Suppressed apoptosis in the inflamed gastric mucosa of Helicobacter pylori-colonized iNOS-knockout mice.
Deregulated cell turnover in Helicobacter pylori (H. pylori)-colonized gastric mucosa has been suggested to be linked to the gastric carcinogenesis pathway. We previously reported attenuation of apoptosis and enhancement of cellular proliferation in the H. pylori-colonized gastric mucosa of Mongolian gerbils as compared to that in mice, which might reflect a specific link between H. pylori colonization and carcinogenesis in the Mongolian gerbils; the difference between the two strains could be attributable to differences in the host genetic background. Inducible-type nitric oxide synthase (iNOS) is thought to participate in not only the inflammatory response, but also in the regulation of gastric mucosal cell turnover in H. pylori-colonized gastric mucosa. Thus, the present study was designed to examine gastric leukocyte activation and epithelial cell apoptosis in the gastric mucosa following H. pylori inoculation in iNOS-knockout mice.


METHODS
iNOS-knockout mice (iNOS(-/-)) and their iNOS(+/+) littermates were orally inoculated with the Sydney strain of H. pylori (SS1, 10(8) colony-forming units [CFU]). H. pylori infection was confirmed by microaerobic bacterial culture. The stomach of each mouse was evaluated 14 weeks and 30 weeks after the inoculation. Gastric mucosal accumulation of polymorphonuclear leukocytes (PMN) was assessed by determining the myeloperoxidase (MPO) activity and histological score based on the updated Sydney system. The level of apoptosis was determined by estimation of the cytoplasmic levels of mono- and oligonucleosomes and by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling method.


RESULTS
The SS1-inoculated mice showed persistent H. pylori colonization for 12 weeks. While gastric mucosal PMN infiltration increased following SS1 inoculation in both iNOS(+/+) and iNOS(-/-)strains, enhanced DNA fragmentation was observed in only SS1-colonized iNOS(+/+) mice, and not in the iNOS(-/-) mice. In conclusion, although the recruitment of PMN in response to H. pylori was evoked even in the gastric mucosa of iNOS(-/-) mice, epithelial cell apoptosis induced by H. pylori was attenuated in this strain. These data suggest that iNOS may play an important role in promoting apoptosis in the H. pylori-infected inflamed gastric mucosa, and that persistent inflammation without apoptosis in iNOS(-/-) mice with H. pylori infection may be linked to preneoplastic transformation.
Miyazawa
Masaharu
M
Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan.
Suzuki
Hidekazu
H
Masaoka
Tatsuhiro
T
Kai
Akemi
A
Suematsu
Makoto
M
Nagata
Hiroshi
H
Miura
Soichiro
S
Ishii
Hiromasa
H
D000818:Animals; D017209:Apoptosis; D002455:Cell Division; D005753:Gastric Mucosa / Q000201:enzymology / Q000382:microbiology / Q000473:pathology*; D005756:Gastritis / Q000201:enzymology / Q000382:microbiology / Q000473:pathology*; D016481:Helicobacter Infections / Q000201:enzymology / Q000382:microbiology / Q000473:pathology*; D016480:Helicobacter pylori / Q000502:physiology; D020287:In Situ Nick-End Labeling; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009504:Neutrophils / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II; D009573:Nitrites / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism; D011230:Precancerous Conditions / Q000473:pathology; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism
D009566:Nitrates; D009573:Nitrites; D018809:Proliferating Cell Nuclear Antigen; D009195:Peroxidase; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse