Hypothesis

Pain sensitivity measured by a standardized thermal threshold test reflects senescent cell burden in the dorsal root ganglia and predicts epigenetic age acceleration across multiple clocks, even after adjusting for chronological age, comorbidities, and self‑reported pain.

Mechanistic Rationale

Senescent cells secrete SASP factors such as IL‑6, TNF‑α, and NGF that sensitize nociceptors and promote neuroinflammation, lowering heat and pressure pain thresholds【https://pmc.ncbi.nlm.nih.gov/articles/PMC6710702/】. Simultaneously, SASP drives epigenetic remodeling in circulating immune cells, advancing DNAmAge, PhenoAge, and GrimAge【https://doi.org/10.1186/s13059-021-02585-8】. Thus, pain threshold serves as a functional readout of the SASP‑immune‑epigenetic axis.

Novel Insight

We propose that the relationship is mediated by microglial priming in the spinal cord: senescent‑derived SASP enters CSF, activates spinal microglia, which then release BDNF and CCL2, further increasing neuronal excitability and lowering pain thresholds【https://pmc.ncbi.nlm.nih.gov/articles/PMC10872439/】. This central amplification creates a feedback loop that synchronizes peripheral nociceptor sensitization with systemic epigenetic aging.

Testable Predictions

1. Individuals with lower heat pain thresholds will show higher CSF levels of SASP cytokines (IL‑6, TNF‑α, NGF) and increased microglial activation markers (TSPO PET signal) compared with high‑threshold peers, independent of self‑reported pain scores.
2. Senolytic treatment (dasatinib + quercetin) will raise pain thresholds and reduce CSF SASP levels, accompanied by a measurable decrease in epigenetic age acceleration after 12 weeks.
3. The predictive power of pain threshold for epigenetic age will exceed that of conventional biomarkers (CRP, IL‑6, leukocyte telomere length) in a multivariate model.

Experimental Design

• Recruit 200 participants aged 45‑80 stratified by pain threshold (low, medium, high) using a 1‑second 48 °C heat pulse.
• Collect blood for epigenetic clocks (Horvath, Hannum, PhenoAge, GrimAge), plasma cytokines, and leukocyte telomere length.
• Perform lumbar puncture for CSF IL‑6, TNF‑α, NGF, and TSPO PET imaging for microglial activation.
• Apply senolytic or placebo for 12 weeks in a randomized double‑blind trial, then repeat all measures.
• Use linear mixed models to test threshold as predictor of epigenetic age change, adjusting for age, sex, BMI, and comorbidities.

Falsifiability

If senolytic therapy does not alter pain threshold or CSF SASP despite reducing circulating senescent cells, or if pain threshold fails to predict epigenetic age after controlling for CSF SASP levels, the hypothesis would be refuted.