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

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.