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Kurokawa R, Kurokawa M, Mitsutake A, Nakaya M, Baba A, Nakata Y, Moritani T, Abe O. Clinical and neuroimaging review of triplet repeat diseases. Jpn J Radiol 2023; 41:115-130. [PMID: 36169768 PMCID: PMC9889482 DOI: 10.1007/s11604-022-01343-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Accepted: 09/18/2022] [Indexed: 02/04/2023]
Abstract
Triplet repeat diseases (TRDs) refer to a group of diseases caused by three nucleotide repeats elongated beyond a pathologic threshold. TRDs are divided into the following four groups depending on the pathomechanisms, although the pathomechanisms of several diseases remain unelucidated: polyglutamine disorders, caused by a pathologic repeat expansion of CAG (coding the amino acid glutamine) located within the exon; loss-of-function repeat disorders, characterized by the common feature of a loss of function of the gene within which they occur; RNA gain-of-function disorders, involving the production of a toxic RNA species; and polyalanine disorders, caused by a pathologic repeat expansion of GCN (coding the amino acid alanine) located within the exon. Many of these TRDs manifest through neurologic symptoms; moreover, neuroimaging, especially brain magnetic resonance imaging, plays a pivotal role in the detection of abnormalities, differentiation, and management of TRDs. In this article, we reviewed the clinical and neuroimaging features of TRDs. An early diagnosis of TRDs through clinical and imaging approaches is important and may contribute to appropriate medical intervention for patients and their families.
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Affiliation(s)
- Ryo Kurokawa
- Department of Radiology, Graduate School of Medicine, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8655 Japan ,Division of Neuroradiology, Department of Radiology, University of Michigan, 1500 E Medical Center Dr, Ann Arbor, MI 48109 USA
| | - Mariko Kurokawa
- Department of Radiology, Graduate School of Medicine, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8655 Japan ,Division of Neuroradiology, Department of Radiology, University of Michigan, 1500 E Medical Center Dr, Ann Arbor, MI 48109 USA
| | - Akihiko Mitsutake
- Department of Neurology, International University of Health and Welfare, Mita Hospital, 1-4-3 Mita, Minato-ku, Tokyo, 108-8329 Japan
| | - Moto Nakaya
- Department of Radiology, Graduate School of Medicine, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8655 Japan
| | - Akira Baba
- Division of Neuroradiology, Department of Radiology, University of Michigan, 1500 E Medical Center Dr, Ann Arbor, MI 48109 USA
| | - Yasuhiro Nakata
- Department of Neuroradiology, Tokyo Metropolitan Neurological Hospital, 2-6-1 Musashidai, Fuchu, Tokyo 183-0042 Japan
| | - Toshio Moritani
- Division of Neuroradiology, Department of Radiology, University of Michigan, 1500 E Medical Center Dr, Ann Arbor, MI 48109 USA
| | - Osamu Abe
- Department of Radiology, Graduate School of Medicine, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8655 Japan
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2
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Nieuwenhuis S, Widomska J, Blom P, ‘t Hoen PBAC, van Engelen BGM, Glennon JC. Blood Transcriptome Profiling Links Immunity to Disease Severity in Myotonic Dystrophy Type 1 (DM1). Int J Mol Sci 2022; 23:3081. [PMID: 35328504 PMCID: PMC8954763 DOI: 10.3390/ijms23063081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 02/01/2022] [Accepted: 03/03/2022] [Indexed: 02/01/2023] Open
Abstract
The blood transcriptome was examined in relation to disease severity in type I myotonic dystrophy (DM1) patients who participated in the Observational Prolonged Trial In DM1 to Improve QoL- Standards (OPTIMISTIC) study. This sought to (a) ascertain if transcriptome changes were associated with increasing disease severity, as measured by the muscle impairment rating scale (MIRS), and (b) establish if these changes in mRNA expression and associated biological pathways were also observed in the Dystrophia Myotonica Biomarker Discovery Initiative (DMBDI) microarray dataset in blood (with equivalent MIRS/DMPK repeat length). The changes in gene expression were compared using a number of complementary pathways, gene ontology and upstream regulator analyses, which suggested that symptom severity in DM1 was linked to transcriptomic alterations in innate and adaptive immunity associated with muscle-wasting. Future studies should explore the role of immunity in DM1 in more detail to assess its relevance to DM1.
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Affiliation(s)
- Sylvia Nieuwenhuis
- Center for Molecular and Biomolecular Informatics (CMBI), Radboud Institute for Molecular Life Sciences, Radboud University Medical Centre, 6500 HB Nijmegen, The Netherlands; (S.N.); (P.-B.A.C.‘t.H.)
