Hypothesis

Precise restoration of mitochondrially encoded tRNA lysine (MT‑TK) reduces heteroplasmic mutation burden and reprograms nuclear epigenetic aging signatures through a retrograde mitokine signal.

Mechanistic Basis

Mitochondrial DNA encodes 22 tRNAs essential for intra‑mitochondrial translation. Among them, MT‑TK is frequently mutated in aging tissues, leading to ribosomal stalling, reduced synthesis of COX1, and increased release of mitochondrial‑derived peptides (MDPs) such as humanin. Accurate MT‑TK translation improves the stoichiometry of OXPHOS subunits, lowering electron leak and ROS while enhancing the production of a specific COX1‑derived mitokine that travels to the nucleus and activates SIRT1‑dependent deacetylation of histone H3K9ac. This shifts chromatin toward a youthful state, decreasing p16^INK4a expression and senescence-associated secretory phenotype (SASP).

Testable Predictions

1. Base‑editing of the MT‑TK m.8344A>G point mutation in vivo will lower heteroplasmy below 10% in skeletal muscle and brain of mtDNA mutator mice.
2. Corrected MT‑TK will increase mitochondrial translation efficiency by ≥30% measured by puromycin incorporation into nascent mitochondrial polypeptides.
3. Elevated COX1‑derived mitokine levels will correlate with increased nuclear SIRT1 activity and reduced H3K9ac in neurons.
4. Treated animals will show delayed onset of age‑related phenotypes: improved grip strength, extended median lifespan by ~15%, and reduced cortical neuronal loss compared with untreated controls.

Experimental Design

• Model: POLG^mut/mut mice exhibiting accelerated mtDNA mutagenesis.
• Intervention: AAV9‑mitoCas9‑BE3 delivering an adenine base editor targeting MT‑TK m.8344A>G, with a mitochondrial targeting signal (MitoTS) and a tRNA‑specific guide RNA.
• Controls: (i) AAV9‑mitoCas9‑BE3 with non‑targeting guide, (ii) wild‑type littermates.
• Readouts: heteroplasmy quantification by duplex sequencing, mitochondrial translation assay (S35‑methionine incorporation), COX1 mitokine ELISA, nuclear SIRT1 activity assay, chromatin immunoprecipitation for H3K9ac, behavioral tests (rotarod, grip strength), survival analysis, histology for neurodegeneration.

Potential Outcomes

• Support: Significant heteroplasmy reduction, improved translation, elevated mitokine, restored nuclear SIRT1/H3K9ac balance, and phenotypic rescue would confirm that a single mtDNA‑encoded tRNA acts as a linchpin linking mitochondrial fidelity to nuclear aging.
• Refutation: Lack of heteroplasmy shift, no change in mitokine levels, or absence of nuclear epigenetic or phenotypic improvements would falsify the hypothesis, indicating that mtDNA tRNA defects are downstream rather than drivers of aging.

This framework directs precision mitochondrial genome editing toward a mechanistic node that can be quantitatively monitored, offering a falsifiable path to test whether fixing a specific mtRNA reshapes the nuclear aging program.