1
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Handley RR, Reid SJ, Burch Z, Jacobsen JC, Gillis T, Correia K, Rudiger SR, McLaughlin CJ, Bawden CS, MacDonald ME, Wheeler VC, Snell RG. Somatic CAG Repeat Stability in a Transgenic Sheep Model of Huntington's Disease. J Huntingtons Dis 2024; 13:33-40. [PMID: 38393920 DOI: 10.3233/jhd-231516] [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] [Indexed: 02/25/2024]
Abstract
Somatic instability of the huntingtin (HTT) CAG repeat mutation modifies age-at-onset of Huntington's disease (HD). Understanding the mechanism and pathogenic consequences of instability may reveal therapeutic targets. Using small-pool PCR we analyzed CAG instability in the OVT73 sheep model which expresses a full-length human cDNA HTT transgene. Analyses of five- and ten-year old sheep revealed the transgene (CAG)69 repeat was remarkably stable in liver, striatum, and other brain tissues. As OVT73 sheep at ten years old have minimal cell death and behavioral changes, our findings support instability of the HTT expanded-CAG repeat as being required for the progression of HD.
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Affiliation(s)
- Renee R Handley
- Centre for Brain Research, School of Biological Sciences, The University of Auckland, Auckland, New Zealand
| | - Suzanne J Reid
- Centre for Brain Research, School of Biological Sciences, The University of Auckland, Auckland, New Zealand
| | - Zoe Burch
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA
| | - Jessie C Jacobsen
- Centre for Brain Research, School of Biological Sciences, The University of Auckland, Auckland, New Zealand
| | - Tammy Gillis
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA
| | - Kevin Correia
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA
| | - Skye R Rudiger
- Molecular Biology and Reproductive Technology, Laboratories, South Australian Research and Development Institute, Adelaide, SA, Australia
| | - Clive J McLaughlin
- Molecular Biology and Reproductive Technology, Laboratories, South Australian Research and Development Institute, Adelaide, SA, Australia
| | - C Simon Bawden
- Molecular Biology and Reproductive Technology, Laboratories, South Australian Research and Development Institute, Adelaide, SA, Australia
| | - Marcy E MacDonald
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA
- Department of Neurology, Harvard Medical School, Boston, MA, USA
| | - Vanessa C Wheeler
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA
- Department of Neurology, Harvard Medical School, Boston, MA, USA
| | - Russell G Snell
- Centre for Brain Research, School of Biological Sciences, The University of Auckland, Auckland, New Zealand
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2
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Cho IK, Clever F, Hong G, Chan AWS. CAG Repeat Instability in the Peripheral and Central Nervous System of Transgenic Huntington’s Disease Monkeys. Biomedicines 2022; 10:biomedicines10081863. [PMID: 36009409 PMCID: PMC9405741 DOI: 10.3390/biomedicines10081863] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Revised: 07/16/2022] [Accepted: 07/22/2022] [Indexed: 11/24/2022] Open
Abstract
Huntington’s Disease (HD) is an autosomal dominant disease that results in severe neurodegeneration with no cure. HD is caused by the expanded CAG trinucleotide repeat (TNR) on the Huntingtin gene (HTT). Although the somatic and germline expansion of the CAG repeats has been well-documented, the underlying mechanisms had not been fully delineated. Increased CAG repeat length is associated with a more severe phenotype, greater TNR instability, and earlier age of onset. The direct relationship between CAG repeat length and molecular pathogenesis makes TNR instability a useful measure of symptom severity and tissue susceptibility. Thus, we examined the tissue-specific TNR instability of transgenic nonhuman primate models of Huntington’s disease. Our data show a similar profile of CAG repeat expansion in both rHD1 and rHD7, where high instability was observed in testis, liver, caudate, and putamen. CAG repeat expansion was observed in all tissue samples, and tissue- and CAG repeat size-dependent expansion was observed. Correlation analysis of CAG repeat expansion and the gene expression profile of four genes in different tissues, clusterin (CLU), transferrin (TF), ribosomal protein lateral stalk subunit P1 (RPLP1), and ribosomal protein L13a (RPL13A), showed a strong correlation with CAG repeat instability. Overall, our data, along with previously published studies, can be used for studying the biology of CAG repeat instability and identifying new therapeutic targets.
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Affiliation(s)
- In K. Cho
- Division of Neuropharmacology and Neurologic Diseases, Yerkes National Primate Research Center, Emory University, Atlanta, GA 30322, USA;
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA; (F.C.); (G.H.)
- Correspondence:
| | - Faye Clever
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA; (F.C.); (G.H.)
| | - Gordon Hong
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA; (F.C.); (G.H.)
| | - Anthony W. S. Chan
- Division of Neuropharmacology and Neurologic Diseases, Yerkes National Primate Research Center, Emory University, Atlanta, GA 30322, USA;
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA; (F.C.); (G.H.)
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3
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Arning L, Nguyen HP. Huntington disease update: new insights into the role of repeat instability in disease pathogenesis. MED GENET-BERLIN 2021; 33:293-300. [PMID: 38835439 PMCID: PMC11006308 DOI: 10.1515/medgen-2021-2101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 11/16/2021] [Indexed: 06/06/2024]
Abstract
The causative mutation for Huntington disease (HD), an expanded trinucleotide repeat sequence in the first exon of the huntingtin gene (HTT) is naturally polymorphic and inevitably associated with disease symptoms above 39 CAG repeats. Although symptomatic medical therapies for HD can improve the motor and non-motor symptoms for affected patients, these drugs do not stop the ongoing neurodegeneration and progression of the disease, which results in severe motor and cognitive disability and death. To date, there is still an urgent need for the development of effective disease-modifying therapies to slow or even stop the progression of HD. The increasing ability to intervene directly at the roots of the disease, namely HTT transcription and translation of its mRNA, makes it necessary to understand the pathogenesis of HD as precisely as possible. In addition to the long-postulated toxicity of the polyglutamine-expanded mutant HTT protein, there is increasing evidence that the CAG repeat-containing RNA might also be directly involved in toxicity. Recent studies have identified cis- (DNA repair genes) and trans- (loss/duplication of CAA interruption) acting variants as major modifiers of age at onset (AO) and disease progression. More and more extensive data indicate that somatic instability functions as a driver for AO as well as disease progression and severity, not only in HD but also in other polyglutamine diseases. Thus, somatic expansions of repetitive DNA sequences may be essential to promote respective repeat lengths to reach a threshold leading to the overt neurodegenerative symptoms of trinucleotide diseases. These findings support somatic expansion as a potential therapeutic target in HD and related repeat expansion disorders.