- Department of Cognitive Neuroscience, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Centre, 6525 EN Nijmegen, The Netherlands;
| | - Joanna Widomska
- Department of Cognitive Neuroscience, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Centre, 6525 EN Nijmegen, The Netherlands;
| | - Paul Blom
- VDL Enabling Technologies Group B.V., 5651 GH Eindhoven, The Netherlands;
| | - Peter-Bram A. C. ‘t Hoen
- Center for Molecular and Biomolecular Informatics (CMBI), Radboud Institute for Molecular Life Sciences, Radboud University Medical Centre, 6500 HB Nijmegen, The Netherlands; (S.N.); (P.-B.A.C.‘t.H.)
| | - Baziel G. M. van Engelen
- Department of Neurology, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Centre, 6500 HB Nijmegen, The Netherlands;
| | - Jeffrey C. Glennon
- Department of Cognitive Neuroscience, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Centre, 6525 EN Nijmegen, The Netherlands;
- Conway Institute of Biomolecular and Biomedical Research, School of Medicine, University College Dublin, D04 V1W8 Dublin, Ireland
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3
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Nakamori M, Mochizuki H. Targeting Expanded Repeats by Small Molecules in Repeat Expansion Disorders. Mov Disord 2020; 36:298-305. [DOI: 10.1002/mds.28397] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 10/20/2020] [Accepted: 10/26/2020] [Indexed: 12/14/2022] Open
Affiliation(s)
- Masayuki Nakamori
- Department of Neurology Osaka University Graduate School of Medicine Osaka Japan
| | - Hideki Mochizuki
- Department of Neurology Osaka University Graduate School of Medicine Osaka Japan
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4
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Nieuwenhuis S, Okkersen K, Widomska J, Blom P, 't Hoen PAC, van Engelen B, Glennon JC. Insulin Signaling as a Key Moderator in Myotonic Dystrophy Type 1. Front Neurol 2019; 10:1229. [PMID: 31849810 PMCID: PMC6901991 DOI: 10.3389/fneur.2019.01229] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Accepted: 11/05/2019] [Indexed: 12/15/2022] Open
Abstract
Myotonic dystrophy type 1 (DM1) is an autosomal dominant genetic disease characterized by multi-system involvement. Affected organ system includes skeletal muscle, heart, gastro-intestinal system and the brain. In this review, we evaluate the evidence for alterations in insulin signaling and their relation to clinical DM1 features. We start by summarizing the molecular pathophysiology of DM1. Next, an overview of normal insulin signaling physiology is given, and evidence for alterations herein in DM1 is presented. Clinically, evidence for involvement of insulin signaling pathways in DM1 is based on the increased incidence of insulin resistance seen in clinical practice and recent trial evidence of beneficial effects of metformin on muscle function. Indirectly, further support may be derived from certain CNS derived symptoms characteristic of DM1, such as obsessive-compulsive behavior features, for which links with altered insulin signaling has been demonstrated in other diseases. At the basic scientific level, several pathophysiological mechanisms that operate in DM1 may compromise normal insulin signaling physiology. The evidence presented here reflects the importance of insulin signaling in relation to clinical features of DM1 and justifies further basic scientific and clinical, therapeutically oriented research.
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Affiliation(s)
- Sylvia Nieuwenhuis
- Department of Cognitive Neuroscience, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, Netherlands
| | - Kees Okkersen
- Department of Neurology, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, Netherlands
| | - Joanna Widomska
- Department of Cognitive Neuroscience, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, Netherlands
| | - Paul Blom
- VDL Enabling Technologies Group B.V., Eindhoven, Netherlands
| | - Peter A C 't Hoen
- Centre for Molecular and Biomolecular Informatics, Radboud Institute for Molecular Life Sciences, Radboud University Medical Centre, Nijmegen, Netherlands
| | - Baziel van Engelen
- Department of Neurology, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, Netherlands
| | - Jeffrey C Glennon
- Department of Cognitive Neuroscience, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, Netherlands
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Casa V, Runfola V, Micheloni S, Aziz A, Dilworth FJ, Gabellini D. Polycomb repressive complex 1 provides a molecular explanation for repeat copy number dependency in FSHD muscular dystrophy. Hum Mol Genet 2017; 26:753-767. [PMID: 28040729 PMCID: PMC5409123 DOI: 10.1093/hmg/ddw426] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Accepted: 12/15/2016] [Indexed: 11/13/2022] Open
Abstract
Repression of repetitive elements is crucial to preserve genome integrity and has been traditionally ascribed to constitutive heterochromatin pathways. FacioScapuloHumeral Muscular Dystrophy (FSHD), one of the most common myopathies, is characterized by a complex interplay of genetic and epigenetic events. The main FSHD form is linked to a reduced copy number of the D4Z4 macrosatellite repeat on 4q35, causing loss of silencing and aberrant expression of the D4Z4-embedded DUX4 gene leading to disease. By an unknown mechanism, D4Z4 copy-number correlates with FSHD phenotype. Here we show that the DUX4 proximal promoter (DUX4p) is sufficient to nucleate the enrichment of both constitutive and facultative heterochromatin components and to mediate a copy-number dependent gene silencing. We found that both the CpG/GC dense DNA content and the repetitive nature of DUX4p arrays are important for their repressive ability. We showed that DUX4p mediates a copy number-dependent Polycomb Repressive Complex 1 (PRC1) recruitment, which is responsible for the copy-number dependent gene repression. Overall, we directly link genetic and epigenetic defects in FSHD by proposing a novel molecular explanation for the copy number-dependency in FSHD pathogenesis, and offer insight into the molecular functions of repeats in chromatin regulation.
