FIBER-DEFICIENT DIET INHIBITS COLITIS THROUGH REGULATION OF THE NICHE AND METABOLISM OF A GUT PATHOBIONT

Abstract

Abstract Fiber free exclusive enteral nutrition (EEN) is an effective steroid-sparing treatment used to induce clinical remission in children with Crohn’s disease (CD). However, the mechanism underlying the beneficial effects of EEN remains obscure. We have generated a novel mouse strain that harbors mutations in two CD susceptibility genes (i.e, NOD2 and CYBB) and found that these mice spontaneously develop an early-onset (4 weeks of age), TH1-type gut inflammation, that closely recapitulates the human disease when exposed to a specific murine microbiota. Disease in Nod2/Cybb (DKO) mutants was triggered by a single mucus-dwelling anaerobe, Mucispirillum schaedleri, which markedly accumulates in the intestinal lumen and mucus layer prior to disease development. Given that our mouse model resembles early-onset CD, we have established a novel humanized mouse model of early-onset CD in which germ-free Nod2/Cybb mutants were colonized with microbiotas from early-onset-CD patients and their healthy first-degree relatives. We have found that the early-onset-CD-associated microbiota triggered intestinal inflammation in gnotobiotic DKO mice with all the hallmarks of the human disease. Using the murine and humanized models of early-onset CD we have found that administration of a fiber-free diet prevents the development of colitis and inhibits intestinal inflammation in colitic animals. Furthermore, identification of Mucispirillum as a trigger in our mouse model has allowed us to study the effects of dietary interventions on disease-causing microbes. Remarkably, we have found that a fiber-free diet alters the intestinal localization of Mucispirillum. Mechanistically, the absence of dietary fiber reduces the availability of nutrients and impairs Mucispirillum’s unique metabolic pathway in the intestinal mucus. Thus, appropriate localization of the pathobiont in the mucus layer is critical for the onset of disease, which can be disrupted by fiber exclusion. These results suggest that probing the intestinal niche and metabolism of disease-causing microbes will likely lead to the discovery of novel, more targeted therapies for the treatment of CD.