Protective mechanism of homologous lactic acid bacteria against cholestatic liver injury in snakehead fish

Cholestatic liver injury, a typical symptom of hepatobiliary syndrome, is usually accompanied by bile acid (BA) metabolism disorders and intestinal microbiota imbalance. Lactic acid bacteria (LAB) play an active role in regulating liver and gallbladder diseases and the balance of intestinal microbiota. In the study, the protective mechanism of homologous LAB (Lactococcus lactis L19, Genbank: MT102745.1) isolated from the intestine of snakehead fish (Channa argus, C. argus) against lithocholic acid (LCA)-induced cholestatic liver injury in C. argus was explored. Biochemical results illustrated that LCA feeding markedly increased the serum AST, ALT, ALP, TBA, TBIL and DBIL activities and treatment with L19 diet reversed the increase of these BA biomarkers. Liver histology results identified the amelioration of LCA-induced cholestasis after L19 treatment. Gene analysis indicated that L19 activated fxr and regulated BA metabolism, including promoted BA transport from the liver into the intestine by inducing the expressions of fxr-target genes bsep, mrp2, mrp3, mrp4, and Ost beta, and reduced BA reabsorption by inhibiting the expression of ntcp. In addition, L19 reduced BA synthesis by inhibiting the expressions of fxr-target genes cyp7a1, cyp8b1, cyp27a1, and hmgcr via the Fxr-Shp signaling pathway, and promoted BA metabolism by inducing the expression of sult2a1. Protein analysis indicated that L19 promoted BA metabolism and transport through activating the Fxr-target proteins Bsep, Shp and Cyp7a1. Intestinal microbiota analysis demonstrated that the LCA group was dominated by Proteobacteria and Chlamydiae, while L19 treatment can reduce the abundance of Proteobacteria, increase the abundance of Firmicutes, and regulate the composition of intestinal microbiota. For the first time, we found that L. lactis L19 can activate Fxr, regulate BA metabolism and intestinal microbiota to exert protective effects against cholestatic liver injury. Therefore, L. lactis L19 might be a potent measure for the prevention against LCA-induced cholestatic liver injury of fish, possibly via Fxr-Bsep and Fxr-Shp signal pathway and intestinal microbiota alteration.