Mitochondrial iron-sulfur mechanisms in Friedreich's ataxia

University Of California At Davis, Davis CA

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Abstract

DESCRIPTION (provided by applicant): Friedreich's ataxia (FRDA) is an inherited mitochondrial neurodegenerative and demyelinating disease that affects thousands in the US, and several thousands more worldwide. Friedreich's ataxia results from a deficiency in the expression of the mitochondrial frataxin protein. In the previous grant period, we achieved our aims by demonstrating that frataxin makes intimate contact with the iron-sulfur cluster machinery of the mitochondria and alters iron-sulfur transcripts specifically, and that iron-sulfur cluster defects are the earliest observable problems in frataxin-deficient cells, and that consequent defects include heme deficiency and inflammation. In the current proposal, we will extend our understanding of how the defect in iron-sulfur cluster synthesis causes neurodegeneration, demyelination, and cardiodegeneration. Aim 1 is focused on site directed mutagenesis and binding studies to determine the contacts of frataxin with ISCU, ISD11, GRP75 and Hsc20. Aim 2 is focused on determining pathophysiological consequences of iron-sulfur deficiency in dorsal root ganglial and Schwann cell lines, in terms of beta-oxidation, protein insolubility, bioenergetics, heme deficiency and inflammation. Aim 3 is directed at the confirmation of the strongest defects observed in Aim 2, by measuring these parameters in primary DRG neurons and Schwann cells from the best mouse model of Friedreich's ataxia, and by microarray. Aim 4 will investigate the two most likely pathophysiological mechanisms for the cardiodegeneration that is lethal to most Friedreich's patients, i.e. the beta-oxidative and desmosomal hypotheses. Aim 5 is to test mechanism-based compounds for rescue of the pathophysiological consequences observed in Aims 2, 3, and 4, in cell lines, primary cells, and whole animals. These aims are tightly focused on the pathophysiological mechanism(s) of Friedreich's ataxia, and therapeutic means to inhibit these processes. PUBLIC HEALTH RELEVANCE: Friedreich's Ataxia is the most common autosomal recessive ataxia, and occurs with a frequency of 1/50,000 individuals. Several thousand Americans have been diagnosed with Friedreich's ataxia. Friedreich's results in a decreased expression of the mitochondrial protein frataxin. Our work is tightly focused on the function of frataxin, and the pathophysiologic mechanisms of neuro- and cardio-degeneration that result from frataxin-deficiency. Our work (Aim 5) is specifically focused on the translational goal of screening and testing mechanism-based drugs for potential Friedreich's ataxia therapy.