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de Reus AJEM, Basak O, Dykstra W, van Asperen JV, van Bodegraven EJ, Hol EM. GFAP-isoforms in the nervous system: Understanding the need for diversity. Curr Opin Cell Biol 2024; 87:102340. [PMID: 38401182 DOI: 10.1016/j.ceb.2024.102340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Accepted: 01/30/2024] [Indexed: 02/26/2024]
Abstract
Glial fibrillary acidic protein (GFAP) is an intermediate filament (IF) protein expressed in specific types of glial cells in the nervous system. The expression of GFAP is highly regulated during brain development and in neurological diseases. The presence of distinct GFAP-isoforms in various cell types, developmental stages, and diseases indicates that GFAP (post-)transcriptional regulation has a role in glial cell physiology and pathology. GFAP-isoforms differ in sub-cellular localisation, IF-network assembly properties, and IF-dynamics which results in distinct molecular interactions and mechanical properties of the IF-network. Therefore, GFAP (post-)transcriptional regulation is likely a mechanism by which radial glia, astrocytes, and glioma cells can modulate cellular function.
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Affiliation(s)
- Alexandra J E M de Reus
- Department of Translational Neuroscience, Brain Center, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
| | - Onur Basak
- Department of Translational Neuroscience, Brain Center, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
| | - Werner Dykstra
- Department of Translational Neuroscience, Brain Center, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
| | - Jessy V van Asperen
- Institut NeuroMyoGène (INMG), Unité Physiopathologie et Génétique du Neurone et du Muscle, Unversité Claude Bernard Lyon 1 CNRS UMR 5261, INSERM U1315, Lyon, France
| | - Emma J van Bodegraven
- Department of Translational Neuroscience, Brain Center, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
| | - Elly M Hol
- Department of Translational Neuroscience, Brain Center, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands.
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2
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Uceda-Castro R, van Asperen JV, Vennin C, Sluijs JA, van Bodegraven EJ, Margarido AS, Robe PAJ, van Rheenen J, Hol EM. GFAP splice variants fine-tune glioma cell invasion and tumour dynamics by modulating migration persistence. Sci Rep 2022; 12:424. [PMID: 35013418 PMCID: PMC8748899 DOI: 10.1038/s41598-021-04127-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 12/16/2021] [Indexed: 12/26/2022] Open
Abstract
Glioma is the most common form of malignant primary brain tumours in adults. Their highly invasive nature makes the disease incurable to date, emphasizing the importance of better understanding the mechanisms driving glioma invasion. Glial fibrillary acidic protein (GFAP) is an intermediate filament protein that is characteristic for astrocyte- and neural stem cell-derived gliomas. Glioma malignancy is associated with changes in GFAP alternative splicing, as the canonical isoform GFAPα is downregulated in higher-grade tumours, leading to increased dominance of the GFAPδ isoform in the network. In this study, we used intravital imaging and an ex vivo brain slice invasion model. We show that the GFAPδ and GFAPα isoforms differentially regulate the tumour dynamics of glioma cells. Depletion of either isoform increases the migratory capacity of glioma cells. Remarkably, GFAPδ-depleted cells migrate randomly through the brain tissue, whereas GFAPα-depleted cells show a directionally persistent invasion into the brain parenchyma. This study shows that distinct compositions of the GFAPnetwork lead to specific migratory dynamics and behaviours of gliomas.
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Affiliation(s)
- Rebeca Uceda-Castro
- Division of Molecular Pathology, Oncode Institute, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Jessy V van Asperen
- Department of Translational Neuroscience, University Medical Center Utrecht Brain Center, Utrecht University, Utrecht, The Netherlands
| | - Claire Vennin
- Division of Molecular Pathology, Oncode Institute, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Jacqueline A Sluijs
- Department of Translational Neuroscience, University Medical Center Utrecht Brain Center, Utrecht University, Utrecht, The Netherlands
| | - Emma J van Bodegraven
- Department of Translational Neuroscience, University Medical Center Utrecht Brain Center, Utrecht University, Utrecht, The Netherlands
| | - Andreia S Margarido
- Division of Molecular Pathology, Oncode Institute, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Pierre A J Robe
- Department of Neurology and Neurosurgery, University Medical Center Utrecht Brain Center, University Utrecht, Utrecht, The Netherlands
| | - Jacco van Rheenen
- Division of Molecular Pathology, Oncode Institute, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
| | - Elly M Hol
- Department of Translational Neuroscience, University Medical Center Utrecht Brain Center, Utrecht University, Utrecht, The Netherlands.
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3
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van Asperen JV, Robe PA, Hol EM. GFAP Alternative Splicing and the Relevance for Disease – A Focus on Diffuse Gliomas. ASN Neuro 2022; 14:17590914221102065. [PMID: 35673702 PMCID: PMC9185002 DOI: 10.1177/17590914221102065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Glial fibrillary acidic protein (GFAP) is an intermediate filament protein that is
characteristic for astrocytes and neural stem cells, and their malignant analogues in
glioma. Since the discovery of the protein 50 years ago, multiple alternative splice
variants of the GFAP gene have been discovered, leading to different GFAP isoforms. In
this review, we will describe GFAP isoform expression from gene to protein to network,
taking the canonical isoforms GFAPα and the main alternative variant GFAPδ as the starting
point. We will discuss the relevance of studying GFAP and its isoforms in disease, with a
specific focus on diffuse gliomas.
