Abstract
BackgroundAlthough bacteria are implicated in the pathogenesis of chronic inflammatory bowel diseases (IBD), mechanisms of intestinal injury and immune activation remain unclear. Identification of adherent-invasive Escherichia coli (AIEC) strains in IBD patients offers an opportunity to characterize the pathogenesis of microbial-induced intestinal inflammation in IBD. Previous studies have focused on the invasive phenotype of AIEC and the ability to replicate and survive in phagocytes. However, the precise mechanisms by which these newly identified microbes penetrate the epithelial lining remain to be clarified. Therefore, the aim of this study was to delineate the effects of AIEC, strain LF82 (serotype O83:H1) on model polarized epithelial monolayers as a contributor to intestinal injury in IBD.ResultsInfection of T84 and Madin-Darby Canine Kidney-I polarized epithelial cell monolayers with AIEC, strain LF82 led to a reduction in transepithelial electrical resistance and increased macromolecular (10 kilodalton dextran) flux. Basolateral AIEC infection resulted in more severe disruption of the epithelial barrier. Increased permeability was accompanied by a redistribution of the tight junction adaptor protein, zonula occludens-1, demonstrated by confocal microscopy and formation of gaps between cells, as shown by transmission electron microscopy. After 4 h of infection of intestine 407 cells, bacteria replicated in the cell cytoplasm and were enclosed in membrane-bound vesicles positive for the late endosomal marker, LAMP1.ConclusionThese findings indicate that AIEC, strain LF82 disrupts the integrity of the polarized epithelial cell barrier. This disruption enables bacteria to penetrate into the epithelium and replicate in the host cell cytoplasm. These findings provide important links between microbes related to IBD, the intestinal epithelial cell barrier and disease pathogenesis.
Highlights
Bacteria are implicated in the pathogenesis of chronic inflammatory bowel diseases (IBD), mechanisms of intestinal injury and immune activation remain unclear
When the pathogen was introduced into the basolateral aspect of monolayers there was an 81% reduction in transepithelial electrical resistance (TER), relative to sham control monolayers, with adherent-invasive Escherichia coli (AIEC) infection (p < 0.001), compared to a 50% reduction with Enterohemorrhagic E. coli (EHEC) infection (p < 0.01; t test of AIEC vs. EHEC: p = 0.052)
Our findings indicate that infection of polarized monolayers with AIEC, strain LF82 leads to disruption of epithelial cell monolayers, as demonstrated by both reduced transepithelial electrical resistance and increased macromolecular permeability, as well as morphological defects in the structure of the apical junctional complexes (AJCs) of infected monolayers
Summary
Bacteria are implicated in the pathogenesis of chronic inflammatory bowel diseases (IBD), mechanisms of intestinal injury and immune activation remain unclear. Identification of adherent-invasive Escherichia coli (AIEC) strains in IBD patients offers an opportunity to characterize the pathogenesis of microbial-induced intestinal inflammation in IBD. The aim of this study was to delineate the effects of AIEC, strain LF82 (serotype O83:H1) on model polarized epithelial monolayers as a contributor to intestinal injury in IBD. The inflammatory bowel diseases (IBD), Crohn disease and ulcerative colitis, are relatively common chronic disorders considered to develop due to an aberrant immune response to intestinal microbes in a genetically susceptible host [1]. Further support for the involvement of microbes in the pathogenesis of IBD is based on the observation that colitis does not occur in most gene knock-out models of IBD when animals are reared in germ-free conditions [5,6]. Absence of Faecalibacterium prausnitzii from the ileum of patients with Crohn disease undergoing surgical resection was associated with recurrence of disease, suggesting a protective role for this commensal organism [10]
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