Gut microbiota dysbiosis has been implicated in a variety of systemic disorders, notably metabolic diseases including obesity and impaired liver function, but the underlying mechanisms are uncertain. To investigate this question, we transferred caecal microbiota from either obese or lean mice to antibiotic-free, conventional wild-type mice. We found that transferring obese-mouse gut microbiota to mice on normal chow (NC) acutely reduces markers of hepatic gluconeogenesis with decreased hepatic PEPCK activity, compared to non-inoculated mice, a phenotypic trait blunted in conventional NOD2 KO mice. Furthermore, transferring of obese-mouse microbiota changes both the gut microbiota and the microbiome of recipient mice. We also found that transferring obese gut microbiota to NC-fed mice then fed with a high-fat diet (HFD) acutely impacts hepatic metabolism and prevents HFD-increased hepatic gluconeogenesis compared to non-inoculated mice. Moreover, the recipient mice exhibit reduced hepatic PEPCK and G6Pase activity, fed glycaemia and adiposity. Conversely, transfer of lean-mouse microbiota does not affect markers of hepatic gluconeogenesis. Our findings provide a new perspective on gut microbiota dysbiosis, potentially useful to better understand the aetiology of metabolic diseases.

Objective To identify a causal mechanism responsible for the enhancement of insulin resistance and hyperglycaemia following periodontitis in mice fed a fat-enriched diet. Design We set-up a unique animal model of periodontitis in C57Bl/6 female mice by infecting the periodontal tissue with specific and alive pathogens like Porphyromonas gingivalis (Pg), Fusobacterium nucleatum and Prevotella intermedia. The mice were then fed with a diabetogenic/non-obesogenic fat-enriched diet for up to 3 months. Alveolar bone loss, periodontal microbiota dysbiosis and features of glucose metabolism were quantified. Eventually, adoptive transfer of cervical (regional) and systemic immune cells was performed to demonstrate the causal role of the cervical immune system. Results Periodontitis induced a periodontal microbiota dysbiosis without mainly affecting gut microbiota. The disease concomitantly impacted on the regional and systemic immune response impairing glucose metabolism. The transfer of cervical lymph-node cells from infected mice to naive recipients guarded against periodontitis-aggravated metabolic disease. A treatment with inactivated Pg prior to the periodontal infection induced specific antibodies against Pg and protected the mouse from periodontitis-induced dysmetabolism. Finally, a 1-month subcutaneous chronic infusion of low rates of lipopolysaccharides from Pg mimicked the impact of periodontitis on immune and metabolic parameters. Conclusions We identified that insulin resistance in the high-fat fed mouse is enhanced by pathogen-induced periodontitis. This is caused by an adaptive immune response specifically directed against pathogens and associated with a periodontal dysbiosis.

After more than one and a half century, i.e. since Louis Pasteur work on microbes, fermentation, and diseases, biological science has made a giant step in bacteria knowledge. Thanks to an ultra-powerful "microscope", i.e. ultra-fast DNA sequencing, scientists have been able to read and group within a catalog over the last decade, the gene code of bacteria, i.e. the metagenome at the surface of our epithelia. More recently, live bacteria within adipose tissue, defining a tissue microbiota, as well as bacterial fragments such as DNA within the liver, the brain and the blood have been identified. Metagenomic analyses from large cohorts of patients have uncovered tight correlations between bacterial genes within our intestine and mouth and diseases such as metabolic diseases, diabetes, obesity, some liver diseases, kidney and heart failure as well as vascular diseases. Some causal mechanisms have been proposed in rodents and can set the soil for novel therapeutic strategies that could interfere with both the microbes and the corresponding host targets.

Objective: To demonstrate that glycemia and insulin resistance are controlled by a mechanism involving the adaptive immune system and gut microbiota crosstalk.Methods: We triggered the immune system with microbial extracts specifically from the intestinal ileum contents of HFD-diabetic mice by the process of immunization. 35 days later, immunized mice were fed a HFD for up to two months in order to challenge the development of metabolic features. The immune responses were quantified. Eventually, adoptive transfer of immune cells from the microbiota-immunized mice to naive mice was performed to demonstrate the causality of the microbiota-stimulated adaptive immune system on the development of metabolic disease. The gut microbiota of the immunized HFD-fed mice was characterized in order to demonstrate whether the manipulation of the microbiota to immune system interaction reverses the causal deleterious effect of gut microbiota dysbiosis on metabolic disease.Results: Subcutaneous injection (immunization procedure) of ileum microbial extracts prevented hyperglycemia and insulin resistance in a dose-dependent manner in response to a HFD. The immunization enhanced the proliferation of CD4 and CD8 T cells in lymphoid organs, also increased cytokine production and antibody secretion. As a mechanism explaining the metabolic improvement, the immunization procedure reversed gut microbiota dysbiosis. Finally, adoptive transfer of immune cells from immunized mice improved metabolic features in response to HFD.Conclusions: Glycemia and insulin sensitivity can be regulated by triggering the adaptive immunity to microbiota interaction. This reduces the gut microbiota dysbiosis induced by a fat-enriched diet. (C) 2016 The Authors. Published by Elsevier GmbH. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Plus d’un siècle et demi depuis les premiers travaux de Louis Pasteur sur le rôle des microbes dans la fermentation et dans les maladies, la science semble franchir une nouvelle étape majeure dans la connaissance de l’écosystème bactérien qui nous entoure et nous colonise. En effet, depuis une décennie, le séquençage de l’ADN à ultra-haut débit a permis de déchiffrer et de regrouper dans un catalogue le code génétique des bactéries (métagénome) présentes à la surface de nos épithéliums buccaux, intestinaux ou pulmonaires. Des bactéries vivantes ainsi que des fragments bactériens ont également été récemment mis en évidence dans les tissus profonds comme le tissu adipeux, le foie, le cerveau et le sang, définissant ainsi un microbiote tissulaire ou endo-microbiote. L’analyse des métagénomes obtenus à partir de grandes cohortes de patients a surtout conduit à revisiter la stratification de certaines maladies, en particulier métaboliques, hépatiques, rénales, cardiovasculaires ou neurodégénératives. Ainsi, des données du métagénome ont-elles permis d’établir des corrélations entre fréquence de certaines bactéries (ou de leurs gènes) de l’intestin et ces affections. Certaines approches expérimentales ont également suggéré l’existence d’un lien causal entre une dysbiose buccale et/ou intestinale et ces pathologies, permettant d’envisager de nouvelles stratégies thérapeutiques ciblant les deux intervenants dans ce dialogue permanent établi entre notre tube digestif et les bactéries qui l’habitent.

These days, the gut microbiota is universally recognized as an active organ that can modulate the overall host metabolism by promoting multiple functions, from digestion to the systemic maintenance of overall host physiology. Dysbiosis, the alteration of the complex ecologic system of gut microbes, is associated with and causally responsible for multiple types of pathologies. Among the latters, metabolic diseases such as type 2 diabetes and obesity are each distinguishable by a unique gut microbiota profile. Interestingly, the specific microbiota typically found in the blood of diabetic patients also has been observed at the level of atherosclerotic plaque. Here, we report evidence from the literature, as well as a few controversial reports, regarding the putative role of gut microbiota dysbiosis-induced cardiovascular diseases, such as atherosclerosis, which are common comorbidities of metabolic dysfunction.