Overexpression of β2-adrenergic receptors in mouse liver alters the expression of gluconeogenic and glycolytic enzymes

Abstract

In the livers of humans and many other mammalian species, β2-adrenergic receptors (β2-ARs) play an important role in the modulation of glucose production by glycogenolysis and gluconeogenesis. In male mice and rats, however, the expression and physiological role of hepatic β2-ARs are rapidly lost with development under normal physiological conditions. We previously described a line of transgenic mice, F28 (André C, Erraji L, Gaston J, Grimber G, Briand P, and Guillet JG. Eur J Biochem 241: 417–424, 1996), which carry the human β2-AR gene under the control of its own promoter. In these mice, hepatic β2-AR levels are shown to increase rapidly after birth and, as in humans, be maintained at an elevated level in adulthood. F28 mice display strongly enhanced adenylyl cyclase responses to β-AR agonists in their livers and, compared with normal mice, have increased basal hepatic adenylyl cyclase activity. In this report we demonstrate that, under normal physiological conditions, this increased β2-AR activity affects the expression of the gluconeogenic and glycolytic key enzymes phospho enolpyruvate carboxykinase, glucose-6-phosphatase, and l-pyruvate kinase and considerably decreases hepatic glycogen levels. Furthermore, we show that the effects of β-adrenergic ligands on liver glycogen observed in humans are reproduced in these mice: liver glycogen levels are strongly decreased by the β2-AR agonist clenbuterol and increased by the β-AR antagonist propranolol. These transgenic mice open new perspectives for studying in vivo the hepatic β2-AR system physiopathology and for testing the effects of β-AR ligands on liver metabolism.