Lucie Geurts

Changes in gut microbiota control inflammation in obese mice through a mechanism involving GLP-2-driven improvement of gut permeability

Background and aims: Obese and diabetic mice display enhanced intestinal permeability and metabolic endotoxaemia that participate in the occurrence of metabolic disorders. Our recent data support the idea that a selective increase of Bifidobacterium spp. reduces the impact of high-fat diet-induced metabolic endotoxaemia and inflammatory disorders. Here, we hypothesised that prebiotic modulation of gut microbiota lowers intestinal permeability, by a mechanism involving glucagon-like peptide-2 (GLP-2) thereby improving inflammation and metabolic disorders during obesity and diabetes. Methods: Study 1: ob/ob mice (Ob-CT) were treated with either prebiotic (Ob-Pre) or non-prebiotic carbohydrates as control (Ob-Cell). Study 2: Ob-CT and Ob-Pre mice were treated with GLP-2 antagonist or saline. Study 3: Ob-CT mice were treated with a GLP-2 agonist or saline. We assessed changes in the gut microbiota, intestinal permeability, gut peptides, intestinal epithelial tight-junction proteins ZO-1 and occludin (qPCR and immunohistochemistry), hepatic and systemic inflammation. Results: Prebiotic-treated mice exhibited a lower plasma lipopolysaccharide (LPS) and cytokines, and a decreased hepatic expression of inflammatory and oxidative stress markers. This decreased inflammatory tone was associated with a lower intestinal permeability and improved tight-junction integrity compared to controls. Prebiotic increased the endogenous intestinotrophic proglucagon-derived peptide (GLP-2) production whereas the GLP-2 antagonist abolished most of the prebiotic effects. Finally, pharmacological GLP-2 treatment decreased gut permeability, systemic and hepatic inflammatory phenotype associated with obesity to a similar extent as that observed following prebiotic-induced changes in gut microbiota. Conclusion: We found that a selective gut microbiota change controls and increases endogenous GLP-2 production, and consequently improves gut barrier functions by a GLP-2-dependent mechanism, contributing to the improvement of gut barrier functions during obesity and diabetes.

Cross-talk between Akkermansia muciniphila and intestinal epithelium controls diet-induced obesity

Obesity and type 2 diabetes are characterized by altered gut microbiota, inflammation, and gut barrier disruption. Microbial composition and the mechanisms of interaction with the host that affect gut barrier function during obesity and type 2 diabetes have not been elucidated. We recently isolated Akkermansia muciniphila, which is a mucin-degrading bacterium that resides in the mucus layer. The presence of this bacterium inversely correlates with body weight in rodents and humans. However, the precise physiological roles played by this bacterium during obesity and metabolic disorders are unknown. This study demonstrated that the abundance of A. muciniphila decreased in obese and type 2 diabetic mice. We also observed that prebiotic feeding normalized A. muciniphila abundance, which correlated with an improved metabolic profile. In addition, we demonstrated that A. muciniphila treatment reversed high-fat diet-induced metabolic disorders, including fat-mass gain, metabolic endotoxemia, adipose tissue inflammation, and insulin resistance. A. muciniphila administration increased the intestinal levels of endocannabinoids that control inflammation, the gut barrier, and gut peptide secretion. Finally, we demonstrated that all these effects required viable A. muciniphila because treatment with heat-killed cells did not improve the metabolic profile or the mucus layer thickness. In summary, this study provides substantial insight into the intricate mechanisms of bacterial (i.e., A. muciniphila) regulation of the cross-talk between the host and gut microbiota. These results also provide a rationale for the development of a treatment that uses this human mucus colonizer for the prevention or treatment of obesity and its associated metabolic disorders.

