[Show abstract][Hide abstract] ABSTRACT: Nucleophosmin (NPM) is a multifunctional nucleolar protein that has been linked with nucleolar stress. In non-neuronal cell lines, NPM may enhance or inhibit the activity of tumor suppressor p53, a major apoptotic protein. The relationship between NPM and p53 in the central nervous system (CNS) remains unknown. Here, we assessed the role of NPM in the CNS using a model of seizure-induced neurodegeneration. We show that NPM overexpression is neuroprotective against kainic acid-induced excitotoxicity, and that downregulation of NPM is pro-apoptotic in a p53-independent manner. These results suggest a key role for NPM in promoting neuronal survival and a novel mechanism of neuronal degeneration triggered by nucleolar stress.
Full-text · Article · Dec 2011 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Alzheimers disease (AD) is the most common age-related dementia, currently affecting more than 5 million patients in the US alone, and is characterized by the presence of both extracellular plaques and intraneuronal tangles in the brain of a patient with dementia. Alois Alzheimer first described the pathology associated with the disease over 100 years ago, and during the past three decades our understanding of the disease and of potential ways to treat it has increased tremendously. In this article we describe our current understanding of both the pathophysiology of Alzheimers disease and current and future therapeutic interventions, including symptomatic relief, disease modification, and the reversal of synaptic and neuronal loss.
[Show abstract][Hide abstract] ABSTRACT: It is ironic that the p53 “tumor antigen”, first discovered more than 20 years ago, was initially thought to play a major
role in promoting tumorigenesis (Parada et al. 1984). It was not long after, however, that the p53 protein was found to be
a potent tumor suppressor. In fact, since the mid1990s, p53 has been regarded as the “guardian of the genome” on the basis
of its ability to block the proliferation of cells with mutated DNA (Lane 1992). For more than two decades, tumor suppressor
p53 has been among the most widely studied proteins. Notably, the myriad cellular functions in which p53 is involved continue
to increase (Levine et al. 2006; Efeyan and Serrano 2007; Fuster et al. 2007).
The human p53 protein consists of 393 amino acid residues and has a molecular weight of approximately 53 kDa. The p53 gene
product is a modular molecule that consists of three well-characterized functional domains: an N-terminal transactivation
domain (residues 1–42), a central sequence-specific DNA binding domain (residues 102–292), and a highly basic C-terminal domain
that regulates p53 oligomerization and sequence-specific DNA binding (Fig. 15.1) (Prives and Hall 1999; Lavin and Gueven 2006).
[Show abstract][Hide abstract] ABSTRACT: Alzheimer's disease (AD) is pathologically characterized by accumulation of beta-amyloid (Abeta) protein deposits and/or neurofibrillary tangles in association with progressive cognitive deficits. Although numerous studies have demonstrated a relationship between brain pathology and AD progression, the Alzheimer's pathological hallmarks have not been found in the AD retina. A recent report showed Abeta plaques in the retinas of APPswe/PS1DeltaE9 transgenic mice. We now report the detection of Abeta plaques with increased retinal microvascular deposition of Abeta and neuroinflammation in Tg2576 mouse retinas. The majority of Abeta-immunoreactive plaques were detected from the ganglion cell layer to the inner plexiform layer, and some plaques were observed in the outer nuclear layer, photoreceptor outer segment, and optic nerve. Hyperphosphorylated tau was labeled in the corresponding areas of the Abeta plaques in adjacent sections. Although Abeta vaccinations reduced retinal Abeta deposits, there was a marked increase in retinal microvascular Abeta deposition as well as local neuroinflammation manifested by microglial infiltration and astrogliosis linked with disruption of the retinal organization. These results provide evidence to support further investigation of the use of retinal imaging to diagnose AD and to monitor disease activity.
Full-text · Article · Nov 2009 · American Journal Of Pathology
[Show abstract][Hide abstract] ABSTRACT: Redox factor-1 (Ref-1), also known as HAP1, APE or APEX, is a multifunctional protein that regulates gene transcription as well as the response to oxidative stress. By interacting with transcription factors such as AP-1, NF-kappaB and p53, and directly participating in the cleavage of apurininic/apyrimidinic DNA lesions, Ref-1 plays crucial roles in both cell death signaling pathways and DNA repair, respectively. Oxidative stress induced by aggregated beta-amyloid (Abeta) peptide, altered DNA repair and transcriptional activation of cell death pathways have been implicated in the pathophysiology of Alzheimer's disease (AD). Here we show that varying concentrations of Abeta(1-42) differentially regulate Ref-1 expression, Ref-1 function and neuronal survival in vitro. Abeta (5.0 muM) caused a relatively rapid decrease in Ref-1 expression and activity associated with extensive DNA damage and neuronal degeneration. In contrast, Ref-1 induction occurred in cells exposed to Abeta (1.0 muM) without significant neuronal cell death. Abeta-induced attenuation of Ref-1 expression and endonuclease activity, and neuronal cell death were prevented by the anti-oxidant, catalase. Similar differential effects on Ref-1 expression and cell viability were observed in N2A neuroblastoma cells treated with either high or low dose hydrogen peroxide. These findings demonstrate the differential regulation of Ref-1 expression by varying degrees of oxidative stress. Parallels between the Ref-1 response to Abeta and H(2)O(2) suggest similarities between DNA repair pathways activated by different inducers of oxidative stress. In AD brain, colocalization of Ref-1 and Abeta the absence of significant DNA damage are consistent with the cell culture results and suggests that Ref-1 may play a more neuroprotective role under these conditions. Modulation of Ref-1 expression and activity by local variations in Abeta concentration may be an important determinant of neuronal vulnerability to oxidative stress in AD.
