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INTESTINAL INFLAMMATION INTERFERES WITH THE EXPRESSION AND TRAFFICKING OF THE GLUT-2 GLUCOSE TRANSPORTER: ROLE OF GLCNACT-IV GLYCOSYLTRANSFERASE

JM Rybicka, WK Macnaughton
Mucosal Inflammation Research Group, University Of Calgary, Calgary, Alberta

The cause of weight loss in Crohn's disease is not clear, but may be due in part to impaired nutrient absorption. Glucose is an essential energy source which is absorbed primarily by the glucose transporter, GLUT-2. GLUT-2 activity is regulated by trafficking of the transporter from the basolateral to the apical membrane of the enterocyte. This process depends on GLUT-2 glycosylation by GlcNAcT-IV glycosyltransferase (GnT-IVa). We hypothesized that during intestinal inflammation GLUT-2 trafficking is impaired. To test this hypothesis we used a rat model of jejunitis in which 40 mg TNBS in 0.5 mL 50% EtOH was instilled into the jejunal lumen. Controls received saline by the same route. Rats were studied 7 days after treatment. Jejunal TNBS/EtOH resulted in significant damage along the small intestine. GLUT-2 mRNA and protein expression were decreased in duodenum and jejunum from TNBS-treated animals compared to controls (p<0.05). Using an antibody that recognizes an epitope of GLUT-2 that is accessible only when GLUT-2 is located basolaterally, we showed that basolateral GLUT-2 protein levels were decreased (p<0.01) in inflamed vs. control jejunum. To determine the mechanism underlying inflammation-induced changes in GLUT-2 expression, Caco-2 cells were treated with TNF-alpha (3 ng/mL), IFN-gamma (10 ng/mL) and IL-1beta (5 ng/mL). GLUT-2 mRNA expression was decreased (p<0.05), while protein expression was increased 24 hr following cytokine treatment (p<0.01). However, cellular fractionation studies revealed that basolateral GLUT-2 was decreased (p<0.05), while cytosolic GLUT-2 was elevated after cytokine treatment. The apical to basolateral flux of the non-metabolizable glucose analogue, ³H-2-deoxy-D-glucose, was decreased (p<0.001) at 24, 48 and 72 hours following treatment with either cytokines or the N-glycosylation inhibitor, tunicomysin. Although GnT-IVa mRNA expression increased transiently at 6 hr following cytokine treatment, protein expression was decreased at 48 and 72 hr. In conclusion, glucose transport during intestinal inflammation may be reduced as a result of impaired trafficking of GLUT-2 to the apical membrane of the enterocyte. This may be due to a cytokine-induced decrease in GnT-IVa expression, which would result in a decrease in the glycosylation required for GLUT-2 trafficking.

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