New insights concerning insulin synthesis and its secretion in rat hippocampus and cerebral cortex: Amyloid-β1–42-induced reduction of proinsulin level via glycogen synthase kinase-3β

• Published in: Cellular signalling 2014-02, Vol.26 (2), p.253-259
• Main Authors: Nemoto, Takayuki, Toyoshima-Aoyama, Fumiyo, Yanagita, Toshihiko, Maruta, Toyoaki, Fujita, Hiroshi, Koshida, Tomohiro, Yonaha, Tetsu, Wada, Akihiko, Sawaguchi, Akira, Murakami, Manabu
• Format: Article
• Language: English
• Subjects: Alzheimer's disease; Amyloid beta-Peptides - pharmacology; Animals; Aβ1–42; Calcium-Binding Proteins - metabolism; Cell Survival - drug effects; Cells, Cultured; Cerebral Cortex - cytology; Cerebral Cortex - drug effects; Cerebral Cortex - metabolism; Exocytosis - drug effects; Gene Expression Regulation - drug effects; Glycogen Synthase Kinase 3 - antagonists & inhibitors; Glycogen Synthase Kinase 3 - genetics; Glycogen Synthase Kinase 3 - metabolism; Glycogen Synthase Kinase 3 beta; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; GSK-3β; Hippocampal neurons; Hippocampus - cytology; Hippocampus - drug effects; Hippocampus - metabolism; Insulin - genetics; Insulin - metabolism; Lithium Chloride - pharmacology; Nerve Tissue Proteins - metabolism; Peptide Fragments - pharmacology; pHluorin; Proinsulin; Proinsulin - genetics; Proinsulin - metabolism; Rats; Rats, Wistar; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; RNA Interference; RNA, Small Interfering - metabolism
• ISSN: 0898-6568; 1873-3913
• DOI: 10.1016/j.cellsig.2013.11.017

The reduction of insulin levels in hippocampal areas is associated with Alzheimer's disease. The present study using rat brain explores the mechanisms of insulin synthesis and secretion, as well as amyloid-β1–42 (Aβ1–42)-induced reduction of proinsulin expression. After confirming the expression of insulin mRNA and proinsulin in rat brain, we visualized and analyzed the motion of insulin secretion in rat hippocampal neurons using pH-sensitive green fluorescent protein (pHluorin) fused to the insulin. In the rat hippocampal neurons expressing insulin–pHluorin, time-lapse confocal laser scanning microscopy revealed the appearance of fluorescent spots induced by depolarization after stimulation with 50mM KCl. In these fluorescent spots, Ca2+-dependent activator protein for secretion 2 (CAPS2), which is the regulator of the dense-core vesicle involving neuronal peptides, was co-localized with insulin–pHluorin. However, Aβ1–42-induced reduction of proinsulin in rat hippocampal neurons was inhibited by treatment with lithium and transfection with glycogen synthase kinase-3β (GSK-3β) siRNA. These results demonstrate that synthesized insulin is secreted from rat hippocampal and cortical neuron's dense-core vesicles, and that activation of GSK-3β in Aβ1–42-induced Alzheimer's model hippocampal neurons decreases the insulin synthesis. •Insulin is secreted from the hippocampus in the brain.•Proinsulin levels decrease in Aβ1–42-induced Alzheimer's model hippocampus.•GSK-3β activity is involved in Aβ1–42-induced reduction of proinsulin.•GSK-3β inhibition by lithium abolishes Aβ1–42-induced reduction of proinsulin.