-
Molecular Therapy : the Journal of the... Jun 2023Huntington's disease (HD) is a severe neurodegenerative disorder caused by the expansion of the CAG trinucleotide repeat tract in the huntingtin gene. Inheritance of...
Huntington's disease (HD) is a severe neurodegenerative disorder caused by the expansion of the CAG trinucleotide repeat tract in the huntingtin gene. Inheritance of expanded CAG repeats is needed for HD manifestation, but further somatic expansion of the repeat tract in non-dividing cells, particularly striatal neurons, hastens disease onset. Called somatic repeat expansion, this process is mediated by the mismatch repair (MMR) pathway. Among MMR components identified as modifiers of HD onset, MutS homolog 3 (MSH3) has emerged as a potentially safe and effective target for therapeutic intervention. Here, we identify a fully chemically modified short interfering RNA (siRNA) that robustly silences Msh3 in vitro and in vivo. When synthesized in a di-valent scaffold, siRNA-mediated silencing of Msh3 effectively blocked CAG-repeat expansion in the striatum of two HD mouse models without affecting tumor-associated microsatellite instability or mRNA expression of other MMR genes. Our findings establish a promising treatment approach for patients with HD and other repeat expansion diseases.
Topics: Animals; Mice; Corpus Striatum; Huntingtin Protein; Huntington Disease; Neostriatum; RNA, Double-Stranded; RNA, Small Interfering; Trinucleotide Repeat Expansion; MutS Homolog 3 Protein
PubMed: 37177784
DOI: 10.1016/j.ymthe.2023.05.006 -
Neurotherapeutics : the Journal of the... Oct 2019
Topics: Bulbo-Spinal Atrophy, X-Linked; DNA Repeat Expansion; Friedreich Ataxia; Genetic Therapy; Humans; Huntington Disease; Trinucleotide Repeat Expansion
PubMed: 31907874
DOI: 10.1007/s13311-019-00823-3 -
Proceedings of the National Academy of... Jul 2023Aberrant alternative splicing of mRNAs results in dysregulated gene expression in multiple neurological disorders. Here, we show that hundreds of mRNAs are incorrectly...
Aberrant alternative splicing of mRNAs results in dysregulated gene expression in multiple neurological disorders. Here, we show that hundreds of mRNAs are incorrectly expressed and spliced in white blood cells and brain tissues of individuals with fragile X syndrome (FXS). Surprisingly, the gene is transcribed in >70% of the FXS tissues. In all -expressing FXS tissues, RNA itself is mis-spliced in a CGG expansion-dependent manner to generate the little-known -217 RNA isoform, which is comprised of exon 1 and a pseudo-exon in intron 1. -217 is also expressed in FXS premutation carrier-derived skin fibroblasts and brain tissues. We show that in cells aberrantly expressing mis-spliced , antisense oligonucleotide (ASO) treatment reduces -217, rescues full-length RNA, and restores FMRP (Fragile X Messenger RibonucleoProtein) to normal levels. Notably, gene reactivation in transcriptionally silent FXS cells using 5-aza-2'-deoxycytidine (5-AzadC), which prevents DNA methylation, increases -217 RNA levels but not FMRP. ASO treatment of cells prior to 5-AzadC application rescues full-length expression and restores FMRP. These findings indicate that misregulated RNA-processing events in blood could serve as potent biomarkers for FXS and that in those individuals expressing , ASO treatment may offer a therapeutic approach to mitigate the disorder.
Topics: Humans; Fragile X Syndrome; Trinucleotide Repeat Expansion; Oligonucleotides, Antisense; Decitabine; Fragile X Mental Retardation Protein; Oligonucleotides; RNA
PubMed: 37364131
DOI: 10.1073/pnas.2302534120 -
Brain : a Journal of Neurology Jul 2021Oculopharyngodistal myopathy (OPDM) is an adult-onset neuromuscular disease characterized by progressive ocular, facial, pharyngeal and distal limb muscle involvement....
