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Scientific Reports Jan 2024Huntington'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...
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 Hdh 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 Hdh 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.
Topics: Animals; Mice; Corpus Striatum; Exons; Huntington Disease; RNA Interference; RNA, Messenger; RNA, Small Interfering
PubMed: 38267530
DOI: 10.1038/s41598-024-52667-3 -
The EMBO Journal Jan 2024Expansion mutations in polyalanine stretches are associated with a growing number of diseases sharing a high degree of genotypic and phenotypic commonality. These...
Expansion mutations in polyalanine stretches are associated with a growing number of diseases sharing a high degree of genotypic and phenotypic commonality. These similarities prompted us to query the normal function of physiological polyalanine stretches and to investigate whether a common molecular mechanism is involved in these diseases. Here, we show that UBA6, an E1 ubiquitin-activating enzyme, recognizes a polyalanine stretch within its cognate E2 ubiquitin-conjugating enzyme USE1. Aberrations in this polyalanine stretch reduce ubiquitin transfer to USE1 and, subsequently, polyubiquitination and degradation of its target, the ubiquitin ligase E6AP. Furthermore, we identify competition for the UBA6-USE1 interaction by various proteins with polyalanine expansion mutations in the disease state. The deleterious interactions of expanded polyalanine tract proteins with UBA6 in mouse primary neurons alter the levels and ubiquitination-dependent degradation of E6AP, which in turn affects the levels of the synaptic protein Arc. These effects are also observed in induced pluripotent stem cell-derived autonomic neurons from patients with polyalanine expansion mutations, where UBA6 overexpression increases neuronal resilience to cell death. Our results suggest a shared mechanism for such mutations that may contribute to the congenital malformations seen in polyalanine tract diseases.
Topics: Humans; Animals; Mice; Ubiquitination; Ubiquitin; Ubiquitin-Activating Enzymes; Mutation; Peptides
PubMed: 38177505
DOI: 10.1038/s44318-023-00018-9 -
BioRxiv : the Preprint Server For... Dec 2023Expansion of trinucleotide repeats causes Huntington's disease, Fragile X syndrome and over twenty other monogenic disorders. How mismatch repair protein MutSβ and...
Expansion of trinucleotide repeats causes Huntington's disease, Fragile X syndrome and over twenty other monogenic disorders. How mismatch repair protein MutSβ and large repeats of CNG (N=A, T, C or G) cooperate to drive the expansion is poorly understood. Contrary to expectations, we find that MutSβ prefers to bind the stem of an extruded (CNG) hairpin rather than the hairpin end or hairpin-duplex junction. Structural analyses reveal that in the presence of MutSβ, CNG repeats with N:N mismatches adopt a B form-like pseudo-duplex, with one or two CNG repeats slipped out forming uneven bubbles that partly mimic insertion-deletion loops of mismatched DNA. When the extruded hairpin exceeds 40-45 repeats, it can be bound by three or more MutSβ molecules, which are resistant to ATP-dependent dissociation. We envision that such MutSβ-CNG complexes recruit MutLγ endonuclease to nick DNA and initiate the repeat expansion process. To develop drugs against the expansion diseases, we have identified lead compounds that prevent MutSβ binding to CNG repeats but not to mismatched DNA.
PubMed: 38168405
DOI: 10.1101/2023.12.12.571350 -
The Journal of Clinical Investigation Jan 2024Myotonic dystrophy type 1 (DM1) is an autosomal dominant disorder caused by an unstable expanded CTG repeat located in the 3'-UTR of the DM1 protein kinase (DMPK) gene....
Myotonic dystrophy type 1 (DM1) is an autosomal dominant disorder caused by an unstable expanded CTG repeat located in the 3'-UTR of the DM1 protein kinase (DMPK) gene. The pathogenic mechanism results in misregulated alternative splicing of hundreds of genes, creating the dilemma of establishing which genes contribute to the mechanism of DM1 skeletal muscle pathology. In this issue of the JCI, Cisco and colleagues systematically tested the combinatorial effects of DM1-relevant mis-splicing patterns in vivo and identified the synergistic effects of mis-spliced calcium and chloride channels as a major contributor to DM1 skeletal muscle impairment. The authors further demonstrated the therapeutic potential for calcium channel modulation to block the synergistic effects and rescue myopathy.
