Schoenfeld Robert A, Napoli Eleonora, Wong Alice, Zhan Shan, Reutenauer Laurence, Morin Dexter, Buckpitt Alan R, Taroni Franco, Lonnerdal Bo, Ristow Michael, Puccio Hélène, Cortopassi Gino A
Department of Molecular Biosciences, University of California, Davis 95616, USA.
Hum Mol Genet. 2005 Dec 15;14(24):3787-99. doi: 10.1093/hmg/ddi393. Epub 2005 Oct 20.
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.
铁调素mRNA的缺乏会改变转录组，引发弗里德赖希共济失调中的神经和心脏变性。我们对小鼠铁调素缺乏的心脏组织、肝脏组织和心肌细胞进行了微阵列分析，观察到转录本下调与上调的比例接近2:1，且转录变化定位于线粒体。综合所有针对铁调素缺乏的细胞和组织的小鼠及人类微阵列数据，最一致下调的转录本是血红素途径的线粒体粪卟啉原氧化酶（CPOX）和成熟T细胞增殖1，后者是酵母COX23的同源物，被认为作为线粒体金属伴侣发挥作用。定量RT-PCR研究证实，小鼠心脏在10周时Isu1、CPOX和亚铁螯合酶显著下调。正如预期的如果血红素途径受到抑制，我们观察到突变细胞对氨基乙酰丙酸依赖性毒性具有抗性。与此一致，我们观察到细胞中原卟啉IX水平升高、线粒体血红素a和血红素c水平降低以及细胞色素氧化酶活性降低，表明原卟啉IX和血红素a之间存在缺陷。突变体和对照中的铁螯合酶活性相似，而突变体中的锌螯合酶活性略有升高，支持了亚铁螯合酶金属特异性改变的观点。这些结果表明，铁调素缺乏会导致血红素途径后期出现缺陷。由于共济失调症状也出现在其他血红素缺乏疾病中，我们在铁调素缺乏细胞中观察到的血红素缺陷可能是病理生理过程的原发性因素。