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Affiliation(s)
- Valentina Casa
- Gene Expression and Muscular Dystrophy Unit, Division of Regenerative Medicine, IRCCS San Raffaele Scientific Institute, Milan 20132, Italy.,Università Vita-Salute San Raffaele, Milan 20132, Italy
| | - Valeria Runfola
- Gene Expression and Muscular Dystrophy Unit, Division of Regenerative Medicine, IRCCS San Raffaele Scientific Institute, Milan 20132, Italy
| | - Stefano Micheloni
- Gene Expression and Muscular Dystrophy Unit, Division of Regenerative Medicine, IRCCS San Raffaele Scientific Institute, Milan 20132, Italy
| | - Arif Aziz
- The Sprott Center for Stem Cell Research, Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON K1Y 4E9, Canada
| | - F Jeffrey Dilworth
- The Sprott Center for Stem Cell Research, Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON K1Y 4E9, Canada
| | - Davide Gabellini
- Gene Expression and Muscular Dystrophy Unit, Division of Regenerative Medicine, IRCCS San Raffaele Scientific Institute, Milan 20132, Italy.,Dulbecco Telethon Institute, Milan 20132, Italy
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6
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Ueki J, Nakamori M, Nakamura M, Nishikawa M, Yoshida Y, Tanaka A, Morizane A, Kamon M, Araki T, Takahashi MP, Watanabe A, Inagaki N, Sakurai H. Myotonic dystrophy type 1 patient-derived iPSCs for the investigation of CTG repeat instability. Sci Rep 2017; 7:42522. [PMID: 28211918 PMCID: PMC5304155 DOI: 10.1038/srep42522] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Accepted: 01/09/2017] [Indexed: 02/08/2023] Open
Abstract
Myotonic dystrophy type 1 (DM1) is an autosomal-dominant multi-system disease caused by expanded CTG repeats in dystrophia myotonica protein kinase (DMPK). The expanded CTG repeats are unstable and can increase the length of the gene with age, which worsens the symptoms. In order to establish a human stem cell system suitable for the investigation of repeat instability, DM1 patient-derived iPSCs were generated and differentiated into three cell types commonly affected in DM1, namely cardiomyocytes, neurons and myocytes. Then we precisely analysed the CTG repeat lengths in these cells. Our DM1-iPSCs showed a gradual lengthening of CTG repeats with unchanged repeat distribution in all cell lines depending on the passage numbers of undifferentiated cells. However, the average CTG repeat length did not change significantly after differentiation into different somatic cell types. We also evaluated the chromatin accessibility in DM1-iPSCs using ATAC-seq. The chromatin status in DM1 cardiomyocytes was closed at the DMPK locus as well as at SIX5 and its promoter region, whereas it was open in control, suggesting that the epigenetic modifications may be related to the CTG repeat expansion in DM1. These findings may help clarify the role of repeat instability in the CTG repeat expansion in DM1.
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Affiliation(s)
- Junko Ueki
- Center for iPS Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.,Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, 54 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Masayuki Nakamori
- Department of Neurology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Masahiro Nakamura
- Center for iPS Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Misato Nishikawa
- Center for iPS Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Yoshinori Yoshida
- Center for iPS Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Azusa Tanaka
- Center for iPS Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Asuka Morizane
- Center for iPS Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Masayoshi Kamon
- Department of Peripheral Nervous System Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-Higashi, Kodaira, Tokyo 187-8502, Japan
| | - Toshiyuki Araki
- Department of Peripheral Nervous System Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-Higashi, Kodaira, Tokyo 187-8502, Japan
| | - Masanori P Takahashi
- Department of Neurology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.,Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, 1-7 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Akira Watanabe
- Center for iPS Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Nobuya Inagaki
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, 54 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Hidetoshi Sakurai
- Center for iPS Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
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7
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Essebier A, Vera Wolf P, Cao MD, Carroll BJ, Balasubramanian S, Bodén M. Statistical Enrichment of Epigenetic States Around Triplet Repeats that Can Undergo Expansions. Front Neurosci 2016; 10:92. [PMID: 27013954 PMCID: PMC4782033 DOI: 10.3389/fnins.2016.00092] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Accepted: 02/23/2016] [Indexed: 12/18/2022] Open
Abstract
More than 30 human genetic diseases are linked to tri-nucleotide repeat expansions. There is no known mechanism that explains repeat expansions in full, but changes in the epigenetic state of the associated locus has been implicated in the disease pathology for a growing number of examples. A comprehensive comparative analysis of the genomic features associated with diverse repeat expansions has been lacking. Here, in an effort to decipher the propensity of repeats to undergo expansion and result in a disease state, we determine the genomic coordinates of tri-nucleotide repeat tracts at base pair resolution and computationally establish epigenetic profiles around them. Using three complementary statistical tests, we reveal that several epigenetic states are enriched around repeats that are associated with disease, even in cells that do not harbor expansion, relative to a carefully stratified background. Analysis of over one hundred cell types reveals that epigenetic states generally tend to vary widely between genic regions and cell types. However, there is qualified consistency in the epigenetic signatures of repeats associated with disease suggesting that changes to the chromatin and the DNA around an expanding repeat locus are likely to be similar. These epigenetic signatures may be exploited further to develop models that could explain the propensity of repeats to undergo expansions.
