FGF21 requires βklotho to act in vivo

Abstract

FGF21 has gradually become a focal point in metabolic research given its intriguing and complex biology and relevance to drug discovery. Despite the large amount of accumulated data, there remains a dearth of understanding of FGF21 physiology at the molecular/whole organism level. The scaffold protein βklotho (KLB) has previously been demonstrated in vitro to function as a co-factor permitting FGF21 mediated FGF receptor activation. However, the requirement for KLB in the propagation of FGF21 action in living animals has yet to be evaluated. To answer this question, we tested FGF21 in mice with total body ablation of KLB (KLBKO) and found no detectable activity. Firstly, we demonstrate that the disruption of KLB entirely abrogates acute FGF21 signaling in adipose tissue. We go on to show that this signaling defect translates to the absence of FGF21 mediated metabolic improvements in DIO mice. Indeed, KLBKO mice are totally refractory to FGF21-induced normalization of glucose homeostasis, attenuation of dyslipidemia, elevation of energy expenditure and weight loss. The lack of FGF21-driven effects was further substantiated at the transcriptional level with no FGF21 target gene signature detectable in adipose tissue and liver of KLBKO animals. Taken together our data show that KLB is a vital component of the FGF21 in vivo signaling machinery and is critically required for FGF21 action at the whole organism level.

Figure 1. Expression of FGFR/Klotho receptor components (A–F), KLB protein expression in liver and WAT (G).

Induction of immediate early genes EGR-1 (H) and cFOS (I) expression in WAT of WT and KLBKO animals following acute FGF21 treatment. Statistical analysis was performed using one-way ANOVA, followed by Dunnett’s multiple comparisons test where appropriate. Differences were considered significant when P≤0.05.

Figure 2. Following chronic FGF21 treatment we assessed weight loss (A), fat mass loss (B), food intake (C) and energy expenditure in WT (D) and KLBKO mice (E).

Statistical analysis was performed using one-way ANOVA, followed by Dunnett’s multiple comparisons test where appropriate. Differences were considered significant when P≤0.05.

Figure 3. To determine the effect of chronic FGF21 on circulating hormones and metabolites we measured plasma glucose (A), insulin (B), cholesterol (C), β-Hydroxybutyrate (D), adiponectin (E).

Statistical analysis was performed using one-way ANOVA, followed by Dunnett’s multiple comparisons test where appropriate. Differences were considered significant when P≤0.05.