Methyl indole-3-acetate mediates myricetin-induced brown adipose tissue activation and reproductive-metabolic improvement in PCOS mice

Abstract In brief: Polycystic ovary syndrome (PCOS) is a common endocrine disorder with limited treatments. This study shows that the flavonoid myricetin increases the gut metabolite methyl indole-3-acetate, which activates brown fat to improve PCOS symptoms in mice. Abstract: Polycystic ovary syndrome (PCOS) is frequently associated with alterations in gut microbiota composition, although the specific microbial metabolites that influence ovarian function remain incompletely understood. Myricetin has been reported to improve reproductive and metabolic features in experimental PCOS models and to activate brown adipose tissue (BAT); however, whether these effects are mediated by the gut microbiota has not been clarified. In dehydroepiandrosterone-induced PCOS mice, myricetin treatment was associated with improved estrous cyclicity, ovarian morphology, fertility, and insulin sensitivity. These changes coincided with notable shifts in gut microbial composition and the serum metabolome. Integrated multiomics analysis suggested that methyl indole-3-acetate (MIA), a microbiota-derived tryptophan metabolite, was among the metabolites most consistently elevated following myricetin administration. Fecal microbiota transplantation from myricetin-treated donors partially improved ovarian function and glucose homeostasis in recipient mice. Supplementation with MIA enhanced BAT thermogenesis and the expression of thermogenic genes, whereas surgical removal of interscapular BAT attenuated the metabolic improvements observed with MIA. Together, these results suggest that myricetin may improve PCOS-like reproductive and metabolic disturbances through microbiota remodeling and elevated production of MIA, which supports BAT activity. This study identifies MIA as a previously unrecognized microbiota-derived metabolite that links gut microbial metabolism to BAT function and reproductive outcomes, providing new mechanistic insight into how dietary compounds may influence ovarian function in PCOS.