The intestinal crypt is a site of potential interactions between microbiota products, stem cells, and other cell types found in this niche, including Paneth cells, and thus offers a potential for ...commensal microbes to influence the host epithelium. However, the complexity of this microenvironment has been a challenge to deciphering the underlying mechanisms. We used in vitro cultured organoids of intestinal crypts from mice, reinforced with in vivo experiments, to examine the crypt-microbiota interface. We find that within the intestinal crypt, Lgr5+ stem cells constitutively express the cytosolic innate immune sensor Nod2 at levels much higher than in Paneth cells. Nod2 stimulation by its bona fide agonist, muramyl-dipeptide (MDP), a peptidoglycan motif common to all bacteria, triggers stem cell survival, which leads to a strong cytoprotection against oxidative stress-mediated cell death. Thus, gut epithelial restitution is Nod2 dependent and triggered by the presence of microbiota-derived molecules.
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•The bacterial peptidoglycan motif MDP induces higher yield of intestinal organoids in vitro•Nod2 is expressed in Lgr5+ intestinal epithelial stem cells•Stem cell-expressed Nod2 is sufficient to provide cytoprotection•MDP protects stem cells from stress in vivo in a Nod2-dependent manner
The intestinal crypt is the site of epithelial regeneration and of potential interactions between microbiota products and stem cells. Nigro et al. show that intestinal Lgr5+ stem cells express the cytosolic innate immune sensor Nod2, whose stimulation by the bacterial ligand muramyl-dipeptide affords potent cytoprotection to the stem cells.
Microbial pathogens possess a diversity of weapons that disrupt host homeostasis and immune defenses, thus resulting in the establishment of infection. The best-characterized system mediating ...bacterial protein delivery into target eukaryotic cells is the type III secretion system (T3SS) expressed by Gram-negative bacteria, including the human enteric pathogens Shigella, Salmonella, Yersinia, and enteropathogenic/enterohemorragic Escherichia coli (EPEC/EHEC). The emerging global view is that these T3SS-bearing pathogens share similarities in their ability to target key cellular pathways such as the cell cytoskeleton, trafficking, cell death/survival, and the NF-κB and MAPK signaling pathways. In particular, multiple host proteins are targeted in a given pathway, and different T3SS effectors from various pathogens share functional similarities.
Convergent targeting strategies are shared by Shigella, Salmonella, Yersinia, and EPEC/EHEC to hijack host responses.
An impressive diversity of interactions takes place between the T3SS effectors and their cellular targets belonging to key cellular pathways.
Modulation of host responses occurs during the entire course of infection, with T3SS effectors acting sequentially and displaying antagonistic effects on a given cellular pathway.
One given effector may ensure a diversity of action towards different cell types while infection proceeds.
Both innate and adaptive immune responses are modulated by T3SS effectors.
The modulation of the intestinal microbiota by high-fat diet (HFD) has a major impact on both immunological and metabolic functions of the host. Taking this into consideration, the aim of this ...contribution is to review the impact of HFD on microbiota profile and small intestinal physiology before and after the onset of obesity and its metabolic complications. Evidence from animal studies suggest that before the onset of obesity and its metabolic complications, HFD induces intestinal dysbiosis - encompassing changes in composition balance and massive redistribution with bacteria occupying intervillous spaces and crypts - associated with early physiopathological changes, predominantly in the ileum, such as low-grade inflammation, decreased antimicrobial peptides expression, impaired mucus production, secretion and layer's thickness, and decreased expression of tight junction proteins. With time, major inflammatory signals (e.g. toll-like receptor-4 dependent) become activated, thereby stimulating proinflammatory cytokines secretion in the small intestine. This inflammatory state might subsequently exacerbate disruption of the mucus layer barrier and increase epithelial permeability of the small intestine, thereby creating an environment that facilitates the passage of bacterial components (e.g. lipopolysaccharide, peptidoglycan and flagellin) and metabolites from the intestinal lumen (e.g. secondary bile acids) to the circulation and peripheral tissues (i.e. leaky gut), eventually promoting the development of systemic inflammation, obesity, adiposity, insulin resistance and glucose intolerance preceding hyperglycemia. Although the mechanisms are still not completely understood, prebiotics, probiotics, polyphenols, peroxisome proliferator-activated receptor-γ agonists (such as rosiglitazone) and exercise have been shown to reverse HFD-induced intestinal phenotype and to attenuate the severity of obesity and its associated metabolic complications.
