Chronic psychological stress impairs sperm quality via a gut-endotoxin-testis axis.

BACKGROUND: Chronic psychological stress is increasingly recognized as a risk factor for male infertility, but the underlying mechanisms remain incompletely understood. This study aimed to investigate whether chronic stress (CS) induced-alterations of the gut microbiota and its metabolites contribute to sperm quality impairment via a gut-testis axis. METHODS: Male C57BL/6 mice were subjected to chronic unpredictable mild stress for 10 weeks. Gut barrier integrity, systemic inflammation, and testicular phenotypes were assessed. Gut microbiota and its metabolites were profiled by 16S rRNA gene sequencing, shotgun metagenomics, and metabolomics. The contribution of the microbiota was interrogated by fecal microbiota transplantation (FMT) and probed further by oral sodium butyrate (NaB) supplementation. Intestinal barrier function was assessed by in vivo FITC‑dextran translocation and ex vivo Ussing chamber assays, blood-testis barrier (BTB) integrity by Evans blue extravasation, and the requirement for TLR4 signaling was examined pharmacologically. RESULTS: CS induced marked gut dysbiosis, characterized by depletion of butyrate-producing taxa such as Lachnospiraceae and by reduced cecal and circulating butyrate. These changes were accompanied by impaired intestinal barrier function, endotoxemia (elevated LPS and LBP), increased BTB permeability and activation of testicular TLR4/NF-κB signaling. Fecal microbiota from CS donors was sufficient to reproduce intestinal barrier disruption, testicular inflammation and impaired sperm quality in healthy recipients, and pharmacological TLR4 blockade attenuated testicular injury in these recipients. Conversely, oral NaB restored intestinal barrier function, suppressed testicular TLR4/NF-κB signaling and pro-inflammatory cytokine levels, and rescued sperm quality in CS mice. CONCLUSIONS: These findings delineate a gut-endotoxin-testis axis in mice, in which CS-associated depletion of butyrate‑producing taxa and consequent endotoxin exposure contribute to impaired sperm quality, and identify microbiota- or butyrate-targeted interventions as candidate strategies for psychological stress-related male infertility.