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

## TL;DR

Deficiency in intestinal neutral ceramidase protects against gut inflammation by boosting regulatory T cells through ganglioside GD3.

## Contribution

Identifies GD3 as a functional ligand for Siglec-E on macrophages, linking it to Treg cell generation and intestinal protection.

## Key findings

- IEC NcDase deficiency reduces DSS-induced colitis and increases Treg cells in mice.
- GD3 produced via ST8SIA1 activates Siglec-E on macrophages, promoting IL-33 and Treg cell proliferation.
- Dietary GD3 administration reduces mucosal inflammation via ST2+ Treg cells.

## 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 (Treg) 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+ Treg 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 Treg cells and identifies an activating pathway that follows engagement of Siglec‐E.

Deletion of ASAH2 in intestinal epithelial cells induces the accumulation of ganglioside GD3 via regulating ST8SIA1. GD3 is identified as the glycolipid ligand for the inhibitory receptor Siglec‐E on macrophages. GD3/Siglec‐E ligation polarizes macrophages and promotes the proliferation of colonic ST2+ T regulatory cells via the induction of IL‐33. The administration of dietary GD3 reduces mucosal inflammation via ST2+ Treg cells.