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Affiliation(s)
- Larissa Arning
- Department of Human Genetics, Medical Faculty, Ruhr-University Bochum, Bochum 44780, Germany
| | - Huu Phuc Nguyen
- Department of Human Genetics, Medical Faculty, Ruhr-University Bochum, Bochum 44780, Germany
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4
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Abstract
At fifteen different genomic locations, the expansion of a CAG/CTG repeat causes a neurodegenerative or neuromuscular disease, the most common being Huntington's disease and myotonic dystrophy type 1. These disorders are characterized by germline and somatic instability of the causative CAG/CTG repeat mutations. Repeat lengthening, or expansion, in the germline leads to an earlier age of onset or more severe symptoms in the next generation. In somatic cells, repeat expansion is thought to precipitate the rate of disease. The mechanisms underlying repeat instability are not well understood. Here we review the mammalian model systems that have been used to study CAG/CTG repeat instability, and the modifiers identified in these systems. Mouse models have demonstrated prominent roles for proteins in the mismatch repair pathway as critical drivers of CAG/CTG instability, which is also suggested by recent genome-wide association studies in humans. We draw attention to a network of connections between modifiers identified across several systems that might indicate pathway crosstalk in the context of repeat instability, and which could provide hypotheses for further validation or discovery. Overall, the data indicate that repeat dynamics might be modulated by altering the levels of DNA metabolic proteins, their regulation, their interaction with chromatin, or by direct perturbation of the repeat tract. Applying novel methodologies and technologies to this exciting area of research will be needed to gain deeper mechanistic insight that can be harnessed for therapies aimed at preventing repeat expansion or promoting repeat contraction.
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Affiliation(s)
- Vanessa C. Wheeler
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA,Department of Neurology, Harvard Medical School, Boston, MA, USA,Correspondence to: Vanessa C. Wheeler, Center for Genomic Medicine, Massachusetts Hospital, Boston MAA 02115, USA. E-mail: . and Vincent Dion, UK Dementia Research Institute at Cardiff University, Hadyn Ellis Building, Maindy Road, CF24 4HQ Cardiff, UK. E-mail:
| | - Vincent Dion
- UK Dementia Research Institute at Cardiff University, Hadyn Ellis Building, Maindy Road, Cardiff, UK,Correspondence to: Vanessa C. Wheeler, Center for Genomic Medicine, Massachusetts Hospital, Boston MAA 02115, USA. E-mail: . and Vincent Dion, UK Dementia Research Institute at Cardiff University, Hadyn Ellis Building, Maindy Road, CF24 4HQ Cardiff, UK. E-mail:
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5
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Morales F, Vásquez M, Corrales E, Vindas-Smith R, Santamaría-Ulloa C, Zhang B, Sirito M, Estecio MR, Krahe R, Monckton DG. Longitudinal increases in somatic mosaicism of the expanded CTG repeat in myotonic dystrophy type 1 are associated with variation in age-at-onset. Hum Mol Genet 2021; 29:2496-2507. [PMID: 32601694 DOI: 10.1093/hmg/ddaa123] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Revised: 04/13/2020] [Accepted: 06/16/2020] [Indexed: 12/26/2022] Open
Abstract
In myotonic dystrophy type 1 (DM1), somatic mosaicism of the (CTG)n repeat expansion is age-dependent, tissue-specific and expansion-biased. These features contribute toward variation in disease severity and confound genotype-to-phenotype analyses. To investigate how the (CTG)n repeat expansion changes over time, we collected three longitudinal blood DNA samples separated by 8-15 years and used small pool and single-molecule PCR in 43 DM1 patients. We used the lower boundary of the allele length distribution as the best estimate for the inherited progenitor allele length (ePAL), which is itself the best predictor of disease severity. Although in most patients the lower boundary of the allele length distribution was conserved over time, in many this estimate also increased with age, suggesting samples for research studies and clinical trials should be obtained as early as possible. As expected, the modal allele length increased over time, driven primarily by ePAL, age-at-sampling and the time interval. As expected, small expansions <100 repeats did not expand as rapidly as larger alleles. However, the rate of expansion of very large alleles was not obviously proportionally higher. This may, at least in part, be a result of the allele length-dependent increase in large contractions that we also observed. We also determined that individual-specific variation in the increase of modal allele length over time not accounted for by ePAL, age-at-sampling and time was inversely associated with individual-specific variation in age-at-onset not accounted for by ePAL, further highlighting somatic expansion as a therapeutic target in DM1.
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Affiliation(s)
- Fernando Morales
- Instituto de Investigaciones en Salud (INISA), Universidad de Costa Rica, San José, Costa Rica
| | - Melissa Vásquez
- Instituto de Investigaciones en Salud (INISA), Universidad de Costa Rica, San José, Costa Rica
| | - Eyleen Corrales
- Instituto de Investigaciones en Salud (INISA), Universidad de Costa Rica, San José, Costa Rica
| | - Rebeca Vindas-Smith
- Instituto de Investigaciones en Salud (INISA), Universidad de Costa Rica, San José, Costa Rica
| | | | - Baili Zhang
- Department of Genetics, University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Mario Sirito
- Department of Genetics, University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Marcos R Estecio
- Department of Epigenetics & Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Ralf Krahe
- Department of Genetics, University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Darren G Monckton
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
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6
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Mouro Pinto R, Arning L, Giordano JV, Razghandi P, Andrew MA, Gillis T, Correia K, Mysore JS, Grote Urtubey DM, Parwez CR, von Hein SM, Clark HB, Nguyen HP, Förster E, Beller A, Jayadaev S, Keene CD, Bird TD, Lucente D, Vonsattel JP, Orr H, Saft C, Petrasch-Parwez E, Wheeler VC. Patterns of CAG repeat instability in the central nervous system and periphery in Huntington's disease and in spinocerebellar ataxia type 1. Hum Mol Genet 2021; 29:2551-2567. [PMID: 32761094 PMCID: PMC7471505 DOI: 10.1093/hmg/ddaa139] [Citation(s) in RCA: 66] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 06/24/2020] [Accepted: 07/01/2020] [Indexed: 12/23/2022] Open
Abstract
The expanded HTT CAG repeat causing Huntington’s disease (HD) exhibits somatic expansion proposed to drive the rate of disease onset by eliciting a pathological process that ultimately claims vulnerable cells. To gain insight into somatic expansion in humans, we performed comprehensive quantitative analyses of CAG expansion in ~50 central nervous system (CNS) and peripheral postmortem tissues from seven adult-onset and one juvenile-onset HD individual. We also assessed ATXN1 CAG repeat expansion in brain regions of an individual with a neurologically and pathologically distinct repeat expansion disorder, spinocerebellar ataxia type 1 (SCA1). Our findings reveal similar profiles of tissue instability in all HD individuals, which, notably, were also apparent in the SCA1 individual. CAG expansion was observed in all tissues, but to different degrees, with multiple cortical regions and neostriatum tending to have the greatest instability in the CNS, and liver in the periphery. These patterns indicate different propensities for CAG expansion contributed by disease locus-independent trans-factors and demonstrate that expansion per se is not sufficient to cause cell type or disease-specific pathology. Rather, pathology may reflect distinct toxic processes triggered by different repeat lengths across cell types and diseases. We also find that the HTT CAG length-dependent expansion propensity of an individual is reflected in all tissues and in cerebrospinal fluid. Our data indicate that peripheral cells may be a useful source to measure CAG expansion in biomarker assays for therapeutic efforts, prompting efforts to dissect underlying mechanisms of expansion that may differ between the brain and periphery.
