Intestinal neutral ceramidase exacerbates MASH pathogenesis

Metabolic dysfunction-associated steatotic liver disease and its more severe manifestation, metabolic dysfunction-associated steatohepatitis (MASH), are intimately linked to genetic factors, gut microbiota and barrier alteration. Ceramidases and ceramides are associated with MASH, yet the role of intestinal neutral ceramidase in MASH development remains unclear.

Murine models with intestinal epithelial cell (IEC)-specific depletion of neutral ceramidase (Asah2^ΔIEC ) or aryl hydrocarbon receptor (AhR ^ΔIEC) were subjected to either a Western diet (WD) at 6 weeks old for 10-12 months to induce MASH, or a hydrogenated vegetable oil, sucrose, palmitate and cholesterol (HSPC) diet to accelerate MASH progression. Fecal microbiota transplantation was performed in germ-free mice.

MASH is associated with the induction of neutral ceramidase, which reshapes the intestinal microbiota and metabolite profiles, leading to increased production of 2-hydroxyhippuric acid (2-HHA). We identified 2-HHA as an inhibitor of AhR signalling, a pathway that normally promotes intestinal fucosylation. Elevated 2-HHA suppresses AhR activity, reduces fucosylation and contributes to MASH and associated airway inflammation in mice fed WD or HSPC diet. Notably, IEC-specific deletion of neutral ceramidase decreases 2-HHA levels, restores AhR signalling, enhances fucosylation and protects against MASH. Consistently, intestinal AhR deficiency exacerbates MASH by reducing intestinal fucosylation, whereas supplementation with fucoidan increases fucosylation, improves barrier function and attenuates MASH.

These findings identify intestinal neutral ceramidase as a key driver of MASH through a microbiota-2-HHA-AhR axis that impairs intestinal fucosylation and barrier function, highlighting a potential therapeutic target.