Dissecting the respective roles of microbiota and host genetics in the susceptibility of Card9-/- mice to colitis.

BACKGROUND: The etiology of inflammatory bowel disease (IBD) is unclear but involves both genetics and environmental factors, including the gut microbiota. Indeed, exacerbated activation of the gastrointestinal immune system toward the gut microbiota occurs in genetically susceptible hosts and under the influence of the environment. For instance, a majority of IBD susceptibility loci lie within genes involved in immune responses, such as caspase recruitment domain member 9 (Card9). However, the relative impacts of genotype versus microbiota on colitis susceptibility in the context of CARD9 deficiency remain unknown. RESULTS: Card9 gene directly contributes to recovery from dextran sodium sulfate (DSS)-induced colitis by inducing the colonic expression of the cytokine IL-22 and the antimicrobial peptides Reg3ß and Reg3γ independently of the microbiota. On the other hand, Card9 is required for regulating the microbiota capacity to produce AhR ligands, which leads to the production of IL-22 in the colon, promoting recovery after colitis. In addition, cross-fostering experiments showed that 5 weeks after weaning, the microbiota transmitted from the nursing mother before weaning had a stronger impact on the tryptophan metabolism of the pups than the pups' own genotype. CONCLUSIONS: These results show the role of CARD9 and its effector IL-22 in mediating recovery from DSS-induced colitis in both microbiota-independent and microbiota-dependent manners. Card9 genotype modulates the microbiota metabolic capacity to produce AhR ligands, but this effect can be overridden by the implantation of a WT or "healthy" microbiota before weaning. It highlights the importance of the weaning reaction occurring between the immune system and microbiota for host metabolism and immune functions throughout life. A better understanding of the impact of genetics on microbiota metabolism is key to developing efficient therapeutic strategies for patients suffering from complex inflammatory disorders. Video Abstract.

Protective effects of Saccharomyces boulardii CNCM I-745 in an experimental model of NSAID-induced enteropathy.

Nonsteroidal anti-inflammatory drugs (NSAIDs) induce a broad spectrum of gastro-intestinal adverse effects, including ulceration and bleeding. The pathophysiology of NSAID enteropathy is complex and incompletely understood, but some evidence showed that NSAIDs impair the intestinal barrier and cause a gut dysbiosis. Identifying new treatments aiming to reverse or attenuate NSAID-induced adverse effects would have a significant impact on a high number of patients. The aim of this work is to assess the effects of the probiotic yeast Saccharomyces boulardii CNCM I-745 (Sb) on a model of NSAID-induced enteropathy. Four groups of mice were tested: Control, Indomethacin, Sb, and Sb + Indomethacin. A clinical score was evaluated throughout the experiment. Faecal calprotectin, microbiota and haemoglobin analyses were performed. At the end of the treatments, the small intestine, colon, and caecum lengths, and intestinal permeability were measured. Sections of ileum and jejunum were observed to assess a histological score and ileal cytokines were measured by immunoassay. Indomethacin-treated animals showed an increase in their clinical scores, reflecting a worsening of their general state. Mice co-treated with Sb and indomethacin displayed an improvement of their clinical score in comparison with mice treated with indomethacin alone. Sb prevented the indomethacin-induced shortening of the small intestine and caecum, and significantly attenuated the severity of intestinal lesions. Sb also prevented the increase in faecal calprotectin, reduced faecal haemoglobin, and prevented the increase of intestinal permeability in mice treated with indomethacin. Sb also counteracted the increase of faecal bacteria associated with the pathogenesis of NSAID-enteropathy. In conclusion, our results show a protective effect of Sb in a model of indomethacin-induced enteropathy. Sb improved the intestinal barrier function and exerted a positive action on gut microbiota composition.

Gut barrier-microbiota imbalances in early life lead to higher sensitivity to inflammation in a murine model of C-section delivery.

BACKGROUND: Most interactions between the host and its microbiota occur at the gut barrier, and primary colonizers are essential in the gut barrier maturation in the early life. The mother-offspring transmission of microorganisms is the most important factor influencing microbial colonization in mammals, and C-section delivery (CSD) is an important disruptive factor of this transfer. Recently, the deregulation of symbiotic host-microbe interactions in early life has been shown to alter the maturation of the immune system, predisposing the host to gut barrier dysfunction and inflammation. The main goal of this study is to decipher the role of the early-life gut microbiota-barrier alterations and its links with later-life risks of intestinal inflammation in a murine model of CSD. RESULTS: The higher sensitivity to chemically induced inflammation in CSD mice is related to excessive exposure to a too diverse microbiota too early in life. This early microbial stimulus has short-term consequences on the host homeostasis. It switches the pup's immune response to an inflammatory context and alters the epithelium structure and the mucus-producing cells, disrupting gut homeostasis. This presence of a too diverse microbiota in the very early life involves a disproportionate short-chain fatty acids ratio and an excessive antigen exposure across the vulnerable gut barrier in the first days of life, before the gut closure. Besides, as shown by microbiota transfer experiments, the microbiota is causal in the high sensitivity of CSD mice to chemical-induced colitis and in most of the phenotypical parameters found altered in early life. Finally, supplementation with lactobacilli, the main bacterial group impacted by CSD in mice, reverts the higher sensitivity to inflammation in ex-germ-free mice colonized by CSD pups' microbiota. CONCLUSIONS: Early-life gut microbiota-host crosstalk alterations related to CSD could be the linchpin behind the phenotypic effects that lead to increased susceptibility to an induced inflammation later in life in mice. Video Abstract.