Helicobacter pylori colonization ameliorates glucose homeostasis in mice through a PPAR γ-dependent mechanism

Abstract

Background: There is an inverse secular trend between the incidence of obesity and gastric colonization with Helicobacter pylori, a bacterium that can affect the secretion of gastric hormones that relate to energy homeostasis. H. pylori strains that carry the cag pathogenicity island (PAI) interact more intimately with gastric epithelial cells and trigger more extensive host responses than cag(-) strains. We hypothesized that gastric colonization with H. pylori strains differing in cag PAI status exert distinct effects on metabolic and inflammatory phenotypes.

Methodology/principal findings: To test this hypothesis, we examined metabolic and inflammatory markers in db/db mice and mice with diet-induced obesity experimentally infected with isogenic forms of H. pylori strain 26695: the cag PAI wild-type and its cag PAI mutant strain 99-305. H. pylori colonization decreased fasting blood glucose levels, increased levels of leptin, improved glucose tolerance, and suppressed weight gain. A response found in both wild-type and mutant H. pylori strain-infected mice included decreased white adipose tissue macrophages (ATM) and increased adipose tissue regulatory T cells (Treg) cells. Gene expression analyses demonstrated upregulation of gastric PPAR γ-responsive genes (i.e., CD36 and FABP4) in H. pylori-infected mice. The loss of PPAR γ in immune and epithelial cells in mice impaired the ability of H. pylori to favorably modulate glucose homeostasis and ATM infiltration during high fat feeding.

Conclusions/significance: Gastric infection with some commensal strains of H. pylori ameliorates glucose homeostasis in mice through a PPAR γ-dependent mechanism and modulates macrophage and Treg cell infiltration into the abdominal white adipose tissue.

Figure 1. Effect of Helicobacter pylori infection on infiltration of immune cell subsets into adipose tissue.

Macrophages (F4/80⁺CD11b⁺) and regulatory T cells (CD4⁺CD25⁺Foxp3⁺) were immunophenotyped in white adipose tissue (WAT) from leptin receptor-deficient (db/db) mice infected with either the wild-type H. pylori 98–325 (white bars), the isogenic H. pylori 99–305 (black bars), or uninfected (dashed bars), (n = 10 mice/group). Statistically significant differences (P<0.05) between treatments (*) are indicated.

Figure 2. Effect of Helicobacter pylori infection on fasting blood glucose concentrations in two murine models of obesity.

Panel A: Fasting blood glucose (FBG) concentrations from leptin receptor-deficient (db/db) mice infected with either the wild-type H. pylori 98–325 (solid line), the isogenic H. pylori 99–305 (dotted line), or uninfected (dashed line), (n = 10 mice/group). Blood was obtained on days 0, 7, 14, 35, 50 and 71 of the study. Panel B: FBG concentrations in a mouse model of diet-induced obesity (DIO). Uninfected (control) mice (dashed line) or mice infected with H. pylori 99–305 (dotted line) are shown. Blood was obtained on days 0, 7, 14, 21 and 60 of the study. Panels C & D illustrate the area under the curve calculations for FBG concentrations in the db/db and DIO models, respectively. Statistically significant (P<0.05) differences with the uninfected control mice are indicated (*), (n = 10 mice/group).

Figure 3. Effect of Helicobacter pylori infection on plasma glucose concentrations, obtained from a glucose tolerance test (GTT).

Mice were administered an intraperitoneal glucose challenge (2 g/kg body weight). Panel A: Glucose levels in leptin receptor-deficient (db/db) mice infected with either the wild-type H. pylori 98–325 (solid line), the isogenic H. pylori 99–305 (dotted line), or uninfected (control) (dashed line). Blood was collected before (0), then 15, 60, and 90 minutes after glucose load, (n = 10 mice/group). Panel B: Mouse model of diet-induced obesity; DIO mice infected with H. pylori 99–305 (dotted line), or uninfected (dashed line). Panels C & D illustrate the area under the curve calculations for the glucose concentrations during a GTT in the db/db and DIO models, as in Panels A & B respectively. Blood was collected before (0), then 15, 45, and 90 minutes of glucose load, (n = 10 mice/group). Statistically significant differences (P<0.05) between treatments (*) are indicated.

Figure 4. Effect of Helicobacter pylori infection on plasma glucose concentrations in wild-type and peroxisome proliferator-activated receptor (PPAR) γ null mice.

Mice were administered an intraperitoneal glucose challenge (2 g/Kg body weight). Blood was collected before (0), then 15, 45, 60, and 90 minutes after glucose load, (n = 10 mice/group). Panel A and B: Wild-type and PPAR γ null mice fed regular AIN-93G diets infected with either H. pylori 99–305 or 98–325, when compared to the uninfected group. Panel C and D: Wild-type and PPAR γ null mice fed high-fat diets infected with either H. pylori 99–305 or 98–325, when compared to the uninfected group. Panel C: Plasma glucose levels were significantly lower at 15, 45 and 60 min in wild-type mice, fed high-fat diets infected with H. pylori 99–305 when compared to the uninfected or infected with H. pylori 98–325. Panel D: PPAR γ null mice fed high-fat diets showed significant differences between strains or the uninfected group only at t = 15 min. Statistically significant differences (P<0.05) between treatments (*) are indicated.

Figure 5. Effect of Helicobacter pylori infection on white adipose tissue (WAT) macrophage infiltration in wild-type and peroxisome proliferator-activated receptor (PPAR) γ null mice.

(A) Percentages of F4/80+CD11b+ infiltrating macrophages in WAT in wild-type mice fed high-fat diets, infected with H. pylori 99–305, 98–325 or uninfected controls. (B) Percentages of F4/80+CD11b+ infiltrating macrophages in WAT in PPAR γ null mice fed high-fat diets, infected with H. pylori 99–305, 98–325 or uninfected controls. Statistically significant differences (P<0.05) between treatments (*) are indicated.

Figure 6. Effect of Helicobacter pylori infection on peroxisome proliferator receptor (PPAR) γ responsive gene expression.

Gastric expression of CD36 (A) and fatty acid binding protein (FABP4) (B) was assessed by real-time quantitative RT-PCR in wild type mice fed high-fat diet infected with H. pylori 98–325 or 99–305 strains, or uninfected controls (n = 10). Data are represented as mean ± standard error. Points with an asterisk are significantly different when compared to the wild type control group (P<0.05).