1
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Moldovean-Cioroianu NS. Reviewing the Structure-Function Paradigm in Polyglutamine Disorders: A Synergistic Perspective on Theoretical and Experimental Approaches. Int J Mol Sci 2024; 25:6789. [PMID: 38928495 PMCID: PMC11204371 DOI: 10.3390/ijms25126789] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2024] [Revised: 06/13/2024] [Accepted: 06/17/2024] [Indexed: 06/28/2024] Open
Abstract
Polyglutamine (polyQ) disorders are a group of neurodegenerative diseases characterized by the excessive expansion of CAG (cytosine, adenine, guanine) repeats within host proteins. The quest to unravel the complex diseases mechanism has led researchers to adopt both theoretical and experimental methods, each offering unique insights into the underlying pathogenesis. This review emphasizes the significance of combining multiple approaches in the study of polyQ disorders, focusing on the structure-function correlations and the relevance of polyQ-related protein dynamics in neurodegeneration. By integrating computational/theoretical predictions with experimental observations, one can establish robust structure-function correlations, aiding in the identification of key molecular targets for therapeutic interventions. PolyQ proteins' dynamics, influenced by their length and interactions with other molecular partners, play a pivotal role in the polyQ-related pathogenic cascade. Moreover, conformational dynamics of polyQ proteins can trigger aggregation, leading to toxic assembles that hinder proper cellular homeostasis. Understanding these intricacies offers new avenues for therapeutic strategies by fine-tuning polyQ kinetics, in order to prevent and control disease progression. Last but not least, this review highlights the importance of integrating multidisciplinary efforts to advancing research in this field, bringing us closer to the ultimate goal of finding effective treatments against polyQ disorders.
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Affiliation(s)
- Nastasia Sanda Moldovean-Cioroianu
- Institute of Materials Science, Bioinspired Materials and Biosensor Technologies, Kiel University, Kaiserstraße 2, 24143 Kiel, Germany;
- Faculty of Physics, Babeș-Bolyai University, Kogălniceanu 1, RO-400084 Cluj-Napoca, Romania
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2
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Pandey NK, Varkey J, Ajayan A, George G, Chen J, Langen R. Fluorescent protein tagging promotes phase separation and alters the aggregation pathway of huntingtin exon-1. J Biol Chem 2024; 300:105585. [PMID: 38141760 PMCID: PMC10825056 DOI: 10.1016/j.jbc.2023.105585] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 12/11/2023] [Accepted: 12/13/2023] [Indexed: 12/25/2023] Open
Abstract
Fluorescent protein tags are convenient tools for tracking the aggregation states of amyloidogenic or phase separating proteins, but the effect of the tags is often not well understood. Here, we investigated the impact of a C-terminal red fluorescent protein (RFP) tag on the phase separation of huntingtin exon-1 (Httex1), an N-terminal portion of the huntingtin protein that aggregates in Huntington's disease. We found that the RFP-tagged Httex1 rapidly formed micron-sized, phase separated states in the presence of a crowding agent. The formed structures had a rounded appearance and were highly dynamic according to electron paramagnetic resonance and fluorescence recovery after photobleaching, suggesting that the phase separated state was largely liquid in nature. Remarkably, the untagged protein did not undergo any detectable liquid condensate formation under the same conditions. In addition to strongly promoting liquid-liquid phase separation, the RFP tag also facilitated fibril formation, as the tag-dependent liquid condensates rapidly underwent a liquid-to-solid transition. The rate of fibril formation under these conditions was significantly faster than that of the untagged protein. When expressed in cells, the RFP-tagged Httex1 formed larger aggregates with different antibody staining patterns compared to untagged Httex1. Collectively, these data reveal that the addition of a fluorescent protein tag significantly impacts liquid and solid phase separations of Httex1 in vitro and leads to altered aggregation in cells. Considering that the tagged Httex1 is commonly used to study the mechanisms of Httex1 misfolding and toxicity, our findings highlight the importance to validate the conclusions with untagged protein.
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Affiliation(s)
- Nitin K Pandey
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Jobin Varkey
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Anakha Ajayan
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Gincy George
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Jeannie Chen
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Ralf Langen
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA; Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
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3
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Jiang A, Handley RR, Lehnert K, Snell RG. From Pathogenesis to Therapeutics: A Review of 150 Years of Huntington's Disease Research. Int J Mol Sci 2023; 24:13021. [PMID: 37629202 PMCID: PMC10455900 DOI: 10.3390/ijms241613021] [Citation(s) in RCA: 15] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 08/15/2023] [Accepted: 08/18/2023] [Indexed: 08/27/2023] Open
Abstract
Huntington's disease (HD) is a debilitating neurodegenerative genetic disorder caused by an expanded polyglutamine-coding (CAG) trinucleotide repeat in the huntingtin (HTT) gene. HD behaves as a highly penetrant dominant disorder likely acting through a toxic gain of function by the mutant huntingtin protein. Widespread cellular degeneration of the medium spiny neurons of the caudate nucleus and putamen are responsible for the onset of symptomology that encompasses motor, cognitive, and behavioural abnormalities. Over the past 150 years of HD research since George Huntington published his description, a plethora of pathogenic mechanisms have been proposed with key themes including excitotoxicity, dopaminergic imbalance, mitochondrial dysfunction, metabolic defects, disruption of proteostasis, transcriptional dysregulation, and neuroinflammation. Despite the identification and characterisation of the causative gene and mutation and significant advances in our understanding of the cellular pathology in recent years, a disease-modifying intervention has not yet been clinically approved. This review includes an overview of Huntington's disease, from its genetic aetiology to clinical presentation and its pathogenic manifestation. An updated view of molecular mechanisms and the latest therapeutic developments will also be discussed.
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Affiliation(s)
- Andrew Jiang
- Applied Translational Genetics Group, Centre for Brain Research, School of Biological Sciences, The University of Auckland, Auckland 1010, New Zealand; (R.R.H.); (K.L.); (R.G.S.)
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4
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Incebacak Eltemur RD, Nguyen HP, Weber JJ. Calpain-mediated proteolysis as driver and modulator of polyglutamine toxicity. Front Mol Neurosci 2022; 15:1020104. [PMID: 36385755 PMCID: PMC9648470 DOI: 10.3389/fnmol.2022.1020104] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Accepted: 09/26/2022] [Indexed: 09/22/2023] Open
Abstract
Among posttranslational modifications, directed proteolytic processes have the strongest impact on protein integrity. They are executed by a variety of cellular machineries and lead to a wide range of molecular consequences. Compared to other forms of proteolytic enzymes, the class of calcium-activated calpains is considered as modulator proteases due to their limited proteolytic activity, which changes the structure and function of their target substrates. In the context of neurodegeneration and - in particular - polyglutamine disorders, proteolytic events have been linked to modulatory effects on the molecular pathogenesis by generating harmful breakdown products of disease proteins. These findings led to the formulation of the toxic fragment hypothesis, and calpains appeared to be one of the key players and auspicious therapeutic targets in Huntington disease and Machado Joseph disease. This review provides a current survey of the role of calpains in proteolytic processes found in polyglutamine disorders. Together with insights into general concepts behind toxic fragments and findings in polyglutamine disorders, this work aims to inspire researchers to broaden and deepen the knowledge in this field, which will help to evaluate calpain-mediated proteolysis as a unifying and therapeutically targetable posttranslational mechanism in neurodegeneration.
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Affiliation(s)
- Rana Dilara Incebacak Eltemur
- Department of Human Genetics, Ruhr University Bochum, Bochum, Germany
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, Tübingen, Germany
| | - Huu Phuc Nguyen
- Department of Human Genetics, Ruhr University Bochum, Bochum, Germany
| | - Jonasz Jeremiasz Weber
- Department of Human Genetics, Ruhr University Bochum, Bochum, Germany
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, Tübingen, Germany
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5
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van der Bent ML, Evers MM, Vallès A. Emerging Therapies for Huntington's Disease - Focus on N-Terminal Huntingtin and Huntingtin Exon 1. Biologics 2022; 16:141-160. [PMID: 36213816 PMCID: PMC9532260 DOI: 10.2147/btt.s270657] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 09/14/2022] [Indexed: 11/12/2022]
Abstract
Huntington's disease is a devastating heritable neurodegenerative disorder that is caused by the presence of a trinucleotide CAG repeat expansion in the Huntingtin gene, leading to a polyglutamine tract in the protein. Various mechanisms lead to the production of N-terminal Huntingtin protein fragments, which are reportedly more toxic than the full-length protein. In this review, we summarize the current knowledge on the production and toxicity of N-terminal Huntingtin protein fragments. Further, we expand on various therapeutic strategies targeting N-terminal Huntingtin on the protein, RNA and DNA level. Finally, we compare the therapeutic approaches that are clinically most advanced, including those that do not target N-terminal Huntingtin, discussing differences in mode of action and translational applicability.
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Affiliation(s)
| | - Melvin M Evers
- uniQure biopharma B.V., Department of Research and Development, Amsterdam, the Netherlands
| | - Astrid Vallès
- uniQure biopharma B.V., Department of Research and Development, Amsterdam, the Netherlands
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6
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Subramaniam S. Striatal Induction and Spread of the Huntington’s Disease Protein: A Novel Rhes Route. J Huntingtons Dis 2022; 11:281-290. [PMID: 35871361 PMCID: PMC9484121 DOI: 10.3233/jhd-220548] [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: 11/25/2022]
Abstract
The CAG/CAA expansion encoding polyQ huntingtin (mutant huntingtin [mHTT]) causes Huntington’s disease (HD), which is characterized by atrophy and loss of striatal medium spiny neurons (MSNs), which are preceded by neuropathological alterations in the cortex. Previous studies have shown that mHTT can spread in the brain, but the mechanisms involved in the stereotyped degeneration and dysfunction of the neurons from the striatum to the cortex remain unclear. In this study, we found that the mHTT expression initially restricted in the striatum later spread to the cortical regions in mouse brains. Such transmission was diminished in mice that lacked the striatal-enriched protein Ras-homolog enriched in the striatum (Rhes). Rhes restricted to MSNs was also found in the cortical layers of the brain, indicating a new transmission route for the Rhes protein to the brain. Mechanistically, Rhes promotes such transmission via a direct cell-to-cell contact mediated by tunneling nanotubes (TNTs), the membranous protrusions that enable the transfer of mHTT, Rhes, and other vesicular cargoes. These transmission patterns suggest that Rhes and mHTT are likely co-transported in the brain using TNT-like cell-to-cell contacts. On the basis of these new results, a perspective is presented in this review: Rhes may ignite the mHTT transmission from the striatum that may coincide with HD onset and disease progression through an anatomically connected striato-cortical retrograde route.
