Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C92
The effect of inflammation on human airway epithelial glucose transport and GLUT transporter expression
J. P. Garnett1, T. T. Nguyen1, E. H. Baker1, D. L. Baines1
1. Division of Biomedical Sciences, St George's, University of London, London, United Kingdom.
The glucose concentration of the airway surface liquid (ASL) is tightly regulated by the airway epithelium, which is vital to prevent airway infections. This involves, in part, glucose uptake into airway epithelial cells through facilitated glucose transporters GLUTs (Kalsi et al, 2008). Airway inflammation could disrupt glucose homeostasis in airway epithelial cells via this mechanism. The aim of this study was to investigate the effect of inflammation induced by pro-inflammatory cytokines on glucose transport and expression of GLUT transporters in human H441 and primary human bronchial epithelial cell (HBEC) cultures. Cells were grown at air liquid interface for 7-14 days to form confluent polarised monolayers. Inflammation was induced with a cocktail of cytokines [Tumor Necrosis Factor -α (100 ng/ml), Interferon -γ (100 ng/ml), Lipopolysaccharide (10 μg/ml)] for 0, 24, 48 and 72 hours. Transepithelial electrical resistance (TEER) of the monolayers was measured using an epithelial voltohmmeter. The effect of cytokine treatment on glucose uptake was assessed using radiolabelled glucose (14C-D-glucose, 1μCi) applied to the apical or basolateral surface. GLUT- specific transport was assessed using the pharmacological inhibitor, phloretin (1mM). Cytokine-induced inflammation significantly reduced H441 and HBEC monolayer TEER in a stepwise manner over 72 hours, from 627 ± 40 to 278 ± 15 Ω.cm2 (P<0.0001; n=8) and 440 ± 79 to 221 ± 26 Ω.cm2 (P<0.05; n=4), respectively. This drop in TEER inversely correlated with an enhanced glucose uptake in both H441 and HBEC monolayers. Apical glucose uptake in HBEC monolayers increased by 265 ± 53% (P<0.05; n=3) after 72 hours of cytokine exposure. Comparable apical glucose uptakes were observed in H441 monolayers. No significant difference in basolateral glucose uptake was seen in either cell type. Similarly, when studying GLUT-specific uptake in H441 monolayers, an increase in phloretin-sensitive glucose uptake was present across the apical membrane, but not the basolateral. Western blotting analysis and fluorescence immunocytochemistry (IHC) showed the presence of GLUT2 expression in both HBEC and H441 cells (GLUT2 blocking peptide was applied as a control). Interestingly, upon cytokine exposure, GLUT2 expression noticeably increased over 72 hours in H441 monolayers when observed by IHC. In conclusion, inflammation induced by cytokine exposure had a significant affect on epithelial resistance and apical glucose uptake in both HBEC and H441 cell monolayers. The increase in GLUT-specific glucose uptake corresponds with enhanced GLUT2 expression, suggesting GLUT2 may play an important role in regulating ASL glucose concentration under inflammatory conditions.
Where applicable, experiments conform with Society ethical requirements