Project Summary/Abstract Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in reproductive-aged women worldwide. In addition to infertility, many women with PCOS have metabolic abnormalities that result in an increased risk of type 2 diabetes and cardiovascular disease. Studies have shown that the large intestine contains a complex community of microorganisms (the gut microbiome), that the gut microbiome is altered in humans with metabolic disorders such as obesity and type 2 diabetes, and that changes in the gut microbiome may contribute to metabolic dysregulation. Two recent clinical studies reported that changes in the gut microbiome were associated with PCOS. In addition, we and others demonstrated that the gut microbiome composition was significantly altered in rodent models of PCOS. Our preliminary data with fecal microbiome transplantation in germ-free mice as well as co-housing a PCOS mouse model with healthy mice suggests that the gut microbiome plays a causal role in PCOS and that manipulation of the gut microbiome may improve PCOS symptoms. In addition, studies demonstrated that serum LBP is increased in women with PCOS and PCOS mouse models, suggesting that gut permeability may be altered in PCOS. Collectively, these studies suggest that a microbial imbalance, or “dysbiosis”, in the gut may contribute to the development and pathology of PCOS. Studying the role of the gut microbiome in a PCOS mouse model has several advantages for mechanistic studies including the ability to control for diet and genetics, to use gnotobiotic (germ-free) mice that lack a microbiome to test causality and to knockout genes of interest. We propose to use the letrozole- induced PCOS mouse model to test the hypothesis that androgen action via the androgen receptor results in dysregulation of the gut microbiome and gut epithelial function, which in turns contributes to the development and pathology of PCOS. In Aim 1, we propose to use the androgen receptor antagonist, flutamide to determine if the androgen receptor is necessary for changes in the gut microbiome, gut permeability and the metabolic phenotype. In Aim 2, we will use germ-free mice to determine whether the gut microbiome is necessary and sufficient for development of a metabolic phenotype. Finally, in Aim 3, we will use fecal microbiome transplantation to ascertain whether modulation of the gut microbiome can improve PCOS reproductive or metabolic phenotypes. In addition, we will use metagenomics coupled with transcriptomics to identify which bacterial strains and functions are altered in the letrozole-induced PCOS mouse model in order to identify potential pre- or probiotic therapeutic targets. Results from this proposal have the potential to answer fundamental questions concerning the role of the gut microbiome in the development and pathology of PCOS and expedite development of novel treatment options for women with PCOS (e.g., pre- or probiotic therapies).