title: IGF-1 alleviates NMDA-induced excitotoxicity in cultured hippocampal neurons against autophagy via the NR2B/PI3K-AKT-mTOR pathway.
abstract: Insulin-like growth factor-1 (IGF-1) is a brain-specific multifunctional protein involved in neuronal polarity and axonal guidance. Mature IGF-1 triggers three enzymes, mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K), and phosphoinositide phospholipase C-γ (PLC-γ), which are its predominant downstream regulators. The PI3K-AKT signaling pathway is upstream of the mammalian target of rapamycin (mTOR), which is of great importance in the induction of autophagy. However, whether the neuroprotective effect of IGF-1 against excitotoxicity is mediated by autophagy through the PI3K/AKT/mTOR pathway remains to be elucidated. The induction of autophagy following NMDA treatment was determined by microtubule-associated protein light chain 3 (LC3) conversion and the result of this autophagy was assessed by monitoring the cleavage of caspase 3 in cultured hippocampal neurons. Cell viability was determined using MTT and LDH assay, and PI-staining was used to estimate the fate of autophagy and the protective effect of IGF-1. In addition, IGF-1 was found to decrease autophagy induced by NMDA using transmission electron microscopy and MDC staining. The protective effect of IGF-1 against autophagy was accompanied with up-regulation of phospho-AKT (p-AKT) and phospho-mTOR (p-mTOR), which was blocked by the inhibitor of PI3K. At the same time, the activation of NR2B resulting in the down-regulation of p-AKT and p-mTOR was blocked by IGF-1. Together, these data suggest that NMDA induces the autophagy, followed by apoptosis in cultured hippocampal neurons, and that IGF-1 can block this effect via inhibition of NR2B receptors and activation of the PI3K-AKT-mTOR pathway.
authors.affiliation: Department of Neurobiology and Beijing Institute for Brain Disorders, School of Basic Medical Sciences, Capital Medical University, Beijing, P.R. China; Department of Spine Surgery, Institute of Hard Tissue Development and Regeneration of Harbin Medical University, Second Affiliated Hospital of Harbin Medical University, Harbin, Hei Long Jiang Province, P.R. China.
authors.forename: Yansong
authors.initials: Y
authors.lastname: Wang
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Dongguo
authors.initials: D
authors.lastname: Li
authors.forename: Mi
authors.initials: M
authors.lastname: Li
authors.forename: Peipei
authors.initials: P
authors.lastname: Wang
authors.forename: Jian
authors.initials: J
authors.lastname: Wen
authors.forename: Min
authors.initials: M
authors.lastname: Liang
authors.forename: Bo
authors.initials: B
authors.lastname: Su
authors.forename: Yanling
authors.initials: Y
authors.lastname: Yin
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects*; D000071186:Beclin-1; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005260:Female; D006624:Hippocampus / Q000473:pathology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008954:Models, Biological; D016202:N-Methylaspartate / Q000633:toxicity*; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000473:pathology* / Q000648:ultrastructure; D009498:Neurotoxins / Q000633:toxicity*; D010588:Phagosomes / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D000071186:Beclin-1; D053148:Caspase 3; D007334:Insulin-Like Growth Factor I; D008869:Microtubule-Associated Proteins; D016202:N-Methylaspartate; D009498:Neurotoxins; D058539:Phosphatidylinositol 3-Kinase; D010768:Phosphoserine; D051057:Proto-Oncogene Proteins c-akt; D016194:Receptors, N-Methyl-D-Aspartate; D058570:TOR Serine-Threonine Kinases; C512829:Becn1 protein, rat; C526109:Anxa3 protein, rat; C121001:NR2B NMDA receptor