High mitochondrial DNA copy number has detrimental effects in mice
High mitochondrial DNA copy number has detrimental effects in mice
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DOI：
10.1093/hmg/ddq163
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发表时间：
2010-07-01
影响因子：
3.5
通讯作者：
Suomalainen, Anu
中科院分区：
文献类型：
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作者：
Ylikallio, Emil;Tyynismaa, Henna;Suomalainen, Anu
线粒体DNA(MtDNA)是一种重要的多拷贝基因组，被压缩成称为类核的蛋白质-DNA簇。保持足够的线粒体DNA拷贝数对细胞的生存至关重要。MtDNA的丢失会导致严重的人类症状，而mtDNA拷贝数的增加被认为可以提高小鼠心肌梗死的存活率，并有望成为线粒体疾病的一种治疗策略。然而，调控线粒体DNA数量和组织的机制并不完全清楚。在线粒体DNA存在所需的蛋白质中，只有线粒体解旋酶Twinkle和线粒体转录因子A(TFAM)在生理水平表达时能增加体内mtDNA的拷贝数。在这里，我们研究了Twinkle和TFAM对小鼠线粒体DNA合成和类核结构的影响。利用体内BrdU标记，我们发现Twinkle特异性地调节从头开始的mtDNA合成。值得注意的是，小鼠线粒体DNA拷贝数高伴随着核样增大，这反过来又与转录缺陷、与年龄相关的mtDNA缺失积累和呼吸链(RC)缺陷有关。在双转基因小鼠中同时过表达Twinkle和TFAM对mtDNA拷贝数具有相加效应，使骨骼肌中的mtDNA拷贝数增加6倍。双基因小鼠也表现出进一步的核团增大和RC缺陷的加重。综上所述，我们发现Twinkle作为mtDNA复制启动的调节因子，并提供了高拷贝数和类核结构改变可能损害线粒体功能的证据。
Mitochondrial DNA (mtDNA) is an essential multicopy genome, compacted into protein-DNA clusters called nucleoids. Maintaining an adequate mtDNA copy number is crucial for cellular viability. Loss of mtDNA results in severe human syndromes, whereas increased mtDNA copy number has been suggested to improve survival from myocardial infarction in mice and to be a promising therapeutic strategy for mitochondrial disease. The mechanisms that regulate mtDNA amount and organization are, however, not fully understood. Of the proteins required for mtDNA existence, only the mitochondrial helicase Twinkle and mitochondrial transcription factor A (TFAM) have been shown to increase mtDNA copy number in vivo, when expressed in physiological levels. Here we studied how Twinkle and TFAM affect mtDNA synthesis and nucleoid structure in mice. Using in vivo BrdU labeling, we show that Twinkle specifically regulates de novo mtDNA synthesis. Remarkably, high mtDNA copy number in mice is accompanied by nucleoid enlargement, which in turn correlates with defective transcription, age-related accumulation of mtDNA deletions and respiratory chain (RC) deficiency. Simultaneous overexpression of Twinkle and TFAM in bitransgenic mice has an additive effect on mtDNA copy number, increasing it up to 6-fold in skeletal muscle. Bitransgenic mice also exhibit further enlargement of nucleoids and aggravation of the RC defect. In conclusion, we show that Twinkle acts as a regulator of mtDNA replication initiation, and provide evidence that high mtDNA copy number and alteration of nucleoid architecture may be detrimental to mitochondrial function.