Huntington's Disease and the Striatum

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This new, revised R01 application is based on the success in achieving the goals of a previous R21 award, i.e. the creation of a "striatal-specific" transgenic mouse model of Huntington's disease. In brief, this mouse model, demonstrates medium spiny nuclear inclusions, a motor disorder, and transcriptional dysregulation. Huntington's disease (HD) is an autosomal dominant disorder caused by a mutation in the IT15 gene encoding the protein huntingtin (htt). The mutation consists of an expanded polyglutamine (polyQ) region characterized by GAG repeats (The Huntington's Disease Collaborative Research Group, 1993), and the protein is expressed throughout the nervous system and periphery. Many questions remain as to the pathopnysiology of HD, and answering these questions is crucial to directing therapeutic approaches. Relevant to this proposal, these questions include: 1) Expression of mutant huntingtin in striatal neurons sufficient to produce MSN dysfunction, including transcriptional dysregulation. What are striatal-specific mechanisms of transcriptional dysregulation? And 2) Does loss of striatal brain-derived neurotrophic factor (BDNF) function via deletion of post-synaptic trkB receptors in the adult exacerbate an HD phenotype in a mouse model? Using this new mouse model and the knowledge of the DMA sequence required for gene expression in the striatum, we will investigate the mechanism of transcriptional dysregulation with a focus on acetylation status and protein interaction with striatal-specific regulatory regions of the DARPP-32 gene, using gel-shift, super-shift, and chromatin immunoprecipitation. Using genetically engineered mice with a deletion of the trkB receptor in the striatum, we will use behavioral, morphologic and molecular assays to determine whether or not BDNF/trkB loss of function exacerbates the HD phenotype. Knowledge of striatal-specific transcriptional regulation will also be highly relevant to other diseases of the basal ganglia in which transcriptional dysregulation plays a role. II.