Identification of selective and non-selective C9ORF72 targeting in vivo active siRNAs

Abstract

A hexanucleotide (GC) repeat expansion (HRE) within intron one of is the leading genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). haploinsufficiency, formation of RNA foci, and production of dipeptide repeat (DPR) proteins have been proposed as mechanisms of disease. Here, we report the first example of disease-modifying siRNAs for driven ALS/FTD. Using a combination of reporter assay and primary cortical neurons derived from a C9-ALS/FTD mouse model, we screened a panel of more than 150 fully chemically stabilized siRNAs targeting different transcriptional variants. We demonstrate the lack of correlation between siRNA efficacy in reporter assay versus native environment; repeat-containing mRNA variants are found to preferentially localize to the nucleus, and thus mRNA accessibility and intracellular localization have a dominant impact on functional RNAi. Using a C9-ALS/FTD mouse model, we demonstrate that divalent siRNAs targeting mRNA variants specifically or non-selectively reduce the expression of mRNA and significantly reduce DPR proteins. Interestingly, siRNA silencing all mRNA transcripts was more effective in removing intranuclear mRNA aggregates than targeting only HRE-containing mRNA transcripts. Combined, these data support RNAi-based degradation of as a potential therapeutic paradigm.