Year of Publication

2007

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department

Anatomy and Neurobiology

First Advisor

Dr. Patrick G. Sullivan

Abstract

Mitochondria are essential for promoting cell survival and growth through aerobic metabolism and energy production. Mitochondrial function is typically analyzed using mitochondria freshly isolated from tissues and cells because they yield tightly coupled mitochondria, whereas those from frozen tissue can consist of broken mitochondria and membrane fragments. A method, utilizing a well-characterized cryoprotectant such as dimethyl sulfoxide (DMSO), is described. Such mitochondria show preserved structure and function that presents us with a possible strategy to considerably expand the time-frame and the range of biochemical, molecular and metabolic studies that can be performed without the constraints of mitochondrial longevity ex vivo.

Mitochondrial dysfunction is implicated in Alzheimer’s disease (AD) mainly through oxidative stress and altered metabolism. Mitochondria are isolated from post-mortem brain samples from selective regions of AD and control patients and, utilizing the cryopreservation strategy, analyzed for respiration and oxidative damage. While we did not observe increases in free radicals, we did observe decreased respiration and increases in oxidative damage markers in AD patients, suggesting a role for oxidative stress in mitochondrial dysfunction.

While in the mitochondria, calcium (Ca2+) increases free radical generation by processes not completely understood. A new isoform of nitric oxide synthase (mtNOS) has been isolated and localized to mitochondria; though its existence and physiological role is debated. Nitric oxide synthase (NOS), when activated by Ca2+, produces nitric oxide (NO•) that can interact with ROS producing various reactive nitrogen species (RNS). These highly reactive radical species can damage DNA, proteins and lipids, ultimately resulting in cell death via apoptosis or necrosis.

The current research is aimed at understanding the role of Ca2+ and NOS in oxidative stress leading to mitochondrial dysfunction. We observed a significant reduction in mitochondrial respiration with increasing doses of calcium. We also observed NOS enzyme activity and detected NOS protein in the purified mitochondrial fraction. Lastly, we were also able to show that Ca2+ increased the levels of free radicals and changes in oxidative damage markers. These results suggest the presence of NOS in mitochondria that could play a role in Ca2+ induced mitochondrial dysfunction and potentially leading to cell death as relevant to aging and neurodegenerative diseases.

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