IMPLEMENTATION OF A NOVEL FLUORESCENT HUNTINGTON’S DISEASE MODEL AND BRANAPLAM TO STUDY THE INTERACTION BETWEEN HUNTINGTIN AND HAP40

Abstract

Huntington’s disease (HD) is a neurodegenerative disease caused by a CAG expansion in the HTT gene, which causes an expansion in the polyglutamine tract of the huntingtin protein. In 2018, the cryo-EM structure of the 350 kDa protein huntingtin (Htt) in complex with huntingtin associated protein of 40 kDa (HAP40) was solved, which demonstrated that huntingtin had to be co-translated and complexed with HAP40 to retain structure. However, little is known about HAP40 and thus the biological relevance of this structure. In this project, we transduced cells with fluorescently labelled recombinant apo-Htt or Htt-HAP40 to determine if HAP40 must be complexed with huntingtin in order for huntingtin to have biological activity. This method has not been implemented in HD research and may also improve current fluorescent microscopy models for huntingtin, as it has the advantage of looking at full-length protein rather than small fragments. We also found that with the huntingtin lowering drug branaplam, there is a linear correlation between huntingtin and HAP40 levels, where HAP40 levels will decrease when huntingtin levels are directly decreased as detected by western blot analysis. Furthermore, we found that this lowering effect by branaplam ameliorates DNA repair deficits in HD. With the potential for branaplam to become a treatment for HD, we should continue to test its effect on other HD-associated phenotypes to determine the effect of huntingtin and downstream HAP40 lowering.