Hypothesis

Urolithin A (UA) acts as a ligand for the nuclear receptor PPARδ, facilitating its interaction with the chromatin organizer CTCF to stabilize promoter‑enhancer loops at epigenetic‑clock CpG sites, thereby recruiting TET2‑mediated demethylation and reversing epigenetic age.

Mechanistic Rationale

• PPARδ activation by UA has been shown to increase mitophagy via CAMK2D/Nrf2 pathways4.
• PPARδ physically interacts with CTCF in intestinal epithelial cells, modulating chromatin architecture2.
• CTCF binding protects CpG islands from de novo methylation; loss of CTCF correlates with epigenetic drift2.
• TET2 recruitment to CTCF‑bound sites drives active demethylation, a mechanism implicated in epigenetic rejuvenation1.

Thus, UA‑PPARδ‑CTCF axis could directly link gut‑derived postbiotic signaling to the epigenetic information loss hypothesized as the upstream controller of aging.

Experimental Design

1. In vivo treatment – Aged (20‑month) C57BL/6 mice receive UA (50 mg/kg/day) or vehicle for 8 weeks.
2. Chromatin assays – Perform CUT&RUN for PPARδ, CTCF, and TET2 in colon epithelium; quantify occupancy at a panel of epigenetic‑clock CpGs (e.g., ELOVL2, FHL2).
3. Epigenetic clock – Measure DNA methylation age using the mouse Horvath clock before and after treatment.
4. Hallmark readouts – Assess mitochondrial ROS, mitophagy (LC3‑II/p62), senescence (p16^INK4a), and systemic inflammation (IL‑6, TNFα).
5. Controls – Include PPARδ antagonist (GW9662) and CTCF siRNA‑colon‑derived organoids to test necessity.

Expected Outcomes and Falsifiability

• If hypothesis is correct: UA treatment will increase PPARδ and CTCF co‑occupancy at clock CpGs, boost TET2 binding, reduce methylation age by ≥10%, and improve mitochondrial and inflammatory hallmarks.
• If hypothesis is false: UA will improve mitophagy and inflammation without altering CTCF/PPARδ binding or epigenetic clock age, indicating its effects are downstream of epigenetic regulation.

This design directly tests whether a gut metabolite can modulate the proposed master chromatin controller, bridging the gut‑mitochondria‑epigenome axis.12345