Defective insulin secretion and increased susceptibility to experimental diabetes are induced by reduced Akt activity in pancreatic islet β cells
Ernesto Bernal-Mizrachi, … , Kenneth S. Polonsky, M. Alan Permutt
Ernesto Bernal-Mizrachi, … , Kenneth S. Polonsky, M. Alan Permutt
Published October 1, 2004
Citation Information: J Clin Invest. 2004;114(7):928-936. https://doi.org/10.1172/JCI20016.
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Article Metabolism

Defective insulin secretion and increased susceptibility to experimental diabetes are induced by reduced Akt activity in pancreatic islet β cells

Abstract

The insulin and IGF signaling pathways are critical for development and maintenance of pancreatic β cell mass and function. The serine-threonine kinase Akt is one of several mediators regulated by these pathways. We have studied the role of Akt in pancreatic β cell physiology by generating transgenic mice expressing a kinase-dead mutant of this enzyme in β cells. Reduction of Akt activity in transgenic animals resulted in impaired glucose tolerance due to defective insulin secretion. The mechanisms involved in dysregulation of secretion in these mice lie at the level of insulin exocytosis and are not the result of abnormalities in glucose signaling or function of voltage-gated Ca2+ channels. Therefore, transgenic mice showed increased susceptibility to developing glucose intolerance and diabetes following fat feeding. These observations suggest that Akt plays a novel and important role in the regulation of distal components of the secretory pathway and that this enzyme represents a therapeutic target for improvement of β cell function in diabetes.

Authors

Ernesto Bernal-Mizrachi, Szabolcs Fatrai, James D. Johnson, Mitsuru Ohsugi, Kenichi Otani, Zhiqiang Han, Kenneth S. Polonsky, M. Alan Permutt

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Overexpression of kdAkt inhibits Akt activity and phosphorylation of Akt...
Overexpression of kdAkt inhibits Akt activity and phosphorylation of Akt targets in RIP-kdAkt islets. (A) Total pancreatic islet lysates from RIP-kdAkt and WT mice were immunoblotted with Ab’s against HA, Akt, or actin. Semiquantitation of total Akt protein level in islets from RIP-kdAkt and WT mice was adjusted to actin as loading control (n = 6). (B) Total in vitro Akt kinase activity from 400 μg of islet lysates. Upper blot: Immunoblotting for Akt in the immunoprecipitate. Middle blot and bar graph: In vitro Akt kinase activity assayed by immunoblotting with anti_phospho-GSK3 Ab’s (p-GSK3) with semiquantitative analysis (n = 3). Lower blot: Immunoblotting for Akt in the post-immunoprecipitation supernatant (Post-IP sup). (C and D) Phosphorylation status in islet lysates and semiquantitative analysis of band intensities for phospho-GSK3 (Ser9; n = 5) (C) and phospho-S6K (Thr389; n = 6) (D) in transgenics and WT mice. (E) Immunoblotting for phospho-Foxo1 (Ser256) and actin in lysates from RIP-kdAkt and WT islets. The data are representative of 3 independent experiments done in duplicate. Data for phospho-GSK3 and phospho-S6K were adjusted to actin and are presented as mean ± SE. *P < 0.05.