Hypothesis

Intermittent fasting (IF) sensitizes senescent cells to BCL-2‑selective senolytics (e.g., navitoclax) by shifting their apoptotic reliance from BCL-xL to BCL-2, whereas platelets upregulate MCL-1 through IGF-1 signaling, thereby preserving thrombopoiesis.

Rationale

• Senolytic efficacy hinges on targeting anti‑apoptotic BCL‑family proteins that senescent cells depend on for survival 1.
• Navitoclax’s dose‑limiting thrombocytopenia stems from BCL-xL inhibition essential for platelet lifespan 2.
• IF activates SIRT1 and NAD⁺‑dependent deacetylation, which has been shown to down‑regulate BCL-xL and up‑regulate BCL-2 in various stress‑adapted cells 3.
• Platelets exposed to IF demonstrate increased IGF‑1‑driven MCL-1 transcription, a known compensatory survival pathway that mitigates BCL-xL loss 4.

Predictions

1. In aged or progeroid mice, IF combined with a BCL-2‑selective senolytic will achieve ≥50 % greater senescent cell clearance (measured by p16^INK4a^ positivity) than senolytic alone.
2. Platelet counts will remain within 15 % of baseline in the IF + senolytic group, whereas senolytic alone will cause ≥30 % thrombocytopenia.
3. Functional readouts (grip strength, treadmill endurance) will improve significantly only in the IF + senolytic cohort, correlating with reduced SASP cytokines (IL‑6, MMP‑9) in serum and tissue.

Experimental Design

• Model: Ercc1^−/− progeroid mice (n=10 per group) and naturally aged C57BL/6 mice (n=10 per group).
• Groups: (a) Vehicle control, (b) IF only (24‑h fast every 48 h), (c) Navitoclax only (50 mg/kg weekly, i.p.), (d) IF + Navitoclax (same schedule).
• Duration: 8 weeks, with longitudinal blood draws for CBC and platelet flow cytometry.
• Endpoints:
  • Senescent burden via p16^INK4a^‑GFP reporter fluorescence in lung, liver, and brain.
  • SASP profiling by multiplex ELISA.
  • Platelet lifespan measured by BrdU incorporation and annexin V/PI staining.
  • Functional assays: grip strength, rotarod, six‑minute walk equivalent (mouse treadmill distance).
• Statistical analysis: Two‑way ANOVA with post‑hoc Tukey; significance set at p<0.05.

Mechanistic Insight

IF elevates hepatic FGF21, which paradoxically suppresses BCL-xL transcription in senescent cells through a FOXO3‑dependent mechanism, while simultaneously enhancing IGF‑1‑AKT signaling in megakaryocytes, driving MCL-1 expression. This differential rewiring creates a therapeutic window where BCL-2 inhibition preferentially eliminates senescent cells without compromising platelet survival. If validated, the hypothesis would justify clinical trials pairing time‑restricted eating with next‑gen BCL-2‑selective senolytics, potentially bypassing the thrombocytopenia barrier that has hampered agents like navitoclax.