Bacteroides uniformis CECT 7771 alleviates inflammation within the gut-adipose tissue axis involving TLR5 signaling in obese mice

Abstract

This study investigated the immune mechanisms whereby administration of Bacteroides uniformis CECT 7771 reduces metabolic dysfunction in obesity. C57BL/6 adult male mice were fed a standard diet or a Western diet high in fat and fructose, supplemented or not with B. uniformis CECT 7771 for 14 weeks. B. uniformis CECT 7771 reduced body weight gain, plasma cholesterol, triglyceride, glucose, and leptin levels; and improved oral glucose tolerance in obese mice. Moreover, B. uniformis CECT 7771 modulated the gut microbiota and immune alterations associated with obesity, increasing Tregs and reducing B cells, total macrophages and the M1/M2 ratio in both the gut and epididymal adipose tissue (EAT) of obese mice. B. uniformis CECT 7771 also increased the concentration of the anti-inflammatory cytokine IL-10 in the gut, EAT and peripheral blood, and protective cytokines TSLP and IL-33, involved in Treg induction and type 2 innate lymphoid cells activation, in the EAT. It also restored the obesity-reduced TLR5 expression in the ileum and EAT. The findings indicate that the administration of a human intestinal bacterium with immunoregulatory properties on the intestinal mucosa helps reverse the immuno-metabolic dysfunction caused by a Western diet acting over the gut-adipose tissue axis.

Figure 1

Anthropometric parameters and dietary intake. (A) Total body weight gain, (B) Weekly body weight gain  (C) Visceral adipose tissue (VAT) weight, (D) Epididymal adipose tissue (EAT) weight, (E) Mesenteric adipose tissue (MAT) weight, (F) Cumulative caloric intake from liquid diet, solid food and total caloric intake. Data are expressed as mean and standard error (vertical bars). Significant differences for liquid diets, solid foods, and total caloric intake are represented by uppercase letters, lowercase letters and stars, respectively. Statistically significant differences were established by ANOVA and post hoc student t test (p < 0.05).

Figure 2

Plasma concentrations of (A) cholesterol, (B) triglycerides, (C) glucose, (D) glucose levels for individual time points in a glucose tolerance, (E) AUC values for glucose in a GTT, (F) insulin and (G) leptin. Data are expressed as mean and standard error (vertical bars). Statistically significant differences were established by ANOVA and post hoc student t test (p < 0.05).

Figure 3

Relative expression of (A) TLR2, (B) TLR4 and (C) TLR5 from Peyer´s patches and (D) TLR5 from epididymal adipose tissue. Relative activation of TLR5 using HEK-Blue hTLR5 cells with (E) fecal samples from the SD, HFHFD and HFHFD + B experimental groups and (F) individual bacterial cultures of Phascolarctobacterium faecium (negative control), Clostridium butyricum (positive control), B. uniformis CECT 7771, and recombinant flagellin (RecFLA-ST, 1 μg/ml) (positive control). Control samples consisting of endotoxin-free water were included as negative controls. Data are expressed as mean and standard error (vertical bars). Statistically significant differences were established by ANOVA and post hoc student t test (p < 0.05).

Figure 4

(A) Alpha diversity indices (Shannon’s diversity index, Simpson’s index, Simpson’s reciprocal index and Simpson’s evenness) from each treatment group. (B) Principle coordinates analysis (PCoA) plot using generalized UniFrac distances comparing microbial communities from each treatment group. Group means are indicated by the center of each ellipse. Distance-based non-parametric PERMANOVA tests were conducted at a global level as well as pairwise comparisons of treatment groups. p values of all pairwise comparisons were corrected for multiple comparisons (q) using false discovery rate. (C) Boxplots of gut microbiota taxonomic groups that demonstrated significant differences between treatment groups. Significant differences (p < 0.05) between treatment groups are represented with *.

Figure 5

Heatplot of correlations between anthropometric, metabolic, and immune features with the top 50 most abundant gut microbiota taxonomic groups (classified to the lowest taxonomic level). The relative key color indicates the value of Spearman’s correlation coefficient rho (ρ) (blue = positive; red = negative). p values were adjusted with the false discovery rate method for multiple comparisons. Variable pairs that have an “*” below the diagonal line are significantly correlated and pairs with a “*” above the diagonal line are significantly correlated after adjustment of p values for multiple comparisons (q < 0.05).