Hypothesis

Chronic, continuous suppression of nociceptive signaling with NSAIDs blunts low‑intensity, transient JNK/AP-1 activation that functions as a hormetic longevity signal, thereby accelerating senescent cell accumulation and inflammaging. In contrast, intermittent (pulsatile) NSAID regimens allow periodic JNK/AP-1 spikes, preserving adaptive stress responses while still inhibiting COX‑mediated inflammation.

Background

NSAIDs such as celecoxib, aspirin and ibuprofen extend lifespan in C. elegans through off‑target actions on PDK‑1/insulin‑IGF signaling and antioxidant gene expression, independent of COX‑2 inhibition {Celecoxib extends C. elegans lifespan via PDK-1 inhibition} {Aspirin and ibuprofen upregulate SOD genes}. However, acetaminophen and indomethacin increase oxidative stress in older worms, highlighting age‑dependent toxicity {Age‑dependent NSAID toxicity}. In mammals, transient JNK activation promotes stress resistance, proliferation and survival, whereas sustained JNK drives SASP, fibrosis and chronic inflammation {Transient vs sustained JNK} {JNK and SASP in senescence}. Crucially, no study has examined whether long‑term NSAID use masks the nociceptive‑JNK/AP-1 axis that signals tissue damage and triggers repair.

Mechanistic Rationale

Nociceptors release substance P and CGRP, which can activate TRPV1‑dependent calcium influx and upstream MAPK kinases (MKK4/7) leading to JNK phosphorylation. Low‑level, intermittent JNK‑AP-1 activity induces expression of DNA‑repair genes (e.g., GADD45), antioxidant enzymes (SOD2) and autophagy regulators (LC3B), establishing a hormetic preconditioning state. Continuous COX‑independent NSAID exposure (e.g., celecoxib‑mediated PDK‑1 inhibition) reduces basal insulin/IGF signaling, which downstream attenuates MAPK cascade sensitivity, thereby damping the amplitude of nociceptive‑evoked JNK pulses. Over time, this blunts the hormetic window, allowing damage to accumulate unchecked and tipping JNK signaling toward a chronic, SASP‑promoting mode.

Testable Predictions

1. In aged mice, continuous celecoxib treatment will lower basal p‑JNK levels in dorsal root ganglia and spinal cord compared with vehicle, but will also reduce stress‑induced p‑JNK spikes after a sub‑noxious mechanical stimulus.
2. Intermittent celecoxib dosing (e.g., 3 days on/4 days off) will maintain stress‑induced JNK peaks comparable to untreated controls while still suppressing basal COX‑2‑dependent prostaglandin E2 production.
3. Mice receiving intermittent dosing will exhibit lower senescent cell burden (p16^INK4a^ SA‑β-gal^+), reduced serum IL‑6/IL‑8, and improved grip strength and treadmill endurance versus continuously treated or untreated aged cohorts.
4. Genetic ablation of TRPV1 in nociceptors will abolish the protective effect of intermittent NSAID dosing, confirming that the hypothesis depends on nociceptive‑JNK coupling.

Experimental Approach

• Use 20‑month‑old C57BL/6 mice divided into four groups: vehicle, continuous celecoxib (30 mg/kg/day, oral), intermittent celecoxib (same dose, 3 days on/4 days off), and intermittent celecoxib + TRPV1 antagonist (capsazepine).
• Treat for 8 weeks. Measure baseline and acute (post‑hind‑paw pinch, 0.5 g filament) p‑JNK and p‑c‑Jun in DRG and spinal dorsal horn via Western blot and immunofluorescence.
• Quantify senescent cells in liver, kidney and lung using p16^INK4a^ flow cytometry and SA‑β‑gal staining.
• Assess circulating cytokines (IL‑6, IL‑8, TNF‑α) by Luminex.
• Perform functional assays: grip strength, rotarod, and treadmill exhaustion.
• Expected falsification: If intermittent dosing does not rescue stress‑induced JNK activation or improve senescence/function relative to continuous treatment, the hypothesis is refuted.

This framework directly tests whether preserving the nociceptive‑JNK/AP-1 hormetic signal through pulsatile NSAID inhibition can uncouple analgesia from accelerated aging, providing a mechanistic basis for re‑evaluating chronic pain management strategies.