Activation of alternative NF-kB signaling in the stomach: link to H. pylori virulence factors and effect on gastric inflammation and gastric pathogenesis
Gastroenterology
Cell Biology
Final Report Abstract
H. pylori infection is the main risk factor for gastric cancer development. The immune response elicited by H. pylori is extremely complex and different signalling pathways are activated and contribute to malignant transformation of the gastric epithelium. NF-ĸB is one of the best studied signalling cascades in this context. However, little was known about the alternative or non-canonical arm of the NF-ĸB pathway. We observed that non-canonical NF-ĸB is activated in the stomach of subjects presenting with different degree of inflammation associated with H. pylori infection. Moreover, upregulation of the pathway was detected in gastric tumours. These observations suggested an important role for this pathway in H. pylori-induced gastric pathology. In a next step, we focused on elucidating the molecular mechanism leading to activation of non-canonical NF-ĸB in response to the infection. We observed high levels of the ligands LTα and LTβ in the gastric mucosa of H. pylori-infected individuals, and confirmed by different experimental approaches that epithelial cells express LT in response to H. pylori infection. This occurs in a secondary loop first involving the activation of the canonical arm. Thus, activation of canonical NF-ĸB induces the expression of LT, which activates non-canonical NF-ĸB through LTβR. For this, the presence an intact type IV secretion system in H. pylori is essential. The involvement of LTβR signalling in H. pylori-induces gastric inflammation was confirmed in vivo by scavenging the ligands during infection in mice. Together, we identified a novel signalling pathway orchestrating the immune response to H. pylori. Although our results confirmed an important role of non-canonical NF-ĸB during H. pylori infection, with our animal model we could not establish a clear link to carcinogenesis, since mice did not develop pre-cancerous lesions or gastric tumors. Therefore, we employed the signalling in MyD88 knockout mice upon Helicobacter felis infection. These mice develop severe gastric pathology, which we could link to activated non-canonical NF-ĸB and up-regulated expression of an alternative ligand of the pathway, LIGHT. Since many of our results were based on immortalized cells, we established gastric organoids to study non-canonical NF-ĸB pathway in a more physiological model. We conformed here that the pathway is activated in response to H. pylori infection. More importantly, we have observed that stimulation of organoids with LT or LIGHT leads to increased proliferation in a subset of samples. We are currently trying to identify differential expressed genes between responders and non-responders in order to determine which factors render gastric cells susceptible to non-canonical NF-ĸB stimulation. The role of non-canonical NF-ĸB signalling in gastric carcinogenesis is being further explored using cells where the expression of NIK, a central kinase of the pathway, has been knocked down. Finally, we have established a mouse model expressing LT specifically in the stomach. These mice present alterations in cell proliferation that are exacerbated upon H. pylori infection. Together, our results indicate that non-canonical NF-ĸB signalling pathway is a major contributor to H. pylori-induced gastritis and gastric carcinogenesis. This can eventually have important clinical implications since blocking of the pathway might be considered as a treatment strategy for a subset of gastric cancer patients.
Publications
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Lymphotoxin β receptor signalling executes Helicobacter pylori-driven gastric inflammation in a T4SS-dependent manner. Gut. 2017 Aug;66(8):1369-1381
Mejías-Luque R, Zöller J, Anderl F, Loew-Gil E, Vieth M, Adler T, Engler DB, Urban S, Browning JL, Müller A, Gerhard M, Heikenwalder M
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Increased LIGHT expression and activation of non-canonical NF-κB are observed in gastric lesions of MyD88-deficient mice upon Helicobacter felis infection. Sci Rep. 2019 May 7;9(1):7030
Mejías-Luque R, Lozano-Pope I, Wanisch A, Heikenwälder M, Gerhard M, Obonyo M
