An induction of lipolysis by β3-adrenergic agonist CL316,243 (CL) increases plasma free fatty acid (FFA) level resulting later in ectopic lipid accumulation in liver. The peak of FFA stimulates insulin secretion and causes acute drop of blood glucose (BG) in chow-fed mice. This glucose-lowering effect is attenuated in insulin-resistant dietary obese (DIO) mice. Fibroblast growth factor 21 (FGF21) treatment increases insulin sensitivity while inhibiting lipolysis. Both FGF21 and CL induce uncoupling protein 1 (UCP1) in brown adipose tissue, increasing capacity for combustion of glucose. Thus, the FGF21 treatment has a potential to modulate the glucoregulatory action of CL. Here we aim to characterize the effect of the CL+FGF21 combination and to investigate the role of UCP1 in this effect. DIO C57Bl/6 mice were housed at 30 °C in order to minimize basal adrenergic tone. Animals were treated 2x daily with 65 μg FGF21 or its vehicle for 8 days. This treatment lowered insulin (increased insulin sensitivity) . Subsequently, the mice were injected with 35 μg CL or with saline. CL increased FFA and insulin in control mice, but did not affect BG (probably because of impaired insulin sensitivity) . The day after CL injection, 4-fold rise in ectopic lipid content in liver was observed in comparison to saline-treated group. In FGF21-treated mice, the CL-induced rise of NEFA and insulin was only transient, but sufficient to cause a drop of BG. The hepatic lipid accumulation after CL was completely preveted by FGF21. The same experimental set-up was repeated in DIO UCP1+/+ and -/- mice. Although the BG-lowering effect of the CL+FGF21combination was observed in both genotypes, the effect was significantly stronger in UCP1+/+. Thus, FGF21 sensitizes DIO mice to the BG-lowering effect of adrenergic stimulation while it prevents ectopic lipid accummulation. The drop of BG is observed even in the absence of UCP1, but UCP1 activity is required to reach the maximal BG-lowering effect of the combination.
Czech Science Foundation (19-05356Y)