Author ORCID Identifier

https://orcid.org/0000-0002-9517-6249

Year of Publication

2022

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Chemistry

First Advisor

Dr. Allan Butterfield

Abstract

Oxidative phosphorylation occurs within the inner mitochondrial membrane producing ATP for the cell’s energy needs. The Electron Transport Chain carries out the transfer of electrons from electron carriers through a series of proteins to form a proton gradient across the inner mitochondrial membrane. This gradient acts as the energy source needed to put a phosphate onto ADP and form ATP. With the large amounts of free electrons and oxygen within the mitochondria, an inevitable by-product of free radicals in the form of superoxide are produced. Superoxide (O-̇2) is a reactive radical that can react further to produce hydrogen peroxide, which itself can react with certain reduced metal ions to produce the extremely reactive hydroxyl free radical. When these radicals and reactive oxygen species are kept at low levels, they can act as signaling molecules for the cell. A network of antioxidant proteins helps the cell to keep this redox state. However, when there is an excess of radicals and ROS within the cell, oxidative damage occurs that is detrimental to the cell’s survival.

The brain is composed of different types of cells, neurons, and glia, that are rich in polyunsaturated fatty acids and have an abundance of O2. The combination of these factors is what allows the brain to work with such high function, but it is also this combination that can lead to unfavorable reactions. The abundance of O2 allows for the potential for higher levels of free radicals and reactive oxygen species, which can interact with the polyunsaturated fatty acids in a process called lipid peroxidation. Lipid peroxidation results in the formation of several products, the most salient to this dissertation research is 4-hydroxynonenal (HNE), which has deleterious effects to the cell. Moreover, loss of lipid asymmetry as a result of HNE-mediated inactivation of flippase and the presence of phosphatidylserine on the outer leaflet can signal the cell to initiate apoptosis.

HNE adducts to proteins on cysteine, lysine, or histidine residues. When HNE-adducted Cys or His are located towards the inside of the protein, a conformational change of the protein occurs to bring these residues to the surface of the protein and leads to a loss in function. The adduction of HNE to proteins has been observed in different brain-related diseases such as glioblastoma and Alzheimer disease.

Glioblastoma is one of the most difficult forms of cancer to treat due to the tentacles that limit complete surgical removal of the tumor and its resistance to radiation. Oxidative damage within the tumor cells does not seem to cause the same deadly effects as it would to the surrounding cells. When tumor cells have a large amount of oxidative damage there is a need to rid the cell of the affected proteins. This is achieved in the form of blebbing of extracellular vesicles (EVs). The findings of this dissertation provide significant insights into the mechanism by which these EVs aid in the survival of tumor cells. EVs bleb from the surface of the cell carrying the HNE-adducted proteins into the extracellular space and encounter surrounding glial cells and neurons. When the EVs are taken up by the glial cells, such as astrocytes, this induces the production of ROS in the form of hydrogen peroxide. This ROS is key in inducing proliferation of the tumor cells and furthering radiation resistance.

Alzheimer Disease also is known to have HNE-adducted proteins and oxidative damage. One such pathway affected in AD, the Pentose Phosphate Pathway, depends on the apolipoprotein E (ApoE) allele status of the cell. Three variations of this gene, APOE2, APOE3, or APOE4, with the most common being APOE3. Those individuals who have APOE4 have a higher risk of developing AD. APOE4 allele also is seen in conjunction with higher oxidative damage and HNE production within the cell. The findings in this dissertation research show the correlation between the APOE allele status and oxidative damage has on the expression of the proteins of the Pentose Phosphate Pathway in APOE targeted-replacement mice that contain mutated genes lead to AD.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2022.133

Available for download on Friday, May 10, 2024

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