Anti-gene oligonucleotides targeting Friedreich’s ataxia expanded GAA•TTC repeats increase Frataxin expression

Abstract

ABSTRACTFriedreich’s ataxia (FRDA) is a progressive, autosomal recessive ataxia caused, in the majority of cases, by homozygous expansion of GAA•TTC triplet-repeats in the first intron of thefrataxin(FXN) gene. GAA•TTC repeat expansion results in the formation of non-B DNA intramolecular triplex structure (H-DNA) as well as changes in the epigenetic landscape atFXNloci and heterochromatin formation. Expansion of intronic GAA•TTC repeats is associated with reduced levels ofFXNmRNA and protein resulting in disease development. Previously, we reported that DNA-binding anti-gene oligonucleotides (AGOs) targeting the GAA•TTC repeat expansion abolished H-DNA formation. Here, we demonstrate that targeting repeat-expanded chromosomal DNA using single-strand locked nucleic acid (LNA)-DNA mixmer AGOs increases FXN mRNA and protein expression in patient-derived cells. We examined numerous LNA-DNA AGOs and found that the design, length and their LNA composition have a high impact on the effectiveness of the treatment. Collectively, our results demonstrate the unique capability of specifically designed ONs targeting the GAA•TTC DNA repeats to upregulateFXNgene expression.