Ruminococcus gnavus, a member of the human gut microbiome associated with Crohn's disease, produces an inflammatory polysaccharide.
Henke MT, Kenny DJ, Cassilly CD, Vlamakis H, Xavier RJ, Clardy J
Proc Natl Acad Sci U S A. Jun 2019
COMMENT: Studies previously published associated Ruminococcus gnavus with Crohn's disease. In this work the authors discover that the glucorhamnan polysaccharide, which is composed by a rhamnose backbone and glucose side chains, could be a probable responsible for this association.
Glucorhamnan polysaccharide is synthesized by Ruminococcus gnavus, a usually abundant commensal in human gut microbiome. The findings of this work suggest that glucorhamnan could be involved in the gut inflammation that Crohn’s disease patients suffer. The authors demonstrate that glucorhamnan induces inflammatory cytokine (TNFα) secretion by dendritic cells, in a toll-like receptor 4 (TLR4)-dependent manner.
R. gnavus can utilize mucin as a carbon source (5, 10, 27), and may directly contribute to breakdown in gut barrier function. The degradation of this barrier, or the host’s ability to maintain a bacteria-free zone within the mucin layer, may increase the immune system’s exposure to triggers like the R. gnavus glucorhamnan, which would otherwise not be sensed by the immune system. In this way, mucin destruction and glucorhamnan production by R. gnavus could have profound effects on human inflammatory responses. Ultimately, we have identified a molecular hypothesis that can be interrogated to explain the link between the human gut commensal, R. gnavus, and Crohn’s disease pathology.