C9ORF72 ALS

: from pathology to therapy

Abstract

A hexanucleotide GGGGCC (G4C2) repeat expansion in the chromosome 9 open reading frame 72 (C9ORF72) gene is the most common cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The expansion is transcribed from the sense and the antisense strands and accumulates in the nucleus of cells as RNA foci. Moreover, it is translated into five dipeptide repeat (DPR) proteins that accumulate in the brain and spinal cord and causes a decrease in C9ORF72 transcripts and protein levels. In the present study, we reported that there are very few DPR inclusions in the spinal cord of ALS-C9ORF72 cases and we have assessed the presence of sense and antisense RNA foci in the spinal cords of ten C9ORF72-ALS cases. We have shown that sense RNA foci are more common that antisense foci in the spinal cord, and significantly more common in spinal motor neurons of C9ORF72-ALS cases. This suggests that the presence of intranuclear sense RNA foci may be the main contributor to toxicity. We have designed non-degrading antisense phosphorodiamidate morpholino oligomers (PMOs) that bind, but not degrade G4C2 target transcripts as a potential therapeutic strategy. We tested the PMOs in HEK-293T cells expressing EGFP-72(G4C2) constructs showing that PMOs bind and reduce the number of pathological RNA foci. We have also shown that the use of PMOs reverse C9ORF72-specific phenotypes in neuronal progenitor cells (NPCs) and neurons from C9ORF72-ALS patient-derived induced pluripotent stem cells (iPSC). All together our results suggest that sense RNA foci may be the main contributor to C9ORF72-associated toxicity and that its effect can be mitigated using non-degrading PMOs targeting the G4C2 repeats. Finally, our results highlight an alternative therapeutic approach which consists in blocking the G4C2 expanded RNA transcripts but not degrading them, which may be important given that haploinsufficiency of C9ORF72 may also be a strong component of C9ORF72 ALS pathogenic mechanism.

Date of Award	1 Sept 2017
Original language	English
Awarding Institution	King's College London
Supervisor	Christopher Shaw (Supervisor) & Jean-Marc Gallo (Supervisor)