Max Planck Institute for Biology of Ageing, Cologne, Germany.
Max Planck Institute for Biology of Ageing, Cologne, Germany
J Cell Biol. 2018 May 7;217(5):1601-1611. doi: 10.1083/jcb.201801168. Epub 2018 Mar 8.
Mitochondria contain tens to thousands of copies of their own genome (mitochondrial DNA [mtDNA]), creating genetic redundancy capable of buffering mutations in mitochondrial genes essential for cellular function. However, the mechanisms regulating mtDNA copy number have been elusive. Here we found that DNA synthesis and degradation by mtDNA polymerase γ (POLG) dynamically controlled mtDNA copy number in starving yeast cells dependent on metabolic homeostasis provided by autophagy. Specifically, the continuous mtDNA synthesis by POLG in starving wild-type cells was inhibited by nucleotide insufficiency and elevated mitochondria-derived reactive oxygen species in the presence of autophagy dysfunction. Moreover, after prolonged starvation, 3'-5' exonuclease-dependent mtDNA degradation by POLG adjusted the initially increasing mtDNA copy number in wild-type cells, but caused quantitative mtDNA instability and irreversible respiratory dysfunction in autophagy-deficient cells as a result of nucleotide limitations. In summary, our study reveals that mitochondria rely on the homeostatic functions of autophagy to balance synthetic and degradative modes of POLG, which control copy number dynamics and stability of the mitochondrial genome.
线粒体含有数十到数千份自身基因组（线粒体 DNA [mtDNA]），从而产生遗传冗余，能够缓冲对细胞功能至关重要的线粒体基因的突变。然而，调节 mtDNA 拷贝数的机制一直难以捉摸。在这里，我们发现 mtDNA 聚合酶 γ（POLG）的 DNA 合成和降解在饥饿的酵母细胞中动态控制 mtDNA 拷贝数，这依赖于自噬提供的代谢稳态。具体而言，在自噬功能障碍的情况下，饥饿野生型细胞中由 POLG 连续进行的 mtDNA 合成会受到核苷酸不足和升高的线粒体来源的活性氧的抑制。此外，经过长时间的饥饿后，POLG 依赖于 3'-5'外切酶的 mtDNA 降解调整了野生型细胞中最初增加的 mtDNA 拷贝数，但由于核苷酸限制，在自噬缺陷细胞中导致定量 mtDNA 不稳定性和不可逆的呼吸功能障碍。总之，我们的研究揭示了线粒体依赖于自噬的稳态功能来平衡 POLG 的合成和降解模式，从而控制线粒体基因组的拷贝数动态和稳定性。
