title: SGLT-1-mediated glucose uptake protects intestinal epithelial cells against LPS-induced apoptosis and barrier defects: a novel cellular rescue mechanism?
abstract: Excessive apoptosis induced by enteric microbes leads to epithelial barrier defects. This mechanism has been implicated in the pathogenesis of inflammatory bowel diseases (IBD) and bacterial enteritis. The sodium-dependent glucose cotransporter (SGLT-1) is responsible for active glucose uptake in enterocytes. The aim was to investigate the effects of SGLT-1 glucose uptake on enterocyte apoptosis and barrier defects induced by bacterial lipopolysaccharide (LPS). SGLT-1-transfected Caco-2 cells were treated with LPS (50 mug/mL) in low (5 mM) or high (25 mM) glucose media. LPS in low glucose induced caspase-3 cleavage, DNA fragmentation, and increased paracellular permeability to dextran in epithelial cells. These phenomena were significantly attenuated in high glucose. LPS increased SGLT-1 activity in high, but not low glucose media. Addition of phloridzin, which competitively binds to SGLT-1, inhibited the cytoprotection mediated by high glucose. Western blot showed that LPS in high glucose increased the levels of anti-apoptotic Bcl-2 and Bcl-X(L,) and did not change proapoptotic Bax. Differential extraction of membranous vs. cytosolic cell components demonstrated that high glucose inhibits mitochondrial cytochrome c translocation to cytosol. Collectively, SGLT-1-mediated glucose uptake increases anti-apoptotic proteins, and protects enterocytes from LPS-induced apoptosis and barrier defects. The understanding of this novel glucose-mediated rescue mechanism may lead to therapeutic interventions for various enteric diseases.
authors.affiliation: Department of Biological Sciences, Mucosal Inflammation Research Group, University of Calgary, Calgary, AB, Canada.
authors.forename: Linda C H
authors.initials: LC
authors.lastname: Yu
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Flynn
authors.forename: Jerrold R
authors.initials: JR
authors.lastname: Turner
authors.forename: Andre G
authors.initials: AG
authors.lastname: Buret
mesh_terms: D017209:Apoptosis; D001667:Binding, Competitive; D001692:Biological Transport; D015153:Blotting, Western; D018938:Caco-2 Cells; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D053938:DNA Fragmentation; D020895:Enterocytes / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D004847:Epithelial Cells / Q000166:cytology*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000473:pathology; D007422:Intestines / Q000166:cytology* / Q000473:pathology; D008070:Lipopolysaccharides / Q000378:metabolism*; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000737:chemistry; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D015233:Models, Statistical; D062793:Occludin; D010539:Permeability; D010695:Phlorhizin / Q000494:pharmacology; D011485:Protein Binding; D021381:Protein Transport; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051269:Sodium-Glucose Transporter 1 / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation; D050994:Voltage-Dependent Anion Channels / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: D008070:Lipopolysaccharides; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; D019253:Proto-Oncogene Proteins c-bcl-2; C495674:SLC5A1 protein, human; D051269:Sodium-Glucose Transporter 1; D050994:Voltage-Dependent Anion Channels; D051020:bcl-X Protein; D045304:Cytochromes c; D010695:Phlorhizin; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D005947:Glucose