Intestinal Neutral Ceramidase Deficiency Triggers Regulatory T Cell Response via Gd3 to Protect the Host from Intestinal Inflammation

Abstract Sphingolipids play a crucial role in gut inflammation. Neutral ceramidase (NcDase) serves as a pivotal regulator of ceramide, the central intermediate in sphingolipid metabolism. The contribution of intestinal epithelial cells (IEC) NcDase to colitis is not well understood. Here, a protective mechanism by which IEC NcDase deficiency ( Asah2 ^ΔIEC ) and its‐related gangliosides prevent dextran sulfate sodium (DSS)‐induced colitis in mice is described. Asah2 ^ΔIEC mice display reduced susceptibility to DSS‐induced colitis and increase regulatory T (T _reg ) cells compared to Asah2 ^fl/fl littermates. Deletion of IEC NcDase induces the upregulation of sialyltransferase ST8SIA1 and promotes the sialic‐acid‐containing ganglioside GD3 production. Siglec‐E is a sialic‐acid‐binding lectin expresses predominantly on myeloid cells. Mechanistically, it is identified that GD3 is a functional ligand for Siglec‐E on macrophages and found that GD3/Siglec‐E interaction induced a rapid metabolic rewiring of macrophages that involved the production of IL‐33, which contributes to the generation of ST2 ⁺ Foxp3 ⁺ T _reg cells. Finally, deletion of ST8SIA1 or administration of dietary GD3 induces or reduces mucosal inflammation, respectively. This work defines a critical role for ganglioside GD3 in the induction of colonic T _reg cells and identifies an activating pathway that follows engagement of Siglec‐E.