The Study of Two Strategies for Decreasing Mutant Huntingtin: Degradation by Puromycin SensitiveAminoPeptidase and RNA Interference: A Dissertation

Abstract

Huntington’s disease (HD) is a fatal neurodegenerative disease caused by a CAG repeat expansion in exon 1 of the huntingtin gene, resulting in an expanded polyglutamine (polyQ) repeat in the huntingtin protein. Patients receive symptomatic treatment for motor, emotional, and cognitive impairments; however, there is no treatment to slow the progression of the disease, with death occurring 15-20 years after diagnosis. Mutant huntingtin protein interferes with multiple cellular processes leading to cellular dysfunction and neuronal loss. Due to the complexity of mutant huntingtin toxicity, many approaches to treating each effect are being investigated. Unfortunately, addressing one cause of toxicity might not result in protection from other toxic insults, necessitating a combination of treatments for HD patients. Ideally, single therapy targeting the mutant mRNA or protein could prevent all downstream toxicities caused by mutant huntingtin. In this work, I used animal models to investigate a potential therapeutic target for decreasing mutant huntingtin protein, and I apply bioluminescent imaging to investigate RNA interference to silence mutant huntingtin target sites. The enzyme puromycin sensitive aminopeptidase (PSA) has the unique property of degrading polyQ peptides and been implicated in the degradation of huntingtin. In this study, we looked for an effect of decreased PSA on the pathology and behavior in a mouse model of Huntington’s disease. To achieve this, we crossed HD mice with mice with one functional PSA allele and one inactivated PSA allele. We found that PSA heterozygous HD mice develop a greater number of pathological inclusion bodies, representing an accumulation of mutant huntingtin in neurons. PSA heterozygous HD