Hypothesis

Early‑life activation of nociceptive TRPV1⁺ neurons triggers a hormetic cascade that enhances stress resistance and prolongs lifespan, whereas the same signaling in middle‑ and old‑age shifts to a maladaptive, pro‑inflammatory state that accelerates aging. Pharmacological or genetic suppression of pain pathways will therefore have opposite effects on longevity depending on the age at which it is initiated.

Mechanistic rationale

1. Hormetic ROS/AMPK signaling in youth – TRPV1‑mediated Ca²⁺ influx stimulates mitochondrial ROS production at low, sub‑toxic levels. This activates AMPK and the integrated stress response (ISR) via eIF2α‑phosphorylation, leading to ATF4‑driven transcription of autophagy genes (LC3, p62) and proteasome subunits. The net effect is improved proteostasis and damage clearance.
2. Transition to NF‑κB‑driven inflammaging – With advancing age, cumulative TRPV1 activation sustains NF‑κB signaling in sensory neurons and nearby immune cells, driving IL‑6, TNF‑α and MMP‑1 expression. This chronic ISR becomes maladaptive, suppressing autophagy through sustained mTORC1 activity and promoting tissue degradation.
3. Predicted outcome of manipulation – Ablating or silencing TRPV1⁺ nociceptors early (e.g., postnatal day 10) will blunt the hormetic ROS/AMPK/ISR axis, reducing basal autophagy and stress resistance, thereby shortening lifespan. Inducible ablation late (e.g., 18 months in mice) will remove the NF‑κB‑driven inflammatory tone, lowering systemic cytokines, improving autophagy flux, and extending healthspan and lifespan.

Experimental plan

• Model: TRPV1‑CreERT2 crossed to Rosa26‑DTA (diphtheria toxin A) for inducible, neuron‑specific ablation; include a control group receiving vehicle.
• Intervention windows:
  • Early: tamoxifen at P10 → ablation before weaning.
  • Late: tamoxifen at 18 months → ablation in middle‑aged mice.
• Readouts (performed longitudinally):
  • Survival curves (Kaplan‑Meier) and cause‑of‑death necropsy.
  • Frailty index (grip strength, gait speed, coat condition).
  • Tissue‑specific markers: LC3‑II/I ratio, p62 levels, phospho‑AMPK, phospho‑eIF2α, ATF4, nuclear NF‑κB p65, IL‑6, TNF‑α, MMP‑1 (Western blot/qPCR).
  • Behavioral pain thresholds (hot‑plate, von Frey) to confirm ablation efficacy.
• Predictions:
  • Early‑ablation group: median lifespan ↓ ≈ 15 % vs controls; increased frailty; reduced LC3‑II/I and phospho‑AMPK; elevated p62.
  • Late‑ablation group: median lifespan ↑ ≈ 10‑20 % vs controls; lower frailty; decreased NF‑κB activity, cytokines, and MMP‑1; restored autophagy flux.

Falsifiability

If early‑life TRPV1⁺ ablation does not reduce lifespan or stress‑resistance markers, or if late‑life ablation fails to extend lifespan and lower inflammaging readouts, the hypothesis is refuted. Conversely, observing the predicted age‑dependent effects would support the dual‑role model of nociceptive signaling in aging.

Broader implications

This framework reframes chronic pain not merely as a symptom to be silenced but as a developmental signal whose timing dictates whether it promotes or impairs longevity. It suggests that future analgesics should aim for age‑specific modulation—preserving youthful hormetic TRPV1 activity while inhibiting its pro‑inflammatory isoform in older individuals.