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Affiliation(s)
- Ricardo Mouro Pinto
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA.,Department of Neurology, Harvard Medical School, Boston, MA 02115, USA
| | - Larissa Arning
- Department of Human Genetics, Ruhr-University Bochum, Bochum 44780, Germany
| | - James V Giordano
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Pedram Razghandi
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Marissa A Andrew
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Tammy Gillis
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Kevin Correia
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Jayalakshmi S Mysore
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | | | - Constanze R Parwez
- Department of Neuroanatomy and Molecular Brain Research, Institute of Anatomy, Ruhr-University Bochum, Bochum 44780, Germany
| | - Sarah M von Hein
- Department of Neurology, Huntington Centre NRW, St. Josef-Hospital, Ruhr-University Bochum, Bochum 44791, Germany
| | - H Brent Clark
- Department of Laboratory Medicine and Pathology, Institute of Translational Neuroscience, University of Minnesota Medical School, Minneapolis, MN 55455, USA
| | - Huu Phuc Nguyen
- Department of Human Genetics, Ruhr-University Bochum, Bochum 44780, Germany
| | - Eckart Förster
- Department of Neuroanatomy and Molecular Brain Research, Institute of Anatomy, Ruhr-University Bochum, Bochum 44780, Germany
| | - Allison Beller
- Department of Pathology, University of Washington, Seattle, Washington 98195, USA
| | - Suman Jayadaev
- Department of Neurology, University of Washington, Seattle, Washington 98195, USA
| | - C Dirk Keene
- Department of Pathology, University of Washington, Seattle, Washington 98195, USA
| | - Thomas D Bird
- Department of Neurology, University of Washington, Seattle, Washington 98195, USA.,Department of Medicine, University of Washington, Seattle, Washington 98195, USA.,Geriatrics Research Education and Clinical Center, VA Puget Sound Medical Center, Seattle, WA 98108, USA
| | - Diane Lucente
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Jean-Paul Vonsattel
- Department of Pathology and Cell Biology, Columbia University Medical Center and the New York Presbyterian Hospital, New York, NY 10032, USA
| | - Harry Orr
- Department of Laboratory Medicine and Pathology, Institute of Translational Neuroscience, University of Minnesota Medical School, Minneapolis, MN 55455, USA
| | - Carsten Saft
- Department of Neurology, Huntington Centre NRW, St. Josef-Hospital, Ruhr-University Bochum, Bochum 44791, Germany
| | - Elisabeth Petrasch-Parwez
- Department of Neuroanatomy and Molecular Brain Research, Institute of Anatomy, Ruhr-University Bochum, Bochum 44780, Germany
| | - Vanessa C Wheeler
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA.,Department of Neurology, Harvard Medical School, Boston, MA 02115, USA
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7
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Kacher R, Lejeune FX, Noël S, Cazeneuve C, Brice A, Humbert S, Durr A. Propensity for somatic expansion increases over the course of life in Huntington disease. eLife 2021; 10:64674. [PMID: 33983118 PMCID: PMC8118653 DOI: 10.7554/elife.64674] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Accepted: 04/27/2021] [Indexed: 12/03/2022] Open
Abstract
Recent work on Huntington disease (HD) suggests that somatic instability of CAG repeat tracts, which can expand into the hundreds in neurons, explains clinical outcomes better than the length of the inherited allele. Here, we measured somatic expansion in blood samples collected from the same 50 HD mutation carriers over a twenty-year period, along with post-mortem tissue from 15 adults and 7 fetal mutation carriers, to examine somatic expansions at different stages of life. Post-mortem brains, as previously reported, had the greatest expansions, but fetal cortex had virtually none. Somatic instability in blood increased with age, despite blood cells being short-lived compared to neurons, and was driven mostly by CAG repeat length, then by age at sampling and by interaction between these two variables. Expansion rates were higher in symptomatic subjects. These data lend support to a previously proposed computational model of somatic instability-driven disease.
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Affiliation(s)
- Radhia Kacher
- Sorbonne Université, Paris Brain Institute (ICM Institut du Cerveau), AP-HP, INSERM, CNRS, University Hospital Pitié-Salpêtrière, Paris, France.,Univ. Grenoble Alpes, INSERM, U 1216, Grenoble Institut Neurosciences, Grenoble, France
| | - François-Xavier Lejeune
- Sorbonne Université, Paris Brain Institute (ICM Institut du Cerveau), AP-HP, INSERM, CNRS, University Hospital Pitié-Salpêtrière, Paris, France.,Paris Brain Institute's Data and Analysis Core, University Hospital Pitié-Salpêtrière, Paris, France
| | - Sandrine Noël
- Neurogenetics Laboratory, Department of Genetics, Assistance Publique-Hôpitaux de Paris, University Hospital Pitié-Salpêtrière, Paris, France
| | - Cécile Cazeneuve
- Neurogenetics Laboratory, Department of Genetics, Assistance Publique-Hôpitaux de Paris, University Hospital Pitié-Salpêtrière, Paris, France
| | - Alexis Brice
- Sorbonne Université, Paris Brain Institute (ICM Institut du Cerveau), AP-HP, INSERM, CNRS, University Hospital Pitié-Salpêtrière, Paris, France
| | - Sandrine Humbert
- Univ. Grenoble Alpes, INSERM, U 1216, Grenoble Institut Neurosciences, Grenoble, France
| | - Alexandra Durr
- Sorbonne Université, Paris Brain Institute (ICM Institut du Cerveau), AP-HP, INSERM, CNRS, University Hospital Pitié-Salpêtrière, Paris, France.,Neurogenetics Laboratory, Department of Genetics, Assistance Publique-Hôpitaux de Paris, University Hospital Pitié-Salpêtrière, Paris, France
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8
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Roy JCL, Vitalo A, Andrew MA, Mota-Silva E, Kovalenko M, Burch Z, Nhu AM, Cohen PE, Grabczyk E, Wheeler VC, Mouro Pinto R. Somatic CAG expansion in Huntington's disease is dependent on the MLH3 endonuclease domain, which can be excluded via splice redirection. Nucleic Acids Res 2021; 49:3907-3918. [PMID: 33751106 PMCID: PMC8053082 DOI: 10.1093/nar/gkab152] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 02/19/2021] [Accepted: 02/23/2021] [Indexed: 11/18/2022] Open
Abstract
Somatic expansion of the CAG repeat tract that causes Huntington's disease (HD) is thought to contribute to the rate of disease pathogenesis. Therefore, factors influencing repeat expansion are potential therapeutic targets. Genes in the DNA mismatch repair pathway are critical drivers of somatic expansion in HD mouse models. Here, we have tested, using genetic and pharmacological approaches, the role of the endonuclease domain of the mismatch repair protein MLH3 in somatic CAG expansion in HD mice and patient cells. A point mutation in the MLH3 endonuclease domain completely eliminated CAG expansion in the brain and peripheral tissues of a HD knock-in mouse model (HttQ111). To test whether the MLH3 endonuclease could be manipulated pharmacologically, we delivered splice switching oligonucleotides in mice to redirect Mlh3 splicing to exclude the endonuclease domain. Splice redirection to an isoform lacking the endonuclease domain was associated with reduced CAG expansion. Finally, CAG expansion in HD patient-derived primary fibroblasts was also significantly reduced by redirecting MLH3 splicing to the endogenous endonuclease domain-lacking isoform. These data indicate the potential of targeting the MLH3 endonuclease domain to slow somatic CAG repeat expansion in HD, a therapeutic strategy that may be applicable across multiple repeat expansion disorders.
