Metabolic syndrome and altered gut microbiota in mice lacking Toll-like receptor 5

Abstract

Metabolic syndrome is a group of obesity-related metabolic abnormalities that increase an individual's risk of developing type 2 diabetes and cardiovascular disease. Here, we show that mice genetically deficient in Toll-like receptor 5 (TLR5), a component of the innate immune system that is expressed in the gut mucosa and that helps defend against infection, exhibit hyperphagia and develop hallmark features of metabolic syndrome, including hyperlipidemia, hypertension, insulin resistance, and increased adiposity. These metabolic changes correlated with changes in the composition of the gut microbiota, and transfer of the gut microbiota from TLR5-deficient mice to wild-type germ-free mice conferred many features of metabolic syndrome to the recipients. Food restriction prevented obesity, but not insulin resistance, in the TLR5-deficient mice. These results support the emerging view that the gut microbiota contributes to metabolic disease and suggest that malfunction of the innate immune system may promote the development of metabolic syndrome.

Fig. 1

T5KO mice develop obesity. T5KO mice and WT littermates were monitored for 20 weeks. (A) Body mass. (B) MRI image showing fat distribution. (C) Abdominal photograph of representative 20-week-old male mice. (D) Fat-pad mass. (E) Serum triglycerides. (F) Serum cholesterol. (G) Blood pressure. Results in (A) to (C) are from an individual experiment (n = 20, 10 males and 10 females) and representative of more than six distinct groups of mice. Results in (B) are representative of three separate analyses performed on mice that had median body mass of their litters. Results in (C) to (E) are from a single experiment (n = 6) and representative of several experiments. Results in (G) compare groups (n = 4) of mice with 5 to 10 independent measurements per mouse. *, P < 0.05.

Fig. 2

T5KO exhibit hyperglycemia/insulin resistance. Twenty-week-old T5KO and WT littermate mice were assayed for various parameters of glucose homeostasis. (A) Fifteen-hour fasting blood glucose. (B) Glucose tolerance test. Mice were intraperitoneally injected with glucose (2 g per kg of body mass). (C) Serum insulin after a 5-hour fast. (D) Serum insulin levels before and 2.5 min after challenge with glucose (3 g/kg body mass). (E) Insulin sensitivity. Mice were fasted for 5 hours and intraperitoneally injected with insulin (1.0 U/kg body mass). (F) Hematoxylin and eosin (H&E) stained pancreata were blindly scored for size and number of pancreatic islets. Results in (A), (C), and (F) are from an individual experiment (n = 12 to 13) and representative of more than six distinct groups of mice. Results in (B), (D), and (E) are from a single experiment (n = 6) and representative of several experiments. *, P < 0.05.

Fig. 3

T5KO metabolic syndrome depends on hyperphagia. (A and B) Four-week-old WT and T5KO mice were given a high-fat diet for 8 weeks. (A) Fifteen-hour fasting blood glucose. (B) H&E stained pancreas (P, upper panel) and liver (L, lower panel). Arrows point to inflammatory infiltrates. (C) Mice on a regular diet were monitored for food intake. (D to G) Mice were subjected to food restriction and assayed for (D) body mass and (E) fat-pad mass. (F) Fifteen-hour fasting glucose. (G) Insulin sensitivity measured as described in Fig. 2E. Results in (A) and (B) are from a single experiment (n = 5 to 6) and representative of two independent experiments. Results in (C) are from a single experiment (n = 6) and representative of similar results with several groups of mice. (D) to (G) is from a single experiment (n = 10) and representative of two independent experiments. *, P < 0.05.

Fig. 4

T5KO gut microbiota is necessary and sufficient to transfer metabolic syndrome phenotype to germ-free mice. (A to C) Four-week-old T5KO mice and WT littermates were placed on broad-spectrum antibiotics and monitored for 12 weeks. (A) Fifteen-hour fasting glucose. (B) Food intake. (C) Fat-pad mass. (D to H) Four-week-old WT germ-free mice were intragastrically administered cecal content from WT or T5KO mice and monitored for 7 weeks. (D) Food intake expressed as average consumption per mouse per day 10 to 13 days after transplant. (E) Body mass. (F) Fat-pad mass. (G) Insulin sensitivity. (H) Colonic tumor necrosis factor–α(TNF-α) and IL-1β. Results in (A) to (C) are from a single experiment (n = 5 to 6) and representative of two independent experiments (other shown in fig. S14). Results in (D) to (H) are from a single experiment (n = 5 to 6). *, P < 0.05.