Fusobacterium nucleatum secretes outer membrane vesicles and promotes intestinal inflammation

Authors: ENGEVIK, MELINDAA - Baylor College Of Medicine; DANHOF, HEATHERA - Baylor College Of Medicine; RUAN, WENLY - Baylor College Of Medicine; ENGEVIK, AMY - Vanderbilt University; CHANG-GRAHAM, ALEXANDRA - Baylor College Of Medicine; ENGEVIK, KRISTEN - Baylor College Of Medicine; SHI, ZHONGCHENG - Baylor College Of Medicine; ZHAO, YANLING - Texas Children'S Hospital; BRAND, COLLEEN - Baylor College Of Medicine; KRYSTOFIAK, EVAN - Vanderbilt University; VENABLE, SUSAN - Baylor College Of Medicine; LIU, XINLI - University Of Houston; HIRSCHI, KENDAL - Children'S Nutrition Research Center (CNRC); HYSER, JOSEPH - Baylor College Of Medicine; SPINLER, JENNIFER - Baylor College Of Medicine; BRITTON, ROBERT - Baylor College Of Medicine; VERSALOVIC, JAMES - Baylor College Of Medicine

Submitted to: American Society for Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2021
Publication Date: 3/2/2021
Citation: Engevik, M., Danhof, H., Ruan, W., Engevik, A.C., Chang-Graham, A.L., Engevik, K., Shi, Z., Zhao, Y., Brand, C.K., Krystofiak, E.S., Venable, S., Liu, X., Hirschi, K.D., Hyser, J.M., Spinler, J.K., Britton, R.A., Versalovic, J. 2021. Fusobacterium nucleatum secretes outer membrane vesicles and promotes intestinal inflammation. American Society for Microbiology. 12(2):e02706-e02720. https://doi.org/10.1128/mBio.02706-20.
DOI: https://doi.org/10.1128/mBio.02706-20

Interpretive Summary: The intestine is home to millions of microbes that collectively make up a community called the gut microbiota. Although many gut microbes are beneficial and promote health, some can take advantage of changes in the intestinal environment and promote an immune response, a phenomena known as inflammation. However, chronic inflammation can be harmful to the intestinal tissue and thus controlling inflammation is an important factor in human health. This study focused on a microbe that has been identified in the intestine of patients with digestive diseases. Using a mouse model this study found that, in specific environmental conditions, this microbe secreted compounds that stimulated inflammatory molecules. This finding provides evidence that specific triggers can promote bacteria to make compounds that activate immune responses and promote inflammation. This knowledge can be used to improve gut health and promote immunity.

Technical Abstract: Multiple studies have implicated microbes in the development of inflammation, but the mechanisms remain unknown. Bacteria in the genus Fusobacterium have been identified in the intestinal mucosa of patients with digestive diseases; thus, we hypothesized that Fusobacterium nucleatum promotes intestinal inflammation. The addition of >50 kDa F. nucleatum conditioned media, which contain outer membranevesicles (OMVs), to colonic epithelial cells stimulated secretion of the proinflammatory cytokines interleukin-8 (IL-8) and tumor necrosis factor (TNF). In addition, purified F.nucleatum OMVs, but not compounds <50 kDa, stimulated IL-8 and TNF production; which was decreased by pharmacological inhibition of Toll-like receptor 4 (TLR4). These effects were linked to downstream effectors p-ERK, p-CREB, and NF-kB. F. nucleatum >50-kDa compounds also stimulated TNF secretion, p-ERK, p-CREB, and NF-kB activation in human colonoid monolayers. In mice harboring a human microbiota, pretreatment with antibiotics and a single oral gavage of F. nucleatum resulted in inflammation. Compared to mice receiving vehicle control, mice treated with F. nucleatum showed disruption of the colonic architecture, with increased immune cell infiltration and depleted mucus layers. Analysis of mucosal gene expression revealed increased levels of proinflammatory cytokines (KC, TNF, IL-6, IFN-g, and MCP-1) at day 3 and day5 in F. nucleatum-treated mice compared to controls. These proinflammatory effects were absent in mice who received F. nucleatum without pretreatment with antibiotics, suggesting that an intact microbiome is protective against F. nucleatum-mediated immune responses. These data provide evidence that F. nucleatum promotes proinflammatory signaling cascades in the context of a depleted intestinal microbiome. Several studies have identified an increased abundance of Fusobacterium in the intestinal tracts of patients with colon cancer, liver cirrhosis, primary sclerosing cholangitis, gastroesophageal reflux disease, HIV infection, and alcoholism. However, the direct mechanism(s) of action of Fusobacteriumon pathophysiological within thegastrointestinal tract is unclear. These studies have identified that F. nucleatum subsp.polymorphum releases outer membrane vesicles which activate TLR4 and NF-kB to stimulate proinflammatory signals in vitro. Using mice harboring a human microbiome, we demonstrate that F. nucleatumcan promote inflammation, an effect which required antibiotic-mediated alterations in the gut microbiome. Collectively, these results suggest a mechanism by which F. nucleatum may contribute to intestinal inflammation.