Mitochondrial heteroplasmy governs mito-nuclear peptide signaling that licenses durable OSK-mediated epigenetic rejuvenation

Hypothesis

Chronic elevation of mitochondrial DNA heteroplasmy above ~40% disrupts the secretion of mitochondrial‑derived peptides (MDPs) such as humanin and MOTS‑c, leading to aberrant nuclear lamina remodeling and sustained epigenetic drift that cannot be permanently corrected by OSK alone. Reducing mtDNA heteroplasmy below this threshold restores physiological MDP signaling, which in turn stabilizes lamin A processing and permits OSK‑driven demethylation to persist after transgene clearance.

Rationale

• iPSC clones with high mtDNA deletion heteroplasmy show slowed growth, increased epigenetic age, and a senescence‑like transcriptome that persists after differentiation【1】.
• Mitochondrial stress activates retrograde pathways (AMPK, PGC‑1α, HIF‑1α, NF‑κB) that alter NAD⁺/metabolite ratios and drive nuclear hypermethylation【2】.
• Partial reprogramming with OSK reverses nuclear epigenetic age and extends mouse lifespan, but benefits fade when mtDNA heteroplasmy remains high and epigenetic marks revert after treatment stops【3】【4】.
• Recent work demonstrates that MDPs regulate lamin A/C processing and chromatin organization via direct interaction with LAP2α, linking mitochondrial health to nuclear architecture【5】.

We propose that the missing link is MDP‑mediated control of lamin A isoform balance: high heteroplasmy suppresses MDP release, causing accumulation of pre‑lamin A and progerin‑like species that tether heterochromatin to the nuclear periphery, reinforcing methylation patterns that OSK can only transiently overcome.

Predictions

1. In aged mice, liver heteroplasmy >40% correlates with reduced circulating humanin/MOTS‑c levels and increased nuclear lamin A precursor (pre‑lamin A) abundance.
2. Acute reduction of mtDNA heteroplasmy via mitochondrially targeted base editors (e.g., DdCBE) to <30% restores MDP secretion, normalizes lamin A processing, and decreases nuclear H3K9me3 foci.
3. Sequential treatment—first mtDNA base editing, then cyclic AAV9‑OSK—yields a >2‑fold increase in median lifespan compared with OSK alone, and the epigenetic age reduction persists for at least 8 weeks after OSK transgene clearance.
4. Exogenous supplementation with humanin or MOTS‑c in heteroplasmy‑high, OSK‑treated mice rescues the durability of epigenetic rejuvenation without altering mtDNA load.

Experimental Design

• Model: C57BL/6J mice aged 24 months; stratify by mtDNA heteroplasmy measured by duplex sequencing.
• Intervention A: AAV9‑mito‑DdCBE targeting the common mtDNA deletion (mtΔ4977) to achieve heteroplasmy <30%.
• Intervention B: Cyclic AAV9‑OSK (2 weeks on/1 week off) for 8 weeks.
• Groups: (1) Control (empty AAV), (2) OSK only, (3) mtDNA editing only, (4) mtDNA editing → OSK, (5) OSK + humanin peptide pump.
• Readouts: (a) mtDNA heteroplasmy (qPCR/ddPCR), (b) plasma humanin/MOTS‑c (ELISA), (c) lamin A/C and pre‑lamin A western blot, (d) nuclear morphology (lamin B1 immunofluorescence), (e) epigenetic age (Horvath mouse clock), (f) transcriptomic senescence signature (RNA‑seq), (g) lifespan and healthspan metrics (frailty index, grip strength).

Falsifiability

If mtDNA heteroplasmy reduction fails to raise MDP levels or normalize lamin A processing, or if OSK‑induced epigenetic age reversal persists equally well in high‑heteroplasmy animals, the hypothesis is falsified. Likewise, if exogenous MDP supplementation does not extend the durability of OSK effects in heteroplasmy‑high mice, the proposed MDP‑lamin axis is not required.

This framework shifts the focus from viewing mtDNA as a passive passenger to recognizing its secretory phenotype as a gatekeeper of nuclear chromatin state, providing a clear, testable path toward durable rejuvenation by combining mitochondrial genome repair with epigenetic reprogramming.