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Pattern recognition receptors link metabolite and bacteria-derived inflammation to insulin resistance during obesity. We demonstrate that NOD2 detection of bacterial cell wall peptidoglycan (PGN) regulates metabolic inflammation and insulin sensitivity. An obesity-promoting high-fat diet (HFD) increased NOD2 in hepatocytes and adipocytes, and NOD2(-/-) mice have increased adipose tissue and liver inflammation and exacerbated insulin resistance during a HFD. This effect is independent of altered adiposity or NOD2 in hematopoietic-derived immune cells. Instead, increased metabolic inflammation and insulin resistance in NOD2(-/-) mice is associated with increased commensal bacterial translocation from the gut into adipose tissue and liver. An intact PGN-NOD2 sensing system regulated gut mucosal bacterial colonization and a metabolic tissue dysbiosis that is a potential trigger for increased metabolic inflammation and insulin resistance. Gut dysbiosis in HFD-fed NOD2(-/-) mice is an independent and transmissible factor that contributes to metabolic inflammation and insulin resistance when transferred to WT, germ-free mice. These findings warrant scrutiny of bacterial component detection, dysbiosis, and protective immune responses in the links between inflammatory gut and metabolic diseases, including diabetes., (© 2015 The Authors. Published under the terms of the CC BY 4.0 license.)

Aim: Metabolic syndrome consists of a cluster of clinical and biological abnormalities, influenced by insulin resistance and promoting cardiovascular diseases. We examined the relationships between metabolic syndrome, its various components, insulin resistance, and periodontitis., Materials and Methods: The study included 276 subjects (35-74 years) recruited within a cross-sectional survey on cardiovascular risk factors. Twenty-one were excluded because of infectious risk or total tooth loss. Clinical attachment loss (CAL), probing pocket depth (PD), gingival and plaque indexes were recorded. Periodontitis was classified into moderate and severe forms., Results: The mean age was 58, 41% of the subjects had moderate and 39% had severe periodontitis. In univariate comparisons, periodontitis was associated with metabolic syndrome (p=0.050), most of its components, and HOMA index (homoeostasis model assessment of insulin resistance). After adjustment for confounders, only HOMA index remained associated with severe periodontitis (odds ratio [OR]=3.97 [95% confidence interval: 1.22-12.9], OR=3.78 [1.14-12.5] for third and fourth versus the first quartile of the HOMA index, respectively). The HOMA index was also associated with the number of periodontal sites with CAL>or=4 mm, CAL>or=5 mm, or PD>or=4 mm (greater number for higher HOMA-index values). This relationship disappeared in never-smokers., Conclusions: Our data support the relationships between metabolic disturbances and periodontitis, with a central role of insulin resistance.

Diabetes and obesity are two metabolic diseases characterized by insulin resistance and a low-grade inflammation. Seeking an inflammatory factor causative of the onset of insulin resistance, obesity, and diabetes, we have identified bacterial lipopolysaccharide (LPS) as a triggering factor. We found that normal endotoxemia increased or decreased during the fed or fasted state, respectively, on a nutritional basis and that a 4-week high-fat diet chronically increased plasma LPS concentration two to three times, a threshold that we have defined as metabolic endotoxemia. Importantly, a high-fat diet increased the proportion of an LPS-containing microbiota in the gut. When metabolic endotoxemia was induced for 4 weeks in mice through continuous subcutaneous infusion of LPS, fasted glycemia and insulinemia and whole-body, liver, and adipose tissue weight gain were increased to a similar extent as in high-fat-fed mice. In addition, adipose tissue F4/80-positive cells and markers of inflammation, and liver triglyceride content, were increased. Furthermore, liver, but not whole-body, insulin resistance was detected in LPS-infused mice. CD14 mutant mice resisted most of the LPS and high-fat diet-induced features of metabolic diseases. This new finding demonstrates that metabolic endotoxemia dysregulates the inflammatory tone and triggers body weight gain and diabetes. We conclude that the LPS/CD14 system sets the tone of insulin sensitivity and the onset of diabetes and obesity. Lowering plasma LPS concentration could be a potent strategy for the control of metabolic diseases.

Inflammation plays a role in all stages of atherosclerosis from the formation to the rupture of the plaque. Guided by inflammatory mediators, monocytes bind to an endothelium damaged by cardiovascular risk factors, and then migrate towards the intima where, after incorporating oxidized low-density lipoprotein particles, they are transformed into foam cells. The lipid streak forms and develops as an atherosclerotic plaque, which is susceptible to erosion and rupture. Inflammation fed by excess adipose tissue decreases insulin sensitivity, which is the central feature of the metabolic syndrome. Inflammation therefore appears to be a common factor of atherosclerosis and the metabolic syndrome. The factors triggering this inflammation have yet to be determined. One line of thought would appear to point to diet.

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 naïve 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. [ABSTRACT FROM AUTHOR]