Mitochondrial Iron Overload and Friedreich's Ataxia: The Role of Frataxin in Iron and Haem Metabolism

弗里德赖希共济失调症（FA）是由于缺乏一种被称为卵黄蛋白的蛋白质。对贝克酵母和条件敲除frataxin （KO）小鼠的各种研究表明，frataxin的缺失导致线粒体中有毒铁的积累。最近，各种研究表明，FA患者的线粒体中有铁负荷。在线粒体高度氧化还原活性的环境中，铁可以促进细胞毒性自由基的产生，造成严重的损害。此外，缺乏纤维蛋白的细胞对氧化应激敏感，铁螯合剂可挽救FA患者氧化介导的细胞死亡。事实上，自由基清除剂已被证明可用于治疗这种疾病。DR实验室在NHMRC资助下的研究表明，红血系分化或血红素前体原卟啉IX下调了frataxin （BLOOD 2002;99:3813-22）。这些数据表明fraataxin在铁代谢和FA发病机制中的作用。在这项研究中，我们将继续使用在当前NHMRC资助下开发的实验模型来检查fraataxin在细胞处理铁的方式中的作用。这些包括使用含有反义frataxin cDNA的表达载体产生的低frataxin表达的转染细胞系。在此基础上，我们进一步获得了含frataxin条件的KO小鼠，并产生了繁殖群体。这些动物表现出许多FA的病理特征，是目前最好的疾病模型。事实上，它们对于评估fraataxin在铁代谢中的作用以及作为测试铁结合药物预防所观察到的病理能力的模型至关重要。我们设计了脂溶性螯合剂，可以进入线粒体结合铁（biochem Biophys Acta 2001;1536:133-140），这些配体将在KO小鼠中进行测试，以防止疾病进展。这项令人兴奋的研究对于了解FA的发病机制和创造新的治疗方法至关重要。

Friedreich's ataxia (FA) is due to the lack of a protein known as frataxin. A variety of studies using Baker's yeast and conditional frataxin knockout (KO) mice have shown that deletion of frataxin leads to the accumulation of toxic iron in their mitochondrion. More recently, a variety of studies have shown that FA patients have iron-loading within their mitochondrion. Iron in the highly redox active environment of the mitochondrion could contribute to the generation of cytotoxic radicals that cause severe damage. Further, cells deficient in frataxin are sensitive to oxidant stress and Fe chelators rescue oxidant-mediated death of cells from FA patients. Indeed, free radical scavengers have shown to be of use in the treatment of this disease. Studies in DR's lab during this NHMRC grant have shown that frataxin is down-regulated by erythroid differentiation or the haem precursor, protoporphyrin IX (BLOOD 2002;99:3813-22). These data indicate a role for frataxin in Fe metabolism and the pathogenesis of FA. In this study we will continue to examine the role of frataxin in the way cells handle Fe using experimental models developed under the current NHMRC grant. These include transfected cell lines with low frataxin expression generated using an expression vector containing anti-sense frataxin cDNA. Further we obtained the frataxin conditional KO mouse and generated a breeding colony. These animals display many of the pathological features of FA and are the best current model of the disease. Indeed, they will be critical for assessing the role of frataxin in Fe metabolism and as a model to test the ability of Fe-binding drugs to prevent the pathology observed. We designed lipid-soluble chelators that can enter the mitochondrion to bind Fe (Biochim Biophys Acta 2001;1536:133-140) and these ligands will be tested to prevent disease progression in the KO mice. This exciting research is crucial for understanding the pathogenesis of FA and in creating new therapies.