Hypothesis

Senescent cells function as tunable signaling hubs whose acetyl‑CoA‑dependent histone acetylation acts as a metabolic rheostat that selectively sculpts the SASP. We propose that boosting nuclear acetyl‑CoA via acetate supplementation reprograms the SASP from a predominantly pro‑inflammatory, immune‑attracting profile to a pro‑repair, immunomodulatory secretome. This shift would alter the "hostage negotiator" output: instead of signaling for their own removal, senescent cells would promote stromal regeneration and limit fibrosis, thereby changing the trade‑off between clearance and tissue homeostasis.

Mechanistic Rationale

1. Acetyl‑CoA compartmentalization controls histone acetylation at SASP loci – Nuclear acetyl‑CoA generated by ACSS2 from acetate directly fuels HATs, maintaining open chromatin at specific SASP promoters (PMC8068152).
2. Differential sensitivity of SASP components to acetylation – HDAC1 inhibition preferentially up‑regulates factors such as osteopontin, indicating that individual SASP genes have distinct acetylation thresholds (PMC5748661).
3. Metabolic stress biases SASP composition – During aging, reduced NAD+/NADH and pyruvate dehydrogenase activity lower acetyl‑CoA, favoring a SASP rich in IL‑6, IL‑8, and MMPs that attract immune cells (PMC8068152). Acetate supplementation can bypass this defect, restoring nuclear acetyl‑CoA without relying on glycolytic flux.
4. Immune signaling is modulated by MHC‑I presentation – Senescent cells already hypersensitivity to IFN‑γ and elevated MHC‑I (PMC9901536). A shift in SASP toward TGF‑β, IGF‑1, or amphiregulin would alter the immune contexture from cytotoxic clearance to a tolerogenic, reparative milieu.

Testable Predictions

• In vitro: Human fibroblasts induced to senesce by irradiation will be treated with 5 mM sodium acetate for 48 h. ChIP‑seq for H3K27ac at SASP promoters will show increased acetylation at repair‑associated genes (e.g., TGFB1, IGF1) and decreased acetylation at classic inflammatory SASP genes (e.g., IL6, CXCL8). Secretome profiling (OLINK or mass spectrometry) will reveal a concomitant rise in TGF‑β/IGF‑1 and fall in IL‑6/IL‑8.
• In vivo: Aged (20‑month) mice will receive acetate in drinking water (1 % w/v) for 8 weeks. Compared with controls, acetate‑treated mice will exhibit:
  1. Reduced flow‑cytometric detection of CD8⁺ T cells and NK cells infiltrating senescent cell‑rich areas (p16⁺/SA‑β‑gal⁺).
  2. Increased staining for collagen‑I deposition and α‑SMA‑negative fibroblasts, indicative of enhanced matrix repair rather than fibrosis.
  3. Lower serum SASP inflammatory cytokines (IL‑6, CCL2) and higher tissue levels of TGF‑β and IGF‑1 measured by ELISA.
  4. Functional read‑outs such as improved grip strength and treadmill endurance without a significant change in overall p16⁺ senescent cell burden (to distinguish secretion effects from clearance).

Falsifiability

If acetate treatment fails to alter the acetylation landscape of SASP promoters, does not shift the secretome toward repair factors, or does not modify immune infiltration and tissue repair parameters as described, the hypothesis would be refuted. Conversely, observing the predicted epigenetic and functional changes would support the notion that senescent cells can be metabolically reprogrammed to change their "hostage negotiator" output from a clearance‑centric to a repair‑centric signal.