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Affiliation(s)
- Alexandra Essebier
- School of Chemistry and Molecular Biosciences, The University of Queensland St Lucia, QLD, Australia
| | - Patricia Vera Wolf
- School of Chemistry and Molecular Biosciences, The University of Queensland St Lucia, QLD, Australia
| | - Minh Duc Cao
- School of Chemistry and Molecular Biosciences, The University of Queensland St Lucia, QLD, Australia
| | - Bernard J Carroll
- School of Chemistry and Molecular Biosciences, The University of Queensland St Lucia, QLD, Australia
| | | | - Mikael Bodén
- School of Chemistry and Molecular Biosciences, The University of Queensland St Lucia, QLD, Australia
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8
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Nakamori M, Taylor K, Mochizuki H, Sobczak K, Takahashi MP. Oral administration of erythromycin decreases RNA toxicity in myotonic dystrophy. Ann Clin Transl Neurol 2015; 3:42-54. [PMID: 26783549 PMCID: PMC4704483 DOI: 10.1002/acn3.271] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Accepted: 11/04/2015] [Indexed: 11/08/2022] Open
Abstract
OBJECTIVE Myotonic dystrophy type 1 (DM1) is caused by the expansion of a CTG repeat in the 3' untranslated region of DMPK. The transcripts containing an expanded CUG repeat (CUG (exp)) result in a toxic gain-of-function by forming ribonuclear foci that sequester the alternative splicing factor muscleblind-like 1 (MBNL1). Although several small molecules reportedly ameliorate RNA toxicity, none are ready for clinical use because of the lack of safety data. Here, we undertook a drug-repositioning screen to identify a safe and effective small molecule for upcoming clinical trials of DM1. METHODS We examined the potency of small molecules in inhibiting the interaction between CUG (exp) and MBNL1 by in vitro sequestration and fluorescent titration assays. We studied the effect of lead compounds in DM1 model cells by evaluating foci reduction and splicing rescue. We also tested their effects on missplicing and myotonia in DM1 model mice. RESULTS Of the 20 FDA-approved small molecules tested, erythromycin showed the highest affinity to CUG (exp) and a capacity to inhibit its binding to MBNL1. Erythromycin decreased foci formation and rescued missplicing in DM1 cell models. Both systemic and oral administration of erythromycin in the DM1 model mice showed splicing reversal and improvement of myotonia with no toxicity. Long-term oral administration of erythromycin at the dose used in humans also improved the splicing abnormality in the DM1 model mice. INTERPRETATION Oral erythromycin treatment, which has been widely used in humans with excellent tolerability, may be a promising therapy for DM1.
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Affiliation(s)
- Masayuki Nakamori
- Department of Neurology Osaka University Graduate School of Medicine Osaka Japan
| | - Katarzyna Taylor
- Department of Gene Expression Institute of Molecular Biology and Biotechnology Adam Mickiewicz University Posnan Poland
| | - Hideki Mochizuki
- Department of Neurology Osaka University Graduate School of Medicine Osaka Japan
| | - Krzysztof Sobczak
- Department of Gene Expression Institute of Molecular Biology and Biotechnology Adam Mickiewicz University Posnan Poland
| | - Masanori P Takahashi
- Department of Neurology Osaka University Graduate School of Medicine Osaka Japan
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9
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Lardenoije R, Iatrou A, Kenis G, Kompotis K, Steinbusch HWM, Mastroeni D, Coleman P, Lemere CA, Hof PR, van den Hove DLA, Rutten BPF. The epigenetics of aging and neurodegeneration. Prog Neurobiol 2015; 131:21-64. [PMID: 26072273 PMCID: PMC6477921 DOI: 10.1016/j.pneurobio.2015.05.002] [Citation(s) in RCA: 246] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Revised: 05/13/2015] [Accepted: 05/13/2015] [Indexed: 12/14/2022]
Abstract
Epigenetics is a quickly growing field encompassing mechanisms regulating gene expression that do not involve changes in the genotype. Epigenetics is of increasing relevance to neuroscience, with epigenetic mechanisms being implicated in brain development and neuronal differentiation, as well as in more dynamic processes related to cognition. Epigenetic regulation covers multiple levels of gene expression; from direct modifications of the DNA and histone tails, regulating the level of transcription, to interactions with messenger RNAs, regulating the level of translation. Importantly, epigenetic dysregulation currently garners much attention as a pivotal player in aging and age-related neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, where it may mediate interactions between genetic and environmental risk factors, or directly interact with disease-specific pathological factors. We review current knowledge about the major epigenetic mechanisms, including DNA methylation and DNA demethylation, chromatin remodeling and non-coding RNAs, as well as the involvement of these mechanisms in normal aging and in the pathophysiology of the most common neurodegenerative diseases. Additionally, we examine the current state of epigenetics-based therapeutic strategies for these diseases, which either aim to restore the epigenetic homeostasis or skew it to a favorable direction to counter disease pathology. Finally, methodological challenges of epigenetic investigations and future perspectives are discussed.
