Senescent cells are not merely sources of harmful SASP factors; they also release exosomes enriched in specific microRNAs that promote angiogenesis and stem‑cell activation. In young tissue, senescent fibroblast exosomes contain high levels of miR‑29b‑3p and miR‑146a‑5p, which suppress PTEN and IRAK1 in neighboring endothelial and progenitor cells, thereby enhancing VEGF signaling and dampening NF‑κB‑driven inflammation. With age, the exosomal cargo shifts toward pro‑inflammatory miRNAs (e.g., miR‑155) while regenerative miRNAs decline, converting the senescent secretome from reparative to deleterious. Current senolytic approaches eliminate the entire senescent cell, thereby removing both detrimental SASP and beneficial exosomal signaling, which predicts impaired tissue repair when clearance occurs before the exosomal cargo has fully transitioned to a pathological profile.

Hypothesis: Transient senolytic clearance in aged mice will reduce wound‑fluid exosomal miR‑29b‑3p and miR‑146a‑5p levels, leading to delayed angiogenesis and impaired closure; rescuing the deficit with exogenous exosomes enriched in these miRNAs will restore healing without reinstating harmful SASP.

Testable predictions:

1. Measurement: In p16‑3MR mice treated with a senolytic (e.g., navitoclax) for 3 days post‑wounding, isolate exosomes from wound fluid at 48 h and quantify miR‑29b‑3p and miR‑146a‑5p by RT‑qPCR. Expect ≥40 % reduction versus vehicle‑treated aged controls (based on exosome yield changes reported in irradiated fibroblast transfers) [6].
2. Functional assay: Treat human dermal endothelial cells with exosomes from senolytic‑cleared wounds; assess tube formation and VEGF‑induced phosphorylation. Predict a 30‑50 % decrease in total tube length and p‑VEGFR2 levels compared with exosomes from untreated wounds.
3. Rescue experiment: Co‑administer synthetic exosomes loaded with miR‑29b‑3p/miR‑146a‑5p (10 µg total RNA) alongside senolytics. Anticipate wound closure rates returning to those of senolytic‑only young mice (≈90 % closure by day 10) and a reduction in IL‑6/IL‑1α SASP markers to baseline levels.
4. Specificity control: Use exosomes from senescent cells knocked down for nSMase2 (impairing exosome biogenesis) to confirm that the rescue effect depends on exosomal delivery, not soluble SASP factors.

Mechanistic insight: The hypothesis reframes senescent cells as transient exosome‑mediating hubs that fine‑tune the niche microenvironment. Their loss disrupts a paracrine RNA‑based communication network that sustains progenitor activation and angiogenic sprouting, independent of the canonical SASP. This explains why senolytics improve outcomes in contexts where senescent cells are already locked in a chronic, SASP‑dominant state (e.g., diabetic ulcers) [8] but impair healing when administered too early in the reparative window [1,6]. By distinguishing the exosomal arm of the senescent secretome from the inflammatory SASP, the hypothesis offers a precision strategy: temporally target senolytic clearance or supplement regenerative exosomes to preserve tissue‑repair functions while mitigating age‑related damage.