2893 - Irradiation-Induced Intestinal Injury and Mucus Secretion from Goblet Cells by Activating Endoplasmic Reticulum Stress

Y. Tian¹, L. Xie², and S. Cai³; ¹Institute of Radiotherapy & Oncology, Soochow University, Suzhou, China, ²Department of Radiotherapy and Oncology, The Second Affiliated Hospital of Soochow University, Suzhou, China, ³Department of Radiotherapy and Oncology, The Second Affiliated Hospital of Soochow University, SuZhou, China

Purpose/Objective(s): Radiation-induced intestinal injuries (RIII) commonly occur during abdomin-pelvic cancer radiotherapy, but its pathogenesis is not well understood. Goblet cells (GCs) are specialized epithelial cells that secrete mucus to physically separate the host and its microbiota, thus preventing bacterial invasion and in?ammation to maintain intestinal homeostasis. However, how goblet cells control the amount of mucus they secrete after exposure to ionizing radiation (IR) is unclear. Materials/

Methods: C57BL/6J and germ-free mice were treated with 13 Gy of whole abdominal irradiation (WAI), and the level of mucus secretion was evaluated by periodic acid–Schiff (PAS) staining and MUC2 fluorescence staining. Primary GCs were isolated from the small intestine of mice, and changes in endoplasmic reticulum stress (ERS) were tested via WB, ELISA, and scanning electron microscopy. The ERS inhibitor salubrinal (SAL) was used to detect changes in GCs mucus secretion after IR in vitro and in vivo. Through transcriptome sequencing, 16S rRNA sequencing and LC?MS analysis, key genes and metabolites regulating ERS were identified.
Results: The PAS and MUC2 fluorescence staining results showed that IR significantly reduced GC and mucus secretion in each crypt (P<0.001), while the key proteins ERS, CHOP and Grp78 were significantly activated. Compared to those of the control group, the survival rate of the SAL-treated group was significantly greater (30%) (P<0.05), and the clinical score was improved after WAI. The histological and WB results showed that SAL reversed ERS in the intestine after IR and promoted mucus secretion in GCs, suggesting that ERS is involved in the mucus secretion process. Compared with C57BL/6J mice, germ-free mice irradiated at the same dose also experienced ERS in the intestine, but the amount of mucus remaining unchanged, indicating that the control of mucus secretion by ERS is regulated by the microbiota. 16S rRNA gene-based microbiota analysis and metabolomics analysis indicated that IR regulates the reprogramming of microbial metabolism, particularly the inhibition of tryptophan metabolism. The radioprotective effects of six tryptophan-related indole derivatives were screened at the level of mouse intestinal organoids, and it was found that indole-3-carboxaldehyde (I3A) had the best protective effect. Finally, we found that I3A inhibits ERS and requires the bacterial intracellular sensor Nod2 to promote excessive mucus secretion.
Conclusion: Radiation-induced ER-stress-mediated regulation of mucus secretion is microbiota dependent which promoted the development of radiation-induced intestinal injury and treatment with I3A could promote intestinal recovery by modulating ERS. Our findings provide new insights into the pathogenesis of radiation-induced intestinal injury.