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7
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Calabrese G, Molzahn C, Mayor T. Protein interaction networks in neurodegenerative diseases: from physiological function to aggregation. J Biol Chem 2022; 298:102062. [PMID: 35623389 PMCID: PMC9234719 DOI: 10.1016/j.jbc.2022.102062] [Citation(s) in RCA: 29] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 04/26/2022] [Accepted: 05/18/2022] [Indexed: 11/25/2022] Open
Abstract
The accumulation of protein inclusions is linked to many neurodegenerative diseases that typically develop in older individuals, due to a combination of genetic and environmental factors. In rare familial neurodegenerative disorders, genes encoding for aggregation-prone proteins are often mutated. While the underlying mechanism leading to these diseases still remains to be fully elucidated, efforts in the past 20 years revealed a vast network of protein–protein interactions that play a major role in regulating the aggregation of key proteins associated with neurodegeneration. Misfolded proteins that can oligomerize and form insoluble aggregates associate with molecular chaperones and other elements of the proteolytic machineries that are the frontline workers attempting to protect the cells by promoting clearance and preventing aggregation. Proteins that are normally bound to aggregation-prone proteins can become sequestered and mislocalized in protein inclusions, leading to their loss of function. In contrast, mutations, posttranslational modifications, or misfolding of aggregation-prone proteins can lead to gain of function by inducing novel or altered protein interactions, which in turn can impact numerous essential cellular processes and organelles, such as vesicle trafficking and the mitochondria. This review examines our current knowledge of protein–protein interactions involving several key aggregation-prone proteins that are associated with Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, or amyotrophic lateral sclerosis. We aim to provide an overview of the protein interaction networks that play a central role in driving or mitigating inclusion formation, while highlighting some of the key proteomic studies that helped to uncover the extent of these networks.
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Affiliation(s)
- Gaetano Calabrese
- Michael Smith Laboratories, University of British Columbia, V6T 1Z4 Vancouver BC, Canada.
| | - Cristen Molzahn
- Michael Smith Laboratories, University of British Columbia, V6T 1Z4 Vancouver BC, Canada
| | - Thibault Mayor
- Michael Smith Laboratories, University of British Columbia, V6T 1Z4 Vancouver BC, Canada.
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8
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Weber JJ, Anger SC, Pereira Sena P, Incebacak Eltemur RD, Huridou C, Fath F, Gross C, Casadei N, Riess O, Nguyen HP. Calpains as novel players in the molecular pathogenesis of spinocerebellar ataxia type 17. Cell Mol Life Sci 2022; 79:262. [PMID: 35482253 PMCID: PMC9050766 DOI: 10.1007/s00018-022-04274-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Revised: 03/07/2022] [Accepted: 03/25/2022] [Indexed: 11/23/2022]
Abstract
Spinocerebellar ataxia type 17 (SCA17) is a neurodegenerative disease caused by a polyglutamine-encoding trinucleotide repeat expansion in the gene of transcription factor TATA box-binding protein (TBP). While its underlying pathomechanism is elusive, polyglutamine-expanded TBP fragments of unknown origin mediate the mutant protein’s toxicity. Calcium-dependent calpain proteases are protagonists in neurodegenerative disorders. Here, we demonstrate that calpains cleave TBP, and emerging C-terminal fragments mislocalize to the cytoplasm. SCA17 cell and rat models exhibited calpain overactivation, leading to excessive fragmentation and depletion of neuronal proteins in vivo. Transcriptome analysis of SCA17 cells revealed synaptogenesis and calcium signaling perturbations, indicating the potential cause of elevated calpain activity. Pharmacological or genetic calpain inhibition reduced TBP cleavage and aggregation, consequently improving cell viability. Our work underlines the general significance of calpains and their activating pathways in neurodegenerative disorders and presents these proteases as novel players in the molecular pathogenesis of SCA17.
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Affiliation(s)
- Jonasz Jeremiasz Weber
- Department of Human Genetics, Ruhr University Bochum, Universitätsstraße 150, 44801, Bochum, Germany.,Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076, Tübingen, Germany
| | - Stefanie Cari Anger
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076, Tübingen, Germany
| | - Priscila Pereira Sena
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076, Tübingen, Germany.,Graduate School of Cellular Neuroscience, University of Tübingen, 72074, Tübingen, Germany
| | - Rana Dilara Incebacak Eltemur
- Department of Human Genetics, Ruhr University Bochum, Universitätsstraße 150, 44801, Bochum, Germany.,Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076, Tübingen, Germany
| | - Chrisovalantou Huridou
- Department of Human Genetics, Ruhr University Bochum, Universitätsstraße 150, 44801, Bochum, Germany.,Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076, Tübingen, Germany
| | - Florian Fath
- Department of Human Genetics, Ruhr University Bochum, Universitätsstraße 150, 44801, Bochum, Germany.,Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076, Tübingen, Germany
| | - Caspar Gross
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076, Tübingen, Germany.,NGS Competence Center Tübingen, 72076, Tübingen, Germany
| | - Nicolas Casadei
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076, Tübingen, Germany.,NGS Competence Center Tübingen, 72076, Tübingen, Germany
| | - Olaf Riess
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076, Tübingen, Germany.,NGS Competence Center Tübingen, 72076, Tübingen, Germany
| | - Huu Phuc Nguyen
- Department of Human Genetics, Ruhr University Bochum, Universitätsstraße 150, 44801, Bochum, Germany.
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9
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Marquette A, Aisenbrey C, Bechinger B. Membrane Interactions Accelerate the Self-Aggregation of Huntingtin Exon 1 Fragments in a Polyglutamine Length-Dependent Manner. Int J Mol Sci 2021; 22:ijms22136725. [PMID: 34201610 PMCID: PMC8268948 DOI: 10.3390/ijms22136725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Revised: 06/07/2021] [Accepted: 06/18/2021] [Indexed: 12/04/2022] Open
Abstract
The accumulation of aggregated protein is a typical hallmark of many human neurodegenerative disorders, including polyglutamine-related diseases such as chorea Huntington. Misfolding of the amyloidogenic proteins gives rise to self-assembled complexes and fibres. The huntingtin protein is characterised by a segment of consecutive glutamines which, when exceeding ~ 37 residues, results in the occurrence of the disease. Furthermore, it has also been demonstrated that the 17-residue amino-terminal domain of the protein (htt17), located upstream of this polyglutamine tract, strongly correlates with aggregate formation and pathology. Here, we demonstrate that membrane interactions strongly accelerate the oligomerisation and β-amyloid fibril formation of htt17-polyglutamine segments. By using a combination of biophysical approaches, the kinetics of fibre formation is investigated and found to be strongly dependent on the presence of lipids, the length of the polyQ expansion, and the polypeptide-to-lipid ratio. Finally, the implications for therapeutic approaches are discussed.
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Affiliation(s)
- Arnaud Marquette
- Chemistry Institute UMR7177, University of Strasbourg/CNRS, 67000 Strasbourg, France; (A.M.); (C.A.)
| | - Christopher Aisenbrey
- Chemistry Institute UMR7177, University of Strasbourg/CNRS, 67000 Strasbourg, France; (A.M.); (C.A.)
| | - Burkhard Bechinger
- Chemistry Institute UMR7177, University of Strasbourg/CNRS, 67000 Strasbourg, France; (A.M.); (C.A.)
- Insitut Universitaire de France, 75005 Paris, France
- Correspondence:
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10
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Gao R, Chakraborty A, Geater C, Pradhan S, Gordon KL, Snowden J, Yuan S, Dickey AS, Choudhary S, Ashizawa T, Ellerby LM, La Spada AR, Thompson LM, Hazra TK, Sarkar PS. Mutant huntingtin impairs PNKP and ATXN3, disrupting DNA repair and transcription. eLife 2019; 8:42988. [PMID: 30994454 PMCID: PMC6529219 DOI: 10.7554/elife.42988] [Citation(s) in RCA: 69] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Accepted: 04/16/2019] [Indexed: 11/13/2022] Open
Abstract
How huntingtin (HTT) triggers neurotoxicity in Huntington's disease (HD) remains unclear. We report that HTT forms a transcription-coupled DNA repair (TCR) complex with RNA polymerase II subunit A (POLR2A), ataxin-3, the DNA repair enzyme polynucleotide-kinase-3'-phosphatase (PNKP), and cyclic AMP-response element-binding (CREB) protein (CBP). This complex senses and facilitates DNA damage repair during transcriptional elongation, but its functional integrity is impaired by mutant HTT. Abrogated PNKP activity results in persistent DNA break accumulation, preferentially in actively transcribed genes, and aberrant activation of DNA damage-response ataxia telangiectasia-mutated (ATM) signaling in HD transgenic mouse and cell models. A concomitant decrease in Ataxin-3 activity facilitates CBP ubiquitination and degradation, adversely impacting transcription and DNA repair. Increasing PNKP activity in mutant cells improves genome integrity and cell survival. These findings suggest a potential molecular mechanism of how mutant HTT activates DNA damage-response pro-degenerative pathways and impairs transcription, triggering neurotoxicity and functional decline in HD.
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Affiliation(s)
- Rui Gao
- Department of Neurology, University of Texas Medical Branch, Galveston, United States
| | - Anirban Chakraborty
- Department of Internal Medicine, University of Texas Medical Branch, Galveston, United States
| | - Charlene Geater
- Department of Psychiatry and Human Behavior and the Sue and Bill Gross Stem Cell Center, University of California, Irvine, Irvine, United States
| | - Subrata Pradhan
- Department of Neurology, University of Texas Medical Branch, Galveston, United States
| | - Kara L Gordon
- Department of Neurology, Duke University School of Medicine, Durham, United States
| | - Jeffrey Snowden
- Department of Neurology, University of Texas Medical Branch, Galveston, United States
| | - Subo Yuan
- Department of Neuroscience, Cell Biology and Anatomy, University of Texas Medical Branch, Galveston, United States
| | - Audrey S Dickey
- Department of Neurology, Duke University School of Medicine, Durham, United States
| | - Sanjeev Choudhary
- Department of Biochemistry, Cell Biology and Genetics, Sam Houston State University, Huntsville, United States
| | - Tetsuo Ashizawa
- Department of Neurology, Houston Methodist Research Institute, Houston, United States
| | - Lisa M Ellerby
- Buck Institute for Research on Aging, Novato, United States
| | - Albert R La Spada
- Department of Neurology, Duke University School of Medicine, Durham, United States
| | - Leslie M Thompson
- Department of Psychiatry and Human Behavior and the Sue and Bill Gross Stem Cell Center, University of California, Irvine, Irvine, United States.,Department of Neurobiology and Behavior, University of California, Irvine, Institute for Memory Impairments and Neurological Disorders, Irvine, United States
| | - Tapas K Hazra
- Department of Internal Medicine, University of Texas Medical Branch, Galveston, United States
| | - Partha S Sarkar
- Department of Neurology, University of Texas Medical Branch, Galveston, United States.,Department of Neuroscience, Cell Biology and Anatomy, University of Texas Medical Branch, Galveston, United States
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11
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Abstract
The identification of the mutation causing Huntington's disease (HD) has led to the generation of a large number of mouse models. These models are used to further enhance our understanding of the mechanisms underlying the disease, as well as investigating and identifying therapeutic targets for this disorder. Here we review the transgenic, knock-in mice commonly used to model HD, as well those that have been generated to study specific disease mechanisms. We then provide a brief overview of the importance of standardizing the use of HD mice and describe brief protocols used for genotyping the mouse models used within the Bates Laboratory.
