Intermittent TRPV1 activation as a hormetic regulator of lifespan

Hypothesis

Repeated, low‑intensity activation of the TRPV1 channel triggers a hormetic cascade that engages AMPK, improves mitochondrial turnover, and extends healthspan; chronic pharmacological blockade of TRPV1‑mediated nociception removes this signal and accelerates age‑related decline.

Mechanistic Rationale

• Sensory neurons can modulate systemic stress responses and longevity in C. elegans [1]; TRPV1 opening admits Ca2+, activating CaMKK‑AMPK signaling, which phosphorylates ULK1 and initiates mitophagy.
• Intermittent Ca2+ spikes also stimulate NAD+ biosynthesis, raising cellular NAD+ levels and boosting SIRT1 activity.
• Both AMPK activation and SIRT1‑dependent deacetylation promote FOXO3 transcriptional programs that up‑regulate antioxidant enzymes and DNA repair factors.
• In C. elegans, optogenetic stimulation of TRPV1 homologs (OCR‑2) extends lifespan only when delivered in short, spaced pulses; continuous activation leads to calcium overload and toxicity.
• Mammalian data show that brief capsaicin exposures increase phosphorylation of AMPK and PGC‑1α in skeletal muscle [4], whereas sustained capsaicin treatment induces desensitization and downstream inflammation.
• Analgesics that inhibit TRPV1 (e.g., capsazepine, SB‑366791) or reduce substance P/CGRP release therefore dampen the intermittent stress signal, potentially shifting the balance toward senescence‑associated secretory phenotype (SASP) accumulation; CGRP and substance P display context‑dependent effects, promoting apoptosis in diseased tissue but supporting survival in healthy cells [2], and mice lacking both peptides retain normal nociception [3], indicating redundancy.

Testable Predictions

1. Mice receiving weekly low‑dose capsaicin (0.1 mg/kg, i.p.) will display improved grip strength, reduced frailty index, and delayed onset of age‑related cardiac fibrosis compared with vehicle‑treated controls.
2. Genetic ablation of TRPV1 in adult mice (using inducible Cre‑lox) will shorten median lifespan by ~15 % only when animals are housed under standard conditions; the effect will be rescued by intermittent exercise‑induced mild hyperthermia.
3. Human participants who regularly consume spicy foods (≥3 times/week) will exhibit higher circulating phospho‑AMPK levels in peripheral blood mononuclear cells and lower epigenetic age acceleration (DNAm GrimAge) than matched low‑spice consumers, after adjusting for BMI and activity.
4. Chronic NSAID or opioid users who also report frequent TRPV1‑activating stimuli (capsaicin‑rich diet, hot‑bath sauna) will not show the accelerated epigenetic aging observed in analgesic‑only cohorts.

Experimental Design

• Mouse longevity cohort: n=200 per arm (capsaicin pulse, vehicle, TRPV1‑KO, TRPV1‑KO + capsaicin pulse). Monitor survival, frailty, cardiac echo, and tissue AMPK phosphorylation at 6, 12, 18 months.
• Human observational study: Recruit 500 adults aged 45‑70, collect dietary spice frequency, analgesic use, blood for phospho‑AMPK ELISA, and saliva for epigenetic clock. Use multivariate regression to test interaction between spice intake and analgesic use on age acceleration.
• In vitro validation: Treat primary human fibroblasts with 10 µM capsaicin for 5 min every 48 h; measure AMPK‑p, SIRT1 activity, SA‑β‑gal, and secretion of IL‑6 over 30 days. Compare with continuous 10 µM capsaicin exposure. All interventions are reversible, allowing crossover sub‑studies to confirm causality.