TET2 and TET3 loss disrupts small intestine differentiation and homeostasis.

TET2/3 play a well-known role in epigenetic regulation and mouse development. However, their function in cellular differentiation and tissue homeostasis remains poorly understood. Here we show that ablation of TET2/3 in intestinal epithelial cells results in a murine phenotype characterized by a severe homeostasis imbalance in the small intestine. Tet2/3-deleted mice show a pronounced loss of mature Paneth cells as well as fewer Tuft and more Enteroendocrine cells. Further results show major changes in DNA methylation at putative enhancers, which are associated with cell fate-determining transcription factors and functional effector genes. Notably, pharmacological inhibition of DNA methylation partially rescues the methylation and cellular defects. TET2/3 loss also alters the microbiome, predisposing the intestine to inflammation under homeostatic conditions and acute inflammation-induced death. Together, our results uncover previously unrecognized critical roles for DNA demethylation, possibly occurring subsequently to chromatin opening during intestinal development, culminating in the establishment of normal intestinal crypts.

The microbiota programs DNA methylation to control intestinal homeostasis and inflammation.

Although much research has been done on the diversity of the gut microbiome, little is known about how it influences intestinal homeostasis under normal and pathogenic conditions. Epigenetic mechanisms have recently been suggested to operate at the interface between the microbiota and the intestinal epithelium. We performed whole-genome bisulfite sequencing on conventionally raised and germ-free mice, and discovered that exposure to commensal microbiota induced localized DNA methylation changes at regulatory elements, which are TET2/3-dependent. This culminated in the activation of a set of 'early sentinel' response genes to maintain intestinal homeostasis. Furthermore, we demonstrated that exposure to the microbiota in dextran sodium sulfate-induced acute inflammation results in profound DNA methylation and chromatin accessibility changes at regulatory elements, leading to alterations in gene expression programs enriched in colitis- and colon-cancer-associated functions. Finally, by employing genetic interventions, we show that microbiota-induced epigenetic programming is necessary for proper intestinal homeostasis in vivo.

Chronic inflammation induces a novel epigenetic program that is conserved in intestinal adenomas and in colorectal cancer.

Chronic inflammation represents a major risk factor for tumor formation, but the underlying mechanisms have remained largely unknown. Epigenetic mechanisms can record the effects of environmental challenges on the genome level and could therefore play an important role in the pathogenesis of inflammation-associated tumors. Using single-base methylation maps and transcriptome analyses of a colitis-induced mouse colon cancer model, we identified a novel epigenetic program that is characterized by hypermethylation of DNA methylation valleys that are characterized by low CpG density and active chromatin marks. This program is conserved and functional in mouse intestinal adenomas and results in silencing of active intestinal genes that are involved in gastrointestinal homeostasis and injury response. Further analyses reveal that the program represents a prominent feature of human colorectal cancer and can be used to correctly classify colorectal cancer samples with high accuracy. Together, our results show that inflammatory signals establish a novel epigenetic program that silences a specific set of genes that contribute to inflammation-induced cellular transformation.