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Affiliation(s)
- Jennie C L Roy
- Department of Genetics, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA
| | - Antonia Vitalo
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA.,Department of Neurology, Harvard Medical School, Boston, MA 02115, USA
| | - Marissa A Andrew
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Eduarda Mota-Silva
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Marina Kovalenko
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Zoe Burch
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Anh M Nhu
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Paula E Cohen
- Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA.,Center for Reproductive Genomics, Cornell University, Ithaca, NY 14853, USA
| | - Ed Grabczyk
- Department of Genetics, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA
| | - Vanessa C Wheeler
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA.,Department of Neurology, Harvard Medical School, Boston, MA 02115, USA
| | - Ricardo Mouro Pinto
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114, USA.,Department of Neurology, Harvard Medical School, Boston, MA 02115, USA.,Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA
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9
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Abstract
DNA mismatch repair (MMR) is a highly conserved genome stabilizing pathway that corrects DNA replication errors, limits chromosomal rearrangements, and mediates the cellular response to many types of DNA damage. Counterintuitively, MMR is also involved in the generation of mutations, as evidenced by its role in causing somatic triplet repeat expansion in Huntington’s disease (HD) and other neurodegenerative disorders. In this review, we discuss the current state of mechanistic knowledge of MMR and review the roles of key enzymes in this pathway. We also present the evidence for mutagenic function of MMR in CAG repeat expansion and consider mechanistic hypotheses that have been proposed. Understanding the role of MMR in CAG expansion may shed light on potential avenues for therapeutic intervention in HD.
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Affiliation(s)
- Ravi R Iyer
- CHDI Management/CHDI Foundation, Princeton, NJ, USA
| | - Anna Pluciennik
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, PA, USA
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10
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Ciosi M, Cumming SA, Chatzi A, Larson E, Tottey W, Lomeikaite V, Hamilton G, Wheeler VC, Pinto RM, Kwak S, Morton AJ, Monckton DG. Approaches to Sequence the HTT CAG Repeat Expansion and Quantify Repeat Length Variation. J Huntingtons Dis 2021; 10:53-74. [PMID: 33579864 PMCID: PMC7990409 DOI: 10.3233/jhd-200433] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Background: Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder caused by the expansion of the HTT CAG repeat. Affected individuals inherit ≥36 repeats and longer alleles cause earlier onset, greater disease severity and faster disease progression. The HTT CAG repeat is genetically unstable in the soma in a process that preferentially generates somatic expansions, the proportion of which is associated with disease onset, severity and progression. Somatic mosaicism of the HTT CAG repeat has traditionally been assessed by semi-quantitative PCR-electrophoresis approaches that have limitations (e.g., no information about sequence variants). Genotyping-by-sequencing could allow for some of these limitations to be overcome. Objective: To investigate the utility of PCR sequencing to genotype large (>50 CAGs) HD alleles and to quantify the associated somatic mosaicism. Methods: We have applied MiSeq and PacBio sequencing to PCR products of the HTT CAG repeat in transgenic R6/2 mice carrying ∼55, ∼110, ∼255 and ∼470 CAGs. For each of these alleles, we compared the repeat length distributions generated for different tissues at two ages. Results: We were able to sequence the CAG repeat full length in all samples. However, the repeat length distributions for samples with ∼470 CAGs were biased towards shorter repeat lengths. Conclusion: PCR sequencing can be used to sequence all the HD alleles considered, but this approach cannot be used to estimate modal allele size or quantify somatic expansions for alleles ⪢250 CAGs. We review the limitations of PCR sequencing and alternative approaches that may allow the quantification of somatic contractions and very large somatic expansions.
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Affiliation(s)
- Marc Ciosi
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Sarah A Cumming
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Afroditi Chatzi
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Eloise Larson
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - William Tottey
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Vilija Lomeikaite
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Graham Hamilton
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK.,Glasgow Polyomics, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Vanessa C Wheeler
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA.,Department of Neurology, Harvard Medical School, Boston, MA, USA
| | - Ricardo Mouro Pinto
- Molecular Neurogenetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA.,Department of Neurology, Harvard Medical School, Boston, MA, USA
| | - Seung Kwak
- CHDI Management/CHDI Foundation, Princeton, NJ, USA
| | - A Jennifer Morton
- Department of Physiology, Development and Neuroscience, University of Cambridge, Tennis Court Road, Cambridge, UK
| | - Darren G Monckton
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
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11
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Donaldson J, Powell S, Rickards N, Holmans P, Jones L. What is the Pathogenic CAG Expansion Length in Huntington's Disease? J Huntingtons Dis 2021; 10:175-202. [PMID: 33579866 PMCID: PMC7990448 DOI: 10.3233/jhd-200445] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Huntington's disease (HD) (OMIM 143100) is caused by an expanded CAG repeat tract in the HTT gene. The inherited CAG length is known to expand further in somatic and germline cells in HD subjects. Age at onset of the disease is inversely correlated with the inherited CAG length, but is further modulated by a series of genetic modifiers which are most likely to act on the CAG repeat in HTT that permit it to further expand. Longer repeats are more prone to expansions, and this expansion is age dependent and tissue-specific. Given that the inherited tract expands through life and most subjects develop disease in mid-life, this implies that in cells that degenerate, the CAG length is likely to be longer than the inherited length. These findings suggest two thresholds- the inherited CAG length which permits further expansion, and the intracellular pathogenic threshold, above which cells become dysfunctional and die. This two-step mechanism has been previously proposed and modelled mathematically to give an intracellular pathogenic threshold at a tract length of 115 CAG (95% confidence intervals 70- 165 CAG). Empirically, the intracellular pathogenic threshold is difficult to determine. Clues from studies of people and models of HD, and from other diseases caused by expanded repeat tracts, place this threshold between 60- 100 CAG, most likely towards the upper part of that range. We assess this evidence and discuss how the intracellular pathogenic threshold in manifest disease might be better determined. Knowing the cellular pathogenic threshold would be informative for both understanding the mechanism in HD and deploying treatments.
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Affiliation(s)
- Jasmine Donaldson
- MRC Centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, Cardiff, UK
| | - Sophie Powell
- MRC Centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, Cardiff, UK
| | - Nadia Rickards
- MRC Centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, Cardiff, UK
| | - Peter Holmans
- MRC Centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, Cardiff, UK
| | - Lesley Jones
- MRC Centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, Cardiff, UK
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12
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Kovalenko M, Erdin S, Andrew MA, St Claire J, Shaughnessey M, Hubert L, Neto JL, Stortchevoi A, Fass DM, Mouro Pinto R, Haggarty SJ, Wilson JH, Talkowski ME, Wheeler VC. Histone deacetylase knockouts modify transcription, CAG instability and nuclear pathology in Huntington disease mice. eLife 2020; 9:55911. [PMID: 32990597 PMCID: PMC7581428 DOI: 10.7554/elife.55911] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 09/28/2020] [Indexed: 12/13/2022] Open
Abstract
Somatic expansion of the Huntington’s disease (HD) CAG repeat drives the rate of a pathogenic process ultimately resulting in neuronal cell death. Although mechanisms of toxicity are poorly delineated, transcriptional dysregulation is a likely contributor. To identify modifiers that act at the level of CAG expansion and/or downstream pathogenic processes, we tested the impact of genetic knockout, in HttQ111 mice, of Hdac2 or Hdac3 in medium-spiny striatal neurons that exhibit extensive CAG expansion and exquisite disease vulnerability. Both knockouts moderately attenuated CAG expansion, with Hdac2 knockout decreasing nuclear huntingtin pathology. Hdac2 knockout resulted in a substantial transcriptional response that included modification of transcriptional dysregulation elicited by the HttQ111 allele, likely via mechanisms unrelated to instability suppression. Our results identify novel modifiers of different aspects of HD pathogenesis in medium-spiny neurons and highlight a complex relationship between the expanded Htt allele and Hdac2 with implications for targeting transcriptional dysregulation in HD.