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Affiliation(s)
- Jessy V. van Asperen
- Department of Translational Neuroscience, University Medical Center Utrecht Brain Center, Utrecht University, Utrecht, The Netherlands
| | - Pierre A.J.T. Robe
- Department of Neurology and Neurosurgery, University Medical Center Utrecht Brain Center, University Utrecht, Utrecht, The Netherlands
| | - Elly M. Hol
- Department of Translational Neuroscience, University Medical Center Utrecht Brain Center, Utrecht University, Utrecht, The Netherlands
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Abstract
Fifty years have passed since the discovery of glial fibrillary acidic protein (GFAP) by Lawrence Eng and colleagues. Now recognized as a member of the intermediate filament family of proteins, it has become a subject for study in fields as diverse as structural biology, cell biology, gene expression, basic neuroscience, clinical genetics and gene therapy. This review covers each of these areas, presenting an overview of current understanding and controversies regarding GFAP with the goal of stimulating continued study of this fascinating protein.
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Affiliation(s)
- Albee Messing
- Waisman Center, University of Wisconsin-Madison.,Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin-Madison
| | - Michael Brenner
- Department of Neurobiology, University of Alabama-Birmingham
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5
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Bodegraven EJ, Sluijs JA, Tan AK, Robe PAJT, Hol EM. New GFAP splice isoform (GFAPµ) differentially expressed in glioma translates into 21 kDa N‐terminal GFAP protein. FASEB J 2021; 35:e21389. [DOI: 10.1096/fj.202001767r] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 12/23/2020] [Accepted: 01/07/2021] [Indexed: 11/11/2022]
Affiliation(s)
- Emma J. Bodegraven
- Department of Translational Neurosciences University Medical Center Utrecht Brain CenterUtrecht University Utrecht The Netherlands
| | - Jacqueline A. Sluijs
- Department of Translational Neurosciences University Medical Center Utrecht Brain CenterUtrecht University Utrecht The Netherlands
| | - A. Katherine Tan
- Department of Translational Neurosciences University Medical Center Utrecht Brain CenterUtrecht University Utrecht The Netherlands
- Department of Neurology and Neurosurgery University Medical Center Utrecht Brain CenterUtrecht University Utrecht The Netherlands
| | - Pierre A. J. T. Robe
- Department of Neurology and Neurosurgery University Medical Center Utrecht Brain CenterUtrecht University Utrecht The Netherlands
| | - Elly M. Hol
- Department of Translational Neurosciences University Medical Center Utrecht Brain CenterUtrecht University Utrecht The Netherlands
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6
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Bozic I, Savic D, Lavrnja I. Astrocyte phenotypes: Emphasis on potential markers in neuroinflammation. Histol Histopathol 2020; 36:267-290. [PMID: 33226087 DOI: 10.14670/hh-18-284] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Astrocytes, the most abundant glial cells in the central nervous system (CNS), have numerous integral roles in all CNS functions. They are essential for synaptic transmission and support neurons by providing metabolic substrates, secreting growth factors and regulating extracellular concentrations of ions and neurotransmitters. Astrocytes respond to CNS insults through reactive astrogliosis, in which they go through many functional and molecular changes. In neuroinflammatory conditions reactive astrocytes exert both beneficial and detrimental functions, depending on the context and heterogeneity of astrocytic populations. In this review we profile astrocytic diversity in the context of neuroinflammation; with a specific focus on multiple sclerosis (MS) and its best-described animal model experimental autoimmune encephalomyelitis (EAE). We characterize two main subtypes, protoplasmic and fibrous astrocytes and describe the role of intermediate filaments in the physiology and pathology of these cells. Additionally, we outline a variety of markers that are emerging as important in investigating astrocytic biology in both physiological conditions and neuroinflammation.
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Affiliation(s)
- Iva Bozic
- Institute for Biological Research "Sinisa Stankovic", National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - Danijela Savic
- Institute for Biological Research "Sinisa Stankovic", National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - Irena Lavrnja
- Institute for Biological Research "Sinisa Stankovic", National Institute of Republic of Serbia, University of Belgrade, Belgrade, Serbia.
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Moretti M, Belli G, Morini L, Monti MC, Osculati AMM, Visonà SD. Drug Abuse-Related Neuroinflammation in Human Postmortem Brains: An Immunohistochemical Approach. J Neuropathol Exp Neurol 2020; 78:1059-1065. [PMID: 31559425 DOI: 10.1093/jnen/nlz084] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2019] [Revised: 07/02/2019] [Accepted: 08/09/2019] [Indexed: 12/27/2022] Open
Abstract
The aim of the study was to investigate blood-brain barrier alterations, neuroinflammation, and glial responses in drug abusers. Five immunohistochemical markers (CD3, zonula occludens-1 [ZO-1], intracellular adhesion molecule 1 [ICAM-1], vascular cell adhesion molecule [VCAM-1], and glial fibrillary acidic protein [GFAP]) were assessed on postmortem brain samples collected from drug abusers who died from acute intoxication of cocaine, heroin, or a combination of both, compared with controls. CD3 and ICAM-1 immunopositivity were significantly stronger in drug abusers than in controls. VCAM-1 immunopositivity was similar across drug abuser and control groups. In heroin abusers, significantly lower ZO-1 immunopositivity was observed relative to controls. GFAP positivity did not show significant differences between groups, but its distribution within the brain did differ. Both cocaine and heroin abuse promoted neuroinflammation, increasing expression of ICAM-1 and recruiting CD3+ lymphocytes. Heroin affected the molecular integrity of tight junctions, as reflected by reduced ZO-1 expression. The outcomes of the present study are, overall, consistent with prior available evidence, which is almost exclusively from studies conducted in vitro or in animal models. These findings provide important information about the downstream consequences of neuroinflammation in drug abusers and may help to inform the development of potential therapeutic targets.
