Metabolic Vulnerability and Effects of APOE in Human Neurons with Impaired Endocytic Recycling

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PROJECT SUMMARY Neurodegenerative dementias, including Alzheimer’s disease, inflict devastating cognitive decline, for which there is no cure. Metabolic stress is hypothesized to contribute to the development of dementia: glucose hypometabolism is an early feature in Alzheimer’s (AD) and Parkinson’s disease (PD), and diabetes is a substantial risk factor for developing dementia. However, how metabolic stress combines with genetic neurodegenerative disease risk factors to lead to neuronal death is not well understood, and there are no known ways to boost metabolic resilience in susceptible neurons. To address these knowledge gaps, we have identified genetic targets that maintain cellular energy levels, using a unique screening paradigm that combines cutting- edge, genetically encoded sensors for ATP, the main energy-carrying molecule in cells, with whole-genome CRISPR-based gene manipulations. With this approach, we have identified gene pathways that have a prominent impact on ATP levels when cells are under metabolic stress. In particular, our preliminary data indicate that knockdown of AD/PD disease risk genes associated with endocytic recycling lead to neuronal death specifically when glucose is scarce. One of these genes is SORL1, a risk gene that is potentially causal for AD. SORL1 is known to interact with APOE, and the APOE4 variant is the largest genetic risk factor for AD. But the interaction between APOE and SORL1 or the endocytic recycling pathway is not well understood. Under the mentorship of Dr. Ken Nakamura and Dr. Robert Mahley, in collaboration with Drs. Martin Kampmann and Thomas Graeber, and with the support of the vibrant research community and cores at the Gladstone Institutes and UCSF, I will test the hypothesis that AD risk mutations in endocytic recycling create an energy failure and increases the susceptibility of neurons to lipid deficits and the deleterious effects of APOE expression and APOE4 genotype. I will investigate this hypothesis through the following Aims: 1) Determine the impact of disrupting endocytic recycling on energy consumption and respiration, 2) Determine the effect of impaired glucose metabolism on endosomal protein trafficking, 3) Determine how APOE expression and genotype contribute to metabolic vulnerability and endosomal protein trafficking in endocytic recycling deficient neurons. The proposed studies will also determine if maintaining ATP levels via genetic manipulations or by addressing metabolic deficits have therapeutic potential for treating neuron vulnerability and functional decline. The proposed research and career development plan will build on my previous training and enhance my trajectory toward becoming an independent investigator by developing skills to study energy metabolism and proteostasis in individual neurons, mastering analytical techniques to study metabolic dysfunction and response to metabolic stress on a systems-level, gaining experience with experimental design, communication, and mentorship, and building a foundation of biological understanding of dementia and neurodegenerative disease pathophysiology.