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G-protein coupled receptor 35 (GPR35) regulates the colonic epithelial cell response to enterotoxigenic Bacteroides fragilis.

ABSTRACT: G protein-coupled receptor (GPR)35 is highly expressed in the gastro-intestinal tract, predominantly in colon epithelial cells (CEC), and has been associated with inflammatory bowel diseases (IBD), suggesting a role in gastrointestinal inflammation. The enterotoxigenic Bacteroides fragilis (ETBF) toxin (BFT) is an important virulence factor causing gut inflammation in humans and animal models. We identified that BFT signals through GPR35. Blocking GPR35 function in CECs using the GPR35 antagonist ML145, in conjunction with shRNA knock-down and CRISPRcas-mediated knock-out, resulted in reduced CEC-response to BFT as measured by E-cadherin cleavage, beta-arrestin recruitment and IL-8 secretion. Importantly, GPR35 is required for the rapid onset of ETBF-induced colitis in mouse models. GPR35-deficient mice showed reduced death and disease severity compared to wild-type C57Bl6 mice. Our data support a role for GPR35 in the CEC and mucosal response to BFT and underscore the importance of this molecule for sensing ETBF in the colon.

SUBMITTER: Boleij A

PROVIDER: S-EPMC8121840 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Consumption of a Western-type diet has been linked to gut-microbiota-mediated colon inflammation that constitutes a risk factor for colorectal cancer. A high salt diet (HSD) exacerbates IL-17A-induced inflammation in inflammatory bowel disease and other autoimmune diseases. Enterotoxigenic Bacteroides fragilis (ETBF) is a gut commensal bacterium and reported to be a potent initiator of colitis via secretion of the Bacteroides fragilis toxin (BFT). BFT induces ectodomain cleavage of E-cadherin in colonic epithelial cells, consequently leading to cell rounding, epithelial barrier disruption, and the secretion of IL-8, which promotes tumorigenesis in mice via IL-17A-mediated inflammation. A HSD is characteristic of the Western-type diet and can exhibit inflammatory effects. However, a HSD induces effects in ETBF-induced colitis and tumorigenesis remain unknown. In this study, we investigated HSD effects in ETBF-colonized mice with azoxymethane (AOM)/dextran sulfate sodium (DSS)-induced tumorigenesis as well as ETBF colitis mice. Unexpectedly, ETBF-infected mice fed a HSD exhibited decreased weight loss and splenomegaly and reduction of colon inflammation. The HSD significantly decreased the expression of IL-17A and inducible nitric oxide synthase (iNOS) in the colonic tissues of ETBF-infected mice. In addition, serum levels of IL-17A and nitric oxide (NO) were also diminished. However, HT29/C1 colonic epithelial cells treated with sodium chloride showed no changes in BFT-induced cellular rounding and IL-8 expression. Furthermore, HSD did not affect ETBF colonization in mice. In conclusion, HSD decreased ETBF-induced tumorigenesis through suppression of IL-17A and iNOS expression in the colon. HSD also inhibited colonic polyp numbers in the ETBF-infected AOM/DSS mice. Taken together, these findings suggest that a HSD consumption inhibited ETBF-promoted colon carcinogenesis in mice, indicating that a HSD could have beneficial effects under certain conditions.

Project description:Enterotoxigenic Bacteroides fragilis (ETBF) strains, which produce a 20-kDa zinc metalloprotease toxin (BFT), have been associated with diarrheal disease in animals and young children. Studying a collection of ETBF and nontoxigenic B. fragilis (NTBF) strains, we found that bft and a second metalloprotease gene (mpII) are contained in an approximately 6-kb pathogenicity island (termed B. fragilis pathogenicity island or BfPAI) which is present exclusively in all 113 ETBF strains tested (pattern I). Of 191 NTBF strains, 100 (52%) lack both the BfPAI and at least a 12-kb region flanking BfPAI (pattern II), and 82 of 191 NTBF strains (43%) lack the BfPAI but contain the flanking region (pattern III). The nucleotide sequence flanking the left end of the BfPAI revealed a region with the same organization as the mobilization region of the 5-nitroimidazole resistance plasmid pIP417 and the clindamycin resistance plasmid pBFTM10, that is, two mobilization genes (bfmA and bfmB) organized in one operon and a putative origin of transfer (oriT) located in a small, compact region. The region flanking the right end of the BfPAI contains a gene (bfmC) whose predicted protein shares significant identity to the TraD mobilization proteins encoded by plasmids F and R100 from Escherichia coli. Nucleotide sequence analysis of one NTBF pattern III strain (strain I-1345) revealed that bfmB and bfmC are adjacent to each other and separated by a 16-bp GC-rich sequence. Comparison of this sequence with the appropriate sequence of ETBF strain 86-5443-2-2 showed that in this ETBF strain the 16-bp sequence is replaced by the BfPAI. This result defined the BfPAI as being 6,036 bp in length and its precise integration site as being between the bfmB and bfmC stop codons. The G+C content of the BfPAI (35%) and the flanking DNA (47 to 50%) differ greatly from that reported for the B. fragilis chromosome (42%), suggesting that the BfPAI and its flanking region are two distinct genetic elements originating from very different organisms. ETBF strains may have evolved by horizontal transfer of these two genetic elements into a pattern II NTBF strain.

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G-protein coupled receptor 35 (GPR35) regulates the colonic epithelial cell response to enterotoxigenic Bacteroides fragilis.

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