Purifying Selection against Pathogenic Mitochondrial DNA in Human T Cells

Area of Science:

• Genetics
• Cell Biology
• Biochemistry

Background:

• Mitochondrial diseases often stem from mutations in mitochondrial DNA (mtDNA).
• Cellular heteroplasmy, a mix of mutant and non-mutant mtDNA, is characteristic of these conditions.
• The proportion of mutant mtDNA varies significantly between patients and tissues.

Observation:

• Simultaneous single-cell heteroplasmy and cell state assays were performed on blood cells from patients with A3243G-associated mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes.
• A wide spectrum of heteroplasmy was observed across all blood cell types.
• T cells exhibited markedly reduced heteroplasmy compared to other cell types.

Findings:

• The reduced heteroplasmy in T cells suggests a selective pressure against mutant mtDNA within this lineage.
• This pattern of reduced heteroplasmy in T cells was consistent across multiple patients, including those with and without strokelike episodes.
• The study quantifies heteroplasmy levels at a single-cell resolution across diverse cell types.

Implications:

• Understanding cell-type-specific selection in mtDNA heteroplasmy can inform disease mechanisms.
• Identifying tissues with selective pressures may offer insights into disease progression and therapeutic strategies.
• This research provides a foundation for further investigation into the role of cellular state in mitochondrial disease pathogenesis.