Full-text · Article · Jun 2009 · The Open Neuroscience Journal
[Show abstract][Hide abstract] ABSTRACT: Memory loss is the signature feature of Alzheimer's disease, and therapies that prevent or delay its onset are urgently needed. Effective preventive strategies likely offer the greatest and most widespread benefits. Histone deacetylase (HDAC) inhibitors increase histone acetylation and enhance memory and synaptic plasticity. We evaluated the efficacy of nicotinamide, a competitive inhibitor of the sirtuins or class III NAD(+)-dependent HDACs in 3xTg-AD mice, and found that it restored cognitive deficits associated with pathology. Nicotinamide selectively reduces a specific phospho-species of tau (Thr231) that is associated with microtubule depolymerization, in a manner similar to inhibition of SirT1. Nicotinamide also dramatically increased acetylated alpha-tubulin, a primary substrate of SirT2, and MAP2c, both of which are linked to increased microtubule stability. Reduced phosphoThr231-tau was related to a reduction of monoubiquitin-conjugated tau, suggesting that this posttranslationally modified form of tau may be rapidly degraded. Overexpression of a Thr231-phospho-mimic tau in vitro increased clearance and decreased accumulation of tau compared with wild-type tau. These preclinical findings suggest that oral nicotinamide may represent a safe treatment for AD and other tauopathies, and that phosphorylation of tau at Thr231 may regulate tau stability.
Full-text · Article · Dec 2008 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
[Show abstract][Hide abstract] ABSTRACT: A dinucleotide deletion in human ubiquitin (Ub) B messenger RNA leads to formation of polyubiquitin (UbB)+1, which has been implicated in neuronal cell death in Alzheimer's and other neurodegenerative diseases. Previous studies demonstrate that UbB+1 protein causes proteasome dysfunction. However, the molecular mechanism of UbB+1-mediated neuronal degeneration remains unknown. We now report that UbB+1 causes neuritic beading, impairment of mitochondrial movements, mitochondrial stress and neuronal degeneration in primary neurons. Transfection of UbB+1 induced a buildup of mitochondria in neurites and dysregulation of mitochondrial motor proteins, in particular, through detachment of P74, the dynein intermediate chain, from mitochondria and decreased mitochondria-microtubule interactions. Altered distribution of mitochondria was associated with activation of both the mitochondrial stress and p53 cell death pathways. These results support the hypothesis that neuritic clogging of mitochondria by UbB+1 triggers a cascade of events characterized by local activation of mitochondrial stress followed by global cell death. Furthermore, UbB+1 small interfering RNA efficiently blocked expression of UbB+1 protein, attenuated neuritic beading and preserved cellular morphology, suggesting a potential neuroprotective strategy for certain neurodegenerative disorders.
Full-text · Article · Nov 2007 · Cell Death and Differentiation
[Show abstract][Hide abstract] ABSTRACT: We evaluated the expression of DNA repair proteins, redox factor-1 (Ref-1) and X-ray repair cross-complementing protein 1 (XRCC1), relevant to neurodegeneration following kainic acid-induced seizures in rats. Neurons with oxidative DNA damage exhibited increased expression and colocalization of Ref-1 and XRCC1. Upregulation of DNA repair proteins was also associated with p53 induction and TUNEL. Coexpression of DNA repair proteins and cell death markers following seizures suggests that the DNA repair response may not be sufficient to prevent excitotoxin-induced neurodegeneration.
[Show abstract][Hide abstract] ABSTRACT: Activation of the p53-stress response pathway has been implicated in excitotoxic neuronal cell death. Recent studies have demonstrated an age-dependent induction of both p53 mRNA and protein in the rat brain following lithium-pilocarpine-mediated status epilepticus (LPSE). We investigated whether other proteins that have been shown to participate in the p53 cascade are induced by LPSE. We used immunohistochemistry to examine the expression of Mdm2, Bax, CD95/Fas/APO-1, ATM, Ref-1 and ubiquitin. A significant increase in nuclear Mdm2 immunoreactivity, which colocalized with p53, was observed in cells within hippocampal pyramidal cell layers, dentate gyrus, piriform cortex, amygdala and thalamus. Dual immunofluorescence microscopy revealed a reduction in free ubiquitin expression in cells with p53 and Mdm2 accumulation. Increased immunoreactivity for CD95/Fas/APO-1 and Bax was also detected in the same p53-positive cells. Moreover, expression of Ref-1 and ATM, which are involved in the response to oxidative stress-induced DNA damage and regulation of p53 function, were increased. Colocalization of Ref-1 and p53 suggests that Ref-1 might activate p53 function in LPSE-induced neurodegeneration. In contrast, ATM immunoreactivity was predominantly cytoplasmic suggesting that ATM may not directly modulate p53 activity in injured neurons. These results extend our previous observations with regard to activation and stabilization of p53 in injured central nervous system neurons. The data indicate that p53 induction following LPSE may activate downstream pro-apoptotic genes leading to neurodegeneration.
