Project Summary/Abstract Biochemical analysis and cell based phenotypic assays clearly establish the impact of modulation of the TRiC chaperonin system on mutant Huntingtin protein. To develop an effective TRiC based therapeutic strategy for blunting the pathological impact of mutant HTT, it is essential that studies on TRiC chaperonin interactions with mutant HTT be carried out in an animal model setting as close as possible to the human brain. The studies proposed in this project directly address this central issue. Aim 1: To perform an integrated evaluation of the impact of apiCCT1 delivery to the mouse striatum on mutant HTT biochemistry and quantitative measures of HD pathology. Preliminary data demonstrates that exogenous application of the apical domain of CCT1 in cells is sufficient to modulate aberrant accumulation of mHTT. To form an accurate and quantitative understanding of the impact of apiCCT1 delivery to CNS cells in vivo we will deliver apiCCT1 by several alternative modalities and 1) carry out assessments of the status and levels of aberrant forms of expanded repeat containing HTT including soluble, oligomeric and fibrillar forms, 2) assess the impact on HD pathological phenotypes in HD mouse models, including using reporters for the measure of transcriptional dysregulation, an early, characteristic HD phenotype, and 3) quantitatively assess the efficiency of uptake and subcellular localization of delivered apiCCT1. Aim 2: Evaluate the impact of the modulation of additional components of the TRiC system and TRiC inspired reagents on HD pathology and mutant HTT behavior in mouse brain. In projects 1 and 2 of this proposal, novel TRiC based or TRiC inspired reagents including novel forms of apiCCT1 optimized for therapeutic benefit, other components of the TRiC chaperonin system such as CCT3 and CCT5 and combinations of TRiC inspired reagents, will be developed. In this project, these novel TRiC inspired reagents will be tested in mouse brain for their impact on mutant HTT driven pathology and biochemistry using methodologies used for apiCCT1 in specific aim 1. Aim 3: Bring an optimized TRiC based therapeutic strategy to full scale behavioral testing and evaluation of neuronal trafficking in HD model mice to evaluate the potential clinical utility of this strategy. We will carry out full scale behavioral testing in fragment (R6/2) and full length (BACHD) HD model mice of optimized TRiC chaperonin based therapeutic intervention for HD. These studies will be designed to serve as initial preclinical studies to evaluate TRiC chaperonin therapy for human use. We will use neuronal trafficking assays based on studies already shown to demonstrate the striking impact of TRiC chaperonin activity in cell culture to assess the impact of TRiC chaperonin therapy on this significant parameter of neuronal health and function on full length HD model mice in vivo.