EZH2-mediated H3K27me3 links microbial inosine loss to depression: a gut-brain epigenetic switch

<b>Background:</b> Depression, the second most prevalent neurological disorder globally, affects over 300 million people and presents an urgent public health challenge. While gut microbiota dysbiosis is increasingly recognized as a key contributor to depression, the molecular mechanisms linking microbial imbalance to brain dysfunction remain poorly defined. <b>Methods:</b> We investigated the role of EZH2 in gut microbiota-induced depressive behaviors in mice using the chronic unpredictable mild stress (CUMS), fecal microbiota transplantation, and conditional knockout of EZH2. CUT&Tag sequencing was employed to analyze EZH2-mediated H3K27me3 epigenetic reprogramming. Untargeted metabolomics and luciferase reporter assays were used to identify metabolites that upregulate EZH2 expression. 16S rRNA sequencing combined with metabolic tracing was conducted to trace the microbial origin of inosine. Additionally, natural compound screening identified coumaric acid (CA) as a novel EZH2-targeting degrader. <b>Results:</b> Conditional knockout of neuronal <i>Ezh2</i> abolishes microbiota-induced depressive behaviors and neuronal apoptosis. Mechanistically, reduced abundance of specific microbiota (<i>f_Lachnospiraceae, f_Oscillospiraceae, and f_Erysipelotricaceae</i>) leads to inosine depletion. This depletion subsequently elevates EZH2 transcriptional activity by increasing H3K9ac modification at its locus, mediated through attenuation of the A2aR-cAMP-PKA-CREB-HDAC3 signaling axis. Subsequently, EZH2 silences serotonergic synapse-related genes (e.g., <i>Tph2, Htr2a, Htr6</i>) <i>via</i> H3K27me3 reprogramming, ultimately driving depressive behaviors and neuronal apoptosis in mice. Importantly, CA is identified as a first-in-class EZH2 degrader that binds lysine residues K623/K646 and recruits UBE3A for proteasomal degradation. CA treatment restores synaptic integrity and reverses depressive behaviors with minimal toxicity. <b>Conclusions:</b> Collectively, these findings define a novel "microbiota-inosine-EZH2" axis in depression pathogenesis and highlight EZH2 degradation as a promising therapeutic strategy for microbiota-associated neuropsychiatric disorders.