Iron in Mitochondrial Physiology and Disease

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DESCRIPTION (provided by applicant): A significant portion of cellular iron metabolism occurs in the mitochondria, including iron import, iron-sulfur cluster assembly and heme biosynthesis. Some heme and iron-sulfur clusters are installed into respiratory complexes, while others are exported to the cytosol and other cellular compartments. The entire system is tightly regulated. In this project, iron components and iron-related processes in mitochondria will be investigated from a systems-biology perspective to gain new insights into the metabolism of healthy and diseased states. Isolated and intact mitochondria from yeast and human cells will be subjected to M"ssbauer spectroscopy, electron paramagnetic resonance, electronic absorption spectroscopy and inductively coupled plasma emission mass spectrometry to evaluate the "iron-ome" of the organelle. This biophysical approach will be used to study mitochondria isolated from wild-type yeast cells grown under different conditions (fermenting vs. respiring; Fe deficient vs. Fe replete) and from different genetic strains. The yeast strains to be investigated (depleted in Yah1p, Atm1p, Mrs3p/4p, and Mtm1p) are known to affect iron metabolism, generally by causing iron to accumulate in the mitochondria. There are analogous situations in humans, in which defects in homologous proteins result in iron accumulation. The accumulated iron will be characterized and its reactivity investigated. Low molecular weight mononuclear nonheme complexes that are used in "trafficking" iron in the mitochondria will be isolated by chromatography, and then identified by mass spectrometry and NMR spectroscopy. The metabolic function of these complexes will also be investigated. The iron-ome of mitochondria from human HL60 cells will be compared to that of yeast mitochondria and differences will be interpreted in terms of iron mitochondrial biochemistry and physiology. The project is significant because the mechanism of disease-related Fe accumulation in mitochondria will be explored and iron complexes that are used in cellular trafficking will be isolated and identified. Such knowledge may allow better control of iron trafficking into and out of the organelle. These iron complexes may also play a role in generating reactive oxygen species (ROS) which are thought to be responsible for some aspects of cellular damage and aging. PUBLIC HEALTH RELEVANCE: Iron is exceedingly important in cellular processes; it is found as heme groups and iron-sulfur clusters. Ingested iron is packaged and then sent to the mitochondria, a cellular organelle, where it is converted into these forms. The structure of the packaging material will be determined; this structure probably "tells" the iron where to go within the cell. Methods will be developed to detect all of the different forms of iron in mitochondria isolated from yeast and human cells. In some genetic states, iron aggregates and can cause disease; this aggregated iron will be characterized in an attempt to eliminate it.