•High-fat diet (HFD) impacts immunological and metabolic functions of the host.•Gut dysbiosis, inflammation and leakage are induced by HFD consumption.•These changes seem to be associated the development of obesity and its complications.•Some prebiotics, probiotics and antidiabetics attenuate this HFD-induced phenotype.
Even though tremendous progress has been made in the last decades to elucidate the mechanisms of intestinal homeostasis, dysbiosis and disease, we are only at the beginning of understanding the ...complexity of the gut ecosystem and the underlying interaction networks. We are also only starting to unravel the mechanisms that pathogens have evolved to overcome the barriers imposed by the microbiota and host to exploit the system to their own benefit. Recent work in these domains clearly indicates that the 'traditional Koch's postulates', which state that a given pathogen leads to a distinct disease, are not valid for all 'infectious' diseases, but that a more complete and complex interpretation of Koch's postulates is needed in order to understand and explain them. This review summarises the current understanding of what defines a healthy gut ecosystem and highlights recent progress in uncovering the interplay between the host, its microbiota and invading intestinal pathogens. Based on these recent findings, we propose a new interpretation of Koch's postulates that we term 'ecological Koch's postulates'.
The intestinal epithelium is continuously renewed by intestinal epithelial stem cells (IESCs) positioned at the base of each crypt. Mesenchymal-derived factors are essential to maintain IESCs; ...however, the cellular composition and development of such mesenchymal niche remains unclear. Here, we identify pericryptal CD34⁺ Gp38⁺ αSMA⁻ mesenchymal cells closely associated with Lgr5⁺ IESCs. We demonstrate that CD34⁺ Gp38⁺ cells are the major intestinal producers of the niche factors Wnt2b, Gremlin1, and R-spondin1, and are sufficient to promote maintenance of Lgr5⁺ IESCs in intestinal organoids, an effect mainly mediated by Gremlin1. CD34⁺ Gp38⁺ cells develop after birth in the intestinal submucosa and expand around the crypts during the third week of life in mice, independently of the microbiota. We further show that pericryptal CD34⁺gp38⁺ cells are rapidly activated by intestinal injury, up-regulating niche factors Gremlin1 and R-spondin1 as well as chemokines, proinflammatory cytokines, and growth factors with key roles in gut immunity and tissue repair, including IL-7, Ccl2, Ptgs2, and Amphiregulin. Our results indicate that CD34⁺ Gp38⁺ mesenchymal cells are programmed to develop in the intestine after birth to constitute a specialized microenvironment that maintains IESCs at homeostasis and contribute to intestinal inflammation and repair after injury.
Sporadic colorectal cancer (CRC) is a result of complex interactions between the host and its environment. Environmental stressors act by causing host cell DNA alterations implicated in the onset of ...cancer. Here we investigate the stressor ability of CRC-associated gut dysbiosis as causal agent of host DNA alterations. The epigenetic nature of these alterations was investigated in humans and in mice. Germ-free mice receiving fecal samples from subjects with normal colonoscopy or from CRC patients were monitored for 7 or 14 wk. Aberrant crypt foci, luminal microbiota, and DNA alterations (colonic exome sequencing and methylation patterns) were monitored following human feces transfer. CRC-associated microbiota induced higher numbers of hypermethylated genes in murine colonic mucosa (vs. healthy controls’ microbiota recipients). Several gene promoters including SFRP1,2,3, PENK, NPY, ALX4, SEPT9, and WIF1 promoters were found hypermethylated in CRC but not in normal tissues or effluents from fecal donors. In a pilot study (n = 266), the blood methylation levels of 3 genes (Wif1, PENK, and NPY) were shown closely associated with CRC dysbiosis. In a validation study (n = 1,000), the cumulative methylation index (CMI) of these genes was significantly higher in CRCs than in controls. Further, CMI appeared as an independent risk factor for CRC diagnosis as shown by multivariate analysis that included fecal immunochemical blood test. Consequently, fecal bacterial species in individuals with higher CMI in blood were identified by whole metagenomic analysis. Thus, CRC-related dysbiosis induces methylation of host genes, and corresponding CMIs together with associated bacteria are potential biomarkers for CRC.
