title: Evidence for a causal link between adaptor protein PDZK1 downregulation and Na⁺/H⁺ exchanger NHE3 dysfunction in human and murine colitis.
abstract: A dysfunction of the Na(+)/H(+) exchanger isoform 3 (NHE3) significantly contributes to the reduced salt absorptive capacity of the inflamed intestine. We previously reported a strong decrease in the NHERF family member PDZK1 (NHERF3), which binds to NHE3 and regulates its function in a mouse model of colitis. The present study investigates whether a causal relationship exists between the decreased PDZK1 expression and the NHE3 dysfunction in human and murine intestinal inflammation. Biopsies from the colon of patients with ulcerative colitis, murine inflamed ileal and colonic mucosa, NHE3-transfected Caco-2BBe colonic cells with short hairpin RNA (shRNA) knockdown of PDZK1, and Pdzk1-gene-deleted mice were studied. PDZK1 mRNA and protein expression was strongly decreased in inflamed human and murine intestinal tissue as compared to inactive disease or control tissue, whereas that of NHE3 or NHERF1 was not. Inflamed human and murine intestinal tissues displayed correct brush border localization of NHE3 but reduced acid-activated NHE3 transport activity. A similar NHE3 transport defect was observed when PDZK1 protein content was decreased by shRNA knockdown in Caco-2BBe cells or when enterocyte PDZK1 protein content was decreased to similar levels as found in inflamed mucosa by heterozygote breeding of Pdzk1-gene-deleted and WT mice. We conclude that a decrease in PDZK1 expression, whether induced by inflammation, shRNA-mediated knockdown, or heterozygous breeding, is associated with a decreased NHE3 transport rate in human and murine enterocytes. We therefore hypothesize that inflammation-induced loss of PDZK1 expression may contribute to the NHE3 dysfunction observed in the inflamed intestine.
authors.affiliation: Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Carl-Neuberg-Straße 1, 30625, Hannover, Germany.
authors.forename: Sunil
authors.initials: S
authors.lastname: Yeruva
authors.forename: Giriprakash
authors.initials: G
authors.lastname: Chodisetti
authors.forename: Min
authors.initials: M
authors.lastname: Luo
authors.forename: Mingmin
authors.initials: M
authors.lastname: Chen
authors.forename: Ayhan
authors.initials: A
authors.lastname: Cinar
authors.forename: Lisa
authors.initials: L
authors.lastname: Ludolph
authors.forename: Maria
authors.initials: M
authors.lastname: Lünnemann
authors.forename: Julia
authors.initials: J
authors.lastname: Goldstein
authors.forename: Anurag Kumar
authors.initials: AK
authors.lastname: Singh
authors.forename: Brigitte
authors.initials: B
authors.lastname: Riederer
authors.forename: Oliver
authors.initials: O
authors.lastname: Bachmann
authors.forename: Andre
authors.initials: A
authors.lastname: Bleich
authors.forename: Markus
authors.initials: M
authors.lastname: Gereke
authors.forename: Dunja
authors.initials: D
authors.lastname: Bruder
authors.forename: Susan
authors.initials: S
authors.lastname: Hagen
authors.forename: Peijian
authors.initials: P
authors.lastname: He
authors.forename: Chris
authors.initials: C
authors.lastname: Yun
authors.forename: Ursula
authors.initials: U
authors.lastname: Seidler
mesh_terms: D000818:Animals; D001706:Biopsy; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003092:Colitis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D003106:Colon / Q000378:metabolism* / Q000473:pathology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D016264:Dextran Sulfate; D004195:Disease Models, Animal; D015536:Down-Regulation; D020895:Enterocytes / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007079:Ileitis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D007082:Ileum / Q000378:metabolism* / Q000473:pathology; D018836:Inflammation Mediators / Q000378:metabolism; D016753:Interleukin-10 / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins; D057507:Mice, 129 Strain; D018345:Mice, Knockout; D008871:Microvilli / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D012189:Retrospective Studies; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C556062:IL10 protein, mouse; D018836:Inflammation Mediators; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C484659:PDZK1 protein, human; C514896:PDZK1 protein, mouse; D012333:RNA, Messenger; C499308:Rag2 protein, mouse; C000613385:SLC9A3 protein, human; C000613386:Slc9a3 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; D016264:Dextran Sulfate