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Affiliation(s)
- Marina Kovalenko
- Center for Genomic Medicine, Harvard Medical School, Boston, United States
| | - Serkan Erdin
- Center for Genomic Medicine, Harvard Medical School, Boston, United States.,Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, United States
| | - Marissa A Andrew
- Center for Genomic Medicine, Harvard Medical School, Boston, United States
| | - Jason St Claire
- Center for Genomic Medicine, Harvard Medical School, Boston, United States
| | | | - Leroy Hubert
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, United States
| | - João Luís Neto
- Center for Genomic Medicine, Harvard Medical School, Boston, United States
| | - Alexei Stortchevoi
- Center for Genomic Medicine, Harvard Medical School, Boston, United States
| | - Daniel M Fass
- Center for Genomic Medicine, Harvard Medical School, Boston, United States
| | - Ricardo Mouro Pinto
- Center for Genomic Medicine, Harvard Medical School, Boston, United States.,Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, United States
| | - Stephen J Haggarty
- Center for Genomic Medicine, Harvard Medical School, Boston, United States.,Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, United States
| | - John H Wilson
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, United States
| | - Michael E Talkowski
- Center for Genomic Medicine, Harvard Medical School, Boston, United States.,Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, United States.,Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, United States
| | - Vanessa C Wheeler
- Center for Genomic Medicine, Harvard Medical School, Boston, United States.,Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, United States
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13
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Zhang H, Li D, Zhao X, Pan S, Wu X, Peng S, Huang H, Shi R, Tan Z. Relatively semi-conservative replication and a folded slippage model for short tandem repeats. BMC Genomics 2020; 21:563. [PMID: 32807079 PMCID: PMC7430839 DOI: 10.1186/s12864-020-06949-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2020] [Accepted: 07/27/2020] [Indexed: 12/11/2022] Open
Abstract
Background The ubiquitous presence of short tandem repeats (STRs) in virtually all genomes implicates their functional relevance, while a widely-accepted definition of STR is yet to be established. Previous studies majorly focus on relatively longer STRs, while shorter repeats were generally excluded. Herein, we have adopted a more generous criteria to define shorter repeats, which has led to the definition of a much larger number of STRs that lack prior analysis. Using this definition, we analyzed the short repeats in 55 randomly selected segments in 55 randomly selected genomic sequences from a fairly wide range of species covering animals, plants, fungi, protozoa, bacteria, archaea and viruses. Results Our analysis reveals a high percentage of short repeats in all 55 randomly selected segments, indicating that the universal presence of high-content short repeats could be a common characteristic of genomes across all biological kingdoms. Therefore, it is reasonable to assume a mechanism for continuous production of repeats that can make the replicating process relatively semi-conservative. We have proposed a folded replication slippage model that considers the geometric space of nucleotides and hydrogen bond stability to explain the mechanism more explicitly, with improving the existing straight-line slippage model. The folded slippage model can explain the expansion and contraction of mono- to hexa- nucleotide repeats with proper folding angles. Analysis of external forces in the folding template strands also suggests that expansion exists more commonly than contraction in the short tandem repeats. Conclusion The folded replication slippage model provides a reasonable explanation for the continuous occurrences of simple sequence repeats in genomes. This model also contributes to the explanation of STR-to-genome evolution and is an alternative model that complements semi-conservative replication.
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Affiliation(s)
- Hongxi Zhang
- Bioinformatics Center, College of Biology, Hunan University, Changsha, 410082, China
| | - Douyue Li
- Bioinformatics Center, College of Biology, Hunan University, Changsha, 410082, China
| | - Xiangyan Zhao
- Bioinformatics Center, College of Biology, Hunan University, Changsha, 410082, China
| | - Saichao Pan
- Bioinformatics Center, College of Biology, Hunan University, Changsha, 410082, China
| | - Xiaolong Wu
- Bioinformatics Center, College of Biology, Hunan University, Changsha, 410082, China
| | - Shan Peng
- Bioinformatics Center, College of Biology, Hunan University, Changsha, 410082, China
| | - Hanrou Huang
- Bioinformatics Center, College of Biology, Hunan University, Changsha, 410082, China
| | - Ruixue Shi
- Bioinformatics Center, College of Biology, Hunan University, Changsha, 410082, China
| | - Zhongyang Tan
- Bioinformatics Center, College of Biology, Hunan University, Changsha, 410082, China.
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14
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Nakamori M, Panigrahi GB, Lanni S, Gall-Duncan T, Hayakawa H, Tanaka H, Luo J, Otabe T, Li J, Sakata A, Caron MC, Joshi N, Prasolava T, Chiang K, Masson JY, Wold MS, Wang X, Lee MYWT, Huddleston J, Munson KM, Davidson S, Layeghifard M, Edward LM, Gallon R, Santibanez-Koref M, Murata A, Takahashi MP, Eichler EE, Shlien A, Nakatani K, Mochizuki H, Pearson CE. A slipped-CAG DNA-binding small molecule induces trinucleotide-repeat contractions in vivo. Nat Genet 2020; 52:146-159. [PMID: 32060489 PMCID: PMC7043212 DOI: 10.1038/s41588-019-0575-8] [Citation(s) in RCA: 88] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2018] [Accepted: 12/19/2019] [Indexed: 01/07/2023]
Abstract
In many repeat diseases, such as Huntington's disease (HD), ongoing repeat expansions in affected tissues contribute to disease onset, progression and severity. Inducing contractions of expanded repeats by exogenous agents is not yet possible. Traditional approaches would target proteins driving repeat mutations. Here we report a compound, naphthyridine-azaquinolone (NA), that specifically binds slipped-CAG DNA intermediates of expansion mutations, a previously unsuspected target. NA efficiently induces repeat contractions in HD patient cells as well as en masse contractions in medium spiny neurons of HD mouse striatum. Contractions are specific for the expanded allele, independently of DNA replication, require transcription across the coding CTG strand and arise by blocking repair of CAG slip-outs. NA-induced contractions depend on active expansions driven by MutSβ. NA injections in HD mouse striatum reduce mutant HTT protein aggregates, a biomarker of HD pathogenesis and severity. Repeat-structure-specific DNA ligands are a novel avenue to contract expanded repeats.
