Fibroblast growth factor 21 is not required for the antidiabetic actions of the thiazoladinediones

Abstract

Fibroblast growth factor 21 is an emerging metabolic regulator that was recently proposed to be a fed-state inducible factor in adipose tissue. As mice lacking FGF21 were refractory to treatment with rosiglitazone, FGF21 was suggested to underlie PPARγ-driven pharmacology and side effect profile (Dutchak et al., 2012 [12]). To evaluate FGF21/PPARγ cross-talk we conducted experiments in control and FGF21 null animals and found that rosiglitazone was equally efficacious in both strains. Specifically, diverse endpoints ranging from enhanced glycemic control, improved lipid homeostasis and side effects such as adipose accumulation were evident in both genotypes. Furthermore, the transcriptional signature and cytokine secretion profile of rosiglitazone action were maintained in our FGF21KO animals. Finally, we found that FGF21 in adipose was expressed at comparable levels in fasted and fed states. Thus, our data present a new viewpoint on the FGF21/PPARγ interplay whereby FGF21 is not necessary for the metabolic events downstream of PPARγ.

Keywords: Adiponectin; FGF21; Metabolism; PPARγ; Rosiglitazone.

Supplementary Fig. 1

Using an immunoprecipitation of adipose tissue from both WT and FGF21KO mice treated with either vehicle (−) or rosiglitazone (+) we were unable to detect either basal or ligand stimulated sumoylation of PPARγ. Detection of PPARγ was hindered in in vivo samples by detection of endogenous mouse antibodies at the correct molecular weight for PPARγ.

Figure 1

FGF21 null mice display mild obesity which is exacerbated by a high fat diet. Panel 1. Body weight was determined in a large cohort of chow fed, age matched male WT (n=30) and FGF21KO mice (n=24) (A). In the same cohort we also assessed body composition via qNMR and determined absolute fat mass (B), fat free mass (C) and water mass (D). The measures of both fat mass (E) and fat free mass (F) were then also expressed as a percentage of total body mass. Statistical significance is denoted by *. Differences were considered significant when P≤0.05.Panel 2. At 10 weeks of age WT and FGF21KO mice were fed a HFD for a period of 12 weeks. Following diet exposure we determined body weight (G), absolute fat mass (H), fat free mass (I) and water mass (J). The measures of both fat mass (K) and fat free mass (L) were then also expressed as percentage of total body mass. Statistical significance is denoted by *. Differences were considered significant when P≤0.05.

Figure 2

FGF21 is not required for the metabolic effects of TZD treatment in DIO mice. To determine the extent to which the effects of rosiglitazone are mediated by FGF21 we examined plasma glucose (A), insulin (B), triglycerides (C), Cholesterol (D) and free fatty acids (E), ALT (F) and AST (G) in WT and FGF21 null mice. We also examined the effects of chronic treatment on cumulative body weight change (H), change in fat mass (I) and change in total body water content (J).

Figure 3

Mice lacking FGF21 preserve the transcriptional hallmarks of rosiglitazone treatment. Following treatment with either vehicle or rosiglitazone we assessed gene expression in WAT of WT and FGF21KO mice. Statistical analysis was performed using one-way ANOVA, followed by Dunnett's multiple comparisons test where appropriate. Statistical significance from vehicle was denoted by * while differences between genotypes are indicated with †. Differences were considered significant when P≤0.05.

Figure 4

FGF21KO animals respond to both 3 mg/kg and 10 mg/kg doses of rosiglitazone. FGF21 levels were measured in plasma of WT and FGF21KO mice following treatment with either vehicle or rosiglitazone at either 3 mg/kg or 10 mg/kg using ELISA (A). Following sacrifice of WT and FGF21KO mice we examined plasma glucose (B), insulin (C) and total adiponectin (D). Statistical analysis was performed using one-way ANOVA, followed by Dunnett's multiple comparisons test where appropriate. Statistical significance from vehicle was denoted by *. Differences were considered significant when P≤0.05.

Figure 5

Treatment with rosiglitazone sensitizes to the metabolic effects of FGF21. To assess the potential for interaction between FGF21 and rosiglitazone we compared treatment with either agent alone versus a combination of the two. Following treatment we examine body mass change (A), plasma glucose (B), insulin (C), Cholesterol (D) and free fatty acids (E) in addition to change in total water (F) and fat mass gain/loss (G). Statistical significance from vehicle was denoted by * while differences from rosiglitazone alone are indicated with †. Differences were considered significant when P≤0.05.

Figure 6

FGF21 expression is regulated by the fed to fasted transition in liver and pancreas but not in adipose. FGF21 levels were measured in plasma of fed and fasted mice using ELISA (A). Tissue specific expression of FGF21 was assessed in the pancreas, liver and WAT at the mRNA level (B). Statistical analysis was performed using one-way ANOVA, followed by Dunnett's multiple comparisons test where appropriate. Statistical significance from vehicle was denoted by *. Differences were considered significant when P≤0.05.