We hypothesize that age‑related loss of DNA polymerase β (Polβ) activity does not merely slow BER completion but actively sequesters APE1 at toxic abasic‑site intermediates, thereby diminishing mitochondrial 8‑oxoguanine repair and amplifying cGAS‑STING‑driven neuroinflammation. This sink model predicts that the accumulation of unrepaired abasic sites acts as a molecular trap for APE1, reducing its availability for both nuclear and mitochondrial BER substrates. Consequently, mitochondrial 8‑oxoguanine persists, triggering mtDNA release into the cytosol and chronic activation of the cGAS‑STING pathway, a key driver of age‑associated brain inflammation.

Mechanistic Rationale

• Polβ normally fills the gap after OGG1‑initiated excision and APE1‑mediated nicking, restoring a continuous DNA strand. When Polβ activity falls 50‑75% in aged neurons DNA Polymerase β is a rate‑limiting factor in neuronal BER, with its activity dropping by 50‑75% in aged mouse brains, the pathway stalls at the abasic‑site step.
• Accumulated abasic sites have high affinity for APE1’s AP‑endonucleolytic domain. Biophysical studies show APE1 binds abasic DNA with Kd in the low nanomolar range, effectively competing with its catalytic turnover. This binding reduces the free APE1 pool available to process mitochondrial 8‑oxoguanine lesions generated by OGG1.
• Mitochondrial OGG1 continues to excise 8‑oxoguanine, producing mitochondrial abasic sites that cannot be processed because nuclear‑sequestered APE1 is limiting. The resulting mitochondrial abasic sites destabilize mtDNA, promoting its release into the cytoplasm.
• Cytosolic mtDNA engages cGAS, producing cyclic GMP‑AMP and activating STING, which drives IFN‑β‑dependent transcription of pro‑inflammatory genes (IBA1, cytokines) observed in aged brains The failure to repair mitochondrial 8‑oxoguanine damage leads to mtDNA release into the cytoplasm, which activates the cGAS‑STING neuroinflammatory pathway.
• Chronic cGAS‑STING signaling further suppresses Polβ expression via IFN‑induced transcriptional repressors, creating a feed‑forward loop that worsens BER deficiency.

Testable Predictions

1. Biochemical sequestration – In extracts from aged mouse forebrain, immunoprecipitated APE1 will show increased binding to abasic‑site oligonucleotides compared with young extracts; this interaction will be reduced by Polβ overexpression.
2. Mitochondrial lesion burden – Neurons with Polβ knockdown will exhibit higher mitochondrial 8‑oxoguanine levels (measured by lesion‑specific immunostaining or LC‑MS/MS) and elevated cytosolic mtDNA, whereas Polβ overexpression will lower both.
3. Inflammation read‑out – Polβ‑deficient neurons will display heightened cGAS‑STING activation (phospho‑STING, IFN‑β reporter) and increased secretion of IL‑6/TNF‑α; rescuing Polβ will blunt these responses.
4. Behavioral rescue – Viral delivery of Polβ to the hippocampus of aged mice will improve performance in spatial memory tasks (Morris water maze) and reduce microglial IBA1 staining, correlating with decreased mitochondrial 8‑oxoguanine.

Experimental Approach

• Primary neuron cultures from young and aged mice: transduce with AAV‑Polβ or shRNA‑Polβ; quantify abasic‑site‑APE1 complexes via co‑immunoprecipitation and slot‑dot assays.
• Mitochondrial isolation followed by slot‑blot for 8‑oxoguanine and qPCR for mtDNA copy number in cytosol.
• cGAS‑STING assay: western blot for phospho‑TBK1/IRF3 and ELISA for IFN‑β.
• In vivo: aged C57BL/6 mice receive hippocampal AAV‑Polβ or control; after 4 weeks assess lesion load, neuroinflammation, and cognition.
• Controls: include catalytically dead Polβ mutant to distinguish scaffolding vs. enzymatic effects.

If the data show that restoring Polβ reduces abasic‑site‑APE1 binding, lowers mitochondrial 8‑oxoguanine, diminishes mtDNA release and cGAS‑STING signaling, and rescues cognitive decline, the hypothesis will be supported. Conversely, if Polβ manipulation does not affect APE1 sequestration or mitochondrial lesion burden despite altering nuclear BER, the sink model will be falsified, prompting reevaluation of how BER decline drives neuroinflammation in aging.