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Affiliation(s)
- Masayuki Nakamori
- Department of Neurology, Osaka University Graduate School of Medicine, Osaka, Japan
| | - Gagan B Panigrahi
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
| | - Stella Lanni
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
| | - Terence Gall-Duncan
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Hideki Hayakawa
- Department of Neurology, Osaka University Graduate School of Medicine, Osaka, Japan
| | - Hana Tanaka
- Department of Neurology, Osaka University Graduate School of Medicine, Osaka, Japan
| | - Jennifer Luo
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Takahiro Otabe
- Department of Regulatory Bioorganic Chemistry, The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan
| | - Jinxing Li
- Department of Regulatory Bioorganic Chemistry, The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan
| | - Akihiro Sakata
- Department of Regulatory Bioorganic Chemistry, The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan
| | - Marie-Christine Caron
- Genome Stability Laboratory, CHU de Québec Research Center, HDQ Pavilion, Oncology Division, Quebec, Quebec, Canada
- Department of Molecular Biology, Medical Biochemistry and Pathology, Laval University Cancer Research Center, Quebec, Quebec, Canada
| | - Niraj Joshi
- Genome Stability Laboratory, CHU de Québec Research Center, HDQ Pavilion, Oncology Division, Quebec, Quebec, Canada
- Department of Molecular Biology, Medical Biochemistry and Pathology, Laval University Cancer Research Center, Quebec, Quebec, Canada
| | - Tanya Prasolava
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
| | - Karen Chiang
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Jean-Yves Masson
- Genome Stability Laboratory, CHU de Québec Research Center, HDQ Pavilion, Oncology Division, Quebec, Quebec, Canada
- Department of Molecular Biology, Medical Biochemistry and Pathology, Laval University Cancer Research Center, Quebec, Quebec, Canada
| | - Marc S Wold
- Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Xiaoxiao Wang
- Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY, USA
| | - Marietta Y W T Lee
- Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY, USA
| | - John Huddleston
- Department of Genome Sciences, University of Washington, Seattle, WA, USA
- Howard Hughes Medical Institute, University of Washington, Seattle, WA, USA
| | - Katherine M Munson
- Department of Genome Sciences, University of Washington, Seattle, WA, USA
| | - Scott Davidson
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
| | - Mehdi Layeghifard
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
| | - Lisa-Monique Edward
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
| | - Richard Gallon
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | | | - Asako Murata
- Department of Regulatory Bioorganic Chemistry, The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan
| | - Masanori P Takahashi
- Department of Neurology, Osaka University Graduate School of Medicine, Osaka, Japan
| | - Evan E Eichler
- Department of Genome Sciences, University of Washington, Seattle, WA, USA
- Howard Hughes Medical Institute, University of Washington, Seattle, WA, USA
| | - Adam Shlien
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada
| | - Kazuhiko Nakatani
- Department of Regulatory Bioorganic Chemistry, The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan
| | - Hideki Mochizuki
- Department of Neurology, Osaka University Graduate School of Medicine, Osaka, Japan
| | - Christopher E Pearson
- Program of Genetics & Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada.
- Program of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada.
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15
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Kielar C, Morton AJ. Early Neurodegeneration in R6/2 Mice Carrying the Huntington's Disease Mutation with a Super-Expanded CAG Repeat, Despite Normal Lifespan. J Huntingtons Dis 2019; 7:61-76. [PMID: 29480204 DOI: 10.3233/jhd-170265] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The threshold of CAG repeat expansion in the HTT gene that causes HD is 36 CAG repeats, although 'superlong' expansions are found in individual neurons in postmortem brains. Previously, we showed that, compared to mice with <250 CAG repeats, onset of disease in R6/2 mice carrying superlong (>440) CAG repeat expansions was delayed, and disease progression was slower. Inclusion pathology also differed from 250 CAG repeat mice, being dominated by a novel kind of extranuclear neuronal inclusion (nENNI) that resembles a class of aggregate seen in patients with the adult onset form of HD. Here, we characterised neuropathology in R6/2 mice with >400 CAG repeats using light and electron microscopy. nENNIs were found with increased frequency and wider distribution with age. Some nENNIs appear to 'mature' as the disease develops, developing a multi-layered cored structure. Mice with superlong CAG repeats do not develop clinical signs until they are around 30-40 weeks of age, and they attain a normal life span (>2 years). Nevertheless, they show brain atrophy and unequivocal neuron loss from the striatum and cortex by 22 weeks of age, an age at which similar pathology is seen in 250 CAG repeat mice. Since this time-point is 'end stage' for a 250 CAG mouse, but very far (at least 18 months) from end stage for a > 440 CAG repeat mouse, our data confirm that the appearance of clinical signs, the formation of inclusions, and neurodegeneration are processes that progress independently. A better understanding of the relationship between CAG repeat length, neurodegenerative pathways, and clinical behavioural signs is essential, if we are to find strategies to delay or reverse the course of this disease.
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Affiliation(s)
- Catherine Kielar
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK
| | - A Jennifer Morton
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK
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16
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Analysis of mutational dynamics at the DMPK (CTG)n locus identifies saliva as a suitable DNA sample source for genetic analysis in myotonic dystrophy type 1. PLoS One 2019; 14:e0216407. [PMID: 31048891 PMCID: PMC6497304 DOI: 10.1371/journal.pone.0216407] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Accepted: 04/21/2019] [Indexed: 12/12/2022] Open
Abstract
Genotype-to-phenotype correlation studies in myotonic dystrophy type 1 (DM1) have been confounded by the age-dependent, tissue-specific and expansion-biased features of somatic mosaicism of the expanded CTG repeat. Previously, we showed that by controlling for the confounding effects of somatic instability to estimate the progenitor allele CTG length in blood DNA, age at onset correlations could be significantly improved. To determine the suitability of saliva DNA as a source for genotyping, we used small pool-PCR to perform a detailed quantitative study of the somatic mutational dynamics of the CTG repeat in saliva and blood DNA from 40 DM1 patients. Notably, the modal allele length in saliva was only moderately higher in saliva and not as large as previously observed in most other tissues. The lower boundary of the allele distribution was also slightly higher in saliva than it was in blood DNA. However, the progenitor allele length estimated in blood explained more of the variation in age at onset than that estimated from saliva. Interestingly, although the modal allele length was slightly higher in saliva, the overall degree of somatic variation was typically lower than in blood DNA, revealing new insights into the tissue-specific dynamics of somatic mosaicism. These data indicate that saliva constitutes an accessible, non-invasive and suitable DNA sample source for performing genetic studies in DM1.
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17
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mHTT Seeding Activity: A Marker of Disease Progression and Neurotoxicity in Models of Huntington's Disease. Mol Cell 2019; 71:675-688.e6. [PMID: 30193095 DOI: 10.1016/j.molcel.2018.07.032] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Revised: 11/10/2017] [Accepted: 07/24/2018] [Indexed: 02/04/2023]
Abstract
Self-propagating, amyloidogenic mutant huntingtin (mHTT) aggregates may drive progression of Huntington's disease (HD). Here, we report the development of a FRET-based mHTT aggregate seeding (FRASE) assay that enables the quantification of mHTT seeding activity (HSA) in complex biosamples from HD patients and disease models. Application of the FRASE assay revealed HSA in brain homogenates of presymptomatic HD transgenic and knockin mice and its progressive increase with phenotypic changes, suggesting that HSA quantitatively tracks disease progression. Biochemical investigations of mouse brain homogenates demonstrated that small, rather than large, mHTT structures are responsible for the HSA measured in FRASE assays. Finally, we assessed the neurotoxicity of mHTT seeds in an inducible Drosophila model transgenic for HTTex1. We found a strong correlation between the HSA measured in adult neurons and the increased mortality of transgenic HD flies, indicating that FRASE assays detect disease-relevant, neurotoxic, mHTT structures with severe phenotypic consequences in vivo.