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Affiliation(s)
- Pamela P Farshim
- Department of Neurodegenerative Disease, Huntington's Disease Centre and Dementia Research Institute, University College London Institute of Neurology, London, WC1N 3BG, UK
| | - Gillian P Bates
- Department of Neurodegenerative Disease, Huntington's Disease Centre and Dementia Research Institute, University College London Institute of Neurology, London, WC1N 3BG, UK.
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12
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Abstract
Huntington's disease (HD) is an autosomal dominant progressive neurological disorder characterized by motor, cognitive, and psychiatric symptoms that typically present later on in life, although juvenile cases do exist. The identification of the disease-causing mutation, a CAG triplet repeat expansion in the HTT gene, in 1993 generated numerous investigations into the cellular and molecular pathways underlying the disorder. HD mouse models have played a prominent role in these studies, and the use of these mouse models of HD in the development and evaluation of novel therapeutic strategies is reviewed in this chapter. As new interventions and therapeutic approaches are evaluated and implemented, genetic mouse models will continue to be used with the hope of developing effective treatments for HD.
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Affiliation(s)
- Natalia Kosior
- Centre for Molecular Medicine and Therapeutics, and Department of Medical Genetics, BC Children's Hospital Research Institute, University of British Columbia, Vancouver, BC, Canada
| | - Blair R Leavitt
- Centre for Molecular Medicine and Therapeutics, and Department of Medical Genetics, BC Children's Hospital Research Institute, University of British Columbia, Vancouver, BC, Canada.
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13
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André W, Nondier I, Valensi M, Guillonneau F, Federici C, Hoffner G, Djian P. Identification of brain substrates of transglutaminase by functional proteomics supports its role in neurodegenerative diseases. Neurobiol Dis 2017; 101:40-58. [DOI: 10.1016/j.nbd.2017.01.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Revised: 01/21/2017] [Accepted: 01/25/2017] [Indexed: 12/21/2022] Open
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14
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Chen MZ, Mok SA, Ormsby AR, Muchowski PJ, Hatters DM. N-Terminal Fragments of Huntingtin Longer than Residue 170 form Visible Aggregates Independently to Polyglutamine Expansion. J Huntingtons Dis 2017; 6:79-91. [PMID: 28339398 DOI: 10.3233/jhd-160207] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND A hallmark of Huntington's disease is the progressive aggregation of full length and N-terminal fragments of polyglutamine (polyQ)-expanded Huntingtin (Htt) into intracellular inclusions. The production of N-terminal fragments appears important for enabling pathology and aggregation; and hence the direct expression of a variety of N-terminal fragments are commonly used to model HD in animal and cellular models. OBJECTIVE It remains unclear how the length of the N-terminal fragments relates to polyQ - mediated aggregation. We investigated the fundamental intracellular aggregation process of eight different-length N-terminal fragments of Htt in both short (25Q) and long polyQ (97Q). METHODS N-terminal fragments were fused to fluorescent proteins and transiently expressed in mammalian cell culture models. These included the classic exon 1 fragment (90 amino acids) and longer forms of 105, 117, 171, 513, 536, 552, and 586 amino acids based on wild-type Htt (of 23Q) sequence length nomenclature. RESULTS N-terminal fragments of less than 171 amino acids only formed inclusions in polyQ-expanded form. By contrast the longer fragments formed inclusions irrespective of Q-length, with Q-length playing a negligible role in extent of aggregation. The inclusions could be classified into 3 distinct morphological categories. One type (Type A) was universally associated with polyQ expansions whereas the other two types (Types B and C) formed independently of polyQ length expansion. CONCLUSIONS PolyQ-expansion was only required for fragments of less than 171 amino acids to aggregate. Longer fragments aggregated predominately through a non-polyQ mechanism, involving at least one, and probably more distinct clustering mechanisms.
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Affiliation(s)
- Moore Z Chen
- Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC, Australia
| | - Sue-Ann Mok
- Department of Neurology, University of California San Francisco, San Francisco, CA, USA
| | - Angelique R Ormsby
- Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC, Australia
| | | | - Danny M Hatters
- Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC, Australia
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Lokhande S, Patra BN, Ray A. A link between chromatin condensation mechanisms and Huntington's disease: connecting the dots. MOLECULAR BIOSYSTEMS 2016; 12:3515-3529. [PMID: 27714015 DOI: 10.1039/c6mb00598e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Huntington's disease is a rare neurodegenerative disorder whose complex pathophysiology exhibits system-wide changes in the body, with striking and debilitating clinical features targeting the central nervous system. Among the various molecular functions affected in this disease, mitochondrial dysfunction and transcriptional dysregulation are some of the most studied aspects of this disease. However, there is evidence of the involvement of a mutant Huntingtin protein in the processes of DNA damage, chromosome condensation and DNA repair. This review attempts to briefly recapitulate the clinical features, model systems used to study the disease, major molecular processes affected, and, more importantly, examines recent evidence for the involvement of the mutant Huntingtin protein in the processes regulating chromosome condensation, leading to DNA damage response and neuronal death.
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Affiliation(s)
- Sonali Lokhande
- Keck Graduate Institute of Applied Life Sciences, Claremont, CA 91711, USA.
| | - Biranchi N Patra
- Keck Graduate Institute of Applied Life Sciences, Claremont, CA 91711, USA.
| | - Animesh Ray
- Keck Graduate Institute of Applied Life Sciences, Claremont, CA 91711, USA.
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Clemens LE, Weber JJ, Wlodkowski TT, Yu-Taeger L, Michaud M, Calaminus C, Eckert SH, Gaca J, Weiss A, Magg JCD, Jansson EKH, Eckert GP, Pichler BJ, Bordet T, Pruss RM, Riess O, Nguyen HP. Olesoxime suppresses calpain activation and mutant huntingtin fragmentation in the BACHD rat. Brain 2015; 138:3632-53. [PMID: 26490331 DOI: 10.1093/brain/awv290] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Accepted: 08/11/2015] [Indexed: 12/14/2022] Open
Abstract
Huntington's disease is a fatal human neurodegenerative disorder caused by a CAG repeat expansion in the HTT gene, which translates into a mutant huntingtin protein. A key event in the molecular pathogenesis of Huntington's disease is the proteolytic cleavage of mutant huntingtin, leading to the accumulation of toxic protein fragments. Mutant huntingtin cleavage has been linked to the overactivation of proteases due to mitochondrial dysfunction and calcium derangements. Here, we investigated the therapeutic potential of olesoxime, a mitochondria-targeting, neuroprotective compound, in the BACHD rat model of Huntington's disease. BACHD rats were treated with olesoxime via the food for 12 months. In vivo analysis covered motor impairments, cognitive deficits, mood disturbances and brain atrophy. Ex vivo analyses addressed olesoxime's effect on mutant huntingtin aggregation and cleavage, as well as brain mitochondria function. Olesoxime improved cognitive and psychiatric phenotypes, and ameliorated cortical thinning in the BACHD rat. The treatment reduced cerebral mutant huntingtin aggregates and nuclear accumulation. Further analysis revealed a cortex-specific overactivation of calpain in untreated BACHD rats. Treated BACHD rats instead showed significantly reduced levels of mutant huntingtin fragments due to the suppression of calpain-mediated cleavage. In addition, olesoxime reduced the amount of mutant huntingtin fragments associated with mitochondria, restored a respiration deficit, and enhanced the expression of fusion and outer-membrane transport proteins. In conclusion, we discovered the calpain proteolytic system, a key player in Huntington's disease and other neurodegenerative disorders, as a target of olesoxime. Our findings suggest that olesoxime exerts its beneficial effects by improving mitochondrial function, which results in reduced calpain activation. The observed alleviation of behavioural and neuropathological phenotypes encourages further investigations on the use of olesoxime as a therapeutic for Huntington's disease.
