Elucidation of the mechanism of mitochondrial iron loading in Friedreich's ataxia by analysis of a mouse mutant.
We used the muscle creatine kinase (MCK) conditional frataxin knockout mouse to elucidate how frataxin deficiency alters iron metabolism. This is of significance because frataxin deficiency leads to Friedreich's ataxia, a disease marked by neurologic and cardiologic degeneration. Using cardiac tissues, we demonstrate that frataxin deficiency leads to down-regulation of key molecules involved in 3 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 excessive mitochondrial iron observed. This effect is compounded by increased iron availability for mitochondrial uptake through (i) transferrin receptor1 up-regulation, increasing iron uptake from transferrin; (ii) decreased ferroportin1 expression, limiting iron export; (iii) increased expression of the heme catabolism enzyme heme oxygenase1 and down-regulation of ferritin-H and -L, both likely leading to increased "free iron" for mitochondrial uptake; and (iv) increased expression of the mammalian exocyst protein Sec15l1 and the mitochondrial iron importer mitoferrin-2 (Mfrn2), which facilitate cellular iron uptake and mitochondrial iron influx, respectively. Our results enable the construction of a model explaining the cytosolic iron deficiency and mitochondrial iron loading in the absence of frataxin, which is important for understanding the pathogenesis of Friedreich's ataxia.
Huang
Michael Li-Hsuan
ML
Iron Metabolism and Chelation Program, Discipline of Pathology and Bosch Institute, Blackburn Building, D06, University of Sydney, NSW 2006 Australia.
Becker
Erika M
EM
Whitnall
Megan
M
Suryo Rahmanto
Yohan
Y
Ponka
Prem
P
Richardson
Des R
DR
D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D013437:Carbon-Sulfur Lyases / Q000235:genetics / Q000378:metabolism; D003304:Coproporphyrinogen Oxidase / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D005294:Ferrochelatase / Q000235:genetics / Q000378:metabolism; D005621:Friedreich Ataxia / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D020869:Gene Expression Profiling; D006418:Heme / Q000378:metabolism; D064451:Hepcidins; D006801:Humans; D007501:Iron / Q000378:metabolism*; D033862:Iron-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013154:Spleen / Q000378:metabolism; D014576:Uroporphyrinogen III Synthetase / Q000235:genetics / Q000378:metabolism; D000096923:Frataxin
D023181:Antimicrobial Cationic Peptides; D013437:Carbon-Sulfur Lyases; D003304:Coproporphyrinogen Oxidase; D005294:Ferrochelatase; D006418:Heme; D064451:Hepcidins; D007501:Iron; D033862:Iron-Binding Proteins; D014576:Uroporphyrinogen III Synthetase; D000096923:Frataxin; C080546:cysteine desulfurase