Background

Partial reprogramming with transient OSK/OSKM factors resets age‑associated DNA methylation and restores youthful tissue function without triggering pluripotency or tumor formation [1][2]. Key mechanisms include TET‑dependent DNA demethylation and chromatin remodeling that accesses retained youthful epigenetic information [3][4]. However, the duration and frequency of factor expression that maximizes demethylation while preserving identity remain poorly defined.

Hypothesis

We hypothesize that synchronizing brief OSK expression pulses with periodic elevation of intracellular NAD+ levels enhances TET enzyme activity, thereby prolonging the demethylation window and improving rejuvenation outcomes without increasing the risk of identity loss or tumorigenesis.

Mechanistic Rationale

1. NAD+ as a TET cofactor – TET enzymes require Fe(II) and α‑ketoglutarate; their activity is boosted when the cellular NAD+/NADH ratio is high, which promotes α‑ketoglutarate production via the TCA cycle and suppresses competing hydroxy‑methylation pathways.
2. Temporal overlap – OSK‑induced chromatin opening creates a transient state where DNA is more accessible to TETs. If NAD+ peaks coincide with this window, demethylation efficiency should rise,
3. Feedback limitation – Elevated NAD+ also activates sirtuins, which deacetylate histones and further stabilize a youthful chromatin configuration, reducing the chance that cells drift toward a pluripotent state after OSK withdrawal.

Testable Predictions

• Prediction 1: In aged mouse liver, mice receiving weekly doxycycline‑inducible OSK pulses combined with biweekly NAD+ precursor (e.g., NR) administration will show a greater reduction in epigenetic clock acceleration than OSK alone, measured by Illumina EPIC array at 4, 8, and 12 weeks post‑treatment [3].
• Prediction 2: Single‑cell ATAC‑seq will reveal sustained accessibility at promoters of youth‑associated genes (e.g., Foxg1, Myod1) only in the combined treatment group, indicating prolonged chromatin remodeling.
• Prediction 3: Tumor incidence (checked by histopathology and Ki‑67 staining) will remain at baseline levels in both OSK‑only and OSK+NAD+ groups, confirming that NAD+ boosting does not exacerbate tumorigenic risk.
• Prediction 4: Pharmacological inhibition of TET activity (using Bobcat339) will abolish the additional benefit of NAD+ supplementation, linking the effect directly to TET‑mediated demethylation.

Experimental Design

• Use 18‑month‑old C57BL/6 mice (n=10 per group). Groups: (1) control (vehicle), (2) OSK pulses (1 week on/2 weeks off doxycycline), (3) NAD+ booster (NR 400 mg/kg/day, 5 days on/2 days off), (4) combined OSK+NAD+.
• Collect tissue (liver, muscle, retina) at 4, 8, 12 weeks for epigenetic clock, ATAC‑seq, RNA‑seq, and histology.
• Monitor body weight, glucose tolerance, and survival.

Potential Pitfalls and Mitigation

• NAD+ fluctuations may affect OSK transgene expression – Measure doxycycline levels and OSK mRNA to confirm that NAD+ manipulation does not alter transgene kinetics.
• Off‑target effects of NR – Include a group receiving NR with a sirtuin inhibitor (e.g., EX527) to isolate sirtuin‑dependent contributions.
• Translational relevance – Validate key findings in human iPSC‑derived hepatocytes treated with mRNA‑encoded OSK factors and NR equivalents.

If the hypothesis holds, it would define a simple, metabolically grounded adjuvant that extends the therapeutic window of partial reprogramming, bringing the approach closer to safe, repeatable clinical application.