Altered ENaC expression leads to impaired sodium absorption in the noninflamed intestine in Crohn's disease.
OBJECTIVE
Crohn's disease (CD) is a chronic inflammatory bowel disease. In this study, we have investigated sodium absorption via epithelial sodium channels (ENaC) in the macroscopically noninflamed colon in active CD.


METHODS
Sodium transport via ENaC was investigated in Ussing chambers using biopsy specimens of sigmoid colon from controls and active CD limited to the small intestine. ENaC messenger RNA expression and subcellular localization were studied by real-time polymerase chain reaction and confocal microscopy. Effects of proinflammatory cytokines on ENaC and signaling via mitogen-activated protein kinases were investigated in rat distal colon. Therapeutic inhibition of mitogen-activated protein kinases was studied in CD biopsy specimens.


RESULTS
Electrogenic sodium absorption via ENaC was strongly impaired in the macroscopically noninflamed CD colon because of reduced gamma-ENaC transcription, whereas subcellular localization of ENaC was not changed. In contrast to impaired epithelial sodium transport, epithelial barrier function was not altered in noninflamed CD colon, indicating that paracellular leak flux of ions did not contribute to decreased sodium absorption. Exposure of rat distal colon to tumor necrosis factor alpha led to reduced electrogenic sodium absorption because of impaired transcriptional gamma-ENaC induction, which resembled the changes found in CD. Tumor necrosis factor alpha effects were dependent on extracellular signal-regulated kinase 1/2 but not p38 or c-Jun-N-terminal kinase because inhibition of mitogen-activated protein kinase/extracellular regulated kinase (MEK)1/2 but not inhibition of p38 or c-Jun-N-terminal kinase prevented suppression of ENaC. Finally, therapeutic inhibition of MEK1/2 restored electrogenic sodium absorption in CD.


CONCLUSIONS
In CD, macroscopically noninflamed colon contributes to diarrhea via impaired ENaC-mediated sodium absorption. Inhibition of extracellular signal-regulated kinase might serve as a potential therapeutic strategy for CD diarrhea.
Zeissig
Sebastian
S
Department of Gastroenterology, Infectious Diseases, and Rheumatology, Charité, Campus Benjamin Franklin, Berlin, Germany.
Bergann
Theresa
T
Fromm
Anja
A
Bojarski
Christian
C
Heller
Frank
F
Guenther
Ute
U
Zeitz
Martin
M
Fromm
Michael
M
Schulzke
Jörg-Dieter
JD
D000328:Adult; D000818:Animals; D001706:Biopsy; D015153:Blotting, Western; D003106:Colon / Q000166:cytology / Q000502:physiology*; D003424:Crohn Disease / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D053503:Epithelial Sodium Channels / Q000096:biosynthesis / Q000235:genetics*; D005260:Female; D005500:Follow-Up Studies; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D007408:Intestinal Absorption / Q000502:physiology*; D017136:Ion Transport / Q000502:physiology; D008297:Male; D008875:Middle Aged; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D018408:Patch-Clamp Techniques; D012313:RNA / Q000235:genetics*; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000378:metabolism*; D013057:Spectrum Analysis; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
D053503:Epithelial Sodium Channels; D014409:Tumor Necrosis Factor-alpha; D012313:RNA; D012964:Sodium; D048052:Mitogen-Activated Protein Kinase 3