Hypothesis

Acarbose treatment lowers heat pain thresholds in aged mice, reflecting a reversal of epigenetic age acceleration via microbiome-derived SCFA signaling to the vagus nerve.

Mechanistic Rationale

• Acarbose enriches SCFA-producing taxa (Bacteroidaceae, Bifidobacteriaceae) -> increased colonic butyrate and acetate.
• Butyrate activates FFAR2/3 on afferent vagal fibers, increasing vagal tone and reducing neuroinflammation in the spinal dorsal horn.
• Reduced neuroinflammation normalizes nociceptor sensitization, decreasing the heat pain threshold (i.e., increasing pain sensitivity) toward youthful levels.
• This functional shift parallels reductions in DNAm age and brain-PAD, positioning pain threshold as a peripheral biomarker of biological age.

Predictions

1. Old mice (>=20 mo) fed 400 ppm acarbose for 8 weeks will show a significant left-shift in the Hargreaves test (lower latency) relative to age-matched controls.
2. The magnitude of threshold change will correlate negatively with epigenetic age acceleration (ΔDNAm) and positively with fecal butyrate concentration.
3. Vagal tone, indexed by heart-rate variability (RMSSD), will increase in parallel with pain-threshold shifts.
4. Pharmacological blockade of FFAR2/3 (e.g., with GLPG0974) during acarbose treatment will abolish both the pain-threshold normalization and the epigenetic age benefit.

Experimental Design

• Groups: young (3 mo) control, old control, old + acarbose, old + acarbose + FFAR2/3 antagonist, old + antagonist alone.
• Measurements (baseline and weekly):
  • Pain threshold: Hargreaves test (radiant heat latency) and hot-plate latency.
  • Microbiome: 16S rRNA sequencing; quantify Bacteroidaceae, Bifidobacteriaceae.
  • SCFAs: GC-MS of cecal contents for butyrate, acetate.
  • Vagal tone: ECG-derived HRV (RMSSD).
  • Epigenetic age: Illumina EPIC array on liver DNA; compute DNAm age and ΔDNAm.
  • Neuroinflammation: Iba1 and GFAP immunostaining in spinal cord.
• Statistical plan: ANOVA with post-hoc Tukey; Pearson correlation for threshold vs ΔDNAm and butyrate.

Potential Outcomes

• If acarbose lowers pain thresholds and this shift tracks with reduced ΔDNAm, the hypothesis is supported, indicating that somatosensory phenotyping can serve as a low-cost, functional aging clock.
• If thresholds remain unchanged despite microbiome and epigenetic effects, the link between SCFA-vagal signaling and pain perception is not sufficient to drive behavioral readouts, challenging the notion that pain sensitivity directly mirrors biological age.
• Antagonist rescue experiments that block the effect will confirm the mechanistic pathway involving FFAR2/3-mediated vagal signaling.