Hypothesis

Chronic suppression of prostaglandin synthesis by uninterrupted NSAID use disrupts a feedback loop in which PGE₂ enhances CD44‑mediated dampening of LMW‑HA‑induced NLRP3 activation, leading to unchecked inflammasome signaling, accelerated matrix degradation, and shortened healthspan. Intermittent NSAID dosing allows prostaglandin peaks that restore CD44’s inhibitory tone, permitting LMW‑HA to act as a reparative DAMP rather than a inflammasome toxin.

Mechanistic Rationale

• LMW‑HA engages TLR2/4 and CD44; CD44 normally limits NF‑κB translocation and reduces IL‑1β/TNF‑α output {PMC5760314}.
• PGE₂ signaling through EP2/EP4 receptors raises intracellular cAMP, which promotes CD44 surface retention and its association with phosphatases that de‑phosphorylate IKK, thereby tightening the brake on NF‑κB {jbc.m110.201665}.
• Chronic COX inhibition lowers PGE₂, causing CD44 to shift toward a soluble isoform that loses its inhibitory scaffolding and instead amplifies TLR‑MyD88 signaling, feeding NLRP3 inflammasome assembly {PMC4533115}.
• Unchecked NLRP3 activity drives caspase‑1‑mediated IL‑1β release, catabolic enzyme expression (MMP‑13, ADAMTS‑5) and senescence‑associated secretory phenotype in fibroblasts and chondrocytes, eroding tissue integrity.
• Sensory neuron‑derived CGRP and substance P, released during low‑grade nociceptive tone, up‑regulate HAS2 via cAMP‑PKA‑CREB pathways, favoring HMW‑HA synthesis that buffers fragment load {pubmed 16818787}.

Testable Predictions

1. In aged mouse dermis, continuous NSAID treatment will decrease HMW‑HA/LMW‑HA ratio, increase soluble CD44, and elevate NLRP3 speck formation compared with vehicle.
2. Intermittent NSAID (e.g., 2 days on/5 days off) will restore HMW‑HA predominance, membrane‑bound CD44, and reduce inflammasome activity to levels indistinguishable from untreated controls.
3. Genetic deletion of HAS2 in sensory neurons will abolish the protective effect of intermittent dosing, confirming that neuronal‑derived HA synthesis contributes to the feedback.
4. Administering a EP2 agonist alongside continuous NSAID will mimic intermittent dosing outcomes, rescuing CD44 membrane localization and lowering IL‑1β.

Experimental Design

• Use 20‑month‑old C57BL/6 mice; split into four groups (n=10): vehicle, chronic NSAID (ibuprofen 30 mg/kg/day in chow), intermittent NSAID (same dose 2 days on/5 days off), chronic NSAID + EP2 agonist (PF-04415787).
• After 8 weeks, harvest dermis and knee synovium for HA size distribution by HPLC‑SEC, CD44 isoform profiling by Western blot of membrane vs cytosolic fractions, and inflammasome activation via ASC speck immunofluorescence and caspase‑1 activity assay.
• Measure healthspan indices: grip strength, treadmill endurance, and frailty index.
• Perform correlational analysis between HMW‑HA/LMW‑HA ratio, CD44 membrane fraction, and inflammasome readouts.

If intermittent dosing (or EP2 agonism) normalizes HA scaffolding, preserves CD44 inhibitory function, and suppresses inflammasome signaling while extending healthspan, the hypothesis is supported; failure to observe these changes would falsify the proposed prostaglandin‑CD44‑LMW‑HA axis as a longevity‑modulating pathway.