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Aldous SG, Smith EJ, Landles C, Osborne GF, Cañibano-Pico M, Nita IM, Phillips J, Zhang Y, Jin B, Hirst MB, Benn CL, Bond BC, Edelmann W, Greene JR, Bates GP. A CAG repeat threshold for therapeutics targeting somatic instability in Huntington's disease. Brain 2024; 147:1784-1798. [PMID: 38387080 PMCID: PMC11068328 DOI: 10.1093/brain/awae063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Accepted: 02/07/2024] [Indexed: 02/24/2024] Open
Abstract
The Huntington's disease mutation is a CAG repeat expansion in the huntingtin gene that results in an expanded polyglutamine tract in the huntingtin protein. The CAG repeat is unstable and expansions of hundreds of CAGs have been detected in Huntington's disease post-mortem brains. The age of disease onset can be predicted partially from the length of the CAG repeat as measured in blood. Onset age is also determined by genetic modifiers, which in six cases involve variation in DNA mismatch repair pathways genes. Knocking-out specific mismatch repair genes in mouse models of Huntington's disease prevents somatic CAG repeat expansion. Taken together, these results have led to the hypothesis that somatic CAG repeat expansion in Huntington's disease brains is required for pathogenesis. Therefore, the pathogenic repeat threshold in brain is longer than (CAG)40, as measured in blood, and is currently unknown. The mismatch repair gene MSH3 has become a major focus for therapeutic development, as unlike other mismatch repair genes, nullizygosity for MSH3 does not cause malignancies associated with mismatch repair deficiency. Potential treatments targeting MSH3 currently under development include gene therapy, biologics and small molecules, which will be assessed for efficacy in mouse models of Huntington's disease. The zQ175 knock-in model carries a mutation of approximately (CAG)185 and develops early molecular and pathological phenotypes that have been extensively characterized. Therefore, we crossed the mutant huntingtin allele onto heterozygous and homozygous Msh3 knockout backgrounds to determine the maximum benefit of targeting Msh3 in this model. Ablation of Msh3 prevented somatic expansion throughout the brain and periphery, and reduction of Msh3 by 50% decreased the rate of expansion. This had no effect on the deposition of huntingtin aggregation in the nuclei of striatal neurons, nor on the dysregulated striatal transcriptional profile. This contrasts with ablating Msh3 in knock-in models with shorter CAG repeat expansions. Therefore, further expansion of a (CAG)185 repeat in striatal neurons does not accelerate the onset of molecular and neuropathological phenotypes. It is striking that highly expanded CAG repeats of a similar size in humans cause disease onset before 2 years of age, indicating that somatic CAG repeat expansion in the brain is not required for pathogenesis. Given that the trajectory for somatic CAG expansion in the brains of Huntington's disease mutation carriers is unknown, our study underlines the importance of administering treatments targeting somatic instability as early as possible.
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Affiliation(s)
- Sarah G Aldous
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Edward J Smith
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Christian Landles
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Georgina F Osborne
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Maria Cañibano-Pico
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Iulia M Nita
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Jemima Phillips
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Yongwei Zhang
- Department of Cell Biology, Albert Einstein College of Medicine, New York, NY 10461, USA
| | - Bo Jin
- Department of Cell Biology, Albert Einstein College of Medicine, New York, NY 10461, USA
| | | | - Caroline L Benn
- LoQus23 Therapeutics, Riverside, Babraham Research Campus, Cambridge, CB22 3AT, UK
| | - Brian C Bond
- Prism Training and Consultancy Limited, St John's Innovation Centre, Cambridge, CB4 0WS, UK
| | - Winfried Edelmann
- Department of Cell Biology, Albert Einstein College of Medicine, New York, NY 10461, USA
| | | | - Gillian P Bates
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
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Hoschek F, Natan J, Wagner M, Sathasivam K, Abdelmoez A, von Einem B, Bates GP, Landwehrmeyer GB, Neueder A. Huntingtin HTT1a is generated in a CAG repeat-length-dependent manner in human tissues. Mol Med 2024; 30:36. [PMID: 38459427 PMCID: PMC10924374 DOI: 10.1186/s10020-024-00801-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Accepted: 02/19/2024] [Indexed: 03/10/2024] Open
Abstract
