Acarbose extends lifespan in male mice by fostering a bloom of Muribaculaceae that increases colonic propionate production. Propionate activates hepatic GPR41 (FFAR3), triggering a fibroblast growth factor 21 (FGF21) endocrine response that improves mitochondrial function and suppresses inflammasome activation. Androgen signaling upregulates hepatic GPR41 expression, explaining the stronger effect in males. Therefore, the microbial metabolite propionate is a necessary mediator of acarbose longevity, acting through a GPR41‑FGF21 axis that is potentiated by male sex hormones.

Mechanistic model

1. Carbohydrate maldigestion – Acarbose inhibits intestinal α‑glucosidase, delivering more starch to the distal gut.
2. Microbiota shift – Undigested starch selectively fuels Muribaculaceae, raising luminal propionate ~1.8‑fold.
3. Propionate signaling – Propionate reaches the liver via portal circulation and binds GPR41 on hepatocytes.
4. FGF21 induction – GPR41 activation stimulates a PPARα‑dependent transcriptional program that increases hepatic FGF21 secretion.
5. Systemic effects – FGF21 enhances fatty acid oxidation, improves NAD⁺/NADH redox balance, and inhibits NLRP3 inflammasome activity, thereby reducing oxidative stress and inflammation.
6. Sex dimorphism – Testosterone augments hepatic GPR41 transcription (via androgen response elements), yielding higher FGF21 output in males.
7. Longevity outcome – Improved metabolic homeostasis and reduced inflammasome‑driven damage translate into extended median lifespan.

Testable predictions

• Prediction 1: Germ‑free mice colonized with a defined Muribaculaceae consortium (propionate‑high) will recapitulate the lifespan extension seen with acarbose, even without the drug.
• Prediction 2: Pharmacological or genetic inhibition of hepatic GPR41 (using a liver‑specific Gpr41 knockout or antagonist) will abolish acarbose‑mediated FGF21 elevation and lifespan extension in males.
• Prediction 3: Exogenous propionate supplementation (via drinking water or timed gavage) will mimic acarbose benefits in male mice but show a weaker effect in females unless androgen levels are supplemented.
• Prediction 4: Castration of male mice will reduce hepatic Gpr41 expression and diminish the longevity response to acarbose or propionate, while testosterone replacement restores it.
• Prediction 5: In Muribaculaceae-colonized germ‑free mice, FGF21 deficiency (global or hepatocyte‑specific) will block the lifespan extension, confirming FGF21 as the downstream effector.

Experimental design

Model: Male and female C57BL/6J mice, germ‑free and conventional, with optional liver‑specific Gpr41^−/− and FGF21^−/− alleles.

Groups (n ≥ 30 per sex for survival analysis):

• Control (standard diet)
• Acarbose (200 ppm in diet)
• Muribaculaceae mono‑association (defined consortium)
• Propionate supplementation (200 mM sodium propionate in drinking water)
• Each of the above ± liver‑specific Gpr41 knockout
• Each of the above ± hepatocyte‑specific FGF21 knockout
• Castrated males ± testosterone implant

Interventions start at 8 weeks of age and continue for life.

Readouts:

• Survival curves (median and 90th percentile lifespan)
• Hepatic Gpr41 and FGF21 mRNA/protein (qPCR, ELISA, Western blot)
• Portal and systemic propionate concentrations (LC‑MS)
• Serum FGF21 levels
• Markers of oxidative stress (4‑HNE, protein carbonyls) and inflammasome activation (caspase‑1 cleavage, IL‑1β)
• Metabolic profiling (indirect calorimetry, glucose tolerance, lipidomics)

Statistical analysis: Log‑rank test for survival; two‑way ANOVA with sex and genotype as factors for molecular endpoints; correction for multiple comparisons.

Potential outcomes and interpretation

• If propionate‑high Muribaculaceae or propionate alone extends lifespan in males and this effect is lost in Gpr41^−/− or FGF21^−/− mice, the hypothesis is supported, indicating a causal microbial metabolite–host signaling axis.
• If lifespan extension persists despite Gpr41 or FGF21 loss, the hypothesis is falsified, suggesting alternative mechanisms (e.g., direct intestinal barrier effects, bile‑acid signaling).
• If females show comparable longevity only when propionate is combined with androgen supplementation, the sex‑dimorphism mechanism is validated.

By linking a specific microbial metabolite to a defined hormonal‑signaling pathway, this hypothesis provides a clear, falsifiable route to disentangle correlation from causation in acarbose‑mediated longevity and opens avenues for microbiome‑based therapeutics that bypass the need for α‑glucosidase inhibition.