Hypothesis

Nuclear ACSS2-derived acetyl-CoA in hypothalamic neurons regulates SIRT1 activity, which in turn controls autophagy genes and systemic inflammation, thereby influencing organismal lifespan.

Mechanistic Model

In aging, reduced mitochondrial citrate export lowers nuclear acetyl-CoA from ACLY, shifting reliance to ACSS2-mediated acetate utilization. ACSS2 translocates to the nucleus where it acetylates histones at promoters of autophagy-related genes (e.g., Atg5, Becn1) and anti‑inflammatory genes (e.g., Il10). This acetylation creates a permissive chromatin state that enhances transcription. Simultaneously, elevated histone acetylation promotes SIRT1 recruitment, as SIRT1 preferentially binds acetylated histones and deacetylates downstream targets such as FOXO1 and NF‑κB, amplifying autophagy and dampening inflammasome activation. The resulting increase in neuronal autophagy improves proteostasis and reduces release of pro‑inflammatory cytokines (IL‑1β, TNF‑α) into the circulation, lowering peripheral tissue inflammation and extending healthspan.

Testable Predictions

1. In aged mice, neuron‑specific overexpression of ACSS2 will increase histone H3K9ac at autophagy gene promoters in the hypothalamus, measurable by ChIP‑qPCR.
2. This overexpression will raise SIRT1‑dependent deacetylation of FOXO1 and reduce NF‑κB p65 acetylation in the same tissue.
3. Mice with neuronal ACSS2 gain will show elevated autophagic flux (LC3‑II/I ratio, p62 degradation) in hypothalamic lysates and decreased serum IL‑6 and TNF‑α levels.
4. Consequently, median lifespan will be extended by ~15% compared with wild‑type littermates, an effect that will be abolished by concurrent SIRT1 knock‑down in neurons.
5. Acetate supplementation in drinking water will rescue the lifespan phenotype of ACSS2‑deficient neurons only when SIRT1 is intact.

Potential Experiments

• Generate Camk2a‑Cre;ACSS2^fl/fl (knock‑out) and Camk2a‑Cre;Rosa26^LSL‑ACSS2 (overexpression) lines. Confirm nuclear ACSS2 by subcellular fractionation and western blot.
• Perform ChIP‑seq for H3K9ac and H3K27ac in hypothalamic tissue from young, old, and manipulated mice; focus on autophagy and anti‑inflammatory loci.
• Measure SIRT1 activity using a fluorometric deacetylation assay on hypothalamic extracts; assess FOXO1 and NF‑κB acetylation status by immunoprecipitation‑western.
• Assess autophagy flux with lysosomal inhibition (chloroquine) followed by LC3‑II western; quantify p62 turnover.
• Collect blood at monthly intervals for cytokine ELISA; monitor food intake, body weight, and glucose tolerance.
• Survival analysis (Kaplan‑Meier) under standard chow; repeat with SIRT1 neuronal knock‑down (Camk2a‑Cre;Sirt1^fl/fl) to test epistasis.
• Provide 2% sodium acetate in drinking water to a cohort of ACSS2‑deficient mice; evaluate whether lifespan extension is restored.

If neuronal ACSS2 fails to alter hypothalamic histone acetylation, SIRT1 activity, or systemic inflammation, the hypothesis is falsified. Conversely, confirmation would support a model where compartment‑specific acetyl-CoA production couples neuronal epigenetics to organismal aging via SIRT1‑mediated autophagy and inflammation control.