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Affiliation(s)
- Laura E Clemens
- 1 Institute of Medical Genetics and Applied Genomics, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany 2 Centre for Rare Diseases, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany
| | - Jonasz J Weber
- 1 Institute of Medical Genetics and Applied Genomics, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany 2 Centre for Rare Diseases, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany
| | - Tanja T Wlodkowski
- 1 Institute of Medical Genetics and Applied Genomics, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany 2 Centre for Rare Diseases, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany
| | - Libo Yu-Taeger
- 1 Institute of Medical Genetics and Applied Genomics, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany 2 Centre for Rare Diseases, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany
| | - Magali Michaud
- 3 Trophos SA., Parc Scientifique de Luminy Case 931, 13288 Marseille Cedex 9, France
| | - Carsten Calaminus
- 4 Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, University of Tuebingen, Roentgenweg 13, 72076 Tuebingen, Germany
| | - Schamim H Eckert
- 5 Department of Pharmacology, Goethe University Frankfurt am Main, Max-von-Laue Str. 9, 60438 Frankfurt, Germany
| | - Janett Gaca
- 5 Department of Pharmacology, Goethe University Frankfurt am Main, Max-von-Laue Str. 9, 60438 Frankfurt, Germany
| | - Andreas Weiss
- 6 Novartis Institutes for BioMedical Research, Klybeckstrasse 141, 4057 Basel, Switzerland
| | - Janine C D Magg
- 1 Institute of Medical Genetics and Applied Genomics, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany 2 Centre for Rare Diseases, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany
| | - Erik K H Jansson
- 1 Institute of Medical Genetics and Applied Genomics, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany 2 Centre for Rare Diseases, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany
| | - Gunter P Eckert
- 5 Department of Pharmacology, Goethe University Frankfurt am Main, Max-von-Laue Str. 9, 60438 Frankfurt, Germany
| | - Bernd J Pichler
- 4 Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, University of Tuebingen, Roentgenweg 13, 72076 Tuebingen, Germany
| | - Thierry Bordet
- 3 Trophos SA., Parc Scientifique de Luminy Case 931, 13288 Marseille Cedex 9, France
| | - Rebecca M Pruss
- 3 Trophos SA., Parc Scientifique de Luminy Case 931, 13288 Marseille Cedex 9, France
| | - Olaf Riess
- 1 Institute of Medical Genetics and Applied Genomics, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany 2 Centre for Rare Diseases, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany
| | - Huu P Nguyen
- 1 Institute of Medical Genetics and Applied Genomics, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany 2 Centre for Rare Diseases, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany
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Michalek M, Salnikov E, Bechinger B. Structure and topology of the huntingtin 1-17 membrane anchor by a combined solution and solid-state NMR approach. Biophys J 2013; 105:699-710. [PMID: 23931318 PMCID: PMC3736738 DOI: 10.1016/j.bpj.2013.06.030] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2013] [Revised: 06/07/2013] [Accepted: 06/17/2013] [Indexed: 10/26/2022] Open
Abstract
The very amino-terminal domain of the huntingtin protein is directly located upstream of the protein's polyglutamine tract, plays a decisive role in several important properties of this large protein and in the development of Huntington's disease. This huntingtin 1-17 domain is on the one hand known to markedly increase polyglutamine aggregation rates and on the other hand has been shown to be involved in cellular membrane interactions. Here, we determined the high-resolution structure of huntingtin 1-17 in dodecyl phosphocholine micelles and the topology of its helical domain in oriented phosphatidylcholine bilayers. Using two-dimensional solution NMR spectroscopy the low-energy conformations of the polypeptide were identified in the presence of dodecyl phosphocholine detergent micelles. In a next step a set of four solid-state NMR angular restraints was obtained from huntingtin 1-17 labeled with (15)N and (2)H at selected sites. Of the micellar ensemble of helical conformations only a limited set agrees in quantitative detail with the solid-state angular restraints of huntingtin 1-17 obtained in supported planar lipid bilayers. Thereby, the solid-state NMR data were used to further refine the domain structure in phospholipid bilayers. At the same time its membrane topology was determined and different motional regimes of this membrane-associated domain were explored. The pronounced structural transitions of huntingtin 1-17 upon membrane-association result in a α-helical conformation from K6 to F17, i.e., up to the very start of the polyglutamine tract. This amphipathic helix is aligned nearly parallel to the membrane surface (tilt angle ∼77°) and is characterized by a hydrophobic ridge on one side and an alternation of cationic and anionic residues that run along the hydrophilic face of the helix. This arrangement facilitates electrostatic interactions between huntingtin 1-17 domains and possibly with the proximal polyglutamine tract.
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Affiliation(s)
| | | | - Burkhard Bechinger
- Université de Strasbourg/CNRS, UMR7177, Institut de Chimie, Strasbourg, France
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Arribat Y, Bonneaud N, Talmat-Amar Y, Layalle S, Parmentier ML, Maschat F. A huntingtin peptide inhibits polyQ-huntingtin associated defects. PLoS One 2013; 8:e68775. [PMID: 23861941 PMCID: PMC3701666 DOI: 10.1371/journal.pone.0068775] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2012] [Accepted: 06/06/2013] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Huntington's disease (HD) is caused by the abnormal expansion of the polyglutamine tract in the human Huntingtin protein (polyQ-hHtt). Although this mutation behaves dominantly, huntingtin loss of function also contributes to HD pathogenesis. Indeed, wild-type Huntingtin plays a protective role with respect to polyQ-hHtt induced defects. METHODOLOGY/PRINCIPAL FINDINGS The question that we addressed here is what part of the wild-type Huntingtin is responsible for these protective properties. We first screened peptides from the Huntingtin protein in HeLa cells and identified a 23 aa peptide (P42) that inhibits polyQ-hHtt aggregation. P42 is part of the endogenous Huntingtin protein and lies within a region rich in proteolytic sites that plays a critical role in the pathogenesis process. Using a Drosophila model of HD, we tested the protective properties of this peptide on aggregation, as well as on different polyQ-hHtt induced neuronal phenotypes: eye degeneration (an indicator of cell death), impairment of vesicular axonal trafficking, and physiological behaviors such as larval locomotion and adult survival. Together, our results demonstrate high protective properties for P42 in vivo, in whole animals. These data also demonstrate a specific role of P42 on Huntington's disease model, since it has no effect on other models of polyQ-induced diseases, such as spinocerebellar ataxias. CONCLUSIONS/SIGNIFICANCE Altogether our data show that P42, a 23 aa-long hHtt peptide, plays a protective role with respect to polyQ-hHtt aggregation as well as cellular and behavioral dysfunctions induced by polyQ-hHtt in vivo. Our study also confirms the correlation between polyQ-hHtt aggregation and neuronal defects. Finally, these results strongly suggest a therapeutic potential for P42, specific of Huntington's disease.
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Affiliation(s)
- Yoan Arribat
- Institut de Génomique Fonctionnelle (IGF), CNRS-UMR5203, INSERM-U661, University of Montpellier, Montpellier, France
| | - Nathalie Bonneaud
- Institut de Génomique Fonctionnelle (IGF), CNRS-UMR5203, INSERM-U661, University of Montpellier, Montpellier, France
| | - Yasmina Talmat-Amar
- Institut de Génomique Fonctionnelle (IGF), CNRS-UMR5203, INSERM-U661, University of Montpellier, Montpellier, France
| | - Sophie Layalle
- Institut de Génomique Fonctionnelle (IGF), CNRS-UMR5203, INSERM-U661, University of Montpellier, Montpellier, France
| | - Marie-Laure Parmentier
- Institut de Génomique Fonctionnelle (IGF), CNRS-UMR5203, INSERM-U661, University of Montpellier, Montpellier, France
- * E-mail: (FM); (MLP)
| | - Florence Maschat
- Institut de Génomique Fonctionnelle (IGF), CNRS-UMR5203, INSERM-U661, University of Montpellier, Montpellier, France
- * E-mail: (FM); (MLP)
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Michalek M, Salnikov ES, Werten S, Bechinger B. Membrane interactions of the amphipathic amino terminus of huntingtin. Biochemistry 2013; 52:847-58. [PMID: 23305455 DOI: 10.1021/bi301325q] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The amino-terminal domain of huntingtin (Htt17), located immediately upstream of the decisive polyglutamine tract, strongly influences important properties of this large protein and thereby the development of Huntington's disease. Htt17 markedly increases polyglutamine aggregation rates and the level of huntingtin's interactions with biological membranes. Htt17 adopts a largely helical conformation in the presence of membranes, and this structural transition was used to quantitatively analyze membrane association as a function of lipid composition. The apparent membrane partitioning constants increased in the presence of anionic lipids but decreased with increasing amounts of cholesterol. When membrane permeabilization was tested, a pronounced dye release was observed from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles and 75:25 (molar ratio) POPC/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine vesicles but not across bilayers that better mimic cellular membranes. Solid-state nuclear magnetic resonance structural investigations indicated that the Htt17 α-helix adopts an alignment parallel to the membrane surface, and that the tilt angle (∼75°) was nearly constant in all of the membranes that were investigated. Furthermore, the addition of Htt17 resulted in a decrease in the lipid order parameter in all of the membranes that were investigated. The lipid interactions of Htt17 have pivotal implications for membrane anchoring and functional properties of huntingtin and concomitantly the development of the disease.
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Affiliation(s)
- Matthias Michalek
- Membrane Biophysics and NMR Chemistry Institute UMR7177, University of Strasbourg/CNRS International Center for Frontier Research in Chemistry, 1 rue Blaise Pascal, Strasbourg, France
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22
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Miller JP, Yates BE, Al-Ramahi I, Berman AE, Sanhueza M, Kim E, de Haro M, DeGiacomo F, Torcassi C, Holcomb J, Gafni J, Mooney SD, Botas J, Ellerby LM, Hughes RE. A genome-scale RNA-interference screen identifies RRAS signaling as a pathologic feature of Huntington's disease. PLoS Genet 2012; 8:e1003042. [PMID: 23209424 PMCID: PMC3510027 DOI: 10.1371/journal.pgen.1003042] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Accepted: 08/29/2012] [Indexed: 11/19/2022] Open
Abstract
A genome-scale RNAi screen was performed in a mammalian cell-based assay to identify modifiers of mutant huntingtin toxicity. Ontology analysis of suppressor data identified processes previously implicated in Huntington's disease, including proteolysis, glutamate excitotoxicity, and mitochondrial dysfunction. In addition to established mechanisms, the screen identified multiple components of the RRAS signaling pathway as loss-of-function suppressors of mutant huntingtin toxicity in human and mouse cell models. Loss-of-function in orthologous RRAS pathway members also suppressed motor dysfunction in a Drosophila model of Huntington's disease. Abnormal activation of RRAS and a down-stream effector, RAF1, was observed in cellular models and a mouse model of Huntington's disease. We also observe co-localization of RRAS and mutant huntingtin in cells and in mouse striatum, suggesting that activation of R-Ras may occur through protein interaction. These data indicate that mutant huntingtin exerts a pathogenic effect on this pathway that can be corrected at multiple intervention points including RRAS, FNTA/B, PIN1, and PLK1. Consistent with these results, chemical inhibition of farnesyltransferase can also suppress mutant huntingtin toxicity. These data suggest that pharmacological inhibition of RRAS signaling may confer therapeutic benefit in Huntington's disease.
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Affiliation(s)
- John P. Miller
- The Buck Institute for Research on Aging, Novato, California, United States of America
| | - Bridget E. Yates
- The Buck Institute for Research on Aging, Novato, California, United States of America
| | - Ismael Al-Ramahi
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Ari E. Berman
- The Buck Institute for Research on Aging, Novato, California, United States of America
| | - Mario Sanhueza
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Eugene Kim
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Maria de Haro
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Francesco DeGiacomo
- The Buck Institute for Research on Aging, Novato, California, United States of America
| | - Cameron Torcassi
- The Buck Institute for Research on Aging, Novato, California, United States of America
| | - Jennifer Holcomb
- The Buck Institute for Research on Aging, Novato, California, United States of America
| | - Juliette Gafni
- The Buck Institute for Research on Aging, Novato, California, United States of America
| | - Sean D. Mooney
- The Buck Institute for Research on Aging, Novato, California, United States of America
| | - Juan Botas
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Lisa M. Ellerby
- The Buck Institute for Research on Aging, Novato, California, United States of America
- * E-mail: (LME); (REH)
| | - Robert E. Hughes
- The Buck Institute for Research on Aging, Novato, California, United States of America
- * E-mail: (LME); (REH)
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Figiel M, Szlachcic WJ, Switonski PM, Gabka A, Krzyzosiak WJ. Mouse models of polyglutamine diseases: review and data table. Part I. Mol Neurobiol 2012; 46:393-429. [PMID: 22956270 PMCID: PMC3461215 DOI: 10.1007/s12035-012-8315-4] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2012] [Accepted: 07/29/2012] [Indexed: 12/23/2022]
Abstract
Polyglutamine (polyQ) disorders share many similarities, such as a common mutation type in unrelated human causative genes, neurological character, and certain aspects of pathogenesis, including morphological and physiological neuronal alterations. The similarities in pathogenesis have been confirmed by findings that some experimental in vivo therapy approaches are effective in multiple models of polyQ disorders. Additionally, mouse models of polyQ diseases are often highly similar between diseases with respect to behavior and the features of the disease. The common features shared by polyQ mouse models may facilitate the investigation of polyQ disorders and may help researchers explore the mechanisms of these diseases in a broader context. To provide this context and to promote the understanding of polyQ disorders, we have collected and analyzed research data about the characterization and treatment of mouse models of polyQ diseases and organized them into two complementary Excel data tables. The data table that is presented in this review (Part I) covers the behavioral, molecular, cellular, and anatomic characteristics of polyQ mice and contains the most current knowledge about polyQ mouse models. The structure of this data table is designed in such a way that it can be filtered to allow for the immediate retrieval of the data corresponding to a single mouse model or to compare the shared and unique aspects of many polyQ models. The second data table, which is presented in another publication (Part II), covers therapeutic research in mouse models by summarizing all of the therapeutic strategies employed in the treatment of polyQ disorders, phenotypes that are used to examine the effects of the therapy, and therapeutic outcomes.
