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Project description:Huntington’s disease (HD) is an incurable neurodegenerative disorder caused by genetic expansion of a CAG repeat sequence in one allele of the huntingtin (HTT) gene. Reducing expression of the mutant HTT (mutHTT) protein has remained a clear therapeutic goal but reduction of wild-type HTT (wtHTT) is undesirable as it compromises gene function and potential therapeutic efficacy. One promising allele- selective approach involves targeting the CAG repeat expansion with steric binding small RNAs bearing central mismatches. However, successful genetic encoding requires consistent placement of mismatches to the target within the small RNA guide sequence, which involves 5' processing precision by cellular enzymes. Here, we used small RNA sequencing to monitor processing precision of a limited set of CAG repeat- targeted small RNAs expressed from multiple scaffold contexts. Small RNA sequencing identified expression constructs with high guide strand 5' processing precision that also conferred promising allele-selective inhibition of mutHTT. However, mRNA-seq revealed varying degrees of transcriptome-wide off-target effects, including certain CAG repeat-containing mRNAs. These results support the continued investigation and optimization of genetically encoded repeat-targeted small RNAs for allele-selective HD gene therapy and underscore the value of sequencing methods to balance specificity with allele selectivity during the design and selection process.
2024-05-01 | GSE264218 | GEO
Project description:Huntington’s disease (HD) is an incurable neurodegenerative disorder caused by genetic expansion of a CAG repeat sequence in one allele of the huntingtin (HTT) gene. Reducing expression of the mutant HTT (mutHTT) protein has remained a clear therapeutic goal but reduction of wild-type HTT (wtHTT) is undesirable as it compromises gene function and potential therapeutic efficacy. One promising allele- selective approach involves targeting the CAG repeat expansion with steric binding small RNAs bearing central mismatches. However, successful genetic encoding requires consistent placement of mismatches to the target within the small RNA guide sequence, which involves 5' processing precision by cellular enzymes. Here, we used small RNA sequencing to monitor processing precision of a limited set of CAG repeat- targeted small RNAs expressed from multiple scaffold contexts. Small RNA sequencing identified expression constructs with high guide strand 5' processing precision that also conferred promising allele-selective inhibition of mutHTT. However, mRNA-seq revealed varying degrees of transcriptome-wide off-target effects, including certain CAG repeat-containing mRNAs. These results support the continued investigation and optimization of genetically encoded repeat-targeted small RNAs for allele-selective HD gene therapy and underscore the value of sequencing methods to balance specificity with allele selectivity during the design and selection process.
2024-05-01 | GSE242506 | GEO
Project description:Sequencing-Guided Design of Genetically Encoded Small RNAs Targeting CAG Repeats for Selective Inhibition of Mutant Huntingtin
| PRJNA1102415 | ENA
Project description:Sequencing-Guided Design of Genetically Encoded Small RNAs Targeting CAG Repeats for Selective Inhibition of Mutant Huntingtin [I]
| PRJNA1013598 | ENA
Project description:Sequencing-Guided Design of Genetically Encoded Small RNAs Targeting CAG Repeats for Selective Inhibition of Mutant Huntingtin [II]
| PRJNA1101493 | ENA
Project description:The specific silencing of the gene of interest is the major objective of RNA interference technology; therefore, unique sequences but not abundant sequence repeats are targeted by silencing reagents. Here, we describe the targeting of expanded CAG repeats that occur in transcripts derived from the mutant allele of the gene implicated in Huntington's disease (HD) in the presence of the normal allele and other human mRNAs containing CAG and CUG repeat tracts. We show that a high degree of silencing selectivity may be achieved between the repeated sequences. We demonstrate preferential suppression of the mutant huntingtin allele and concomitant activation of the normal huntingtin allele in cell lines derived from HD patients that were transfected with short RNA duplexes composed of CAG and CUG repeats containing mutations at specific positions. These effects may lead to promising therapeutic modalities for HD, a condition for which no therapy presently exists.
