title: Activation of ERK1/2 and PI3K/Akt by IGF-1 on GAP-43 expression in DRG neurons with excitotoxicity induced by glutamate in vitro.
abstract: Insulin-like growth factor-1 (IGF-1) is a neurotrophic factor and plays an important role in promoting axonal growth from dorsal root ganglion (DRG) neurons. Whether IGF-1 influences growth-associated protein 43 (GAP-43) expression and activates the extracellular signal-regulated protein kinase (ERK1/2) and the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways in DRG neurons with excitotoxicity induced by glutamate (Glu) remains unknown. In this study, embryonic 15-day-old rat DRG explants were cultured for 48 h and then exposed to IGF-1, Glu, Glu + IGF-1, Glu + IGF-1 + PD98059, Glu + IGF-1 + LY294002, Glu + IGF-1 + PD98059 + LY294002 for additional 12 h. The DRG explants were continuously exposed to growth media as control. The levels of GAP-43 mRNA were detected by real time-PCR analysis. The protein levels of GAP-43, phosphorylated ERK1/2, phosphorylated Akt, total ERK1/2, and total Akt were detected by Western blot assay. GAP-43 expression in situ was determined by immunofluorescent labeling. Apoptotic cell death was monitored by Hoechst 33342 staining. IGF-1 alone increased GAP-43 and its mRNA levels in the absence of Glu. The decreased GAP-43 and its mRNA levels caused by Glu could be partially reversed by the presence of IGF-1. IGF-1 rescued neuronal cell death caused by Glu. Neither the ERK1/2 inhibitor PD98059 nor the PI3K inhibitor LY294002 blocked the effect of IGF-1, but both inhibitors together were effective. To validate the impact of GAP-43 expression by IGF-1, GAP-43 induction was blocked by administration of dexamethasone (DEX). IGF-1 partially rescued the decrease of GAP-43 and its mRNA levels induced by DEX. DEX induced an increase of cell apoptosis. IGF-1 may play an important role in neuroprotective effects on DRG neurons through regulating GAP-43 expression with excitotoxicity induced by Glu and the process was involved in both ERK1/2 and PI3K/Akt signaling pathways.
authors.affiliation: Department of Anatomy, Shandong University School of Medicine, Jinan, Shandong 250012, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Liu
authors.forename: Heng
authors.initials: H
authors.lastname: Cai
authors.forename: Ping
authors.initials: P
authors.lastname: Zhang
authors.forename: Hao
authors.initials: H
authors.lastname: Li
authors.forename: Huaxiang
authors.initials: H
authors.lastname: Liu
authors.forename: Zhenzhong
authors.initials: Z
authors.lastname: Li
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001562:Benzimidazoles / Q000378:metabolism; D015153:Blotting, Western; D002465:Cell Movement / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D019922:GAP-43 Protein / Q000235:genetics / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D005786:Gene Expression Regulation / Q000187:drug effects; D018698:Glutamic Acid / Q000633:toxicity*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D009498:Neurotoxins / Q000633:toxicity; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D001562:Benzimidazoles; D019922:GAP-43 Protein; D009498:Neurotoxins; D012333:RNA, Messenger; D018698:Glutamic Acid; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone; D058539:Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C017807:bisbenzimide ethoxide trihydrochloride