Acarbose-induced microbial butyrate triggers gut‑brain AMPK signaling that gates sex‑specific hepatic autophagy flux

Hypothesis

Acarbose extends lifespan not merely by creating systemic glucose scarcity but by shaping the gut microbiome to produce butyrate that activates AMPK in intestinal enteroendocrine cells. This gut‑derived AMPK signal travels via the vagus nerve to the liver, where it modulates the ULK1 phosphorylation pattern in a sex‑dependent manner, thereby determining whether autophagy operates as a nutrient‑rationing program. In males, the signal favors ULK1 activation (promoting autophagy‑mediated recycling), whereas in females estrogen‑biased signaling skews AMPK toward ULK1 inhibition, blunting the autophagic response and limiting lifespan gain.

Mechanistic Model

1. Microbiome shift – Acarbose inhibits α‑glucosidase, increasing colonic carbohydrate load → enriched Roseburia and Faecalibacterium spp. → elevated butyrate.
2. Enteroendocrine AMPK activation – Butyrate binds GPR41/43 on L‑cells, raising intracellular AMP/ATP ratio → AMPK phosphorylation (Thr172).
3. Vagal afferent relay – Activated AMPK triggers release of serotonin and GLP‑1, stimulating vagal terminals that project to the nucleus tractus solitarius and then to the dorsal motor nucleus.
4. Hepatic AMPK‑ULK1 axis – Vagal signaling elevates hepatic AMPK activity. In males, AMPK phosphorylates ULK1 at Ser317/Ser555 (activating sites) and minimally at Ser757 (inhibitory site), promoting autophagosome formation. In females, estradiol enhances AMPK‑mediated phosphorylation of ULK1 at Ser757 via downstream mTORC1 feedback, offsetting activating sites and reducing flux.
5. Outcome – Male livers exhibit increased autophagic turnover of damaged mitochondria and lipid droplets, improving metabolic homeostasis; females show muted autophagy, accounting for the smaller lifespan extension.

Testable Predictions

• Germ‑free mice treated with acarbose will not show increased hepatic butyrate levels, vagal AMPK activation, or lifespan extension in either sex.
• Intestinal‑specific AMPKα1/α2 knockout (using Villin‑Cre) will abolish the sex‑dimorphic lifespan benefit of acarbose, with males losing the ~22% increase and females showing no further change.
• Vagotomy performed before acarbose treatment will prevent the hepatic shift in ULK1 phosphorylation (Ser317/Ser555 vs Ser757) and eliminate the male‑specific longevity gain.
• Pharmacological blockade of GPR41/43 (with antagonist AH7614) during acarbose feeding will reduce intestinal AMPK activation and blunt the autophagy response in male liver.
• Measurements of hepatic LC3‑II/I ratio, p62 degradation, and mitochondrial turnover (via mt‑Keima) will reveal a significant increase only in male mice receiving acarbose, correlating with circulating butyrate concentrations.

By positioning autophagy as a rationing system directed by gut‑brain hormonal signaling, this hypothesis moves beyond the view of acarbose as a simple mTOR inhibitor and provides a clear, falsifiable pathway for the observed sex differences in lifespan extension.