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.

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

“…Human colonic Caco-2 cells transfected with native intestinal SGLT-1 (Turner et al, 1996) were grown in DMEM (Life technologies, Inc., Gaithersburg, MD) that contained 25 mM of glucose as previously described ( [Yu et al, 2005] and [Yu et al, 2006]). The media was supplemented with 10% FBS, 15 mM Hepes, 100 U/ml Penicillin, 0.1 mg/ml Streptomycin (Sigma, St. Louis, MO) and 0.25 mg/ml Geneticin (Life technologies, Inc.) (Turner et al, 1996).…”

“…Physiological extrusion of senescent apoptotic enterocytes does not compromise intestinal barrier function ( [Madara, 1990] and [Watson et al, 2005]). In contrast, exposure to enteric pathogens such as G. duodenalis, Escherichia coli, Salmonella enteritica or Helicobacter pylori induces excessive enterocytic apoptosis, which may adversely affect epithelial tight junctional integrity ( [Jones et al, 2000], [Le'Negrate et al, 2001], [Chin et al, 2002], [Paesold et al, 2002], , [Yu et al, 2005], [Troeger et al, 2007] and [Panaro et al, 2007]). High concentrations of bacterial lipopolysaccharide (LPS) may also increase epithelial apoptosis and intestinal permeability ( [Yu et al, 2005], [Yu et al, 2006] and [Chin et al, 2006]).…”

“…In contrast, exposure to enteric pathogens such as G. duodenalis, Escherichia coli, Salmonella enteritica or Helicobacter pylori induces excessive enterocytic apoptosis, which may adversely affect epithelial tight junctional integrity ( [Jones et al, 2000], [Le'Negrate et al, 2001], [Chin et al, 2002], [Paesold et al, 2002], , [Yu et al, 2005], [Troeger et al, 2007] and [Panaro et al, 2007]). High concentrations of bacterial lipopolysaccharide (LPS) may also increase epithelial apoptosis and intestinal permeability ( [Yu et al, 2005], [Yu et al, 2006] and [Chin et al, 2006]). While it has been established that G. duodenalis-induced intestinal permeability defects require caspase-3 activation and appear to be strain-dependent ( and [Chin et al, 2002]), the mechanisms responsible for G. duodenalis-induced epithelial apoptosis remain incompletely understood.…”

“…Glucosemediated cytoprotection has been documented in a number of cell types, including myocardiocytes, vascular smooth muscle cells, mast cells, T cells and, most recently, in enterocytes ( [Schaffer et al, 2000], [Hall et al, 2001], [Malhotra et al, 2001] and [Yu et al, 2005]). The mechanisms regulating this response remain poorly understood.…”

“…This characteristic has been used for the development of oral rehydration therapy (ORT) to promote electrolyte balance, and manage hypersecretory diarrheal disease (Kimmich and Randles, 1984). Recent observations have described a novel cell rescue mechanism against LPS-induced apoptosis via SGLT-1 activation and enhanced glucose uptake into enterocytes ( [Yu et al, 2005] and [Yu et al, 2006]). Whether this SGLT-1-mediated phenomenon confers cytoprotection against G. duodenalis-induced cellular apoptosis has yet to be explored.…”