SPHK1 deficiency promotes intestinal homeostasis by ameliorating ER stress-induced gastrointestinal injury during murine graft-versus-host disease

Graft-versus-host disease (GVHD) remains a major challenge in successful allogeneic hematopoietic stem cell transplantation. Here, we report that inhibiting sphingosine kinase 1 (SPHK1), an enzyme that phosphorylates sphingosine to bioactive sphingosine-1-phosphate (S1P), effectively ameliorates acute GVHD (aGVHD) without compromising the graft-versus-leukemia effect. The absence of SPHK1 in the host exerts a beneficial effect on maintaining gut homeostasis by limiting intestinal epithelial cell (IEC) and intestinal stem cell (ISC) injury. This reduces gut permeability and prevents bacterial translocation, decreasing MHC II levels in IECs and donor T-cell infiltration. Persistent endoplasmic reticulum (ER) stress is observed during GVHD in the gastrointestinal tract and contributes to IEC injury. SPHK1 deficiency attenuates IEC damage by alleviating ER stress, which can be reversed by supplementation with exogenous S1P. FTY720, an S1P receptor antagonist, significantly inhibits ER stress-induced IEC injury. Our findings highlight the pathogenic role of host SPHK1 in gastrointestinal injury during aGVHD and suggest that targeting SPHK1 could be a therapeutic strategy for managing this condition.