Lactiplantibacillus plantarum AS21 Attenuates Sex-Biased Glucose Intolerance in Aging Mice via Gut Mucosal Microbiota-Derived Citrulline.

Aging-related metabolic decline, particularly impaired glucose tolerance, represents a growing challenge in aging populations. Probiotics are promising modulators of host metabolism; however, how sex differences influence their efficacy in mitigating metabolic aging remains poorly understood. Here, we administered Lactiplantibacillus plantarum AS21 to naturally aged male and female mice for 6 months. We observed a pronounced sexual dimorphism in metabolic decline, with aged males exhibiting more severe glucose intolerance than females. Concurrently, circulating citrulline levels were depleted in males but elevated in females. AS21 intervention significantly ameliorated glucose intolerance in aged males, while exerting minimal effects on metabolically stable females. Microbiota analysis revealed that AS21 reshaped the mucosa-associated microbial communities in males, an effect accompanied by increased abundance of microbial citrulline biosynthesis genes (argF, argI) and restoration of circulating citrulline. In contrast, females maintained stable metabolic and citrulline profiles alongside limited microbial alterations. Furthermore, direct citrulline supplementation recapitulated these metabolic benefits, improving glucose tolerance, enhancing glucose-stimulated insulin secretion (GSIS), and stimulating glucagon-like peptide-1 (GLP-1) release. Collectively, these findings demonstrate that AS21 alleviates age-related glucose dysregulation in male mice-a benefit closely associated with the restoration of microbiota-driven citrulline metabolism. This highlights its potential as a sex-specific, microbiota-targeted strategy for managing metabolic aging.