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Affiliation(s)
| | | | - Luca Morini
- Unit of Legal Medicine and Forensic Sciences
| | | | | | - Silvia Damiana Visonà
- Unit of Biostatistics and Clinical Epidemiology, Department of Public Health, Experimental and Forensic Medicine, University of Pavia, Pavia, Italy
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8
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Li D, Liu X, Liu T, Liu H, Tong L, Jia S, Wang YF. Neurochemical regulation of the expression and function of glial fibrillary acidic protein in astrocytes. Glia 2019; 68:878-897. [PMID: 31626364 DOI: 10.1002/glia.23734] [Citation(s) in RCA: 85] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Revised: 08/27/2019] [Accepted: 09/17/2019] [Indexed: 12/30/2022]
Abstract
Glial fibrillary acidic protein (GFAP), a type III intermediate filament, is a marker of mature astrocytes. The expression of GFAP gene is regulated by many transcription factors (TFs), mainly Janus kinase-2/signal transducer and activator of transcription 3 cascade and nuclear factor κ-light-chain-enhancer of activated B cell signaling. GFAP expression is also modulated by protein kinase and other signaling molecules that are elicited by neuronal activity and hormones. Abnormal expression of GFAP proteins occurs in neuroinflammation, neurodegeneration, brain edema-eliciting diseases, traumatic brain injury, psychiatric disorders and others. GFAP, mainly in α-isoform, is the major component of cytoskeleton and the scaffold of astrocytes, which is essential for the maintenance of astrocytic structure and shape. GFAP also has highly morphological plasticity because of its quick changes in assembling and polymerizing states in response to environmental challenges. This plasticity and its corresponding cellular morphological changes endow astrocytes the functions of physical barrier between adjacent neurons and stabilizer of extracellular environment. Moreover, GFAP colocalizes and even molecularly associates with many functional molecules. This feature allows GFAP to function as a platform for direct interactions between different molecules. Last, GFAP involves transportation and localization of other functional proteins and thus serves as a protein transport guide in astrocytes. This guiding role of GFAP involves an elastic retraction and extension cytoskeletal network that couples with GFAP reassembling, transporting, and membrane protein recycling machinery. This paper reviews our current understanding of the expression and functions of GFAP as well as their regulation.
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Affiliation(s)
- Dongyang Li
- Department of Physiology, Harbin Medical University, Harbin, China
| | - Xiaoyu Liu
- Department of Physiology, Harbin Medical University, Harbin, China
| | - Tianming Liu
- Department of Physiology, Harbin Medical University, Harbin, China
| | - Haitao Liu
- Department of Physiology, Harbin Medical University, Harbin, China
| | - Li Tong
- Department of Physiology, Harbin Medical University, Harbin, China
| | - Shuwei Jia
- Department of Physiology, Harbin Medical University, Harbin, China
| | - Yu-Feng Wang
- Department of Physiology, Harbin Medical University, Harbin, China
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9
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Hol EM, Capetanaki Y. Type III Intermediate Filaments Desmin, Glial Fibrillary Acidic Protein (GFAP), Vimentin, and Peripherin. Cold Spring Harb Perspect Biol 2017; 9:9/12/a021642. [PMID: 29196434 DOI: 10.1101/cshperspect.a021642] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
SummaryType III intermediate filament (IF) proteins assemble into cytoplasmic homopolymeric and heteropolymeric filaments with other type III and some type IV IFs. These highly dynamic structures form an integral component of the cytoskeleton of muscle, brain, and mesenchymal cells. Here, we review the current ideas on the role of type III IFs in health and disease. It turns out that they not only offer resilience to mechanical strains, but, most importantly, they facilitate very efficiently the integration of cell structure and function, thus providing the necessary scaffolds for optimal cellular responses upon biochemical stresses and protecting against cell death, disease, and aging.
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Affiliation(s)
- Elly M Hol
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, 3584 CG Utrecht, The Netherlands.,Netherlands Institute for Neuroscience, an Institute of the Royal Netherlands Academy of Arts and Sciences, 1105 BA Amsterdam, The Netherlands.,Swammerdam Institute for Life Sciences, Center for Neuroscience, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
| | - Yassemi Capetanaki
- Center of Basic Research, Biomedical Research Foundation Academy of Athens, Athens 11527, Greece
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10
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Moeton M, Stassen OMJA, Sluijs JA, van der Meer VWN, Kluivers LJ, van Hoorn H, Schmidt T, Reits EAJ, van Strien ME, Hol EM. GFAP isoforms control intermediate filament network dynamics, cell morphology, and focal adhesions. Cell Mol Life Sci 2016; 73:4101-20. [PMID: 27141937 PMCID: PMC5043008 DOI: 10.1007/s00018-016-2239-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Revised: 04/12/2016] [Accepted: 04/21/2016] [Indexed: 11/01/2022]
Abstract
Glial fibrillary acidic protein (GFAP) is the characteristic intermediate filament (IF) protein in astrocytes. Expression of its main isoforms, GFAPα and GFAPδ, varies in astrocytes and astrocytoma implying a potential regulatory role in astrocyte physiology and pathology. An IF-network is a dynamic structure and has been functionally linked to cell motility, proliferation, and morphology. There is a constant exchange of IF-proteins with the network. To study differences in the dynamic properties of GFAPα and GFAPδ, we performed fluorescence recovery after photobleaching experiments on astrocytoma cells with fluorescently tagged GFAPs. Here, we show for the first time that the exchange of GFP-GFAPδ was significantly slower than the exchange of GFP-GFAPα with the IF-network. Furthermore, a collapsed IF-network, induced by GFAPδ expression, led to a further decrease in fluorescence recovery of both GFP-GFAPα and GFP-GFAPδ. This altered IF-network also changed cell morphology and the focal adhesion size, but did not alter cell migration or proliferation. Our study provides further insight into the modulation of the dynamic properties and functional consequences of the IF-network composition.
