Tamashiro Hiroaki, Ishikawa Kaori, Sadotomo Koichi, Ogasawara Emi, Nakada Kazuto
Graduate School of Science and Technology, University of Tsukuba, Ibaraki, Japan.
Institute of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan.
Aging Cell. 2025 May 2:e70085. doi: 10.1111/acel.70085.
mtDNA mutator mice (Polg mice) have reinforced the mitochondrial theory of aging. These mice accumulate multiple mutations in mtDNA with age due to a homozygous proofreading-deficient mutation in mtDNA polymerase gamma (Polg), resulting in mitochondrial respiratory dysfunction and premature aging phenotypes. However, whether the accumulation of multiple mutations in Polg mice induces mitochondrial respiratory dysfunction remains unclear. Here, we determined the accurate mtDNA genotype, including the frequency of total mutations and the number of non-synonymous substitutions and pathogenic mutations, using next-generation sequencing in the progeny of all three genotypes obtained from the mating of heterozygous mtDNA mutator mice (Polg mice) and examined their correlation with mitochondrial respiratory activity. Although Polg mice showed equivalent mtDNA genotype to Polg (wild-type) mice, the mitochondrial respiratory activity in the Polg mice was mildly reduced. To further investigate the causal relationship between mtDNA genotype and mitochondrial respiratory activity, we experimentally varied the mtDNA genotype in Polg mice. However, mitochondrial respiratory activity was mildly reduced in Polg mice and severely reduced in Polg mice, regardless of the mtDNA genotype. Moreover, by varying the mtDNA genotype, some Polg mice showed mtDNA genotype equivalent to those of Polg mice, but mitochondrial respiratory activity in Polg mice was normal. These results indicate that the mitochondrial respiratory dysfunction observed in mice with proofreading-deficient mutation in Polg is correlated with the nuclear genotype of Polg rather than the mtDNA genotype. Thus, the mitochondrial theory of aging in Polg mice needs further re-examination.
线粒体DNA突变小鼠（Polg小鼠）强化了衰老的线粒体理论。由于线粒体DNA聚合酶γ（Polg）存在纯合校对缺陷突变，这些小鼠随着年龄增长会在mtDNA中积累多个突变，导致线粒体呼吸功能障碍和早衰表型。然而，Polg小鼠中多个突变的积累是否会诱导线粒体呼吸功能障碍仍不清楚。在这里，我们使用下一代测序技术，在杂合线粒体DNA突变小鼠（Polg小鼠）交配产生的所有三种基因型后代中，确定了准确的mtDNA基因型，包括总突变频率、非同义替换数量和致病突变数量，并研究了它们与线粒体呼吸活性的相关性。尽管Polg小鼠的mtDNA基因型与Polg（野生型）小鼠相当，但Polg小鼠的线粒体呼吸活性略有降低。为了进一步研究mtDNA基因型与线粒体呼吸活性之间的因果关系，我们通过实验改变了Polg小鼠的mtDNA基因型。然而，无论mtDNA基因型如何，Polg小鼠的线粒体呼吸活性均略有降低，而Polg小鼠的线粒体呼吸活性则严重降低。此外，通过改变mtDNA基因型，一些Polg小鼠的mtDNA基因型与Polg小鼠相当，但Polg小鼠的线粒体呼吸活性正常。这些结果表明，在Polg中存在校对缺陷突变的小鼠中观察到的线粒体呼吸功能障碍与Polg的核基因型相关，而不是与mtDNA基因型相关。因此，Polg小鼠的衰老线粒体理论需要进一步重新审视。