Involvement of gut microbiota in the development of low-grade inflammation and type 2 diabetes associated with obesity

Obesity is associated with metabolic alterations related to glucose homeostasis and cardiovascular risk factors. These metabolic alterations are associated with low-grade inflammation that contributes to the onset of these diseases. We and others have provided evidence that gut microbiota participates in whole-body metabolism by affecting energy balance, glucose metabolism, and low-grade inflammation associated with obesity and related metabolic disorders. Recently, we defined gut microbiota-derived lipopolysaccharide (LPS) (and metabolic endotoxemia) as a factor involved in the onset and progression of inflammation and metabolic diseases. In this review, we discuss mechanisms involved in the development of metabolic endotoxemia such as the gut permeability. We also discuss our latest discoveries demonstrating a link between the gut microbiota, endocannabinoid system tone, leptin resistance, gut peptides (glucagon-like peptide-1 and -2), and metabolic features. Finally, we will introduce the role of the gut microbiota in specific dietary treatments (prebiotics and probiotics) and surgical interventions (gastric bypass).

A purified membrane protein from Akkermansia muciniphila or the pasteurized bacterium improves metabolism in obese and diabetic mice

Obesity and type 2 diabetes are associated with low-grade inflammation and specific changes in gut microbiota composition. We previously demonstrated that administration of Akkermansia muciniphila to mice prevents the development of obesity and associated complications. However, the underlying mechanisms of this protective effect remain unclear. Moreover, the sensitivity of A. muciniphila to oxygen and the presence of animal-derived compounds in its growth medium currently limit the development of translational approaches for human medicine. We have addressed these issues here by showing that A. muciniphila retains its efficacy when grown on a synthetic medium compatible with human administration. Unexpectedly, we discovered that pasteurization of A. muciniphila enhanced its capacity to reduce fat mass development, insulin resistance and dyslipidemia in mice. These improvements were notably associated with a modulation of the host urinary metabolomics profile and intestinal energy absorption. We demonstrated that Amuc_1100, a specific protein isolated from the outer membrane of A. muciniphila, interacts with Toll-like receptor 2, is stable at temperatures used for pasteurization, improves the gut barrier and partly recapitulates the beneficial effects of the bacterium. Finally, we showed that administration of live or pasteurized A. muciniphila grown on the synthetic medium is safe in humans. These findings provide support for the use of different preparations of A. muciniphila as therapeutic options to target human obesity and associated disorders.

Altered gut microbiota and endocannabinoid system tone in obese and diabetic leptin-resistant mice: impact on apelin regulation in adipose tissue

Growing evidence supports the role of gut microbiota in the development of obesity, type 2 diabetes, and low-grade inflammation. The endocrine activity of adipose tissue has been found to contribute to the regulation of glucose homeostasis and low-grade inflammation. Among the key hormones produced by this tissue, apelin has been shown to regulate glucose homeostasis. Recently, it has been proposed that gut microbiota participate in adipose tissue metabolism via the endocannabinoid system (eCB) and gut microbiota-derived compounds, namely lipopolysaccharide (LPS). We have investigated gut microbiota composition in obese and diabetic leptin-resistant mice (db/db) by combining pyrosequencing and phylogenetic microarray analysis of 16S ribosomal RNA gene sequences. We observed a significant higher abundance of Firmicutes, Proteobacteria, and Fibrobacteres phyla in db/db mice compared to lean mice. The abundance of 10 genera was significantly affected by the genotype. We identified the roles of the eCB and LPS in the regulation of apelinergic system tone (apelin and APJ mRNA expression) in genetic obese and diabetic mice. By using in vivo and in vitro models, we have demonstrated that both the eCB and low-grade inflammation differentially regulate apelin and APJ mRNA expression in adipose tissue. Finally, deep-gut microbiota profiling revealed that the gut microbial community of type 2 diabetic mice is significantly different from that of their lean counterparts. This indicates specific relationships between the gut microbiota and the regulation of the apelinergic system. However, the exact roles of specific bacteria in shaping the phenotype of db/db mice remain to be determined.

