Alzheimer?s disease (AD) is a debilitating and common form of dementia, and a leading cause of death in the United States. Testing of the amyloid hypothesis has overwhelmingly been the focus of research on AD. According to this hypothesis, pathogenic processing of the Alzheimer?s precursor protein (APP) leads to accumulation of plaques containing amyloid beta that are a hallmark, and apparent cause, of AD. Despite much effort, research based on this hypothesis has yet to provide effective therapeutic targets for AD. Thus, alternative hypotheses invoking causal roles for mitochondria and metabolism of lipids and cholesterol in AD pathogenesis have also been proposed. While these hypotheses have been tested in relation to the amyloid hypothesis, a critical mechanistic gap remains in determining whether causal roles for mitochondria and cholesterol/lipid metabolism in AD pathogenesis may be linked with one another. A role for lipid and cholesterol metabolism in AD is supported by the fact that an allele of the ApolipoproteinE (ApoE) gene, encoding the primary carrier of lipids and cholesterol in the brain, is the strongest genetic risk factor for sporadic AD. In contrast, research examining causal roles for mitochondria in AD has focused on bioenergetics and oxidative stress, although mitochondria also play known roles in cholesterol and lipid metabolism. Whether mitochondria influence ApoE expression and/or cholesterol homeostasis in the context of AD remains unexplored and will be the focus of this proposal. Our preliminary data indicates that reduced expression of the mitochondrial membrane transporter SLC25A1 increases levels of ApoE and APP. SLC25A1 shuttles the metabolite citrate from mitochondria to the cytoplasm, where it gets converted to acetyl-CoA that is required for lipid and cholesterol synthesis. The central hypothesis that will be tested in this proposal is that genetic disruption of the SLC25A1 interactome (SLC25A1 and the network of proteins with which it physically interacts) drives increased ApoE expression and changes in cholesterol homeostasis, consequently impacting downstream APP production and processing.
In Aim 1, the trainee will determine whether increased ApoE expression is a specific readout indicating dysfunction of components of the SLC25A1 interactome, or is instead a general response to mitochondrial dysfunction, using immunoblots, quantitative polymerase chain reaction (RT-qPCR), and lipidomics profiling in primary neurons and glia.
In Aim 2, the trainee will determine whether Slc25a1 gene dosage modulates AD pathology in a mouse model of AD, using plate-based immunoassays and immunocytochemistry. Completion of these aims will reveal whether mitochondria contribute to AD pathogenesis through ApoE and/or cholesterol-dependent mechanisms, as well as whether this influence is specific to a certain hub of mitochondrial proteins involved in lipid/cholesterol metabolism. These findings will improve our understanding of mechanisms contributing to AD and suggest novel drug targets for this devastating disease.
As one of the leading causes of death in the U.S., Alzheimer?s disease is a major public health concern and poses a significant burden for sufferers and their caregivers. While it is recognized that mitochondrial dysfunction and cholesterol metabolism contribute to Alzheimer?s pathogenesis, the precise mechanisms by which they do so remain incompletely understood. The proposed research will help to fill in knowledge gaps on how mitochondria and cholesterol metabolism influence one another and drive disease, and this knowledge will help to identify novel drug targets to combat this disease, for which currently available therapeutics have limited efficacy.
