Epithelial RABGEF1 deficiency promotes intestinal inflammation by dysregulating intrinsic MYD88-dependent innate signaling.

Intestinal epithelial cells (IECs) contribute to the regulation of intestinal homeostasis and inflammation through their interactions with the environment and host immune responses. Yet our understanding of IEC-intrinsic regulatory pathways remains incomplete. Here, we identify the guanine nucleotide exchange factor RABGEF1 as a regulator of intestinal homeostasis and innate pathways dependent on IECs. Mice with IEC-specific Rabgef1 deletion (called Rabgef1IEC-KO mice) developed a delayed spontaneous colitis associated with the local upregulation of IEC chemokine expression. In mouse models of colitis based on Interleukin-10 deficiency or dextran sodium sulfate (DSS) exposure, we found that IEC-intrinsic RABGEF1 deficiency exacerbated development of intestinal pathology and dysregulated IEC innate pathways and chemokine expression. Mechanistically, we showed that RABGEF1 deficiency in mouse IECs in vitro was associated with an impairment of early endocytic events, an increased activation of the p38 mitogen-activated protein kinase (MAPK)-dependent pathway, and increased chemokine secretion. Moreover, we provided evidence that the development of spontaneous colitis was dependent on microbiota-derived signals and intrinsic MYD88-dependent pathways in vivo. Our study identifies mouse RABGEF1 as an important regulator of intestinal inflammation, MYD88-dependent IEC-intrinsic signaling, and chemokine production. This suggests that RABGEF1-dependent pathways represent interesting therapeutic targets for inflammatory conditions in the gut.