Gene therapy by proteasome activator, PA28γ, improves motor coordination and proteasome function in Huntington's disease YAC128 mice

Huntington's disease (HD) is neurologically characterized by involuntary movements, associated with degeneration of the medium-sized spiny neurons (MSNs) and ubiquitin-positive neuronal intranuclear inclusions (NIIs). It has been reported that the proteolytic activities of the ubiquitin-proteasome system (UPS) are generally inhibited in HD patient's brain. We previously discovered that a proteasome activator (PA), PA28γ enhances proteasome activities and cell survival in in vitro HD model. In this study, we aimed to find whether PA28γ gene transfer improves the proteasome activities and pathological symptoms in in vivo HD model. We stereotaxically injected lenti-PA28γ virus into the striatum of mutant (MT) YAC128 HD mice and littermate (LM) controls at 14-18 months of age, and validated their behavioral and biochemical changes at 12 weeks after the injection. YAC128 mice showed a significant increase in their peptidyl-glutamyl preferring hydrolytic (PGPH) proteasome activity and the mRNA or protein levels of brain-derived neurotrophic factor (BDNF) and pro-BDNF after lenti-PA28γ injection. The number of ubiquitin-positive inclusion bodies was reduced in the striatum of YAC128 mice after lenti-PA28γ injection. YAC128 mice showed significant improvement of latency to fall on the rota-rod test after lenti-PA28γ injection. These data demonstrate that the gene therapy with PA, PA28γ can improve UPS function as well as behavioral abnormalities in HD model mice.