Hypothesis

Acarbose extends lifespan in male mice primarily by increasing colonic butyrate production, which activates hepatic AMPK through a GPR109A‑dependent cascade, thereby enhancing fatty acid oxidation and reducing oxidative stress. This pathway is blunted in females due to estrogen‑mediated suppression of hepatic GPR109A expression, explaining the observed sex‑dimorphic longevity effect.

Rationale

• Acarbose elevates fecal butyrate, acetate and propionate, correlating with lifespan extension [5].
• Butyrate is a known agonist of the G‑protein coupled receptor GPR109A, which can stimulate AMPK activation in hepatocytes [2].
• Hepatic AMPK activation improves metabolic homeostasis, mimics caloric restriction, and synergizes with rapamycin [3].
• Sex differences in hepatic GPR109A expression have been reported, with higher baseline levels in males and estrogen‑dependent downregulation in females [4].
• The microbiome shift induced by acarbose is diet‑dependent and reversible, suggesting that the metabolite flux, not merely the taxonomic change, drives the phenotype [4].

Predictions

1. Male mice treated with acarbose will show increased hepatic p‑AMPK (Thr172) levels compared with vehicle controls; this increase will be absent in females.
2. Pharmacological inhibition of GPR109A (e.g., with ​) will abolish the acarbose‑induced rise in hepatic AMPK activity and the longevity benefit in males, but will have minimal effect in females.
3. Supplementation with sodium butyrate in germ‑free male mice receiving acarbose will recapitulate the hepatic AMPK activation and lifespan extension seen in conventionally raised mice.
4. Ovariectomized females will exhibit male‑like hepatic AMPK activation and lifespan extension when given acarbose, whereas estrogen replacement will rescue the female‑specific blunting.

Experimental Design

• Cohorts: C57BL/6J males, females, ovariectomized females (± estrogen), and germ‑free males (n=30 per group).
• Treatments: (i) control diet, (ii) acarbose (1000 ppm), (iii) acarbose + GPR109A antagonist, (iv) acarbose + sodium butyrate (150 mM in drinking water).
• Readouts: fecal SCFA quantification (GC‑MS), hepatic p‑AMPK and downstream targets (ACC, PGC‑1α) by Western blot, serum metabolomics, histology for lipid accumulation, and survival monitoring.
• Statistical analysis: Kaplan‑Meier survival curves with log‑rank test; two‑way ANOVA for biochemical endpoints with sex and treatment as factors.

Potential Outcomes

• If predictions hold, the data will support a microbiota‑butyrate‑hepatic AMPK axis as the primary driver of acarbose‑mediated longevity in males, with sex hormones modulating receptor availability.
• Failure to observe sex‑specific differences in hepatic AMPK activation despite equivalent butyrate elevations would falsify the hypothesis, directing focus toward alternative mechanisms (e.g., peripheral insulin signaling or immune modulation).

This framework provides a clear, falsifiable path to disentangle the relative contributions of glucose blunting versus microbiome‑derived signaling in acarbose’s lifespan‑extending action.