SGLT-1-mediated glucose uptake protects human intestinal epithelial cells against Giardia duodenalis-induced apoptosis

Abstract

Infection with Giardia duodenalis is one of the most common causes of waterborne diarrheal disease worldwide. Mechanisms of pathogenesis and host response in giardiasis remain incompletely understood. Previous studies have shown that exposure to G. duodenalis products induce apoptosis in enterocytes. We recently discovered that sodium-dependent glucose cotransporter (SGLT)-1-mediated glucose uptake modulates enterocytic cell death induced by bacterial lipopolysaccharide. The aim of this study was to examine whether enhanced epithelial SGLT-1 activity may constitute a novel mechanism of host defense against G. duodenalis-induced apoptosis. SGLT-1-transfected Caco-2 cells were exposed to G. duodenalis products in low (5 mM) or high (25 mM) glucose media. In low glucose environments, G. duodenalis-induced caspase-3 activation and DNA fragmentation in these cells. These apoptotic phenomena were abolished in the presence of high glucose. A soluble proteolytic fraction of G. duodenalis was found to upregulate SGLT-1-mediated glucose uptake in a dose-and time-dependent manner, in association with increased apical SGLT-1 expression on epithelial cells. Kinetic analysis showed that this phenomenon resulted from an increase in the maximal rate of sugar transport (V max ) by SGLT-1, with no change in the affinity constant (K m ). The addition of phloridzin (a competitive inhibitor for glucose binding to SGLT-1) abolished the antiapoptotic effects exerted by high glucose. Together, the findings indicate that SGLT-1-dependent glucose uptake may represent a novel epithelial cell rescue mechanism against G. duodenalis-induced apoptosis.

The role of the intestinal microvasculature in inflammatory bowel disease: studies with a modified Caco-2 model including endothelial cells resembling the intestinal barrier in vitro

“…A recent study reported a reduction in Caco-2 TER and an increase of paracellular flux after 0.3 µg/mL LPS treatment over a 5-day period. 29 Another study described a stable Caco-2 barrier after 50 µg/mL LPS treatment for 24 hours 30 as was also observed in our study, in which a stable TER was maintained over a 24-hour incubation period after incubation with 1 µg/mL LPS. These findings indicate that the incubation time might be a crucial factor in the outcome of barrier integrity after LPS challenge.…”

Giardia duodenalis Cathepsin B Proteases Degrade Intestinal Epithelial Interleukin-8 and Attenuate Interleukin-8-Induced Neutrophil Chemotaxis

“…Previous reports from our laboratory and others have demonstrated that G. duodenalis trophozoites induce pathophysiological events within intestinal epithelial cells (11,53,65,68,69). As these epithelial cells also participate in the induction of acute intestinal inflammatory responses by secreting chemokines such as CXCL8 (32-34), we investigated whether the attenuation of IL-1␤-induced CXCL8 secretion from CD small intestinal mucosal biopsy tissues implicated a G. duodenalis-mediated modulation of human intestinal epithelial CXCL8.…”

“…Initial experiments were performed to determine whether G. duodenalis NF trophozoites were capable of attenuating IL-1␤-induced CXCL8 secretion from human small intestinal mucosal biopsy tissues. This isolate has previously been used in our laboratory to characterize the pathophysiological effects of G. duodenalis infections (11,65). Adapting from previous studies (52), we developed a novel method of modeling G. duodenalis interactions with human small intestinal tissues, whereby human small intestinal mucosal biopsy tissues collected from the terminal ileum of patients with CD in remission were coincubated with live G. duodenalis trophozoites.…”

“…As these epithelial cells also participate in the induction of acute intestinal inflammatory responses by secreting chemokines such as CXCL8 (32-34), we investigated whether the attenuation of IL-1␤-induced CXCL8 secretion from CD small intestinal mucosal biopsy tissues implicated a G. duodenalis-mediated modulation of human intestinal epithelial CXCL8. Experiments similar to those described above were performed in vitro using the human Caco-2 intestinal epithelial cell line; this cell line has previously been used to delineate pathophysiological events induced by G. duodenalis and other en-teropathogens in human enterocytes (65,70,71) and has welldefined CXCL8 signaling pathways in response to host-and pathogen-induced proinflammatory stimuli such as IL-1␤ and S. Typhimurium (34,72). Our results demonstrate that CXCL8 supernatant levels from Caco-2 monolayers coincubated with several MOIs (1:1, 10:1, and 50:1) of G. duodenalis NF trophozoites administered IL-1␤ were significantly reduced compared to those from control monolayers administered only IL-1␤ (Fig.…”

Commensal bacterial internalization by epithelial cells: An alternative portal for gut leakiness

“…[44][45][46] The lumen-dwelling G. lamblia causes diffuse microvilli shortening, TJ disruption and epithelial cell apoptosis, 47,48 that may partly contribute to bacterial penetration. Moreover, it has been reported that intracellular C. jejuni-containing vacuoles deviate from the canonical endosomal pathways, avoiding delivery into lysosomes.…”