Hypothesis

Nuclear acetyl-CoA levels in senescent cells act as a rheostat that shifts the senescence-associated secretory phenotype (SASP) from a tumor‑suppressive, growth‑arresting state to a pro‑inflammatory, tissue‑damaging state by differentially acetylating histones at NF‑κB versus FOXO3 target promoters.

Mechanistic Rationale

Senocytes integrate metabolic cues into epigenetic decisions via acetyl-CoA–dependent histone acetylation. When nuclear acetyl-CoA is abundant, ACSS2–generated acetyl groups preferentially acetylate H3K27 at promoters of NF‑κB‑driven SASP components (IL-6, IL-8, CCL2), enhancing their transcription and creating a feed‑forward inflammatory loop. Conversely, limited nuclear acetyl-CoA reduces acetylation at these sites while permitting basal acetylation of FOXO3‑controlled promoters (e.g., IGFBP7, p21) that enforce cell-cycle arrest and secrete factors with tumor-suppressive and wound-healing properties. This bias explains the observed context-dependence of SASP: tissues with high acetate uptake or ACSS2 activity (e.g., inflamed macrophages) favor a detrimental SASP, whereas low-acetyl-CoA niches preserve a protective secretome.

Testable Predictions

1. Pharmacological elevation of nuclear acetyl-CoA (via acetate supplementation or ACSS2 over-expression) in senescent fibroblasts will increase NF-κB-p65 binding and H3K27ac at IL6 and IL8 promoters, while decreasing FOXO3 occupancy at IGFBP7.
2. CRISPR-mediated knock-down of ACSS2 in senescent cells will shift SASP composition toward higher IGFBP7 and lower IL-6, independent of p16^INK4a^ levels.
3. In vivo, intermittent acetate dosing in aged mice will elevate SASP inflammatory markers in liver and lung, whereas ACSS2 inhibition will reduce circulating IL-6 without affecting senescent cell burden measured by SA-β-gal.
4. Tumor models co-implanted with senescent stromal cells will show accelerated growth when stromal ACSS2 is high, but suppressed growth when ACSS2 is low, linking the rheostat to paracrine tumor suppression.

Experimental Design

• In vitro: Induce senescence in human IMR-90 fibroblasts via irradiation. Treat groups with (a) sodium acetate (5 mM), (b) ACSS2 siRNA, (c) both, plus controls. Perform ChIP-seq for H3K27ac and p65, RNA-seq for SASP, and secretion assays (ELISA) for IL-6, IL-8, IGFBP7. Validate FOXO3 promoter acetylation by ChIP-qPCR.
• Ex vivo: Isolate senescent cells from young and old mouse livers, manipulate ACSS2 with AAV-mediated over-expression or shRNA, then transplant into syngeneic hosts bearing sub-cutaneous MC38 tumors. Monitor tumor growth and serum cytokines.
• In vivo: Feed aged (20-month) C57BL/6 mice either normal water or water supplemented with 2 % sodium acetate for 4 weeks, with a parallel cohort receiving the ACSS2 inhibitor compound-30. Assess hepatic and lung SASP via multiplex cytometry, quantify senescent cells by p16^INK4a^ immunostaining, and evaluate fibrosis histology.

Potential Implications

If validated, this hypothesis reframes senolytics not as blunt removal tools but as opportunities to metabolically re-program the SASP. Targeting nuclear acetyl-CoA flux could preserve the tumor-suppressive and wound-healing arms of senescence while dampening its chronic inflammatory burden, offering a precision strategy that avoids the tissue-repair deficits seen with continuous senolytic clearance.