Helicobacter pyloriinduces apoptosis of rat gastric parietal cells

Abstract

Gastric Helicobacter pylori infection may lead to multifocal atrophic corpus gastritis associated with loss of epithelial cells as well as glandular structures. The current work investigated H. pylori effects on cell death of isolated, nontransformed rat parietal cells (PC). Highly enriched rat PC (>97%) were isolated from gastric mucosa and cultured in serum-free medium over 24 h. The cells were cocultured over 8 h with cytotoxin-associated immunodominant protein (cagA)+/vacuolating toxin (vacA)+or with cagA−/vacA−H. pylori laboratory strains and also with H. pylori mutants deleted in several genes of the cag pathogenicity island. Staphylococcus aureus or Campylobacter jejuni were used as controls. Apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and electron microscopy. Interleukin (IL)-8 and cytokine-induced neutrophil chemoattractant (CINC)-1 secretion was measured by ELISA. Activation of nuclear factor-κB (NF-κB) was studied in nuclear extracts of PC by electrophoretic mobility shift assay. Apoptosis of PC was induced in a concentration- and time-dependent manner by cagA+/vacA+H. pylori strains but not by cagA−/vacA−negative strains or by the cagE knockout mutant. S. aureusand C. jejuni had no effect. PC showed no IL-8 or CINC-1 secretion on exposure to cagA+/vacA+H. pylori. cagA+/vacA+strains induced activation of NF-κB complexes in nuclear extracts of PC, which were composed of p65 and p50 subunits. No significant stimulation of NF-κB activation was detected by incubation of PC with the cagE knockout mutant. Preincubation of PC with antisense but not missense oligodeoxynucleotides against the p65 subunit significantly reduced DNA binding to the κB recognition sequence. The p65 oligonucleotides as well as the proteasome inhibitor N-CBZ-isoleucin-glutamin-(o-t-butyl-)-alanin-leucin and the nitric oxide synthase inhibitor NG-monomethyl-l-arginine completely prevented PC apoptosis induced by cagA+/vacA+strains. In summary, cagE presence appears to be essential for H. pylori-induced apoptosis of gastric parietal cells, and this effect is dependent on the activation of NF-κB and production of nitric oxide.