Background: NMDA receptor controls synaptic plasticity and memory function. Results: Knockdown of Egr-1 blocks NMDAR-induced PSD-95 down-regulation and AMPA receptor endocytosis. Conclusion: Egr-1 is a mediator of NMDA receptor signaling during the AMPA receptor trafficking. Significance: Elucidation of the mechanism of AMPA receptor trafficking is critical to understand how our brain functions.
Accumulation of amyloid- peptide (A) in the brain is regarded as central to Alzheimer's disease (AD) pathogenesis. A is generated by a sequential cleavage of amyloid precursor protein (APP) by -secretase 1 (BACE-1) followed by ␥-secretase. BACE-1 cleavage of APP is the committed step in A synthesis. Understanding the mechanism by which BACE-1 is activated leading to A synthesis in the brain can provide better understanding of AD pathology and help to develop novel therapies. In this study, we found that the levels of A and BACE-1 are significantly reduced in the brains of mice lacking transcription factor early growth response 1 (Egr-1) when compared with the WT. We demonstrate that in COS-7 cells, Egr-1 binds to the BACE-1 promoter and activates BACE-1 transcription. In rat hippocampal primary neurons, overexpression of Egr-1 induces BACE-1 expression, activates BACE-1, promotes amyloidogenic APP processing, and enhances A synthesis. In mouse hippocampal primary neurons, knockdown of BACE-1 almost completely blocks Egr-1-induced amyloidogenic APP processing and A synthesis. Our data indicate that Egr-1 promotes A synthesis via transcriptional activation of BACE-1 and suggest that Egr-1 plays role in activation of BACE-1 and acceleration of A synthesis in AD brain. Egr-1 is a potential therapeutic target for AD.Progressive accumulation of A 2 in the brain is strongly implicated in the pathogenesis of Alzheimer's disease (AD). A is derived from amyloid precursor protein (APP) (1). In the amyloidogenic pathway, APP is cleaved by -secretase (BACE-1) to generate a 99-amino acid membrane-bound protein C99 and soluble APP. C99 is further cleaved by ␥-secretase to produce the A peptide. APP is also cleaved by ␣-secretase within the A domain generating an 83-kDa protein C83. Subsequent cleavage of C83 by ␥-secretase generates a nontoxic short peptide P3 containing the C-terminal region of A.BACE-1 cleavage of APP is the rate-limiting step in A production. BACE-1 is regarded as the essential enzyme in the A synthesis in the brain (1).A number of studies have shown that the level of BACE-1 protein is significantly up-regulated in AD brain (2-6). It has been suggested that the up-regulation of BACE-1 initiates and/or accelerates A synthesis and promotes AD pathogenesis (1). Determining the mechanism by which BACE-1 is activated in AD brain can provide better understanding of AD pathology and help develop therapies against AD. However, what activates BACE-1 in AD brain is not known. Interestingly, in rat brain, BACE-1 level is elevated following experimental traumatic brain injury (7), transient cerebral ischemia (8), and following occlusion of the middle cerebral artery (9). Oxidative stress induces BACE-1 expression in mouse brains (10) and vascular smooth and HEK-293 cells (11,12). Thus, several cellular events triggered by vascular insults elevate BACE-1 levels in the brain. It has been suggested that the biochemical pathway that is activated by vascular injuries may be involved in up-regulating BAC...
A sporadic form of Alzheimer disease (AD) and vascular dementia share many risk factors, and their pathogenic mechanisms are suggested to be related. Transcription factor early growth response 1 (Egr-1) regulates various vascular pathologies and is up-regulated in both AD brains and AD mouse models; however, its role in AD pathogenesis is unclear. Herein, we report that silencing of Egr-1 in the hippocampus by shRNA reduces tau phosphorylation, lowers amyloid-β (Aβ) pathology, and improves cognition in the 3xTg-AD mouse model. Egr-1 silencing does not affect levels of cyclin-dependent protein kinase 5 (Cdk5), glycogen synthase kinase 3β, protein phosphatase 1, or protein phosphatase 2A, but reduces p35 subunit of Cdk5. Egr-1 silencing also reduces levels of β-secretase 1 (BACE-1) and BACE-1-cleaved amyloid precursor protein (APP) metabolites (secreted APPβ, C99, Aβ40, and Aβ42) but has no effect on presenilin 1 and presenilin 2. In hippocampal primary neurons, Egr-1 binds to BACE-1 and p35 promoters, enhances tau phosphorylation, activates Cdk5 and BACE-1, and accelerates amyloidogenic APP processing. Blocking Cdk5 action blocks Egr-1-induced tau phosphorylation but has no effect on BACE-1 activation and amyloidogenic APP processing. Blocking BACE-1 action, on the other hand, blocks Egr-1-induced amyloidogenic APP processing but does not affect tau phosphorylation. Egr-1 regulates tau phosphorylation and Aβ synthesis in the brain by respectively controlling activities of Cdk5 and BACE-1, suggesting that Egr-1 is a potential therapeutic candidate for the treatment of AD.
BackgroundNuclear restorers of cytoplasmic male fertility (CMS) act to suppress the male sterile phenotype by down-regulating the expression of novel CMS-specifying mitochondrial genes. One such restorer gene is Rfo, which restores fertility to the radish Ogura or ogu CMS. Rfo, like most characterized restorers, encodes a pentatricopeptide repeat (PPR) protein, a family of eukaryotic proteins characterized by tandem repeats of a 35 amino acid motif. While over 400 PPR genes are found in characterized plant genomes and the importance of this gene family in organelle gene expression is widely recognized, few detailed in vivo assessments of primary structure-function relationships in this protein family have been conducted.ResultsIn contrast to earlier studies, which identified 16 or 17 PPR domains in the Rfo protein, we now find, using a more recently developed predictive tool, that Rfo has 18 repeat domains with the additional domain N-terminal to the others. Comparison of transcript sequences from pooled rfo/rfo plants with pooled Rfo/Rfo plants of a mapping population led to the identification of a non-restoring rfo allele with a 12 bp deletion in the fourth domain. Introduction into ogu CMS plants of a genetic construct in which this deletion had been introduced into Rfo led to a partial loss in the capacity to produce viable pollen, as assessed by vital staining, pollen germination and the capacity for seed production following pollination of CMS plants. The degree of viable pollen production among different transgenic plants roughly correlated with the copy number of the introduced gene and with the reduction of the levels of the ORF138 CMS-associated protein. All other constructs tested, including one in which only the C-terminal PPR repeat was deleted and another in which this repeat was replaced by the corresponding domain of the related, non-restoring gene, PPR-A, failed to result in any measure of fertility restoration.ConclusionsThe identification of the additional PPR domain in Rfo indicates that the protein, apart from its N-terminal mitochondrial targeting presequence, consists almost entirely of PPR repeats. The newly identified rfo allele carries the same 4 amino acid deletion as that found in the neighboring, related, non-restoring PPR gene, PPR-A. Introduction of this four amino acid deletion into a central domain the Rfo protein, however, only partially reduces its restoration capacity, even though this alteration might be expected to alter the spacing between the adjoining repeats. All other tested alterations, generated by deleting specific PPR repeats or exchanging repeats with corresponding domains of PPR-A, led to a complete loss of restorer function. Overall we demonstrate that introduction of targeted alterations of Rfo into ogu CMS plants provides a sensitive in vivo readout for analysis of the relationship between primary structure and biological function in this important family of plant proteins.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-01...
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