title: Crohn's disease-associated Escherichia coli survive in macrophages by suppressing NFκB signaling.
abstract: BACKGROUND
  Epidemiological and genetic studies suggest a role for enteric flora in the pathogenesis of Crohn's disease (CD). Crohn's disease-associated Escherichia coli (CDEC) is characterized by their ability to invade epithelial cells and survive and induce high concentration of TNF-α from infected macrophages. However, the molecular mechanisms of CDEC survival in infected macrophages are not completely understood.
  
  
  METHODS
  Intracellular survival of CDEC strain LF82 isolated from inflamed ileum tissue, 13I isolated from inflamed colonic tissue, and control E. coli strains were tested in the murine macrophage cell line, J774A.1 by Gentamicin protection assay. Modulation of intracellular cell signaling pathways by the E. coli strains were assessed by western blot analysis and confocal microscopy.
  
  
  RESULTS
  13I demonstrated increased survival in macrophages with 2.6-fold higher intracellular bacteria compared with LF82, yet both strains induced comparable levels of TNF-α. LF82 and 13I differentially modulated key mitogen-activated protein kinase pathways during the acute phase of infection; LF82 activated all 3 mitogen-activated protein kinase pathways, whereas 13I activated ERK1/2 pathway but not p38 and JNK pathways. Both 13I and LF82 suppressed nuclear translocation of NFκB compared with noninvasive E. coli strains during the acute phase of infection. However, unlike noninvasive E. coli strains, 13I and LF82 infection resulted in chronic activation of NFκB during the later phase of infection.
  
  
  CONCLUSIONS
  Our results showed that CDEC survive in macrophages by initially suppressing NFκB activation. However, persistence of bacterial within macrophages induces chronic activation of NFκB, which correlates with increased TNF-α secretion from infected macrophages.
authors.affiliation: *Division of Digestive Diseases, Epithelial Pathobiology and Mucosal Inflammation Research Unit, Department of Pathology and Laboratory Medicine, Emory University, Atlanta, Georgia; and †Division of Digestive Diseases, Emory University, Atlanta, Georgia; and ‡Division of Digestive Diseases, Atlanta VA Medical Center, Decatur, Georgia.
authors.forename: Khalidur
authors.initials: K
authors.lastname: Rahman
authors.forename: Maiko
authors.initials: M
authors.lastname: Sasaki
authors.forename: Asma
authors.initials: A
authors.lastname: Nusrat
authors.forename: Jan-Michael A
authors.initials: JM
authors.lastname: Klapproth
mesh_terms: D017209:Apoptosis; D001422:Bacterial Adhesion; D015153:Blotting, Western; D002478:Cells, Cultured; D003424:Crohn Disease / Q000382:microbiology*; D004847:Epithelial Cells / Q000382:microbiology*; D004926:Escherichia coli / Q000254:growth & development / Q000302:isolation & purification / Q000472:pathogenicity*; D004927:Escherichia coli Infections / Q000382:microbiology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D008264:Macrophages / Q000382:microbiology*; D018613:Microscopy, Confocal; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D020928:Mitogen-Activated Protein Kinases