Introduction

The interplay of diet and the intestinal microbiome plays a key role in developing colorectal cancer (CRC), with westernization of diets, e.g., an increase in fat and sugar and a decrease in fiber content, being the main contributor. We recently demonstrated that the endoplasmic reticulum unfolded protein response (ER-UPR) effector activating transcription factor 6 (ATF6) is associated with early and late onset of CRC in patients. Furthermore, the overexpression of ATF6 observed in a subset of CRC patients is associated with the presence of certain gut bacteria. The specific expression of activated ATF6 (nATF6) in mouse intestinal epithelial cells (nATF6^IEC) induces spontaneous development of colonic tumors in a microbiota-dependent manner, highlighting the functional relevance of ATF6 as a novel oncogenic driver.

Aims & Methods

To elucidate the adverse role of dietary fat, sugar, and fiber in tumorigenesis, we exposed nATF6^IEC mice under SPF conditions to control (chow) and westernized diets for 7 weeks after weaning. Microbial and metabolite profiles were assessed through deep metagenomic sequencing and targeted/untargeted mass spectrometry (LC-MS) analysis. Microbiota transfer of diet-exposed mice into germ-free recipients was conducted to verify the microbiota-dependent transmissibility of tumor formation. Bismuth(II)subsalicylate (BSS) was used as a dietary additive to validate the impact of bacteria-produced H₂S on tumorigenesis.

Results

Westernized high lard (HL) diet, enriched in fat and sugar and depleted in fermentable fiber, increased tumor burden in biallelic nATF6^IEC mice. Unexpectedly, HL induced de novo tumorigenesis in otherwise tumor-free monoallelic nATF6^IEC mice. Surprisingly, modifying the HL diet by supplementing dietary fiber or lowering fat content failed to protect the HL-induced tumorigenic phenotype. Metabolite profiling clearly differentiated westernized from control diets and tumor bearing from control mice. Transferring microbiota from diet-exposed mice into germ-free nATF6^IEC mice was sufficient to trigger tumorigenesis. Metagenomic profiles of westernized diet-exposed mice identified an increased relative abundance of H₂S-producing Desulfovibrio species and genes related to dissimilatory sulfate reduction. Supplementing westernized diets with the H₂S-scavenger BSS resulted in a drastic change in microbial communities as well as the prevention of tumor formation in monoallelic nATF6^IEC mice.

Conclusion

These results highlight the ability of westernized diets to enhance nATF6-related tumorigenesis while altering metabolite and microbial profiles. Westernized diets favor the growth of sulfate-reducing Desulfovibrionaceae, possibly resulting in increased H₂S production. H₂S scavenging significantly reduces diet-induced colonic tumor susceptibility, clearly demonstrating the impact of diet in shaping cancer-related microbiome alterations.