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G-rich motifs within phosphorothioate-based antisense oligonucleotides (ASOs) drive activation of FXN expression through indirect effects

Wang, Feng
Calvo-Roitberg, Ezequiel
Rembetsy-Brown, Julia M
Fang, Minggang
Sousa, Jacquelyn
Kartje, Zachary J
Krishnamurthy, Pranathi Meda
Lee, Jonathan
Green, Michael R.
Pai, Athma A
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Abstract

Friedreich's ataxia is an incurable disease caused by frataxin (FXN) protein deficiency, which is mostly induced by GAA repeat expansion in intron 1 of the FXN gene. Here, we identified antisense oligonucleotides (ASOs), complementary to two regions within the first intron of FXN pre-mRNA, which could increase FXN mRNA by ∼2-fold in patient fibroblasts. The increase in FXN mRNA was confirmed by the identification of multiple overlapping FXN-activating ASOs at each region, two independent RNA quantification assays, and normalization by multiple housekeeping genes. Experiments on cells with the ASO-binding sites deleted indicate that the ASO-induced FXN activation was driven by indirect effects. RNA sequencing analyses showed that the two ASOs induced similar transcriptome-wide changes, which did not resemble the transcriptome of wild-type cells. This RNA-seq analysis did not identify directly base-paired off-target genes shared across ASOs. Mismatch studies identified two guanosine-rich motifs (CCGG and G4) within the ASOs that were required for FXN activation. The phosphorodiamidate morpholino oligomer analogs of our ASOs did not activate FXN, pointing to a PS-backbone-mediated effect. Our study demonstrates the importance of multiple, detailed control experiments and target validation in oligonucleotide studies employing novel mechanisms such as gene activation.

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Wang F, Calvo-Roitberg E, Rembetsy-Brown JM, Fang M, Sousa J, Kartje ZJ, Krishnamurthy PM, Lee J, Green MR, Pai AA, Watts JK. G-rich motifs within phosphorothioate-based antisense oligonucleotides (ASOs) drive activation of FXN expression through indirect effects. Nucleic Acids Res. 2022 Dec 9;50(22):12657-12673. doi: 10.1093/nar/gkac1108. PMID: 36511872; PMCID: PMC9825156.

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10.1093/nar/gkac1108
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36511872
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© The Author(s) 2022. Published by Oxford University Press on behalf of Nucleic Acids Research. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.Attribution 4.0 International