Institut Jacques Monod, CNRS-Université Paris Diderot, Sorbonne Paris Cité, 15 rue Hélène Brion, 75205 Paris cedex 13, France.
Biochem J. 2012 Feb 1;441(3):945-53. doi: 10.1042/BJ20111574.
Friedreich's ataxia is a hereditary neurodegenerative disease caused by reduced expression of mitochondrial frataxin. Frataxin deficiency causes impairment in respiratory capacity, disruption of iron homoeostasis and hypersensitivity to oxidants. Although the redox properties of NAD (NAD+ and NADH) are essential for energy metabolism, only few results are available concerning homoeostasis of these nucleotides in frataxin-deficient cells. In the present study, we show that the malate-aspartate NADH shuttle is impaired in Saccharomyces cerevisiae frataxin-deficient cells (Δyfh1) due to decreased activity of cytosolic and mitochondrial isoforms of malate dehydrogenase and to complete inactivation of the mitochondrial aspartate aminotransferase (Aat1). A considerable decrease in the amount of mitochondrial acetylated proteins was observed in the Δyfh1 mutant compared with wild-type. Aat1 is acetylated in wild-type mitochondria and deacetylated in Δyfh1 mitochondria suggesting that inactivation could be due to this post-translational modification. Mutants deficient in iron-sulfur cluster assembly or lacking mitochondrial DNA also showed decreased activity of Aat1, suggesting that Aat1 inactivation was a secondary phenotype in Δyfh1 cells. Interestingly, deletion of the AAT1 gene in a wild-type strain caused respiratory deficiency and disruption of iron homoeostasis without any sensitivity to oxidative stress. Our results show that secondary inactivation of Aat1 contributes to the amplification of the respiratory defect observed in Δyfh1 cells. Further implication of mitochondrial protein deacetylation in the physiology of frataxin-deficient cells is anticipated.
弗里德里希共济失调是一种遗传性神经退行性疾病，由线粒体 frataxin 表达减少引起。frataxin 缺乏导致呼吸能力受损、铁稳态紊乱和对氧化剂敏感。尽管 NAD（NAD+ 和 NADH）的氧化还原性质对能量代谢至关重要，但关于 frataxin 缺乏细胞中这些核苷酸的稳态的结果很少。在本研究中，我们表明，由于胞质和线粒体苹果酸脱氢酶同工酶活性降低以及线粒体天冬氨酸转氨酶（Aat1）完全失活，酵母弗里德里希共济失调缺陷细胞（Δyfh1）中的苹果酸-天冬氨酸 NADH 穿梭受损。与野生型相比，Δyfh1 突变体中线粒体乙酰化蛋白的含量明显减少。Aat1 在野生型线粒体中乙酰化，在Δyfh1 线粒体中去乙酰化，表明失活可能是由于这种翻译后修饰。铁硫簇组装缺陷或缺乏线粒体 DNA 的突变体也显示 Aat1 活性降低，表明 Aat1 失活是Δyfh1 细胞中的继发表型。有趣的是，在野生型菌株中删除 AAT1 基因会导致呼吸缺陷和铁稳态紊乱，而对氧化应激没有任何敏感性。我们的结果表明，Aat1 的继发失活导致了在Δyfh1 细胞中观察到的呼吸缺陷的放大。预计线粒体蛋白去乙酰化在 frataxin 缺乏细胞的生理学中具有进一步的意义。
