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As the most known therapeutic component of bear bile acids, ursodeoxycholic acid (UDCA) is an FDA-approved drug for the treatment of primary biliary cirrhosis (PBC), the dissolution of cholesterol gallstones. UDCA produces many beneficial effects on metabolism and immune responses via its interaction with the membrane G protein-coupled bile acid receptor (GPBAR); however, how UDCA interacts with GPBAR and its selective cellular effects remain elusive. In this study, we delineated the interaction of UDCA with GPBAR and activation mechanism of GPBAR by scattered alanine scanning and molecular docking. Our results indicated that transmembrane helix 2 (TM2), TM3, TM5 and TM6 of GPBAR contribute to the interaction of UDCA in GPBAR binding pocket. Moreover, we predicted that the engagement of the 3-OH of UDCA with phenolic oxygen of Y2406.51 in GPBAR plays a key role in GPBAR activation. Unexpectedly, in addition to the well-known roles of intracellular loop2 (ICL2) residues, we identified that ICL3 residues play an important role in G protein coupling to GPBAR in response to UDCA binding. Our study provides a preliminary molecular mechanism of how GPBAR recognizes UDCA and subsequent activation and G protein interaction, which may facilitate the development of new bile acid derivatives as therapeutics. • The scattered alanine scanning method was used to delineate the molecular mechanism of GPBAR activation by UDCA. • TM2, TM3, TM5 and TM6 were identified make contributions in the formation of the binding pocket of UDCA in GPBAR. • UDCA 3-OH and Y2406.51 phenolic oxygen is involved in polar network keeping GPBAR in inactive state in absence of agonist UDCA 3-OH and Y240. phenolic oxygen is involved in polar network keeping GPBAR in inactive state in absence of agonist; • The ICL3 residues are important in G protein coupling by GPBAR in addition to the well-known roles of ICL2 residues. [ABSTRACT FROM AUTHOR]

Idiopathic short stature (ISS) accounts for more than 70% of childhood short stature cases, with an undefined etiology and pathogenesis, leading to limited treatment. However, recent studies have shown that intestinal microbiota may be associated with ISS. This study aimed to characterize the intestinal microbiota in children with ISS, effect of treatment with growth hormones, and association between specific bacterial species and ISS. This study enrolled 55 children, comprising 40 diagnosed with ISS at Jinhua Hospital, Zhejiang University, and 15 healthy controls. The subjects with ISS were divided into the untreated ISS group (UISS group, 22 children who had not been treated with recombinant human growth hormone [rhGH]), treated ISS group (TISS group, 18 children treated with rhGH for 1 year), and control group (NC group, 15 healthy children). High-throughput sequencing was used to determine the intestinal microbiota characteristics. Higher abundances of Bacteroides, Prevotella, Alistipes, Parabacteroides, Agathobacter and Roseburia were found in the UISS and TISS groups than in the control group, whereas Bifidobacterium, Subdoligranulum, and Romboutsia were less abundant. The composition of intestinal microbiota in the UISS and TISS groups was almost identical, except for Prevotella. The TISS group had significantly lower levels of Prevotella than did the UISS group, which were closer to those of the NC group. Receiver operating characteristic curve analysis revealed that the abundances of Prevotella, Bifidobacterium, Bacteroides, and Subdoligranulum were effective in differentiating between the UISS and NC groups. Conclusion: Alterations in intestinal microbiota may be associated with ISS. Specific bacterial species, such as Prevotella, may be potential diagnostic markers for ISS. What is Known: • ISS is associated with the GH-IGF-1 axis. • Recent studies indicated an association between the GH-IGF-1 axis and intestinal microbiota. What is New: • Children with ISS showed alterations in intestinal microbiota, with a relative increase in the abundance of gut inflammation-related bacteria. • The relative abundances of Prevotella, Bacteroides, Bifidobacterium, and Subdoligranulum may serve as potential diagnostic markers. [ABSTRACT FROM AUTHOR]