RNA G‑Quadruplex Reprogramming with Guanine-Rich Antisense Oligonucleotides Inhibits Monoamine Oxidase B's Translation.

The human transcriptome contains secondary RNA structures like RNA G-quadruplexes (rG4s) which regulate biological processes such as translation by ribosome stalling. Canonical rG4s, which are stabilized by both Hoogsteen hydrogen bonds and potassium ions, are known to hinder translation in the 5' untranslated region (5'UTR) of mRNAs. In neurodegenerative diseases, including Parkinson's disease (PD), rG4s have been shown to influence protein synthesis. However, the impact of rG4s in nonmutated therapeutic targets like monoamine oxidase B (MAOB), an enzyme involved in dopamine metabolism, remains unexplored. In this study, an rG4 located in the MAOB mRNA's 5'UTR was identified, and ways to either stabilize or reprogram this rG4 were explored. The translation inhibitory role of the rG4 was demonstrated both in vitro and in cellulo and was shown to be further accentuated in the presence of the PhenDC3 ligand. As an alternative to ligands, which cannot specifically stabilize only one G4, the MOAB rG4 was reprogrammed with G-rich antisense oligonucleotides (G-ASOs) from a two-quartets to three-quartets G4. The G-ASOs, either unmodified DNA or 2'OMe, were shown to both induce a new rG4 folding through intermolecular interactions and to specifically reduce the translation of MAOB both in vitro and in cellulo. These findings propose a targeted approach with which to modulate rG4 structures for therapeutics, suggesting that rG4 folding, when stabilized by G-ASOs, could regulate protein synthesis and even potentially alleviate PD symptoms by reducing MAOB activity. This approach opens new avenues as it could be used to reduce the expression of many therapeutic protein targets.