The primary goal of this project is to test our core hypothesis that brain iron accumulation in Huntington's disease (HD) promotes disease onset and progression. HD is an ultimately fatal neurodegenerative disease that afflicts about 30000 people in the USA alone and has no effective treatments. CAG-repeat expansion within the huntingtin gene results in expression of a polyglutamine-expanded mutant huntingtin protein leading to a number of downstream effects including energetic dysregulation, aberrant glutamate signaling, iron elevation, oxidative and nitrosative stress, and eventually neuronal degeneration and loss. There is growing evidence that dysregulation of iron homeostasis contributes to the pathogenesis of HD as well as ALS, Parkinson's and Alzheimer's diseases. Surprisingly however, little is known about how this occurs in HD and to what degree iron dysregulation contributes to the overall disease process. We have shown for the first time that iron accumulates in mouse HD striatal and cortical neurons, regions where there is significant degeneration. Amyloid precursor protein (APP) has a key role in neuronal iron export. We show significantly decreased levels of APP as well as its iron export ferroxidase activity. We have also demonstrated elevated iron in an inducible mutant huntingtin expressing cell line and shown that nNOS inhibition reverses this. These interesting and important findings point to a link between nitric oxide, APP and iron in HD and form the basis for the proposed studies. Aim 1 will test the hypothesis that nitrosative stress mediates decreased APP protein levels resulting in elevated iron which potentiates neurodegeneration. In Aim 1A we will determine the effect of genetic modulation of APP on outcomes in HD models. In Aim 1B we study the effects of nNOS inhibition on HD outcomes including APP and iron. We will use transgenic and full-length mutant huntingtin mouse models as well as HD cell lines and primary neuron cultures. Aim 2 will test the hypothesis that nutritionally relevant elevated iron intake potentiates brain iron accumulation and neurodegeneration in HD mice. The studies will provide important insights into mechanisms of iron dysregulation in HD. Findings will determine the extent to which dysregulated iron in HD brain potentiates disease; they may validate APP as a novel therapeutic target as well as provide insight into modulatory effects of dietary iron in HD.