BACKGROUND The disease-causing mutation in Huntington disease (HD) is a CAG trinucleotide expansion in the huntingtin (HTT) gene. The mutated CAG tract results in the production of a small RNA, HTT1a, coding for only exon 1 of HTT. HTT1a is generated by a block in the splicing reaction of HTT exon 1 to exon 2 followed by cleavage in intron 1 and polyadenylation. Translation of HTT1a leads to the expression of the highly toxic HTT exon 1 protein fragment. We have previously shown that the levels of HTT1a expression in mouse models of HD is dependent on the CAG repeat length. However, these data are lacking for human tissues. METHODS To answer this question, we developed highly sensitive digital PCR assays to determine HTT1a levels in human samples. These assays allow the absolute quantification of transcript numbers and thus also facilitate the comparison of HTT1a levels between tissues, cell types and across different studies. Furthermore, we measured CAG repeat sizes for every sample used in the study. Finally, we analysed our data with ANOVA and linear modelling to determine the correlation of HTT1a expression levels with CAG repeat sizes. RESULTS In summary, we show that HTT1a is indeed expressed in a CAG repeat-length-dependent manner in human post mortem brain tissues as well as in several peripheral cell types. In particular, PBMCs show a statistically significant positive correlation of HTT1a expression with CAG repeat length, and elevated HTT1a expression levels even in the adult-onset CAG repeat range. CONCLUSIONS Our results show that HTT1a expression occurs throughout a wide range of tissues and likely with all CAG lengths. Our data from peripheral sample sources demonstrate that HTT1a is indeed generated throughout the body in a CAG repeat-length-dependent manner. Therefore, the levels of HTT1a might be a sensitive marker of disease state and/or progression and should be monitored over time, especially in clinical trials targeting HTT expression.
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Affiliation(s)
- Franziska Hoschek
- Department of Neurology, University Hospital Ulm, 89081, Ulm, Germany
| | - Julia Natan
- Department of Neurology, University Hospital Ulm, 89081, Ulm, Germany
| | - Maximilian Wagner
- Department of Neurology, University Hospital Ulm, 89081, Ulm, Germany
| | - Kirupa Sathasivam
- Huntington's Disease Centre, Department of Neurodegenerative Disease, Queen Square Institute of Neurology, University College London, WC1N 3BG, London, UK
| | - Alshaimaa Abdelmoez
- Department of Neurology, University Hospital Ulm, 89081, Ulm, Germany
- Department of Pharmaceutical Organic Chemistry, Faculty of Pharmacy, Assiut University, Assiut, Egypt
| | - Björn von Einem
- Department of Neurology, University Hospital Ulm, 89081, Ulm, Germany
| | - Gillian P Bates
- Huntington's Disease Centre, Department of Neurodegenerative Disease, Queen Square Institute of Neurology, University College London, WC1N 3BG, London, UK
| | | | - Andreas Neueder
- Department of Neurology, University Hospital Ulm, 89081, Ulm, Germany.
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Driscoll R, Hampton L, Abraham NA, Larigan JD, Joseph NF, Hernandez-Vega JC, Geisler S, Yang FC, Deninger M, Tran DT, Khatri N, Godinho BMDC, Kinberger GA, Montagna DR, Hirst WD, Guardado CL, Glajch KE, Arnold HM, Gallant-Behm CL, Weihofen A. Dose-dependent reduction of somatic expansions but not Htt aggregates by di-valent siRNA-mediated silencing of MSH3 in HdhQ111 mice. Sci Rep 2024; 14:2061. [PMID: 38267530 PMCID: PMC10808119 DOI: 10.1038/s41598-024-52667-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Accepted: 01/22/2024] [Indexed: 01/26/2024] Open
Abstract
Huntington's disease (HD) is a progressive neurodegenerative disorder caused by CAG trinucleotide repeat expansions in exon 1 of the HTT gene. In addition to germline CAG expansions, somatic repeat expansions in neurons also contribute to HD pathogenesis. The DNA mismatch repair gene, MSH3, identified as a genetic modifier of HD onset and progression, promotes somatic CAG expansions, and thus presents a potential therapeutic target. However, what extent of MSH3 protein reduction is needed to attenuate somatic CAG expansions and elicit therapeutic benefits in HD disease models is less clear. In our study, we employed potent di-siRNAs to silence mouse Msh3 mRNA expression in a dose-dependent manner in HdhQ111/+ mice and correlated somatic Htt CAG instability with MSH3 protein levels from simultaneously isolated DNA and protein after siRNA treatment. Our results reveal a linear correlation with a proportionality constant of ~ 1 between the prevention of somatic Htt CAG expansions and MSH3 protein expression in vivo, supporting MSH3 as a rate-limiting step in somatic expansions. Intriguingly, despite a 75% reduction in MSH3 protein levels, striatal nuclear HTT aggregates remained unchanged. We also note that evidence for nuclear Msh3 mRNA that is inaccessible to RNA interference was found, and that MSH6 protein in the striatum was upregulated following MSH3 knockdown in HdhQ111/+ mice. These results provide important clues to address critical questions for the development of therapeutic molecules targeting MSH3 as a potential therapeutic target for HD.
