Deciphering Mitochondrial Iron Metabolism Using a Knockout Mouse.

Abstract 1995

Poster Board I-1017

We utilized the muscle creatine kinase conditional frataxin knockout mouse to elucidate how frataxin-deficiency alters iron metabolism. This is of significance since frataxin-deficiency leads to the neuro- and cardio-degenerative disease, Friedreich's ataxia. Using cardiac tissues, we demonstrate that frataxin-deficiency leads to down-regulation of key molecules involved in three mitochondrial utilization pathways: iron-sulfur cluster (ISC) synthesis (iron-sulfur cluster scaffold protein1/2 and the cysteine desulferase, Nfs1); mitochondrial-iron storage (mitochondrial ferritin); and heme synthesis (5-aminolevulinate dehydratase, coproporphyrinogen oxidase, hydroxymethylbilane synthase, uroporphyrinogen III synthase and ferrochelatase). This marked decrease in mitochondrial-iron utilization and resultant reduced release of heme and ISC from the mitochondrion could contribute to the excess mitochondrial-iron observed. Indeed, this effect is compounded by increased iron availability for mitochondrial uptake through: (1) transferrin receptor1 up-regulation that increases iron uptake from transferrin; (2) decreased ferroportin1 expression, limiting iron export; (3) increased expression of the heme catabolism enzyme, heme oxygenase1, and down-regulation of ferritin-H and —L, both of which likely lead to increased “free iron” for mitochondrial uptake; and (4) increased expression of the mammalian exocyst protein, Sec15l1, and the mitochondrial-iron importer, mitoferrin-2 (Mfrn2), that facilitate cellular iron uptake and mitochondrial-iron influx, respectively. This study enables construction of a model explaining the cytosolic iron-deficiency and mitochondrial-iron-loading in the absence of frataxin that is important for understanding the pathogenesis of Friedreich's ataxia.