The molecular response of a toxic GGGGCCexp RNA on the cellular transcriptome in iPS neurons and human CNS tissue.

A mutation in the chromosome 9 open reading frame 72 (C9ORF72) is known as the most common known genetic cause of both familial and sporadic amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) as of today. This mutation consists of a GGGGCC hexanucleotide repeat expansion (HRE) sequence in the C9ORF72 gene which, when transcribed, causes RNA to form toxic foci that sequester certain RNA binding proteins (RBPs). We propose that this would lead to an aberrant transcriptome due to altered functionality of these RBPs. Preliminary data suggest that a novel antisense oligonucleotide (ASO) therapeutic increases cell viability and restores normal expression of some altered genes in neurons differentiated from ALS patient derived induced pluripotent stem cell neurons (iPSN). In order to better understand the mechanism of this disease in patients and to assess the success of treatments with ASOs, we explore potential biomarkers that will help monitoring efficacy of ASO treatment. We are investigating these biomarkers by investigating the transcriptome of mutant iPSNs with and without antisense as well as by investigating the effects of a loss of C9ORF72 gene function on gene expression in healthy iPSNs. A construct containing different repeat lengths of the GGGGCC HRE has also been produced and we are studying the presence of established ALS/FTD C9ORF72 HRE phenomena in cells transfected with these construct to potentially form a new molecular model for the repeat mutation.