Exon 1 Editing of Mutant Huntingtin’s Gene: A Possible Approach to Cure Huntington’s Disease

Huntington’s chorea is a dominant inherited neurodegenerative disease caused by trinucleotide repeat expansion, CAG, in the exon 1 of huntingtin’s (HTT) gene. This mutation codes for an aberrant protein. These proteins gradually lead to a neuronal dysfunction, evolving towards motor, cognitive and psychiatric disorders. The existing therapeutic interventions are focused on treating the clinical symptoms. Hence, a novel therapeutic approach for correcting the pathogenic HTT mutation is needed. In the present project, we targeted the origin of the pathology, namely the mutant HTT allele with a gene editing strategy. We used the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and the CRISPR associated protein 9 (Cas9 nuclease) for an allele-specific inactivation. We designed single guide RNAs (sgRNA), which when hybridized with DNA can be recognized by Cas9 and thus induce a double strand break (DSB) upstream (HTT promoter or exon 1) and downstream of the polyglutamine expansion (intron 1) to induce the deletion of the mutant HTT exon 1. With this technique, we demonstrate that we are able to decrease the expression of HTT RNA. Then, we will show that our strategy of gene delivery by two or three viral vectors does not change the efficiency of the CRISPR/Cas9 system. Indeed, Merienne and al. (2017) presented a two-vector system with proven efficacy. However, we need to deliver more genes to achieve this project. For this, we showed that using multiple genes in a single vector does not change the efficiency of the system mentioned above. Finally, we do not observe an increase in the inflammatory response in vivo in the presence of an increased expression of Cas