Amyloid-beta interrupts the PI3K-Akt-mTOR signaling pathway that could be involved in brain-derived neurotrophic factor-induced Arc expression in rat cortical neurons.
The deposition of amyloid-beta (Abeta) contributes to the pathogenesis of Alzheimer's disease. Even at low levels, Abeta may interfere with various signaling cascades critical for the synaptic plasticity that underlies learning and memory. Brain-derived neurotrophic factor (BDNF) is well known to be capable of inducing the synthesis of activity-regulated cytoskeleton-associated protein (Arc), which plays a fundamental role in modulating synaptic plasticity. Our recent study has demonstrated that treatment of fibrillar Abeta at a nonlethal level was sufficient to impair BDNF-induced Arc expression in cultured rat cortical neurons. In this study, BDNF treatment alone induced the activation of the phosphatidylinositol 3-kinase-Akt-mammlian target of rapamycin (PI3K-Akt-mTOR) signaling pathway, the phosphorylation of eukaryotic initiation factor 4E binding protein (4EBP1) and p70 ribosomal S6 kinase (p70S6K), the dephosphorylation of eukaryotic elongation factor 2 (eEF2), and the expression of Arc. Interrupting the PI3K-Akt-mTOR signaling pathway by inhibitors prevented the effects of BDNF, indicating the involvement of this pathway in BDNF-induced 4EBP1 phosphorylation, p70S6K phosphorylation, eEF2 dephosphorylation, and Arc expression. Nonlethal Abeta pretreatment partially blocked these effects of BDNF. Double- immunofluorescent staining in rat cortical neurons further confirmed the coexistence of eEF2 dephosphorylation and Arc expression following BDNF treatment regardless of the presence of Abeta. These results reveal that, in cultured rat cortical neurons, Abeta interrupts the PI3K-Akt-mTOR signaling pathway that could be involved in BDNF-induced Arc expression. Moreover, this study also provides the first evidence that there is a close correlation between BDNF-induced eEF2 dephosphorylation and BDNF-induced Arc expression. (c) 2009 Wiley-Liss, Inc.
Chen
Tsan-Ju
TJ
Department of Physiology, Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan. tsanju@kmu.edu.tw
Wang
Dean-Chuan
DC
Chen
Shun-Sheng
SS
D016229:Amyloid beta-Peptides / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D009124:Muscle Proteins / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects*; D051058:Oncogene Protein v-akt / Q000378:metabolism; D010446:Peptide Fragments / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases; D013997:Time Factors
D016229:Amyloid beta-Peptides; D051017:Apoptosis Regulatory Proteins; D019208:Brain-Derived Neurotrophic Factor; D004791:Enzyme Inhibitors; D009124:Muscle Proteins; D051058:Oncogene Protein v-akt; D010446:Peptide Fragments; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D058570:TOR Serine-Threonine Kinases; C491788:Nol3 protein, rat; C075222:amyloid beta-protein (1-42); C546845:mTOR protein, rat