| Iron status is higher in the substantia nigra than in other brain regions but can fluctuate as function of diet, genetics, and disease. Because iron can influence neuronal cell death and dopamine function, the body tightly controls the supply of iron needed for tasks such as a cofactor for enzymes but also has mechanisms in place to sequester iron to limit oxidative stress. The major protein that accomplishes this latter task is ferritin, with the ferroxidase properties belonging to the H subunit. In this thesis, mice genetically altered to be heterozygous for a mutation in the H-ferritin gene were utilized to examine the impact of H-ferritin-deficiency on the dopaminergic nigrostriatal system. The distribution of mitochondrial ferritin, a protein structurally and functionally similar to H-ferritin, was also explored in mouse and human brain.;Using high-resolution magic angle spin proton magnetic resonance spectroscopy (HR-MAS 1H MRS), significant increases in glutamate levels were found in the striatum and ventral midbrain in H-ferritin-deficient animals as compared to wild-type. While lactate was increased in the ventral midbrain of H-ferritin-deficient animals, it was decreased in the striatum. Dopamine transporter (DAT) expression in the substantia nigra and striatum was unchanged with age or by the loss of ferritin. Overall, the neurochemical profile is suggestive of neuronal iron deficiency.;Because iron deficiency causes long-term effects on the dopaminergic system and may influence the onset of or susceptibility to neurologic disorders, the number of tyrosine hydroxylase dopaminergic neurons in the substantia nigra pars compacta was evaluated using stereology. The results indicate that there is no loss in dopaminergic cell number with age or genotype. However, when mice are challenged with neurotoxic insult by the pesticides paraquat (1,1'-dimethyl-4,4'-bipyridinium) and maneb (manganese ethylenebisdithiocarbamate), two agents that are effective in inducing selective and irreversible loss of tyrosine hydroxylase-positive neurons in the substantia nigra that is akin to what is seen in Parkinson's disease, there is significant cell loss in the 12 month-old H-ferritin-deficient mice compared to control.;A surprising finding was that H-ferritin was not detectable in the substantia nigra pars compacta at 4, 8, or 12 months of age regardless of genotype or toxin exposure. The lack of detectable H-ferritin in the substantia nigra opened the possibility that another ferritin, such as mitochondrial ferritin (FtMt), could be an anti-oxidant protein in the brain. FtMt has ferroxidase activity and is similar to H-ferritin except for its cellular localization to the mitochondria. Mitochondrial dysfunction has been linked to Parkinson's disease, which further makes mitochondrial ferritin a protein of interest. We found FtMt expression in almost all regions of the brain, although staining intensity varies between regions. Both neurons and oligodendrocytes prominently immunostain for mitochondrial ferritin. Mice deficient in H-ferritin do not differ in the mitochondrial ferritin staining pattern or intensity as compared to C57/BL6 mice, which further supports existing data suggesting that these two proteins are distinct.;Given the importance and relationship between iron and mitochondrial activity, understanding the role of mitochondrial ferritin in neurologic disorders may be important. We explored the expression of FtMt in Restless legs syndrome (RLS), a disorder that involves decreased iron availability in the brain. FtMt levels in human autopsy samples from the putamen and substantia nigra revealed that the RLS nigra had significantly more FtMt than controls; there was not a significant difference in FtMt in the putamen. Immunohistochemical analysis indicated that neuromelanin-containing neurons were the predominant cell type expressing FtMt, and staining intensity in the neurons from the RLS samples was consistently greater than that seen in controls. In addition, cytochrome c oxidase staining, reflective of the number of mitochondria, followed a similar staining pattern to FtMt. The increased number of mitochondria in neurons in RLS coupled with increased FtMt could contribute to insufficient cytosolic iron levels in RLS neurons and the symptoms of this disorder.;Overall, the data presented in this thesis suggest that alterations in ferritin levels, despite relatively low levels of expression of both H-ferritin and mitochondrial ferritin, have a wide-ranging impact on cellular energetics and metabolism. The H-ferritin-deficient mice are a model in which the study of iron mismanagement can be used to study neurological disorders such as Parkinson's disease and may be a model for RLS. |