Topics: Humans; Myotonic Dystrophy; RNA Splicing; Muscle, Skeletal; Alternative Splicing; Ion Channels; Myotonin-Protein Kinase; Trinucleotide Repeat Expansion
PubMed: 38165037
DOI: 10.1172/JCI176089 -
Parkinsonism & Related Disorders Feb 2024
Topics: Humans; Spastic Paraplegia, Hereditary; Fragile X Syndrome; Trinucleotide Repeat Expansion; Fragile X Mental Retardation Protein
PubMed: 38155044
DOI: 10.1016/j.parkreldis.2023.105969 -
Clinica Chimica Acta; International... Jan 2024Fragile X syndrome (FXS) is mainly caused by FMR1 CGG repeat expansions. Other types of mutations, particularly deletions, are also responsible for FXS phenotypes,... (Review)
Review
BACKGROUND
Fragile X syndrome (FXS) is mainly caused by FMR1 CGG repeat expansions. Other types of mutations, particularly deletions, are also responsible for FXS phenotypes, however these mutations are often missed by routine clinical testing.
MATERIALS AND METHODS
Molecular diagnosis in cases of suspected FXS was a combination of PCR and Southern blot. Measurement of the FMRP protein level was useful for detecting potentially deleterious impact.
RESULTS
PCR analysis and Southern blot revealed a case with premutation and suspected deletion alleles. Sanger sequencing showed that the deletion involved 313 bp upstream of repeats and some parts of CGG repeat tract, leaving transcription start site. FMRP was detected in 5.5 % of blood lymphocytes.
CONCLUSION
According to our review of case reports, most patients carrying microdeletion and full mutation had typical features of FXS. To our knowledge, our case is the first to describe mosaicism of a premutation and microdeletion in the FMR1 gene. The patient was probably protected from the effects of the deletion by mosaicism with premutation allele, leading to milder phenotype. It is thus important to consider appropriate techniques for detecting FMR1 variants other than repeat expansions which cannot be detected by routine FXS diagnosis.
Topics: Humans; Fragile X Mental Retardation Protein; Fragile X Syndrome; Mosaicism; Mutation; Trinucleotide Repeat Expansion
PubMed: 38142803
DOI: 10.1016/j.cca.2023.117728 -
Stem Cell Research Feb 2024Friedreich's ataxia (FRDA) is a rare neurodegenerativedisorder caused by over expansion of GAA repeats in thefirstintron ofFXN gene. Here, we generated two iPSC lines...
Generation and characterization of two human iPSC lines, IGIBi014-A and IGIBi015-A, from Friedreich's ataxia (FRDA) patients with pathogenic (GAA/TTC)n repeat expansion in first intron of the Frataxin (FXN) gene.
Friedreich's ataxia (FRDA) is a rare neurodegenerativedisorder caused by over expansion of GAA repeats in thefirstintron ofFXN gene. Here, we generated two iPSC lines from FRDA patients with biallelic expansion of GAA repeats in the first intron ofFXNgene.IGIBi014-A and IGIBi015-Aboth iPSC lines demonstrated characteristics of pluripotency, normal karyotypes (46, XY),the capacity to differentiate into all three germ layers, and the ability to sustain the GAA repeat expansion with decreased FXN mRNA expression. These cell lines will be utilized to comprehend the pathophysiology of the illness and the FRDA's predictive phenotypes.
Topics: Humans; Friedreich Ataxia; Introns; Frataxin; Induced Pluripotent Stem Cells; Cell Line; Trinucleotide Repeat Expansion
PubMed: 38141359
DOI: 10.1016/j.scr.2023.103289 -
International Journal of Molecular... Dec 2023Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder that affects older premutation carriers (55-200 CGG repeats) of the fragile X gene....
Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder that affects older premutation carriers (55-200 CGG repeats) of the fragile X gene. Despite the high prevalence of the FXTAS disorder, neuropathology studies of individuals affected by FXTAS are limited. We performed hematoxylin and eosin (H&E) staining in the hippocampus of 26 FXTAS cases and analyzed the tissue microscopically. The major neuropathological characteristics were white matter disease, intranuclear inclusions in neurons and astrocytes, and neuron loss. Astrocytes contained more and larger inclusions than neurons. There was a negative correlation between age of death and CGG repeat length in cases over the age of 60. The number of astroglial inclusions (CA3 and dentate gyrus) and the number of CA3 neuronal inclusions increased with elevated CGG repeat length. In the two cases with a CGG repeat size less than 65, FXTAS intranuclear inclusions were not present in the hippocampus, while in the two cases with less than 70 (65-70) CGG repeat expansion, neurons and astrocytes with inclusions were occasionally identified in the CA1 sub-region. These findings add hippocampus neuropathology to the previously reported changes in other areas of the brain in FXTAS patients, with implications for understanding FXTAS pathogenesis.
Topics: Humans; Tremor; Gray Matter; Fragile X Mental Retardation Protein; Fragile X Syndrome; Ataxia; Hippocampus; Trinucleotide Repeat Expansion
PubMed: 38139097
DOI: 10.3390/ijms242417266 -
Cell Dec 2023Short tandem repeat (STR) instability causes transcriptional silencing in several repeat expansion disorders. In fragile X syndrome (FXS), mutation-length expansion of a...
Short tandem repeat (STR) instability causes transcriptional silencing in several repeat expansion disorders. In fragile X syndrome (FXS), mutation-length expansion of a CGG STR represses FMR1 via local DNA methylation. Here, we find megabase-scale H3K9me3 domains on autosomes and encompassing FMR1 on the X chromosome in FXS patient-derived iPSCs, iPSC-derived neural progenitors, EBV-transformed lymphoblasts, and brain tissue with mutation-length CGG expansion. H3K9me3 domains connect via inter-chromosomal interactions and demarcate severe misfolding of TADs and loops. They harbor long synaptic genes replicating at the end of S phase, replication-stress-induced double-strand breaks, and STRs prone to stepwise somatic instability. CRISPR engineering of the mutation-length CGG to premutation length reverses H3K9me3 on the X chromosome and multiple autosomes, refolds TADs, and restores gene expression. H3K9me3 domains can also arise in normal-length iPSCs created with perturbations linked to genome instability, suggesting their relevance beyond FXS. Our results reveal Mb-scale heterochromatinization and trans interactions among loci susceptible to instability.
Topics: Humans; Fragile X Syndrome; Trinucleotide Repeat Expansion; DNA Methylation; Mutation; Fragile X Mental Retardation Protein
PubMed: 38134876
DOI: 10.1016/j.cell.2023.11.019 -
Metabolites Dec 2023Huntington's disease (HD) is a progressive, fatal neurodegenerative disease characterized by motor, cognitive, and psychiatric symptoms. The precise mechanisms of HD... (Review)
Review
Huntington's disease (HD) is a progressive, fatal neurodegenerative disease characterized by motor, cognitive, and psychiatric symptoms. The precise mechanisms of HD progression are poorly understood; however, it is known that there is an expansion of the trinucleotide cytosine-adenine-guanine (CAG) repeat in the Huntingtin gene. Important new strategies are of paramount importance to identify early biomarkers with predictive value for intervening in disease progression at a stage when cellular dysfunction has not progressed irreversibly. Metabolomics is the study of global metabolite profiles in a system (cell, tissue, or organism) under certain conditions and is becoming an essential tool for the systemic characterization of metabolites to provide a snapshot of the functional and pathophysiological states of an organism and support disease diagnosis and biomarker discovery. This review briefly highlights the historical progress of metabolomic methodologies, followed by a more detailed review of the use of metabolomics in HD research to enable a greater understanding of the pathogenesis, its early prediction, and finally the main technical platforms in the field of metabolomics.
PubMed: 38132886
DOI: 10.3390/metabo13121203