Role of Bile Salt Hydrolase (BSH) Overexpression in Polycystic Ovary Syndrome (PCOS) - LET COHORT 3

OBJECTIVE: This study investigates the mechanistic role of gut microbial bile acid modifications on the metabolic and reproductive features of Polycystic Ovary Syndrome (PCOS). MATERIALS AND METHODS: We compared two PCOS-like mouse models using (1) 5 week daily oral gavage of letrozole (LET), and (2) 90 day subcutaneous release of dihydrotestosterone (DHT). We introduced a stably colonized engineered native bacteria (ENB) that overexpresses bile salt hydrolase (BSH) using a single oral gavage, thus facilitating bile acid deconjugation in the gut and changing the luminal bile acid pool, verified by targeted metabolomics. We analyzed the estrous cycle through vaginal cytology, and collected serum and reproductive tissues to measure hormone levels and evaluate ovarian histology. We assessed metabolic phenotype through an insulin tolerance test, EchoMRI body compositional analysis, and fasted and fed levels of insulin, glucose, and incretins. Stool was collected for 16S and untargeted metabolomics, and liver for RNA-seq. RESULTS: Both DHT and LET mouse models mimic the metabolic and reproductive features of PCOS, including insulin resistance, hyperglycemia, anovulation, cystic follicles, and hyperandrogenism. Increased adiposity was observed in the DHT model but not in the LET model, presenting both lean and obese models of PCOS. Introduction of BSH-expressing ENB restored insulin sensitivity and blood glucose levels in the LET mice without significant change in adiposity. BSH-treated LET mice also had decreased ovary weights and a decrease in serum luteinizing hormone (LH) levels with no change in follicle-stimulating hormone (FSH) levels. Stool metabolomics and 16S analyses are ongoing to characterize differences between conditions in each model at the level of the gut. CONCLUSIONS: Taken together, these results suggest that microbiome modulation of bile acids plays a key role in the pathogenesis of PCOS. Comparison of lean and obese models of PCOS provide clues about the role of adiposity in altered insulin signaling and other manifestations of the syndrome. Additionally, differential modulation of LH and FSH implicate non-hypothalamic modulation by bile acid signaling, perhaps at the site of the ovaries or liver. IMPACT STATEMENT: Despite affecting 10-15% of reproductive age women, PCOS is not well understood and often ineffectively treated. Common interventions like weight loss can be unattainable, or an infeasible solution, particularly for those with insulin resistance independent of obesity. This study illustrates the potential of the gut microbiome as a diagnostic tool and/or therapeutic target for PCOS, and reveals novel crosstalk between the microbiome, gut, and HPG axis.