Background:Weighted co-expression network analysis (WGCNA) is a powerful systems biology method to describe the correlation of gene expression based on the microarray database, which can be used to facilitate the discovery of therapeutic targets or candidate biomarkers in diseases.Objective:To explore the key genes in the development of Alzheimer’s disease (AD) by using WGCNA.Methods:The whole gene expression data GSE1297 from AD and control human hippocampus was obtained from the GEO database in NCBI. Co-expressed genes were clustered into different modules. Modules of interest were identified through calculating the correlation coefficient between the module and phenotypic traits. GO and pathway enrichment analyses were conducted, and the central players (key hub genes) within the modules of interest were identified through network analysis. The expression of the identified key genes was confirmed in AD transgenic mice through using qRT-PCR.Results: Two modules were found to be associated with AD clinical severity, which functioning mainly in mineral absorption, NF-κB signaling, and cGMP-PKG signaling pathways. Through analysis of the two modules, we found that metallothionein (MT), Notch2, MSX1, ADD3, and RAB31 were highly correlated with AD phenotype. Increase in expression of these genes was confirmed in aged AD transgenic mice.Conclusion:WGCNA analysis can be used to analyze and predict the key genes in AD. MT1, MT2, MSX1, NOTCH2, ADD3, and RAB31 are identified to be the most relevant genes, which may be potential targets for AD therapy.

Reactive astrogliosis and early synaptic degeneration are two characteristic hallmarks in AD brains, but a direct link between the two events has not been established. Here we show that CIP2A, a cancerous protein with high expression level in astrocytes, is upregulated in AD patients and 3xTg-AD transgenic mice. Overexpression of CIP2A in astrocytes through AAV infection both in cultured cells and in mice brains results in activation of astrocytes, increased production of cytokines and Aβ, and synaptic degeneration indicated by decreased levels of synaptic proteins, spine loss and impairment in LTP. As a result of synaptic degeneration, CIP2A overexpression in astrocytes in vivo induces significant deficits in visual episodic memory detected by novel objective recognition test and spatial memory detected by Morris water maze. We conclude that CIP2A-promoted astrogliosis induces synaptic degeneration and cognitive deficits in Alzheimer's disease.

Intracellular accumulation of the hyperphosphorylated tau is a pathological hallmark in the brain of Alzheimer disease. Activation of extrasynaptic NMDA receptors (E-NMDARs) induces excitatory toxicity that is involved in Alzheimer's neurodegeneration. However, the intrinsic link between E-NMDARs and the tau-induced neuronal damage remains elusive. In the present study, we showed in cultured primary cortical neurons that activation of E-NMDA receptors but not synaptic NMDA receptors dramatically increased tau mRNA and protein levels, with a simultaneous neuronal degeneration and decreased neuronal survival. Memantine, a selective antagonist of E-NMDARs, reversed E-NMDARs-induced tau overexpression. Activation of E-NMDARs in wild-type mouse brains resulted in neuron loss in hippocampus, whereas tau deletion in neuronal cultures and in the mouse brains rescued the E-NMDARs-induced neuronal death and degeneration. The E-NMDARs-induced tau overexpression was correlated with a reduced ERK phosphorylation, whereas the increased MEK activity, decreased binding and activity of ERK phosphatase to ERK, and increased ERK phosphorylation were observed in tau knockout mice. On the contrary, addition of tau proteins promoted ERK dephosphorylation in vitro. Taking together, these results indicate that tau overexpression mediates the excitatory toxicity induced by E-NMDAR activation through inhibiting ERK phosphorylation.

MicroRNAs have been implicated in diverse physiological and pathological processes. We previously reported that aberrant microRNA‐124 (miR‐124)/non‐receptor–type protein phosphatase 1 (PTPN1) signaling plays an important role in the synaptic disorders associated with Alzheimer's disease (AD). In this study, we further investigated the potential role of miR‐124/PTPN1 in the tau pathology of AD. We first treated the mice with intra‐hippocampal stereotactic injections. Then, we used quantitative real‐time reverse transcription PCR (qRT‐PCR) to detect the expression of microRNAs. Western blotting was used to measure the level of PTPN1, the level of tau protein, the phosphorylation of tau at AD‐related sites, and alterations in the activity of glycogen synthase kinase 3β (GSK‐3β) and protein phosphatase 2 (PP2A). Immunohistochemistry was also used to detect changes in tau phosphorylation levels at AD‐related sites and somadendritic aggregation. Soluble and insoluble tau protein was separated by 70% formic acid (FA) extraction to examine tau solubility. Finally, behavioral experiments (including the Morris water maze, fear conditioning, and elevated plus maze) were performed to examine learning and memory ability and emotion‐related behavior. We found that artificially replicating the abnormalities in miR‐124/PTPN1 signaling induced AD‐like tau pathology in the hippocampus of wild‐type mice, including hyperphosphorylation at multiple sites, insolubility and somadendritic aggregation, as well as learning/memory deficits. We also found that disruption of miR‐124/PTPN1 signaling was caused by the loss of RE1‐silencing transcription factor protein, which can be initiated by Aβ insults or oxidative stress, as observed in the brains of P301S mice. Correcting the deregulation of miR‐124/PTPN1 signaling rescued the tau pathology and learning/memory impairments in the P301S mice. We also found that miR‐124/PTPN1 abnormalities induced activation of glycogen synthase kinase 3 (GSK‐3) and inactivation of protein phosphatase 2A (PP2A) by promoting tyrosine phosphorylation, implicating an imbalance in tau kinase/phosphatase. Thus, targeting the miR‐124/PTPN1 signaling pathway is a promising therapeutic strategy for AD. image

CDK5 activation promotes ischemic neuronal death in stroke, with the recognized activation mechanism being calpain-dependent p35 cleavage to p25. Here we reported that CDK5-Tyr15 phosphorylation by zinc induced CDK5 activation in brain ischemic injury. CDK5 activation and CDK5-Tyr15 phosphorylation were observed in the hippocampus of the rats that had been subjected to middle cerebral artery occlusion, both of which were reversed by pretreatment with zinc chelator; while p35 cleavage and calpain activation in ischemia were not reversed. Zinc incubation resulted in CDK5-Tyr15 phosphorylation and CDK5 activation, without increasing p35 cleavage in cultured cells. Site mutation experiment confirmed that zinc-induced CDK5 activation was dependent on Tyr15 phosphorylation. Further exploration showed that Src kinase contributed to zinc-induced Tyr15 phosphorylation and CDK5 activation. Src kinase inhibition or expression of an unphosphorylable mutant Y15F-CDK5 abolished Tyr15 phosphorylation, prevented CDK5 activation and protected hippocampal neurons from ischemic insult in rats. We conclude that zinc-induced CDK5-Tyr15 phosphorylation underlies CDK5 activation and promotes ischemic neuronal death in stroke.