Novel L-RNA Aptamer Controls APP Gene Expression in Cells by Targeting RNA G-Quadruplex Structure

Guanine quadruplex (G4) structure is a four-stranded nucleic acid secondary structure motif with unique chemical properties and important biological roles. Amyloid precursor protein (APP) is an Alzheimer's disease (AD)-related gene, and recently, we reported the formation of RNA G4 (rG4) at the 3'UTR of APP mRNA and demonstrated its repressive role in translation. Herein, we apply rG4-SELEX to develop a novel L-RNA aptamer, L-Apt.8f, which binds to APP 3'UTR D-rG4 strongly with subnanomolar affinity. We structurally characterize the aptamer and find that it contains a thermostable and parallel G4 motif, and mutagenesis analysis identifies the key nucleotides that are involved in the target recognition. We also reveal that the L-Apt.8f-APP D-rG4 interaction is enantiomeric-, magnesium ion-, and potassium ion-dependent. Notably, L-Apt.8f preferentially recognizes APP rG4 over other structural motifs, and it can control the APP reporter gene and native transcript translation in cells. Our work introduces a novel strategy and reports a new L-aptamer candidate to target APP 3'UTR rG4 structure, which laid the foundation for further applying L-RNA as an important class of biomolecule for practical L-aptamer-based targeting and controlling of gene expression in cells.