Evidence for Constitutive Microbiota-Dependent Short-Term Control of Food Intake in Mice: Is There a Link with Inflammation, Oxidative Stress, Endotoxemia, and GLP-1?

Aims: Although prebiotics, probiotics, and fecal transplantation can alter the sensation of hunger and/or feeding behavior, the role of the constitutive gut microbiota in the short-term regulation of food intake during normal physiology is still unclear. Results: An antibiotic-induced microbiota depletion study was designed to compare feeding behavior in conventional and microbiota-depleted mice. Tissues were sampled to characterize the time profile of microbiota-derived signals in mice during consumption of either standard or high-fat food for 1 h. Pharmacological and genetic tools were used to evaluate the contribution of postprandial endotoxemia and inflammatory responses in the short-term regulation of food intake. We observed constitutive microbial and macronutrient-dependent control of food intake at the time scale of a meal; that is, within 1 h of food introduction. Specifically, microbiota depletion increased food intake, and the microbiota-derived anorectic effect became significant during the consumption of high-fat but not standard food. This anorectic effect correlated with a specific postprandial microbial metabolic signature, and did not require postprandial endotoxemia or an NOD-, LRR-, and Pyrin domain-containing protein 3-inflammasome-mediated inflammatory response. Innovation and Conclusion: These findings show that the gut microbiota controls host appetite at the time scale of a meal under normal physiology. Interestingly, a microbiota-derived anorectic effect develops specifically with a high-fat meal, indicating that gut microbiota activity is involved in the satietogenic properties of foods. Antioxid. Redox Signal. 37, 349-369.

A periplasmic cupredoxin with a green CuT1.5 center is involved in bacterial copper tolerance

The importance of copper resistance pathways in pathogenic bacteria is now well recognized, since macrophages use copper to fight bacterial infections. Additionally, considering the increase of antibiotic resistance, growing attention is given to the antimicrobial properties of copper. It is of primary importance to understand how bacteria deal with copper. The Cu-resistant cuproprotein CopI is present in many human bacterial pathogens and environmental bacteria and crucial under microaerobiosis (conditions for most pathogens to thrive within their host). Hence, understanding its mechanism of function is essential. CopI proteins share conserved histidine, cysteine, and methionine residues that could be ligands for different copper binding sites, among which the cupredoxin center could be involved in the protein function. Here, we demonstrated that Vibrio cholerae and Pseudomonas aeruginosa CopI restore the Cu-resistant phenotype in the Rubrivivax gelatinosus ΔcopI mutant. We identified that Cys125 (ligand in the cupredoxin center) and conserved histidines and methionines are essential for R. gelatinosus CopI (RgCopI) function. We also performed spectroscopic analyses of the purified RgCopI protein and showed that it is a green cupredoxin able to bind a maximum of three Cu(II) ions: (i) a green Cu site (CuT1.5), (ii) a type 2 Cu binding site (T2) located in the N-terminal region, and (iii) a third site with a yet unidentified location. CopI is therefore one member of the poorly described CuT1.5 center cupredoxin family. It is unique, since it is a single-domain cupredoxin with more than one Cu site involved in Cu resistance.

Dietary switch to Western diet induces hypothalamic adaptation associated with gut microbiota dysbiosis in rats

BACKGROUND

Early hyperphagia and hypothalamic inflammation encountered after Western diet (WD) are linked to rodent propensity to obesity. Inflammation in several brain structures has been associated with gut dysbiosis. Since gut microbiota is highly sensitive to dietary changes, we hypothesised that immediate gut microbiota adaptation to WD in rats is involved in inflammation-related hypothalamic modifications.

METHODS

We evaluated short-term impact of WD consumption (2 h, 1, 2 and 4 days) on hypothalamic metabolome and caecal microbiota composition and metabolome. Data integration analyses were performed to uncover potential relationships among these three datasets. Finally, changes in hypothalamic gene expression in absence of gut microbiota were evaluated in germ-free rats fed WD for 2 days.

RESULTS

WD quickly and profoundly affected the levels of several hypothalamic metabolites, especially oxidative stress markers. In parallel, WD consumption reduced caecal microbiota diversity, modified its composition towards pro-inflammatory profile and changed caecal metabolome. Data integration identified strong correlations between gut microbiota sub-networks, unidentified caecal metabolites and hypothalamic oxidative stress metabolites. Germ-free rats displayed reduced energy intake and no changes in redox homoeostasis machinery expression or pro-inflammatory cytokines after 2 days of WD, in contrast to conventional rats, which exhibited increased SOD2, GLRX and IL-6 mRNA levels.

CONCLUSION

A potentially pro-inflammatory gut microbiota and an early hypothalamic oxidative stress appear shortly after WD introduction. Tripartite data integration highlighted putative links between gut microbiota sub-networks and hypothalamic oxidative stress. Together with the absence of hypothalamic modifications in germ-free rats, this strongly suggests the involvement of the microbiota-hypothalamus axis in rat adaptation to WD introduction and in energy homoeostasis regulation.