One of them involves the direct communication between the cytosols of two adjoining cells through gap junction channels, while the other depends upon the release of "gliotransmitters" that activates membrane receptors on neighboring cells. In this review we summarize evidence in favor of these two mechanisms of Ca(2+) wave transmission and we discuss that they may not be mutually exclusive, but are likely to work in conjunction to coordinate the activity of a group of cells. To address a key question regarding the functional consequences following the passage of a Ca(2+) wave, we list, in this review, some of the potential intracellular targets of these Ca(2+) transients in astrocytes, and discuss the functional consequences of the activation of these targets for the interactions that astrocytes maintain with themselves and with other cellular partners, including those at the glial/vasculature interface and at perisynaptic sites where astrocytic processes tightly interact with neurons.
Collapse
Affiliation(s)
- Eliana Scemes
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
| | | |
Collapse
|
160
|
Verkhratsky A, Toescu EC. Neuronal-glial networks as substrate for CNS integration. J Cell Mol Med 2006. [DOI: 10.1111/j.1582-4934.2006.tb00445.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
|
161
|
Abstract
Astrocytes have been considered, for a long time, as the support and house-keeping cells of the nervous system. Indeed, the astrocytes play very important metabolic roles in the brain, but the catalogue of nervous system functions or activities that involve directly glial participation has extended dramatically in the last decade. In addition to the further refining of the signalling capacity of the neuroglial networks and the detailed reassessment of the interactions between glia and vascular bed in the brain, one of the important salient features of the increased glioscience activity in the last few years was the morphological and functional demonstration that protoplasmic astrocytes occupy well defined spatial territories, with only limited areas of morphological overlapping, but still able to communicate with adjacent neighbours through intercellular junctions. All these features form the basis for a possible reassessment of the nature of integration of activity in the central nervous system that could raise glia to a role of central integrator.
Collapse
Affiliation(s)
- A Verkhratsky
- Faculty of Life Sciences, The University of Manchester, Manchester, UK.
| | | |
Collapse
|
162
|
Nagai K, Nagasawa K, Matsunaga R, Yamaji M, Fujimoto S. Novel Na+-independent and adenine-specific transport system for adenine in primary cultured rat cortical neurons. Neurosci Lett 2006; 407:244-8. [PMID: 16978783 DOI: 10.1016/j.neulet.2006.08.052] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Revised: 08/10/2006] [Accepted: 08/21/2006] [Indexed: 12/15/2022]
Abstract
Endogenous adenine is an important modulator of cell survival and activity in the central nervous system. In the present study, we examined the transport mechanisms for adenine in primary cultured rat cortical neurons and astrocytes. [3H]Adenine was time-dependently taken up into neurons, but not into astrocytes. In kinetic analysis, the [3H]adenine uptake by neurons was observed to be saturable, and an Eadie-Hofstee plot showed that a single component was involved in the uptake, with kinetic parameters of Km=6.09 microM and Vmax=0.340 nmol/mg protein per min. In inhibition assaying by nucleobases and nucleosides, and inhibitors for equilibrative nucleoside transporters, organic ion transporters and peptide transporters, which were reported to transport nucleobases and their analogues, the [3H]adenine uptake by neurons was found to be significantly inhibited by excess concentrations of adenine, hypoxanthine and adenosine, and was greatly reduced only by the addition of adenine. Therefore, it was indicated that adenine in the extracellular fluid in the central nervous system is taken up into neurons, but not into astrocytes, and that neurons may present a novel Na+ -independent and adenine-specific transport system.
Collapse
Affiliation(s)
- Katsuhito Nagai
- Department of Environmental Biochemistry, Kyoto Pharmaceutical University, Misasagi, Kyoto, Japan.
| | | | | | | | | |
Collapse
|
163
|
Aremu DA, Meshitsuka S. Some aspects of astroglial functions and aluminum implications for neurodegeneration. ACTA ACUST UNITED AC 2006; 52:193-200. [PMID: 16529821 DOI: 10.1016/j.brainresrev.2006.02.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2005] [Revised: 01/24/2006] [Accepted: 02/02/2006] [Indexed: 01/29/2023]
Abstract
The present decade had witnessed an unprecedented attention focused on glial cells as a result of their unusual physiological roles that are being unraveled. It is now known that, rather than being a mere supporter of neurons, astroglia are actively involved in their modulation. The aluminum hypothesis seems to have been laid to rest, probably due to contradictory epidemiological reports on it as a causative factor of neurodegenerative diseases. Surprisingly, newer scientific evidences continue to appear and recent findings have implicated astrocytes as the principal target of its toxic action. In view of the likely detrimental effects of the interaction between these two infamous partners in neuroscience on neurons and nervous system, we have reviewed some aspects of glia-neuron interaction and discussed the implications of aluminum-impaired astrocytic functions on neurodegeneration. Because sporadic causes still account for the majority of the neurodegenerative diseases of which Alzheimer's disease is the most prominent, it has been suggested that neurotoxicologists should not relent in screening for the environmental agents, such as aluminum, and that considerable attention should be given to glial cells in view of the likely implications of environmental toxicants on their never-imagined newly reported roles in the central nervous system (CNS).
Collapse
Affiliation(s)
- David A Aremu
- Division of Medical Environmentology, Department of Social Medicine, Graduate School of Medical Sciences, Tottori University, Yonago 683-8503, Japan.
| | | |
Collapse
|
164
|
Abstract
Alterations in synaptic strength are thought to represent the cellular basis of learning and memory. While such processes appear to be fundamental to all synapses, until recently there has been a relative dearth of information regarding synaptic 'memory' processes in autonomic circuits. Here we examine recent advances in our understanding of plasticity at glutamatergic synapses onto magnocellular neurosecretory cells in the hypothalamus, paying particular attention to the contributions of noradrenaline in coding long-lasting pre- and postsynaptic changes in efficacy. We also highlight recent work demonstrating that glial cells play a crucial role in the induction of long-term potentiation. Based on the work reviewed here, we have a clearer picture of the synaptic and cellular mechanisms that allow autonomic pathways to learn and remember.
