Syndecan-1 Acts in Synergy with Tight Junction Through Stat3 Signaling to Maintain Intestinal Mucosal Barrier and Prevent Bacterial Translocation.

BACKGROUND: Intestinal epithelial tight junction (TJ) is the principal determinant of mucosal permeability, defects of which have been correlated to inflammatory bowel disease. In this study, we investigated whether syndecan-1 (Sdc1), the predominant cell surface heparan sulfate proteoglycan, affects TJ proteins to protect intestinal barrier function.

METHODS: The role of Sdc1 in barrier function was examined in cultured colonic epithelial cells and dextran sodium sulfate-induced colitis mouse model. Barrier function was determined by transepithelial electrical resistance, bacterial translocation, and FITC-dextran flux. Canonical TJ proteins ZO-1 and occludin were measured by Western blot and immunofluoresence. Role of the Stat3 pathway was detected by Western blot and chromatin immunoprecipitation.

RESULTS: Overexpressed Sdc1 in Caco-2 cells attenuated transepithelial electrical resistance reduction, prevented bacterial translocation, and repressed FITC-dextran flux, whereas Sdc1 knockdown in HT29 cells resulted in a greater loss of barrier function. Supplementation of exogenous Sdc1 in colitis mice ameliorated the activity of colitis and barrier defect. Mechanistically, Sdc1 significantly modulated expressions of ZO-1 and occludin by activating Stat3, which directly bound to the promoter regions of ZO-1 and occludin. Furthermore, ZO-1 and occludin were found to bind to each other, and their repression could induce Sdc1 upregulation.

CONCLUSIONS: Sdc1 plays an important role in protecting the intestinal barrier function and preventing bacterial translocation, in synergy with TJ through Stat3 signaling in an Sdc1/Stat3/ZO-1 and occludin feedback loop. Sdc1 participates in the mechanism that is related to intestinal barrier function and colitis and represents a therapeutic target for novel anti-inflammatory bowel disease strategies.