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Affiliation(s)
- Martina Moeton
- Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
| | - Oscar M J A Stassen
- Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
- Soft Tissue Biomechanics & Engineering, Department of biomedical engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Jacqueline A Sluijs
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands
| | - Vincent W N van der Meer
- Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
| | - Liselot J Kluivers
- Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
| | - Hedde van Hoorn
- Physics of Life Processes, Leiden Institute of Physics, Leiden, The Netherlands
| | - Thomas Schmidt
- Physics of Life Processes, Leiden Institute of Physics, Leiden, The Netherlands
| | - Eric A J Reits
- Cell Biology and Histology, AMC Medical Center, Amsterdam, The Netherlands
| | - Miriam E van Strien
- Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands
| | - Elly M Hol
- Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands.
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands.
- Swammerdam Institute for Life Sciences, Center for Neuroscience, University of Amsterdam, Amsterdam, The Netherlands.
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12
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Moeton M, Kanski R, Stassen OMJA, Sluijs JA, Geerts D, Tijn P, Wiche G, Strien ME, Hol EM. Silencing GFAP isoforms in astrocytoma cells disturbs laminin‐dependent motility and cell adhesion. FASEB J 2014; 28:2942-54. [DOI: 10.1096/fj.13-245837] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Martina Moeton
- Astrocyte Biology and NeurodegenerationNetherlands Institute for NeuroscienceAmsterdamThe Netherlands
| | - Regina Kanski
- Astrocyte Biology and NeurodegenerationNetherlands Institute for NeuroscienceAmsterdamThe Netherlands
| | - Oscar M. J. A. Stassen
- Astrocyte Biology and NeurodegenerationNetherlands Institute for NeuroscienceAmsterdamThe Netherlands
| | - Jacqueline A. Sluijs
- Astrocyte Biology and NeurodegenerationNetherlands Institute for NeuroscienceAmsterdamThe Netherlands
- Department of Translational NeuroscienceBrain Center Rudolf MagnusUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Dirk Geerts
- Department of Pediatric Oncology and HematologyErasmus University Medical CenterRotterdamThe Netherlands
| | - Paula Tijn
- Astrocyte Biology and NeurodegenerationNetherlands Institute for NeuroscienceAmsterdamThe Netherlands
- Hubrecht InstituteUtrechtThe Netherlands
| | - Gerhard Wiche
- Department of Biochemistry and Cell BiologyMax F. Perutz LaboratoriesUniversity of ViennaViennaAustria
| | - Miriam E. Strien
- Astrocyte Biology and NeurodegenerationNetherlands Institute for NeuroscienceAmsterdamThe Netherlands
| | - Elly M. Hol
- Astrocyte Biology and NeurodegenerationNetherlands Institute for NeuroscienceAmsterdamThe Netherlands
- Department of Translational NeuroscienceBrain Center Rudolf MagnusUniversity Medical Center UtrechtUtrechtThe Netherlands
- Swammerdam Institute for Life SciencesCenter for NeuroscienceUniversity of AmsterdamAmsterdamThe Netherlands
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13
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Proteomic analysis reveals differentially regulated protein acetylation in human amyotrophic lateral sclerosis spinal cord. PLoS One 2013; 8:e80779. [PMID: 24312501 PMCID: PMC3846615 DOI: 10.1371/journal.pone.0080779] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Accepted: 10/04/2013] [Indexed: 12/13/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a progressive fatal neurodegenerative disease that primarily affects motor neurons in the brain and spinal cord. Histone deacetylase (HDAC) inhibitors have neuroprotective effects potentially useful for the treatment of neurodegenerative diseases including ALS; however, the molecular mechanisms underlying their potential efficacy is not well understood. Here we report that protein acetylation in urea-soluble proteins is differently regulated in post-mortem ALS spinal cord. Two-dimensional electrophoresis (2-DE) analysis reveals several protein clusters with similar molecular weight but different charge status. Liquid chromatography and tandem mass spectrometry (LC-MS/MS) identifies glial fibrillary acidic protein (GFAP) as the dominant component in the protein clusters. Further analysis indicates six heavily acetylated lysine residues at positions 89, 153, 189, 218, 259 and 331 of GFAP. Immunoprecipitation followed by Western blotting confirms that the larger form of GFAP fragments are acetylated and upregulated in ALS spinal cord. Further studies demonstrate that acetylation of the proteins additional to GFAP is differently regulated, suggesting that acetylation and/or deacetylation play an important role in pathogenesis of ALS.