Collapse
Affiliation(s)
- Grant R J Gordon
- Hotchkiss Brain Institute and the Department of Physiology and Biophysics, University of Calgary, Calgary, AB, Canada
| | | |
Collapse
|
165
|
Abstract
Neuronal-glial circuits underlie integrative processes in the nervous system. Function of glial syncytium is, to a very large extent, regulated by the intracellular calcium signaling system. Glial calcium signals are triggered by activation of multiple receptors, expressed in glial membrane, which regulate both Ca2+ entry and Ca2+ release from the endoplasmic reticulum. The endoplasmic reticulum also endows glial cells with intracellular excitable media, which is able to produce and maintain long-ranging signaling in a form of propagating Ca2+ waves. In pathological conditions, calcium signals regulate glial response to injury, which might have both protective and detrimental effects on the nervous tissue.
Collapse
|
166
|
Ahmad S, Ahmad A, White CW. Purinergic signaling and kinase activation for survival in pulmonary oxidative stress and disease. Free Radic Biol Med 2006; 41:29-40. [PMID: 16781450 DOI: 10.1016/j.freeradbiomed.2006.03.004] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/11/2005] [Revised: 02/27/2006] [Accepted: 03/02/2006] [Indexed: 10/24/2022]
Abstract
Stimulus-induced release of endogenous ATP into the extracellular milieu has been shown to occur in a variety of cells, tissues, and organs. Extracellular ATP can propagate signals via P2 receptors that are essential for growth and survival of cells. Abundance of P2 receptors, their multiple isoforms, and their ubiquitous distribution indicate that they transmit vital signals. Pulmonary epithelium and endothelium are rich in both P2X and P2Y receptors. ATP release from lung tissue and cells occurs upon stimulation both in vivo and in vitro. Extracellular ATP can activate signaling cascades composed of protein kinases including extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3-kinase (PI3K). Here we summarize progress related to release of endogenous ATP and nucleotide signaling in pulmonary tissues upon exposure to oxidant stress. Hypoxic, hyperoxic, and ozone exposures cause a rapid increase of extracellular ATP in primary pulmonary endothelial and epithelial cells. Extracellular ATP is critical for survival of these cells in high oxygen and ozone concentrations. The released ATP, upon binding to its specific receptors, triggers ERK and PI3K signaling and renders cells resistant to these stresses. Impairment of ATP release and transmission of such signals could limit cellular survival under oxidative stress. This may further contribute to disease pathogenesis or exacerbation.
Collapse
Affiliation(s)
- Shama Ahmad
- Department of Pediatrics, National Jewish Medical and Research Center, 1400 Jackson Street, Denver, CO 80206, USA.
| | | | | |
Collapse
|
167
|
Suadicani SO, Brosnan CF, Scemes E. P2X7 receptors mediate ATP release and amplification of astrocytic intercellular Ca2+ signaling. J Neurosci 2006; 26:1378-85. [PMID: 16452661 PMCID: PMC2586295 DOI: 10.1523/jneurosci.3902-05.2006] [Citation(s) in RCA: 422] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Modulation of synaptic transmission and brain microcirculation are new roles ascribed to astrocytes in CNS function. A mechanism by which astrocytes modify neuronal activity in the healthy brain depends on fluctuations of cytosolic Ca2+ levels, which regulate the release of "gliotransmitters" via an exocytic pathway. Under pathological conditions, however, the participation of other pathways, including connexin hemichannels and the pore-forming P2X7R, have been proposed but remain controversial. Through the use of genetically modified 1321N1 human astrocytoma cells and of spinal cord astrocytes derived from neonatal Cx43- and P2X7R-null mice, we provide strong evidence that P2X7Rs, but not Cx43 hemichannels, are sites of ATP release that promote the amplification of Ca2+ signal transmission within the astrocytic network after exposure to low divalent cation solution. Moreover, our results showing that gap junction channel blockers (heptanol, octanol, carbenoxolone, flufenamic acid, and mefloquine) are antagonists of the P2X7R indicate the inadequacy of using these compounds as evidence for the participation of connexin hemichannels as sites of gliotransmitter release.
Collapse
Affiliation(s)
- Sylvia O Suadicani
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
| | | | | |
Collapse
|
168
|
Moalem G, Tracey DJ. Immune and inflammatory mechanisms in neuropathic pain. ACTA ACUST UNITED AC 2006; 51:240-64. [PMID: 16388853 DOI: 10.1016/j.brainresrev.2005.11.004] [Citation(s) in RCA: 570] [Impact Index Per Article: 31.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2005] [Revised: 11/16/2005] [Accepted: 11/17/2005] [Indexed: 12/22/2022]
Abstract
Tissue damage, inflammation or injury of the nervous system may result in chronic neuropathic pain characterised by increased sensitivity to painful stimuli (hyperalgesia), the perception of innocuous stimuli as painful (allodynia) and spontaneous pain. Neuropathic pain has been described in about 1% of the US population, is often severely debilitating and largely resistant to treatment. Animal models of peripheral neuropathic pain are now available in which the mechanisms underlying hyperalgesia and allodynia due to nerve injury or nerve inflammation can be analysed. Recently, it has become clear that inflammatory and immune mechanisms both in the periphery and the central nervous system play an important role in neuropathic pain. Infiltration of inflammatory cells, as well as activation of resident immune cells in response to nervous system damage, leads to subsequent production and secretion of various inflammatory mediators. These mediators promote neuroimmune activation and can sensitise primary afferent neurones and contribute to pain hypersensitivity. Inflammatory cells such as mast cells, neutrophils, macrophages and T lymphocytes have all been implicated, as have immune-like glial cells such as microglia and astrocytes. In addition, the immune response plays an important role in demyelinating neuropathies such as multiple sclerosis (MS), in which pain is a common symptom, and an animal model of MS-related pain has recently been demonstrated. Here, we will briefly review some of the milestones in research that have led to an increased awareness of the contribution of immune and inflammatory systems to neuropathic pain and then review in more detail the role of immune cells and inflammatory mediators.
