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Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Cumming, Robert C.

Abstract

Alzheimer’s disease (AD), a progressive and irreversible neurodegenerative disorder, and is the leading cause of dementia worldwide. It has been posited that AD is caused by the gradual deposition of toxic amyloid-b (Ab) plaques in the brain- that cause oxidative stress and eventually leads to neuronal death and synaptic loss. However, multiple therapies that either interfere with the production, or enhance the removal of Ab from the brain, have ultimately failed to slow or prevent AD. With the ever-increasing burden of AD worldwide, there exists an urgent need for novel therapeutic targets. The adult human brain is an energy demanding organ, and numerous studies have shown pronounced reductions in glucose metabolism in AD brains, which precipitates neurodegeneration and memory loss. Specifically, significant losses in brain glycolysis have been observed, while several lines of evidence also demonstrate that the preservation of glycolysis provides key advantages to central nervous system (CNS) cells in AD. However, the mechanisms governing shifts between mitochondrial oxidative phosphorylation (OXPHOS) and glycolysis for ATP generation are poorly understood. Therefore, I aimed to investigate which proteins are involved in promoting metabolic shifts in CNS cells. I focused on p66Shc, an adaptor protein whose canonical functions include apoptotic signalling and ROS production, but recent studies have implicated p66Shc in cellular metabolism. I demonstrate that in cultured CNS cells, expression and activation of p66Shc promotes OXPHOS, increases mitochondrial ROS- and represses glycolytic enzyme expression. p66Shc silencing, however, upregulates glycolytic enzymes, lowers ROS, and protects cells against Ab toxicity. I also determined that p66Shc silencing lowers levels of kelch-like ECH associated protein 1 (KEAP1), which results in increased stabilization of the transcription factor nuclear erythroid 2-related factor 2 (NRF2). Elevated NRF2 promotes increased levels of hypoxia-inducible factor 1α and subsequent elevations in glycolytic enzyme expression. I also showed that protective effects of p66Shc against Ab are NRF2 mediated, and transgenic AD mouse brains have higher p66Shc and KEAP1, but lower NRF2 levels, relative to wildtype mice. Together, these findings reveal a novel mechanism of cellular metabolic regulation, and highlights p66Shc as a potential therapeutic target for the treatment of AD.

Summary for Lay Audience

Alzheimer’s disease (AD) is a disorder of the brain that is characterized by progressive loss of memory and brain function. It was first reported by Alois Alzheimer in 1907, who studied the brain of one of his patients and discovered the presence of plaques and tangles, now known to be composed of the proteins amyloid-b (Ab) and tau, respectively. For ~40 years, most research and pharmaceutical medications have focused on removing Ab from the brain of patients as a treatment for the disease, but these efforts have failed. With the increasing burden of AD worldwide, new treatments are desperately needed. Our brains require significant amounts of energy to operate, which is generated in cells using glucose as a fuel. This is accomplished in two ways: through glycolysis in the cytoplasm, or via oxidative phosphorylation (OXPHOS) in the mitochondria, which also generates harmful reactive oxygen species (ROS) as a by-product. Collectively, these processes are termed glucose metabolism. Several studies have implicated reductions in brain glucose metabolism in causing brain cell death, eventually leading to loss of memory and brain function. However, the underlying processes that govern brain glucose metabolism are not well understood. My goal was to investigate which proteins control glucose metabolism in brain cells. I focused on p66Shc, a protein that increases ROS production and promotes cell death but has recently also been reported to play a role in cellular metabolism. In this thesis, I discovered that the p66Shc protein promotes OXPHOS, represses glycolysis, triggers more ROS production, and leads to the death of cultured brain cells when exposed to Ab. Conversely, brain cells that do not have p66Shc have higher glycolysis, lower OXPHOS, decreased ROS, and are more resistant to Ab toxicity. Moreover, brain cells lacking p66Shc have lower levels of the protein KEAP1 and higher levels of NRF2. These changes cause increased cellular levels of the HIF-1α protein, leading to higher glycolysis. In this thesis, I uncovered a novel mechanism of how p66Shc controls cellular metabolism, and present p66Shc as a potential therapeutic target for the treatment of AD.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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