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Reusswig F, Yilmaz M, Brechtenkamp M, Krueger I, Metz LM, Klöcker N, Lammert E, Elvers M. The NMDA receptor regulates integrin activation, ATP release and arterial thrombosis through store-operated Ca 2+ entry in platelets. Front Cardiovasc Med 2023; 10:1171831. [PMID: 37252113 PMCID: PMC10217778 DOI: 10.3389/fcvm.2023.1171831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Accepted: 04/27/2023] [Indexed: 05/31/2023] Open
Abstract
Introduction Platelet activation and thrombus formation is crucial for hemostasis, but also trigger arterial thrombosis. Calcium mobilization plays an important role in platelet activation, because many cellular processes depend on the level of intracellular Ca2+ ([Ca2+](i)), such as integrin activation, degranulation, cytoskeletal reorganization. Different modulators of Ca2+ signaling have been implied, such as STIM1, Orai1, CyPA, SGK1, etc. Also, the N-methyl-D-aspartate receptor (NMDAR) was identified to contribute to Ca2+ signaling in platelets. However, the role of the NMDAR in thrombus formation is not well defined. Methods In vitro and in vivo analysis of platelet-specific NMDAR knock-out mice. Results In this study, we analyzed Grin1fl/fl-Pf4-Cre+ mice with a platelet-specific knock-out of the essential GluN1 subunit of the NMDAR. We found reduced store-operated Ca2+ entry (SOCE), but unaltered store release in GluN1-deficient platelets. Defective SOCE resulted in reduced Src and PKC substrate phosphorylation following stimulation of glycoprotein (GP)VI or the thrombin receptor PAR4 followed by decreased integrin activation but unaltered degranulation. Consequently, thrombus formation on collagen under flow conditions was reduced ex vivo, and Grin1fl/fl-Pf4-Cre+ mice were protected against arterial thrombosis. Results from human platelets treated with the NMDAR antagonist MK-801 revealed a crucial role of the NMDAR in integrin activation and Ca2+ homeostasis in human platelets as well. Conclusion NMDAR signaling is important for SOCE in platelets and contributes to platelet activation and arterial thrombosis. Thus, the NMDAR represents a novel target for anti-platelet therapy in cardiovascular disease (CVD).
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Affiliation(s)
- Friedrich Reusswig
- Department of Vascular- and Endovascular Surgery, University Hospital Düsseldorf, Heinrich-Heine University, Düsseldorf, Germany
| | - Münteha Yilmaz
- Department of Vascular- and Endovascular Surgery, University Hospital Düsseldorf, Heinrich-Heine University, Düsseldorf, Germany
| | - Marius Brechtenkamp
- Department of Vascular- and Endovascular Surgery, University Hospital Düsseldorf, Heinrich-Heine University, Düsseldorf, Germany
| | - Irena Krueger
- Department of Vascular- and Endovascular Surgery, University Hospital Düsseldorf, Heinrich-Heine University, Düsseldorf, Germany
| | - Lisa Maria Metz
- Department of Vascular- and Endovascular Surgery, University Hospital Düsseldorf, Heinrich-Heine University, Düsseldorf, Germany
| | - Nikolaj Klöcker
- Institute of Neural and Sensory Physiology, Medical Faculty and University Hospital Düsseldorf, Heinrich-Heine University, Düsseldorf, Germany
| | - Eckhard Lammert
- Institute for Vascular and Islet Cell Biology, German Diabetes Center (DDZ), Leibniz Center for Diabetes Research at Heinrich-Heine University, Düsseldorf, Germany
- German Center for Diabetes Research (DZD e.V.), Helmholtz Zentrum München, Neuherberg, Germany
- Institute of Metabolic Physiology, Heinrich Heine University, Düsseldorf, Germany
| | - Margitta Elvers
- Department of Vascular- and Endovascular Surgery, University Hospital Düsseldorf, Heinrich-Heine University, Düsseldorf, Germany
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Glutamate-Gated NMDA Receptors: Insights into the Function and Signaling in the Kidney. Biomolecules 2020; 10:biom10071051. [PMID: 32679780 PMCID: PMC7407907 DOI: 10.3390/biom10071051] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 07/10/2020] [Accepted: 07/13/2020] [Indexed: 12/21/2022] Open
Abstract
N-Methyl-d-aspartate receptor (NMDAR) is a glutamate-gated ionotropic receptor that intervenes in most of the excitatory synaptic transmission within the central nervous system (CNS). Aside from being broadly distributed in the CNS and having indispensable functions in the brain, NMDAR has predominant roles in many physiological and pathological processes in a wide range of non-neuronal cells and tissues. The present review outlines current knowledge and understanding of the physiological and pathophysiological functions of NMDAR in the kidney, an essential excretory and endocrine organ responsible for the whole-body homeostasis. The review also explores the recent findings regarding signaling pathways involved in NMDAR-mediated responses in the kidney. As established from diverse lines of research reviewed here, basal levels of receptor activation within the kidney are essential for the maintenance of healthy tubular and glomerular function, while a disproportionate activation can lead to a disruption of NMDAR's downstream signaling pathways and a myriad of pathophysiological consequences.
