Secretion of Acid Sphingomyelinase and Ceramide by Endothelial Cells Contributes to Radiation-Induced Intestinal Toxicity

Abstract

Ceramide-induced endothelial cell apoptosis boosts intestinal stem cell radiosensitivity. However, the molecular connection between these two cellular compartments has not been clearly elucidated. Here we report that Ceramide and its related enzyme acid sphingomyelinase (ASM) are secreted by irradiated endothelial cells and act as bystander factors to enhance the radiotoxicity of intestinal epithelium. Ceramide and the 2 isoforms of ASM were acutely secreted in the blood serum of wild-type mice after 15Gy radiation dose, inducing a gastrointestinal syndrome. Interestingly, serum Ceramide was not enhanced in irradiated ASMKO mice, which are unable to develop intestinal failure injury. Since ASM/Ceramide were secreted by primary endothelial cells, their contribution was studied in intestinal epithelium dysfunction using co-culture of primary endothelial cells and intestinal T84 cells. Adding exogenous ASM or Ceramide enhanced epithelial cell growth arrest and death. Conversely, blocking their secretion by endothelial cells using genetic, pharmacological, or immunological approaches abolished intestinal T84 cell radiosensitivity. Use of enteroid models revealed ASM and Ceramide-mediated deleterious mode-of-action: when Ceramide reduced the number of intestinal crypt-forming enteroids without affecting their structure, ASM induced a significant decrease of enteroid growth without affecting their number. Identification of specific and different roles for Ceramide and ASM secreted by irradiated endothelial cells opens new perspectives in the understanding of intestinal epithelial dysfunction after radiation and defines a new class of potential therapeutic radiomitigators.