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Affiliation(s)
- Maciej Figiel
- Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznan, Poland.
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Zheng S, Ghitani N, Blackburn JS, Liu JP, Zeitlin SO. A series of N-terminal epitope tagged Hdh knock-in alleles expressing normal and mutant huntingtin: their application to understanding the effect of increasing the length of normal Huntingtin's polyglutamine stretch on CAG140 mouse model pathogenesis. Mol Brain 2012; 5:28. [PMID: 22892315 PMCID: PMC3499431 DOI: 10.1186/1756-6606-5-28] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Accepted: 08/09/2012] [Indexed: 12/19/2022] Open
Abstract
Background Huntington’s disease (HD) is an autosomal dominant neurodegenerative disease that is caused by the expansion of a polyglutamine (polyQ) stretch within Huntingtin (htt), the protein product of the HD gene. Although studies in vitro have suggested that the mutant htt can act in a potentially dominant negative fashion by sequestering wild-type htt into insoluble protein aggregates, the role of the length of the normal htt polyQ stretch, and the adjacent proline-rich region (PRR) in modulating HD mouse model pathogenesis is currently unknown. Results We describe the generation and characterization of a series of knock-in HD mouse models that express versions of the mouse HD gene (Hdh) encoding N-terminal hemaglutinin (HA) or 3xFlag epitope tagged full-length htt with different polyQ lengths (HA7Q-, 3xFlag7Q-, 3xFlag20Q-, and 3xFlag140Q-htt) and substitution of the adjacent mouse PRR with the human PRR (3xFlag20Q- and 3xFlag140Q-htt). Using co-immunoprecipitation and immunohistochemistry analyses, we detect no significant interaction between soluble full-length normal 7Q- htt and mutant (140Q) htt, but we do observe N-terminal fragments of epitope-tagged normal htt in mutant htt aggregates. When the sequences encoding normal mouse htt’s polyQ stretch and PRR are replaced with non-pathogenic human sequence in mice also expressing 140Q-htt, aggregation foci within the striatum, and the mean size of htt inclusions are increased, along with an increase in striatal lipofuscin and gliosis. Conclusion In mice, soluble full-length normal and mutant htt are predominantly monomeric. In heterozygous knock-in HD mouse models, substituting the normal mouse polyQ and PRR with normal human sequence can exacerbate some neuropathological phenotypes.
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Affiliation(s)
- Shuqiu Zheng
- Department of Neuroscience, University of Virginia School of Medicine, Charlottesville, VA 22908, Box 801392, USA
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Hogel M, Laprairie RB, Denovan-Wright EM. Promoters are differentially sensitive to N-terminal mutant huntingtin-mediated transcriptional repression. PLoS One 2012; 7:e41152. [PMID: 22815947 PMCID: PMC3399790 DOI: 10.1371/journal.pone.0041152] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2012] [Accepted: 06/18/2012] [Indexed: 11/18/2022] Open
Abstract
Huntington’s disease (HD) is a neurodegenerative disorder caused by the inheritance of one mutant copy of the huntingtin gene. Mutant huntingtin protein (mHtt) contains an expanded polyglutamine repeat region near the N-terminus. Cleavage of mHtt releases an N-terminal fragment (N-mHtt) which accumulates in the nucleus. Nuclear accumulation of N-mHtt has been directly associated with cellular toxicity. Decreased transcription is among the earliest detected changes that occur in the brains of HD patients, animal and cellular models of HD. Transcriptional dysregulation may trigger many of the perturbations that occur later in disease progression. An understanding of the effects of mHtt may lead to strategies to slow the progression of HD. Current models of N-mHtt-mediated transcriptional dysregulation suggest that abnormal interactions between N-mHtt and transcription factors impair the ability of these transcription factors to associate at N-mHtt-affected promoters and properly regulate gene expression. We tested various aspects of the current models using two N-mHtt-affected promoters in two cell models of HD using overexpression of known N-mHtt-interacting transcription factors, promoter deletion and mutation analyses and in vitro promoter binding assays. Consequently, we proposed a new model of N-mHtt-mediated transcriptional dysregulation centered on the presence of N-mHtt at promoters. In this model, N-mHtt interacts with multiple partners whose presence and affinity for N-mHtt influence the severity of gene dysregulation. We concluded that simultaneous interaction of N-mHtt with multiple binding partners within the transcriptional machinery would explain the gene-specificity of N-mHtt-mediated transcriptional dysregulation, as well as why some genes are affected early in disease progression while others are affected later. Our model explains why alleviating N-mHtt-mediated transcriptional dysregulation through overexpression of N-mHtt-interacting proteins has proven to be difficult and suggests that the most realistic strategy for restoring gene expression across the spectrum of N-mHtt affected genes is by reducing the amount of soluble nuclear N-mHtt.
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Affiliation(s)
- Matthew Hogel
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Robert B. Laprairie
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Eileen M. Denovan-Wright
- Laboratory of Molecular Neurobiology, Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada
- * E-mail:
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Landles C, Weiss A, Franklin S, Howland D, Bates G. Caspase-6 does not contribute to the proteolysis of mutant huntingtin in the HdhQ150 knock-in mouse model of Huntington's disease. PLOS CURRENTS 2012; 4:e4fd085bfc9973. [PMID: 22919566 PMCID: PMC3423312 DOI: 10.1371/4fd085bfc9973] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Bowles KR, Brooks SP, Dunnett SB, Jones L. Gene expression and behaviour in mouse models of HD. Brain Res Bull 2012; 88:276-84. [PMID: 21854837 DOI: 10.1016/j.brainresbull.2011.07.021] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2011] [Revised: 07/27/2011] [Accepted: 07/31/2011] [Indexed: 01/09/2023]
Abstract
Huntington's disease (HD) is an autosomal dominant neurodegenerative disease, resulting in expansion of the CAG repeat in exon 1 of the HTT gene. The resulting mutant huntingtin protein has been implicated in the disruption of a variety of cellular functions, including transcription. Mouse models of HD have been central to the development of our understanding of gene expression changes in this disease, and are now beginning to elucidate the relationship between gene expression and behaviour. Here, we review current mouse models of HD and their characterisation in terms of gene expression. In addition, we look at how this can inform behaviours observed in mouse models of disease. The relationship between gene expression and behaviour in mouse models of HD is important, as this will further our knowledge of disease progression and its underlying molecular events, highlight new treatment targets, and potentially provide new biomarkers for therapeutic trials.
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Affiliation(s)
- K R Bowles
- Department of Psychological Medicine, MRC centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, Wales, UK
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Inhibiting the nucleation of amyloid structure in a huntingtin fragment by targeting α-helix-rich oligomeric intermediates. J Mol Biol 2011; 415:900-17. [PMID: 22178478 DOI: 10.1016/j.jmb.2011.12.011] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Revised: 11/01/2011] [Accepted: 12/05/2011] [Indexed: 01/31/2023]
Abstract
Although oligomeric intermediates are transiently formed in almost all known amyloid assembly reactions, their mechanistic roles are poorly understood. Recently, we demonstrated a critical role for the 17-amino-acid N-terminus (htt(NT) segment) of huntingtin (htt) in the oligomer-mediated amyloid assembly of htt N-terminal fragments. In this mechanism, the htt(NT) segment forms the α-helix-rich core of the oligomers, leaving much of the polyglutamine (polyQ) segment disordered and solvent-exposed. Nucleation of amyloid structure occurs within this local high concentration of disordered polyQ. Here we demonstrate the kinetic importance of htt(NT) self-assembly by describing inhibitory htt(NT)-containing peptides that appear to work by targeting nucleation within the oligomer fraction. These molecules inhibit amyloid nucleation by forming mixed oligomers with the htt(NT) domains of polyQ-containing htt N-terminal fragments. In one class of inhibitors, nucleation is passively suppressed due to the reduced local concentration of polyQ within the mixed oligomer. In the other class, nucleation is actively suppressed by a proline-rich polyQ segment covalently attached to htt(NT). Studies with D-amino acid and scrambled sequence versions of htt(NT) suggest that inhibition activity is strongly linked to the propensity of inhibitory peptides to make amphipathic α-helices. Htt(NT) derivatives with C-terminal cell-penetrating peptide segments also exhibit excellent inhibitory activity. The htt(NT)-based peptides described here, especially those with protease-resistant d-amino acids and/or with cell-penetrating sequences, may prove useful as lead therapeutics for inhibiting the nucleation of amyloid formation in Huntington's disease.
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Ruiz M, Déglon N. Viral-mediated overexpression of mutant huntingtin to model HD in various species. Neurobiol Dis 2011; 48:202-11. [PMID: 21889981 DOI: 10.1016/j.nbd.2011.08.023] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2011] [Revised: 08/11/2011] [Accepted: 08/18/2011] [Indexed: 12/12/2022] Open
Abstract
Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an expansion of CAG repeats in the huntingtin (Htt) gene. Despite intensive efforts devoted to investigating the mechanisms of its pathogenesis, effective treatments for this devastating disease remain unavailable. The lack of suitable models recapitulating the entire spectrum of the degenerative process has severely hindered the identification and validation of therapeutic strategies. The discovery that the degeneration in HD is caused by a mutation in a single gene has offered new opportunities to develop experimental models of HD, ranging from in vitro models to transgenic primates. However, recent advances in viral-vector technology provide promising alternatives based on the direct transfer of genes to selected sub-regions of the brain. Rodent studies have shown that overexpression of mutant human Htt in the striatum using adeno-associated virus or lentivirus vectors induces progressive neurodegeneration, which resembles that seen in HD. This article highlights progress made in modeling HD using viral vector gene transfer. We describe data obtained with of this highly flexible approach for the targeted overexpression of a disease-causing gene. The ability to deliver mutant Htt to specific tissues has opened pathological processes to experimental analysis and allowed targeted therapeutic development in rodent and primate pre-clinical models.
