Addressing RNA integrity to determine the impact of mitochondrial DNA mutations on brain mitochondrial function with age.

Wei Wang,James B Stewart,Janne M Strand,Katja Scheffler,Magnar Bjørås,Ying Esbensen,Lars Eide,John R Battista

doi:10.1371/journal.pone.0096940

Abstract

Mitochondrial DNA (mtDNA) mutations can result in mitochondrial dysfunction, but emerging experimental data question the fundamental role of mtDNA mutagenesis in age-associated mitochondrial impairment. The multicopy nature of mtDNA renders the impact of a given mtDNA mutation unpredictable. In this study, we compared mtDNA stability and mtRNA integrity during normal aging. Seven distinct sites in mouse brain mtDNA and corresponding mtRNA were analyzed. Accumulation of mtDNA mutations during aging was highly site-specific. The variation in mutation frequencies overrode the age-mediated increase by more than 100-fold and aging generally did not influence mtDNA mutagenesis. Errors introduced by mtRNA polymerase were also site-dependent and up to two hundred-fold more frequent than mtDNA mutations, and independent of mtDNA mutation frequency. We therefore conclude that mitochondrial transcription fidelity limits the impact of mtDNA mutations.

Highlights

The mitochondrial theory of aging postulates that mutations in mitochondrial DNA accumulate with age and result in impaired quality and activity of the mtDNA-encoded proteins
Mitochondrial dysfunction associated with accumulation of clonal expansions of deletion mutations are reported in nucleoside reverse transcriptase inhibitor (NRTI)treated individuals [2,3] and neurodegenerative disorders including Multiple Sclerosis, Alzheimer’s Disease and Parkinson’s Disease [4]
To investigate the impact of mtDNA mutations with age, we developed an assay to determine mitochondrial RNA (mtRNA) integrity with high resolution and used this technology to compare mtDNA mutagenesis and mtRNA error frequency in brains from young mice with those from old mice, which were associated with impaired mitochondrial function

Summary

Introduction

The mitochondrial theory of aging postulates that mutations in mitochondrial DNA (mtDNA) accumulate with age and result in impaired quality and activity of the mtDNA-encoded proteins. The Polg mutator demonstrates that mtDNA mutations can result in pathology and shortened lifespan [8]. This model has been used to demonstrate the correlation between mtDNA mutations, mitochondrial dysfunction and premature aging, it is questionable to what extent this genetic mitochondrial mutator model represents the molecular mechanisms that underlie mitochondrial dysfunction during normal aging. Accumulation of mtDNA deletions correlated with the phenotype and mutation frequency during normal aging [10]. In view of the relatively high tolerance for mtDNA deletion mutations, there is an unexplained discrepancy between the observed mutation frequency during normal aging and the age-associated dysfunction [12,13,14]

Methods

Results

Conclusion