Hypothesis

Intermittent hormetic stress transiently increases senescent cell burden but simultaneously enhances immune-mediated clearance, such that combining hormesis with senolytic drugs yields a greater reduction in persistent senescent cells and longer lifespan than either intervention alone.

Mechanistic Rationale

Hormetic interventions (e.g., intermittent fasting, exercise, mild heat shock) activate FOXO-dependent antioxidant programs and also trigger a brief NF‑κB pulse that can upregulate senescence-associated secretory phenotype (SASP) components in a subset of cells[1][2]. This NF‑κB pulse is short‑lived because hormesis also induces expression of immune‑activating ligands such as NKG2D and ICAM‑1, which promote recognition and phagocytosis by natural killer cells and macrophages[5]. In contrast, senolytics (e.g., dasatinib + quercetin) directly induce apoptosis of cells with high SCARA3/p16^INK4a^ expression, removing the source of chronic SASP[3][4)]. The hypothesis posits that the hormesis‑induced immune priming lowers the threshold for senolytic efficacy, allowing lower drug doses or shorter treatment windows to achieve comparable senescent cell depletion.

Predictions

1. A single hormetic bout will cause a measurable rise in p16^INK4a^+ cells and SASP factors (IL‑6, MCP‑1) within 6‑24 h, followed by a accelerated decline compared with untreated controls.
2. Mice receiving hormesis followed by a senolytic regimen will show a greater cumulative reduction in p16^INK4a^+ cells and SASP markers at 7 days post‑treatment than mice receiving either hormesis or senolytics alone.
3. The combined treatment will extend median lifespan by > 30 % over controls, exceeding the additive expectation of the individual interventions (≈ 16 % from hormesis + 36 % from senolytics).
4. Depletion of NK cells or macrophages will abolish the enhanced clearance observed with hormesis + senolytics, returning the phenotype to that of senolytics alone.

Experimental Design

Model: C57BL/6J mice, aged 18 months (n = 10 per group). Groups: (i) Control (vehicle), (ii) Intermittent fasting (24 h fast twice weekly) as hormesis, (iii) Senolytic (dasatinib 5 mg/kg + quercetin 50 mg/kg, i.p., once weekly for 3 weeks), (iv) Hormesis → Senolytic (fasting schedule followed 2 h later by senolytic dosing), (v) Hormesis → Senolytic + anti‑NK1.1 antibody (NK‑cell depletion), (vi) Hormesis → Senolytic + clodronate liposomes (macrophage depletion). Readouts: Flow cytometry for p16^INK4a^+CD45^− cells in spleen, liver, and adipose tissue; ELISA for plasma IL‑6, MCP‑1; immunofluorescence for NKG2D ligands on senescent cells; NK cell (NK1.1^+) and macrophage (F4/80^+) activity assays; survival monitoring. Timeline: Baseline measurements, interventions for 8 weeks, then follow‑up for lifespan.

Potential Outcomes and Interpretation

If prediction 1 holds, it confirms that hormesis can transiently elevate senescent markers—a direct test of the claim that hormesis ‘convinces cells they are about to die’. If prediction 2 is satisfied, the synergy validates the mechanistic link between hormesis‑induced immune priming and senolytic action. Failure to observe accelerated clearance (prediction 1) or lack of lifespan extension beyond additive effects (prediction 3) would falsify the hypothesis, suggesting hormesis does not generate a senescent‑cell‑prone state amenable to immune removal. Depletion experiments (prediction 4) would pinpoint the effector immune cells responsible.

This framework directly tests whether the ‘threat‑response’ language of hormesis can be harnessed to improve damage‑removal strategies, moving beyond compensatory survival toward genuine repair.