Exp Clin Endocrinol Diabetes 2007; 115 - P01_060
DOI: 10.1055/s-2007-972316

Orexin-A inhibits glucagon secretion and gene expression by Foxo1 dependent pathway

E Göncz 1, C Grötzinger 1, S Mergler 1, BF El-Zayat 2, M Theodoropoulou 3, GK Stalla 3, B Wiedenmann 1, MZ Strowski 1, U Plöckinger 1
  • 1Charité-Universitätsmedizin Berlin, Med. Klinik m.S. Gastroenterologie, Berlin, Germany
  • 2Philipps-Universität Marburg, Klinik für Unfall-, Wiederherstellungs- und Handchirurgie, Marburg, Germany
  • 3Max Planck Institut für Psychiatrie, München, Germany

Background and aim: Orexin-A (OXA) regulates food intake and energy homeostasis. In vivo, OXA increases insulin secretion and inhibits glucagon secretion, suggesting a role OXA in regulating glucose homeostasis. However, it is not known whether the effects of OXA are mediated through a direct interaction with the pancreatic A-cells. Aim of the study was to study the effects of OXA on glucagon producing cells and characterize the underlying intracellular mechanisms.

Methods: The effects of OXA on glucagon secretion were evaluated using an in situ perfused rat pancreas model and clonal pancreatic A-cells (InR1-G9). Glucagon was measured by RIA. OXR-1 expression in InR1-G9 cells was detected by western blot and immunofluorescence. The effects of OXA on intracellular cyclic AMP, AKT, PDK-1 were measured by ELISA and western blots, changes of the intracellular calcium (Ca2+) by Fura-2 measurements. Proglucagon and Foxo1 mRNA levels were quantified by real-time PCR. Silencing of foxo1 in InR1-G9 cells was performed by transfection with short interfering RNA (siRNA).

Results: OXR-1 expression in InR1-G9 cells was detected by western blots and immunofluorescence. OXA inhibited glucagon secretion from perfused rat pancreas and InR1-G9 cells, and proglucagon gene expression in InR1-G9 cells. OXA decreased intracellular cyclic AMP and Ca2+ concentrations, and increased the phosphorylation of AKT und PDK-1. PI-3 kinase inhibitor blocked the effects of OXA on proglucagon gene expression. Silencing of foxo1 had no effects on basal proglucagon gene expression; however the inhibitory effect of OXA on glucagon gene expression was reversed.

Conclusions: Our study provides the first in vitro evidence for the interaction of OXA with pancreatic glucagon cells. OXA inhibits glucagon secretion and proglucagon gene expression. Furthermore, we demonstrate that Foxo1 mediates the inhibition of proglucagon gene expression in response to OXA treatment. Inhibition of glucagon secretion by OXA may have potential implication at lowering hyperglucagonemia frequently seen in type 2 diabetes.