Several neurodegenerative conditions such as sporadic Creutzfeldt-Jakob disease (sCJD), Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD) are associated with imbalance of iron homeostasis in diseased brains, raising the possibility that redox-iron induced oxidative damage plays a significant role in the neurotoxicity associated with these disorders. Recent evidence from the Singh laboratory indicates a significant reduction of ferroxidase activity in sCJD affected human and scrapie infected mouse brains. Combined with the fact that sCJD brains show a phenotype of 'apparent'iron deficiency despite the presence of normal or increased brain iron levels, these observations suggest dysregulation of the normal iron homeostatic machinery in diseased brains. A recent report demonstrates decreased ferroxidase activity leading to iron accumulation in AD brains, suggesting that this phenomenon is shared by neurodegenerative disorders of disparate etiology. In an independent set of studies, the Mukhopadhayay laboratory reported that ceruloplasmin (Cp), a major ferroxidase in the brain, is down regulated by reactive oxygen species (ROS). Since iron is highly redox-active and a major contributor of ROS if mismanaged, it is likely that once initiated by a specific disease process, iron imbalance is perpetuated by ROS through down regulation of major brain ferroxidases. Based on these observations, we hypothesize that ROS mediated misregulation of brain specific ferroxidases contributes to iron imbalance in AD and sCJD. The proposed studies will test this hypothesis in two specific aims.
In aim 1, the role of ROS in regulating specific ferroxidases will be investigated in cell models o AD and prion disease. Once the ferroxidases have been identified, their regulation will be compared with Cp which is known to be regulated by an mRNA decay mechanism in response to ROS. Subsequently, the minimal region of 3'UTR and binding proteins responsible for regulating ROS-mediated Cp activity will be identified.
In aim 2, the ferroxidases identified in ai 1 will be evaluated for their expression and activity in mouse models of AD and scrapie infection during disease progression. The results will be compared with human brain tissue from AD and sCJD cases using ferroxidase assay and immunohistochemistry as the read-out. Successful completion of these studies will clarify the role of major brain ferroxidases in iron dyshomeostasis associated with AD and sCJD brains, and provide the ground-work for future studies on the mechanism of brain iron dyshomeostasis in PD, HD, and other neurodegenerative conditions associated with brain iron imbalance.
Accumulation of iron in diseased brains is a common feature of several neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease, Huntington's disease, and sporadic Creutzfeldt-Jakob disease (sCJD). Since excess iron is redox-active, it is a significant cause of neurotoxicity in these disorders. Normally, brai iron metabolism is maintained by a group of proteins that regulate its uptake, release, and storage. Ceruplasmin (Cp) is a brain ferroxidase that regulates release of excess iron from cells. In this proposal we will investigate whether dysfunction of Cp or other brain ferroxidases causes accumulation of iron in diseased brains. These studies will clarify the cause of iron accumulation in AD and sCJD brains, and help in the development of therapeutic strategies aimed at restoring normal brain iron levels.
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