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Affiliation(s)
- Roy Lardenoije
- School for Mental Health and Neuroscience (MHeNS), Department of Psychiatry and Neuropsychology, Maastricht University, Universiteitssingel 50, 6200 MD Maastricht, The Netherlands
| | - Artemis Iatrou
- School for Mental Health and Neuroscience (MHeNS), Department of Psychiatry and Neuropsychology, Maastricht University, Universiteitssingel 50, 6200 MD Maastricht, The Netherlands
| | - Gunter Kenis
- School for Mental Health and Neuroscience (MHeNS), Department of Psychiatry and Neuropsychology, Maastricht University, Universiteitssingel 50, 6200 MD Maastricht, The Netherlands
| | - Konstantinos Kompotis
- Center for Integrative Genomics, University of Lausanne, Genopode Building, 1015 Lausanne-Dorigny, Switzerland
| | - Harry W M Steinbusch
- School for Mental Health and Neuroscience (MHeNS), Department of Psychiatry and Neuropsychology, Maastricht University, Universiteitssingel 50, 6200 MD Maastricht, The Netherlands
| | - Diego Mastroeni
- School for Mental Health and Neuroscience (MHeNS), Department of Psychiatry and Neuropsychology, Maastricht University, Universiteitssingel 50, 6200 MD Maastricht, The Netherlands; L.J. Roberts Alzheimer's Disease Center, Banner Sun Health Research Institute, 10515 W. Santa Fe Drive, Sun City, AZ 85351, USA
| | - Paul Coleman
- L.J. Roberts Alzheimer's Disease Center, Banner Sun Health Research Institute, 10515 W. Santa Fe Drive, Sun City, AZ 85351, USA
| | - Cynthia A Lemere
- Center for Neurologic Diseases, Department of Neurology, Brigham and Women's Hospital, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Patrick R Hof
- Fishberg Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, NY 10029, USA
| | - Daniel L A van den Hove
- School for Mental Health and Neuroscience (MHeNS), Department of Psychiatry and Neuropsychology, Maastricht University, Universiteitssingel 50, 6200 MD Maastricht, The Netherlands; Laboratory of Translational Neuroscience, Department of Psychiatry, Psychosomatics and Psychotherapy, University of Wuerzburg, Fuechsleinstrasse 15, 97080 Wuerzburg, Germany
| | - Bart P F Rutten
- School for Mental Health and Neuroscience (MHeNS), Department of Psychiatry and Neuropsychology, Maastricht University, Universiteitssingel 50, 6200 MD Maastricht, The Netherlands.
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10
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Large expansion of CTG•CAG repeats is exacerbated by MutSβ in human cells. Sci Rep 2015; 5:11020. [PMID: 26047474 PMCID: PMC4457148 DOI: 10.1038/srep11020] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 05/12/2015] [Indexed: 11/08/2022] Open
Abstract
Trinucleotide repeat expansion disorders (TRED) are caused by genomic expansions of trinucleotide repeats, such as CTG and CAG. These expanded repeats are unstable in germline and somatic cells, with potential consequences for disease severity. Previous studies have demonstrated the involvement of DNA repair proteins in repeat instability, although the key factors affecting large repeat expansion and contraction are unclear. Here we investigated these factors in a human cell model harboring 800 CTG•CAG repeats by individually knocking down various DNA repair proteins using short interfering RNA. Knockdown of MSH2 and MSH3, which form the MutSβ heterodimer and function in mismatch repair, suppressed large repeat expansions, whereas knockdown of MSH6, which forms the MutSα heterodimer with MSH2, promoted large expansions exceeding 200 repeats by compensatory increases in MSH3 and the MutSβ complex. Knockdown of topoisomerase 1 (TOP1) and TDP1, which are involved in single-strand break repair, enhanced large repeat contractions. Furthermore, knockdown of senataxin, an RNA/DNA helicase which affects DNA:RNA hybrid formation and transcription-coupled nucleotide excision repair, exacerbated repeat instability in both directions. These results indicate that DNA repair factors, such as MutSβ play important roles in large repeat expansion and contraction, and can be an excellent therapeutic target for TRED.
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11
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Bayot A, Rustin P. Friedreich's ataxia, frataxin, PIP5K1B: echo of a distant fracas. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2013; 2013:725635. [PMID: 24194977 PMCID: PMC3806116 DOI: 10.1155/2013/725635] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Accepted: 08/12/2013] [Indexed: 01/15/2023]
Abstract
"Frataxin fracas" were the words used when referring to the frataxin-encoding gene (FXN) burst in as a motive to disqualify an alternative candidate gene, PIP5K1B, as an actor in Friedreich's ataxia (FRDA) (Campuzano et al., 1996; Cossee et al., 1997; Carvajal et al., 1996). The instrumental role in the disease of large triplet expansions in the first intron of FXN has been thereafter fully confirmed, and this no longer suffers any dispute (Koeppen, 2011). On the other hand, a recent study suggests that the consequences of these large expansions in FXN are wider than previously thought and that the expression of surrounding genes, including PIP5K1B, could be concurrently modulated by these large expansions (Bayot et al., 2013). This recent observation raises a number of important and yet unanswered questions for scientists and clinicians working on FRDA; these questions are the substratum of this paper.
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Affiliation(s)
- Aurélien Bayot
- INSERM UMR 676, Bâtiment Ecran, Hôpital Robert Debré, 48 boulevard Sérurier, 75019 Paris, France
- Université Paris 7, Faculté de Médecine Denis Diderot, Site Robert Debré, 48 boulevard Sérurier, 75019 Paris, France
| | - Pierre Rustin
- INSERM UMR 676, Bâtiment Ecran, Hôpital Robert Debré, 48 boulevard Sérurier, 75019 Paris, France
- Université Paris 7, Faculté de Médecine Denis Diderot, Site Robert Debré, 48 boulevard Sérurier, 75019 Paris, France
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12
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Wang J, Yu JT, Tan MS, Jiang T, Tan L. Epigenetic mechanisms in Alzheimer's disease: implications for pathogenesis and therapy. Ageing Res Rev 2013; 12:1024-41. [PMID: 23688931 DOI: 10.1016/j.arr.2013.05.003] [Citation(s) in RCA: 80] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 05/08/2013] [Indexed: 12/14/2022]
Abstract
The vast majority of Alzheimer's disease (AD) are late-onset forms (LOAD) likely due to the interplay of environmental influences and individual genetic susceptibility. Epigenetic mechanisms, including DNA methylation, histone modifications and non-coding RNAs, constitute dynamic intracellular processes for translating environmental stimuli into modifications in gene expression. Over the past decade it has become increasingly clear that epigenetic mechanisms play a pivotal role in aging the pathogenesis of AD. Here, we provide a review of the major mechanisms for epigenetic modification and how they are reportedly altered in aging and AD. Moreover, we also consider how aberrant epigenetic modifications may lead to AD pathogenesis, and we review the therapeutic potential of epigenetic treatments for AD.