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Affiliation(s)
- Rachelle Driscoll
- Translational Sciences, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Lucas Hampton
- Neurodegenerative Diseases Research Unit, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Neeta A Abraham
- Neurodegenerative Diseases Research Unit, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - J Douglas Larigan
- Biotherapeutics and Medicinal Sciences, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Nadine F Joseph
- Neurodegenerative Diseases Research Unit, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Juan C Hernandez-Vega
- Neurodegenerative Diseases Research Unit, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Sarah Geisler
- Translational Sciences, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Fu-Chia Yang
- Translational Sciences, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Matthew Deninger
- Atalanta Therapeutics, 51 Sleeper Street, Boston, MA, 02210, USA
| | - David T Tran
- Atalanta Therapeutics, 51 Sleeper Street, Boston, MA, 02210, USA
| | - Natasha Khatri
- Atalanta Therapeutics, 51 Sleeper Street, Boston, MA, 02210, USA
| | | | | | - Daniel R Montagna
- Neurodegenerative Diseases Research Unit, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Warren D Hirst
- Neurodegenerative Diseases Research Unit, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Catherine L Guardado
- Neurodegenerative Diseases Research Unit, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - Kelly E Glajch
- Neurodegenerative Diseases Research Unit, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | - H Moore Arnold
- Translational Sciences, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA
| | | | - Andreas Weihofen
- Neurodegenerative Diseases Research Unit, Biogen, 225 Binney Street, Cambridge, MA, 02142, USA.
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Speidell A, Bin Abid N, Yano H. Brain-Derived Neurotrophic Factor Dysregulation as an Essential Pathological Feature in Huntington's Disease: Mechanisms and Potential Therapeutics. Biomedicines 2023; 11:2275. [PMID: 37626771 PMCID: PMC10452871 DOI: 10.3390/biomedicines11082275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 08/07/2023] [Accepted: 08/09/2023] [Indexed: 08/27/2023] Open
Abstract
Brain-derived neurotrophic factor (BDNF) is a major neurotrophin whose loss or interruption is well established to have numerous intersections with the pathogenesis of progressive neurological disorders. There is perhaps no greater example of disease pathogenesis resulting from the dysregulation of BDNF signaling than Huntington's disease (HD)-an inherited neurodegenerative disorder characterized by motor, psychiatric, and cognitive impairments associated with basal ganglia dysfunction and the ultimate death of striatal projection neurons. Investigation of the collection of mechanisms leading to BDNF loss in HD highlights this neurotrophin's importance to neuronal viability and calls attention to opportunities for therapeutic interventions. Using electronic database searches of existing and forthcoming research, we constructed a literature review with the overarching goal of exploring the diverse set of molecular events that trigger BDNF dysregulation within HD. We highlighted research that investigated these major mechanisms in preclinical models of HD and connected these studies to those evaluating similar endpoints in human HD subjects. We also included a special focus on the growing body of literature detailing key transcriptomic and epigenetic alterations that affect BDNF abundance in HD. Finally, we offer critical evaluation of proposed neurotrophin-directed therapies and assessed clinical trials seeking to correct BDNF expression in HD individuals.
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Affiliation(s)
- Andrew Speidell
- Department of Neurological Surgery, Washington University School of Medicine in St. Louis, St. Louis, MO 63110, USA; (A.S.); (N.B.A.)
| | - Noman Bin Abid
- Department of Neurological Surgery, Washington University School of Medicine in St. Louis, St. Louis, MO 63110, USA; (A.S.); (N.B.A.)
| | - Hiroko Yano
- Department of Neurological Surgery, Washington University School of Medicine in St. Louis, St. Louis, MO 63110, USA; (A.S.); (N.B.A.)
- Department of Neurology, Washington University School of Medicine in St. Louis, St. Louis, MO 63110, USA
- Department of Genetics, Washington University School of Medicine in St. Louis, St. Louis, MO 63110, USA
- Hope Center for Neurological Disorders, Washington University School of Medicine in St. Louis, St. Louis, MO 63110, USA
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