Hypothesis

The age‑dependent decline of mitochondrial OGG1 creates a stoichiometric mismatch with APE1, causing accumulation of toxic abasic sites that preferentially activate the cGAS‑STING pathway via mitochondrial DNA release, rather than simple 8-oxoG load.

Rationale

• Mitochondrial OGG1 expression drops ~2‑fold in aged brains 1.
• APE1 activity also declines, but neuron‑specific APE1 loss accelerates cognitive aging and reduces LTP 2.
• When OGG1 excises 8-oxoG, it leaves an abasic site that APE1 must cleave; if APE1 is limiting, abasic intermediates persist 6.
• Persistent abasic sites can destabilize mitochondrial DNA, promoting its escape into the cytosol where it activates cGAS‑STING 1.
• Current single‑target OGG1 overexpression may worsen the bottleneck if APE1 is not concurrently restored.

Predictions

1. In aged neurons, the ratio of OGG1 activity to APE1 activity will correlate inversely with cytosolic mtDNA levels and STING phosphorylation.
2. Restoring APE1 to match OGG1 overexpression will reduce abasic site accumulation, limit mtDNA release, and lower neuroinflammation more effectively than OGG1 overexpression alone.
3. Pharmacological stabilization of the OGG1‑APE1 interaction (e.g., via a small‑molecule bridging compound) will improve BER flux without increasing toxic intermediates.

Experimental Design

• Model: Primary hippocampal neurons from young (3 mo) and aged (24 mo) mice; also human iPSC‑derived neurons.
• Interventions: (a) Mito‑targeted OGG1 overexpression (AAV‑mito‑OGG1), (b) Mito‑targeted APE1 overexpression (AAV‑mito‑APE1), (c) Combined OGG1+APE1 overexpression, (d) Control virus.
• Readouts:
  • 8-oxoG levels by LC‑MS/MS 3
  • Abasic site quantification using aldehyde‑reactive probe assay
  • Cytosolic mtDNA measured by qPCR of mitochondrial genes in cytosolic fraction
  • STING phosphorylation and IFN‑β expression via Western blot and ELISA
  • Mitochondrial respiration (Seahorse XF)
  • Behavioral assays (Morris water maze) in vivo.
• Analysis: Compare OGG1:APE1 activity ratios (measured by enzyme activity assays) with each readout; test whether combined rescue normalizes ratios and reduces STING signaling.

Potential Outcomes and Interpretation

• If the hypothesis is correct, combined OGG1+APE1 restoration will lower cytosolic mtDNA and STING activation despite similar 8-oxoG reductions as OGG1 alone, indicating that abasic site clearance is the key inflammatory trigger.
• If OGG1 alone suffices, then abasic sites are not limiting and the bottleneck hypothesis fails.
• A negative result (no change in STING signaling despite corrected ratio) would suggest alternative sources of mtDNA release or that other BER steps (Polβ, ligase III) dominate.

This framework directly tests whether balancing BER enzyme stoichiometry prevents toxic intermediate‑driven innate immune activation, offering a mechanistic refinement to current single‑target antioxidant DNA repair strategies.