Ultrasensitive deletion detection links mitochondrial DNA replication, disease, and aging.

Area of Science:

• Genetics
• Molecular Biology
• Aging Research

Background:

• Acquired mitochondrial genome (mtDNA) deletions are key features of aging and mitochondrial diseases.
• These deletions cause focal mitochondrial respiratory deficiency, impacting cellular function.

Purpose of the Study:

• To develop a sensitive method for quantifying deletions in circular mtDNA molecules.
• To investigate the link between mtDNA deletions, aging, and POLG-related mitochondrial diseases.

Main Methods:

• Developed LostArc, an ultrasensitive method for quantifying deletions in circular mtDNA.
• Analyzed skeletal muscle from individuals with and without POLG pathogenic variants using LostArc.
• Employed unsupervised bioinformatic analyses to identify deletion patterns.

Main Results:

• Quantified 35 million mtDNA deletions across ~470,000 unique spans in skeletal muscle.
• Found that the fraction of deleted mtDNA (ablation) explains aging and POLG-disease phenotypes.
• Identified distinct age- and disease-correlated deletion patterns.

Conclusions:

• Replication by DNA polymerase γ is implicated as the primary driver of mtDNA deletions.
• Minimal purifying selection against mtDNA deletions occurs in postmitotic muscle fibers via mitophagy.
• MtDNA deletions are likely initiated by replication fork stalling during strand displacement synthesis.