CD73 Blockade Aggravate Dextran-Sodium-Sulfate-Induced Colitis via Down Regulating Inosine.

BACKGROUND: CD73, a pivotal enzyme in the purinergic signaling cascade, modulates the concentrations of adenosine and inosine. These metabolites are involved in immune responses and inflammatory processes. This study aims to investigate the function of CD73 in the pathogenesis of inflammatory bowel disease (IBD) and explore the potential mechanism. METHODS: Dextran-Sodium-Sulfate (DSS)-induced colitis mice models were established by orally administering 3% DSS. CD73 was blocked by intraperitoneal injection of Adenosine 5'- (α, β-methylene) diphosphate (APCP). Inosine was supplemented by intraperitoneal injection. Hematoxylin-eosin (H&E), PAS and Alcian blue staining were used to evaluate the inflammation infiltration and colon damage. Serum IL-6 levels were detected by ELISA assay. High-performance liquid chromatography-mass spectrometry (LC-MS) was used to investigate the level of inosine. RESULTS: Blockade of CD73 by APCP aggravated disease severity in DSS-induced colitis mice models, characterized by increased weight loss, colon shortening and pathological damage, increased disease activity and IL-6 production. Blocking CD73 impairs intestinal barrier function and integrity by reducing the expression of tight junction proteins (claudin-1, occludin and ZO-1), both in colon tissues and intestinal epithelial cell-MODE-K. In addition, APCP increased oxidative stress in colon tissue and MODE-K (increased MDA level, decreased SOD and GSH activities). Moreover, blocking CD73 reduced inosine levels in vivo and in vitro. We found that inosine treatment significantly ameliorated DSS-induced colitis in mice, as demonstrated by decreased weight loss, less colon shortening and histological injury, reduced disease activity and IL-6 production. Notably, the effects of inosine on MODE-K cells were opposite to those of APCP, including the effects on the expression of oxidative stress molecules and tight junction proteins. CONCLUSION: This study indicates that CD73 exerts a protective effect in the progress of DSS-induced colitis. Inosine supplementation might be a potential therapeutic strategy for colitis.