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Abstract
INTRODUCTION NMDA receptor (NMDAR) is an ionotropic glutamate receptor with a high permeability to calcium and a unique feature of controlling numerous calcium-dependent processes. Apart from being widely distributed in the CNS, the presence of NMDAR and its potential significance in a variety of non-neuronal cells and tissues has become an interesting research topic. AREAS COVERED The current review summarizes prevailing knowledge on the role of NMDARs in the kidney, bone and parathyroid gland, three main organs responsible for calcium homeostasis, as well as in the heart, an organ whose function is highly dependable on balanced intracellular calcium concentrations. The review also examines studies that have advanced our understanding of the therapeutic potential of NMDAR agonists and antagonists in renal, cardiovascular and bone pathologies. EXPERT OPINION NMDARs have a preeminent role in many physiological and pathological processes outside the CNS. In certain organs and/or disease conditions, activating the NMDAR leads to beneficial effects for the target organ, whereas in other diseases cell signaling downstream of NMDAR activation can exacerbate their pathology. Therefore, targeting NMDARs therapeutically is rather intricate work, and surely requires more extensive investigation in order to properly tune up the diverse NMDAR's actions translating them into beneficial cellular responses.
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Affiliation(s)
- Milica Bozic
- Institute for Biomedical Research (IRB Lleida), Nephrology Research Department , Edificio Biomedicina 1. Lab B1-10, Lleida , Spain +34 973 003 650 ; +34 973 702 213 ;
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Bozic M, Valdivielso JM. Calcium signaling in renal tubular cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:933-44. [PMID: 22453977 DOI: 10.1007/978-94-007-2888-2_42] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The kidney handles calcium by filtration and reabsorption. About 60% of the plasma calcium is filterable, and 99% is reabsorbed in the tubule. In the proximal tubule, the reabsorption is passive and paracellular, but in the distal tubule is active and transcellular. Thus, renal tubular cells are exposed to very high concentrations of calcium in both, the extracellular and the intracellular compartments. Extracellular calcium signaling is transmitted by the calcium sensing receptor, located both in the luminal and basolateral sides of tubular cells. This receptor is able to control levels of extracellular calcium and acts in consequence to maintain calcium homeostasis. Furthermore, renal tubular cells possess several calcium channels that regulate some of the cell functions. Among those, voltage gated calcium channels, transient receptor potential channels and N-methyl-D-aspartate receptor channels have been reported to control several functions. Those functions include survival, apoptosis, differentiation, epithelial-mesenchymal transition, and active vitamin D and renin synthesis.
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Affiliation(s)
- Milica Bozic
- Nephrology Research Laboratory, IRB Lleida, University Hospital Arnau de Vilanova, Rovira Roure 80, Planta 1, 25198 Lleida, Spain.
