Inhibition of PolyGA Dipeptide Repeat Protein Aggregation by Nucleic Acid Aptamers in C9 Amyotrophic Lateral Sclerosis-Frontotemporal Dementia Models.

Abstract

Hexanucleotide (GGGGCC) repeat expansion in non-coding region of C9ORF72 is the main genetic cause of amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD). Gain of toxic function, via RNA or proteins, or loss of function via haploinsufficiency, are probable mechanisms of disease progression. Expanded GGGGCC repeat codes for dipeptide repeat (DPR) proteins which form inclusions in the brain. Among all the dipeptides, aggregates formed by polyGA sequence are the most toxic. In this work, inhibition of aggregation of polyGA DPRs using aptamers has been explored as a therapeutic strategy to delay disease progression. Target-specific, high-affinity RNA aptamers were selected against monomeric (GA)₃₀. Selected aptamers showed significant inhibition of aggregation of (GA)₃₀ in vitro. Inhibitory RNA sequences were seen to form typical secondary structures which was missing in a non-inhibitory sequence. Some of the RNA aptamers showed increased solubilisation of DPRs formed by (GA)₃₀ and (GA)₆₀ in a neuronal cell model of ALS-FTD. Decreased aggregation was accompanied by lower oxidative stress and improved cell survival. Importantly, expression level of one of the markers of autophagy was significantly enhanced in the presence of aptamers, explaining lower aggregation observed in these cells. Thus, aptamers may be developed as potential therapeutic agents in C9 ALS-FTD.