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Affiliation(s)
- Jun Wang
- Department of Neurology, Qingdao Municipal Hospital, School of Medicine, Qingdao University, China
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13
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Mechanisms of RNA-induced toxicity in CAG repeat disorders. Cell Death Dis 2013; 4:e752. [PMID: 23907466 PMCID: PMC3763438 DOI: 10.1038/cddis.2013.276] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Revised: 06/21/2013] [Accepted: 06/28/2013] [Indexed: 01/27/2023]
Abstract
Several inherited neurodegenerative disorders are caused by CAG trinucleotide repeat expansions, which can be located either in the coding region or in the untranslated region (UTR) of the respective genes. Polyglutamine diseases (polyQ diseases) are caused by an expansion of a stretch of CAG repeats within the coding region, translating into a polyQ tract. The polyQ tract expansions result in conformational changes, eventually leading to aggregate formation. It is widely believed that the aggregation of polyQ proteins is linked with disease development. In addition, in the last couple of years, it has been shown that RNA-mediated mechanisms also have a profound role in neurotoxicity in both polyQ diseases and diseases caused by elongated CAG repeat motifs in their UTRs. Here, we review the different molecular mechanisms assigned to mRNAs with expanded CAG repeats. One aspect is the mRNA folding of CAG repeats. Furthermore, pathogenic mechanisms assigned to CAG repeat mRNAs are discussed. First, we discuss mechanisms that involve the sequestration of the diverse proteins to the expanded CAG repeat mRNA molecules. As a result of this, several cellular mechanisms are aberrantly regulated. These include the sequestration of MBNL1, leading to misregulated splicing; sequestration of nucleolin, leading to reduced cellular rRNA; and sequestration of proteins of the siRNA machinery, resulting in the production of short silencing RNAs that affect gene expression. Second, we discuss the effect of expanded CAG repeats on the subcellular localization, transcription and translation of the CAG repeat mRNA itself. Here we focus on the MID1 protein complex that triggers an increased translation of expanded CAG repeat mRNAs and a mechanism called repeat-associated non-ATG translation, which leads to proteins aberrantly translated from CAG repeat mRNAs. In addition, therapeutic approaches for CAG repeat disorders are discussed. Together, all the findings summarized here show that mutant mRNA has a fundamental role in the pathogenesis of CAG repeat diseases.
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14
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Tan L, Yu JT, Hu N, Tan L. Non-coding RNAs in Alzheimer's Disease. Mol Neurobiol 2012; 47:382-93. [DOI: 10.1007/s12035-012-8359-5] [Citation(s) in RCA: 122] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2012] [Accepted: 09/27/2012] [Indexed: 11/28/2022]
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15
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Abstract
The importance of various classes of regulatory non-protein-coding RNA molecules (ncRNAs) in the normal functioning of the CNS is becoming increasingly evident. ncRNAs are involved in neuronal cell specification and patterning during development, but also in higher cognitive processes, such as structural plasticity and memory formation in the adult brain. We discuss advances in understanding of the function of ncRNAs in the CNS, with a focus on the potential involvement of specific species, such as microRNAs, endogenous small interfering RNAs, long intergenic non-coding RNAs, and natural antisense transcripts, in various neurodegenerative disorders. This emerging field is anticipated to profoundly affect clinical research, diagnosis, and therapy in neurology.
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16
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Sølvsten C, Nielsen AL. FMR1 CGG repeat lengths mediate different regulation of reporter gene expression in comparative transient and locus specific integration assays. Gene 2011; 486:15-22. [PMID: 21767618 DOI: 10.1016/j.gene.2011.06.034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Revised: 06/24/2011] [Accepted: 06/30/2011] [Indexed: 01/10/2023]
Abstract
The Fragile X mental retardation (FMR1) gene contains a polymorphic CGG trinucleotide repeat in the 5'-untranslated region. The repeat length in the normal population is between 5 and 54 repeats. A repeat length between 55 and 200 is defined as the pre-mutation repeat size. Elderly carriers of the pre-mutation can develop the progressive neurodegenerative disease Fragile X-associated tremor/ataxia syndrome (FXTAS). In FXTAS the FMR1 mRNA levels are increased and it is hypothesized that FXTAS is caused by a RNA gain of function mechanism. Repeat lengths beyond 200 CGGs are defined as the full-mutation and causes Fragile X-syndrome which is the most common inherited form of mental retardation. The full-mutation results in the absence of the FMR1 mRNA and protein, FMRP, through abnormal CpG methylation and FMR1 gene silencing. In this report we have used the Flp-In T-REx system to generate locus directed stable cell lines harboring the FMR1 5'-UTR with varying CGG repeat lengths in front of a reporter gene. By this system the influence of various CGG repeat lengths for reporter gene expression can be comparatively examined in cell lines where the only genetic difference is CGG repeat lengths. In such cell lines we find that a full-mutation CGG repeat confers inhibition of reporter gene expression, whereas a pre-mutation CGG repeat did not increase reporter gene expression. In transient transfection assays using the same expression vectors the pre-mutation and full-mutation CGG repeats increased reporter gene expression. This study shows that locus directed integration of model FMR1 CGG transgenes could be a new basic tool to further elucidating the basic molecular mechanisms behind transcriptional deregulation of the FMR1 gene in fragile X-syndrome and FXTAS.
