Iron-dependent regulation of frataxin expression: implications for treatment of Friedreich ataxia.
Friedreich ataxia (FA) is a progressive neurodegenerative disease caused by expansion of a trinucleotide repeat within the first intron of the gene that encodes frataxin. In our study, we investigated the regulation of frataxin expression by iron and demonstrated that frataxin mRNA levels decrease significantly in multiple human cell lines treated with the iron chelator, desferal (DFO). In addition, frataxin mRNA and protein levels decrease in fibroblast and lymphoblast cells derived from both normal controls and from patients with FA when treated with DFO. Lymphoblasts and fibroblasts of FA patients have evidence of cytosolic iron depletion, as indicated by increased levels of iron regulatory protein 2 (IRP2) and/or increased IRE-binding activity of IRP1. We postulate that this inferred cytosolic iron depletion occurs as frataxin-deficient cells overload their mitochondria with iron, a downstream regulatory effect that has been observed previously when mitochondrial iron-sulfur cluster assembly is disrupted. The mitochondrial iron overload and presumed cytosolic iron depletion potentially further compromise function in frataxin-deficient cells by decreasing frataxin expression. Thus, our results imply that therapeutic efforts should focus on an approach that combines iron removal from mitochondria with a treatment that increases cytosolic iron levels to maximize residual frataxin expression in FA patients.
Li
Kuanyu
K
National Institute of Child Health and Human Development, molecular Medicine Program, Bethesda, MD 20892, USA.
Besse
Edward K
EK
Ha
Dung
D
Kovtunovych
Gennadiy
G
Rouault
Tracey A
TA
D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D003676:Deferoxamine / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005621:Friedreich Ataxia / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007501:Iron / Q000378:metabolism*; D007502:Iron Chelating Agents / Q000494:pharmacology; D019190:Iron Overload / Q000378:metabolism*; D035942:Iron Regulatory Protein 2 / Q000235:genetics / Q000378:metabolism; D033862:Iron-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D000096923:Frataxin
D003676:Deferoxamine; D007501:Iron; D007502:Iron Chelating Agents; D035942:Iron Regulatory Protein 2; D033862:Iron-Binding Proteins; D012333:RNA, Messenger; D000096923:Frataxin