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14
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Thomsen R, Pallesen J, Daugaard TF, Børglum AD, Nielsen AL. Genome wide assessment of mRNA in astrocyte protrusions by direct RNA sequencing reveals mRNA localization for the intermediate filament protein nestin. Glia 2013; 61:1922-37. [DOI: 10.1002/glia.22569] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 07/31/2013] [Accepted: 08/05/2013] [Indexed: 12/26/2022]
Affiliation(s)
- Rune Thomsen
- Department of Biomedicine; Aarhus University; Aarhus Denmark
| | - Jonatan Pallesen
- Department of Biomedicine; Aarhus University; Aarhus Denmark
- Center for Integrative Sequencing, iSEQ, Department of Biomedicine; Aarhus University; Aarhus Denmark
- Lundbeck Foundation Initiative for Integrative Psychiatric Research, iPSYCH, Department of Biomedicine; Aarhus University; Aarhus Denmark
| | | | - Anders D. Børglum
- Department of Biomedicine; Aarhus University; Aarhus Denmark
- Center for Integrative Sequencing, iSEQ, Department of Biomedicine; Aarhus University; Aarhus Denmark
- Lundbeck Foundation Initiative for Integrative Psychiatric Research, iPSYCH, Department of Biomedicine; Aarhus University; Aarhus Denmark
- Center for Psychiatric Research; Aarhus University Hospital; Aarhus Denmark
| | - Anders L. Nielsen
- Department of Biomedicine; Aarhus University; Aarhus Denmark
- Center for Integrative Sequencing, iSEQ, Department of Biomedicine; Aarhus University; Aarhus Denmark
- Lundbeck Foundation Initiative for Integrative Psychiatric Research, iPSYCH, Department of Biomedicine; Aarhus University; Aarhus Denmark
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15
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Thomsen R, Daugaard TF, Holm IE, Nielsen AL. Alternative mRNA splicing from the glial fibrillary acidic protein (GFAP) gene generates isoforms with distinct subcellular mRNA localization patterns in astrocytes. PLoS One 2013; 8:e72110. [PMID: 23991052 PMCID: PMC3753360 DOI: 10.1371/journal.pone.0072110] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 07/06/2013] [Indexed: 11/20/2022] Open
Abstract
The intermediate filament network of astrocytes includes Glial fibrillary acidic protein (Gfap) as a major component. Gfap mRNA is alternatively spliced resulting in generation of different protein isoforms where Gfapα is the most predominant isoform. The Gfapδ isoform is expressed in proliferating neurogenic astrocytes of the developing human brain and in the adult human and mouse brain. Here we provide a characterization of mouse Gfapδ mRNA and Gfapδ protein. RT-qPCR analysis showed that Gfapδ mRNA and Gfapα mRNA expression is coordinately increased in the post-natal period. Immunohistochemical staining of developing mouse brain samples showed that Gfapδ is expressed in the sub-ventricular zones in accordance with the described localization in the developing and adult human brain. Immunofluorescence analysis verified incorporation of Gfapδ into the Gfap intermediate filament network and overlap in Gfapδ and Gfapα subcellular localization. Subcellular mRNA localization studies identified different localization patterns of Gfapδ and Gfapα mRNA in mouse primary astrocytes. A larger fraction of Gfapα mRNA showed mRNA localization to astrocyte protrusions compared to Gfapδ mRNA. The differential mRNA localization patterns were dependent on the different 3′-exon sequences included in Gfapδ and Gfapα mRNA. The presented results show that alternative Gfap mRNA splicing results in isoform-specific mRNA localization patterns with resulting different local mRNA concentration ratios which have potential to participate in subcellular region-specific intermediate filament dynamics during brain development, maintenance and in disease.
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Affiliation(s)
- Rune Thomsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
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16
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Kamphuis W, Mamber C, Moeton M, Kooijman L, Sluijs JA, Jansen AHP, Verveer M, de Groot LR, Smith VD, Rangarajan S, Rodríguez JJ, Orre M, Hol EM. GFAP isoforms in adult mouse brain with a focus on neurogenic astrocytes and reactive astrogliosis in mouse models of Alzheimer disease. PLoS One 2012. [PMID: 22912745 DOI: 10.1371/journal.pone.0042823]] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Glial fibrillary acidic protein (GFAP) is the main astrocytic intermediate filament (IF). GFAP splice isoforms show differential expression patterns in the human brain. GFAPδ is preferentially expressed by neurogenic astrocytes in the subventricular zone (SVZ), whereas GFAP(+1) is found in a subset of astrocytes throughout the brain. In addition, the expression of these isoforms in human brain material of epilepsy, Alzheimer and glioma patients has been reported. Here, for the first time, we present a comprehensive study of GFAP isoform expression in both wild-type and Alzheimer Disease (AD) mouse models. In cortex, cerebellum, and striatum of wild-type mice, transcripts for Gfap-α, Gfap-β, Gfap-γ, Gfap-δ, Gfap-κ, and a newly identified isoform Gfap-ζ, were detected. Their relative expression levels were similar in all regions studied. GFAPα showed a widespread expression whilst GFAPδ distribution was prominent in the SVZ, rostral migratory stream (RMS), neurogenic astrocytes of the subgranular zone (SGZ), and subpial astrocytes. In contrast to the human SVZ, we could not establish an unambiguous GFAPδ localization in proliferating cells of the mouse SVZ. In APPswePS1dE9 and 3xTgAD mice, plaque-associated reactive astrocytes had increased transcript levels of all detectable GFAP isoforms and low levels of a new GFAP isoform, Gfap-ΔEx7. Reactive astrocytes in AD mice showed enhanced GFAPα and GFAPδ immunolabeling, less frequently increased vimentin and nestin, but no GFAPκ or GFAP(+1) staining. In conclusion, GFAPδ protein is present in SVZ, RMS, and neurogenic astrocytes of the SGZ, but also outside neurogenic niches. Furthermore, differential GFAP isoform expression is not linked with aging or reactive gliosis. This evidence points to the conclusion that differential regulation of GFAP isoforms is not involved in the reorganization of the IF network in reactive gliosis or in neurogenesis in the mouse brain.
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Affiliation(s)
- Willem Kamphuis
- Netherlands Institute for Neuroscience - an Institute of the Royal Netherlands Academy of Arts and Sciences, Department of Astrocyte Biology & Neurodegeneration, Amsterdam, The Netherlands.