Collapse
Affiliation(s)
- Gila Moalem
- School of Medical Sciences, University of New South Wales, Sydney, Australia
| | | |
Collapse
|
169
|
Bragg AD, Amiry-Moghaddam M, Ottersen OP, Adams ME, Froehner SC. Assembly of a perivascular astrocyte protein scaffold at the mammalian blood–brain barrier is dependent on α-syntrophin. Glia 2006; 53:879-90. [PMID: 16609960 DOI: 10.1002/glia.20347] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
alpha-Syntrophin, a member of the dystrophin-associated protein complex, is required for proper localization of the water channel aquaporin-4 at the blood-brain barrier. Mice lacking alpha-syntrophin have reduced levels of aquaporin-4 in perivascular astroglial endfeet. Consequently, they exhibit reduced edema and infarct volume in brain trauma models and reduced K+ clearance from the neuropil, leading to increased seizure susceptibility. We have used the alpha-syntrophin null mice to investigate whether alpha-syntrophin is required for proper localization of other components of the dystrophin complex at the blood-brain barrier. We find that alpha-syntrophin is required for the full recruitment of gamma2-syntrophin and alpha-dystrobrevin-2 to glial endfeet in adult cerebellum. In contrast, the localization of beta1- and beta2-syntrophin and alpha-dystrobrevin-1 at the blood-brain barrier is not dependent on the presence of alpha-syntrophin. The localization patterns of alpha-dystrobrevin-1 and -2 in wild type cerebellum are strikingly different; while alpha-dystrobrevin-1 is present in glial endfeet throughout the cerebellum, alpha-dystrobrevin-2 is restricted to glial endfeet in the granular layer alone. Finally, we show that the enrichment of dystrophin in glial endfeet depends on the presence of alpha-syntrophin. This finding is the first demonstration that dystrophin localization is dependent on syntrophin. Since the localization of gamma2-syntrophin, alpha-dystrobrevin-2, and dystrophin is contingent on alpha-syntrophin, we conclude that alpha-syntrophin is a central organizer of the astrocyte dystrophin complex, an important molecular scaffold for localization of aquaporin-4 at the blood-brain barrier.
Collapse
Affiliation(s)
- April D Bragg
- Department of Physiology and Biophysics, Health Sciences Building, Rm G424, 1959 NE Pacific St, University of Washington, Seattle, 98195, USA.
| | | | | | | | | |
Collapse
|
170
|
Hung AC, Chu YJ, Lin YH, Weng JY, Chen HB, Au YC, Sun SH. Roles of protein kinase C in regulation of P2X7 receptor-mediated calcium signalling of cultured type-2 astrocyte cell line, RBA-2. Cell Signal 2005; 17:1384-96. [PMID: 15985361 DOI: 10.1016/j.cellsig.2005.02.009] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2004] [Revised: 02/16/2005] [Accepted: 02/22/2005] [Indexed: 11/26/2022]
Abstract
The role of protein kinase C (PKC) on regulation of P2X(7) receptor-mediated Ca(2+) signalling was examined on RBA-2 astrocytes. Activation of PKC decreased the receptor-mediated Ca(2+) signalling and the decrease was restored by PKC inhibitors. Down regulation of PKC also caused a decrease in the Ca(2+) signalling. Thus PKC might play a dual role on the P2X(7) receptor signalling. Successive stimulation of the P2X(7) receptor induced a gradual decline of Ca(2+) signalling but PKC inhibitors failed to restore the decline. Nevertheless, PMA stimulated translocation of PKC-alpha, -betaI, -betaII, and -gamma, but only anti-PKC-gamma co-immunoprecipitated the receptors. To examine the role of PKC-gamma, Ca(2+) signalling was measured by Ca(2+) imaging. Our results revealed that the agonist-stimulated Ca(2+) signalling were reduced in the cells that the transfection of either P2X(7) receptor or PKC-gamma morpholino antisense oligo was identified. Thus, we concluded that PKC-gamma interacted with P2X(7) receptor complex and positively regulated the receptor-mediated Ca(2+) signalling.
Collapse
Affiliation(s)
- Amos C Hung
- Institute of Neuroscience, College of Life Science, National Yang-Ming University and Brain Research Center, Shi-Pai, Taipei 112, Taiwan, ROC
| | | | | | | | | | | | | |
Collapse
|
171
|
Locovei S, Wang J, Dahl G. Activation of pannexin 1 channels by ATP through P2Y receptors and by cytoplasmic calcium. FEBS Lett 2005; 580:239-44. [PMID: 16364313 DOI: 10.1016/j.febslet.2005.12.004] [Citation(s) in RCA: 415] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2005] [Accepted: 12/01/2005] [Indexed: 11/24/2022]
Abstract
The ability for long-range communication through intercellular calcium waves is inherent to cells of many tissues. A dual propagation mode for these waves includes passage of IP3 through gap junctions as well as an extracellular pathway involving ATP. The wave can be regenerative and include ATP-induced ATP release via an unknown mechanism. Here, we show that pannexin 1 channels can be activated by extracellular ATP acting through purinergic receptors of the P2Y group as well as by cytoplasmic calcium. Based on its properties, including ATP permeability, pannexin 1 may be involved in both initiation and propagation of calcium waves.
