Hypothesis

Intermittent dasatinib + quercetin (D+Q) treatment does more than clear senescent cells; it reprograms the tissue niche via sustained alteration of extracellular vesicle (EV) cargo that suppresses mTOR activity in neighboring cells long after drug washout. In contrast, rapamycin’s lifespan extension depends on continuous mTORC1 inhibition within each cell and rapidly reverses upon cessation because it does not remodel the niche.

Mechanistic basis

1. Senolytic‑EV shift – D+Q‑induced apoptosis of senescent cells releases EVs enriched in anti‑inflammatory miRNAs (e.g., miR‑146a, miR‑21) and depleted of SASP‑promoting cargos, as shown in lung and intestine models [2][5]. These EVs are taken up by stem/progenitor cells, where they activate AMPK and inhibit mTORC1 signaling through PTEN up‑regulation, creating a cell‑autonomous low‑mTOR state that persists because the EVs remain in the extracellular matrix for weeks [6].
2. Epigenetic niche memory – The reduced SASP lowers NF‑κB signaling in stromal cells, leading to decreased H3K27ac at promoters of mTOR‑activating genes (e.g., Rheb, RagA). This chromatin state is maintained through cycles of cell division, effectively “locking” a low‑mTOR transcriptional program in the niche [3].
3. Rapamycin lacks this loop – Rapamycin inhibits mTORC1 directly but does not alter EV composition or SASP; upon washout, mTORC1 reactivates because the upstream inhibitory signals (AMPK, PTEN) are not reinforced by niche‑derived cues.

Testable predictions

• Prediction 1: In aged mice receiving intermittent D+Q (3 days/month for 6 months), tissue EV fractions isolated 4 weeks after the last dose will show a sustained increase in miR‑146a and a decrease in IL‑1β‑encoding mRNA relative to rapamycin‑treated controls (measured by small‑RNA seq) [2][6].
• Prediction 2: Stem cell niches from D+Q‑treated mice will exhibit reduced phospho‑S6K and increased AMPK phosphorylation for at least 8 weeks post‑treatment, whereas rapamycin‑treated mice will revert to baseline within 2 weeks of drug cessation [3][4].
• Prediction 3: Functional readouts (grip strength, glucose tolerance) will remain improved in D+Q mice after washout, while rapamycin mice will show loss of benefit correlating with mTORC1 reactivation.

Experimental design

• Groups: (1) Vehicle, (2) Intermittent D+Q (5 mg/kg dasatinib + 50 mg/kg quercetin, 3 d/mo), (3) Chronic rapamycin (14 ppm diet), (4) Intermittent rapamycin matched to D+Q schedule, (5) D+Q + rapamycin combo.
• Duration: 6 months treatment, followed by 8‑week washout.
• Readouts: EV miRNA profiling, SASP cytokines, p‑S6K/p‑AMPK in isolated stem cells, methylation senescence clocks, tissue histology, behavioral assays.
• Statistical plan: Two‑way ANOVA with treatment and time as factors; falsification if D+Q does not sustain EV miRNA shift or niche mTOR suppression beyond washout while rapamycin does.

If D+Q‑induced niche reprogramming persists, it would demonstrate that senolytics achieve genuine rejuvenation by altering the tissue environment, whereas mTOR inhibition merely mimics a hard‑pressed state without lasting structural change.