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17
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Kamphuis W, Mamber C, Moeton M, Kooijman L, Sluijs JA, Jansen AHP, Verveer M, de Groot LR, Smith VD, Rangarajan S, Rodríguez JJ, Orre M, Hol EM. GFAP isoforms in adult mouse brain with a focus on neurogenic astrocytes and reactive astrogliosis in mouse models of Alzheimer disease. PLoS One 2012; 7:e42823. [PMID: 22912745 PMCID: PMC3418292 DOI: 10.1371/journal.pone.0042823] [Citation(s) in RCA: 215] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Accepted: 07/11/2012] [Indexed: 11/19/2022] Open
Abstract
Glial fibrillary acidic protein (GFAP) is the main astrocytic intermediate filament (IF). GFAP splice isoforms show differential expression patterns in the human brain. GFAPδ is preferentially expressed by neurogenic astrocytes in the subventricular zone (SVZ), whereas GFAP(+1) is found in a subset of astrocytes throughout the brain. In addition, the expression of these isoforms in human brain material of epilepsy, Alzheimer and glioma patients has been reported. Here, for the first time, we present a comprehensive study of GFAP isoform expression in both wild-type and Alzheimer Disease (AD) mouse models. In cortex, cerebellum, and striatum of wild-type mice, transcripts for Gfap-α, Gfap-β, Gfap-γ, Gfap-δ, Gfap-κ, and a newly identified isoform Gfap-ζ, were detected. Their relative expression levels were similar in all regions studied. GFAPα showed a widespread expression whilst GFAPδ distribution was prominent in the SVZ, rostral migratory stream (RMS), neurogenic astrocytes of the subgranular zone (SGZ), and subpial astrocytes. In contrast to the human SVZ, we could not establish an unambiguous GFAPδ localization in proliferating cells of the mouse SVZ. In APPswePS1dE9 and 3xTgAD mice, plaque-associated reactive astrocytes had increased transcript levels of all detectable GFAP isoforms and low levels of a new GFAP isoform, Gfap-ΔEx7. Reactive astrocytes in AD mice showed enhanced GFAPα and GFAPδ immunolabeling, less frequently increased vimentin and nestin, but no GFAPκ or GFAP(+1) staining. In conclusion, GFAPδ protein is present in SVZ, RMS, and neurogenic astrocytes of the SGZ, but also outside neurogenic niches. Furthermore, differential GFAP isoform expression is not linked with aging or reactive gliosis. This evidence points to the conclusion that differential regulation of GFAP isoforms is not involved in the reorganization of the IF network in reactive gliosis or in neurogenesis in the mouse brain.
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Affiliation(s)
- Willem Kamphuis
- Netherlands Institute for Neuroscience - an Institute of the Royal Netherlands Academy of Arts and Sciences, Department of Astrocyte Biology & Neurodegeneration, Amsterdam, The Netherlands.
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18
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Boyd SE, Nair B, Ng SW, Keith JM, Orian JM. Computational characterization of 3' splice variants in the GFAP isoform family. PLoS One 2012; 7:e33565. [PMID: 22479412 PMCID: PMC3316583 DOI: 10.1371/journal.pone.0033565] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 02/16/2012] [Indexed: 12/26/2022] Open
Abstract
Glial fibrillary acidic protein (GFAP) is an intermediate filament (IF) protein specific to central nervous system (CNS) astrocytes. It has been the subject of intense interest due to its association with neurodegenerative diseases, and because of growing evidence that IF proteins not only modulate cellular structure, but also cellular function. Moreover, GFAP has a family of splicing isoforms apparently more complex than that of other CNS IF proteins, consistent with it possessing a range of functional and structural roles. The gene consists of 9 exons, and to date all isoforms associated with 3' end splicing have been identified from modifications within intron 7, resulting in the generation of exon 7a (GFAPδ/ε) and 7b (GFAPκ). To better understand the nature and functional significance of variation in this region, we used a Bayesian multiple change-point approach to identify conserved regions. This is the first successful application of this method to a single gene--it has previously only been used in whole-genome analyses. We identified several highly or moderately conserved regions throughout the intron 7/7a/7b regions, including untranslated regions and regulatory features, consistent with the biology of GFAP. Several putative unconfirmed features were also identified, including a possible new isoform. We then integrated multiple computational analyses on both the DNA and protein sequences from the mouse, rat and human, showing that the major isoform, GFAPα, has highly conserved structure and features across the three species, whereas the minor isoforms GFAPδ/ε and GFAPκ have low conservation of structure and features at the distal 3' end, both relative to each other and relative to GFAPα. The overall picture suggests distinct and tightly regulated functions for the 3' end isoforms, consistent with complex astrocyte biology. The results illustrate a computational approach for characterising splicing isoform families, using both DNA and protein sequences.
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Affiliation(s)
- Sarah E. Boyd
- School of Mathematical Sciences, Monash University, Clayton, Victoria, Australia
| | - Betina Nair
- Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia
| | - Sze Woei Ng
- Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia
| | - Jonathan M. Keith
- School of Mathematical Sciences, Monash University, Clayton, Victoria, Australia
| | - Jacqueline M. Orian
- Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia
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Van Den Berge SA, Middeldorp J, Zhang CE, Curtis MA, Leonard BW, Mastroeni D, Voorn P, Van De Berg WDJ, Huitinga I, Hol EM. Longterm quiescent cells in the aged human subventricular neurogenic system specifically express GFAP-delta. Aging Cell 2010; 9:313-26. [PMID: 20121722 DOI: 10.1111/j.1474-9726.2010.00556.x] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
A main neurogenic niche in the adult human brain is the subventricular zone (SVZ). Recent data suggest that the progenitors that are born in the human SVZ migrate via the rostral migratory stream (RMS) towards the olfactory bulb (OB), similar to what has been observed in other mammals. A subpopulation of astrocytes in the SVZ specifically expresses an assembly-compromised isoform of the intermediate filament protein glial fibrillary acidic protein (GFAP-delta). To further define the phenotype of these GFAP-delta expressing cells and to determine whether these cells are present throughout the human subventricular neurogenic system, we analysed SVZ, RMS and OB sections of 14 aged brain donors (ages 74-93). GFAP-delta was expressed in the SVZ along the ventricle, in the RMS and in the OB. The GFAP-delta cells in the SVZ co-expressed the neural stem cell (NSC) marker nestin and the cell proliferation markers proliferating cell nuclear antigen (PCNA) and Mcm2. Furthermore, BrdU retention was found in GFAP-delta positive cells in the SVZ. In the RMS, GFAP-delta was expressed in the glial net surrounding the neuroblasts. In the OB, GFAP-delta positive cells co-expressed PCNA. We also showed that GFAP-delta cells are present in neurosphere cultures that were derived from SVZ precursors, isolated postmortem from four brain donors (ages 63-91). Taken together, our findings show that GFAP-delta is expressed in an astrocytic subpopulation in the SVZ, the RMS and the OB. Importantly, we provide the first evidence that GFAP-delta is specifically expressed in longterm quiescent cells in the human SVZ, which are reminiscent of NSCs.