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Bozic M, de Rooij J, Parisi E, Ortega MR, Fernandez E, Valdivielso JM. Glutamatergic signaling maintains the epithelial phenotype of proximal tubular cells. J Am Soc Nephrol 2011; 22:1099-111. [PMID: 21597037 DOI: 10.1681/asn.2010070701] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Epithelial-mesenchymal transition (EMT) contributes to the progression of renal tubulointerstitial fibrosis. The N-methyl-d-aspartate receptor (NMDAR), which is present in proximal tubular epithelium, is a glutamate receptor that acts as a calcium channel. Activation of NMDAR induces actin rearrangement in cells of the central nervous system, but whether it helps maintain the epithelial phenotype of the proximal tubule is unknown. Here, knockdown of NMDAR1 in a proximal tubule cell line (HK-2) induced changes in cell morphology, reduced E-cadherin expression, and increased α-SMA expression. Induction of EMT with TGF-β1 led to downregulation of both E-cadherin and membrane-associated β-catenin, reorganization of F-actin, expression of mesenchymal markers de novo, upregulation of Snail1, and increased cell migration; co-treatment with NMDA attenuated all of these changes. Furthermore, NMDA reduced TGF-β1-induced phosphorylation of Erk1/2 and Akt and the activation of Ras, suggesting that NMDA antagonizes TGF-β1-induced EMT by inhibiting the Ras-MEK pathway. In the unilateral ureteral obstruction model, treatment with NMDA blunted obstruction-induced upregulation of α-SMA, FSP1, and collagen I and downregulation of E-cadherin. Taken together, these results suggest that NMDAR plays a critical role in preserving the normal epithelial phenotype and modulating tubular EMT.
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Affiliation(s)
- Milica Bozic
- Nephrology Research Laboratory, IRB LLEIDA, University Hospital Arnau de Vilanova, Lleida, Spain
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Tiago T, Marques-da-Silva D, Samhan-Arias AK, Aureliano M, Gutierrez-Merino C. Early disruption of the actin cytoskeleton in cultured cerebellar granule neurons exposed to 3-morpholinosydnonimine-oxidative stress is linked to alterations of the cytosolic calcium concentration. Cell Calcium 2011; 49:174-83. [PMID: 21356558 DOI: 10.1016/j.ceca.2011.01.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2010] [Revised: 01/29/2011] [Accepted: 01/31/2011] [Indexed: 02/07/2023]
Abstract
Cytoskeleton damage is a frequent feature in neuronal cell death and one of the early events in oxidant-induced cell injury. This work addresses whether actin cytoskeleton reorganization is an early event of SIN-1-induced extracellular nitrosative/oxidative stress in cultured cerebellar granule neurons (CGN). The actin polymerization state, i.e. the relative levels of G-/F-actin, was quantitatively assessed by the ratio of the fluorescence intensities of microscopy images obtained from CGN double-labelled with Alexa594-DNase-I (for actin monomers) and Bodipy-FL-phallacidin (for actin filaments). Exposure of CGN to a flux of peroxynitrite as low as 0.5-1μM/min during 30min (achieved with 0.1mM SIN-1) was found to promote alterations of the actin cytoskeleton dynamics as it increases the G-actin/F-actin ratio. Because L-type voltage-operated Ca(2+) channels (L-VOCC) are primary targets in CGN exposed to SIN-1, the possible role of Ca(2+) dynamics on the perturbation of the actin cytoskeleton was also assessed from the cytosolic Ca(2+) concentration response to the L-VOCC's agonist FPL-64176 and to the L-VOCC's blocker nifedipine. The results showed that SIN-1 induced changes in the actin polymerization state correlated with its ability to decrease Ca(2+) influx through L-VOCC. Combined analysis of cytosolic Ca(2+) concentration and G-actin/F-actin ratio alterations by SIN-1, cytochalasin D, latrunculin B and jasplakinolide support that disruption of the actin cytoskeleton is linked to cytosolic calcium concentration changes.
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Affiliation(s)
- Teresa Tiago
- Dept. Biochemistry and Molecular Biology, Faculty of Sciences, University of Extremadura, 06006-Badajoz, Spain
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Chen Y, Li M. Interactions between CAP70 and actinfilin are important for integrity of actin cytoskeleton structures in neurons. Neuropharmacology 2005; 49:1026-41. [PMID: 16054660 DOI: 10.1016/j.neuropharm.2005.05.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2005] [Revised: 05/11/2005] [Accepted: 05/26/2005] [Indexed: 10/25/2022]
Abstract
The integrity of dynamic actin structures is coupled to a variety of neurological processes. Actin-binding proteins play a critical role in regulating actin structure dynamics. A link between actin-binding proteins and receptor interacting scaffolding proteins may provide a conduit for transmitting signaling events to the cytoskeleton. Actinfilin is a brain-enriched actin-binding protein, though its functions are currently unknown. We report here that actinfilin interacts with the multi-PDZ domain protein CAP70. Recombinant expression of an actin-binding domain of actinfilin progressively causes marked changes of cellular morphology. The effect on cell morphology may be reduced by co-expression with CAP70. Mutation of actinfilin lacking the ability to interact with CAP70 abolished the effect by CAP70. The evidence suggests a role of actinfilin and possible regulation by scaffolding proteins.