Invasive bacteria actively induce their own uptake by phagocytosis in normally nonphagocytic cells and then either establish a protected niche within which they survive and replicate, or disseminate ...from cell to cell by means of an actin-based motility process. The mechanisms underlying bacterial entry, phagosome maturation, and dissemination reveal common strategies as well as unique tactics evolved by individual species to establish infection.
Despite the recognized capacity of the gut microbiota to regulate intestinal lipid metabolism, the role of specific commensal species remains undefined. Here, we aimed to understand the bacterial ...effectors and molecular mechanisms by which Lactobacillus paracasei and Escherichia coli regulate lipid metabolism in enterocytes. We show that L-lactate produced by L. paracasei inhibits chylomicron secretion from enterocytes and promotes lipid storage by a mechanism involving L-lactate absorption by enterocytes, its conversion to malonyl-CoA, and the subsequent inhibition of lipid beta-oxidation. In contrast, acetate produced by E. coli also inhibits chylomicron secretion by enterocytes but promotes lipid oxidation by a mechanism involving acetate absorption by enterocytes, its metabolism to acetyl-CoA and AMP, and the subsequent upregulation of the AMPK/PGC-1α/PPARα pathway. Our study opens perspectives for developing specific bacteria- and metabolite-based therapeutic interventions against obesity, atherosclerosis, and malnutrition by targeting lipid metabolism in enterocytes.
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•Fermentation products secreted by gut commensals regulate enterocyte lipid metabolism•L-lactate secreted by L. paracasei promotes lipid storage by generating malonyl-CoA•Acetate secreted by E. coli promotes lipid oxidation via AMPK/PGC-1α/PPARα pathway
Araújo et al. demonstrate that L-lactate and acetate produced by commensal bacteria differentially program enterocyte metabolism and secretion of absorbed dietary lipids. L. paracasei-produced L-lactate induces enterocytes to store lipids through its conversion to malonyl-CoA, while E. coli-produced acetate induces enterocytes to oxidize lipids by upregulating the AMPK/PGC-1α/PPARα pathway.
Quantitative reverse transcription PCR analysis is an important tool to monitor changes in gene expression in animal models. The rabbit is a widely accepted and commonly used animal model in the ...study of human diseases and infections by viral, fungal, bacterial and protozoan pathogens. Only a limited number of rabbit genes have, however, been analyzed by this method as the rabbit genome sequence remains unfinished. Recently, increasing coverage of the genome has permitted the prediction of a growing number of genes that are relevant in the context of the immune response. We hereby report the design of twenty-four quantitative PCR primer pairs covering common cytokines, chemoattractants, antimicrobials and enzymes for a rapid, sensitive and quantitative analysis of the rabbit immune response. Importantly, all primer pairs were designed to be used under identical experimental conditions, thereby enabling the simultaneous analysis of all genes in a high-throughput format. This tool was used to analyze the rabbit innate immune response to infection with the human gastrointestinal pathogen Shigella flexneri. Beyond the known inflammatory mediators, we identified IL-22, IL-17A and IL-17F as highly upregulated cytokines and as first responders to infection during the innate phase of the host immune response. This set of qPCR primers also provides a convenient tool for monitoring the rabbit immune response during infection with other pathogens and other inflammatory conditions.
What is COVID‐19? What are the causes, parameters, and effects of this disease? What are the short‐ and long‐term prospects? Philippe Sansonetti, Infectious disease specialist and Chief Editor of ...EMBO Molecular Medicine, explains why the fate of the epidemic is in our hands.
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