MOLECULAR MECHANISMS OF OLFACTORY NEURODEGENERATION

Olfactory sensory decline has been associated with normal aging as well as neurodegenerative disorders, yet the underlying mechanisms are unclear. The overall aim of this dissertation was to investigate the fundamental molecular and cellular mechanisms associated with olfactory neurodegeneration. This investigation uses an integrative approach, combining proteomics and gene expression analyses with cellular and tissuelevel characterization. Using these approaches, two model systems were investigated: 1) normally aging C57BL/6 mice of ages 1.5-, 6- and 20-months; and 2) a mouse model of elevated endogenous oxidative stress-associated neurodegeneration, namely, the Harlequin mutant mouse. The first specific aim was to test the hypothesis that oxidative stress is associated with aging of the olfactory system. Using proteomics, I demonstrated that olfactory aging was accompanied primarily by increased oxidative stress-, mitochondrial metabolism- and synaptic/transport-associated changes. The second specific aim was to test the hypothesis that the olfactory system accumulates oxidative stress-mediated macromolecular damage over time, predisposing it to neurodegeneration. Two types of protein oxidation, namely, carbonylation and nitration, accumulated with aging in the olfactory system. Protein and cellular targets of oxidative stress-associated damage were identified using redox proteomics coupled with immunohistochemical localization. The third specific aim was to test the hypothesis that elevated oxidative stress in the olfactory system results in apoptosis/neurodegeneration. The Harlequin mutant mouse was critically selected and validated as a model for studies of oxidative stress-associated olfactory neurodegeneration at both the cellular and molecular levels. The Harlequin mouse had decreased levels and altered distribution of apoptosis inducing factor protein in mature olfactory sensory neurons, increased oxidative DNA damage and apoptosis in the olfactory epithelium, and pronounced cytoskeletal disorganization. The molecular studies confirmed and extended our cellular data and identified several significantly regulated genes associated with elevated oxidative stress and apoptosis. This novel study, by combining contemporary proteomics and genomics with cellular and tissue-level analyses, has provided a road map for understanding fundamental molecular mechanisms of olfactory degeneration.