Depletion of Blautia Species in the Microbiota of Obese Children Relates to Intestinal Inflammation and Metabolic Phenotype Worsening

Abstract

Cross-sectional studies conducted with obese and control subjects have suggested associations between gut microbiota alterations and obesity, but the links with specific disease phenotypes and proofs of causality are still scarce. The present study aimed to profile the gut microbiota of lean and obese children with and without insulin resistance to characterize associations with specific obesity-related complications and understand the role played in metabolic inflammation. Through massive sequencing of 16S rRNA gene amplicons and data analysis using a novel permutation approach, we have detected decreased incidence of Blautia species, especially Blautia luti and B. wexlerae, in the gut microbiota of obese children, which was even more pronounced in cases with both obesity and insulin resistance. There was also a parallel increase in proinflammatory cytokines and chemokines (gamma interferon [IFN-γ], tumor necrosis factor alpha [TNF-α], and monocyte chemoattractant protein 1 [MCP-1]) in feces of obese children compared to those of lean ones. B. luti and B. wexlerae were also shown to exert an anti-inflammatory effect in peripheral blood mononuclear cell cultures in vitro, compared to non-obesity-associated species. We suggest that the depletion of B. luti and B. wexlerae species in the gut ecosystem may occur in cases of obesity and contribute to metabolic inflammation leading to insulin resistance.IMPORTANCE Child obesity constitutes a risk factor for developing insulin resistance which, if sustained, could lead to more severe conditions like type 2 diabetes (T2D) in adulthood. Our study identified previously unknown species whose depletion (Blautia luti and Blautia wexlerae) is associated with insulin resistance in obese individuals. Our results also indicate that these bacterial species might help to reduce inflammation causally linked to obesity-related complications. Childhood is considered a window of opportunity to tackle obesity. These new findings provide, therefore, valuable information for the future design of microbiota-based strategies for the early prevention of obesity-related complications.

Keywords: Blautia luti; Blautia wexlerae; PBMCs; childhood obesity; children; gut inflammation; gut microbiota; inflammation; insulin resistance; microbiota; obesity; permubiome; probiotics.

FIG 1

Beta diversity of the gut microbiota profiles from normal weight and obese children. A principal-coordinate analysis (PCoA) of dissimilarities among samples is shown, with marginal boxplots disclosing the distribution of the two most informative principal coordinates (PC) of the multidimensional analysis. Blue data points correspond to outliers. The color key for the scatter- and boxplots indicate the study groups of children. PERMANOVA values = 2.08 and 1.68 (P < 0.005) for comparison using two-group (lean versus obese) and three-group (lean versus obese versus obese+IR) configurations, respectively.

FIG 2

OTUs with differential abundances among child groups. A permutation-based test was performed between pairs of groups to disclose taxonomic features associated with different conditions. Differential abundance was assumed when corrected P values were <0.1 (FDR test). Respective P values supporting the biomarker discovery approach are shown accordingly along with a color key for boxplots. Blue data points indicate outliers. Taxonomic identification of OTUs was based on SINA aligner using default parameters; shown are reliable identifications based on the SILVA database with the level of sequence identity (within paretheses) against their last common ancestor (lca). If genus was identified, we further identified the OTU at the species level in a BLAST-based approach (top alignment score and length) against the NCBI 16S reference database and classifier algorithms implemented in DADA2 with the combined RefSeq+RDP database. The sequence identity is shown. f, family; g, genus.

FIG 3

Links between gut microbiota and inflammatory markers. (A) Spearman correlations between the OTUs selected and the proinflammatory markers analyzed. The strongest correlations supported by larger ρ values are highlighted accordingly (positive are shaded blue and negative are shaded red). Asterisks indicate correlation with corrected P values of ≤0.05. (B) Scatterplots of selected correlations between fecal cytokines and OTUs exhibiting top ρ values. The axes were plotted as log-transformed data, and linear correlations (slope as red line) as well as confidence intervals (gray shadow) are drawn in all cases. (C) Anti-inflammatory to proinflammatory cytokine ratios (IL-4/IFN-γ and IL-4/TNF-α individually represented) detected upon exposure of PBMC cultures to different bacterial stimuli in vitro. The botton barplot represent the sum of both cytokine ratios. Differences between the effects of different bacterial stimuli established by one-way ANOVA with Bonferroni correction for multiple testing at a P value of <0.05 are shown in bar graphs.