Pili-like proteins of Akkermansia muciniphila modulate host immune responses and gut barrier function

Abstract

Gut barrier function is key in maintaining a balanced response between the host and its microbiome. The microbiota can modulate changes in gut barrier as well as metabolic and inflammatory responses. This highly complex system involves numerous microbiota-derived factors. The gut symbiont Akkermansia muciniphila is positively correlated with a lean phenotype, reduced body weight gain, amelioration of metabolic responses and restoration of gut barrier function by modulation of mucus layer thickness. However, the molecular mechanisms behind its metabolic and immunological regulatory properties are unexplored. Herein, we identify a highly abundant outer membrane pili-like protein of A. muciniphila MucT that is directly involved in immune regulation and enhancement of trans-epithelial resistance. The purified Amuc_1100 protein and enrichments containing all its associated proteins induced production of specific cytokines through activation of Toll-like receptor (TLR) 2 and TLR4. This mainly leads to high levels of IL-10 similar to those induced by the other beneficial immune suppressive microorganisms such as Faecalibacterium prausnitzii A2-165 and Lactobacillus plantarum WCFS1. Together these results indicate that outer membrane protein composition and particularly the newly identified highly abundant pili-like protein Amuc_1100 of A. muciniphila are involved in host immunological homeostasis at the gut mucosa, and improvement of gut barrier function.

Metabolic characterization and viable delivery of Akkermansia muciniphila for its future application

“…Limited growth was also observed when large amounts of tryptone, a tryptic digest of casein, were added as nitrogen source in combination with monosaccharides (Ottman et al, 2017b). This can be due to the presence of either amino acids or glycans in both complex substrates.…”

“…Growth was determined by measuring the optical density at 600 nm. High-pressure liquid chromatography (HPLC) was used to determine sugar consumption and SCFA production, as described before , Ottman et al, 2017b. Glucosamine (GlcN) concentration was determined by reagent free ion chromatography using a Dionex™ ICS-5000 (Thermo Scientific, Sunnyville, CA, USA), with a Dionex CarboPac PA20 Analytic column and 20mM NaOH as eluent.…”

“…Additionally, it was shown in vitro that an A. muciniphila outer membrane complex could modulate the immune response. The effect was traced back to a single pili-associated protein encoded by the DNA at locus Amuc_1100 (Ottman, et al, 2017b). Such mechanistic studies are needed for the definition and final use of therapeutic microbes.…”

“…The genome scale constraint based model of A. muciniphila AkkMuc_588 reported previously (Ottman et al, 2017b) was used to assess growth potential on different media. The core of the model is S the stoichiometric matrix.…”

“…The growth on different sugars was compared with predictions from the A. muciniphila model as presented before (Ottman et al, 2017b). The initial version of the model (AkkMuc_588 v1) predicted growth on all sugars testes, except GlcN, as discussed above.…”