Iron metabolism in mice with partial frataxin deficiency

Friedreich ataxia (FRDA), the most common autosomal recessive inherited ataxic disorder, is the consequence of deficiency of the mitochondrial protein frataxin, typically caused by homozygous intronic GAA expansions in the corresponding gene. The yeast frataxin homologue (yfh1p) is required for cellular respiration. Yfh1p appears to regulate mitochondrial iron homeostasis and protect from free radical toxicity. Complete loss of frataxin in knockout mice leads to early embryonic lethality, indicating an important role for frataxin during development. Heterozygous littermates with partial frataxin deficiency are apparently healthy and have no obvious phenotype. Here we evaluate iron metabolism and sensitivity to dietary and parenteral iron loading in heterozygote frataxin knockout mice (Fx(+/-)). Iron concentrations in the liver, heart, pancreas and spleen, and cellular iron distribution patterns were compared between wild type and Fx(+/-) mice. Response to parenteral iron challenge was not different between Fx(+/-) mice and wild type littermates, while sporadic iron deposits were observed in the hearts of dietary iron-loaded Fx(+/-) mice. Finally, we evaluated the effect of partial frataxin deficiency on susceptibility to cardiac damage in the mouse model of hereditary hemochromatosis (HH), the Hfe knockout mice. HH, an iron overload disease, is one of the most frequent genetic diseases in populations of European origin. By breeding Hfe(-/-) with Fx(+/-) mice, we obtained compound mutant mice lacking both Hfe and one frataxin allele. Sparse iron deposits in areas of mild to moderate cardiac fibrosis were found in the majority of these mice. However, they did not develop any neurological symptoms. Our studies indicate an association between frataxin deficiency, iron deposits and cardiac fibrosis, but no obvious association between iron accumulation and neurodegeneration similar to FRDA could be detected in our model. In addition, these results suggest that frataxin mutations may have a modifier role in HH, that predisposes to cardiomyopathy.