Gut microbiota controls adipose tissue expansion, gut barrier and glucose metabolism: novel insights into molecular targets and interventions using prebiotics

Crosstalk between organs is crucial for controlling numerous homeostatic systems (e.g. energy balance, glucose metabolism and immunity). Several pathological conditions, such as obesity and type 2 diabetes, are characterised by a loss of or excessive inter-organ communication that contributes to the development of disease. Recently, we and others have identified several mechanisms linking the gut microbiota with the development of obesity and associated disorders (e.g. insulin resistance, type 2 diabetes, hepatic steatosis). Among these, we described the concept of metabolic endotoxaemia (increase in plasma lipopolysaccharide levels) as one of the triggering factors leading to the development of metabolic inflammation and insulin resistance. Growing evidence suggests that gut microbes contribute to the onset of low-grade inflammation characterising these metabolic disorders via mechanisms associated with gut barrier dysfunctions. We have demonstrated that enteroendocrine cells (producing glucagon-like peptide-1, peptide YY and glucagon-like peptide-2) and the endocannabinoid system control gut permeability and metabolic endotoxaemia. Recently, we hypothesised that specific metabolic dysregulations occurring at the level of numerous organs (e.g. gut, adipose tissue, muscles, liver and brain) rely from gut microbiota modifications. In this review, we discuss the mechanisms linking gut permeability, adipose tissue metabolism, and glucose homeostasis, and recent findings that show interactions between the gut microbiota, the endocannabinoid system and the apelinergic system. These specific systems are discussed in the context of the gut-to-peripheral organ axis (intestine, adipose tissue and brain) and impacts on metabolic regulation. In the present review, we also briefly describe the impact of a variety of non-digestible nutrients (i.e. inulin-type fructans, arabinoxylans, chitin glucans and polyphenols). Their effects on the composition of the gut microbiota and activity are discussed in the context of obesity and type 2 diabetes.

Intestinal epithelial MyD88 is a sensor switching host metabolism towards obesity according to nutritional status

Obesity is associated with a cluster of metabolic disorders, low-grade inflammation and altered gut microbiota. Whether host metabolism is controlled by intestinal innate immune system and the gut microbiota is unknown. Here we report that inducible intestinal epithelial cell-specific deletion of MyD88 partially protects against diet-induced obesity, diabetes and inflammation. This is associated with increased energy expenditure, an improved glucose homeostasis, reduced hepatic steatosis, fat mass and inflammation. Protection is transferred following gut microbiota transplantation to germ-free recipients. We also demonstrate that intestinal epithelial MyD88 deletion increases anti-inflammatory endocannabinoids, restores antimicrobial peptides production and increases intestinal regulatory T cells during diet-induced obesity. Targeting MyD88 after the onset of obesity reduces fat mass and inflammation. Our work thus identifies intestinal epithelial MyD88 as a sensor changing host metabolism according to the nutritional status and we show that targeting intestinal epithelial MyD88 constitutes a putative therapeutic target for obesity and related disorders.

Saccharomyces boulardii Administration Changes Gut Microbiota and Reduces Hepatic Steatosis, Low-Grade Inflammation, and Fat Mass in Obese and Type 2 Diabetic db/db Mice

