The NF-κB-Regulated miR-221/222/Syndecan-1 Axis and Intestinal Mucosal Barrier Function in Radiation Enteritis

Radiation enteritis (RE) is the most common complication of pelvic radiation therapy, but proven therapies are lacking. Barrier function defects are closely associated with numerous inflammatory disorders. In this study, we investigated whether barrier dysfunction contributes to RE and whether syndecan-1 (Sdc1) protects intestinal barrier function in RE. The mechanism was also elucidated.

Blood, urine, and tissue samples were collected from 21 patients with cervical cancer who experienced RE during radiation therapy. The samples were used to detect inflammatory responses and barrier function. The role of Sdc1 in barrier function was examined in cultured fetal human colon (FHC) cells exposed to radiation and an induced mouse RE model. Barrier function was determined by zonula occludens (ZO)-1 and occludin expression, transepithelial electrical resistance (TEER), and fluorescein isothiocyanate-dextran (FD4) flux. The role of the nuclear factor (NF)-κB-P65 pathway was detected by Western blotting and chromatin immunoprecipitation. The role of miR-221/222 was assessed by real-time polymerase chain reaction and luciferase reporter assays.

Patients with RE exhibited obvious pathologic and ultramicrostructural inflammatory injury and barrier disruption in the intestinal mucosa, as well as higher serum lipopolysaccharide (LPS), LPS-binding protein, and cytokine levels and a higher urine lactulose-to-mannitol ratio. Overexpression of Sdc1 in irradiated FHC cells reversed TEER suppression, repressed FD4 flux, and upregulated ZO-1 and occludin expression. Exogenous low-molecular-weight heparin supplementation in RE mice ameliorated the activity of enteritis and barrier defects. Mechanistically, irradiation-activated P65 increased the transcription of miR-221/222 via direct binding to the promoter regions, and miR-221/222 then posttranscriptionally suppressed the Sdc1 gene by binding to its 3'-untranslated region.

The findings suggest that Sdc1 protects barrier function and controls inflammation during RE under transcriptional regulation by the NF-κB pathway and miR-221/222. The network including NF-κB, miR-221/222, and Sdc1 is important in the pathogenesis of RE, and Sdc1 might represent a therapeutic target for novel anti-RE strategies.