Mitochondrial Theory of Aging

What it proposes

Mitochondria are the dominant source of ROS in most cells; mitochondrial DNA (mtDNA) is poorly protected and accumulates mutations with age; damaged mitochondria leak more electrons, generate more ROS, and accelerate further damage — a “vicious cycle”.

Refinements over time

• Mitochondrial dynamics: fission, fusion, and mitophagy maintain mitochondrial network quality. Aging disrupts these dynamics as much as it damages individual organelles.
• Heteroplasmy and clonal expansion: mtDNA mutations in a single cell can expand clonally, eventually impairing that cell’s function.
• Cross-talk with the nucleus: retrograde signalling from mitochondria shapes nuclear gene expression and stress responses.
• Mitohormesis: moderate mitochondrial stress is beneficial; the “vicious cycle” framing is incomplete.

Evidence

• mtDNA-mutator mice (impaired mtDNA proofreading) show progeroid phenotypes.
• VO₂max declines steadily with age, partly reflecting mitochondrial capacity.
• Urolithin A, exercise, NAD+ precursors, and rapamycin all improve mitochondrial function with measurable healthspan benefits.

Related entries

Mitochondrial dysfunction, Mitophagy, Free radical theory.