Collapse
Affiliation(s)
- Silviu Locovei
- Department of Physiology and Biophysics, University of Miami, School of Medicine, P.O. Box 016430, 1600 NW 10th Avenue, Miami, FL 33136, USA
| | | | | |
Collapse
|
172
|
Nagai K, Nagasawa K, Fujimoto S. Transport mechanisms for adenosine and uridine in primary-cultured rat cortical neurons and astrocytes. Biochem Biophys Res Commun 2005; 334:1343-50. [PMID: 16043124 DOI: 10.1016/j.bbrc.2005.07.032] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2005] [Accepted: 07/07/2005] [Indexed: 11/22/2022]
Abstract
Endogenous adenosine and uridine are important modulators of neural survival and activity. In the present study, we examined transport mechanisms of adenosine and uridine in primary-cultured rat cortical neurons, and compared the results for neurons with those for astrocytes. Reverse transcription-polymerase chain reaction identified the mRNAs for ENT1, ENT2, and CNT2, but not CNT1 and CNT3, in neurons and astrocytes. [3H]Adenosine and [3H]uridine were time-, temperature-, and concentration-dependently taken up into neurons and astrocytes. In kinetic analyses, the uptake of both substrates by neurons and astrocytes consisted of two and one, respectively, saturable transport components. The uptake clearance for both substrates by neurons was greater than that by astrocytes. The relative contribution of the high-affinity major component of both substrates to total uptake was estimated to be approximately 80% in neurons. The uptake of [3H]adenosine and [3H]uridine by both neurons and astrocytes was almost entirely Na+-independent, and sensitive to micro, but not nano, molar concentrations of nitrobenzylmercaptopurine riboside, which are transport characteristics of ENT2. Therefore, it was indicated that adenosine and uridine are more efficiently taken up into neurons than into astrocytes, and ENT2 may predominantly contribute to the transport of the nucleosides as a high-affinity transport system in neurons, as in the case of astrocytes.
Collapse
Affiliation(s)
- Katsuhito Nagai
- Department of Environmental Biochemistry, Kyoto Pharmaceutical University, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.
| | | | | |
Collapse
|
173
|
Koizumi S, Fujishita K, Inoue K. Regulation of cell-to-cell communication mediated by astrocytic ATP in the CNS. Purinergic Signal 2005; 1:211-7. [PMID: 18404506 PMCID: PMC2096541 DOI: 10.1007/s11302-005-6321-y] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2004] [Revised: 02/16/2005] [Accepted: 02/25/2005] [Indexed: 01/03/2023] Open
Abstract
It has become apparent that glial cells, especially astrocytes, not merely supportive but are integrative, being able to receive inputs, assimilate information and send instructive chemical signals to other neighboring cells including neurons. At first, the excitatory neurotransmitter glutamate was found to be a major extracellular messenger that mediates these communications because it can be released from astrocytes in a Ca(2+)-dependent manner, diffused, and can stimulate extra-synaptic glutamate receptors in adjacent neurons, leading to a dynamic modification of synaptic transmission. However, recently extracellular ATP has come into the limelight as an important extracellular messenger for these communications. Astrocytes express various neurotransmitter receptors including P2 receptors, release ATP in response to various stimuli and respond to extracellular ATP to cause various physiological responses. The intercellular communication "Ca(2+) wave" in astrocytes was found to be mainly mediated by the release of ATP and the activation of P2 receptors, suggesting that ATP is a dominant "gliotransmitter" between astrocytes. Because neurons also express various P2 receptors and synapses are surrounded by astrocytes, astrocytic ATP could affect neuronal activities and even dynamically regulate synaptic transmission in adjacent neurons as if forming a "tripartite synapse". In this review, we summarize the role of astrocytic ATP, as compared with glutamate, in gliotransmission and synaptic transmission in neighboring cells, mainly focusing on the hippocampus. Dynamic communication between astrocytes and neurons mediated by ATP would be a key event in the processing or integration of information in the CNS.
Collapse
Affiliation(s)
- Schuichi Koizumi
- Division of Pharmacology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya, Tokyo, 158-8501, Japan,
| | | | | |
Collapse
|
174
|
Bennett MR, Farnell L, Gibson WG. A quantitative model of purinergic junctional transmission of calcium waves in astrocyte networks. Biophys J 2005; 89:2235-50. [PMID: 16055527 PMCID: PMC1366726 DOI: 10.1529/biophysj.105.062968] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
A principal means of transmitting intracellular calcium (Ca2+) waves at junctions between astrocytes involves the release of the chemical transmitter adenosine triphosphate (ATP). A model of this process is presented in which activation of purinergic P2Y receptors by ATP triggers the release of ATP, in an autocrine manner, as well as concomitantly increasing intracellular Ca2+. The dependence of the temporal characteristics of the Ca2+ wave are shown to critically depend on the dissociation constant (K(R)) for ATP binding to the P2Y receptor type. Incorporating this model astrocyte into networks of these cells successfully accounts for many of the properties of propagating Ca2+ waves, such as the dependence of velocity on the type of P2Y receptor and the time-lag of the Ca2+ wave behind the ATP wave. In addition, the conditions under which Ca2+ waves may jump from one set of astrocytes across an astrocyte-free lane to another set of astrocytes are quantitatively accounted for by the model. The properties of purinergic transmission at astrocyte junctions may determine many of the characteristics of Ca2+ propagation in networks of these cells.
Collapse
Affiliation(s)
- M R Bennett
- The Neurobiology Laboratory, Institute for Biomedical Research, Department of Physiology, University of Sydney, New South Wales, Australia.
| | | | | |
Collapse
|
175
|
Neary JT, Kang Y, Tran M, Feld J. Traumatic injury activates protein kinase B/Akt in cultured astrocytes: role of extracellular ATP and P2 purinergic receptors. J Neurotrauma 2005; 22:491-500. [PMID: 15853465 DOI: 10.1089/neu.2005.22.491] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Protein kinase B/Akt is a key signaling molecule that regulates cell survival, growth, and metabolism, and inhibits apoptosis. Traumatic brain injury (TBI) activates Akt, and Akt has been implicated in neuronal survival after TBI, but little is known about injury-induced Akt activation in astrocytes, cells that exhibit hypertrophic and hyperplastic responses to CNS injury. Here we have investigated the effect of mechanical strain on Akt activation in primary cultures of rat cortical astrocytes growing on deformable Silastic membranes. When astrocytes were subjected to mechanical strain (50 msec; 5-7.5 mm displacement), we observed an increase in phosphorylation of serine 473, a key indicator of Akt activation. Akt phosphorylation was increased at 3 min postinjury, was maximal from 5 to 10 min, and declined gradually thereafter. Akt activation was also dependent on the severity of the injury. Stretch-induced Akt phosphorylation was attenuated by blocking calcium influx and phosphoinositide 3-kinase (PI3K), an upstream activator of Akt. In addition, we found that ATP is rapidly released after mechanical strain and that the P2 purinergic receptor antagonist iso-pyridoxal-5'-phosphate-6-azophenyl-2',5'disulfonate (PPADS) attenuated trauma-induced Akt activation. We conclude that mechanical strain causes activation of Akt in astrocytes via stimulation of P2 receptors. This suggests that P2 receptor/Akt signaling promotes astrocyte survival and growth, and this process may play a role in the generation of reactive gliosis after TBI.