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Middeldorp J, Boer K, Sluijs JA, De Filippis L, Encha-Razavi F, Vescovi AL, Swaab DF, Aronica E, Hol EM. GFAPdelta in radial glia and subventricular zone progenitors in the developing human cortex. Development 2010; 137:313-21. [PMID: 20040497 DOI: 10.1242/dev.041632] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
A subpopulation of glial fibrillary acidic protein (GFAP)-expressing cells located along the length of the lateral ventricles in the subventricular zone (SVZ) have been identified as the multipotent neural stem cells of the adult mammalian brain. We have previously found that, in the adult human brain, a splice variant of GFAP, termed GFAPdelta, was expressed specifically in these cells. To investigate whether GFAPdelta is also present in the precursors of SVZ astrocytes during development and whether GFAPdelta could play a role in the developmental process, we analyzed GFAPdelta expression in the normal developing human cortex and in the cortex of foetuses with the migration disorder lissencephaly type II. We demonstrated for the first time that GFAPdelta is specifically expressed in radial glia and SVZ neural progenitors during human brain development. Expression of GFAPdelta in radial glia starts at around 13 weeks of pregnancy and disappears before birth. GFAPdelta is continuously expressed in the SVZ progenitors at later gestational ages and in the postnatal brain. Co-localization with Ki67 proved that these GFAPdelta-expressing cells are able to proliferate. Furthermore, we showed that the expression pattern of GFAPdelta was disturbed in lissencephaly type II. Overall, these results suggest that the adult SVZ is indeed a remnant of the foetal SVZ, which develops from radial glia. Furthermore, we provide evidence that GFAPdelta can distinguish resting astrocytes from proliferating SVZ progenitors.
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Affiliation(s)
- Jinte Middeldorp
- Department of Astrocyte Biology & Neurodegeneration, Netherlands Institute for Neuroscience, An Institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands
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Bargagna-Mohan P, Paranthan RR, Hamza A, Dimova N, Trucchi B, Srinivasan C, Elliott GI, Zhan CG, Lau DL, Zhu H, Kasahara K, Inagaki M, Cambi F, Mohan R. Withaferin A targets intermediate filaments glial fibrillary acidic protein and vimentin in a model of retinal gliosis. J Biol Chem 2010; 285:7657-69. [PMID: 20048155 DOI: 10.1074/jbc.m109.093765] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Gliosis is a biological process that occurs during injury repair in the central nervous system and is characterized by the overexpression of the intermediate filaments (IFs) glial fibrillary acidic protein (GFAP) and vimentin. A common thread in many retinal diseases is reactive Müller cell gliosis, an untreatable condition that leads to tissue scarring and even blindness. Here, we demonstrate that the vimentin-targeting small molecule withaferin A (WFA) is a novel chemical probe of GFAP. Using molecular modeling studies that build on the x-ray crystal structure of tetrameric vimentin rod 2B domain we reveal that the WFA binding site is conserved in the corresponding domain of tetrameric GFAP. Consequently, we demonstrate that WFA covalently binds soluble recombinant tetrameric human GFAP at cysteine 294. In cultured primary astrocytes, WFA binds to and down-regulates soluble vimentin and GFAP expression to cause cell cycle G(0)/G(1) arrest. Exploiting a chemical injury model that overexpresses vimentin and GFAP in retinal Müller glia, we demonstrate that systemic delivery of WFA down-regulates soluble vimentin and GFAP expression in mouse retinas. This pharmacological knockdown of soluble IFs results in the impairment of GFAP filament assembly and inhibition of cell proliferative response in Müller glia. We further show that a more severe GFAP filament assembly deficit manifests in vimentin-deficient mice, which is partly rescued by WFA. These findings illustrate WFA as a chemical probe of type III IFs and illuminate this class of withanolide as a potential treatment for diverse gliosis-dependent central nervous system traumatic injury conditions and diseases, and for orphan IF-dependent pathologies.
