Hypothesis

Core idea

We hypothesize that specific mitochondrial DNA heteroplasmies increase the release of mitochondrial DNA fragments into the cytosol, where they activate the cGAS‑STING innate immune pathway, driving chronic low‑grade inflammation (inflammaging). Intermittent fasting reduces this pathogenic signaling by enhancing mitophagy‑dependent clearance of damaged mitochondria and limiting mtDNA release, an effect that depends on NAD⁺‑dependent SIRT3 activation.

Mechanistic reasoning

1. Heteroplasmy → mitochondrial instability – Pathogenic heteroplasmies (e.g., m.3243A>G, m.1555A>G) impair electron‑transport chain function, raising mitochondrial ROS and causing permeability transition pore opening, which favors mtDNA nucleoid escape (ref: [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC6184556/).
2. Escaped mtDNA → cGAS‑STING activation – Cytosolic mtDNA is a potent ligand for cGAS, leading to STING‑dependent IFN‑β and NF‑κB signaling, inflammasome priming, and senescence‑associated secretory phenotype (SASP) (ref: [5] https://doi.org/10.1038/nature12474).
3. Intermittent fasting → mitophagy – Fasting elevates NAD⁺, activates SIRT3, which deacetylates and activates mitophagy regulators (e.g., LC3, PINK1/Parkin), selectively removing mitochondria with high ROS and high heteroplasmy load (ref: [6] https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/intermittent-fasting-promotes-adipocyte-mitochondrial-fusion-through-sirt3mediated-deacetylation-of-mdh2/B19A226CD1CA3DB3414825585EF3BE52).
4. Result – Reduced mtDNA release diminishes cGAS‑STING signaling, lowering inflammasome activity and systemic inflammation.

Testable predictions

• Prediction 1: In human peripheral blood monocytes, individuals with >5% heteroplasmy at m.3243A>G will show higher cytosolic mtDNA levels and increased phospho‑STING signaling compared with heteroplasmy‑negative controls.
• Prediction 2: A 4‑week intermittent fasting regimen (16:8 daily) will decrease heteroplasmy‑associated cytosolic mtDNA and phospho‑STING in the same individuals, correlating with reduced plasma IL‑6 and CRP.
• Prediction 3: Pharmacological inhibition of SIRT3 (e.g., using 3‑TYPV) will block the fasting‑induced reduction in cytosolic mtDNA and phospho‑STING, demonstrating SIRT3 dependence.

Experimental approach

• Recruit 60 volunteers aged 60‑80, stratify by measured m.3243A>G heteroplasmy (>5% vs <1%) using droplet digital PCR.
• Collect blood at baseline, after 2 weeks, and after 4 weeks of supervised 16:8 intermittent fasting.
• Isolate monocytes; quantify cytosolic mtDNA by qPCR after subcellular fractionation; measure phospho‑STING and downstream IRF3 phosphorylation by Western blot.
• Plasma cytokines (IL‑6, TNF‑α, CRP) measured by ELISA.
• In a subset, treat monocytes ex vivo with SIRT3 inhibitor during fasting serum to test necessity.

Falsifiability

If intermittent fasting does not reduce cytosolic mtDNA or phospho‑STING in high‑heteroplasmy participants, or if reductions occur equally in low‑heteroplasmy individuals, the hypothesis that heteroplasmy‑driven mtDNA release mediates inflammaging and is specifically mitigated by fasting‑induced mitophagy would be falsified.

Broader impact

Confirming this link would reposition mtDNA heteroplasmy not as a passive marker but as an active driver of innate immune activation, suggesting that targeting mtDNA quality control (e.g., via NAD⁺ boosters or mitophagy inducers) could be a more precise anti‑inflammaging strategy than global antioxidant approaches.