Study on the efficacy and mechanism of fecal microbiota transplantation for depression based on circadian rhythm

BACKGROUND: Depression is closely associated with disruptions in circadian rhythms, and emerging evidence highlights critical roles of gut dysbiosis in its pathogenesis. However, the mechanisms by which FMT chronotherapy influences circadian gene in depression-via gut microbiota-remain poorly understood. METHODS: In this study, we established a chronic unpredictable mild stress (CUMS) mouse model and performed fecal microbiota transplantation (FMT) using donor microbiota from healthy mice at two distinct circadian time points-zeitgeber time (ZT) 4 or ZT16 to identify the optimal timing for FMT based on behavioral assessments. Integrating omics dependent mechanisms of antidepressant effects mediated by these key functional bacteria. RESULTS: Health-FMT significantly alleviated depressive-like behaviors, with superior efficacy at ZT4. It restored circadian gene expressions and attenuated neuroinflammation expression in the hippocampus and prefrontal cortex. 16S rRNA sequencing revealed that Health-FMT reduced uncultured_bacterium_g_Alistipes abundance, a genus linked to tryptophan availability. Tryptophan supplementation regulated circadian gene expressions, inflammatory factors, brain-derived neurotrophic factors (BDNF), microglial and astrocytic activation, and exerted antidepressant effects via the ERK signaling pathway. CONCLUSIONS: These findings suggest that Health-FMT exerts antidepressant effects by restoring gut homeostasis, particularly by reducing Alistipes, thereby rebalancing tryptophan metabolic and circadian gene expressions. These findings offer a new possible mechanism and novel insights into the microbiota-gut-brain axis in depression, and underscore the importance of chronotherapy in FMT-based therapeutic strategies.