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Affiliation(s)
- Marta Ruiz
- Atomic Energy Commission (CEA), Institute of Biomedical Imaging (I2BM), Molecular Imaging Research Center (MIRCen), Fontenay-aux-Roses, France
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Ratovitski T, Chighladze E, Waldron E, Hirschhorn RR, Ross CA. Cysteine proteases bleomycin hydrolase and cathepsin Z mediate N-terminal proteolysis and toxicity of mutant huntingtin. J Biol Chem 2011; 286:12578-89. [PMID: 21310951 DOI: 10.1074/jbc.m110.185348] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
N-terminal proteolysis of huntingtin is thought to be an important mediator of HD pathogenesis. The formation of short N-terminal fragments of huntingtin (cp-1/cp-2, cp-A/cp-B) has been demonstrated in cells and in vivo. We previously mapped the cp-2 cleavage site by mass spectrometry to position Arg167 of huntingtin. The proteolytic enzymes generating short N-terminal fragments of huntingtin remain unknown. To search for such proteases, we conducted a genome-wide screen using an RNA-silencing approach and an assay for huntingtin proteolysis based on the detection of cp-1 and cp-2 fragments by Western blotting. The primary screen was carried out in HEK293 cells, and the secondary screen was carried out in neuronal HT22 cells, transfected in both cases with a construct encoding the N-terminal 511 amino acids of mutant huntingtin. For additional validation of the hits, we employed a complementary assay for proteolysis of huntingtin involving overexpression of individual proteases with huntingtin in two cell lines. The screen identified 11 enzymes, with two major candidates to carry out the cp-2 cleavage, bleomycin hydrolase (BLMH) and cathepsin Z, which are both cysteine proteases of a papain-like structure. Knockdown of either protease reduced cp-2 cleavage, and ameliorated mutant huntingtin induced toxicity, whereas their overexpression increased the cp-2 cleavage. Both proteases partially co-localized with Htt in the cytoplasm and within or in association with early and late endosomes, with some nuclear co-localization observed for cathepsin Z. BLMH and cathepsin Z are expressed in the brain and have been associated previously with neurodegeneration. Our findings further validate the cysteine protease family, and BLMH and cathepsin Z in particular, as potential novel targets for HD therapeutics.
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Affiliation(s)
- Tamara Ratovitski
- Division of Neurobiology, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.
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31
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Abstract
It has been more than 17 years since the causative mutation for Huntington's disease was discovered as the expansion of the triplet repeat in the N-terminal portion of the Huntingtin (HTT) gene. In the intervening time, researchers have discovered a great deal about Huntingtin's involvement in a number of cellular processes. However, the role of Huntingtin in the key pathogenic mechanism leading to neurodegeneration in the disease process has yet to be discovered. Here, we review the body of knowledge that has been uncovered since gene discovery and include discussions of the HTT gene, CAG triplet repeat expansion, HTT expression, protein features, posttranslational modifications, and many of its known protein functions and interactions. We also highlight potential pathogenic mechanisms that have come to light in recent years.
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Affiliation(s)
- Karen N McFarland
- Department of Neurology, University of Florida, Gainesville, FL 32610-0236, USA.
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32
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Jones L, Hughes A. Pathogenic mechanisms in Huntington's disease. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2011; 98:373-418. [PMID: 21907095 DOI: 10.1016/b978-0-12-381328-2.00015-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Huntington's disease (HD) is an autosomal dominant, progressive neurodegenerative disorder presenting in midlife. Multiple pathogenic mechanisms which hypothesise how the expanded CAG repeat causes manifest disease have been suggested since the mutation was first detected. These mechanisms include events that operate at both the gene and protein levels. It has been proposed that somatic instability of the CAG repeat could underlie the striatal-specific pathology observed in HD, although how this occurs and what consequences this has in the disease state remain unknown. The form in which the Htt protein exists within the cell has been extensively studied in terms of both its role in aggregate formation and its cellular processing. Protein-protein interactions, post-translational modifications and protein cleavage have all been suggested to contribute to HD pathogenesis. The potential downstream effects of the mutant Htt protein are also noted here. In particular, the adverse effect of the mutant Htt protein on cellular protein degradation, subcellular transport and transcription are explored, and its role in energy metabolism and excitotoxicity investigated. Elucidating the mechanisms at work in HD pathogenesis and determining when they occur in relation to disease is an important step in the pathway to therapeutic interventions.
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Affiliation(s)
- Lesley Jones
- MRC Centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, UK
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33
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Modulation of mutant huntingtin N-terminal cleavage and its effect on aggregation and cell death. Neurotox Res 2010; 20:120-33. [PMID: 21116768 PMCID: PMC3110280 DOI: 10.1007/s12640-010-9227-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2010] [Revised: 10/14/2010] [Accepted: 10/27/2010] [Indexed: 11/02/2022]
Abstract
Huntington's disease (HD) is a neurodegenerative disorder caused by a polyglutamine expansion near the N-terminus of huntingtin. A neuropathological hallmark of Huntington's disease is the presence of intracellular aggregates composed of mutant huntingtin N-terminal fragments in human postmortem brain, animal models, and cell culture models. It has been found that N-terminal fragments of the mutant huntingtin protein are more toxic than the full-length protein. Therefore, proteolytic processing of mutant huntingtin may play a key event in the pathogenesis of HD. Here, we present evidence that the region in huntingtin covering amino acids 116 to 125 is critical for N-terminal proteolytic processing. Within this region, we have identified mutations that either strongly reduce or enhance N-terminal cleavage. We took advantage of this effect and demonstrate that the mutation Δ121-122 within the putative cleavage region enhances N-terminal cleavage of huntingtin and the aggregation of N-terminal fragments. Furthermore, this particular deletion increased the activation of apoptotic processes and decreased neuronal cell viability. Our data indicate that the N-terminal proteolytic processing of mutant huntingtin can be modulated with an effect on aggregation and cell death rate.
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Baratchi S, Kanwar RK, Kanwar JR. Survivin: A target from brain cancer to neurodegenerative disease. Crit Rev Biochem Mol Biol 2010; 45:535-54. [DOI: 10.3109/10409238.2010.516740] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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35
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Miller JP, Holcomb J, Al-Ramahi I, de Haro M, Gafni J, Zhang N, Kim E, Sanhueza M, Torcassi C, Kwak S, Botas J, Hughes RE, Ellerby LM. Matrix metalloproteinases are modifiers of huntingtin proteolysis and toxicity in Huntington's disease. Neuron 2010; 67:199-212. [PMID: 20670829 DOI: 10.1016/j.neuron.2010.06.021] [Citation(s) in RCA: 129] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/15/2010] [Indexed: 01/27/2023]
Abstract
Proteolytic cleavage of huntingtin (Htt) is known to be a key event in the pathogenesis of Huntington's disease (HD). Our understanding of proteolytic processing of Htt has thus far focused on the protease families-caspases and calpains. Identifying critical proteases involved in Htt proteolysis and toxicity using an unbiased approach has not been reported. To accomplish this, we designed a high-throughput western blot-based screen to examine the generation of the smallest N-terminal polyglutamine-containing Htt fragment. We screened 514 siRNAs targeting the repertoire of human protease genes. This screen identified 11 proteases that, when inhibited, reduced Htt fragment accumulation. Three of these belonged to the matrix metalloproteinase (MMP) family. One family member, MMP-10, directly cleaves Htt and prevents cell death when knocked down in striatal Hdh(111Q/111Q) cells. Correspondingly, MMPs are activated in HD mouse models, and loss of function of Drosophila homologs of MMPs suppresses Htt-induced neuronal dysfunction in vivo.
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Affiliation(s)
- John P Miller
- Buck Institute for Age Research, Novato, CA 94945, USA
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36
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Zuccato C, Valenza M, Cattaneo E. Molecular Mechanisms and Potential Therapeutical Targets in Huntington's Disease. Physiol Rev 2010; 90:905-81. [DOI: 10.1152/physrev.00041.2009] [Citation(s) in RCA: 626] [Impact Index Per Article: 44.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the gene encoding for huntingtin protein. A lot has been learned about this disease since its first description in 1872 and the identification of its causative gene and mutation in 1993. We now know that the disease is characterized by several molecular and cellular abnormalities whose precise timing and relative roles in pathogenesis have yet to be understood. HD is triggered by the mutant protein, and both gain-of-function (of the mutant protein) and loss-of-function (of the normal protein) mechanisms are involved. Here we review the data that describe the emergence of the ancient huntingtin gene and of the polyglutamine trait during the last 800 million years of evolution. We focus on the known functions of wild-type huntingtin that are fundamental for the survival and functioning of the brain neurons that predominantly degenerate in HD. We summarize data indicating how the loss of these beneficial activities reduces the ability of these neurons to survive. We also review the different mechanisms by which the mutation in huntingtin causes toxicity. This may arise both from cell-autonomous processes and dysfunction of neuronal circuitries. We then focus on novel therapeutical targets and pathways and on the attractive option to counteract HD at its primary source, i.e., by blocking the production of the mutant protein. Strategies and technologies used to screen for candidate HD biomarkers and their potential application are presented. Furthermore, we discuss the opportunities offered by intracerebral cell transplantation and the likely need for these multiple routes into therapies to converge at some point as, ideally, one would wish to stop the disease process and, at the same time, possibly replace the damaged neurons.
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Affiliation(s)
- Chiara Zuccato
- Department of Pharmacological Sciences and Centre for Stem Cell Research, Università degli Studi di Milano, Milan, Italy
| | - Marta Valenza
- Department of Pharmacological Sciences and Centre for Stem Cell Research, Università degli Studi di Milano, Milan, Italy
| | - Elena Cattaneo
- Department of Pharmacological Sciences and Centre for Stem Cell Research, Università degli Studi di Milano, Milan, Italy
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Landles C, Sathasivam K, Weiss A, Woodman B, Moffitt H, Finkbeiner S, Sun B, Gafni J, Ellerby LM, Trottier Y, Richards WG, Osmand A, Paganetti P, Bates GP. Proteolysis of mutant huntingtin produces an exon 1 fragment that accumulates as an aggregated protein in neuronal nuclei in Huntington disease. J Biol Chem 2010; 285:8808-23. [PMID: 20086007 DOI: 10.1074/jbc.m109.075028] [Citation(s) in RCA: 241] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Huntingtin proteolysis has been implicated in the molecular pathogenesis of Huntington disease (HD). Despite an intense effort, the identity of the pathogenic smallest N-terminal fragment has not been determined. Using a panel of anti-huntingtin antibodies, we employed an unbiased approach to generate proteolytic cleavage maps of mutant and wild-type huntingtin in the HdhQ150 knock-in mouse model of HD. We identified 14 prominent N-terminal fragments, which, in addition to the full-length protein, can be readily detected in cytoplasmic but not nuclear fractions. These fragments were detected at all ages and are not a consequence of the pathogenic process. We demonstrated that the smallest fragment is an exon 1 huntingtin protein, known to contain a potent nuclear export signal. Prior to the onset of behavioral phenotypes, the exon 1 protein, and possibly other small fragments, accumulate in neuronal nuclei in the form of a detergent insoluble complex, visualized as diffuse granular nuclear staining in tissue sections. This methodology can be used to validate the inhibition of specific proteases as therapeutic targets for HD by pharmacological or genetic approaches.
