Toll-like receptor (TLR) 2 induced through TLR4 signaling initiated byHelicobacter pyloricooperatively amplifies iNOS induction in gastric epithelial cells

Abstract

Cell-surface Toll-like receptors (TLRs) initiate innate immune responses, such as inducible nitric oxide synthase (iNOS) induction, to microorganisms' surface pathogens. TLR2 and TLR4 play important roles in gastric mucosa infected with Helicobacter pylori (H. pylori), which contains lipopolysaccharide (LPS) as a pathogen. The present study investigates their physiological roles in the innate immune response of gastric epithelial cells to H. pylori-LPS. Changes in the expression of iNOS, TLR2, and TLR4, as well as downstream activation of mitogen-activated protein kinases and nuclear factor-kappaB (NF-kappaB), were analyzed in normal mouse gastric mucosal GSM06 cells following stimulation with H. pylori-LPS and interferon-gamma. Specific inhibitors for mitogen-activated protein kinases, NF-kappaB, and small interfering RNA for TLR2 or TLR4 were employed. The immunohistochemistry of TLR2 was examined in human gastric mucosa. H. pylori-LPS stimulation induced TLR2 in GSM06 cells, but TLR4 was unchanged. TLR2 induction resulted from TLR4 signaling that propagated through extracellular signal-related kinase and NF-kappaB activation, as corroborated by the decline in TLR4 expression on small interfering RNA treatment and pretreatment with inhibitors. The induction of iNOS and the associated nitric oxide production in response to H. pylori-LPS stimulation were inhibited by declines in not only TLR4 but also TLR2. Increased expression of TLR2 was identified in H. pylori-infected human gastric mucosa. TLR4 signaling initiated by H. pylori-LPS and propagated via extracellular signal-regulated kinase and NF-kappaB activation induced TLR2 expression in gastric epithelial cells. Induced TLR2 cooperated with TLR4 to amplify iNOS induction. This positive correlation may constitute a mechanism for stimulating the innate immune response against various bacterial pathogens, including H. pylori-LPS.

Helicobacter pylori Activates Calpain via Toll-Like Receptor 2 To Disrupt Adherens Junctions in Human Gastric Epithelial Cells

“…Infection with H. pylori enhances gastric epithelial expression of TLR2 in vitro and is associated with strongly upregulated apical epithelial expression of TLR2 in human gastric biopsy specimens (43). H. pylori lipopolysaccharide has been shown to activate epithelial TLR2 to stimulate cell proliferation and the production of inflammatory chemokines via induction of mitogen-activated protein kinase (MAPK) (52) and NF-B (36) signaling, respectively.…”

“…In airway epithelia, toll-like receptor 2 (TLR2)-induced calcium fluxes have been shown to mediate bacterially induced calpain activation, leading to cleavage of E-cadherin (8). H. pylori lipopolysaccharide is a TLR2 agonist, and TLR2 expression is strongly upregulated on the apical surface of the gastric mucosa of H. pylori-infected patients and H. pylori-challenged cultured gastric epithelial cells (36,43,52). In light of these findings, we hypothesized that calpain may mediate H. pylori-induced AJ defects and aimed to assess the roles of TLR2 and calpain in H. pyloriinduced AJ disruption using human samples and an in vitro gastric epithelial model.…”

No associations of Toll-like receptor 2 (TLR2) -196 to -174del polymorphism with the risk of Helicobacter pylori seropositivity, gastric atrophy, and gastric cancer in Japanese

“…Some studies have provided strong evidence that TLR4 is expressed by gastric epithelial cells and the LPS of H. pylori is involved in the signaling pathways leading to the production of proinfl ammatory cytokines [20][21][22]; however, some other studies have shown contradictory results; e.g., the study by Smith et al [11] revealed that H. pylori LPS is a TLR2 ligand and not a TLR4 ligand. Later, it was also shown that TLR4 signaling initiated by H. pylori LPS induced TLR2 expression in gastric epithelial cells [23]. For the association between polymorphisms in the TLR genes and the risk of gastric cancer, associations between polymorphisms in the TLR4 gene and the risk of gastric cancer are well documented, although there exists only one report regarding the association between polymorphisms in the TLR2 gene and the risk of gastric cancer [12].…”

Toll-Like Receptors are Associated with Helicobacter pylori Infection and Gastric Mucosa Pathology

“…For example, in addition to monocyte differentiation antigen (CD14) and myeloid differentiation protein (MD-2), TLR4 can interact with LPS, and this interaction induces signal transduction pathways that activate NF-κB and cause the expression of several cytokines, including TNF-α, IL-1β, IL-6 and IL-12 (29). Additionally, TLR2 induces cell proliferation and TLR4 activation expression via the MEK1/2-ERK/2 pathway (13,30).…”