I004 Impact of selective lowering of mutant-Huntingtin by antisense oligonucleotides (ASOs)

<h3></h3> Huntington Disease (HD) is a neurodegenerative disorder caused by the abnormal expansion of a glutamine-encoding CAG repeat in the huntingtin (HTT) gene. There is no treatment to delay or prevent HD pathogenesis but approaches using antisense oligonucleotides (ASO) represent a promising strategy. Here, we investigate the use of mutant allele selective ASO on human HD model to investigate its potential benefits over a non-selective HTT silencing approach. We identified two induced pluripotent stem cell (iPSCs) lines derived from HD patient with 109 and 69Q repeats both heterozygotes for a specific single nucleotide polymorphism (SNP) only present on mutant-HTT isoform. We use an ASO targeting this SNP (ASO_SNP) to silence specifically mutant-HTT. We describe here the selectivity and functional impact of ASO_SNP and of ASO_PAN, a ‘pan-allelic’ ASO targeting both wt and mut-HTT mRNA, in a cortico-cortical networks from human HD neurons in microfluidic devices. We observed an efficient HTT-lowering activity for both ASOs and selective mutant-HTT-lowering only for ASO_SNP. We explored the capacity of both ASOs to rescue neuronal dysfunctions induced by HD. First, we observed that while non-selective silencing of both wt and mut-HTT impairs BDNF-containing-vesicle trafficking, the selective lowering of mut-HTT, with ASO_SNP, improved vesicles mobility. Next, we investigated ASOs effects on synaptic transmission and found that while silencing mut-HTT did not restore post-synaptic survival pathways in this model, it increased the number of synapses. Finally, we found that silencing both HTT alleles exacerbated HD dysfunctions in contrast to the use of mut-HTT selective silencing.