Age-related metabolic alterations in amyloid processing in Alzheimer's disease

University Of California-Irvine, Irvine CA

Investigators

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Abstract

Our strategic goal is to validate a new paradigm for the age-related causative mechanisms of Alzheimer's disease (AD) by interventions in cellular and amyloid metabolism with small molecules. Specifically, we hypothesize that age-related metabolic changes alter the processing and accumulation of amyloid aggregates inside neurons leading to neurodegeneration. This hypothesis is the inverse of the common formulation of the amyloid hypothesis, which proposes that soluble Aß is secreted from neurons, aggregates in the extracellular space and causes neurodegeneration from the outside. Based on new preliminary data, we propose two alternatives that a) age-related metabolic shifts lead to increased iAß aggregation and death, or b) age-related intraneuronal amyloid (iAß) aggregation leads to neuronal metabolic dysfunction and death. Recent clinical trials of drugs that inhibit secretion of Aß and decrease the concentration of Aß in the interstitial fluid exacerbate cognitive dysfunction in humans and have no effect on plaque accumulation. These results encourage the alternative amyloid hypothesis and suggest that an age-related intracellular retention and accumulation of insoluble long Aßs may initiate pathogenesis leading to neurodegeneration. Our proposal combines 26 years of Charles Glabe's expertise on amyloid aggregation and conformation specific antibodies with Greg Brewer's 30 years of experience in culturing brain neurons and their age-related metabolic changes. Brewer's studies suggest that an oxidative shift in the brain NADH/NAD redox state is upstream of age-related deficits in glucose uptake, mitochondrial deficits and defenses against oxyradicals. Here, we will test the hypothesis that this age-related oxidative shift directs amyloid processing toward a more pathogenic aggregation-prone state that overwhelms proteostasis or conversely, that age-related changes in iAß proteostasis combine with and worsen age-related metabolic changes to promote neurodegeneration. We propose interventions to test key predictions of our hypothesis at three levels: a) in primary AD-transgenic (AD- Tg) neuron cultures from aged compared to those from younger mice and aged non-Tg mice, b) in AD-Tg mouse brain and c) iAß levels in human AD cases. In aim 1, we will evaluate metabolic interventions for downstream effects on iAß processing. In aim 2, we will use gamma secretase inhibitors and modulators for their downstream impact on neurodegenerative metabolism. In aim 3, based on our new findings, we will demonstrate target validity by using safe small molecule precursors to NADH and a Nrf2 inducer or gamma secretase modulator in combination to determine their efficacy to decrease iAß levels and improve metabolic function. Together with our unique tools of end-specific and conformation-dependent antibodies and culture of neurons from adult and aged mice, we will determine the mechanistic basis for an age-related metabolic shift in Aß processing. The completion of this project may initiate a paradigm shift for an age-related metabolic basis of iAß processing as a mechanism of neuronal degeneration underlying cognitive dysfunction in AD. An accurate understanding of the disease mechanisms will provide a better focus for development of drugs that prevent or reverse cognitive decline.