Severe downregulation of the NHE3 adapterprotein PDZK1 (NHERF3) in colonic mucosa of patients with active IBD – Implications for the dysregulation of salt and water transport

K. Schröder; B. Riederer; O. Bachmann; K. Franke; H. Lenzen; C. Meyer; J. Wedemeyer; M. P. Manns; U. Seidler

doi:10.1055/s-2007-988421

Zeitschrift für Gastroenterologie, Inhaltsverzeichnis

Severe downregulation of the NHE3 adapterprotein PDZK1 (NHERF3) in colonic mucosa of patients with active IBD – Implications for the dysregulation of salt and water transport

K Schröder ¹, B Riederer ¹, O Bachmann ¹, K Franke ¹, H Lenzen ¹, C Meyer ¹, J Wedemeyer ¹, MP Manns ¹, U Seidler ¹

¹Hannover Medical School, Dept. Of Gastroenterology, Hepatology and Endocrinology, Hannover, Germany

Abstract

Aims: Acute flares of UC (ulcerative colitis) an CD (Crohn's disease) are often accompanied by severe diarrhea. A major causative factor is the complete loss of sodium absorptive capacity of the inflamed colonic mucosa of patients with acute UC or CD. Intestinal cell lines incubated with TNFα and IFNγ showed downregulation of the major transport protein for intestinal salt absorption, the Na+/H+ exchanger isoform 3 (NHE3) mRNA expression, but surprisingly, we did not find this in the colon of mouse models for IBD. We found, however, a severe downregulation of the NHE3 adapter protein PDZK1 (NHERF3), which is a major regulator of intestinal NHE3 transport activity (Hillesheim 2007, Cinar et al. 2007, Lamprecht et al. 2006).

Aim: To investigate the mRNA expression levels of NHE3, PDZK1, NHERF1 (another NHE3-binding adapter protein), the proinflammatory cytokine TNFα, the integral brush border membrane protein villin, and several control genes in colonic mucosa of patients with active UC and CD and healthy controls.

Methods: Biopsies were taken from the colon of patients with UC and CD and appropriate controls. mRNA levels for the respective genes were quantified by real-time PRC. Biopsies from the same area were sent for histology, and the degree of inflammation was graded.

Results:

1. We found villin to be the optimal internal control for an epithelial-specific gene with minimal changes of expression levels during inflammation.

2. mRNA expression levels for TNFα were elevated in mucosa from IBD patients compared to controls.

3. NHE3 mRNA expression was not significantly altered in any part of the inflamed colon and any stage of inflammation.

4. PDZK1 mRNA expression levels were significantly lower in inflamed mucosa in both UC and CD patients, and inversely correlated with the degree of inflammation.

5. The enterocyte exression levels of NHERF1, another PDZ adapter protein of the same family, were not different between inflamed and normal mucosa.

Discussion/conclusion: In the inflamed colonic mucosa of patients with IBD, expression levels for the transport protein for electroneutral salt absorption, NHE3, are not altered, but there is a severe downregulation of the NHE3 adapter protein PDZK1.