title: Downregulation of the NHE3-binding PDZ-adaptor protein PDZK1 expression during cytokine-induced inflammation in interleukin-10-deficient mice.
abstract: BACKGROUND
  Impaired salt and water absorption is an important feature in the pathogenesis of diarrhea in inflammatory bowel disease (IBD). We analyzed the expression of proinflammatory cytokines in the infiltrating immune cells and the function and expression of the Na(+)/H(+) exchanger isoform 3 (NHE3) and its regulatory PDZ-adaptor proteins NHERF1, NHERF2, and PDZK1 in the colon of interleukin-10-deficient (IL-10(-/-)) mice.
  
  
  RESULTS
  Gene and protein expression were analyzed by real-time reverse transcription polymerase chain reaction (qRT-PCR), in situ RT-PCR, and immunohistochemistry. NHE3 activity was measured fluorometrically in apical enterocytes within isolated colonic crypts. Mice developed chronic colitis characterized by a typical immune cell infiltration composed of T-lymphocytes and macrophages, with high levels of gene and protein expression of the proinflammatory cytokines interleukin-1β and tumor necrosis factor-α. In parallel, inducible nitric oxide synthase expression was increased while procaspase 3 expression was unaffected. Interferon-γ expression remained low. Although acid-activated NHE3 activity was significantly decreased, the inflammatory process did not affect its gene and protein expression or its abundance and localization in the apical membrane. However, expression of the PDZ-adaptor proteins NHERF2 and PDZK1 was downregulated. NHERF1 expression was unchanged. In a comparative analysis we observed the PDZK1 downregulation also in the DSS (dextran sulphate sodium) model of colitis.
  
  
  CONCLUSIONS
  The impairment of the absorptive function of the inflamed colon in the IL-10(-/-) mouse, in spite of unaltered NHE3 expression and localization, is accompanied by the downregulation of the NHE3-regulatory PDZ adaptors NHERF2 and PDZK1. We propose that the downregulation of PDZ-adaptor proteins may be an important factor leading to NHE3 dysfunction and diarrhea in the course of the cytokine-mediated inflammatory process in these animal models of IBD.
authors: Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany. Lenzen.Henrike@mh-hannover.de
authors: Henrike
authors: H
authors: Lenzen
authors: Maria
authors: M
authors: Lünnemann
authors: Andre
authors: A
authors: Bleich
authors: Michael P
authors: MP
authors: Manns
authors: Ursula
authors: U
authors: Seidler
authors: Anne
authors: A
authors: Jörns
mesh_terms: D000818:Animals; D016264:Dextran Sulfate / Q000633:toxicity; D003967:Diarrhea / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D004195:Disease Models, Animal; D015536:Down-Regulation; D015212:Inflammatory Bowel Diseases / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D016753:Interleukin-10; D053583:Interleukin-1beta / Q000096:biosynthesis / Q000235:genetics; D007408:Intestinal Absorption; D047908:Intracellular Signaling Peptides and Proteins / Q000096:biosynthesis* / Q000235:genetics; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis / Q000235:genetics
chemical_list: C556062:IL10 protein, mouse; D053583:Interleukin-1beta; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C514896:PDZK1 protein, mouse; D010750:Phosphoproteins; C000613386:Slc9a3 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D014409:Tumor Necrosis Factor-alpha; C093376:sodium-hydrogen exchanger regulatory factor; D016753:Interleukin-10; D016264:Dextran Sulfate