Hypothesis

Reduced base excision repair (BER) capacity in dorsal root ganglia (DRG) neurons, specifically loss of OGG1 activity, leads to accumulation of mitochondrial 8‑oxoguanine (8‑oxoG) lesions. This oxidative DNA damage alters neuronal excitability and lowers pain thresholds, making pain sensitivity a direct readout of BER efficiency and, consequently, biological age.

Mechanistic Rationale

1. Oxidative lesion buildup – Aging neurons show declining OGG1 and APE1 activity, resulting in persistent 8‑oxoG in both nuclear and mitochondrial DNA {4}. In DRG, mitochondrial 8‑oxoG impairs oxidative phosphorylation, increasing reactive oxygen species (ROS) production and creating a feed‑forward loop of damage.
2. Neuronal excitability shift – 8‑oxoG in mitochondrial genomes reduces ATP availability, causing depolarization‑dependent upregulation of Nav1.7 and TRPV1 channels. Electrophysiological studies link mitochondrial dysfunction to heightened nociceptive firing {2】.
3. Epigenetic coupling – Persistent oxidative stress activates PARP1, consuming NAD+ and altering sirtuin‑mediated deacetylation of histones. This drift mirrors epigenetic‑clock acceleration observed in chronic pain cohorts {1】.
4. Bidirectional validation – OGG1 overexpression in mitochondria reverses neuroinflammation and restores youthful transcriptional profiles in brain {6】. Extending this to DRG should normalize pain thresholds without altering actual tissue injury.

Testable Predictions

• Prediction 1: Older mice (≥20 mo) will exhibit significantly lower OGG1 protein levels in L4‑L6 DRG compared with young mice (3 mo), correlating with higher 8‑oxoG signal (immunohistochemistry) and reduced hot‑plate and von Frey thresholds.
• Prediction 2: Viral‑mediated OGG1 rescue specifically in DRG of aged mice will increase pain thresholds to youthful levels within 7 days, without changing peripheral inflammation markers.
• Prediction 3: The magnitude of pain‑threshold improvement after OGG1 rescue will inversely predict the change in epigenetic age (measured by mouse Horvath clock) in the same animals.
• Prediction 4: In humans, individuals with experimentally induced low OGG1 activity (via pharmacologic PARP inhibition that shifts BER balance) will show acute reductions in pressure pain tolerance, measurable before any detectable change in circulating inflammatory cytokines.

Experimental Outline

Animal arm

• Use C57BL/6 mice, young and aged.
• Quantify OGG1, APE1, and 8‑oxoG in DRG lysates (Western blot, dot‑blot).
• Conduct behavioral pain assays (hot‑plate, acetone drop, von Frey).
• Inject AAV9‑OGG1-mito or AAV9‑GFP control into DRG via intrathecal route.
• Re‑test pain thresholds and collect tissue for epigenetic‑clock analysis (pyrosequencing of CpG sites).

Human arm

• Recruit healthy volunteers stratified by self‑reported pain tolerance.
• Measure ex vivo OGG1 activity in isolated peripheral blood mononuclear cells (PBMCs) as a surrogate for neuronal BER capacity.
• Apply a standardized pressure pain threshold test (algometer).
• Correlate OGG1 activity, pain threshold, and epigenetic age (e.g., GrimAge) using linear regression.
• Optional: acute PARP inhibition with olaparib low dose to transiently reduce BER and retest pain tolerance.

Falsifiability

If OGG1 levels in DRG do not correlate with pain thresholds across age, or if OGG1 overexpression fails to alter nociception despite verified mitochondrial rescue, the hypothesis is refuted. Similarly, if pain‑threshold changes do not track epigenetic‑age shifts, the proposed functional link collapses.

Implications

Establishing pain sensitivity as a rapid, noninvasive proxy for BER‑driven biological aging would provide a functional bridge between molecular damage metrics and clinical phenotyping. It could accelerate trials targeting DNA repair in age‑related pain disorders and refine epigenetic‑clock validation by anchoring them to a measurable sensory endpoint.