Repression of Gut Microbiota-Derived GM3 by Insoluble Fiber Attenuates the Colorectal Tumorigenesis in mice

• We have discovered an alternative mechanism mediated by insoluble dietary fiber that contributes to the prevention of colorectal tumorigenesis, potentially accounting for the paradoxical role of SCFAs. • Microbial enzyme encoded by K12373 promotes tumorigenic glycosphingolipid GM3 production, which can be suppressed by high-fiber diet. • As a key node in glycosphingolipid metabolism, K12373 directs metabolic flux primarily towards the GM3 branch and, to a lesser extent, the Gb3 branch, thus illustrating a classic metabolic branch point model in microbiome-host interaction. The generally accepted mechanism by which insoluble dietary fiber (IDF) inhibits colorectal cancer (CRC) progression involves the modulation of gut microbiota to stimulate short-chain fatty acids (SCFAs) production. However, the paradoxical role of SCFAs, which can also epigenetically upregulate oncogenes and potentially favor tumor progression, suggests that additional pathways may contribute to the protective effects of IDF. In this study, we aimed to investigate these alternative mechanisms. Mice were assigned to four groups: normal control, AOM/DSS-induced CRC model, CRC model fed a high-fiber diet, and CRC model treated with antibiotics. IDF intervention suppressed CRC progression in AOM/DSS-induced mice, and antibiotic-induced microbiota depletion completely prevented tumorigenesis, establishing the essential role of gut microbiota. Metagenomic sequencing of fecal samples from control, model, and IDF-treated groups revealed that IDF reshaped the gut microbial community and specifically reduced the levels of the microbial enzyme encoded by K12373 and its carrier, Paramuribaculum intestinale —both of which were elevated in AOM/DSS-induced mice. Bioinformatic annotation indicated that K12373 encodes a putative hexosaminidase involved in glycosphingolipid metabolism, a pathway responsible for generating tumor-associated gangliosides GM3 and Gb3. Notably, only GM3 was consistently elevated in CRC model mice and suppressed by both IDF and antibiotic treatment. Furthermore, in APC min/+ mice, exogenous GM3 exacerbated tumor proliferation, whereas Gb3 showed no significant effect. These findings demonstrate that IDF delays CRC progression, at least in part, by inhibiting gut microbiota-dependent GM3 production. Exogenous GM3 can inhibit apoptosis in HT-29 cells and promote cancer cell proliferation. Collectively, our study reveals a crucial link between dietary fiber, gut microbiota, and glycosphingolipid metabolism in CRC, offering novel insights for dietary and microbiota-targeted interventions.