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17
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Wojciechowska M, Krzyzosiak WJ. CAG repeat RNA as an auxiliary toxic agent in polyglutamine disorders. RNA Biol 2011; 8:565-71. [PMID: 21593608 DOI: 10.4161/rna.8.4.15397] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Over 20 genetic loci with abnormal expansions of short tandem repeats have been associated with human hereditary neurological diseases. Of these, specific trinucleotide repeats located in non-coding and coding regions of individual genes implicated in these disorders are strongly overrepresented. Expansions of CTG, CGG and CAG repeats are linked to, respectively, myotonic dystrophy type 1 (DM1), fragile X-associated tremor/ataxia syndrome (FXTAS), as well as Huntington's disease (HD) and a number of spinocerebellar ataxias (SCAs). Expanded CAG repeats in translated exons trigger the most disorders for which a protein gain-of-function mechanism has been proposed to explain neurodegeneration by polyglutamine-rich (poly-Q) proteins. However, the results of last years showed that RNA composed of mutated CAG repeats can also be toxic and contribute to pathogenesis of polyglutamine disorders through an RNA-mediated gain-of-function mechanism. This mechanism has been best characterized in the non-coding repeat disorder DM1 and is also implicated in several other diseases, such as FXTAS, spinocerebellar ataxia type 8 (SCA8), Huntington's disease-like 2 (HDL2), as well as in myotonic dystrophy type 2 (DM2), spinocerebellar ataxia type 10 (SCA10) and type 31 (SCA31). In this review, we summarize recent findings that emphasize the participation of coding mutant CAG repeat RNA in the pathogenesis of polyglutamine disorders, and we discuss the basis of an RNA gain-of-function model in non-coding diseases such as DM1, FXTAS and SCA8.
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Affiliation(s)
- Marzena Wojciechowska
- Laboratory of Cancer Genetics, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland
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18
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Qureshi IA, Mehler MF. Diagnosing and Treating Nervous System Disorders by Targeting Novel Classes of Non-coding RNAs. INTERNATIONAL DRUG DISCOVERY 2011; 6:30-36. [PMID: 26659096 PMCID: PMC4675140] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Affiliation(s)
- Irfan A Qureshi
- Rosyln and Leslie Goldstein Laboratory for Stem Cell Biology and Regenerative Medicine, Albert Einstein College of Medicine ; Institute for Brain Disorders and Neural Regeneration, Albert Einstein College of Medicine ; Departments of Neurology, Albert Einstein College of Medicine ; Rose F. Kennedy Center for Research on Intellectual and Developmental Disabilities, Albert Einstein College of Medicine
| | - Mark F Mehler
- Rosyln and Leslie Goldstein Laboratory for Stem Cell Biology and Regenerative Medicine, Albert Einstein College of Medicine ; Institute for Brain Disorders and Neural Regeneration, Albert Einstein College of Medicine ; Departments of Neurology, Albert Einstein College of Medicine ; Neuroscience, Albert Einstein College of Medicine ; Psychiatry and Behavioral Sciences, Albert Einstein College of Medicine ; Rose F. Kennedy Center for Research on Intellectual and Developmental Disabilities, Albert Einstein College of Medicine
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19
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Abstract
CCTG tetranucleotide repeat expansion is associated with a hereditary neurological disease called myotonic dystrophy type 2 (DM2). The underlying reasons that lead to genetic instability and thus repeat expansion during DNA replication remains elusive. Here, we have shown CCTG repeats have a high propensity to form metastable hairpin and dumbbell structures using high-resolution nuclear magnetic resonance (NMR) spectroscopy. When the repeat length is equal to three, a hairpin with a two-residue CT loop is formed. In addition to the hairpin, a dumbbell structure with two CT-loops is formed when the repeat length is equal to four. Nuclear Overhauser effect (NOE) and chemical shift data reveal both the hairpin and dumbbell structures contain a flexible stem comprising a C-bulge and a T·T mismatch. With the aid of single-site mutation samples, NMR results show these peculiar structures undergo dynamic conformational exchange. In addition to the intrinsic flexibility in the stem region of these structures, the exchange process also serves as an origin of genetic instability that leads to repeat expansion during DNA replication. The structural features provide important drug target information for developing therapeutics to inhibit the expansion process and thus the onset of DM2.
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Affiliation(s)
- Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
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20
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Qureshi IA, Mehler MF. Non-coding RNA networks underlying cognitive disorders across the lifespan. Trends Mol Med 2011; 17:337-46. [PMID: 21411369 DOI: 10.1016/j.molmed.2011.02.002] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Revised: 02/04/2011] [Accepted: 02/08/2011] [Indexed: 02/06/2023]
Abstract
Non-coding RNAs (ncRNAs) and their associated regulatory networks are increasingly being implicated in mediating a complex repertoire of neurobiological functions. Cognitive and behavioral processes are proving to be no exception. In this review, we discuss the emergence of many novel, diverse and rapidly expanding classes and subclasses of short and long ncRNAs. We briefly review the life cycles and molecular functions of these ncRNAs. We also examine how ncRNA circuitry mediates brain development, plasticity, stress responses and aging, and highlight its potential roles in the pathophysiology of cognitive disorders, including neural developmental and age-associated neurodegenerative diseases, as well as those that manifest throughout the lifespan.
