Anti-gene oligonucleotides targeting Friedreich's ataxia expanded GAA⋅TTC repeats increase Frataxin expression

Friedreich's ataxia is a progressive, autosomal recessive ataxia caused, in most cases, by homozygous expansion of GAA⋅TTC triplet-repeats in the first intron of the Frataxin gene. GAA⋅TTC repeat expansion results in the formation of a non-B-DNA intramolecular triplex as well as changes in the epigenetic landscape at the Frataxin locus. Expansion of intronic GAA⋅TTC repeats is associated with reduced levels of Frataxin mRNA and protein, resulting in disease development. In our previous study, we demonstrated that DNA-binding anti-gene oligonucleotides specifically targeting the GAA⋅TTC repeat expansion effectively disrupted the formation of intramolecular triplex structures. In this study, we extend these findings by showing that targeting repeat-expanded chromosomal DNA with anti-gene oligonucleotides leads to an increase in Frataxin mRNA and protein levels in cells derived from Friedreich's ataxia patients. We examined numerous anti-gene oligonucleotides and found that the design, length, and their locked nucleic acid composition have a high impact on the effectiveness of the treatment. Collectively, our results demonstrate the unique capability of specifically designed oligonucleotides targeting the GAA⋅TTC DNA repeats to upregulate Frataxin gene expression.