M04 Preventing Formation Of Toxic N-terminal Huntingtin Fragments Through Antisense Oligonucleotide-mediated Protein Modification

Abstract

Several studies have implicated the importance of proteolytic cleavage of the mutant huntingtin protein in Huntington disease (HD) pathogenesis and it is generally accepted that N-terminal polyglutamine-containing huntingtin fragments are more toxic than full-length huntingtin protein. While recent publications have shown promising results reducing mutant huntingtin toxicity by lowering huntingtin levels using antisense oligonucleotides, there is some concern regarding unwanted side effects caused by lowering huntingtin protein levels too much. In our study we reduce mutant huntingtin toxicity by modifying the huntingtin protein to prevent proteolytic cleavage and subsequent formation of toxic N-terminal huntingtin fragments. Using antisense oligonucleotides, we induce skipping of huntingtin exon 12 that encodes important cleavage sites. In vitro studies showed successful exon skipping and appearance of a shorter huntingtin protein, that is resistant to caspase 6 cleavage. Pilot studies in the YAC128 transgenic HD mouse model revealed skipping of human huntingtin exon 12 after a single intracerebroventricular injection of antisense oligonucleotides. We have recently started a follow-up study to assess the longitudinal phenotypical effect of antisense oligonucleotide-mediated exon skipping in YAC128 HD mice.