Increasing evidence implicates mitochondrial dysfunction in the pathogenesis of Parkinson's disease (PD): on average, PD patients have a modest, systemic defect in complex I activity;one causative gene encodes a mitochondrial kinase (PINKi);two other causative genes encode proteins (parkin &DJ-i) that traffic in and out of mitochondria;and systemic inhibition of mitochondria] function accurately reproduces many features of PD. This program brings together 4 established investigators - Tim Greenamyre, Jun Chen, Valerian Kagan and Teresa Hastings - who are each individually interested in the pathogenesis of PD and the roles that mitochondria play in this disorder. Moreover, the director of this program's neuropathology core, Charleen Chu, also has an interest and track record in mitochondria and PD. Greenamyre (Project 1) will study how iron accumulates in PD via a novel pathway mediated by transferrin and a previously unrecognized mitochondrial transferrin receptor (TfR2) that is selectively localized in substantia nigra dopaminergic neurons. Kagan (Project 2) is studying mechanisms and consequences of the interactions of alpha-synuclein with cytochrome c via binding to the mitochondrial anionic phospholipid, cardiolipin. This complex of alphasynuclein-cardiolipin-cytochrome c may prevent apoptosome formation while also promoting oxidative stress via a novel peroxidase activity. Chen (Project 3) will study mechanisms and relevance of HSP27 translocation to mitochondria and the ASKi/JNK apoptotic pathway in PD. Hastings (Project 4) will study the roles of mitochondrial selenoproteins, such as glutathione peroxidase 4 and thioredoxin reductase 2, in neurodegeneration in PD. The individual projects are supported by 2 scientific cores. The Molecular Core (Guodong Cao) will assist each project with design and production of constructs for gene overexpression or gene silencing, generation of transient and stable transfections, and production of viral vectors for in vivo gene transfer. As pathogenic mechanisms are defined in model systems in Projects 1-4, their relevance will be confirmed in postmortem human tissue in collaboration with the Neuropathology Core (Charleen Chu). The overall Program is unified and strengthened by (i) numerous scientific interactions between the projects;(ii) the use of a common set of in vitro and in vivo model systems;and (iii) the scientific cores, which will be used by each project.
As the second most common neurodegenerative disorder, PD affects 1.5 million individuals in the United States. The cause of neurodegeneration in PD is uncertain, but mitochondrial impairment has been strongly implicated. This Program will determine the roles of mitochondrial proteins in causing neurodegeneration, and each project will test novel therapeutic concepts designed to slow or stop the disease process. PROJECT 1 Principal Investigator: J. Timothy Greenamyre Title: Mechanisms &Consequences of Iron Accumulation in PD Description (provided by applicant): Our laboratory has shown that systemic inhibition of mitochondrial complex I with rotenone reproduces in rats and monkeys many features of PD, including dopaminergic degeneration, Lewy body and neurite (alpha-synuclein) pathology, DJ-i modification and translocation to mitochondria, and impairment of the ubiquitin-proteasome system. Most recently, we have found that there is iron deposition in substantia nigra of rotenone treated rats and monkeys, which appears identical to that seen in PD brains. In this model, transferrin (Tf) becomes oxidized (at Cys26o) and accumulates in nigral dopaminergic neurons. In collaboration with Charleen Chu, director of the Neuropathology Core, Greenamyre has found a similar - previously undescribed - accumulation of transferrin in nigral neurons in human postmortem specimens from PD cases. Additionally, he has found that transferrin receptor 2 (TfR2): (i) has a mitochondrial targeting sequence;(ii) is localized, in part, in mitochondria;and (iii) protein is selectively expressed in nigral dopamine neurons in rats.
Aim 1 : We will determine the sequence of cell types that accumulate iron after rotenone using the in vivo model and organotypic midbrain slice cultures, and we vAW ultimately assess this in human postmortem specimens across Braak staging.
Aim 2 : We will characterize (i) the oxidation state and distributions of Tf and TfR2 in the rotenone brain, (ii) the functional consequences of Tf oxidation, and (iii) ultimately, the distributions and oxidation states of these proteins in human specimens.
Aim 3 : We will assess the functional role of TfR2 by overexpressing or silencing the TfR2 gene under basal conditions and with rotenone treatment. Outcomes to be measured include: aspects of iron homeostasis, oxidative stress, a-synuclein/cytochrome c interactions, activation of cell death and protective mechanisms and cell viability.
Aim 4 : Lastly, we will manipulate - via viral-mediated gene transfer - proteins that regulate or chelate iron. We will look at the effects of manipulating ferritin and frataxin on rotenone-induced toxicity. We believe this project will elucidate (i) the mechanisms by which iron accumulates in PD and (ii) its role in PD pathogenesis.
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