Diabetes 2013 July-29

 

Glucagon increases circulating fibroblast growth factor 21 independently of endogenous insulin levels: a novel mechanism of glucagon-stimulated lipolysis?

Diabetologia. 2013 Mar;56(3):588-97.

Arafat AM, Kaczmarek P, Skrzypski M, Pruszyńska-Oszmalek E, Kołodziejski P, Szczepankiewicz D, Sassek M, Wojciechowicz T, Wiedenmann B, Pfeiffer AF, Nowak KW, Strowski MZ.

Department of Endocrinology, Diabetes and Nutrition, Charité-University Medicine Berlin, Berlin, Germany.

 

Abstract

AIMS/HYPOTHESIS:

Glucagon reduces body weight by modifying food intake, glucose/lipid metabolism and energy expenditure. All these physiological processes are also controlled by fibroblast growth factor 21 (FGF-21), a circulating hepatokine that improves the metabolic profile in obesity and type 2 diabetes. Animal experiments have suggested a possible interaction between glucagon and FGF-21 however, the metabolic consequences of this crosstalk are not understood.

METHODS:

The effects of exogenous glucagon on plasma FGF-21 levels and lipolysis were evaluated in healthy volunteers and humans with type 1 diabetes, as well as in rodents with streptozotocin (STZ)-induced insulinopenic diabetes. In vitro, the role of glucagon on FGF-21 secretion and lipolysis was studied using isolated primary rat hepatocytes and adipocytes. Fgf-21 expression in differentiated rat pre-adipocytes was suppressed by small interfering RNA and released FGF-21 was immunoneutralised by polyclonal antibodies.

RESULTS:

Glucagon induced lipolysis in healthy human volunteers, patients with type 1 diabetes, mice and rats with STZ-induced insulinopenic diabetes, and in adipocytes isolated from diabetic and non-diabetic animals. In addition, glucagon increased circulating FGF-21 in healthy humans and rodents, as well as in patients with type 1 diabetes, and insulinopenic rodents. Glucagon stimulated FGF-21 secretion from isolated primary hepatocytes and adipocytes derived from animals with insulinopenic diabetes. Furthermore, FGF-21 stimulated lipolysis in primary adipocytes isolated from non-diabetic and diabetic rats. Reduction of Fgf-21 expression (by approximately 66%) or immunoneutralisation of released FGF-21 markedly attenuated glucagon-stimulated lipolysis in adipocytes.

CONCLUSIONS/INTERPRETATION:

These results indicate that glucagon increases circulating FGF-21 independently of endogenous insulin levels. FGF-21 participates in glucagon-induced stimulation of lipolysis.

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