Collapse
Affiliation(s)
- Joseph T Neary
- Research Service, VA Medical Center, Departments of Pathology, Biochemistry and Molecular Biology and Neuroscience Program, University of Miami School of Medicine, Miami, Florida
| | | | | | | |
Collapse
|
176
|
Gordon GRJ, Baimoukhametova DV, Hewitt SA, Rajapaksha WRAKJS, Fisher TE, Bains JS. Norepinephrine triggers release of glial ATP to increase postsynaptic efficacy. Nat Neurosci 2005; 8:1078-86. [PMID: 15995701 DOI: 10.1038/nn1498] [Citation(s) in RCA: 241] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2005] [Accepted: 06/09/2005] [Indexed: 11/08/2022]
Abstract
Glial cells actively participate in synaptic transmission. They clear molecules from the synaptic cleft, receive signals from neurons and, in turn, release molecules that can modulate signaling between neuronal elements. Whether glial-derived transmitters can contribute to enduring changes in postsynaptic efficacy, however, remains to be established. In rat hypothalamic paraventricular nucleus, we demonstrate an increase in the amplitude of miniature excitatory postsynaptic currents in response to norepinephrine that requires the release of ATP from glial cells. The increase in quantal efficacy, which likely results from an insertion of AMPA receptors, is secondary to the activation of P2X(7) receptors, an increase in postsynaptic calcium and the activation of phosphatidylinositol 3-kinase. The gliotransmitter ATP, therefore, contributes directly to the regulation of postsynaptic efficacy at glutamatergic synapses in the CNS.
Collapse
Affiliation(s)
- Grant R J Gordon
- Hotchkiss Brain Institute and the Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1
| | | | | | | | | | | |
Collapse
|
177
|
Pellegatti P, Falzoni S, Pinton P, Rizzuto R, Di Virgilio F. A novel recombinant plasma membrane-targeted luciferase reveals a new pathway for ATP secretion. Mol Biol Cell 2005; 16:3659-65. [PMID: 15944221 PMCID: PMC1182305 DOI: 10.1091/mbc.e05-03-0222] [Citation(s) in RCA: 225] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
ATP is emerging as an ubiquitous extracellular messenger. However, measurement of ATP concentrations in the pericellular space is problematic. To this aim, we have engineered a firefly luciferase-folate receptor chimeric protein that retains the N-terminal leader sequence and the C-terminal GPI anchor of the folate receptor. This chimeric protein, named plasma membrane luciferase (pmeLUC), is targeted and localized to the outer aspect of the plasma membrane. PmeLUC is sensitive to ATP in the low micromolar to millimolar level and is insensitive to all other nucleotides. To identify pathways for nonlytic ATP release, we transfected pmeLUC into cells expressing the recombinant or native P2X7 receptor (P2X7R). Both cell types release large amounts of ATP (100-200 microM) in response to P2X7R activation. This novel approach unveils a hitherto unsuspected nonlytic pathway for the release of large amounts of ATP that might contribute to spreading activation and recruitment of immune cells at inflammatory sites.
Collapse
Affiliation(s)
- Patrizia Pellegatti
- Department of Experimental and Diagnostic Medicine, Section of General Pathology and Interdisciplinary Center for the Study of Inflammation, University of Ferrara, Ferrara 44100, Italy
| | | | | | | | | |
Collapse
|
178
|
Cunha RA. Neuroprotection by adenosine in the brain: From A(1) receptor activation to A (2A) receptor blockade. Purinergic Signal 2005; 1:111-34. [PMID: 18404497 PMCID: PMC2096528 DOI: 10.1007/s11302-005-0649-1] [Citation(s) in RCA: 404] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Accepted: 11/10/2004] [Indexed: 12/11/2022] Open
Abstract
Adenosine is a neuromodulator that operates via the most abundant inhibitory adenosine A(1) receptors (A(1)Rs) and the less abundant, but widespread, facilitatory A(2A)Rs. It is commonly assumed that A(1)Rs play a key role in neuroprotection since they decrease glutamate release and hyperpolarize neurons. In fact, A(1)R activation at the onset of neuronal injury attenuates brain damage, whereas its blockade exacerbates damage in adult animals. However, there is a down-regulation of central A(1)Rs in chronic noxious situations. In contrast, A(2A)Rs are up-regulated in noxious brain conditions and their blockade confers robust brain neuroprotection in adult animals. The brain neuroprotective effect of A(2A)R antagonists is maintained in chronic noxious brain conditions without observable peripheral effects, thus justifying the interest of A(2A)R antagonists as novel protective agents in neurodegenerative diseases such as Parkinson's and Alzheimer's disease, ischemic brain damage and epilepsy. The greater interest of A(2A)R blockade compared to A(1)R activation does not mean that A(1)R activation is irrelevant for a neuroprotective strategy. In fact, it is proposed that coupling A(2A)R antagonists with strategies aimed at bursting the levels of extracellular adenosine (by inhibiting adenosine kinase) to activate A(1)Rs might constitute the more robust brain neuroprotective strategy based on the adenosine neuromodulatory system. This strategy should be useful in adult animals and especially in the elderly (where brain pathologies are prevalent) but is not valid for fetus or newborns where the impact of adenosine receptors on brain damage is different.