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Affiliation(s)
- Ying Chen
- Department of Neuroscience and High Throughput Biology Center, Johns Hopkins University School of Medicine, BRB311, Baltimore, MD 21205, USA
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Arundine M, Chopra GK, Wrong A, Lei S, Aarts MM, MacDonald JF, Tymianski M. Enhanced vulnerability to NMDA toxicity in sublethal traumatic neuronal injury in vitro. J Neurotrauma 2004; 20:1377-95. [PMID: 14748985 DOI: 10.1089/089771503322686166] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Traumatic brain injury causes neuronal disruption and triggers secondary events leading to additional neuronal death. To study injuries triggered by secondary events, we exposed cultured cortical neurons to sublethal mechanical stretch, thus eliminating confounding death from primary trauma. Sublethally stretched neurons maintained cell membrane integrity, viability, and electrophysiological function. However, stretching induced in the cells a heightened vulnerability to subsequent challenges with L-glutamate or NMDA. This heightened vulnerability was specifically mediated by NMDA receptors (NMDARs), as stretched neurons did not become more vulnerable to either kainate toxicity or to that induced by the Ca(2+) ionophore A23187. Stretch-enhanced vulnerability to NMDA occurred independently of endogenous glutamate release, but required Ca(2+) and Na(+) influx through NMDARs. Stretch did not affect the electrophysiological properties of NMDARs nor excitatory synaptic activity, indicating that specificity of enhanced vulnerability to NMDA involves postsynaptic mechanisms downstream from NMDARs. To test whether this specificity requires physical interactions between NMDARs and cytoskeletal elements, we perturbed actin filaments and microtubules, both of which are linked to NMDARs. This had no effect on the stretch-induced vulnerability to NMDA, suggesting that sublethal stretch does not affect cell survival through the cytoskeleton. Our data illustrate that sublethal in vitro stretch injury triggers distinct signaling pathways that lead to secondary injury, rather than causing a generalized increase in vulnerability to secondary insults.
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Affiliation(s)
- Mark Arundine
- Toronto Western Hospital Research Institute, Toronto, Ontario, Canada
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Shiraishi Y, Mizutani A, Yuasa S, Mikoshiba K, Furuichi T. Glutamate-induced declustering of post-synaptic adaptor protein Cupidin (Homer 2/vesl-2) in cultured cerebellar granule cells. J Neurochem 2003; 87:364-76. [PMID: 14511114 DOI: 10.1046/j.1471-4159.2003.02003.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cupidin (Homer 2/vesl-2) is a post-synaptic adaptor protein that associates with glutamate receptor complexes and the actin cytoskeleton. We analyzed the developmental and activity-dependent localization of Cupidin in mouse cerebellar granule cells. Cupidin is predominantly localized to granule cell post-synapses connecting with mossy fiber terminals in developing post-natal cerebellum, but is diminished in adult cerebellum. In cultured granule cells 7 days in vitro, Cupidin was present as synaptic and extra-synaptic punctate clusters that largely co-localized with the actin-cytoskeletal binding partners F-actin and drebrin, as well as a post-synaptic scaffold protein PSD-95. Upon stimulation with glutamate, Cupidin clusters were rapidly dissociated without protein degradation, and by short-term but not sustained stimulation they were recovered after post-incubation without glutamate. The glutamate-induced declustering of Cupidin preceded that of F-actin and drebrin, was elicited by NMDA receptor-mediated Ca2+ influx, and was followed by a downstream pathway including MAPK/ERK and protein tyrosine kinase. Specific isoforms with post-translational modification were reduced depending on Ca2+-dependent protein phosphatase activity. In cultured hippocampal neurons, Homer family members Homer 1, Cupidin/Homer 2 and Homer 3 showed similar glutamate-induced declustering. We suggest that Cupidin acts as a mobile adaptor protein that changes the distribution states, clustered versus declustered, in response to synaptic activity.
