Date of Award
Doctor of Philosophy (PhD)
Mutations in superoxide dismutase 1 (SOD1) are known to cause dominantly-inherited amyotrophic lateral sclerosis (ALS), a rapidly-fatal adult-onset neurodegenerative disorder defined by motor neuron loss and progressive paralysis. In the past twenty years, research into the disorder has been driven by the creation of numerous transgenic animal models that have yielded multiple theories on the pathogenesis of the disease. Patients and animal models with SOD1 mutations express the defective protein in every cell, yet the disease only affects tissues in the neuromuscular axis. In this dissertation, I present original work exploring two aspects of SOD1 ALS. The first details the biochemical characterization of recently discovered canine SOD1 mutations that have been found to cause canine degenerative myelopathy (DM), the only naturally occurring non-human ALS model. My research showed that, like in human ALS and transgenic rodent models, canine DM is accompanied by an increase in detergent-insoluble mutant SOD1 in the spinal cords of diseased animals. Also, these mutations retained full enzymatic activity and aggregate in cell culture, confirming that a toxic gain-of-function mechanism is at play in this model. The second part of this dissertation describes research into the tissue specificity of the disease. By developing a novel stable isotope labeling kinetics (SILK) method to measure long-lived proteins, I was able to determine the turnover rate of wild-type, mutant, and misfolded SOD1 in rodent tissues both affected and unaffected in disease and in cerebral spinal fluid (CSF) from healthy human subjects. The results indicated that SOD1 is a long-lived protein with significantly slower turnover in the tissues most affected in ALS. In agreement with studies in vitro, the turnover rates for mutant and misfolded SOD1 were accelerated compared to wild-type protein, reflecting increased protein instability; yet a significant difference in turnover between affected and unaffected tissues remained. Finally, by applying this novel SILK method to human subjects, I was able to confirm that SOD1 is a long-lived protein in human CSF and, by extension, in the central nervous system. These results validate the first method for measuring SOD1 turnover in vivo and strongly suggest an important role for the slow turnover of SOD1 in the tissue specificity of the ALS.
Chair and Committee
Timothy M. Miller
Randall Bateman, Marc Diamond, Paul T. Kotzbauer, Conrad C. Weihl,
Crisp, Matthew James, "Superoxide Dismutase 1: Novel Insights on Disease Models and Tissue Specificity in Amyotrophic Lateral Sclerosis" (2016). Arts & Sciences Electronic Theses and Dissertations. 766.