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Affiliation(s)
- Christian Landles
- Department Medical and Molecular Genetics, King's College London School of Medicine, King's College London, London SE1 9RT, United Kingdom
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38
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Bredesen DE. Neurodegeneration in Alzheimer's disease: caspases and synaptic element interdependence. Mol Neurodegener 2009; 4:27. [PMID: 19558683 PMCID: PMC2709109 DOI: 10.1186/1750-1326-4-27] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Accepted: 06/26/2009] [Indexed: 11/10/2022] Open
Abstract
Extensive genetic, biochemical, and histological evidence has implicated the amyloid-β peptide (Aβ) in Alzheimer's disease pathogenesis, and several mechanisms have been suggested, such as metal binding, reactive oxygen species production, and membrane pore formation. However, recent evidence argues for an additional role for signaling mediated by the amyloid precursor protein, APP, in part via the caspase cleavage of APP at aspartate 664. Here we review the effects and implications of this cleavage event, and propose a model of Alzheimer's disease that focuses on the critical nature of this cleavage and its downstream effects.
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Affiliation(s)
- Dale E Bredesen
- Buck Institute for Age Research, 8001 Redwood Blvd,, Novato, CA USA 94945.
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39
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Ratovitski T, Gucek M, Jiang H, Chighladze E, Waldron E, D'Ambola J, Hou Z, Liang Y, Poirier MA, Hirschhorn RR, Graham R, Hayden MR, Cole RN, Ross CA. Mutant huntingtin N-terminal fragments of specific size mediate aggregation and toxicity in neuronal cells. J Biol Chem 2009; 284:10855-67. [PMID: 19204007 DOI: 10.1074/jbc.m804813200] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Huntingtin proteolysis is implicated in Huntington disease pathogenesis, yet, the nature of huntingtin toxic fragments remains unclear. Huntingtin undergoes proteolysis by calpains and caspases within an N-terminal region between amino acids 460 and 600. We have focused on proteolytic steps producing shorter N-terminal fragments, which we term cp-1 and cp-2 (distinct from previously described cp-A/cp-B). We used HEK293 cells to express the first 511 residues of huntingtin and further define the cp-1 and cp-2 cleavage sites. Based on epitope mapping with huntingtin-specific antibodies, we found that cp-1 cleavage occurs between residues 81 and 129 of huntingtin. Affinity and size exclusion chromatography were used to further purify huntingtin cleavage products and enrich for the cp-1/cp-2 fragments. Using mass spectrometry, we found that the cp-2 fragment is generated by cleavage of huntingtin at position Arg(167). This site was confirmed by deletion analysis and specific detection with a custom-generated cp-2 site neo-epitope antibody. Furthermore, alterations of this cleavage site resulted in a decrease in toxicity and an increase in aggregation of huntingtin in neuronal cells. These data suggest that cleavage of huntingtin at residue Arg(167) may mediate mutant huntingtin toxicity in Huntington disease.
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Affiliation(s)
- Tamara Ratovitski
- Division of Neurobiology, Department of Psychiatry, Mass Spectrometry and Proteomics Facility, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
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40
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Abstract
Huntington's disease (HD) is a devastating autosomal dominant neurodegenerative disease caused by a CAG trinucleotide repeat expansion encoding an abnormally long polyglutamine tract in the huntingtin protein. Much has been learnt since the mutation was identified in 1993. We review the functions of wild-type huntingtin. Mutant huntingtin may cause toxicity via a range of different mechanisms. The primary consequence of the mutation is to confer a toxic gain of function on the mutant protein and this may be modified by certain normal activities that are impaired by the mutation. It is likely that the toxicity of mutant huntingtin is revealed after a series of cleavage events leading to the production of N-terminal huntingtin fragment(s) containing the expanded polyglutamine tract. Although aggregation of the mutant protein is a hallmark of the disease, the role of aggregation is complex and the arguments for protective roles of inclusions are discussed. Mutant huntingtin may mediate some of its toxicity in the nucleus by perturbing specific transcriptional pathways. HD may also inhibit mitochondrial function and proteasome activity. Importantly, not all of the effects of mutant huntingtin may be cell-autonomous, and it is possible that abnormalities in neighbouring neurons and glia may also have an impact on connected cells. It is likely that there is still much to learn about mutant huntingtin toxicity, and important insights have already come and may still come from chemical and genetic screens. Importantly, basic biological studies in HD have led to numerous potential therapeutic strategies.
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41
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Bockamp E, Sprengel R, Eshkind L, Lehmann T, Braun JM, Emmrich F, Hengstler JG. Conditional transgenic mouse models: from the basics to genome-wide sets of knockouts and current studies of tissue regeneration. Regen Med 2008; 3:217-35. [DOI: 10.2217/17460751.3.2.217] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Many mouse models are currently available, providing avenues to elucidate gene function and to recapitulate specific pathological conditions. To a large extent, successful translation of clinical evidence or analytical data into appropriate mouse models is possible through progress in transgenic or gene-targeting technology. Beginning with a review of standard mouse transgenics and conventional gene targeting, this article will move on to discussing the basics of conditional gene expression: the tetracycline (tet)-off and tet-on systems based on the transactivators tet-controlled transactivator (Tta) and reverse tet-on transactivator (rtTA) that allow downregulation or induction of gene expression; Cre or Flp recombinase-mediated modifications, including excision, inversion, insertion and interchromosomal translocation; combination of the tet and Cre systems, permitting inducible knockout, reporter gene activation or activation of point mutations; the avian retroviral system based on delivery of rtTA specifically into cells expressing the avian retroviral receptor, which enables cell type-specific, inducible gene expression; the tamoxifen system, one of the most frequently applied steroid receptor-based systems, allows rapid activation of a fusion protein between the gene of interest and a mutant domain of the estrogen receptor, whereby activation does not depend on transcription; and techniques for cell type-specific ablation. The diphtheria toxin receptor system offers the advantage that it can be combined with the ‘zoo’ of Cre recombinase driver mice. Having described the basics we move on to the cutting edge: generation of genome-wide sets of conditional knockout mice. To this end, large ongoing projects apply two strategies: gene trapping based on random integration of trapping vectors into introns leading to truncation of the transcript, and gene targeting, representing the directed approach using homologous recombination. It can be expected that in the near future genome-wide sets of such mice will be available. Finally, the possibilities of conditional expression systems for investigating gene function in tissue regeneration will be illustrated by examples for neurodegenerative disease, liver regeneration and wound healing of the skin.
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Affiliation(s)
- Ernesto Bockamp
- Johannes Gutenberg-Universität Mainz, Institute of Toxicology/Mouse Genetics, Obere Zahlbacher Str. 67,55131, Mainz, Germany
| | - Rolf Sprengel
- Max Planck Institute for Medical Research, D-69120 Heidelber, Germany
| | - Leonid Eshkind
- Johannes Gutenberg-Universität Mainz, Institute of Toxicology/Mouse Genetics, Obere Zahlbacher Str. 67,55131, Mainz, Germany
| | - Thomas Lehmann
- TRM-Leipzig, Philipp-Rosenthal-Strasse 55, University of Leipzig, 04103 Leipzig, Germany
| | - Jan M Braun
- University of Leipzig, Institute of Clinical Immunology and Transfusion Medicine (IKIT), Germany
| | - Frank Emmrich
- University of Leipzig, Institute of Clinical Immunology and Transfusion Medicine (IKIT), Germany
| | - Jan G Hengstler
- Dortmund University of Technology, Leibniz Research Centre for Working Environment and Human Factors (IfADo), Institute of Legal Medicine and Rudolf-Boehm Institute of Pharmacology and Toxicology, University of Leipzig, Ardeystrasse 67, 44139 Dortmund, Germany
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Colomer Gould VF, Goti D, Pearce D, Gonzalez GA, Gao H, Bermudez de Leon M, Jenkins NA, Copeland NG, Ross CA, Brown DR. A mutant ataxin-3 fragment results from processing at a site N-terminal to amino acid 190 in brain of Machado-Joseph disease-like transgenic mice. Neurobiol Dis 2007; 27:362-9. [PMID: 17632007 PMCID: PMC2040168 DOI: 10.1016/j.nbd.2007.06.005] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2007] [Revised: 05/29/2007] [Accepted: 06/04/2007] [Indexed: 11/28/2022] Open
Abstract
Machado-Joseph disease also called spinocerebellar ataxia type 3 (MJD/SCA3) is a hereditary and neurodegenerative movement disorder caused by ataxin-3 with a polyglutamine expansion (mutant ataxin-3). Neuronal loss in MJD/SCA3 is associated with a mutant ataxin-3 toxic fragment. Defining mutant ataxin-3 proteolytic site(s) could facilitate the identification of the corresponding enzyme(s). Previously, we reported a mutant ataxin-3 mjd1a fragment in the brain of transgenic mice (Q71) that contained epitopes C-terminal to amino acid 220. In this study, we generated and characterized neuroblastoma cells and transgenic mice expressing mutant ataxin-3 mjd1a lacking amino acids 190-220 (deltaQ71). Less deltaQ71 than Q71 fragments were detected in the cell but not mouse model. The transgenic mice developed an MJD/SCA3-like phenotype and their brain homogenates had a fragment containing epitopes C-terminal to amino acid 220. Our results support the toxic fragment hypothesis and narrow the mutant ataxin-3 cleavage site to the N-terminus of amino acid 190.
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Affiliation(s)
- Veronica F Colomer Gould
- Department of Psychiatry, Johns Hopkins University School of Medicine, 600 N. Wolfe Street, Meyer Research Building, Room 4-158, Baltimore, MD 21287, USA.
