Temporal SASP Switch Inhibition as a Priming Strategy to Enhance Senolytic Specificity and Preserve Beneficial Senescence in Aging

Hypothesis

We hypothesize that a brief, intermittent inhibition of the IL‑1α/IL‑1β feedback loop that drives the transition from immunosuppressive to pro‑inflammatory SASP will 'prime' senescent cells for subsequent senolytic clearance while preserving the early, tissue‑reparative SASP phase. This two‑step regimen—first a senomorphic that blocks IL‑1α signaling (e.g., neutralizing antibody or small‑molecule IL‑1R antagonist), followed after a defined interval by a senolytic targeting SCAPs (e.g., navitoclax)—should increase the proportion of senescent cells eliminated in aged tissues, reduce off‑target toxicity, and retain beneficial transient senescence in wound healing.

Mechanistic Rationale

1. SASP temporal switch – Early SASP is dominated by TGF‑β1/3 and is immunosuppressive/pro‑fibrotic; later SASP shifts to IL‑1β, IL‑6, IL‑8 via an IL‑1α autocrine loop that activates NF‑κB and cGAS‑STING [2]. Inhibiting IL‑1α/IL‑1R prevents this feed‑forward, locking cells in the early SASP state.
2. SCAP dependence – Early SASP senescent cells retain high BCL‑2/BCL‑xL expression but lower dependence on Src‑family kinases; late SASP upregulates MCL‑1 and BFL‑1, altering SCAP profiles [1]. Priming with IL‑1 blockade may maintain BCL‑2/BCL‑xL dominance, making cells more sensitive to navitoclax.
3. Preservation of beneficial senescence – Transient senescence in wound healing relies on early SASP to recruit macrophages and stimulate matrix deposition without chronic inflammation [4]. By blocking the IL‑1α‑driven switch, we impede the deleterious late SASP while leaving the early reparative signals intact.

Testable Predictions

• Prediction 1: In aged mouse skin, a 48‑hour IL‑1RA treatment followed by navitoclax will reduce p16+ cell burden by >70% (vs ~45% with navitoclax alone) [1] while maintaining TGF‑β1 levels comparable to untreated wounds.
• Prediction 2: The same regimen will decrease serum IL‑6 and TNF‑α by >50% and increase wound closure rate by 30% relative to vehicle.
• Prediction 3: Off‑target effects such as thrombocytopenia (platelet count drop <150 k/µL) will be significantly less frequent than with navitoclax monotherapy.
• Prediction 4: Single‑cell RNA‑seq will show enrichment of an early SASP signature (TGF‑β1, SERPINE1) and depletion of late SASP cytokines (IL1B, CXCL8) after IL‑1RA pretreatment.

Experimental Design

1. Animals: 20‑month‑old C57BL/6 mice, full‑thickness dorsal excisional wounds (n=10 per group).
2. Groups: (a) Vehicle control, (b) Navitoclax alone (10 mg/kg, oral, days 3‑5), (c) IL‑1RA (anakinra 100 mg/kg i.p., days 0‑2), (d) IL‑1RA → navitoclax (same schedule).
3. Readouts: Flow cytometry for p16+Cd45− cells, ELISA for SASP cytokines in wound tissue and plasma, platelet counts, histology for collagen deposition (Masson’s Trichrome), wound area measurement over 14 days.
4. Analysis: Two‑way ANOVA with post‑hoc Tukey; significance set at p<0.05.

If the combined regimen outperforms monotherapies in senescent cell clearance without exacerbating thrombocytopenia or impairing early wound‑healing SASP, the hypothesis is supported. Failure to improve clearance or a worsening of platelet counts would falsify the premise that IL‑1α blockade preserves SCAP sensitivity and beneficial SASP.