Oculopharyngodistal myopathy (OPDM) is an adult-onset neuromuscular disease characterized by progressive ocular, facial, pharyngeal and distal limb muscle involvement. Trinucleotide repeat expansions in LRP12 or GIPC1 were recently reported to be associated with OPDM. However, a significant portion of OPDM patients have unknown genetic causes. In this study, long-read whole-genome sequencing and repeat-primed PCR were performed and we identified GGC repeat expansions in the NOTCH2NLC gene in 16.7% (4/24) of a cohort of Chinese OPDM patients, designated as OPDM type 3 (OPDM3). Methylation analysis indicated that methylation levels of the NOTCH2NLC gene were unaltered in OPDM3 patients, but increased significantly in asymptomatic carriers. Quantitative real-time PCR analysis indicated that NOTCH2NLC mRNA levels were increased in muscle but not in blood of OPDM3 patients. Immunofluorescence on OPDM muscle samples and expressing mutant NOTCH2NLC with (GGC)69 repeat expansions in HEK293 cells indicated that mutant NOTCH2NLC-polyglycine protein might be a major component of intranuclear inclusions, and contribute to toxicity in cultured cells. In addition, two RNA-binding proteins, hnRNP A/B and MBNL1, were both co-localized with p62 in intranuclear inclusions in OPDM muscle samples. These results indicated that a toxic protein gain-of-function mechanism and RNA gain-of-function mechanism may both play a vital role in the pathogenic processes of OPDM3. This study extended the spectrum of NOTCH2NLC repeat expansion-related diseases to a predominant myopathy phenotype presenting as OPDM, and provided evidence for possible pathogenesis of these diseases.
Topics: Asian People; China; Cohort Studies; Female; Humans; Male; Muscular Dystrophies; Pedigree; Trinucleotide Repeat Expansion
PubMed: 33693509
DOI: 10.1093/brain/awab077 -
Neuron Apr 2022In Huntington's disease (HD), the uninterrupted CAG repeat length, but not the polyglutamine length, predicts disease onset. However, the underlying pathobiology remains...
In Huntington's disease (HD), the uninterrupted CAG repeat length, but not the polyglutamine length, predicts disease onset. However, the underlying pathobiology remains unclear. Here, we developed bacterial artificial chromosome (BAC) transgenic mice expressing human mutant huntingtin (mHTT) with uninterrupted, and somatically unstable, CAG repeats that exhibit progressive disease-related phenotypes. Unlike prior mHTT transgenic models with stable, CAA-interrupted, polyglutamine-encoding repeats, BAC-CAG mice show robust striatum-selective nuclear inclusions and transcriptional dysregulation resembling those in murine huntingtin knockin models and HD patients. Importantly, the striatal transcriptionopathy in HD models is significantly correlated with their uninterrupted CAG repeat length but not polyglutamine length. Finally, among the pathogenic entities originating from mHTT genomic transgenes and only present or enriched in the uninterrupted CAG repeat model, somatic CAG repeat instability and nuclear mHTT aggregation are best correlated with early-onset striatum-selective molecular pathogenesis and locomotor and sleep deficits, while repeat RNA-associated pathologies and repeat-associated non-AUG (RAN) translation may play less selective or late pathogenic roles, respectively.
Topics: Animals; Chromosomes, Artificial, Bacterial; Disease Models, Animal; Humans; Huntingtin Protein; Huntington Disease; Mice; Mice, Transgenic; Nerve Tissue Proteins; Neurons; Nuclear Proteins; Trinucleotide Repeat Expansion
PubMed: 35114102
DOI: 10.1016/j.neuron.2022.01.006 -
Journal of Huntington's Disease 2021DNA damage repair (DDR) mechanisms have been implicated in a number of neurodegenerative diseases (both genetically determined and sporadic). Consistent with this,... (Review)
Review
DNA damage repair (DDR) mechanisms have been implicated in a number of neurodegenerative diseases (both genetically determined and sporadic). Consistent with this, recent genome-wide association studies in Huntington's disease (HD) and other trinucleotide repeat expansion diseases have highlighted genes involved in DDR mechanisms as modifiers for age of onset, rate of progression and somatic instability. At least some clinical genetic modifiers have been shown to have a role in modulating trinucleotide repeat expansion biology and could therefore provide new disease-modifying therapeutic targets. In this review, we focus on key considerations with respect to drug discovery and development using DDR mechanisms as a target for trinucleotide repeat expansion diseases. Six areas are covered with specific reference to DDR and HD: 1) Target identification and validation; 2) Candidate selection including therapeutic modality and delivery; 3) Target drug exposure with particular focus on blood-brain barrier penetration, engagement and expression of pharmacology; 4) Safety; 5) Preclinical models as predictors of therapeutic efficacy; 6) Clinical outcome measures including biomarkers.
