Mechanism underlying inhibition of intestinal apical Cl–/OH– exchange following infection with enteropathogenic E. coli

Abstract

Enteropathogenic E. coli (EPEC) is a major cause of infantile diarrhea, but the pathophysiology underlying associated diarrhea is poorly understood. We examined the role of the luminal membrane Cl -/OH -exchange process in EPEC pathogenesis using in vitro and in vivo models. Cl -/OH -exchange activity was measured as OH -gradient-driven 36 Cl -uptake. EPEC infection (60 minutes-3 hours) inhibited apical Cl -/OH -exchange activity in human intestinal Caco-2 and T84 cells. This effect was dependent upon the bacterial type III secretory system (TTSS) and involved secreted effector molecules EspG and EspG2, known to disrupt the host microtubular network. The microtubule-disrupting agent colchicine (100 μM, 3 hours) also inhibited 36 Cl -uptake. The plasma membrane expression of major apical anion exchanger DRA (SLC26A3) was considerably reduced in EPEC-infected cells, corresponding with decreased Cl -/OH -exchange activity. Confocal microscopic studies showed that EPEC infection caused a marked redistribution of DRA from the apical membrane to intracellular compartments. Interestingly, infection of cells with an EPEC mutant deficient in espG significantly attenuated the decrease in surface expression of DRA protein as compared with treatment with wild-type EPEC. EPEC infection in vivo (1 day) also caused marked redistribution of surface DRA protein in the mouse colon. Our data demonstrate that EspG and EspG2 play an important role in contributing to EPEC infection-associated inhibition of luminal membrane chloride transport via modulation of surface DRA expression.

Enteric pathogens and gut function: Role of cytokines and STATs

“…There are additional reports in which the antisecretory effects of C. rodentium infection in vivo were attributed to reduced expression of the anion exchanger DRA (SLC26A3) on the apical membrane in the colon 46 and are similar to the observed effects of EPEC in vitro. 47 The antisecretory effect of infection, however, may be offset in part by the inhibition of fluid absorption through reduced expression of aquaporins. 46 Missing from in vitro models, therefore, is the highly integrated environment that pathogens encounter in vivo.…”

Acid-Base Disturbances in Gastrointestinal Disease

“…Enterotoxin obtained from pathogenic E. coli activates guanylyl cyclase, which increases cyclic GMP levels, stimulating Cl Ϫ secretion in intestinal epithelial cells (34). Experimental studies also suggested that inflammation downregulates both the intestinal Cl Ϫ / HCO 3 Ϫ exchanger and Na ϩ /K ϩ -ATPase and also increases gut water permeability nonspecifically (35,36). Replacement of the fluid and electrolytes that are lost in these infectious diarrheas with either hypotonic oral solutions or intravenous solutions, along with appropriate antibiotic therapy, remains the centerpiece of treatment (Table 4) (27).…”

The role of epithelial malfunction in the pathogenesis of enteropathogenic E. coli-induced diarrhea

“…29 This effect appears to be mediated by EspG-and EspG2-dependent disruption of the microtubular network. 29 EPEC-induced microtubule dysfunction alters the membrane targeting of the Cl À /HCO 3 À exchanger DRA, resulting in reduced Cl À uptake and its accumulation in the lumen, driving water loss.…”

“…29 This effect appears to be mediated by EspG-and EspG2-dependent disruption of the microtubular network. 29 EPEC-induced microtubule dysfunction alters the membrane targeting of the Cl À /HCO 3 À exchanger DRA, resulting in reduced Cl À uptake and its accumulation in the lumen, driving water loss. 29 These results have recently been corroborated by a study showing an important downregulation of DRA mRNA in mice challenged with Citrobacter rodentium, a natural mouse pathogen used as an animal model of EPEC infection.…”

“…29 EPEC-induced microtubule dysfunction alters the membrane targeting of the Cl À /HCO 3 À exchanger DRA, resulting in reduced Cl À uptake and its accumulation in the lumen, driving water loss. 29 These results have recently been corroborated by a study showing an important downregulation of DRA mRNA in mice challenged with Citrobacter rodentium, a natural mouse pathogen used as an animal model of EPEC infection. 30 Furthermore, EPEC virulence factors, EspF, Map, Tir, and intimin, have been shown to act together to rapidly inactivate SGLT-1, a cotransporter responsible for about 70% of the total fluid uptake in the small intestine.…”