Reduced NHE3-mediated Na⁺ absorption increases survival and decreases the incidence of intestinal obstructions in cystic fibrosis mice

Abstract

In cystic fibrosis, impaired secretion resulting from loss of activity of the cystic fibrosis transmembrane conductance regulator (CFTR) causes dehydration of intestinal contents and life-threatening obstructions. Conversely, impaired absorption resulting from loss of the NHE3 Na+/H+ exchanger causes increased fluidity of the intestinal contents and diarrhea. To test the hypothesis that reduced NHE3-mediated absorption could increase survival and prevent some of the intestinal pathologies of cystic fibrosis, Cftr/Nhe3 double heterozygous mice were mated and their offspring analyzed. Cftr-null mice lacking one or both copies of the NHE3 gene exhibited increased fluidity of their intestinal contents, which prevented the formation of obstructions and increased survival. Goblet cell hyperplasia was eliminated, but not the accumulation of Paneth cell granules or increased cell proliferation in the crypts. Microarray analysis of small intestine RNA from Cftr-null, NHE3-null, and double-null mice all revealed downregulation of genes involved in xenobiotic metabolism, including a cohort of genes involved in glutathione metabolism. Expression of energy metabolism genes was altered, but there were no changes in genes involved in inflammation. Total intracellular glutathione was increased in the jejunum of all of the mutants and the ratio of reduced to oxidized glutathione was reduced in Cftr-null mutants, indicating that CFTR deficiency affects intestinal glutathione metabolism. The data establish a major role for NHE3 in regulating the fluidity of the intestinal contents and show that reduced NHE3-mediated absorption reverses some of the intestinal pathologies of cystic fibrosis, thus suggesting that it may serve as a potential therapeutic target.

The epithelial sodium/proton exchanger, NHE3, is necessary for renal and intestinal calcium (re)absorption

“…Genotyping was performed by PCR as described (11). Standard pelleted chow (PicoLab Rodent Diet 5053; 20% wt/wt protein, 4.5% wt/wt fat, 0.81% wt/wt calcium, 1.07% wt/wt potassium, 0.30% wt/wt sodium; and 2.2 IU/g vitamin D3) and drinking water were available ad libitum.…”

AE2 Cl−/HCO3−exchanger is required for normal cAMP-stimulated anion secretion in murine proximal colon

“…Segments of the intestinal tract of mice ϳ18 days old (n ϭ 3) were processed and stained with Alcian blue and periodic acid-Schiff as described previously (6). With this procedure, acidic mucins stain blue and neutral mucins stain magenta.…”

“…RNA extractions were performed by using TRI Reagent (Molecular Research Center, Cincinnati, OH) according to the manufacturer's protocol with one extra extraction and two extra precipitation steps. Microarrays spotted with 70-mer oligonucleotides were hybridized with cDNA samples labeled with Cy3 and Cy5 fluorophores by the University of Cincinnati Genomics and Microarray Laboratory core facility, and statistical analyses of the resulting data were performed exactly as previously described (6). The data and experimental details have been deposited in GEO (#GSE19075).…”

The Cystic Fibrosis Intestine

“…Use of talniflumate (LoMucin), a pharmacological agent that inhibits Cl 2 / HCO 3 2 exchange involved in intestinal NaCl absorption, improved survival of CF mice and tended to reduce mucus accumulation (Walker et al 2005). Similarly, loss of NaCl absorption mediated by NHE in the intestine reduced the incidence of intestinal obstruction in CF mice (Bradford et al 2009). …”