Cytokine-dependent transcriptional down-regulation of epithelial sodium channel in ulcerative colitis.
OBJECTIVE
The main limiting factor for sodium absorption in distal colon is the amiloride-sensitive epithelial sodium channel (ENaC). This study aimed to characterize mechanisms involved in the dysregulation of ENaC expression in ulcerative colitis (UC).


METHODS
Epithelial preparations from surgically removed inflamed and control sigmoid colons were used. Active electrogenic Na(+) transport (J(Na)) was determined after 8-hour aldosterone stimulation in Ussing-chambers (corrected for the altered epithelial/subepithelial resistance ratio). Subsequently, ENaC alpha-, beta-, and gamma-subunits were analyzed immunohistochemically and in Western and Northern blots (corrected for the inflammatory increase in subepithelial protein content). To study gene regulation, the promoters of beta- and gamma-ENaC were analyzed in reporter gene assays.


RESULTS
In controls, aldosterone stimulated J(Na) and induced ENaC beta- and gamma-subunit expression, whereas this response was virtually abolished in UC. Preservation of surface epithelium in UC was indicated by unchanged ENaC alpha-subunit expression, which points also against a mere immaturity or epithelial cell loss. Inhibition of electrogenic sodium transport as well as beta- and gamma-ENaC mRNA expression could be mimicked in control colon by in vitro preexposure for 8 hours to tumor necrosis factor alpha and interferon gamma. Promoter analysis revealed that down-regulation of beta- and gamma-ENaC gene expression was primarily induced by tumor necrosis factor alpha.


CONCLUSIONS
We conclude that, in UC, elevated proinflammatory cytokines selectively impair beta- and gamma-ENaC expression, which contributes to diarrhea by reducing colonic sodium absorption.
Amasheh
Salah
S
Department of Clinical Physiology, Campus Benjamin Franklin, Charité-University Medicine Berlin, Hindenburgdamm 30, 12200 Berlin, Germany.
Barmeyer
Christian
C
Koch
Corinna Swanette
CS
Tavalali
Shida
S
Mankertz
Joachim
J
Epple
Hans-Jörg
HJ
Gehring
Maren Melanie
MM
Florian
Peter
P
Kroesen
Anton-Josef
AJ
Zeitz
Martin
M
Fromm
Michael
M
Schulzke
Jörg-Dieter
JD
D000970:Antineoplastic Agents / Q000494:pharmacology; D003093:Colitis, Ulcerative / Q000276:immunology / Q000473:pathology / Q000503:physiopathology*; D003106:Colon / Q000187:drug effects / Q000473:pathology; D003967:Diarrhea / Q000276:immunology / Q000473:pathology / Q000503:physiopathology; D015536:Down-Regulation; D053503:Epithelial Sodium Channels; D006801:Humans; D007150:Immunohistochemistry; D007371:Interferon-gamma / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D018161:Receptors, Mineralocorticoid / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D000970:Antineoplastic Agents; D053503:Epithelial Sodium Channels; D012333:RNA, Messenger; D018161:Receptors, Mineralocorticoid; C507048:SCNN1B protein, human; D015222:Sodium Channels; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D012964:Sodium