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Affiliation(s)
- Paola Bargagna-Mohan
- Departmentsof Ophthalmology & Visual Sciences, University of Kentucky, Lexington, Kentucky 40536, USA
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Martinian L, Boer K, Middeldorp J, Hol EM, Sisodiya SM, Squier W, Aronica E, Thom M. Expression patterns of glial fibrillary acidic protein (GFAP)-delta in epilepsy-associated lesional pathologies. Neuropathol Appl Neurobiol 2009. [DOI: 10.1111/j.1365-2990.2008.00996.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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23
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Andreiuolo F, Junier MP, Hol EM, Miquel C, Chimelli L, Leonard N, Chneiweiss H, Daumas-Duport C, Varlet P. GFAPδ immunostaining improves visualization of normal and pathologic astrocytic heterogeneity. Neuropathology 2009; 29:31-9. [DOI: 10.1111/j.1440-1789.2008.00936.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Perng MD, Wen SF, Gibbon T, Middeldorp J, Sluijs J, Hol EM, Quinlan RA. Glial fibrillary acidic protein filaments can tolerate the incorporation of assembly-compromised GFAP-delta, but with consequences for filament organization and alphaB-crystallin association. Mol Biol Cell 2008; 19:4521-33. [PMID: 18685083 DOI: 10.1091/mbc.e08-03-0284] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The glial fibrillary acidic protein (GFAP) gene is alternatively spliced to give GFAP-alpha, the most abundant isoform, and seven other differentially expressed transcripts including GFAP-delta. GFAP-delta has an altered C-terminal domain that renders it incapable of self-assembly in vitro. When titrated with GFAP-alpha, assembly was restored providing GFAP-delta levels were kept low (approximately 10%). In a range of immortalized and transformed astrocyte derived cell lines and human spinal cord, we show that GFAP-delta is naturally part of the endogenous intermediate filaments, although levels were low (approximately 10%). This suggests that GFAP filaments can naturally accommodate a small proportion of assembly-compromised partners. Indeed, two other assembly-compromised GFAP constructs, namely enhanced green fluorescent protein (eGFP)-tagged GFAP and the Alexander disease-causing GFAP mutant, R416W GFAP both showed similar in vitro assembly characteristics to GFAP-delta and could also be incorporated into endogenous filament networks in transfected cells, providing expression levels were kept low. Another common feature was the increased association of alphaB-crystallin with the intermediate filament fraction of transfected cells. These studies suggest that the major physiological role of the assembly-compromised GFAP-delta splice variant is as a modulator of the GFAP filament surface, effecting changes in both protein- and filament-filament associations as well as Jnk phosphorylation.
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Affiliation(s)
- Ming-Der Perng
- School of Biological and Biomedical Sciences, The University of Durham, Durham DH1 3LE, United Kingdom
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Blechingberg J, Lykke-Andersen S, Jensen TH, Jørgensen AL, Nielsen AL. Regulatory mechanisms for 3'-end alternative splicing and polyadenylation of the Glial Fibrillary Acidic Protein, GFAP, transcript. Nucleic Acids Res 2007; 35:7636-50. [PMID: 17981838 PMCID: PMC2190720 DOI: 10.1093/nar/gkm931] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The glial fibrillary acidic protein, GFAP, forms the intermediate cytoskeleton in cells of the glial lineage. Besides the common GFAPα transcript, the GFAPε and GFAPκ transcripts are generated by alternative mRNA 3′-end processing. Here we use a GFAP minigene to characterize molecular mechanisms participating in alternative GFAP expression. Usage of a polyadenylation signal within the alternatively spliced exon 7a is essential to generate the GFAPκ and GFAPκ transcripts. The GFAPκ mRNA is distinct from GFAPε mRNA given that it also includes intron 7a. Polyadenylation at the exon 7a site is stimulated by the upstream splice site. Moreover, exon 7a splice enhancer motifs supported both exon 7a splicing and polyadenylation. SR proteins increased the usage of the exon 7a polyadenylation signal but not the exon 7a splicing, whereas the polypyrimidine tract binding (PTB) protein enhanced both exon 7a polyadenylation and exon 7a splicing. Finally, increasing transcription by the VP16 trans-activator did not affect the frequency of use of the exon 7a polyadenylation signal whereas the exon 7a splicing frequency was decreased. Our data suggest a model with the selection of the exon 7a polyadenylation site being the essential and primary event for regulating GFAP alternative processing.
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Affiliation(s)
- Jenny Blechingberg
- Institute of Human Genetics, The Bartholin Building, University of Aarhus, DK-8000 Aarhus C, Denmark
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Blechingberg J, Holm IE, Nielsen KB, Jensen TH, Jørgensen AL, Nielsen AL. Identification and characterization of GFAPkappa, a novel glial fibrillary acidic protein isoform. Glia 2007; 55:497-507. [PMID: 17203480 DOI: 10.1002/glia.20475] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Glial fibrillary acidic protein (GFAP) is the principal component of the intermediary filaments in mature astrocytes of the central nervous system (CNS). The protein consists of three domains: the head, the coiled-coil, and the tail. Here, we describe the isolation of an evolutionary conserved novel GFAP isoform, GFAPkappa, produced by alternative splicing and polyadenylation of the 3'-region of the human GFAP pre-mRNA. As a consequence, the resulting human GFAPkappa protein harbors a nonconserved C-terminal tail sequence distinct from the tails of GFAPalpha, the predominant GFAP isoform, and GFAPepsilon, an isoform which also results from alternative splicing. The head and coiled-coil rod domains are identical between the three GFAP isoforms. Interestingly, GFAPkappa is incapable of forming homomeric filaments, and increasing GFAPkappa expression levels causes a collapse of intermediate filaments formed by GFAPalpha. In searching for a biological relevance of GFAPkappa, we noticed that mRNA expression levels of GFAPalpha, GFAPepsilon, and GFAPkappa are gradually increased during development of the embryonic pig brain. However, whereas the GFAPalpha/GFAPepsilon ratio is constant, the GFAPkappa/GFAPepsilon ratio decreases during brain development. Furthermore, in glioblastoma tumors, an increased GFAPkappa/GFAPepsilon ratio is detected. Our results suggest that the relative expression level of the GFAPkappa isoform could modulate the properties of GFAP intermediate filaments and perhaps thereby influencing the motility of GFAP positive astrocytes and progenitor cells within the CNS.
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Affiliation(s)
- Jenny Blechingberg
- Institute of Human Genetics, The Bartholin Building, University of Aarhus, Aarhus C DK-8000, Denmark
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