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Acta Physiologica 2009; Volume 195, Supplement 669
The 88th Annual Meeting of The German Physiological Society
3/22/2009-3/25/2009
Giessen, Germany
DOWNREGULATION OF NA+/H+ EXCHANGER ISOFORM 3 (NHE3) FUNCTION, BUT NOT EXPRESSION, IN COLONIC MUCOSA OF PATIENTS WITH ULCERATIVE COLITIS MAY BE RELATED TO LOSS OF PDZK1 ADAPTOR PROTEIN EXPRESSION
Abstract number: P173
Yeruva1 S., Farkas2 K., Schroeder1 K., Hubricht1 J., Riederer1 B., Bachmann1 O., Rakonczay2 Z., Molnar2 T., Nagy2 F., Wedemeyer1 J., Raddatz3 D., Hegyi2 P., Seidler1 U.
1Dept. Of. Gastroenterology, Hepatology and endocrinology, Hannover medical School, Hannover
2First Department of Medicine, University of Szeged, Szeged, Hungary
3Dept. Of. Gastroenterology, University clinic Goettingen, Gttingen
Background and aims:
A major causative factor of diarrhoea in Ulcerative Colitis (UC) and Crohn's disease patients is the loss of Na+ absorptive capacity of the inflamed colonic mucosa. Previous experiments in the IL-10 ko model of intestinal inflammation showed that in the chronic stage, NHE3 mRNA and protein expression was normal but transport activity and regulation severely decreased. We wanted to study NHE3 expression, localization on the brush border membrane, and functional activity in anatomically and histologically defined pool of mucosal biopsies from UC patients.
Methods:
In biopsies of patients with the histological grade "active UC of moderate severity", and healthy controls, we investigated the mRNA expression levels of NHE3, PDZK1, NHERF1 (NHE3-binding adapter proteins), TNF-a, villin, as well as other housekeeping genes by real-time PCR, the brush border membrane localisation of NHE3 by immunohistochemistry and confocal microscopy, the Na+ absorptive capacity by 22Na+ isotope fluxes in mini-Ussing chambers, and the NHE3 activity microfluorometrically in BCECF-loaded NHE3 expressing surface colonocytes within isolated crypts.
Results:
In moderately inflamed sigmoid colon of UC patients, neither NHE3 mRNA expression nor the abundance of NHE3 in the brush border membrane was significantly altered compared to healthy controls. The expression of PDZK1 was reduced to 20% of the levels in healthy controls, whereas NHERF1 mRNA expression was unaltered. Active Na+ absorption was strongly reduced in mucosal tissue from UC patients and acid-activated NHE3 transport activity were significantly decreased in the surface cells of colonic crypts.
Discussion/Conclusion:
In the moderately inflamed sigmoid colon of UC patients, NHE3 expression and brush border membrane localization was unaltered, but its transport activity was decreased. Based on the observations in PDZK1 knockdown cells, we believe that the severe downregulation of the NHE3-binding PDZ protein PDZK1 is a major factor causing the NHE3 dysfunction. This may in part explain the disturbed salt and fluid absorptive capacity of the colonic mucosa of inflammatory bowel disease patients.
To cite this abstract, please use the following information:
Acta Physiologica 2009; Volume 195, Supplement 669 :P173