Voluntary wheel running has no impact on brain and liver mitochondrial DNA copy number or mutation measures in the PolG mouse model of aging

Abstract

The mitochondrial theory of aging attributes much of the aging process to mitochondrial DNA damage. The polymerase gamma (PolG) mutant mouse was designed to evaluate this theory and thus carries a mutated proofreading region of polymerase gamma (D257A) that exclusively transcribes the mitochondrial genome. As a result, PolG D257A mice accumulate mitochondrial DNA (mtDNA) mutations that lead to premature aging, as evidenced by hair loss, weight loss, kyphosis, increased rates of apoptosis, organ damage, and an early death, occurring around 12 months of age. Research has shown that exercise decreases skeletal muscle mtDNA mutations and normalizes protein levels in PolG mice. However, brain mtDNA changes with exercise in PolG mice have not been studied. We found no effects of exercise on mtDNA mutations or copy number in either the brain or liver of PolG mice, despite changes to body mass. Our results suggest that mitochondrial mutations play little role in exercise-brain interactions in the PolG model of accelerated aging. In addition to evaluating the effect of exercise on mtDNA outcomes, we also implemented novel methods for both extracting mtDNA and measuring mtDNA mutations, with aims for improving the efficiency and accuracy of these methods.

Complementary Square-Wave Voltammetry and LC-MS/MS Analysis to Elucidate Induced Damaged and Mutated Mitochondrial and Nuclear DNA from in Vivo Knockdown of the BRCA1 Gene in the Mouse Skeletal Muscle

“…Indeed, we detected a mutation frequency that was approximately 70 times higher in KO mtDNA compared to the nDNA, which is consistent with what is known about the mutation rates between the two. , Specifically, the point mutation, G→A, hypothesized through these analyses has been shown to be 70 times more prevalent in mtDNA than in nDNA in previous pyrosequencing studies in Drosophilia . The mutation frequency we calculated based on the LC-MS/MS results and compared to the known mtDNA base content is on the order of that detected in the POLG mutator mouse, a model known to accumulate mtDNA mutations due to the expression of deficient polymerase γ protein …”

“…71 The mutation frequency we calculated based on the LC-MS/MS results and compared to the known mtDNA base content is on the order of that detected in the POLG mutator mouse, a model known to accumulate mtDNA mutations due to the expression of deficient polymerase γ protein. 63 The impact of Brca1 on the skeletal system is still a burgeoning and intense area of research. Brca1 has been shown to localize in both the nucleus and mitochondria, and its loss drastically impacts the musculature of an organism.…”

“…1 Additionally, this elevated frequency is consistent with elevated mutation rates reported in DNA polymerase γ (POLG) mouse models carrying specific mutations in the proofreading region that were shown to exhibit increased levels of mtDNA mutations determined using qPCR 62 and next-generation sequencing (NGS). 63 A similar calculation in Brca1KO smi nDNA leads to a mutation frequency estimate of 7 × 10 −4 −1.0 × 10 −3 .…”

Age-related accumulation of de novo mitochondrial mutations in mammalian oocytes and somatic tissues

“…Mitochondria, the powerhouses of the cell, have their own genomes. Multicopy mitochondrial DNA (mtDNA) genomes-e.g., present in thousands of copies in brain and skeletal muscle and in approximately 200,000 copies in mature oocytes [16][17][18][19][20]-are transmitted in mammals through the maternal lineage. Studying how mutations in mtDNA accumulate with age is critical because of their association with numerous human genetic diseases (reviewed in [21]) as well as with aging phenotypes [22], including Parkinson's and Alzheimer's diseases [23,24].…”

Metabolic landscape in cardiac aging: insights into molecular biology and therapeutic implications

“…For example, a recent study reported that a POLG-mutant mouse carrying a D257A mutation in a key residue of mitochondrial DNA polymerase experienced a loss of mtDNA stability, leading to a significant acceleration of aging processes. 278,279 Moreover, increased mtDNA mutation burden contributes to abnormal mitochondrial biogenesis resulting in programmed cell death in cardiomyocytes 280,281 (Fig. 4).…”