We hypothesize that the rate of aging is principally governed by the activity of nuclear-encoded proteins that safeguard mitochondrial genome integrity and function, rather than by the accumulation of mtDNA mutations per se. Specifically, diminished proofreading or processivity of nuclear‑encoded DNA polymerase gamma (POLG) and reduced mitochondrial transcription factor A (TFAM) binding capacity accelerate mtDNA damage signaling, increase reactive oxygen species (ROS), and trigger inflammaging, whereas restoring these nuclear factors extends lifespan even when mtDNA mutation load remains unchanged.

This hypothesis extends the observation that Polg mutator mice with artificially high mtDNA mutation burdens show premature aging, yet natural aging involves only low‑level heteroplasmy that correlates poorly with phenotype【3】. It also reconciles why nuclear interventions such as TERT overexpression or Yamanaka factor reprogramming yield robust lifespan extension【3】, while mtDNA‑centric approaches like MOTS‑c supplementation improve metabolic health without comparable longevity effects【4】【5】.

Mechanistically, we propose that age‑dependent decline in NAD+ reduces SIRT3 activity, leading to hyperacetylation and inhibition of POLG and TFAM. Acetylated POLG exhibits lower fidelity, increasing mtDNA strand breaks; acetylated TFAM shows diminished affinity for mtDNA, impairing nucleoid packaging and transcription. The resulting mitochondrial stress activates cGAS‑STING and NF‑κB pathways, driving systemic inflammation—a hallmark of aging. Consequently, boosting nuclear POLG/TFAM function (e.g., via NAD+ precursors, SIRT3 activators, or targeted expression of acetylation‑resistant mutants) should preserve mtDNA stability, lower ROS, and delay inflammatory cascades.

Testable predictions:

1. In aged wild‑type mice, hepatic and muscular POLG and TFAM acetylation will rise correlates with increased mtDNA damage markers (8‑oxoguanine, deletions) and inflammasome activation.
2. Pharmacological elevation of NAD+ (NR or NMN) or genetic overexpression of a deacetylation‑mimetic POLG (K→R mutants) will reduce mtDNA damage and inflammasome signaling without altering overall mtDNA copy number.
3. Mice expressing acetylation‑resistant POLG/TFAM will exhibit median lifespan extensions of ≥20 % compared with controls, despite similar mtDNA heteroplasmy levels as measured by duplex sequencing.
4. Conversely, knocking down POLG or TFAM in young mice will recapitulate age‑like mtDNA damage and inflammation, shortening lifespan.

Experimental approach: Use liver‑specific AAV vectors to deliver either wild‑type POLG/TFAM, acetylation‑resistant mutants, or shRNA controls in 20‑month‑old mice. Assess mtDNA lesion frequency by qPCR‑based lesion assay, ROS production via MitoSOX, serum IL‑6/TNF‑α, and frailty index over 6 months. Parallel cohorts will receive NAD+ booster supplementation to test synergy. Lifespan will be monitored until natural death.

Falsification would occur if enhancing nuclear POLG/TFAM activity fails to improve mtDNA integrity, reduce inflammasome signaling, or extend lifespan, indicating that mtDNA sequence itself is the primary driver. This reframes the mitochondrial contribution to aging from a passive mutational read‑out to an active, nuclear‑regulated signaling hub.