Investigating the role of Oxr1 in mitochondria

Oxidative stress (OS) and mitochondrial dysfunction are common features of neurodegenerative disease, suggesting that antioxidant defence systems are critical for cell survival in the central nervous system (CNS). Oxidation resistance 1 (OXR1) has emerged as an essential antioxidant protein that controls the susceptibility of neurons to OS; however, the function of this novel protein is unknown. The overall goal of this thesis was to investigate the potential role of Oxr1 in mitochondria and to understand more regarding the function of the gene in the oxidative stress response in vitro and in vivo. It was demonstrated that different isoforms of Oxr1 are expressed in specific sub-cellular compartments and certain mitochondrial Oxr1 isoforms are associated with mitochondrial membrane. In addition, it was shown that over-expression of the shortest isoform of Oxr1 in the cytoplasm is protective; both against oxidative stress-induced apoptosis and against mitochondrial morphological changes caused by disease-associated TDP-43 mutations. Analysis of mitochondrial metabolism and fusion and fission proteins in Oxr1 knockout (bella) tissue indicated that that Oxr1 deletion alone does not trigger overt mitochondrial dysfunction but it may influence aspects of mitochondrial morphology. To ascertain whether loss of Oxr1 in specific neuronal populations would render them more susceptible to cell death, the conditional deletion of Oxr1 in mouse dopaminergic neurons was studied. Preliminary data showed that aged mice displayed no motor or pathological abnormalities in the midbrain, suggesting that this particular conditional deletion does not lead to significant neurodegeneration. Finally, ENU mutagenesis screening of Oxr1 identified a point mutation in the highly-conserved TLDc domain of Oxr1 (Y644H). In vitro analysis suggested that this mutant rendered cells more vulnerable to oxidative stress, demonstrating that this region of the protein is functionally important. Taken together, these studies deepen the understanding of Oxr1 as a novel antioxidant protein and offer new and important insights into its role in the OS-response and its potential use in future antioxidant therapies.