β-cell FMO3-produced TMAO prevents NF-κB-mediated senescence and inflammation in ageing and diabetic conditions.

Human cells utilize gut microbiota-derived metabolites to control systemic metabolism. Trimethylamine N-oxide (TMAO) is traditionally considered a hepatocyte-derived metabolite from microbial trimethylamine. Here we show that pancreatic β-cells also produce TMAO as an autocrine and intracellular metabolite to maintain β-cell function. β-cells synthesize TMAO via flavin-containing monooxygenase 3 (FMO3), but this machinery deteriorates in humans and rodents under diabetic and ageing conditions. β-cell-specific deletion of FMO3 depletes intracellular TMAO, leading to senescence, inflammation, and defective glucose-stimulated insulin secretion, causing age-dependent glucose intolerance in mice. Loss of FMO3 triggers nuclear factor kappa-B (NF-κB) activation, promoting senescent and inflammatory responses. Mechanistically, TMAO binds to inhibitor of kappa B alpha (IκBα), which inhibits IκBα degradation and NF-κB nuclear translocation, thereby blocking NF-κB-mediated transcription of senescent and inflammatory programs. Replenishment of FMO3 reduces NF-κB activation and senescence in aged human islets. Our findings reveal a protective role of β-cell-derived TMAO against ageing-related β-cell dysfunction.