title: Loss of downregulated in adenoma (DRA) impairs mucosal HCO3(-) secretion in murine ileocolonic inflammation.
abstract: BACKGROUND
  Ileocolonic luminal pH has been reported to be abnormally low in inflammatory bowel disease (IBD) patients, and one of the causative factors may be reduced epithelial HCO(3)(-) secretory rate (J(HCO3)(-)). Disturbances in J(HCO3)(-) may occur due to inflammation-induced changes in the crypt and villous architecture, or due to the effect of proinflammatory cytokines on epithelial ion transporters.
  
  
  METHODS
  To discriminate between these possibilities, the tumor necrosis factor alpha (TNF-α) overexpressing (TNF(+/ΔARE)) mouse model was chosen, which displays high proinflammatory cytokine levels in both ileum and colon, but develops only mild colonic histopathology and diarrhea. HCO(3)(-) secretion, mRNA expression, immunohistochemistry, and fluid absorptive capacity were measured in ileal and mid-colonic mucosa of TNF(+/ΔARE) and wildtype (WT) (TNF(+/+)) mice in Ussing chambers, and in anesthetized mice in vivo.
  
  
  RESULTS
  The high basal J(HCO3)(-) observed in WT ileal and mid-colonic mucosa were luminal Cl(-) -dependent and strongly decreased in TNF(+/ΔARE) mice. Downregulated in adenoma (DRA) mRNA and protein expression was strongly decreased in TNF(+/ΔARE) ileocolon, whereas cystic fibrosis transmembrane conductance regulator (CFTR), Na(+) /H(+) exchanger 3 (NHE3), Na(+) /HCO(3)(-) cotransporter (NBC), and epithelial sodium channel (ENaC) expression was not significantly altered. This indicates that the severe defect in ileocolonic J(HCO3)(-) was due to DRA downregulation. Fluid absorption was severely depressed in the ileum but only mildly affected in the mid-distal colon, preventing the development of overt diarrhea.
  
  
  CONCLUSIONS
  Even mild ileocolonic inflammation may result in a decrease of epithelial HCO(3)(-) secretion, which may contribute to alterations in surface pH, intestinal flora, and mucus barrier properties.
authors.affiliation: Department of Gastroenterology, Hannover Medical School, Germany.
authors.forename: Fang
authors.initials: F
authors.lastname: Xiao
authors.forename: Marina
authors.initials: M
authors.lastname: Juric
authors.forename: Junhua
authors.initials: J
authors.lastname: Li
authors.forename: Brigitte
authors.initials: B
authors.lastname: Riederer
authors.forename: Sunil
authors.initials: S
authors.lastname: Yeruva
authors.forename: Anurag Kumar
authors.initials: AK
authors.lastname: Singh
authors.forename: Lifei
authors.initials: L
authors.lastname: Zheng
authors.forename: Silke
authors.initials: S
authors.lastname: Glage
authors.forename: George
authors.initials: G
authors.lastname: Kollias
authors.forename: Pradeep
authors.initials: P
authors.lastname: Dudeja
authors.forename: De-An
authors.initials: DA
authors.lastname: Tian
authors.forename: Gang
authors.initials: G
authors.lastname: Xu
authors.forename: Jinxia
authors.initials: J
authors.lastname: Zhu
authors.forename: Oliver
authors.initials: O
authors.lastname: Bachmann
authors.forename: Ursula
authors.initials: U
authors.lastname: Seidler
mesh_terms: D000818:Animals; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D015153:Blotting, Western; D003092:Colitis / Q000378:metabolism / Q000473:pathology*; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism; D005260:Female; D007082:Ileum / Q000378:metabolism / Q000473:pathology*; D007249:Inflammation / Q000378:metabolism / Q000473:pathology*; D007413:Intestinal Mucosa / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism; D000076988:Sulfate Transporters; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*
chemical_list: D017920:Antiporters; D001639:Bicarbonates; D053503:Epithelial Sodium Channels; D012333:RNA, Messenger; C489860:Slc26a3 protein, mouse; C498899:Slc4a4 protein, mouse; C000613386:Slc9a3 protein, mouse; D027982:Sodium-Bicarbonate Symporters; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000076988:Sulfate Transporters; D014409:Tumor Necrosis Factor-alpha