title: Probiotic bacteria regulate intestinal epithelial permeability in experimental ileitis by a TNF-dependent mechanism.
abstract: BACKGROUND
  We previously showed that the probiotic mixture, VSL#3, prevents the onset of ileitis in SAMP/YitFc (SAMP) mice, and this effect was associated with stimulation of epithelial-derived TNF. The aim of this study was to determine the mechanism(s) of VSL#3-mediated protection on epithelial barrier function and to further investigate the "paradoxical" effects of TNF in preventing SAMP ileitis.
  
  
  METHODS
  Permeability was evaluated in SAMP mice prior to the onset of inflammation and during established disease by measuring transepithelial electrical resistance (TEER) on ex vivo-cultured ilea following exposure to VSL#3 conditioned media (CM), TNF or VSL#3-CM + anti-TNF. Tight junction (TJ) proteins were assessed by qRT-PCR, Western blot, and confocal microscopy, and TNFRI/TNFRII expression measured in freshly isolated intestinal epithelial cells (IEC) from SAMP and control AKR mice.
  
  
  RESULTS
  Culture with either VSL#3-CM or TNF resulted in decreased ileal paracellular permeability in pre-inflamed SAMP, but not SAMP with established disease, while addition of anti-TNF abrogated these effects. Modulation of the TJ proteins, claudin-2 and occludin, occurred with a significant decrease in claudin-2 and increase in occludin following stimulation with VSL#3-CM or TNF. TNF protein levels increased in supernatants of SAMP ilea incubated with VSL#3-CM compared to vehicle, while IEC-derived TNFR mRNA expression decreased in young, and was elevated in inflamed, SAMP versus AKR mice.
  
  
  CONCLUSIONS
  Our data demonstrate that the previously established efficacy of VSL#3 in preventing SAMP ileitis is due to direct innate and homeostatic effects of TNF on the gut epithelium, modulation of the TJ proteins, claudin-2 and occludin, and overall improvement of intestinal permeability.
authors: Division of Gastroenterology and Liver Disease, Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America.
authors: Daniele
authors: D
authors: Corridoni
authors: Luca
authors: L
authors: Pastorelli
authors: Benedetta
authors: B
authors: Mattioli
authors: Silviu
authors: S
authors: Locovei
authors: Dai
authors: D
authors: Ishikawa
authors: Kristen O
authors: KO
authors: Arseneau
authors: Marcello
authors: M
authors: Chieppa
authors: Fabio
authors: F
authors: Cominelli
authors: Theresa T
authors: TT
authors: Pizarro
mesh_terms: D000818:Animals; D001419:Bacteria; D005786:Gene Expression Regulation / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D007079:Ileitis / Q000378:metabolism* / Q000382:microbiology / Q000473:pathology / Q000517:prevention & control*; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism* / Q000382:microbiology / Q000473:pathology; D051379:Mice; D010539:Permeability / Q000187:drug effects; D019936:Probiotics / Q000494:pharmacology*; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D019108:Tight Junctions / Q000187:drug effects / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha