Effects of the gut microbiota on host adiposity are modulated by the short-chain fatty-acid binding G protein-coupled receptor, Gpr41

Abstract

The distal human intestine harbors trillions of microbes that allow us to extract calories from otherwise indigestible dietary polysaccharides. The products of polysaccharide fermentation include short-chain fatty acids that are ligands for Gpr41, a G protein-coupled receptor expressed by a subset of enteroendocrine cells in the gut epithelium. To examine the contribution of Gpr41 to energy balance, we compared Gpr41-/- and Gpr41+/+ mice that were either conventionally-raised with a complete gut microbiota or were reared germ-free and then cocolonized as young adults with two prominent members of the human distal gut microbial community: the saccharolytic bacterium, Bacteroides thetaiotaomicron and the methanogenic archaeon, Methanobrevibacter smithii. Both conventionally-raised and gnotobiotic Gpr41-/- mice colonized with the model fermentative community are significantly leaner and weigh less than their WT (+/+) littermates, despite similar levels of chow consumption. These differences are not evident when germ-free WT and germ-free Gpr41 knockout animals are compared. Functional genomic, biochemical, and physiologic studies of germ-free and cocolonized Gpr41-/- and +/+ littermates disclosed that Gpr41-deficiency is associated with reduced expression of PYY, an enteroendocrine cell-derived hormone that normally inhibits gut motility, increased intestinal transit rate, and reduced harvest of energy (short-chain fatty acids) from the diet. These results reveal that Gpr41 is a regulator of host energy balance through effects that are dependent upon the gut microbiota.

Fig. 1.

Microbiota-mediated increase in adiposity is blunted in Bt/Ms cocolonized gnotobiotic Gpr41−/− mice. (A) Weights of both epididymal fat pads in Gpr41−/− and +/+ littermates that are GF, or raised GF and then colonized at 4 to 6 weeks of age with Bt and Ms (n, 8–14 males per group; three independent experiments). (B) Weight gain (n, 4–9 mice per group; followed one to two times per week for up to 4 weeks, between 5 and 9 weeks of age in the case of GF animals, and for 4 weeks after gavage in the case of Bt/Ms cocolonized gnotobiotic animals). Mean values ± SEM are plotted. *, P < 0.05, **, P < 0.01. N.S., not significantly different.

Fig. 2.

Microbiota-mediated increase in adiposity is blunted in CONV-R Gpr41−/− mice. (A) Epididymal fat-pad weights (values from both fat pads were combined for each animal; n, 12 males per group). (B) Weight gain (n, 6 per group; followed one to two times per week for up to 4 weeks, between the ages of 5 and 9 weeks). (C) Adiposity in CONV-R WT and knockout mice, defined by DEXA (n, 9–13 males per group; 8–10 weeks old). (D and E) Fasting (4 h) serum leptin levels plotted against percentage total body fat (n, 5 per group). *, P < 0.05, **, P < 0.01 (Student's t test).

Fig. 3.

Increased rate of intestinal transit in Bt/Ms colonized gnotobiotic Gpr41−/− mice. (A) Fasting serum PYY levels in GF and Bt/Ms cocolonized, Gpr41−/− and +/+ mice (n = four to eight per group; two independent experiments; all samples assayed in duplicate). (B and C) Gut transit time measured by oral gavage of a fluorescently labeled nonabsorbable substrate (fluorescine isothiocyanate-dextran; 70,000 MW) in GF and cocolonized WT and Gpr41-deficient animals. (B and C) Distribution of fluorescence signal intensity 60 min after gavage along the length of the gut; data are plotted as a fraction of total fluorescence in B. No signal was observed in the ceca or colons in any of the animals. Panel (C) presents the calculated geometric center of the fluorescence (n = 4–8 animals analyzed per group). *, P < 0.05, **, P < 0.01, ***, P < 0.005.

Fig. 4.

Gnotobiotic Gpr41−/− mice extract fewer calories from their polysaccharide-rich chow diet and excrete more SCFAs. (A) Dietary energy intake in GF and Bt/Ms cocolonized +/+ and Gpr41−/− littermates (calories of chow consumed per day monitored concurrently with body weight, as in Fig. 1). (B) Bomb calorimetry-based assessment of remaining calories in the feces of colonized (Bt/Ms) Gpr41−/− and +/+ mice (n = 6–7 per group). (C) GC-MS assay of cecal SCFA levels (n = 5–7 per group; each sample assayed in duplicate). (D) GC-MS study of fecal SFCAs from the same mice assayed in (C). *,P < 0.05, **, P < 0.01, ***, P < 0.005. (Student's t test used for comparisons of two groups.)