Institute of Zoology, University of Regensburg, Regensburg, Germany.
PLoS One. 2011;6(7):e21017. doi: 10.1371/journal.pone.0021017. Epub 2011 Jul 11.
Friedreich's ataxia (FA), the most frequent form of inherited ataxias in the Caucasian population, is caused by a reduced expression of frataxin, a highly conserved protein. Model organisms have contributed greatly in the efforts to decipher the function of frataxin; however, the precise function of this protein remains elusive. Overexpression studies are a useful approach to investigate the mechanistic actions of frataxin; however, the existing literature reports contradictory results. To further investigate the effect of frataxin overexpression, we analyzed the consequences of overexpressing human (FXN) and fly (FH) frataxins in Drosophila.
METHODOLOGY/PRINCIPAL FINDINGS: We obtained transgenic flies that overexpressed human or fly frataxins in a general pattern and in different tissues using the UAS-GAL4 system. For both frataxins, we observed deleterious effects at the biochemical, histological and behavioral levels. Oxidative stress is a relevant factor in the frataxin overexpression phenotypes. Systemic frataxin overexpression reduces Drosophila viability and impairs the normal embryonic development of muscle and the peripheral nervous system. A reduction in the level of aconitase activity and a decrease in the level of NDUF3 were also observed in the transgenic flies that overexpressed frataxin. Frataxin overexpression in the nervous system reduces life span, impairs locomotor ability and causes brain degeneration. Frataxin aggregation and a misfolding of this protein have been shown not to be the mechanism that is responsible for the phenotypes that have been observed. Nevertheless, the expression of human frataxin rescues the aconitase activity in the fh knockdown mutant.
CONCLUSION/SIGNIFICANCE: Our results provide in vivo evidence of a functional equivalence for human and fly frataxins and indicate that the control of frataxin expression is important for treatments that aim to increase frataxin levels.
弗里德赖希共济失调（FA）是白种人群体中最常见的遗传性共济失调形式，由 frataxin 表达减少引起，frataxin 是一种高度保守的蛋白质。模式生物在阐明 frataxin 功能方面做出了巨大贡献；然而，这种蛋白质的确切功能仍然难以捉摸。过表达研究是研究 frataxin 机械作用的有用方法；然而，现有文献报告了相互矛盾的结果。为了进一步研究 frataxin 过表达的影响，我们分析了在果蝇中过表达人（FXN）和果蝇（FH）frataxin 的后果。
方法/主要发现：我们使用 UAS-GAL4 系统获得了在一般模式和不同组织中过表达人或果蝇 frataxin 的转基因果蝇。对于这两种 frataxin，我们在生化、组织学和行为水平上都观察到了有害影响。氧化应激是 frataxin 过表达表型的一个相关因素。全身性 frataxin 过表达降低了果蝇的存活率，并损害了肌肉和外周神经系统的正常胚胎发育。还观察到过表达 frataxin 的转基因果蝇中 aconitase 活性水平降低和 NDUF3 水平降低。神经系统中 frataxin 的过表达降低了寿命，损害了运动能力，并导致大脑退化。已经表明，frataxin 聚集和错误折叠不是导致观察到的表型的机制。然而，人 frataxin 的表达可以挽救 fh 敲低突变体中的 aconitase 活性。
结论/意义：我们的结果提供了体内证据，证明人源和果蝇 frataxin 具有功能等效性，并表明 frataxin 表达的控制对于旨在增加 frataxin 水平的治疗方法很重要。
