Let-7b Is Involved in the Inflammation and Immune Responses Associated with Helicobacter pylori Infection by Targeting Toll-Like Receptor 4

Abstract

ObjectivesToll-like receptors (TLRs) are important initiators in native immune responses to microbial infections. TLR4 is up-regulated in response to H.pylori infection in gastric epithelial cells. However, the regulatory mechanisms for the expression of TLR4 in H.pylori infection have not been clearly defined. The aims of this study are to present the evidence that microRNA let-7b directly regulates TLR4 expression in human gastric epithelial cells, and subsequently influences the activation of NF-κB and the expression of the downstream genes in H.pylori infection.MethodsThe expression of let-7b was determined in gastric mucosa specimens and in two gastric epithelial cell lines using quantitative RT-PCR. The expression of TLR4 was determined by immunohistochemistry staining and RT-PCR. The potential target of let-7b was identified by luciferase reporter assay and Western blot. Let-7b mimics and inhibitors were used to examine the effects of let-7b on NF-κB activity. The expression of the downstream genes of NF-κB was also determined in cells infected with H.pylori 26695.ResultsLet-7b was significantly decreased in gastric mucosa specimens and in gastric epithelial cell lines (AGS, GES-1) infected with H.pylori 26695 (cagA+). Let-7b was complementary to the 3′-UTR of TLR4 mRNA and regulated TLR4 expression via post-transcriptional suppression in gastric epithelium. Infection of H.pylori induced the expression of TLR4 and activated NF-κB in AGS and GES-1 cells. Overexpression of let-7b by mimics downregulated TLR4, and subsequently attenuated NF-κB, MyD88, NF-κB1/p50, RelA/p65. The expression of IL-8, COX-2 and CyclinD1 was inhibited in H.pylori infected cells with let-7b overexpression. Both TAK-242 (TLR4 inhibitor) and SN50 (NF-κB inhibitor) significantly inhibited the H.pylori induced downregulation of let-7b.ConclusionsLet-7b targets at TLR4 mRNA, and regulates the activation of NF-κB and the expression of the downstream genes related to the inflammation and immune responses in H.pylori infection.

Altered gene expression and possible immunodeficiency in cases of sudden infant death syndrome

“…After this activation, a significant downregulation of MyD88-mRNA occurs, probably to limit the extent and duration of the inflammation. In a study of Helicobacter Pylori in humans, postinfection negative regulation of inflammation was achieved by downregulation of MyD88 through the upregulation of the miRNA Let-7b (14). Interestingly, Let-7b is reported to be upregulated in the brains of SIDS infants (15).…”

Faecal microRNAs: indicators of imbalance at the host-microbe interface?

“…Mmu-let-7b-3p has also been shown to mediate the epithelial innate immune response via TLR signalling (Hu et al, 2009). Furthermore, let-7b is also known to target Tlr4 and regulates the activation of NF-κB and the expression of downstream genes related to immune responses in Helicobacter pylori infection (Teng et al, 2013) while also binding to the Muc1 gene in epithelial cells (Inyawilert et al, 2015). miR-141-3p is expressed in immune cells (natural killer cells, leukocytes) and both inflamed and noninflamed epithelial cells in the small and large intestine (Lee et al, 2015).…”

MicroRNA let-7 Modulates the Immune Response to Mycobacterium tuberculosis Infection via Control of A20, an Inhibitor of the NF-κB Pathway

“…Expectedly, the level of pre-let-7f was also reduced in Mtb-infected compared to uninfected cells ( Figures S2E and S2F). Several reports have pointed to a role of let-7 family members in the immune response to pathogens Teng et al, 2013). It therefore appeared likely that the differential regulation of let-7f influences the immune response to Mtb infection.…”