Schroeder Elizabeth A, Shadel Gerald S
Department of Pathology, Yale University School of Medicine, New Haven, CT 06520, United States; Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, United States.
Department of Pathology, Yale University School of Medicine, New Haven, CT 06520, United States; Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, United States.
Mech Ageing Dev. 2014 Jan;135:41-9. doi: 10.1016/j.mad.2013.12.002. Epub 2013 Dec 25.
Mitochondrial DNA (mtDNA) exists in multiple copies per cell and is essential for oxidative phosphorylation. Depleted or mutated mtDNA promotes numerous human diseases and may contribute to aging. Reduced TORC1 signaling in the budding yeast, Saccharomyces cerevisiae, extends chronological lifespan (CLS) in part by generating a mitochondrial ROS (mtROS) signal that epigenetically alters nuclear gene expression. To address the potential requirement for mtDNA maintenance in this response, we analyzed strains lacking the mitochondrial base-excision repair enzyme Ntg1p. Extension of CLS by mtROS signaling and reduced TORC1 activity, but not caloric restriction, was abrogated in ntg1Δ strains that exhibited mtDNA depletion without defects in respiration. The DNA damage response (DDR) kinase Rad53p, which transduces pro-longevity mtROS signals, is also activated in ntg1Δ strains. Restoring mtDNA copy number alleviated Rad53p activation and re-established CLS extension following mtROS signaling, indicating that Rad53p senses mtDNA depletion directly. Finally, DDR kinases regulate nucleus-mitochondria localization dynamics of Ntg1p. From these results, we conclude that the DDR pathway senses and may regulate Ntg1p-dependent mtDNA stability. Furthermore, Rad53p senses multiple mitochondrial stresses in a hierarchical manner to elicit specific physiological outcomes, exemplified by mtDNA depletion overriding the ability of Rad53p to transduce an adaptive mtROS longevity signal.
线粒体DNA（mtDNA）在每个细胞中以多个拷贝存在，对氧化磷酸化至关重要。mtDNA的减少或突变会引发多种人类疾病，并可能导致衰老。在出芽酵母酿酒酵母中，TORC1信号通路的减弱部分通过产生一种线粒体ROS（mtROS）信号来延长时序寿命（CLS），该信号可通过表观遗传方式改变核基因表达。为了探究在这种反应中对mtDNA维持的潜在需求，我们分析了缺乏线粒体碱基切除修复酶Ntg1p的菌株。在表现出线粒体DNA耗竭但呼吸无缺陷的ntg1Δ菌株中，mtROS信号传导和TORC1活性降低导致的CLS延长被消除，但热量限制导致的CLS延长未受影响。转导促长寿mtROS信号的DNA损伤反应（DDR）激酶Rad53p在ntg1Δ菌株中也被激活。恢复mtDNA拷贝数可减轻Rad53p的激活，并在mtROS信号传导后重新建立CLS延长，这表明Rad53p直接感知线粒体DNA耗竭。最后，DDR激酶调节Ntg1p的核-线粒体定位动态。从这些结果中，我们得出结论，DDR途径感知并可能调节Ntg1p依赖的mtDNA稳定性。此外，Rad53p以分级方式感知多种线粒体应激，以引发特定的生理结果，例如线粒体DNA耗竭优先于Rad53p转导适应性mtROS长寿信号的能力。