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Affiliation(s)
- Irfan A Qureshi
- Rosyln and Leslie Goldstein Laboratory for Stem Cell Biology and Regenerative Medicine, Albert Einstein College of Medicine, Bronx, New York, NY 10461, USA.
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21
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Mehler MF. Epigenetics and neuropsychiatric diseases: introduction and meeting summary. Ann N Y Acad Sci 2010; 1204 Suppl:E1-7. [PMID: 20840163 DOI: 10.1111/j.1749-6632.2010.05717.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This volume is an outgrowth of a symposium entitled "Epigenetics and Neuropsychiatric Diseases: Mechanisms Mediating Nature and Nurture" presented at the 88th Annual Conference of the Association for Nervous and Mental Diseases, held on December 5, 2008 at the New York Academy of Medicine. Dolores Malaspina (New York University Medical Center) and Mark F. Mehler (Albert Einstein College of Medicine) organized the symposium as two sessions, "Epigenetics and Brain Behavior Relationships" and "Epigenetics and Neuropsychiatric Diseases." The symposium brought together basic and translational neuroscientists, neurologists, psychiatrists, neuropsychologists, neuropsycho-pharmacologists, and other allied biomedical professionals to establish an enduring dialogue and collaborative interactions concerning epigenetics and epigenomic medicine as a "new science" of brain and behavior relationships. This new discipline has begun to revolutionize our understanding of nervous system development in many specific areas, including neural stem cell biology, fate decisions, and cell diversity and connectivity; learning and memory; neuronal and neural network homeostasis; plasticity and stress responses; the pathogenesis of neuropsychiatric diseases and novel therapeutic interventions involving dynamic cellular reprogramming; reorganization of synaptic and neural network connections; and remodeling of the brain parenchyma and its systemic connections to promote restoration of higher-order cognitive, behavioral, and sensorimotor functions.
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Affiliation(s)
- Mark F Mehler
- Department of Neurology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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22
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Kumari D, Usdin K. The distribution of repressive histone modifications on silenced FMR1 alleles provides clues to the mechanism of gene silencing in fragile X syndrome. Hum Mol Genet 2010; 19:4634-42. [PMID: 20843831 DOI: 10.1093/hmg/ddq394] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Fragile X syndrome (FXS) is the most common heritable cause of intellectual disability and the most common known cause of autism. Most cases of FXS result from the expansion of a CGG·CCG repeat in the 5' UTR of the FMR1 gene that leads to gene silencing. It has previously been shown that silenced alleles are associated with histone H3 dimethylated at lysine 9 (H3K9Me2) and H3 trimethylated at lysine 27 (H3K27Me3), modified histones typical of developmentally repressed genes. We show here that these alleles are also associated with elevated levels of histone H3 trimethylated at lysine 9 (H3K9Me3) and histone H4 trimethylated at lysine 20 (H4K20Me3). All four of these modified histones are present on exon 1 of silenced alleles at levels comparable to that seen on pericentric heterochromatin. The two groups of histone modifications show a different distribution on fragile X alleles: H3K9Me2 and H3K27Me3 have a broad distribution, whereas H3K9Me3 and H4K20Me3 have a more focal distribution with the highest level of these marks being present in the vicinity of the repeat. This suggests that the trigger for gene silencing may be local to the repeat itself and perhaps involves a mechanism similar to that involved in the formation of pericentric heterochromatin.
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Affiliation(s)
- Daman Kumari
- Section on Gene Structure and Disease, Laboratory of Molecular and Cellular Biology, National Institute of Diabetes and Digestive and Kidney Disease/NIH, Bethesda, MD 20892-0830, USA.
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23
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McIvor EI, Polak U, Napierala M. New insights into repeat instability: role of RNA•DNA hybrids. RNA Biol 2010; 7:551-8. [PMID: 20729633 DOI: 10.4161/rna.7.5.12745] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Expansion of tandem repeat sequences is responsible for more than 20 human diseases. Several cis elements and trans factors involved in repeat instability (expansion and contraction) have been identified. However no comprehensive model explaining large intergenerational or somatic changes of the length of the repeating sequences exists. Several lines of evidence, accumulated from different model studies, indicate that transcription through repeat sequences is an important factor promoting their instability. The persistent interaction between transcription template DNA and nascent RNA (RNA•DNA hybrids, R loops) was shown to stimulate genomic instability. Recently, we demonstrated that cotranscriptional RNA•DNA hybrids are preferentially formed at GC-rich trinucleotide and tetranucleotide repeat sequences in vitro as well as in human genomic DNA. Additionally, we showed that cotranscriptional formation of RNA•DNA hybrids at CTG•CAG and GAA•TTC repeats stimulate instability of these sequences in both E. coli and human cells. Our results suggest that persistent RNA•DNA hybrids may also be responsible for other downstream effects of expanded trinucleotide repeats, including gene silencing. Considering the extent of transcription through the human genome as well as the abundance of GC-rich and/or non-canonical DNA structure forming tandem repeats, RNA•DNA hybrids may represent a common mutagenic conformation. Hence, R loops are potentially attractive therapeutic target in diseases associated with genomic instability.
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Affiliation(s)
- Elizabeth I McIvor
- Department of Biochemistry and Molecular Biology and Center for Cancer Epigenetics, University of Texas MD Anderson Cancer Center, Houston, TX, USA
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