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Affiliation(s)
- Yoko Shiraishi
- Laboratory for Molecular Neurogenesis, RIKEN Brain Science Institute, Wako, Saitama, Japan
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10
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Abstract
The unipolar brush cell (UBC), a small interneuron occurring at high density in the granular layer of the mammalian vestibulocerebellum, receives a giant glutamatergic synapse from a single mossy fiber (MF) rosette, usually on a brush of dendritic branchlets. MF stimulation produces a current in the UBC several orders of magnitude greater in duration than at other glutamatergic synapses. We assumed that the cytoskeleton would have a special role in plasticity of the MF-UBC synapse. Neurofilaments and microtubules are enriched in the UBC somatodendritic compartment but are conspicuously absent in close proximity to the giant synapse, where standard electron microscopy reveals a granulo-flocculent material. Because osmium tetroxide fixation during sample preparation for standard electron microscopy destabilizes actin filaments, we hypothesized that this subsynaptic granulo-flocculent material is actin-based. After actin stabilization, we observed prominent, but loosely organized, bundles of microfilaments at the subsynaptic region of the MF-UBC synapse that linked the postsynaptic density with the cytoskeletal core of the dendritic branchlets. Confocal fluorescence microscopy and pre- and postembedding immunogold labeling with phalloidin and actin antibodies showed that these microfilaments consist of f-actin and contain little beta-actin. This extraordinary postsynaptic actin apparatus is ideally situated to form a dynamic framework for glutamate receptors and other postsynaptic molecules, and to mediate activity-dependent plastic rearrangements of the giant synapse.
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Affiliation(s)
- M R Diño
- Northwestern University Institute for Neuroscience, Chicago, Illinois 60611, USA
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Itzstein C, Espinosa L, Delmas PD, Chenu C. Specific antagonists of NMDA receptors prevent osteoclast sealing zone formation required for bone resorption. Biochem Biophys Res Commun 2000; 268:201-9. [PMID: 10652236 DOI: 10.1006/bbrc.2000.2097] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
N-Methyl-d-aspartate (NMDA) glutamate receptors, widely distributed in the nervous system, have recently been identified in bone. They are expressed and are functional in osteoclasts. In the present work, we have studied the effects of specific antagonists of NMDA receptors on osteoclast activation and bone resorption. Using an in vitro assay of bone resorption, we showed that several antagonists of NMDA receptors binding to different sites of the receptor inhibit bone resorption. Osteoclast activation requires adhesion to the bone surface, cytoskeletal reorganization and survival. We demonstrated by autoradiography that the specific NMDA receptor channel blocker, MK 801, binds to osteoclasts. This antagonist had no effect on osteoclast attachment to bone and did not induce osteoclast apoptosis. In contrast, MK 801 rapidly decreased the percentage of osteoclasts with actin ring structures that are associated with actively resorbing osteoclasts. These results suggest that NMDA receptors expressed by osteoclasts may be involved in adhesion-induced formation of the sealing zone required for bone resorption.
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Affiliation(s)
- C Itzstein
- INSERM Unit 403, Hôpital E. Herriot, Pavillon F, Lyon Cedex 03, 69437, France
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12
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Abstract
Excitatory synaptic activity governs excitotoxicity and modulates the distribution of NMDA receptors (NMDARs) among synaptic and extrasynaptic sites of central neurons. We investigated whether NMDAR localization was functionally linked to excitotoxicity by perturbing F-actin, a cytoskeletal protein that participates in targeting synaptic NMDARs in dendritic spines. Depolymerizing F-actin did not affect NMDA-evoked whole-cell currents. However, the number of dendritic NMDAR clusters and the NMDAR-mediated component of miniature spontaneous EPSCs were reduced, whereas the number of AMPA receptor clusters and AMPA receptor-mediated component of EPSCs was unchanged. This selective perturbation of synaptically activated NMDARs had no effect on neuronal death or the accumulation of (45)Ca(2+) evoked by applying exogenous NMDA or L-glutamate, which reach both synaptic and extrasynaptic receptors. However, it increased survival and decreased (45)Ca(2+) accumulation in neurons exposed to oxygen glucose deprivation, which causes excitotoxicity by glutamate release at synapses. Thus, synaptically and extrasynaptically activated NMDARs are equally capable of excitotoxicity. However, their relative contributions vary with the location of extracellular excitotoxin accumulation, a factor governed by the mechanism of extracellular neurotransmitter accumulation, not the synaptic activation of NMDARs.
