Ulcerative Colitis Patients in Remission Have an Enhanced Secretory Response to Forskolin in Proximal Colon and a Reduced Response in Distal Colon, While Ca2+ Mediated Secretion Remains Unaffected

Abstract

Backgrounds/Aims: Macroautophagy is a bulk degradation system that enables recycling of long-lived proteins and damaged organelles. It is at the crossroads of innate and adaptive immunity, inflammation and apoptosis. Previous studies have associated the NOD2 frameshift 1007fs mutation with a defect of autophagy induction and an increased intestinal permeability. The aim of this study was to investigate the role of autophagy in the intestinal permeability and to define the involvement of NOD2 and its variant 1007fs. Methods: Paracellular permeability was assessed by FITC 4kD Dextran flux and transepithelial resistance in Caco2 monolayers. Stably transfected cells with the wild-type or 1007fs NOD2 variant were also used. Activation of autophagy was induced by 24H of nutrient starvation and rapamycin treatment. Results: Nutrient starvation of Caco-2 monolayers increased significantly the paracellular permeability compared to basal conditions (respectively, 10.84% vs 0.84% of 4kD FITC dextran; P<0.001). Autophagy induction was also associated with a decrease of transepithelial resistance of Caco2 monolayer. Similar results were obtained after induction of autophagy by rapamycin treatment. When transfected with the wild-type form of NOD2, Caco-2 cells were resistant to autophagy induced paracellular permeability (1.96% of 4kD FITC and 1.86% respectively for basal and autophagy induced permeability). In contrast, Caco-2 cells carrying 1007fs NOD2 variant exhibited an increased paracellular permeability after induction of autophagy (4.69% of 4kD FITC and 29.09% respectively for basal and experimental condition; P<0.001). Conclusion: In this In Vitro model, macroautophagy is associated with increased paracellular permeability. These results suggest a new putative role of NOD2 in the intestinal homeostasis by its capacity to reverse mediated autophagic effects. Finally, these data reinforce the impact of 1007fs NOD2 variant, in the intestinal barrier alteration featured in Crohn's Disease. Together, these data provide a link between autophagy, intestinal permeability and NOD2 Crohn's Disease associated mutations.