Final Report Summary - POLYQ/AR (POLYGLUTAMINE DISEASES: IMPACT OF PROTEIN AND CELL CONTEXT ON NEUROTOXICITY)
In this application, we proposed to test the effect of different factors to disease pathogenesis, including protein context, protein-protein interaction, and cell context. This hypothesis is based on our preliminary data, which support the idea that the polyQ tract is not the sole determinant of disease pathogenesis. Based on the preliminary data described above, we are currently testing the central hypothesis that the toxicity of polyQ-AR is influenced at the post-translational level by phosphorylation of specific residues in the disease protein, by aberrant interaction with the Akt effector FOXO, and by tissue-specificity of disease protein expression. To test the hypothesis of this application, we are pursuing the following three specific aims:
Specific Aim 1: To characterize the impact of protein kinase A (PKA) on mutant AR toxicity.
Specific Aim 2: To characterize the role of FOXO in polyglutamine disease.
Specific Aim 3: Polyglutamine diseases: is the disease mechanism cell-autonomous?
With respect to Aim 1, we found that activation of PKA modifies the phosphorylation state of mutant AR. We obtained evidence that activation of PKA is protective in cultured cells. Indeed, activation of PKA reduces the cell death and toxicity caused by polyQ-AR. Importantly, activation of PKA reduced the accumulation of polyQ-AR in micro-oligomers, which are likely to represent toxic species.
To test the effect of protein-protein interaction in SBMA pathogenesis, we proposed to test the effect of FOXO activation in disease pathogenesis. We are investigating whether activation of FOXO is altered in the muscle of SBMA mice due to aberrant interaction with polyQ-AR. This hypothesis is based on our preliminary data, which show that activation of the insulin-like growth factor 1 (IGF-1)/Akt selectively in the muscle of SBMA mice reduces the toxicity of polyQ-AR. We previously showed that IGF-1 overexpression leads to Akt activation in skeletal muscle, and this in turn results in phosphorylation of polyQ-AR at serine 215 and serine 792. FOXO is a substrate of Akt, and phosphorylation of FOXO leads to its inactivation through nuclear exclusion of the protein. Because FOXO plays a major role in muscle atrophy, we proposed to test the hypothesis that aberrant interaction between FOXO and polyQ-AR results in overactivation of FOXO and muscle atrophy. We obtained evidence that phosphorylation of Akt, which is a measure of activation, is altered in the muscle of SBMA mice. This is consistent with the idea that FOXO is aberrantly activated in SBMA muscle.
To test the effect of cell-context in SBMA pathogenesis, we proposed to generate mice that express mutant AR in specific tissues. We generated mice for inducible expression of polyQ-AR in specific tissues.
Our results allowed us to identify important modifiers of polyQ-AR toxicity, i.e. PKA and FOXO. We propose such modifiers as novel therapeutic targets for SBMA.