Collapse
Affiliation(s)
- Rodrigo A Cunha
- Center for Neuroscience of Coimbra, Institute of Biochemistry, Faculty of Medicine, University of Coimbra, Coimbra, Portugal,
| |
Collapse
|
179
|
Pearson RA, Dale N, Llaudet E, Mobbs P. ATP Released via Gap Junction Hemichannels from the Pigment Epithelium Regulates Neural Retinal Progenitor Proliferation. Neuron 2005; 46:731-44. [PMID: 15924860 DOI: 10.1016/j.neuron.2005.04.024] [Citation(s) in RCA: 238] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2004] [Revised: 02/28/2005] [Accepted: 04/20/2005] [Indexed: 10/25/2022]
Abstract
The retinal pigment epithelium (RPE) plays an essential role in the normal development of the underlying neural retina, but the mechanisms by which this regulation occurs are largely unknown. Ca2+ transients, induced by the neurotransmitter ATP acting on purinergic receptors, both increase proliferation and stimulate DNA synthesis in neural retinal progenitor cells. Here, we show that the RPE regulates proliferation in the underlying neural retina by the release of a soluble factor and identify that factor as ATP. Further, we show that this ATP is released by efflux through gap junction connexin 43 hemichannels, the opening of which is evoked by spontaneous elevations of Ca2+ in trigger cells in the RPE. This release mechanism is localized within the RPE cells to the membranes facing the neural retina, a location ideally positioned to influence neural retinal development. ATP released from RPE hemichannels speeds both cell division and proliferation in the neural retina.
Collapse
Affiliation(s)
- Rachael A Pearson
- Department of Physiology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
| | | | | | | |
Collapse
|
180
|
Haas B, Schipke CG, Peters O, Söhl G, Willecke K, Kettenmann H. Activity-dependent ATP-waves in the mouse neocortex are independent from astrocytic calcium waves. ACTA ACUST UNITED AC 2005; 16:237-46. [PMID: 15930372 DOI: 10.1093/cercor/bhi101] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
In the corpus callosum, astrocytic calcium waves propagate via a mechanism involving ATP-release but not gap junctional coupling. In the present study, we report for the neocortex that calcium wave propagation depends on functional astrocytic gap junctions but is still accompanied by ATP-release. In acute slices obtained from the neocortex of mice deficient for astrocytic expression of connexin43, the calcium wave did not propagate. In contrast, in the corpus callosum and hippocampus of these mice, the wave propagated as in control animals. In addition to calcium wave propagation in astrocytes, ATP-release was recorded as a calcium signal from 'sniffer cells', a cell line expressing high-affinity purinergic receptors placed on the surface of the slice. The astrocyte calcium wave in the neocortex was accompanied by calcium signals in the 'sniffer cell' population. In the connexin43-deficient mice we recorded calcium signals from sniffer cells also in the absence of an astrocytic calcium wave. Our findings indicate that astrocytes propagate calcium signals by two separate mechanisms depending on the brain region and that ATP release can propagate within the neocortex independent from calcium waves.
Collapse
Affiliation(s)
- Brigitte Haas
- Cellular Neuroscience, Max-Delbrück-Center for Molecular Medicine, and Institute of Genetics, Division of Molecular Genetics, University of Bonn, 53117 Bonn, Germany Eschenallee 3, 14050 Berlin, Germany
| | | | | | | | | | | |
Collapse
|
181
|
Parkinson FE, Xiong W, Zamzow CR. Astrocytes and neurons: different roles in regulating adenosine levels. Neurol Res 2005; 27:153-60. [PMID: 15829178 DOI: 10.1179/016164105x21878] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
OBJECTIVES Adenosine is an endogenous nucleoside that signals through G-protein coupled receptors. Extracellular adenosine is required for receptor activation and two pathways have been identified for formation and cellular release of adenosine. The CLASSICAL pathway relies on intracellular formation of adenosine from adenine nucleotides and cellular efflux of adenosine via equilibrative nucleoside transporters (ENTs). The ALTERNATE pathway involves cellular release of adenine nucleotides, hydrolysis via ecto-5'-nucleotidases and extracellular formation of adenosine. METHODS A rat model of cerebral ischemia and primary cultures of rat forebrain astrocytes and neurons were used. RESULTS Using a rat model of cerebral ischemia, the ENT1 inhibitor nitrobenzylmercaptopurine ribonucleoside (NBMPR) significantly increased post-ischemic forebrain adenosine levels and significantly decreased hippocampal neuron injury relative to saline-treatment. NBMPR-induced increases in adenosine receptor activation were not detected, suggesting that altering the intracellular:extracellular distribution of adenosine can affect ischemic outcome. Using primary cultures of rat forebrain astrocytes and neurons, adenosine release was evoked by ischemic-like conditions. Dipyridamole, an inhibitor of ENTs, was more effective at inhibiting adenosine release from neurons than from astrocytes. In contrast, alpha , beta-methylene ADP, an inhibitor of ecto-5'-nucleotidase, was effective at inhibiting adenosine release from astrocytes, but not from neurons. Thus, during ischemic-like conditions, neurons released adenosine via the CLASSICAL pathway, while astrocytes released adenosine via the ALTERNATE pathway. DISCUSSION These cell type differences in pathways for adenosine formation during ischemia may allow transport inhibitors to block simultaneously adenosine release from neurons and adenosine uptake into astrocytes. In principle, this could improve neuronal ATP levels without decreasing adenosine receptor activation.
Collapse
Affiliation(s)
- Fiona E Parkinson
- Department of Pharmacology and Therapeutics, University of Manitoba, A203-753 McDermot Avenue, Winnipeg MB Canada R3E 0T6.
| | | | | |
Collapse
|
182
|
Davalos D, Grutzendler J, Yang G, Kim JV, Zuo Y, Jung S, Littman DR, Dustin ML, Gan WB. ATP mediates rapid microglial response to local brain injury in vivo. Nat Neurosci 2005; 8:752-8. [PMID: 15895084 DOI: 10.1038/nn1472] [Citation(s) in RCA: 2717] [Impact Index Per Article: 143.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2005] [Accepted: 04/27/2005] [Indexed: 01/11/2023]
Abstract
Parenchymal microglia are the principal immune cells of the brain. Time-lapse two-photon imaging of GFP-labeled microglia demonstrates that the fine termini of microglial processes are highly dynamic in the intact mouse cortex. Upon traumatic brain injury, microglial processes rapidly and autonomously converge on the site of injury without cell body movement, establishing a potential barrier between the healthy and injured tissue. This rapid chemotactic response can be mimicked by local injection of ATP and can be inhibited by the ATP-hydrolyzing enzyme apyrase or by blockers of G protein-coupled purinergic receptors and connexin channels, which are highly expressed in astrocytes. The baseline motility of microglial processes is also reduced significantly in the presence of apyrase and connexin channel inhibitors. Thus, extracellular ATP regulates microglial branch dynamics in the intact brain, and its release from the damaged tissue and surrounding astrocytes mediates a rapid microglial response towards injury.
