The 8-oxoG-APE1 Feedback Loop: A Mechanistic Basis for Synergistic BER Enhancement in Aging Neurons

Hypothesis

Base excision repair (BER) declines in aging neurons, with OGG1 and APE1 acting as co-limiting factors PMC8836551. While interventions like mitochondrial OGG1 overexpression PMC10247526 or BDNF-induced APE1 upregulation PMC3948322 partially rescue BER, no study has tested simultaneous enhancement. I propose that 8-oxoG accumulation in aging neurons triggers a negative feedback loop that suppresses APE1 activity post-translationally, and that combined OGG1/APE1 upregulation synergistically restores BER by breaking this cycle. This mechanism links the genotoxic and signaling roles of 8-oxoG Frontiers in Aging to APE1 regulation, offering a testable framework for therapeutic development.

Mechanistic Rationale

The dramatic reduction in APE1 ligation activity during neuronal differentiation—despite minimal protein loss PMC5576894—suggests post-translational control. 8-oxoG itself may act as a signaling molecule, not just a mutagen. In non-neuronal contexts, oxidized bases can activate stress kinases like JNK or p38 MAPK, which modify repair enzymes. In neurons, sustained 8-oxoG accumulation could phosphorylate APE1, inhibiting its endonuclease or ligation-stimulation functions. This creates a vicious cycle: high 8-oxoG reduces APE1 activity, further impairing BER and elevating 8-oxoG. Simultaneously, 8-oxoG in gene promoters might epigenetically suppress APE1 transcription, compounding the issue. The "two faces" of 8-oxoG then converge: its regulatory role in neuronal plasticity Frontiers in Aging may involve tuning APE1 levels to balance damage repair and adaptive gene expression.

Testable Predictions

This hypothesis yields specific, falsifiable predictions:

1. Synergy in BER restoration: Combined overexpression of mitochondrial OGG1 and APE1 in aged neurons will reduce 8-oxoG levels more than either alone, approaching basal levels of ~21 RFU PMC8836551. Measure via immunofluorescence or ELISA in primary neuron cultures.
2. Post-translational regulation: 8-oxoG accumulation correlates with APE1 phosphorylation at specific sites (e.g., Thr233 in human APE1). Use phospho-specific antibodies or mass spectrometry in neurons with OGG1 inhibition.
3. Pathway involvement: Inhibiting stress kinases (e.g., JNK) will rescue APE1 activity in high-8-oxoG conditions without changing protein levels. Test with kinase inhibitors in differentiated neurons.
4. Functional outcomes: Simultaneous OGG1/APE1 enhancement will improve dendritic spine density and LTP more than single interventions, linking BER synergy to cognitive metrics seen in APE1 knockout models PMC9662274.

Falsifiability and Implications

The hypothesis is falsified if: (a) 8-oxoG levels do not correlate with APE1 post-translational modifications, (b) combined OGG1/APE1 overexpression shows no additive effect on BER, or (c) 8-oxoG signaling is independent of APE1 regulation. If validated, it suggests therapeutic strategies should co-target OGG1 and APE1 via dual interventions (e.g., BDNF plus OGG1 agonists) to disrupt the feedback loop, potentially restoring BER capacity in aging or neurodegeneration.