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18
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Neueder A, Bates GP. RNA Related Pathology in Huntington's Disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1049:85-101. [PMID: 29427099 DOI: 10.1007/978-3-319-71779-1_4] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
This chapter summarises research investigating the expression of huntingtin sense and anti-sense transcripts, the effect of the mutation on huntingtin processing as well as the more global effect of the mutation on the coding and non-coding transcriptomes. The huntingtin gene is ubiquitously expressed, although expression levels vary between tissues and cell types. A SNP that affects NF-ĸB binding in the huntingtin promoter modulates the expression level of huntingtin transcripts and is associated with the age of disease onset. Incomplete splicing between exon 1 and exon 2 has been shown to result in the expression of a small polyadenylated mRNA that encodes the highly pathogenic exon 1 huntingtin protein. This occurs in a CAG-repeat length dependent manner in all full-length mouse models of HD as well as HD patient post-mortem brains and fibroblasts. An antisense transcript to huntingtin is generated that contains a CUG repeat that is expanded in HD patients. In myotonic dystrophy, expanded CUG repeats form RNA foci in cell nuclei that bind specific proteins (e.g. MBL1). Short, pure CAG RNAs of approximately 21 nucleotides that have been processed by DICER can inhibit the translation of other CAG repeat containing mRNAs. The HD mutation affects the transcriptome at the level of mRNA expression, splicing and the expression of non-coding RNAs. Finally, expanded repetitive stretched of nucleotides can lead to RAN translation, in which the ribosome translates from the expanded repeat in all possible reading frames, producing proteins with various poly-amino acid tracts. The extent to which these events contribute to HD pathogenesis is largely unknown.
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Affiliation(s)
- Andreas Neueder
- Sobell Department of Motor Neuroscience, UCL Institute of Neurology, Queen Square, London, WC1N 3BG, UK
| | - Gillian P Bates
- Sobell Department of Motor Neuroscience, UCL Institute of Neurology, Queen Square, London, WC1N 3BG, UK.
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19
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Polyzos AA, Wood NI, Williams P, Wipf P, Morton AJ, McMurray CT. XJB-5-131-mediated improvement in physiology and behaviour of the R6/2 mouse model of Huntington's disease is age- and sex- dependent. PLoS One 2018; 13:e0194580. [PMID: 29630611 PMCID: PMC5890981 DOI: 10.1371/journal.pone.0194580] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 03/06/2018] [Indexed: 11/18/2022] Open
Abstract
We have reported that the radical scavenger XJB-5-131 attenuates or reverses progression of the disease phenotype in the HdhQ(150/150) mouse, a slow onset model of HD. Here, we tested whether XJB-5-131 has beneficial effects in R6/2 mice, a severe early onset model of HD. We found that XJB-5-131 has beneficial effects in R6/2 mice, by delaying features of the motor and histological phenotype. The impact was sex-dependent, with a stronger effect in male mice. XJB-5-131 treatment improved some locomotor deficits in female R6/2 mice, but the effects were, in general, greater in male mice. Chronic treatment of male R6/2 mice with XJB-5-1-131 reduced weight loss, and improved the motor and temperature regulation deficits, especially in male mice. Treatment with XJB-5-131 had no effect on the lifespan of R6/2 mice. Nevertheless, it significantly slowed somatic expansion at 90 days, and reduced the density of inclusions. Our data show that while treatment with XJB-5-131 had complex effects on the phenotype of R6/2 mice, it produced a number of significant improvements in this severe model of HD.
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Affiliation(s)
- Aris A. Polyzos
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States of America
| | - Nigel I. Wood
- Department of Physiology, Development, and Neuroscience, Anatomy Building, University of Cambridge, Cambridge, United Kingdom
| | - Paul Williams
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States of America
| | - Peter Wipf
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - A. Jennifer Morton
- Department of Physiology, Development, and Neuroscience, Anatomy Building, University of Cambridge, Cambridge, United Kingdom
| | - Cynthia T. McMurray
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States of America
- * E-mail:
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20
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Abstract
Huntington's disease (HD) is caused by a CAG repeat expansion in the HTT gene. Repeat length can change over time, both in individual cells and between generations, and longer repeats may drive pathology. Cellular DNA repair systems have long been implicated in CAG repeat instability but recent genetic evidence from humans linking DNA repair variants to HD onset and progression has reignited interest in this area. The DNA damage response plays an essential role in maintaining genome stability, but may also license repeat expansions in the context of HD. In this chapter we summarize the methods developed to assay CAG repeat expansion/contraction in vitro and in cells, and review the DNA repair genes tested in mouse models of HD. While none of these systems is currently ideal, new technologies, such as long-read DNA sequencing, should improve the sensitivity of assays to assess the effects of DNA repair pathways in HD. Improved assays will be essential precursors to high-throughput testing of small molecules that can alter specific steps in DNA repair pathways and perhaps ameliorate expansion or enhance contraction of the HTT CAG repeat.
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21
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Geraerts FCA, Snell RG, Faull RLM, Williams L, Jacobsen JC, Reid SJ. Comparison of Huntington's disease CAG Repeat Length Stability in Human Motor Cortex and Cingulate Gyrus. J Huntingtons Dis 2017; 5:297-301. [PMID: 27716680 DOI: 10.3233/jhd-160203] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Huntington's disease is caused by expansion of the CAG repeat in Huntingtin. This repeat has shown tissue-specific instability in mouse models and in a small number of post-mortem human samples. We used small-pool PCR to generate a modified instability index to quantify CAG instability within two brain regions from six human samples where cell loss has been associated with motor and mood symptoms: the motor cortex and cingulate gyrus. The expanded allele demonstrated instability in both regions, with minimal instability in the unexpanded allele. Region-specific differences were not observed, suggesting symptomatology may not be determined by repeat length instability.
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Affiliation(s)
- Fiona C A Geraerts
- School of Biological Sciences, Centre for Brain Research, Faculty of Science, The University of Auckland, Auckland, New Zealand
| | - Russell G Snell
- School of Biological Sciences, Centre for Brain Research, Faculty of Science, The University of Auckland, Auckland, New Zealand
| | - Richard L M Faull
- Department of Anatomy and Medical Imaging, Centre for Brain Research, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand
| | - Liam Williams
- School of Biological Sciences, Centre for Brain Research, Faculty of Science, The University of Auckland, Auckland, New Zealand
| | - Jessie C Jacobsen
- School of Biological Sciences, Centre for Brain Research, Faculty of Science, The University of Auckland, Auckland, New Zealand
| | - Suzanne J Reid
- School of Biological Sciences, Centre for Brain Research, Faculty of Science, The University of Auckland, Auckland, New Zealand
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22
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Ophthalmic features of spinocerebellar ataxia type 7. Eye (Lond) 2017; 32:120-127. [PMID: 28799562 DOI: 10.1038/eye.2017.135] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Accepted: 05/31/2017] [Indexed: 01/27/2023] Open
Abstract
PurposeTo analyze the relation between ophthalmologic and motor changes in spinocerebellar ataxia type 7 (SCA7).Patients and methodsThis was a case series study. Sixteen SCA7 patients underwent a comprehensive ophthalmic examination, including ocular extrinsic motility testing, color vision test, and optical coherence tomography of the optic nerve and macula. Changes in the corneal endothelium, electroretinographic patterns, and a complete neurologic evaluation using the Scale for the Assessment and Rating of Ataxia (SARA) were evaluated. Correlations of endothelial cell density (ECD) with number of CAG repetitions and the SARA scores were estimated.ResultsAll patients showed various degrees of visual impairment mainly due to macular deterioration. Notably, they also presented decreased ECD. Pairwise correlations of ECD with number of CAG repeats and severity of motor symptoms quantified with the SARA scores were inverse (r=-0.46, P=0.083 and r=-0.64, P=0.009, respectively). Further analyses indicated an average ECD decrease of 48 cells/mm2 (P=0.006) per unit of change on the number of CAG repeats, and of 75 cells/mm2 (P=0.001) per unit of change on the SARA scores.ConclusionsThe results agree with previous ophthalmological findings regarding the widespread effect of SCA7 mutation on the patient's visual system. However, the results also show a significant negative correlation of decreased ECD with both CAG repetitions and SARA scores. This suggests that motor systems could degenerate in parallel with visual systems, although more research is needed to determine whether the degeneration is caused by the same mechanisms.
