Exercise-Induced Changes in Enterohepatic Communication Are Linked to Liver Steatosis Resolution

Background/Objectives: This study aimed to investigate the effects of long-term aerobic exercise on high-fat diet (HFD)-induced hepatic steatosis and its underlying enterohepatic communication mechanisms. Methods: C57BL/6J mice were divided into four groups: normal-diet with sedentary (ND-SED), normal-diet with exercise (ND-EXE), HFD with sedentary (HFD-SED), and HFD with exercise (HFD-EXE). After 16 weeks of HFD feeding, ND-EXE and HFD-EXE groups underwent an 8-week aerobic exercise intervention. Hepatic lipid accumulation was assessed via histology and triglyceride (TG) quantification. Liver function and glucose tolerance were evaluated. Gut microbiota composition (16S rRNA sequencing), hepatic bile acid profiles (LC-MS metabolomics), and gene expression were analyzed. Results: HFD induced hepatic steatosis, glucose intolerance, and liver injury in mice, all of which were ameliorated by exercise. Compared to HFD-SED mice, which exhibited impaired gut microbiota diversity, exercise restored key genera such as Faecalibaculum, and Turicibacter. Functional analysis revealed that exercise modulated microbiota shifts in lipid metabolism and secondary bile acid biosynthesis. HFD-EXE mice displayed altered hepatic bile acid composition, characterized by increased tauroursodeoxycholic acid (TUDCA) and reduced taurohyodeoxycholic acid (THDCA). Notably, TUDCA levels correlated with Turicibacter abundance, while deoxycholic acid (DCA) was associated with Faecalibaculum, independent of precursor availability. Exercise also suppressed hepatic endoplasmic reticulum (ER) stress and downregulated lipogenic genes via the inositol-requiring enzyme 1 alpha (IRE1α)- spliced X-box binding protein 1 (Xbp1s) pathway, while concurrently activating farnesoid X receptor (FXR) signaling to enhance fatty acid oxidation through the FXR-short heterodimer partner (SHP) related to hepatic secondary bile acid abundance change. Conclusions: The beneficial effect of long-term aerobic exercise on high-fat diet-induced hepatic steatosis in mice is potentially mediated through structural changes in the gut microbiota, which influence the abundance of hepatic secondary bile acids (TUDCA, DCA) and subsequently regulate the expression of genes involved in lipid metabolism.