Hypothesis

Combining a low, steady-state AAV‑OSK vector with periodic, high‑peak mRNA‑OSK pulses produces a synergistic epigenetic reset that extends healthspan more effectively than either approach alone, without increasing tumor formation.

Rationale

• AAV‑OSK delivers sustained, sub‑threshold OSK expression that keeps chromatin in a permissive state, maintaining baseline activity of TET‑mediated demethylation and reducing heterochromatin loss associated with aging【5】.
• mRNA‑OSK provides short, high‑amplitude bursts that drive rapid nucleosome remodeling and activate mitochondrial biogenesis via PGC‑1α, a pathway shown to be engaged by transient OSKM expression【2】.
• The low‑dose AAV component reduces the total OSK exposure needed from mRNA alone, lowering the dose‑dependent risk of oncogenic transformation linked to prolonged high OSKM levels【1】.
• Omitting c‑Myc (using OSK) further curtails pluripotency induction and tumorigenic potential across both platforms【2】.
• This dual‑kinetic strategy exploits temporal complementarity: AAV primes the epigenome for a more efficient response to mRNA pulses, while mRNA pulses prevent the accumulation of chronic AAV‑mediated transgene expression that could trigger immune clearance or insertional effects.

Experimental Design

Model: Progeroid Ercc1‑/− mice and aged wild‑type C57BL/6J mice. Groups (n=15 per sex):

1. Vehicle control
2. AAV‑OSK alone (low dose, 1e11 vg per mouse, single intravenous injection)
3. mRNA‑OSK alone (modified mRNA‑LNP, 2 µg per dose, administered twice weekly for 4 weeks)
4. Combined therapy: AAV‑OSK (same low dose) + mRNA‑OSK pulses (same regimen as group 3)
5. AAV‑OSKM (positive control for tumorigenic risk)

Readouts (collected at baseline, 4 weeks, 12 weeks, and 24 weeks):

• Tumor surveillance: necropsy, histopathology, Ki‑67 staining
• Lifespan and healthspan: median survival, frailty index, grip strength
• Epigenetic age: blood and tissue DNA methylation clocks (Horvath mouse clock)
• Transcriptomics: RNA‑seq of liver, muscle, brain to assess OSK target engagement and PGC‑1α activation
• Mitochondrial function: Seahorse OCR, ATP levels, ROS production
• Immune response: anti‑AAV antibodies, cytokine profiling (IL‑6, TNF‑α)

Predicted Outcomes

• Group 4 will show a greater increase in median lifespan (≥50% over control) compared with groups 2 or 3 alone, reflecting synergistic rejuvenation.
• Tumor incidence in group 4 will remain statistically indistinguishable from controls and significantly lower than group 5 (AAV‑OSKM), confirming that the reduced OSK exposure mitigates oncogenic risk.
• Epigenetic age reversal will be strongest in group 4, with a ΔAge of −1.5 to −2.0 years in liver and muscle.
• Mitochondrial OCR and ATP production will be elevated in group 4, driven by PGC‑1α upregulation without the glycolytic shift seen with sustained high OSKM.
• Anti‑AAV titers will be modest, and cytokine spikes will be transient, indicating low immunogenicity.

Potential Pitfalls and Mitigations

• Immune clearance of AAV: Use liver‑specific promoters and transient immunosuppression (e.g., short‑course corticosteroids) if needed.
• Variable mRNA delivery: Optimize LNP composition for each tissue; include a tracking reporter to confirm uptake.
• Dose‑response uncertainty: Perform a pilot dose‑escalation for AAV‑OSK (0.5×, 1×, 2×) to identify the minimal effective priming level before combining with mRNA.

This hypothesis is directly falsifiable: if the combined regimen fails to surpass the monotherapy benefits in lifespan extension or shows increased tumorigenicity, the proposed synergy would be refuted.