Circadian dysregulation disrupts gut microbe-related bile acid metabolism

Background: Disturbance of circadian rhythm leads to abnormalities in bile acid (BA) and lipid metabolism, and it is of great significance to explore the relationship between them. This study explored the effects of circadian dysregulation on the rhythms of intestinal BA metabolism. Method: Period circadian clock 1/period circadian clock 2 (Per1/Per2) double gene knockout (DKO) and wild-type (WT) male C57BL/6 mice were fed with a control or high-fat diet for 16 weeks. We measure plasma parameters of mice. Pathological changes including those in liver and intestine were detected by hematoxylin and eosin (H&E) and oil O staining. Western blot was used to detect the intestinal core rhythm protein clock circadian regulator (CLOCK), nuclear receptor subfamily 1, group D, member 1 (REV-ERBα), Farnesoid X receptor (FXR), Small heterodimer partner (SHP), and Fibroblast growth factor 15 (FGF15) expressions. We analyzed the bile acid and intestinal flora profile in the mice intestine tissues by BA-targeted metabolomics detection and high-throughput sequencing. Results: Rhythmic chaos affected lipid metabolism and lipid accumulation in mice liver and intestine, and diurnal fluctuations of plasma triglycerides (TGs) were absent in normal-feeding DKO mice. The normal circadian fluctuations of the CLOCK and REV-ERBα observed in wild mice disappeared (normal diet) or were reversed (high-fat diet) in DKO mice. In WT mice intestine, total BA and conjugated BA were affected by circadian rhythm under both normal and high-fat diets, while these circadian fluctuations disappeared in DKO mice. Unconjugated BA seemed to be affected exclusively by diet (significantly increased in the high-fat group) without obvious fluctuations associated with circadian rhythm. Correlation analysis showed that the ratio of conjugated/unconjugated BA was positively correlated with the presence of Bacteroidetes and displayed a circadian rhythm. The expression levels of BA receptor pathway protein FXR, SHP, and FGF15 were affected by the ratio of conjugated/unconjugated BA. Conclusion: Bacteroidetes-related diurnal changes to intestinal ratios of conjugated/unconjugated BA have the potential to regulate diurnal fluctuations in liver BA synthesis via FXR-FGF15. The inverted intestinal circadian rhythm observed in DKO mice fed with a high-fat diet may be an important reason for their abnormal circadian plasma TG rhythms and their susceptibility to lipid metabolism disorders.