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Inhibition of mutant huntingtin expression by RNA duplex targeting expanded CAG repeats.

ABSTRACT: 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.

SUBMITTER: Fiszer A

PROVIDER: S-EPMC3141264 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature

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Inhibition of mutant huntingtin expression by RNA duplex targeting expanded CAG repeats.

Fiszer Agnieszka A Mykowska Agnieszka A Krzyzosiak Wlodzimierz J WJ

Nucleic acids research 20110322 13

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 silencin ...[more]

PMID: 21427085

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Allele-selective inhibition of mutant huntingtin expression with antisense oligonucleotides targeting the expanded CAG repeat.

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.

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Allele-specific silencing of mutant huntingtin and ataxin-3 genes by targeting expanded CAG repeats in mRNAs.

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Sequencing-Guided Design of Genetically Encoded Small RNAs Targeting CAG Repeats for Selective Inhibition of Mutant Huntingtin

Project description:This SuperSeries is composed of the SubSeries listed below.

2024-05-01 | GSE264444 | GEO

Sequencing-Guided Design of Genetically Encoded Small RNAs Targeting CAG Repeats for Selective Inhibition of Mutant Huntingtin [II]

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.

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Sequencing-Guided Design of Genetically Encoded Small RNAs Targeting CAG Repeats for Selective Inhibition of Mutant Huntingtin [I]

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Mutant CAG repeats of Huntingtin transcript fold into hairpins, form nuclear foci and are targets for RNA interference.

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An Expanded CAG Repeat in Huntingtin Causes +1 Frameshifting.

Project description:Maintenance of triplet decoding is crucial for the expression of functional protein because deviations either into the -1 or +1 reading frames are often non-functional. We report here that expression of huntingtin (Htt) exon 1 with expanded CAG repeats, implicated in Huntington pathology, undergoes a sporadic +1 frameshift to generate from the CAG repeat a trans-frame AGC repeat-encoded product. This +1 recoding is exclusively detected in pathological Htt variants, i.e. those with expanded repeats with more than 35 consecutive CAG codons. An atypical +1 shift site, UUC C at the 5' end of CAG repeats, which has some resemblance to the influenza A virus shift site, triggers the +1 frameshifting and is enhanced by the increased propensity of the expanded CAG repeats to form a stem-loop structure. The +1 trans-frame-encoded product can directly influence the aggregation of the parental Htt exon 1.

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Self-duplexing CUG repeats selectively inhibit mutant huntingtin expression.

Project description:Huntington's disease (HD) is a neurodegenerative genetic disorder caused by the expansion of the CAG repeat in the translated sequence of the HTT gene. This expansion generates a mutant huntingtin protein that contains an abnormally elongated polyglutamine tract, which, together with mutant transcript, causes cellular dysfunction. Currently, there is no curative treatment available to patients suffering from HD; however, the selective inhibition of the mutant allele expression is a promising therapeutic option. In this study, we developed a new class of CAG repeat-targeting silencing reagents that consist of self-duplexing CUG repeats. Self-duplex formation was induced through one or several U-base substitutions. A number of self-duplexing guide-strand-only short interfering RNAs have been tested through transfection into cells derived from HD patients, showing distinct activity profiles. The best reagents were highly discriminatory between the normal and mutant HTT alleles (allele selectivity) and the HTT transcript and other transcripts containing shorter CAG repeats (gene selectivity). We also demonstrated that the self-duplexing CUG repeat short interfering RNAs use the RNA interference pathway to elicit silencing, and repeat-targeting reagents showed similar activity and selectivity when expressed from short hairpin RNA vectors to achieve more durable silencing effects.

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