Quercetin ameliorates PCOS ovarian fibrosis by modulating short-chain fatty acid synthesis via increased akkermansia muciniphila abundance

BACKGROUND: Polycystic Ovary Syndrome (PCOS) is a common endocrine disorder causing anovulatory infertility, characterized by critical ovarian fibrosis that impairs follicular development. Current pharmacological treatments for ovarian fibrosis in PCOS are limited. Quercetin, a natural flavonoid found in plants and traditional medicine, shows therapeutic promise for PCOS, though its direct effects on ovarian fibrosis and gut microbiota-mediated mechanisms remain unclear. METHODS: The PCOS mouse model was established by administering letrozole in combination with a high-fat diet. To determine the optimal therapeutic dosage, PCOS mice were randomly assigned to three quercetin treatment groups: low-dose group (PCOS + LT), medium-dose group (PCOS + T), and high-dose group (PCOS + HT). Body weight and serum hormone levels (LH, FSH, T and AMH) were systematically measured across all groups to determine the most effective concentration. Reproductive function was assessed by monitoring the estrous cycle (vaginal smears). Insulin resistance was evaluated using glucose tolerance test (GTT) and insulin tolerance test (ITT). After the medium dose was identified as the optimal intervention dose of quercetin, subsequent experiments were conducted to investigate the underlying mechanisms. Ovarian tissue was analyzed for morphology, inflammation and fibrosis. Additionally, the intestinal mucosal structure and permeability were examined. Feces were collected for comprehensive gut microbiota composition analysis (16S rRNA gene sequencing) and fecal short-chain fatty acids (SCFAs) analysis, followed by a correlation analysis to link gut changes with physiological and ovarian outcomes. Furthermore, a fibrotic cell model was established in KGN cells via dihydrotestosterone (DHT)-induction to investigate the regulatory effects of acetic acid at different concentrations on the TGF-β signaling pathway. RESULTS: Our research indicated that medium-dose quercetin restored PCOS mice estrous cyclicity, improved insulin sensitivity, and ameliorated the level of ovarian fibrosis. 16S rRNA sequencing results showed that quercetin significantly increased the proportion of Akkermansia in the mouse gut microbiota. Furthermore, quercetin promoted the content of several short-chain fatty acids, particularly acetate. HE staining of the mouse intestinal mucosa revealed that quercetin was able to alleviate the structural disorder of the intestinal mucosa. Furthermore, quercetin promoted the expression of the intestinal barrier proteins ZO-1 and Occludin in PCOS mice and significantly improved intestinal mucosal permeability. In vitro studies revealed that acetic acid modulates TGF-β1 expression through the suppression of SMAD3 phosphorylation and the promotion of SMAD7 expression. CONCLUSION: Our findings suggest quercetin alleviates PCOS-related ovarian fibrosis by modulating gut microbiota and promoting SCFA production. This research highlights a novel mechanism for treating PCOS-related ovarian fibrosis, warranting further investigation.