The Sodium/Hydrogen Exchanger 2 (Slc9a2/NHE2) is Involved in the Differentiation of Colonic Intestinal Epithelial Cells

Abstract

BackgroundBoth sodium/hydrogen exchanger 2 and 3 (NHE2 and NHE3) isoforms of the Slc9 family Na+/H+ exchangers are expressed in the luminal membrane of the intestinal enterocytes, but in contrast to the deletion of NHE3, the deletion of NHE2 does not result in diarrhea, hyperaldosteronism, or reduced survival in mice.Aim and methodsTo further analyze the physiological role of NHE2 in the intestinal epithelial cells, we fluorometrically measured the intracellular pH (pHi) along the colonic cryptal axis of NHE2−/− mice, and in the intestinal epithelial Caco 2Bbe (C2Bbe) after stable lentiviral sh‐mediated NHE2 silencing. RNA and protein expression were assessed by qPCR, Western analysis and immunohistochemistry, and proliferative, migratory, and functional features of colonic cells in vivo and in vitro were assessed by enzymatic and functional assays.ResultsSteady‐state pHI was significantly decreased in C2Bbe/shNHE2 compared to empty‐vector transfected C2Bbe cells. In the colonic crypts, the pHi in the cryptal base was significantly lower than in the surface region, and the acidic zone along the crypt axis was significantly longer in colonic crypts from NHE2−/− mice. NHE2−/− colonic crypts were elongated with a much longer proliferation zone but with less proliferating cells per crypt area. Cell proliferation in C2Bbe/shNHE2 cells was reduced compared to empty‐vector transfected C2Bbe. The expression and activity of alkaline phosphatase (an enterocyte differentiation marker), was significantly reduced in NHE2−/− colonic mucosa and in C2Bbe/shNHE2 cells. However, the number of goblet cells and mucin 2 (Muc2) expression was increased in the NHE2−/− compared to the WT colon, accompanied by formation of a thicker mucus layer. The shift from absorptive to secretory differentiation program was accompanied by a decrease in Hes1 expression, as a downstream transcription factor of Notch signaling that supports the development of absorptive enterocytes.ConclusionsThe results suggest that NHE2 expression and/or function is activated when the intestinal cells emerge from the stem cell niche, and that this is essential for the establishment of the pHi gradient along the colonic crypt axis. Its activity facilitates enterocyte proliferation and differentiation along the crypt axis.Support or Funding InformationVolkswagen Foundation (VW‐Vorab), SFB621/C9, Se460/9‐4 and 21‐1.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.