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Abstract
Mitochondria play a central role in the survival and death of neurons. The detailed bioenergetic mechanisms by which isolated mitochondria generate ATP, sequester Ca(2+), generate reactive oxygen species, and undergo Ca(2+)-dependent permeabilization of their inner membrane are currently being applied to the function of mitochondria in situ within neurons under physiological and pathophysiological conditions. Here we review the functional bioenergetics of isolated mitochondria, with emphasis on the chemiosmotic proton circuit and the application (and occasional misapplication) of these principles to intact neurons. Mitochondria play an integral role in both necrotic and apoptotic neuronal cell death, and the bioenergetic principles underlying current studies are reviewed.
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Affiliation(s)
- D G Nicholls
- Department of Pharmacology, University of Dundee, Dundee, Scotland.
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Abstract
In the adult brain, actin is concentrated in dendritic spines where it can produce rapid changes in their shape. Through various synaptic junction proteins, this postsynaptic actin is linked to neurotransmitter receptors, influencing their function and, in turn, being influenced by them. Thus, the actin cytoskeleton is emerging as a key mediator between signal transmission and anatomical plasticity at excitatory synapses.
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Affiliation(s)
- A Matus
- Friedrich Miecher Institute PO Box 2543, 4002, Basel, Switzerland.
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van Rossum D, Hanisch UK. Cytoskeletal dynamics in dendritic spines: direct modulation by glutamate receptors? Trends Neurosci 1999; 22:290-5. [PMID: 10370249 DOI: 10.1016/s0166-2236(99)01404-6] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A wide heterogeneity in dendritic-spine morphology is observed and ultrastructural changes can be induced following experimental stimulation of neurons. Morphological adaptation of a given spine might, thus, reflect its history or the current state of synaptic activity. These changes could conceivably result from rearrangements of the cytoskeleton that is subjacent to excitatory synapses. This article dicusses the direct and indirect interactions, between glutamate receptors and the cytoskeletal proteins, which include PDZ-containing proteins, actin and tubulin, as well as associated proteins. In fact, the synaptic-activity-controlled balancing of monomeric, dimeric and polymeric forms of actin and tubulin might underlie the changes in spine shape. These continuous adaptations could be relevant for physiological events, such as learning and the formation of memory.
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Affiliation(s)
- D van Rossum
- Max Delbrück Centre for Molecular Medicine, 13092 Berlin-Buch, Germany
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Johnson BD. The company they keep: ion channels and their intracellular regulatory partners. ADVANCES IN SECOND MESSENGER AND PHOSPHOPROTEIN RESEARCH 1999; 33:203-28. [PMID: 10218120 DOI: 10.1016/s1040-7952(99)80011-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- B D Johnson
- Department of Physiology and Neurobiology, University of Connecticut, Storrs 06269, USA
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Abstract
Neuronal degeneration and cell death can result from excessive activation of receptors for the excitatory neurotransmitter glutamate; however, the very earliest changes in cytoskeletal organization have not been well documented. We have used an in vitro model system to examine the early consequences of intense glutamate receptor activation on dendritic spine synapses. Cultured hippocampal neurons exposed to NMDA for as little as 5 min exhibited a rapid and extensive loss of dendritic spines. Staining for the presynaptic marker synapsin 1 and the postsynaptic density proteins PSD-95 and the NR1 subunit of NMDA receptors remained intact. The disappearance of spines was accompanied by a selective loss of filamentous actin staining at synapses. The NMDA-induced loss of spine actin was time- and concentration-dependent and blocked by NMDA receptor antagonists. The effect was mimicked by L-glutamate, AMPA, and ionomycin but not by agonists of L-type calcium channels or of metabotropic glutamate receptors. The effect of NMDA on local actin assembly was strongly attenuated by pretreatment with an actin stabilizing compound or by an antagonist of the calcium-dependent protein phosphatase calcineurin. Immunoreactivity for calcineurin was enriched at synapses together with F-actin. These results indicate that the actin-mediated stability of synaptic structure is disrupted by intense glutamate receptor activity and that calcineurin blockers may be useful in preventing such destabilization.
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