ABSTRACT Growing evidence shows that gut microbes are key factors involved in the regulation of energy homeostasis, metabolic inflammation, lipid metabolism, and glucose metabolism. Therefore, gut microbiota modulations caused by selectively fermented oligosaccharides or probiotic bacteria constitute an interesting target in the physiopathology of obesity. However, to date, no probiotic yeast has been investigated in this context. Therefore, our study aimed to evaluate the impact of the most-studied probiotic yeast (i.e., Saccharomyces boulardii Biocodex) on obesity and associated metabolic features, such as fat mass development, hepatic steatosis, and low-grade inflammation, in obese mice. S. boulardii was administered daily by oral gavage to leptin-resistant obese and type 2 diabetic mice (db/db) for 4 weeks. We found that S. boulardii-treated mice exhibited reduced body weight, fat mass, hepatic steatosis, and inflammatory tone. Interestingly, these effects of S. boulardii on host metabolism were associated with local effects in the intestine. S. boulardii increased cecum weight and cecum tissue weight but also induced dramatic changes in the gut microbial composition at the phylum, family, and genus levels. These gut microbiota changes in response to S. boulardii may also be correlated with the host metabolism response. In conclusion, this study demonstrates for the first time that S. boulardii may act as a beneficial probiotic treatment in the context of obesity and type 2 diabetes. IMPORTANCE To date, no probiotic yeast have been investigated in the context of obesity and type 2 diabetes. Here we found that type 2 diabetic and obese mice (db/db) treated with Saccharomyces boulardii exhibited reduced body weight, fat mass, hepatic steatosis, and inflammatory tone. These effects on host metabolism were associated with local effects in the intestine. Importantly, by using pyrosequencing, we found that S. boulardii treatment induces changes of the gut microbiota composition at the phylum, family, and genus levels. Moreover, we found that gut microbiota changes in response to S. boulardii were correlated with several host metabolism responses. To date, no probiotic yeast have been investigated in the context of obesity and type 2 diabetes. Here we found that type 2 diabetic and obese mice (db/db) treated with Saccharomyces boulardii exhibited reduced body weight, fat mass, hepatic steatosis, and inflammatory tone. These effects on host metabolism were associated with local effects in the intestine. Importantly, by using pyrosequencing, we found that S. boulardii treatment induces changes of the gut microbiota composition at the phylum, family, and genus levels. Moreover, we found that gut microbiota changes in response to S. boulardii were correlated with several host metabolism responses.

Adipose tissue NAPE-PLD controls fat mass development by altering the browning process and gut microbiota

Obesity is a pandemic disease associated with many metabolic alterations and involves several organs and systems. The endocannabinoid system (ECS) appears to be a key regulator of energy homeostasis and metabolism. Here we show that specific deletion of the ECS synthesizing enzyme, NAPE-PLD, in adipocytes induces obesity, glucose intolerance, adipose tissue inflammation and altered lipid metabolism. We report that Napepld-deleted mice present an altered browning programme and are less responsive to cold-induced browning, highlighting the essential role of NAPE-PLD in regulating energy homeostasis and metabolism in the physiological state. Our results indicate that these alterations are mediated by a shift in gut microbiota composition that can partially transfer the phenotype to germ-free mice. Together, our findings uncover a role of adipose tissue NAPE-PLD on whole-body metabolism and provide support for targeting NAPE-PLD-derived bioactive lipids to treat obesity and related metabolic disorders.

Tetrahydro iso-alpha acids from hops improve glucose homeostasis and reduce body weight gain and metabolic endotoxemia in high-fat diet-fed mice.

Obesity and related metabolic disorders such as insulin resistance and type 2 diabetes are associated with a low-grade inflammatory state possibly through changes in gut microbiota composition and the development of higher plasma lipopolysaccharide (LPS) levels, i.e. metabolic endotoxemia. Various phytochemical compounds have been investigated as potential tools to regulate these metabolic features. Humulus lupulus L. (hops) contains several classes of compounds with anti-inflammatory potential. Recent evidence suggests that hops-derived compounds positively impact adipocyte metabolism and glucose tolerance in obese and diabetic rodents via undefined mechanisms. In this study, we found that administration of tetrahydro iso-alpha acids (termed META060) to high-fat diet (HFD)-fed obese and diabetic mice for 8 weeks reduced body weight gain, the development of fat mass, glucose intolerance, and fasted hyperinsulinemia, and normalized insulin sensitivity markers. This was associated with reduced portal plasma LPS levels, gut permeability, and higher intestinal tight junction proteins Zonula occludens-1 and occludin. Moreover, META060 treatment increased the plasma level of the anti-inflammatory cytokine interleukin-10 and decreased the plasma level of the pro-inflammatory cytokine granulocyte colony-stimulating factor. In conclusion, this research allows us to decipher a novel mechanism contributing to the positive effects of META060 treatment, and supports the need to investigate such compounds in obese and type 2 diabetic patients.