| S-EPMC3141264 | biostudies-literature
Project description:Huntington's disease is an incurable neurodegenerative disorder caused by expansion of a CAG trinucleotide repeat within one allele of the huntingtin (HTT) gene. Agents that block expression of mutant HTT and preserve expression of wild-type HTT target the cause of the disease and are an alternative for therapy. We have previously demonstrated that mismatch-containing duplex RNAs complementary to the expanded trinucleotide repeat are potent and allele-selective inhibitors of mutant HTT expression, but the mechanism of allele selectivity was not explored. We now report that anti-CAG duplex RNA preferentially recruits argonaute 2 (AGO2) to mutant rather than wild-type HTT mRNA. Efficient inhibition of mutant HTT protein expression requires less AGO2 than needed for inhibiting wild-type expression. In contrast, inhibiting the expression of mutant HTT protein is highly sensitive to reduced expression of GW182 (TNRC6A) and its two paralogs, a protein family associated with miRNA action. Allele-selective inhibition may involve cooperative binding of multiple protein-RNA complexes to the expanded repeat. These data suggest that allele-selective inhibition proceeds through an RNA interference pathway similar to that used by miRNAs and that discrimination between mutant and wild-type alleles of HTT mRNA is highly sensitive to the pool of AGO2 and GW182 family proteins inside cells.
| S-EPMC3526262 | biostudies-literature
Project description:Huntington's disease (HD) is a polyglutamine disorder caused by a CAG expansion in the Huntingtin (HTT) gene exon 1. This expansion encodes a mutant protein whose abnormal function is traditionally associated with HD pathogenesis; however, recent evidence has also linked HD pathogenesis to RNA stable hairpins formed by the mutant HTT expansion. Here, we have shown that a locked nucleic acid-modified antisense oligonucleotide complementary to the CAG repeat (LNA-CTG) preferentially binds to mutant HTT without affecting HTT mRNA or protein levels. LNA-CTGs produced rapid and sustained improvement of motor deficits in an R6/2 mouse HD model that was paralleled by persistent binding of LNA-CTG to the expanded HTT exon 1 transgene. Motor improvement was accompanied by a pronounced recovery in the levels of several striatal neuronal markers severely impaired in R6/2 mice. Furthermore, in R6/2 mice, LNA-CTG blocked several pathogenic mechanisms caused by expanded CAG RNA, including small RNA toxicity and decreased Rn45s expression levels. These results suggest that LNA-CTGs promote neuroprotection by blocking the detrimental activity of CAG repeats within HTT mRNA. The present data emphasize the relevance of expanded CAG RNA to HD pathogenesis, indicate that inhibition of HTT expression is not required to reverse motor deficits, and further suggest a therapeutic potential for LNA-CTG in polyglutamine disorders.
| S-EPMC5096913 | biostudies-literature
Project description:Expanded trinucleotide repeats cause many neurological diseases. These include Machado-Joseph disease (MJD) and Huntington's disease (HD), which are caused by expanded CAG repeats within an allele of the ataxin-3 (ATXN3) and huntingtin (HTT) genes, respectively. Silencing expression of these genes is a promising therapeutic strategy, but indiscriminate inhibition of both the mutant and wild-type alleles may lead to toxicity, and allele-specific approaches have required polymorphisms that differ among individuals. We report that peptide nucleic acid and locked nucleic acid antisense oligomers that target CAG repeats can preferentially inhibit mutant ataxin-3 and HTT protein expression in cultured cells. Duplex RNAs were less selective than single-stranded oligomers. The activity of the peptide nucleic acids does not involve inhibition of transcription, and differences in mRNA secondary structure or the number of oligomer binding sites may be important. Antisense oligomers that discriminate between wild-type and mutant genes on the basis of repeat length may offer new options for developing treatments for MJD, HD and related hereditary diseases.
| S-EPMC2765218 | biostudies-literature
Project description:Huntington's disease (HD) is a currently incurable neurodegenerative disease caused by the expansion of a CAG trinucleotide repeat within the huntingtin (HTT) gene. Therapeutic approaches include selectively inhibiting the expression of the mutated HTT allele while conserving function of the normal allele. We have evaluated a series of antisense oligonucleotides (ASOs) targeted to the expanded CAG repeat within HTT mRNA for their ability to selectively inhibit expression of mutant HTT protein. Several ASOs incorporating a variety of modifications, including bridged nucleic acids and phosphorothioate internucleotide linkages, exhibited allele-selective silencing in patient-derived fibroblasts. Allele-selective ASOs did not affect the expression of other CAG repeat-containing genes and selectivity was observed in cell lines containing minimal CAG repeat lengths representative of most HD patients. Allele-selective ASOs left HTT mRNA intact and did not support ribonuclease H activity in vitro. We observed cooperative binding of multiple ASO molecules to CAG repeat-containing HTT mRNA transcripts in vitro. These results are consistent with a mechanism involving inhibition at the level of translation. ASOs targeted to the CAG repeat of HTT provide a starting point for the development of oligonucleotide-based therapeutics that can inhibit gene expression with allelic discrimination in patients with HD.
| S-EPMC2991413 | biostudies-literature