Lowering bile acid pool size with a synthetic farnesoid X receptor (FXR) agonist induces obesity and diabetes through reduced energy expenditure

Abstract

We evaluated the metabolic impact of farnesoid X receptor (FXR) activation by administering a synthetic FXR agonist (GW4064) to mice in which obesity was induced by a high fat diet. Administration of GW4064 accentuated body weight gain and glucose intolerance induced by the high fat diet and led to a pronounced worsening of the changes in liver and adipose tissue. Mechanistically, treatment with GW4064 decreased bile acid (BA) biosynthesis, BA pool size, and energy expenditure, whereas reconstitution of the BA pool in these GW4064-treated animals by BA administration dose-dependently reverted the metabolic abnormalities. Our data therefore suggest that activation of FXR with synthetic agonists is not useful for long term management of the metabolic syndrome, as it reduces the BA pool size and subsequently decreases energy expenditure, translating as weight gain and insulin resistance. In contrast, expansion of the BA pool size, which can be achieved by BA administration, could be an interesting strategy to manage the metabolic syndrome.

Figures

FIGURE 1.

FXR ligands affect metabolic control in mice fed a high fat diet. A, body weight (BW) change and cumulative food intake of C57BL/6J mice during 3 months on different diets/treatments. Food intake was measured daily for 1 week at day 14. C denotes control diet; F denotes high fat diet; FW denotes high fat diet + GW4064, and FA denotes high fat diet + CA. B, comparison of liver, epWAT, and BAT tissue weight after 3 months of treatment with different diets. C, comparison of the BA pool size and composition in enterohepatic organs of mice treated with different diets for 2 months. Abbreviations used are as follows: T, Tauro; U, Urso; and M, Muri. D, serum glucose and insulin levels after 6 h of fasting and 70 days on the indicated treatments. E, glucose levels during an OGTT and IPITT in mice on the different diets for 72 and 80 days, respectively. Data are expressed as the mean ± S.E. (n = 5). *, p < 0.05; **, p < 0.01 versus high fat diet (F).

FIGURE 2.

Changes in liver, epWAT, and BAT histology and energy expenditure induced by FXR ligands. A, hematoxylin and eosin (HE)-stained liver, epWAT, and BAT sections of mice treated with control or high fat diet and exposed to the same treatments as specified in Fig. 1B. Abbreviations are as in Fig. 1. Scale bar, 50 μm. B, O2 consumption (VO2) and CO2 production (VCO2) by indirect calorimetry in mice on the different diets for 3 months. The acclimation time in the chambers was 2 h. The VO2 was normalized to body weight to the 0.75 power. The right panel represents the averaged VO2 and VCO2. C, mRNA expression levels of indicated genes in liver, ileum, BAT, and epWAT of mice after 2 months of treatment with different diets. Data are expressed as the mean ± S.E. (n = 5). *, p < 0.05, or **, p < 0.01 versus high fat diet (F).

FIGURE 3.

FXR agonists do not affect adipocyte differentiation and insulin sensitivity in vitro and in vivo. A, insulin-stimulated glucose uptake after adipocyte differentiation of 3T3-L1 cells with or without GW4064 or CDCA. Cells were stimulated with insulin (5 μg/ml) for 12 h, and the decrease of glucose in the medium was measured (left panel). TG content in these differentiated 3T3-L1 cells is shown in the right panel. C denotes control medium; W indicates medium with 10 μm GW4064; CD indicates medium with 20 μm CDCA. B, mRNA expression levels of Pparγ, aP2, Fas, and ACC1 in 3T3-L1 cells, as specified in A. C, determination of Akt/PKB or IRS-1 phosphorylation levels by Western blotting in differentiated 3T3-L1 cells. Cells were cultured with or without GW4064 or CDCA and stimulated with 5 μg/ml insulin for 5 min. Western blotting was performed with anti-Ser-473-phosphorylated Akt, total Akt, anti-Ser-307-phosphorylated IRS-1, or total IRS-1 antibodies. D, determination of Akt/PKB phosphorylation levels by Western blotting with anti-Ser-473-phosphorylated Akt or total Akt antibody in epWAT. Protein extracts were prepared from epWAT of C57BL/6J mice, which were fed a high fat diet with or without GW4064 for 76 days.

FIGURE 4.

CA coadministration overcomes the negative effects of GW4064 by restoring the BA pool. A, body weight of C57BL/6J mice after 76 days on different diets/treatments. Abbreviations are as in Fig. 1. Different doses of CA (0.125, 0.25, or 0.5% w/w) were supplemented to a high fat diet + GW4064. B, comparison of epWAT tissue weight after 76 days on the different diets. C, AUC of glucose levels during an OGTT after 60 days on the different diets. D, comparison of BA pool size and composition in enterohepatic organs in C57BL/6J mice treated with different diets for 10 days. Data are expressed as the mean ± S.E. (n = 5). *, p < 0.05, or **, p < 0.01, versus F and #, p < 0.05, or ##, p < 0.01, versus high fat diet + GW4064.

FIGURE 5.

Changes in energy metabolism after FXR activation using GW4064. Administration of a synthetic FXR agonist to high fat fed mice leads to a reduction in bile acid synthesis and as a consequence to a reduced bile acid pool size. This translates into reduced energy expenditure in brown adipose tissue, TG accumulation in WAT, BAT, and liver, and insulin resistance.