Classical and Alternative Pathway Nuclear Factor-κB Signalling Differentially Regulate Gastric Epithelial Responses to Helicobacter felis Infection

Abstract

Introduction Classical pathway NF-κB signalling is implicated in the pathogenesis of several inflammation associated cancers, including colitis associated colon cancer and Helicobacter associated gastric cancer. However, the role of individual NF-κB family members and the function of alternative pathway NF-κB signalling have not previously been assessed in this context. We have therefore investigated whether abrogation of classical and alternative pathway NF-κB signalling altered murine responses to Helicobacter felis infection. Methods 6-week-old female NF-κB1 null (p50-/-), NF-κB2 null (p52-/-), c-Rel null and C57BL/6 mice were infected with H. felis by oral gavage and culled 6 weeks later. Tissues were processed for histological analysis and immunohistochemistry. Results H. felis infection of wild-type mice resulted in gastric atrophy (29% fewer parietal cells were observed in infected than in control mice (p < 0.05, 1-way ANOVA and Holm Sidak post hoc test)), a 1.5-fold increase in the number of Ki67 positive proliferating cells and no significant change in the number of active caspase 3 positive apoptotic cells. Animals with abrogated classical pathway NF-κB signalling also developed gastric atrophy after H. felis infection. However, whereas infected c-Rel null animals showed similar parietal cell, proliferation and apoptotic indices to infected wild-type mice, p50-/- animals developed more severe pathology with significantly increased inflammation scores (p < 0.05, Mann–Whitney U) and a more marked 62% reduction in parietal cell number (p < 0.05, 1-way ANOVA). This was associated with significant 2.1-fold and 7.6-fold increases in the number of proliferating and apoptotic cells, respectively (p < 0.05, 2-way ANOVA). By contrast, infected p52-/- mice showed much lower inflammation scores than wild-type mice (p < 0.05, MWU) following H. felis infection and did not develop gastric atrophy, with only 3% parietal cell loss (p < 0.05, 1-way ANOVA). In addition, these mice showed no significant changes in proliferation or apoptosis following infection with H. felis , and demonstrated similar proliferation and apoptotic indices to untreated wild-type mice. Conclusion NF-κB1 mediated signalling protects the gastric mucosa from Helicobacter induced atrophy, whereas alternative pathway NF-κB signalling is required for the development of both inflammation and atrophy following infection with this organism. This supports the hypothesis that classical and alternative pathway signalling differentially affect long-term outcomes, including carcinogenesis, following H. felis infection in C57BL/6 mice.