NR1H4 and polycystic ovary syndrome: Bacteroides vulgatus also acts independently of bile acids via its metabolite guanidine, activating the farnesoid X receptor (FXR) pathway, which subsequently inhibits L-cell secretion of glucagon-like peptide-1 (GLP-1), leading to insulin resistance and ovarian dysfunction and thereby causing PCOS-like symptoms (Yun et al., 2024).