Topics: Animals; DNA Damage; DNA Mismatch Repair; Drug Development; Drug Discovery; Humans; Huntingtin Protein; Huntington Disease; Trinucleotide Repeat Expansion
PubMed: 32925081
DOI: 10.3233/JHD-200421 -
Neurobiology of Disease Dec 2019Myotonic Dystrophy type 1 (DM1) is a neuromuscular disease showing strong genetic anticipation, and is caused by the expansion of a CTG repeat tract in the 3'-UTR of the... (Review)
Review
Myotonic Dystrophy type 1 (DM1) is a neuromuscular disease showing strong genetic anticipation, and is caused by the expansion of a CTG repeat tract in the 3'-UTR of the DMPK gene. Congenital Myotonic Dystrophy (CDM1) represents the most severe form of the disease, with prenatal onset, symptoms distinct from adult onset DM1, and a high rate of perinatal mortality. CDM1 is usually associated with very large CTG expansions, but this correlation is not absolute and cannot explain the distinct clinical features and the strong bias for maternal transmission. This review focuses upon the molecular and epigenetic factors that modulate disease severity and might be responsible for CDM1. Changes in the epigenetic status of the DM1 locus and in gene expression have recently been observed. Increasing evidence supports a role of a CTCF binding motif as a cis-element, upstream of the DMPK CTG tract, whereby CpG methylation of this site regulates the interaction of the insulator protein CTCF as a modulating trans-factor responsible for the inheritance and expression of CDM1.
Topics: Animals; DNA Methylation; Epigenesis, Genetic; Humans; Myotonic Dystrophy; Myotonin-Protein Kinase; Trinucleotide Repeat Expansion
PubMed: 31326502
DOI: 10.1016/j.nbd.2019.104533 -
DNA Repair Oct 2022Trinucleotide repeat instability is a driver of human disease. Large expansions of (GAA) repeats in the first intron of the FXN gene are the cause Friedreich's ataxia... (Review)
Review
Trinucleotide repeat instability is a driver of human disease. Large expansions of (GAA) repeats in the first intron of the FXN gene are the cause Friedreich's ataxia (FRDA), a progressive degenerative disorder which cannot yet be prevented or treated. (GAA) repeat instability arises during both replication-dependent processes, such as cell division and intergenerational transmission, as well as in terminally differentiated somatic tissues. Here, we provide a brief historical overview on the discovery of (GAA) repeat expansions and their association to FRDA, followed by recent advances in the identification of triplex H-DNA formation and replication fork stalling. The main body of this review focuses on the last decade of progress in understanding the mechanism of (GAA) repeat instability during DNA replication and/or DNA repair. We propose that the discovery of additional mechanisms of (GAA) repeat instability can be achieved via both comparative approaches to other repeat expansion diseases and genome-wide association studies. Finally, we discuss the advances towards FRDA prevention or amelioration that specifically target (GAA) repeat expansions.
Topics: DNA Replication; Friedreich Ataxia; Genome-Wide Association Study; Humans; Iron-Binding Proteins; Trinucleotide Repeat Expansion
PubMed: 35952488
DOI: 10.1016/j.dnarep.2022.103385 -
Journal of Huntington's Disease 2021At fifteen different genomic locations, the expansion of a CAG/CTG repeat causes a neurodegenerative or neuromuscular disease, the most common being Huntington's disease... (Review)
Review
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.
Topics: Animals; Disease Models, Animal; Genes, Modifier; Genomic Instability; Huntington Disease; Myotonic Dystrophy; Trinucleotide Repeat Expansion
PubMed: 33579861
DOI: 10.3233/JHD-200426