Collapse
Affiliation(s)
- Dimitrios Davalos
- Molecular Neurobiology Program, Department of Physiology and Neuroscience, New York University School of Medicine, 540 First Avenue, New York, New York 10016, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
183
|
Abstract
The mechanisms by which uridine triphosphate (UTP) stimulates ATP release from Schwann cells cultured from the sciatic nerve were investigated using online bioluminescence techniques. UTP, a P2Y(2) and P2Y(4) receptor agonist, stimulated ATP release from Schwann cells in a dose-dependent manner with an ED(50) of 0.24 microm. UTP-stimulated ATP release occurs through P2Y(2) receptors as it was blocked by suramin which inhibits P2Y(2) but not P2Y(4) receptors. Furthermore, positive immunostaining of P2Y(2) receptors on Schwann cells was revealed and GTP, an equipotent agonist with UTP at rat P2Y(4) receptors, did not significantly stimulate ATP release. UTP-stimulated ATP release involved second messenger pathways as it was attenuated by the phospholipase C inhibitor U73122, the protein kinase C inhibitor chelerytherine chloride, the IP(3) formation inhibitor lithium chloride, the cell membrane-permeable Ca(2+) chelator BAPTA-AM and the endoplasmic reticulum Ca(2+)-dependent ATPase inhibitor thapsigargin. Evidence that ATP may be stored in vesicles that must be transported to the cell membrane for exocytosis was found as release was significantly reduced by the Golgi-complex inhibitor brefeldin A, microtubule disruption with nocodazole, F-actin disruption with cytochalasin D and the specific exocytosis inhibitor botulinum toxin A. ATP release from Schwann cells also involves anion transport as it was significantly reduced by cystic fibrosis transmembrane conductance regulator inhibitor glibencamide and anion transporter inhibitor furosemide. We suggest that UTP-stimulated ATP release is mediated by activation of P2Y(2) receptors that initiate an IP(3)-Ca(2+) cascade and protein kinase C which promote exocytosis of ATP from vesicles as well as anion transport of ATP across the cell membrane.
Collapse
Affiliation(s)
- Guo Jun Liu
- The Neurobiology Laboratory, Department of Physiology & Institute for Biomedical Research, University of Sydney, NSW, 2006 Australia
| | | | | |
Collapse
|
184
|
Abstract
Emerging studies indicate that connexins have activities completely unrelated to gap junctions and, conversely, that non-connexin proteins can form gap junction channels.
Collapse
Affiliation(s)
- Charles Stout
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | |
Collapse
|
185
|
Suadicani SO, Flores CE, Urban-Maldonado M, Beelitz M, Scemes E. Gap junction channels coordinate the propagation of intercellular Ca2+ signals generated by P2Y receptor activation. Glia 2005; 48:217-29. [PMID: 15390120 PMCID: PMC2586889 DOI: 10.1002/glia.20071] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Astrocytes express gap junction proteins and multiple types of P2Y receptors (P2YRs) that contribute to the propagation of intercellular Ca(2+) waves (ICW). To gain access to the role played by gap junctional communication in ICW propagation generated by P2YR activation, we selectively expressed P2Y(1,2,4)R subtypes and Cx43 in the human 1321N1 astrocytoma cell line, which lacks endogenous P2 receptors. Fluorescence recovery after photobleaching revealed that 1321N1 cells are poorly dye-coupled and do not propagate ICW. Forced expression of Cx43 in 1321N1 cells (which did not show functional hemichannels) increased dye coupling and allowed short-range ICW transmission that was mainly mediated by intercellular diffusion of Ca(2+) generated in the stimulated cells. Astrocytoma clones expressing each of the P2YR subtypes were also able to propagate ICWs that were likely dependent on IP(3) generation. These waves exhibited properties particular to each P2YR subtype. Co-expression of eGFP-hCx43 and P2Y(1)R modified the properties of P2Y(1)R-generated ICW to those characteristics of P2Y(2)R. Increased coupling in P2Y(4)R clones induced by expression of eGFP-hCx43 abolished the ICWs observed in uncoupled P2Y(4)R clones. No changes in the behavior of ICWs generated in P2Y(2)R clones were observed after forced expression of Cx43. These data indicate that in 1321N1 cells gap junctional communication provides intercellular integration of Ca(2+) signals generated by P2YR activation, thus coordinating the propagation of intercellular calcium waves.
Collapse
Affiliation(s)
- S O Suadicani
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
| | | | | | | | | |
Collapse
|
186
|
Abstract
Neuronal activity can stimulate an increase in astrocyte intracellular calcium concentration, which is propagated through neighboring astrocytes as a "calcium wave"; these calcium waves are accompanied by the release of glutamate. Sodium-dependent glutamate uptake leads to a secondary astrocytic sodium wave, accompanied by a wave of increased glucose uptake and metabolism. This metabolic wave may enable astrocytes to provide lactate as an energy source to neighboring active neurons and perhaps to distant neurons as well. Thus, one function of long-range intercellular calcium signaling in astrocytes may be to spatially coordinate their function in supporting neuronal metabolism.
