Proteome profiling of intestinal cultures treated with Bacteroides fragilis vesicles revealed new mechanisms of anti-inflammatory response

Abstract

Abstract The gut is under complex attack by a large number of biologically active molecules, including bacterial enzymes, metabolites, nucleic acids and immuno-active compounds. Most of these components are presented in outer membrane vesicles (OMVs), which are actively produced by all bacterial types. Bacteroides fragilis, as a member of the gut microbiota, has unique OMV’s components that are known to have both pathogenic and positive immunomodulatory properties. Bacteroides fragilis OMVs are well characterized by proteomic and metabolomic methods and therefore represent a suitable comprehensive framework for assessing the overall molecular impact of bacterial OMVs on intestinal cultures. We studied proteomic changes in colon (HT-29) and rectal (SW837) adenocarcinoma cell lines treated with OMVs isolated from enterotoxigenic Bacteroides fragilis BOB25 strain (ETBF) and non-toxigenic Bacteroides fragilis JIM10 strain (NTBF). Cell lines were incubated with ETBF and NTBF OMVs for three and five hours and then the total proteome of the cell lines was isolated and annotated using 2D electrophoresis with the following mass spectrometric identification of proteomic differences. As a result, the SW837 cell line showed a more significant range of proteome differences than the HT-29 cell line, including not only up and down regulated proteins involved in cytoskeletal reorganization and cell adhesion, but also proteins involved in cell proliferation and pro-inflammatory response. We found that the SW837 cell line treated with NTBF OMVs secrete IL18, that plays a profound role in the initiation phase of an immune response by recruiting dendritic cells (DCs). ETBF OMVs demonstrated the simultaneous coexistence of cell proliferation and apoptosis promoting factors. We hypothesize that both types of OMVs may contribute to the anti-inflammatory effects, as the same proteins were found to be affected in cell lines treated with ETBF and NTBF OMVs. However, the presence of a toxin in ETBF OMV may delay anti-inflammatory activity until the cell has fully repaired the damaged cytoskeleton.