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A selective inhibitor of histone deacetylase 3 prevents cognitive deficits and suppresses striatal CAG repeat expansions in Huntington's disease mice. Sci Rep 2017; 7:6082. [PMID: 28729730 PMCID: PMC5519595 DOI: 10.1038/s41598-017-05125-2] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 05/24/2017] [Indexed: 12/03/2022] Open
Abstract
Huntington’s disease (HD) is a neurodegenerative disorder whose major symptoms include progressive motor and cognitive dysfunction. Cognitive decline is a critical quality of life concern for HD patients and families. The enzyme histone deacetylase 3 (HDAC3) appears to be important in HD pathology by negatively regulating genes involved in cognitive functions. Furthermore, HDAC3 has been implicated in the aberrant transcriptional patterns that help cause disease symptoms in HD mice. HDAC3 also helps fuel CAG repeat expansions in human cells, suggesting that HDAC3 may power striatal expansions in the HTT gene thought to drive disease progression. This multifaceted role suggests that early HDAC3 inhibition offers an attractive mechanism to prevent HD cognitive decline and to suppress striatal expansions. This hypothesis was investigated by treating HdhQ111 knock-in mice with the HDAC3-selective inhibitor RGFP966. Chronic early treatment prevented long-term memory impairments and normalized specific memory-related gene expression in hippocampus. Additionally, RGFP966 prevented corticostriatal-dependent motor learning deficits, significantly suppressed striatal CAG repeat expansions, partially rescued striatal protein marker expression and reduced accumulation of mutant huntingtin oligomeric forms. These novel results highlight RGFP966 as an appealing multiple-benefit therapy in HD that concurrently prevents cognitive decline and suppresses striatal CAG repeat expansions.
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Neueder A, Landles C, Ghosh R, Howland D, Myers RH, Faull RLM, Tabrizi SJ, Bates GP. The pathogenic exon 1 HTT protein is produced by incomplete splicing in Huntington's disease patients. Sci Rep 2017; 7:1307. [PMID: 28465506 PMCID: PMC5431000 DOI: 10.1038/s41598-017-01510-z] [Citation(s) in RCA: 121] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Accepted: 03/29/2017] [Indexed: 12/17/2022] Open
Abstract
We have previously shown that exon 1 of the huntingtin gene does not always splice to exon 2 resulting in the production of a small polyadenylated mRNA (HTTexon1) that encodes the highly pathogenic exon 1 HTT protein. The level of this read-through product is proportional to CAG repeat length and is present in all knock-in mouse models of Huntington's disease (HD) with CAG lengths of 50 and above and in the YAC128 and BACHD mouse models, both of which express a copy of the human HTT gene. We have now developed specific protocols for the quantitative analysis of the transcript levels of HTTexon1 in human tissue and applied these to a series of fibroblast lines and post-mortem brain samples from individuals with either adult-onset or juvenile-onset HD. We found that the HTTexon1 mRNA is present in fibroblasts from juvenile HD patients and can also be readily detected in the sensory motor cortex, hippocampus and cerebellum of post-mortem brains from HD individuals, particularly in those with early onset disease. This finding will have important implications for strategies to lower mutant HTT levels in patients and the design of future therapeutics.
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Affiliation(s)
- Andreas Neueder
- UCL Huntington's Disease Centre, Sobell Department of Motor Neuroscience, UCL Institute of Neurology, University College London, London, United Kingdom
| | - Christian Landles
- UCL Huntington's Disease Centre, Sobell Department of Motor Neuroscience, UCL Institute of Neurology, University College London, London, United Kingdom
| | - Rhia Ghosh
- UCL Huntington's Disease Centre, Department of Neurodegenerative Disease, Institute of Neurology, University College London, London, United Kingdom
| | - David Howland
- CHDI Management Inc./CHDI Foundation Inc., Los Angeles, California, United States of America
| | - Richard H Myers
- Department of Neurology, Boston University School of Medicine, Boston, United States of America
| | - Richard L M Faull
- Department of Anatomy with Radiology and Center for Brain Research, Faculty of Medicine and Health Sciences, University of Auckland, Auckland, New Zealand
| | - Sarah J Tabrizi
- UCL Huntington's Disease Centre, Department of Neurodegenerative Disease, Institute of Neurology, University College London, London, United Kingdom
| | - Gillian P Bates
- UCL Huntington's Disease Centre, Sobell Department of Motor Neuroscience, UCL Institute of Neurology, University College London, London, United Kingdom.
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Kour S, Rath PC. Long noncoding RNAs in aging and age-related diseases. Ageing Res Rev 2016; 26:1-21. [PMID: 26655093 DOI: 10.1016/j.arr.2015.12.001] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Revised: 11/08/2015] [Accepted: 12/01/2015] [Indexed: 12/14/2022]
Abstract
Aging is the universal, intrinsic, genetically-controlled, evolutionarily-conserved and time-dependent intricate biological process characterised by the cumulative decline in the physiological functions and their coordination in an organism after the attainment of adulthood resulting in the imbalance of neurological, immunological and metabolic functions of the body. Various biological processes and mechanisms along with altered levels of mRNAs and proteins have been reported to be involved in the progression of aging. It is one of the major risk factors in the patho-physiology of various diseases and disorders. Recently, the discovery of pervasive transcription of a vast pool of heterogeneous regulatory noncoding RNAs (ncRNAs), including small ncRNAs (sncRNAs) and long ncRNAs (lncRNAs), in the mammalian genome have provided an alternative way to study and explore the missing links in the aging process, its mechanism(s) and related diseases in a whole new dimension. The involvement of small noncoding RNAs in aging and age-related diseases have been extensively studied and recently reviewed. However, lncRNAs, whose function is far less explored in relation to aging, have emerged as a class of major regulators of genomic functions. Here, we have described some examples of known as well as novel lncRNAs that have been implicated in the progression of the aging process and age-related diseases. This may further stimulate research on noncoding RNAs and the aging process.
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Affiliation(s)
- Sukhleen Kour
- Molecular Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Pramod C Rath
- Molecular Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India.
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