Date of Award
Doctor of Philosophy
Molecular Biology, Microbiology and Biochemistry
In neurons, mitochondrial quantity and basal cellular respiration are maintained with age, but alterations in other key functions and quantities make these cells susceptible to the pathology of age-related neurodegenerative disease. We observed age-related decreases in cytochrome C, cardiolipin, cytochrome C oxidase (CCO) function, and glutamate response that render cells less capable of responding to stress. Rescue experiments showed that estrogen is a promising treatment in restoring neuron function with age. After finding key differences in CCO, we examined the electron transport chain more closely and found age-related deficits in quantity or function for each individual complex. Our experiments support a lack of endogenous substrates or a failure of upstream complexes to transport electrons to complex IV with age, ultimately leading to age-related neurodegeneration. Reactive oxygen species production may add to the problem by degrading macromolecules such as nucleic acid, cardiolipin, and proteins. Increased ROS may also lead to a redox imbalance in the neuron, reducing the potential for energy production. Also, epigenetic controls such as DNA methylation, histone acetylation ubiquitination and phosphorylation that persist in culture independent of aging hormone levels, vasculature, and immune system may be partly responsible for the observed age-related deficiencies as has been previously observed in aging human muscle (Ronn et al., 2008). This compelling cumulative evidence suggests an age-related deficiency in electron transport via quinones from complexes I to III, and age-related deficiencies in substrates, cofactors, and quantity or function for complex IV. These studies add to the growing body of evidence that dysfunction in the enzyme complexes of the electron transport chain lead to neurodegeneration in senescence-related diseases. In an attempt to integrate our age-related findings with Alzheimer's Disease (AD) pathology, we sequentially isolated the electron transport chain complexes using selective mitochondrial inhibitors in cortical neurons removed from the 3xTg-AD mouse model, which harbors mutations in the PS1, APPSwe and tauP301L genes and follows the proposed temporal development of human AD pathology (Oddo et al., 2003a; 2003b). Overall, we did not detect 3xTg-AD cortical neuron deficits at the four electron transport complexes of mitochondria or in NAD(P)H oxidase (NOX), an extramitochondrial oxygen consumer and regulator of NAD(P)+/NAD(P)H homeostasis (Morre et al., 2000).
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