Bile acids (BAs) affect the intestinal environment by ensuring barrier integrity, maintaining microbiota balance, regulating epithelium turnover, and modulating the immune system. As a master regulator of BA homeostasis, farnesoid X receptor (FXR) is severely compromised in patients with inflammatory bowel disease (IBD) and colitis-associated colorectal cancer (CAC). At the front line, gut macrophages react to the microbiota and metabolites that breach the epithelium. We aim to study the role of the BA/FXR axis in macrophages. This study demonstrates that inflammation-induced epithelial abnormalities compromised FXR signaling and altered BAs’ profile in a mouse CAC model. Further, gut macrophage–intrinsic FXR sensed aberrant BAs, leading to pro-inflammatory cytokines’ secretion, which promoted intestinal stem cell proliferation. Mechanistically, activation of FXR ameliorated intestinal inflammation and inhibited colitis-associated tumor growth, by regulating gut macrophages’ recruitment, polarization, and crosstalk with Th17 cells. However, deletion of FXR in bone marrow or gut macrophages escalated the intestinal inflammation. In summary, our study reveals a distinctive regulatory role of FXR in gut macrophages, suggesting its potential as a therapeutic target for addressing IBD and CAC.

Bile acids (BA) not only influence the gut microbiome composition but are also metabolized by gut bacteria to form various microbial BAs. Among these, 3-oxo-lithocholic acid (3-oxo-LCA) and isoallo-LCA have been reported to modulate host immunity, suppress intestinal pathogens, and provide antiaging benefits, suggesting that they could also affect intestinal epithelial cells and colorectal cancer progression. To investigate the impact of 3-oxo-LCA on intestinal tumorigenesis, we evaluated its activity in vitro on mouse and human colorectal cancer cell lines, as well as primary mouse intestinal organoids and patient-derived colorectal cancer organoids, and in vivo using a genetically engineered mouse model, cell line–derived syngeneic and xenograft tumors, and patient-derived xenografts. 3-Oxo-LCA functioned as a potent FXR agonist that restored FXR signaling both in vitro and in vivo. Activation of FXR signaling reduced the growth of colorectal cancer cell lines and suppressed the proliferation of intestinal stem cells in both mouse organoids and patient-derived colorectal cancer organoids. In the APCMin/+ genetically engineered mouse model, 3-oxo-LCA reduced BA levels, enhanced gut barrier function, decreased tumor burden, and suppressed tumor initiation. Furthermore, 3-oxo-LCA significantly inhibited tumor progression in syngeneic and xenograft mouse models and promoted apoptosis within the tumors. Together, these results underscore the function of 3-oxo-LCA as an FXR agonist with the ability to inhibit colorectal cancer tumorigenesis and progression by modulating epithelial cell growth and death. Significance: The microbial bile acid 3-oxo-LCA activates FXR signaling in intestinal epithelial cells that inhibits cancer stem cell proliferation and induces apoptosis, highlighting the potential of 3-oxo-LCA for treating intestinal tumorigenesis.

Dysregulated bile acid (BA)/lipid metabolism and gut bacteria dysbiosis are tightly associated with the development of obesity and non-alcoholic fatty liver disease (NAFLD). The orphan nuclear receptor, Small Heterodimer Partner (SHP/NR0B2), is a key regulator of BA/lipid metabolism, and its gene-regulating function is markedly enhanced by phosphorylation at Thr-58 mediated by a gut hormone, fibroblast growth factor-15/19 (FGF15/19). To investigate the role of this phosphorylation in whole-body energy metabolism, we generated transgenic SHP-T58A knock-in mice. Compared with wild-type (WT) mice, the phosphorylation-defective SHP-T58A mice gained weight more rapidly with decreased energy expenditure and increased lipid/BA levels. This obesity-prone phenotype was associated with the upregulation of lipid/BA synthesis genes and downregulation of lipophagy/β-oxidation genes. Mechanistically, defective SHP phosphorylation selectively impaired its interaction with LRH-1, resulting in de-repression of SHP/LRH-1 target BA/lipid synthesis genes. Remarkably, BA composition and selective gut bacteria which are known to impact obesity, were also altered in these mice. Upon feeding a high-fat diet, fatty liver developed more severely in SHP-T58A mice compared to WT mice. Treatment with antibiotics substantially improved the fatty liver phenotypes in both groups but had greater effects in the T58A mice so that the difference between the groups was largely eliminated. These results demonstrate that defective phosphorylation at a single nuclear receptor residue can impact whole-body energy metabolism by altering BA/lipid metabolism and gut bacteria, promoting complex metabolic disorders like NAFLD. Since posttranslational modifications generally act in gene- and context-specific manners, the FGF15/19-SHP phosphorylation axis may allow more targeted therapy for NAFLD.

1. The gut microbiota, often regarded as a metabolic and signaling “organ,” profoundly influences host metabolism, physiology, and immunity through its dynamic interactions with host-derived and di...