Collapse
Affiliation(s)
- Andrew Charles
- Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, 710 Westwood Plaza, Los Angeles, CA 90095, USA.
| |
Collapse
|
187
|
Bernardinelli Y, Magistretti PJ, Chatton JY. Astrocytes generate Na+-mediated metabolic waves. Proc Natl Acad Sci U S A 2004; 101:14937-42. [PMID: 15466714 PMCID: PMC522032 DOI: 10.1073/pnas.0405315101] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2004] [Indexed: 11/18/2022] Open
Abstract
Glutamate-evoked Na+ increase in astrocytes has been identified as a signal coupling synaptic activity to glucose consumption. Astrocytes participate in multicellular signaling by transmitting intercellular Ca2+ waves. Here we show that intercellular Na+ waves are also evoked by activation of single cultured cortical mouse astrocytes in parallel with Ca2+ waves; however, there are spatial and temporal differences. Indeed, maneuvers that inhibit Ca2+ waves also inhibit Na+ waves; however, inhibition of the Na+/glutamate cotransporters or enzymatic degradation of extracellular glutamate selectively inhibit the Na+ wave. Thus, glutamate released by a Ca2+ wave-dependent mechanism is taken up by the Na+/glutamate cotransporters, resulting in a regenerative propagation of cytosolic Na+ increases. The Na+ wave gives rise to a spatially correlated increase in glucose uptake, which is prevented by glutamate transporter inhibition. Therefore, astrocytes appear to function as a network for concerted neurometabolic coupling through the generation of intercellular Na+ and metabolic waves.
Collapse
Affiliation(s)
- Yann Bernardinelli
- Department of Physiology, University of Lausanne, CH-1005 Lausanne, Switzerland
| | | | | |
Collapse
|
188
|
Même W, Ezan P, Venance L, Glowinski J, Giaume C. ATP-induced inhibition of gap junctional communication is enhanced by interleukin-1 beta treatment in cultured astrocytes. Neuroscience 2004; 126:95-104. [PMID: 15145076 DOI: 10.1016/j.neuroscience.2004.03.031] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/23/2004] [Indexed: 11/23/2022]
Abstract
Nucleotides are signaling molecules involved in variety of interactions between neurons, between glial cells as well as between neurons and glial cells. In addition, ATP and other nucleotides are massively released following brain insults, including inflammation, and may thereby be involved in mechanisms of cerebral injury. Recent concepts have shown that in astrocytes intercellular communication through gap junctions may play an important role in neuroprotection. Therefore, we have studied the effects of nucleotides on gap junction communication in astrocytes. Based on measurement of intercellular dye coupling and recording of junctional currents, the present study shows that ATP (10-100 microM) induces a rapid and a concentration-dependent inhibition of gap junction communication in cultured cortical astrocytes from newborn mice. Effects of agonists and antagonists of purinergic receptors indicate that the inhibition of gap junctional communication by ATP mainly involves the stimulation of metabotropic purinergic 1 (P2Y(1)) receptors. Pretreatment with the pro-inflammatory cytokine interleukin-1beta (10 ng/ml, 24 h), which has no effect by itself on gap junctional communication, increases the inhibitory effect of ATP and astrocytes become sensitive to uridine 5'-triphosphate (UTP). As indicated by the enhanced expression of P2Y(2) receptor mRNA, P2Y(2) receptors are responsible for the increased responses evoked by ATP and UTP in interleukin-1beta-treated cells. In addition, the effect of endothelin-1, a well-known inhibitor of gap junctional communication in astrocytes was also exacerbated following interleukin-1beta treatment. We conclude that ATP decreases intercellular communication through gap junctions in astrocytes and that the increased sensitivity of gap junction channels to nucleotides and endothelin-1 is a characteristic feature of astrocytes exposed to pro-inflammatory treatments.
Collapse
Affiliation(s)
- W Même
- INSERM U114, Collège de France, 11 Place Marcelin Berthelot, 75231 Paris, Cedex 05, France
| | | | | | | | | |
Collapse
|
189
|
Fellin T, Carmignoto G. Neurone-to-astrocyte signalling in the brain represents a distinct multifunctional unit. J Physiol 2004; 559:3-15. [PMID: 15218071 PMCID: PMC1665073 DOI: 10.1113/jphysiol.2004.063214] [Citation(s) in RCA: 206] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Astrocytes can respond to neurotransmitters released at the synapse by generating elevations in intracellular Ca(2+) concentration ([Ca(2+)](i)) and releasing glutamate that signals back to neurones. This discovery opens new perspectives for the possible participation of these glial cells in actual information processing by the brain and raises the hypothesis that astrocyte activation by neuronal signals plays a key role in distinct, functional events. Depending on the level of neuronal activity, the [Ca(2+)](i) response that is activated by neurotransmitters can either remain restricted to an astrocytic process or it can propagate as an intracellular [Ca(2+)](i) wave to other astrocytic processes in contact with different neurones, astrocytes, microglia or endothelial cells of cerebral arterioles. Glutamate release triggered by the [Ca(2+)](i) rise at the astrocytic process represents a feedback, short-distance signal that affects synaptic transmission locally. The release of glutamate as well as of other compounds far away from the site of initial activation represents a feedforward, long-distance signal that can be involved in the regulation of distinct processes. For instance, through the release of vasoactive molecules from the astrocytic processes in contact with cerebral arterioles, the neurone-astrocyte-endothelial cell signalling pathway plays a pivotal role in the neuronal control of vascular tone. In this article we will review recent results that should persuade us to reshape our current thinking on the roles of astroglial cells in the brain. We propose that neurones and astrocytes represent an integral unit that has a distinctive role in different fundamental events in brain function. Furthermore, while recent findings provide important evidences for the vesicular hypothesis of glutamate release, we discuss also the proposals for a possible physiological role of hemichannels and purinergic P2X(7) receptors in glutamate release from astrocytes. A full clarification of the functional significance of the bidirectional communication that astrocytes establish with neurones as well as with other brain cells represents one of the most intriguing challenges in neurobiological research at the moment and should fuel stimulating debates in years to come.
Collapse
Affiliation(s)
- Tommaso Fellin
- Istituto CNR di Neuroscienze and Dipartimento di Scienze Biomediche Sperimentali, Università di Padova, Viale G. Colombo 3, 35121 Padova, Italy
| | | |
Collapse
|