Hypothesis

Pain tolerance reflects sensory neuron splicing dysregulation and predicts biological age.

Mechanistic basis

• Heat pain detection relies on TRPV1 and SCN9A channels whose pre‑mRNAs are prone to intron retention when splicing condensates gelate due to age‑related ATP decline.
• Intron‑containing transcripts produce non‑functional or altered‑function isoforms, shifting neuronal excitability and raising heat pain thresholds while leaving pressure thresholds relatively unchanged [2].
• This splicing noise accumulates in parallel with systemic transcriptomic dysregulation captured by epigenetic clocks, making pain threshold a functional readout of the same underlying process.

Novel prediction

Individuals with higher heat pain thresholds will show elevated intron retention ratios for nociceptor genes in circulating neuronal extracellular vesicles (EVs). Combining EV splicing score with pain threshold will yield a composite biomarker that outperforms GrimAge in predicting mortality and multimorbidity.

Experimental design (testable & falsifiable)

1. Recruit 500 adults aged 30‑80, stratified by sex and comorbidities.
2. Quantify heat and pressure pain thresholds using standardized protocols.
3. Isolate blood‑derived EVs enriched for neuronal markers (L1CAM+) and perform long‑read RNA‑seq to measure intron retention in TRPV1, SCN9A, KCNS1, etc.
4. Calculate an EV splicing dysregulation index (average log2 retention ratio).
5. Estimate epigenetic age with GrimAge.
6. Follow participants for 5 years for all‑cause mortality and onset of age‑related diseases.
7. Test whether (pain threshold + splicing index) predicts outcomes better than GrimAge alone (nested likelihood‑ratio test, AUC comparison).

Falsification: If the composite score shows no significant improvement over GrimAge (p > 0.05) and no correlation with EV intron retention, the hypothesis is refuted.

Expected impact

A ten‑minute pain sensitivity test paired with a minimally invasive EV assay could bridge subjective sensation and molecular aging, offering a low‑cost, dynamic clock that reflects nervous‑system‑specific wear and tear. It's quick, don't need fancy equipment, and we can repeat it over time to track changes.