Gut Microbiota-Derived Indole-3-Acetic Acid Induces PCOS by Disrupting Granulosa Cell Function under Metabolic Stress

Background Polycystic ovary syndrome (PCOS) is a multifactorial reproductive and metabolic disorder, but the mechanisms linking metabolic stress to ovarian dysfunction remain incompletely understood. Gut microbiota-derived metabolites have emerged as important mediators of host metabolism; however, their contribution to PCOS pathogenesis, particularly within the ovarian microenvironment, remains poorly defined. This study aimed to identify microbiota-associated metabolic alterations in PCOS and determine their functional relevance under metabolically stressed conditions. Results Integrated clinical microbiota and metabolomic profiling revealed altered gut microbial composition and indole-related metabolic signatures in women with PCOS and overweight/obesity. Among the altered features, Bacteroides fragilis and indole-3-acetic acid (IAA) were selectively enriched and positively correlated. IAA was increased not only in fecal metabolic profiles but also in serum and follicular fluid, suggesting a link between gut-associated metabolic changes and the ovarian follicular microenvironment. Functional experiments showed that neither B. fragilis nor IAA alone was sufficient to induce PCOS-like phenotypes under basal conditions. In contrast, both B. fragilis and IAA promoted ovarian dysfunction, endocrine disturbance, and estrous cycle abnormalities under high-fat diet (HFD)-induced metabolic stress. At the cellular level, IAA suppressed granulosa cell proliferation by inhibiting G1/S cell-cycle progression and activating aryl hydrocarbon receptor (AHR) signaling. Pharmacological inhibition or knockdown of AHR partially reversed IAA-induced cell-cycle arrest. Moreover, lipotoxic stress enhanced IAA-induced AHR activation and cell-cycle inhibition, potentially through increased oxidative and endoplasmic reticulum stress. Conclusions These findings identify a context-dependent B. fragilis –IAA–AHR axis that links gut microbial metabolism to ovarian dysfunction under metabolic stress. The study provides mechanistic insight into the gut–ovary interaction in PCOS and suggests that microbiota-derived indole metabolites may contribute to disease progression in a metabolically permissive host environment.