The mtDNA Mutation Spectrum of the Progeroid Polg Mutator Mouse Includes Abundant Control Region Multimers

Abstract

Summary Polg mtDNA mutator mice are important models for investigating the role of acquired mtDNA mutations in aging. Despite extensive study, there remains little consensus on either the etiology of the progeroid phenotype or the mtDNA mutation spectrum induced by disrupted polymerase-γ function. To investigate the latter we have developed a novel, pragmatic approach we term “Mito-seq”, applying next generation sequencing to enriched, native mtDNA. Regardless of detection parameters we observed an increase of at least two orders of magnitude in the number of mtDNA single nucleotide variants in Polg mutator mice compared to controls. We found no evidence for the accumulation of canonical mtDNA deletions but multimers of the mtDNA control region were identified in brain and heart. These control region multimers (CRMs) contained heterogeneous breakpoints and formed species that excluded the majority of mtDNA genes. CRMs demonstrate that polymerase-γ 3′–5′ exonuclease activity is required for preserving mtDNA integrity.

The role of mitochondria in aging

“…The mtDNA mutator mice are homozygous for a knock-in mutation that leads to the expression of a proofreading-deficient catalytic subunit of mtDNA polymerase (PolgA mut ). The expression of PolgA mut causes extensive mtDNA mutagenesis with the formation of three different forms of mtDNA mutations: random point mutations, linear molecules with large deletions, and, in certain tissues, molecules containing multimers of the control region (an area of the mitochondrial genome that contains noncoding mtDNA) (58,60,61). Furthermore, a single report has argued that a fourth type of mtDNA mutation, consisting of circular mtDNA molecules with large deletions, is prevalent and even drives the premature aging phenotype (60).…”

High-fat diet and FGF21 cooperatively promote aerobic thermogenesis in mtDNA mutator mice

“…These mice express a proofreading-deficient version of the nuclear-encoded mitochondrial DNA polymerase gamma and, consequently, accumulate point mutations and deletions in their mitochondrial genome (7). These mice display a premature aging phenotype that substantially manifests around 9 mo of age with symptoms such as weight loss, s.c. lipodystrophy, alopecia, infertility, and anemia, ultimately resulting in death around 12 mo (6).…”

Mitochondrial DNA mutations in disease and aging

“…There has been one study arguing that a third type of mutation, circular mtDNA molecules with deletions, drives the phenotype of mtDNA mutator mice (Vermulst et al, 2008). However, this study has been refuted in several independent studies, in which sensitive PCR assays (Edgar et al, 2009;Kraytsberg et al, 2009) or deep sequencing (Williams et al, 2010;Ameur et al, 2011) could not detect any significant levels of circular mtDNA molecules with deletions in various tissues of mtDNA mutator mice. In addition, the biochemical phenotype in mtDNA mutator mice is fully consistent with the idea that point mutations of mtDNA create amino acid substitutions of respiratory chain subunits, which explains the observed decline in the stability of the respiratory chain complexes (Edgar et al, 2009).…”