ICAM-5 Attenuates Amyloid Beta Protein Induced Neuronal Degeneration by ERM/PI3K/Akt Pathway

Abstract: Backgroud Alzheimer’s disease(AD) is a neurodegenerative disorder pathologically by accumulation of amyloid beta protein(Aβ),a major constituent of extracellular senile plaque(SP) and intracellular neurofibrillary tangles(NFTs) and loss of cholinergic neurons.Neuronal degeneration and apoptosis are involved in three stage including signal transduction,gene regulation and apoptosis execution.Activation of signal transduction procedure is the essential condition of initiating neuron apoptosis and regulates cell survival and death.The mechanism of neuronal degeneration or apoptosis includes two major cell death signaling pathways which are mitochondrial death pathway and death receptor pathway.The two pathways start caspase cascade reaction at last and lead neurons death. Besides,abnormal of cell cycle also affects neuron survival.In the process of neurons apoptosis,there also exist relative anti-apoptosis signaling pathways.The typical one is phosphatidylinositol 3-kinase(PI3K)/Akt pathway.Intercellular adhesion molecule-5(ICAM-5,telencephalin) is a cell adhesion molecule expressed in the somatodendritic membrane of telencephalic neurons in mammalian brain.It induces dendritic outgrowth and is involved in regulation of memory formation and learning.ICAM-5 cytoplasmic region binds ERM(ezrin/radixin/moesin) family proteins that link membrane proteins to actin cytoskeleton.And phosphorylation of ERM can initiate PI3K/Akt pathway.But there is no research on whether ICAM-5 can abate Aβneurotoxicity or is involved in signaling transduction.Objective To explor whether ICAM-5 can abate neurotoxicity of Aβand initiate PI3K/Akt pathway,and provide relative basis for prevention and cure of AD and other neurodegenerative diseases.Methods 1.The control neuronal model PAJU-NEO was established by transfected PAJU cells with empty vector pcDNA3.1.And PAJU cells were obtained by successive passage of PAJU-ICAM-5 without pressure selection.It was identified by immunofluorescence and western blotting.2. We treated PAJU-ICAM-5 and PAJU-NEO cells with different concentrations of Aβin different times.To detect neuronal survival rate with MTT and apoptosis rate with Hoechst 33258 and flow cytometry. Western blotting was used to find out effect of Aβon expression of ICAM-5.3.To measuer process of PAJU-ICAM-5 and PAJU-NEO cells cultured in different concentrations of Aβin different times.And immunofluorescence was used to observe neurites damage.4.Western blotting was used to find out phosphorylation of Ezrin(Thr567),Radixin (Thr564) and Moesin(Thr558),PI3K(Tyr508,p85α) and Akt(Ser473). Results 1.Neuronal model PAJU-NEO was established and express neo resistivity.2.We discovered that nomalexpression of ICAM-5 can protect neurons from Aβneurotoxicity(Aβ_(42) 1.0nmol/L) induced apoptosis, as indicated by increase neuronal survival rate and decrease damage of neurites(Aβ_(42) and Aβ_(35) 0.5,0.8nmol/L) and apoptosis rate.Meanwhile, ICAM-5 expression down regulation present due to long time expose to Aβ. 3.Furthermore,ICAM-5 interacted with ezrin-radixin-moesin(ERM) protein family in PAJU cells,and active phosphorylation of Ezrin(Thr567), Radixin(Thr564) and Moesin(Thr558).Phosphorylated ERM activated phosphorylation of PI3K(TyrS08,p85α),which made activation of Akt (Ser473) directly.4.Western blot analysis showed that 30μM of the LY294002 markedly inhibited ICAM-5,phospho-ERM,phospho-PI3K and phospho-Akt in PAJU cells,while the total ERM,PI3K and Akt expression in both PAJU-ICAM-5 and PAJU-NEO cell lines was identical in nontreated and treated cells.It suggested that LY294002 play a role on this pathway in the biological regulation of this marker.Conclusion 1.Here we demonstrate for the first time that nomalexpression of ICAM-5 in human neuroblastoma PAJU cells can protect the neurons from Aβneurotoxicity as indicated by reduce apoptosis and neurites degeneration,increase neuronal survival rate.2.Long time expose to Aβmay reduce expression level of ICAM-5.3.We also demonstrate for the first time that ICAM-5 attenuates amyloid beta protein induced neuronal degeneration by ERM/PI3K/Akt pathway.4.LY294002 may be a biological regulative marker of ERM/PI3K/Akt pathway…
Key words: ICAM-5/telencephalin; PAJU cell; neuronal degeneration; amyloid beta protein; ezrin-radixin-moesin (ERM); PI3K/Akt pathway

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