Hypothesis

We propose that age‑related decline of mitochondrial OGG1 (mtOGG1) leads to persistent AP sites after incomplete 8‑oxoG excision, which act as scaffolds for PARP1 binding. Chronic PARP1 activation consumes NAD+, impairing sirtuin‑dependent deacetylation of NF‑κB and promoting a pro‑inflammatory state. Simultaneously, unrepaired AP sites increase the likelihood of mitochondrial DNA strand breaks, facilitating mtDNA release into the cytosol where it activates the cGAS‑STING pathway. This dual mechanism explains why mtOGG1 restoration reduces inflammation beyond simple lesion removal.

Mechanistic Model

1. BER stall – Reduced mtOGG1 activity causes accumulation of 8‑oxoG and downstream AP sites (see OGG1 decline in AD brains).

2. PARP1 recruitment – AP sites are known PARP1 substrates; persistent sites sustain PARP1 activity, lowering NAD+ levels (APE1 deficiency accelerates decline).

3. NAD+ depletion – Low NAD+ reduces SIRT3 activity, increasing mitochondrial ROS and further damaging mtDNA.

4. mtDNA release – Strand breaks at AP sites promote mtDNA efflux, engaging cGAS‑STING (mtOGG1 prevents mtDNA escape).

5. Inflammatory amplification – cGAS‑STING drives IFN‑β and NF‑κB signaling, while NAD+ loss diminishes SIRT1‑mediated NF‑κB deacetylation, creating a feed‑forward loop.

Testable Predictions

• In aged mouse hippocampi, mtOGG1 knockdown will increase AP‑site immunoreactivity, PARP1 autophosphorylation, and cytosolic mtDNA compared with controls.
• Pharmacological PARP inhibition will rescue NAD+ levels and suppress cGAS‑STING activation despite low mtOGG1.
• Overexpressing a catalytically dead mtOGG1 (binding‑competent but excision‑deficient) will not ameliorate inflammation, confirming the need for AP‑site resolution.

Experimental Approach

• Generate neuron‑specific mtOGG1‑conditional KO and rescue lines; assess 8‑oxoG, AP sites (using aldehyde‑reactive probe), PAR (PARP1 product), NAD+/NADH ratio, cytosolic mtDNA (qPCR), and STING phosphorylation.
• Treat cohorts with PARP inhibitor (Olaparib) or NAD+ booster (NR) and measure microglial activation (Iba1), cytokine levels, and behavior (Morris water maze).
• Use proximity ligation assay to detect AP‑site–PARP1 complexes in isolated mitochondria.

Potential Confounds

Compensatory upregulation of nuclear BER enzymes could mask mitochondrial effects; isolating mitochondrial fractions and using mtDNA‑specific lesions controls for this.