title: Frataxin deficiency alters heme pathway transcripts and decreases mitochondrial heme metabolites in mammalian cells.
abstract: Deficiency of the frataxin mRNA alters the transcriptome, triggering neuro- and cardiodegeneration in Friedreich's ataxia. We microarrayed murine frataxin-deficient heart tissue, liver tissue and cardiocytes and observed a transcript down-regulation to up-regulation ratio of nearly 2:1 with a mitochondrial localization of transcriptional changes. Combining all mouse and human microarray data for frataxin-deficient cells and tissues, the most consistently decreased transcripts were mitochondrial coproporphyrinogen oxidase (CPOX) of the heme pathway and mature T-cell proliferation 1, a homolog of yeast COX23, which is thought to function as a mitochondrial metallochaperone. Quantitative RT-PCR studies confirmed the significant down-regulation of Isu1, CPOX and ferrochelatase at 10 weeks in mouse hearts. We observed that mutant cells were resistant to aminolevulinate-dependent toxicity, as expected if the heme pathway was inhibited. Consistent with this, we observed increased cellular protoporphyrin IX levels, reduced mitochondrial heme a and heme c levels and reduced activity of cytochrome oxidase, suggesting a defect between protoporphyrin IX and heme a. Fe-chelatase activities were similar in mutants and controls, whereas Zn-chelatase activities were slightly elevated in mutants, supporting the idea of an altered metal-specificity of ferrochelatase. These results suggest that frataxin deficiency causes defects late in the heme pathway. As ataxic symptoms occur in other diseases of heme deficiency, the heme defect we observe in frataxin-deficient cells could be primary to the pathophysiological process.
authors.affiliation: Department of Molecular Biosciences, University of California, Davis 95616, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Schoenfeld
authors.forename: Eleonora
authors.initials: E
authors.lastname: Napoli
authors.forename: Alice
authors.initials: A
authors.lastname: Wong
authors.forename: Shan
authors.initials: S
authors.lastname: Zhan
authors.forename: Laurence
authors.initials: L
authors.lastname: Reutenauer
authors.forename: Dexter
authors.initials: D
authors.lastname: Morin
authors.forename: Alan R
authors.initials: AR
authors.lastname: Buckpitt
authors.forename: Franco
authors.initials: F
authors.lastname: Taroni
authors.forename: Bo
authors.initials: B
authors.lastname: Lonnerdal
authors.forename: Michael
authors.initials: M
authors.lastname: Ristow
authors.forename: Hélène
authors.initials: H
authors.lastname: Puccio
authors.forename: Gino A
authors.initials: GA
authors.lastname: Cortopassi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D003304:Coproporphyrinogen Oxidase / Q000235:genetics / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D005294:Ferrochelatase / Q000235:genetics / Q000378:metabolism; D006321:Heart / Q000196:embryology; D006418:Heme / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D033862:Iron-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008322:Mammals; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D009206:Myocardium / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D011524:Protoporphyrins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D015032:Zinc / Q000378:metabolism; D000096923:Frataxin
chemical_list: D003304:Coproporphyrinogen Oxidase; D045304:Cytochromes c; D005294:Ferrochelatase; D006418:Heme; D033862:Iron-Binding Proteins; D011518:Proto-Oncogene Proteins; D011524:Protoporphyrins; D015032:Zinc; D000096923:Frataxin; C082870:MTCP1 protein, human; C028025:protoporphyrin IX