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43
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Millecamps S, Gowing G, Corti O, Mallet J, Julien JP. Conditional NF-L transgene expression in mice for in vivo analysis of turnover and transport rate of neurofilaments. J Neurosci 2007; 27:4947-56. [PMID: 17475803 PMCID: PMC6672085 DOI: 10.1523/jneurosci.5299-06.2007] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
We generated mice with doxycycline control of a human neurofilament light (NF-L) transgene in the context of the absence (tTA;hNF-L;NF-L(-/-)) or presence (tTA;hNF-L;NF-L(+/-)) of endogenous mouse NF-L proteins. Doxycycline treatment caused the rapid disappearance of human NF-L (hNF-L) mRNA in tTA;hNF-L mice, but the hNF-L proteins remained with a half-life of 3 weeks in the brain. In the sciatic nerve, the disappearance of hNF-L proteins after doxycycline treatment occurred in synchrony along the sciatic nerve, suggesting a proteolysis of NF proteins along the entire axon. The presence of permanent NF network in tTA;hNF-L;NF-L(+/-) mice further stabilized and extended longevity of hNF-L proteins by several months. Surprisingly, after cessation of doxycycline treatment, there was no evidence of leading front of newly synthesized hNF-L proteins migrating into sciatic nerve axons devoid of NF structures. The hNF-L proteins detected at weekly intervals reappeared and accumulated in synchrony at similar rate along nerve segments, a phenomenon consistent with a fast hNF-L transport into axons. We estimated the hNF-L transport rate to be of approximately 10 mm/d in axons devoid of NF structures based on the use of an adenovirus encoding tet-responsive transcriptional activator to transactivate the hNF-L transgene in hypoglossal motor neurons. These results provide in vivo evidence that the stationary NF network in axons is a key determinant of half-life and transport rate of NF proteins.
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Affiliation(s)
- Stéphanie Millecamps
- Centre de Recherche du Centre Hospitalier de l'Université Laval, Department of Anatomy and Physiology of Laval University, Quebec, Canada G1V 4G2
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 7091, Université Pierre et Marie Curie-Paris 6, Hôpital de la Pitié-Salpêtrière, 75013 Paris, France, and
| | - Geneviève Gowing
- Centre de Recherche du Centre Hospitalier de l'Université Laval, Department of Anatomy and Physiology of Laval University, Quebec, Canada G1V 4G2
| | - Olga Corti
- Institut National de la Santé et de la Recherche Médicale U679, Hôpital de la Pitié-Salpêtrière, 75651 Paris, Cedex 13, France
| | - Jacques Mallet
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 7091, Université Pierre et Marie Curie-Paris 6, Hôpital de la Pitié-Salpêtrière, 75013 Paris, France, and
| | - Jean-Pierre Julien
- Centre de Recherche du Centre Hospitalier de l'Université Laval, Department of Anatomy and Physiology of Laval University, Quebec, Canada G1V 4G2
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44
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Schilling G, Klevytska A, Tebbenkamp ATN, Juenemann K, Cooper J, Gonzales V, Slunt H, Poirer M, Ross CA, Borchelt DR. Characterization of Huntingtin Pathologic Fragments in Human Huntington Disease, Transgenic Mice, and Cell Models. J Neuropathol Exp Neurol 2007; 66:313-20. [PMID: 17413322 DOI: 10.1097/nen.0b013e318040b2c8] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Huntington disease (HD) is caused by the expansion of a glutamine (Q) repeat near the N terminus of huntingtin (htt), resulting in altered conformation of the mutant protein to produce, most prominently in brain neurons, nuclear and cytoplasmic inclusion pathology. The inclusions and associated diffuse accumulation of mutant htt in nuclei are composed of N-terminal fragments of mutant protein. Here, we used a panel of peptide antibodies to characterize the htt protein pathologies in brain tissues from human HD, and a transgenic mouse model created by expressing the first 171 amino acids of human htt with 82Q (htt-N171-82Q). In tissues from both sources, htt pathologic features in nuclei were detected by antibodies to htt peptides 1-17 and 81-90 but not 115-129 (wild-type huntingtin numbering with 23 repeats). Human HEK 293 cells transfected with expression vectors that encode either the N-terminal 233 amino acids of human htt (htt-N233-82Q) or htt-N171-18Q accumulated smaller N-terminal fragments with antibody-binding characteristics identical to those of pathologic peptides. We conclude that the mutant htt peptides that accumulate in pathologic structures of human HD and httN171-82Q in mice are produced by similar, yet to be defined, proteolytic events in a region of the protein near or within amino acids 90-115.
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Affiliation(s)
- Gabriele Schilling
- Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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Li S, Li XJ. Multiple pathways contribute to the pathogenesis of Huntington disease. Mol Neurodegener 2006; 1:19. [PMID: 17173700 PMCID: PMC1764744 DOI: 10.1186/1750-1326-1-19] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2006] [Accepted: 12/16/2006] [Indexed: 01/24/2023] Open
Abstract
Huntington disease (HD) is caused by expansion of a polyglutamine (polyQ) domain in the protein known as huntingtin (htt), and the disease is characterized by selective neurodegeneration. Expansion of the polyQ domain is not exclusive to HD, but occurs in eight other inherited neurodegenerative disorders that show distinct neuropathology. Yet in spite of the clear genetic defects and associated neurodegeneration seen with all the polyQ diseases, their pathogenesis remains elusive. The present review focuses on HD, outlining the effects of mutant htt in the nucleus and neuronal processes as well as the role of cell-cell interactions in HD pathology. The widespread expression and localization of mutant htt and its interactions with a variety of proteins suggest that mutant htt engages multiple pathogenic pathways. Understanding these pathways will help us to elucidate the pathogenesis of HD and to target therapies effectively.
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Affiliation(s)
- Shihua Li
- Department of Human Genetics, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322, USA
| | - Xiao-Jiang Li
- Department of Human Genetics, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322, USA
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Rockabrand E, Slepko N, Pantalone A, Nukala VN, Kazantsev A, Marsh JL, Sullivan PG, Steffan JS, Sensi SL, Thompson LM. The first 17 amino acids of Huntingtin modulate its sub-cellular localization, aggregation and effects on calcium homeostasis. Hum Mol Genet 2006; 16:61-77. [PMID: 17135277 DOI: 10.1093/hmg/ddl440] [Citation(s) in RCA: 210] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A truncated form of the Huntington's disease (HD) protein that contains the polyglutamine repeat, Httex1p, causes HD-like phenotypes in multiple model organisms. Molecular signatures of pathogenesis appear to involve distinct domains within this polypeptide. We studied the contribution of each domain, singly or in combination, to sub-cellular localization, aggregation and intracellular Ca2+ ([Ca2+]i) dynamics in cells. We demonstrate that sub-cellular localization is most strongly influenced by the first 17 amino acids, with this sequence critically controlling Httex1p mitochondrial localization and also promoting association with the endoplasmic reticulum (ER) and Golgi. This domain also enhances the formation of visible aggregates and together with the expanded polyQ repeat acutely disrupts [Ca2+]i levels in glutamate-challenged PC12 cells. Isolated cortical mitochondria incubated with Httex1p resulted in uncoupling and depolarization of these organelles, further supporting the idea that Httex1p-dependent mitochondrial dysfunction could be instrumental in promoting acute Ca2+ dyshomeostasis. Interestingly, neither mitochondrial nor ER associations seem to be required to promote long-term [Ca2+]i dyshomeostasis.
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Affiliation(s)
- Erica Rockabrand
- Department of Psychiatry and Human Behavior, University of California, Gillespie 2121, Irvine, CA 92697, USA
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Gusella JF, MacDonald ME. Huntington's disease: seeing the pathogenic process through a genetic lens. Trends Biochem Sci 2006; 31:533-40. [PMID: 16829072 DOI: 10.1016/j.tibs.2006.06.009] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2006] [Revised: 06/05/2006] [Accepted: 06/27/2006] [Indexed: 02/03/2023]
Abstract
Thirteen years ago, the culmination of genetic rather than biochemical strategies resulted in the identification of the root cause of Huntington's disease: an expanded CAG trinucleotide repeat that leads to an elongated polyglutamine tract in the huntingtin protein. Since then, biochemical and cell biological attempts to elucidate pathogenesis have largely focused on N-terminal polyglutamine-containing huntingtin fragments. However, continued application of genetic strategies has suggested that the disease process is, in fact, triggered by the presence of expanded polyglutamine in intact huntingtin. An increased emphasis on the earliest presymptomatic stages of the disease, facilitated by incorporating genetic lessons from human patients into the search for biochemical targets, could provide a route to a rational treatment to prevent or slow the onset of this devastating neurodegenerative disorder.
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Affiliation(s)
- James F Gusella
- Molecular Neurogenetics Unit, Center for Human Genetic Research, Massachusetts General Hospital, Richard B. Simches Research Center, 185 Cambridge Street, Boston, MA 02114, USA.
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Schilling B, Gafni J, Torcassi C, Cong X, Row RH, LaFevre-Bernt MA, Cusack MP, Ratovitski T, Hirschhorn R, Ross CA, Gibson BW, Ellerby LM. Huntingtin phosphorylation sites mapped by mass spectrometry. Modulation of cleavage and toxicity. J Biol Chem 2006; 281:23686-97. [PMID: 16782707 DOI: 10.1074/jbc.m513507200] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Huntingtin (Htt) is a large protein of 3144 amino acids, whose function and regulation have not been well defined. Polyglutamine (polyQ) expansion in the N terminus of Htt causes the neurodegenerative disorder Huntington disease (HD). The cytotoxicity of mutant Htt is modulated by proteolytic cleavage with caspases and calpains generating N-terminal polyQ-containing fragments. We hypothesized that phosphorylation of Htt may modulate cleavage and cytotoxicity. In the present study, we have mapped the major phosphorylation sites of Htt using cell culture models (293T and PC12 cells) expressing full-length myc-tagged Htt constructs containing 23Q or 148Q repeats. Purified myc-tagged Htt was subjected to mass spectrometric analysis including matrix-assisted laser desorption/ionization mass spectrometry and nano-HPLC tandem mass spectrometry, used in conjunction with on-target alkaline phosphatase and protease digestions. We have identified more than six novel serine phosphorylation sites within Htt, one of which lies in the proteolytic susceptibility domain. Three of the sites have the consensus sequence for ERK1 phosphorylation, and addition of ERK1 inhibitor blocks phosphorylation at those sites. Other observed phosphorylation sites are possibly substrates for CDK5/CDC2 kinases. Mutation of amino acid Ser-536, which is located in the proteolytic susceptibility domain, to aspartic acid, inhibited calpain cleavage and reduced mutant Htt toxicity. The results presented here represent the first detailed mapping of the phosphorylation sites in full-length Htt. Dissection of phosphorylation modifications in Htt may provide clues to Huntington disease pathogenesis and targets for therapeutic development.
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Affiliation(s)
- Birgit Schilling
- The Buck Institute for Age Research, Novato, California 94945, USA
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