Background: Cholestatic liver diseases (CLD) are characterized by abnormal bile acid metabolites with altered gut microbiota, mainly including primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). We have shown that vancomycin pretreatment aggravates partial bile duct ligation(pBDL)-induced cholestasis and fibrosis with decreased abundance of Clostridium XIVa, which is thought to be the major bacterial cluster that converts primary bile acids to secondary bile acids. As the most extensively studied species in cluster XIVa, the function of Clostridium scindens (C. scindens) in CLD remains unknown. This study aimed to determine whether C. scindens plays a protective role in CLD and explore the underlying mechanisms.
Method: C57BL/6J mice were exposed to water containing 0.5 g/L vancomycin for 3 weeks and switched to water, followed by daily gavage of C. scindens or vehicle for 4 days. Then all mice were administrated to pBDL, repeated with 4 days of vancomycin treatment and 4 days of C. scindens or vehicle. Mice were sacrificed through 2 rounds of vancomycin and C. scindens or vehicle treatment after pBDL and liver tissues were fixed formalin for histology. The bile acids profile of liver and feces were determined by HPLC-MS/MS and microbial profiles were determined by 16s rRNA sequencing. The intestinal FXR-FGF15/19 pathway was tested by western blot or qPCR. LX2 or primary hepatic stellate cells (HSCs) were treated with 25 μmol/L taurocholic acid (TCA) for 24 h.
Results: Gavage of C. scindens alleviated severe liver injury and fibrosis induced by the administration of vancomycin in a pBDL-induce CLD mouse model. Compared to controls, mice gavaged with C. scindens exhibited decreased collagen deposition, including significant decreases in Sirius red-positive area, mRNA levels of fibrosis-associated genes and protein levels of a-SMA.C. scindens activated intestinal FXR/FGF15 axis, including increased mRNA level of FXR and increased protein level of FGF15, which contributes to the downregulation of CYP7A1 expressions in liver. Consistent with this, we observed restoration of bile acids homeostasis after oral gavage of C. scindens, with reductions in total and primary bile acids from liver tissues. Furthermore, Taurine-conjugated bile acids, especially TCA, were dramatically increased after vancomycin administration and reduced to base level due to C. scindens gavage. Invitro results showed that TCA stimulation increases the expression of fibrosis-associated genes in LX2 and primary HSCs.
Conclusion: C. scindens alleviates liver fibrosis and cholestasis via activating intestinal FXR/FGF15 axis and suppressing hepatic CYP7A1 expression. The reduction of taurine-conjugated bile acids mediates the protective effect of C. scindens in CLD.

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