[Show abstract][Hide abstract] ABSTRACT: Activation of the tumor suppressor gene, p53, has been strongly implicated in selective neuronal cell death. This study investigated p53 expression in the immature and adult rat brain following status epilepticus induced by the administration of lithium-pilocarpine (LPSE). Both p53 mRNA and protein were examined in relation to neuronal degeneration using in situ hybridization and immunohistochemistry, respectively. Injured cells with eosinophilic cytoplasm with increased p53 mRNA were observed in hippocampal subfields, piriform cortex, amygdala and thalamus. p53 mRNA levels reached a peak by 8 h and returned to baseline by 24 h after the onset of LPSE. The magnitude of p53 mRNA induction was greatest in 21-day-old rats. In contrast to the cellular expression pattern of p53 mRNA, immunohistochemistry demonstrated that p53 protein was increased in all of the eosinophilic cells. Further, double-labeling studies revealed that p53 protein was elevated in neurons that were degenerating. This was supported by colocalization of activated caspase 3 in some cells with damaged DNA. These results provide additional evidence for a critical role for the p53 pathway in excitotoxic neuronal cell death due to status epilepticus.
[Show abstract][Hide abstract] ABSTRACT: The mechanisms underlying kainate (KA) neurotoxicity are still not well understood. We previously reported that KA-mediated neuronal damage in organotypic cultures of hippocampal slices was associated with p53 induction. Recently, both bax and caspase-3 have been demonstrated to be key components of the p53-dependent neuronal death pathway. Caspase activation has also been causally related to the release of mitochondrial cytochrome c (Cyto C) in the cytoplasm as a result of the collapse of the mitochondrial membrane potential (ΔψM) and the opening of mitochondrial permeability transition pores (mPTP). In the present study, we observed a rapid induction of bax in hippocampal slice cultures after KA treatment. In addition, the levels of Cyto C and caspase-3 were increased in the cytosol while the level of the caspase-9 precursor was decreased. There was also a complete reduction of Rhodamine 123 fluorescence after KA treatment, an indication of ΔψM dissipation. Furthermore, inhibition of mPTP opening by cyclosporin A partially prevented Cyto C release, caspase activation and neuronal death. These data suggest the involvement of bax, several caspases, as well as Cyto C release in KA-elicited neuronal death. Finally, inhibition of caspase-3 activity by z-VAD-fmk only partially protected neurons from KA toxicity, implying that multiple mechanisms may be involved in KA excitotoxicity.
[Show abstract][Hide abstract] ABSTRACT: Fas (CD95/APO-1), a transmembrane glycoprotein and receptor for the Fas ligand, plays an important role in apoptosis. The present study examined whether excitotoxic cell death induces Fas expression in the adult rat brain. Although relatively light immunostaining was observed in control brain sections, significantly increased Fas immunoreactivity was seen from 4 h to 5 days after the onset of kainic acid-induced seizures. Increased expression of both Fas mRNA and protein were also evident by reverse transcription polymerase chain reaction and Western blotting, respectively. Fas induction was correlated with neuronal apoptosis as demonstrated by colocalization of Fas and terminal dT-mediated dUTP nick end-labeling (TUNEL). Cells with increased Fas-expression were also immunoreactive for tumor suppressor p53 and neuronal specific nuclear protein (NeuN). These results suggest that Fas receptor may contribute to excitotoxic neuronal death in cooperation with p53, and further implicates the Fas pathway in the pathophysiology of neurodegenerative diseases.
[Show abstract][Hide abstract] ABSTRACT: Neuronal death through activation of the p53 stress response pathway has been implicated in the pathogenesis of neurodegenerative disorders. The mechanisms regulating p53 accumulation and function in neurons are poorly understood. Recent evidence has demonstrated that Mdm2 is a major inhibitor of p53 that binds to and targets p53 for ubiquitin-mediated degradation. Here we demonstrate increased expression and co-localization of p53 and Mdm2 in the nuclei of degenerating neurons following treatment with either the excitotoxin, kainic acid, or the topoisomerase I inhibitor, camptothecin. Co-immunoprecipitation studies showed that p53-Mdm2 complexes were present in neuronal lysates. Dual immunofluorescence microscopy demonstrated that these complexes accumulated in neurons with a striking decrease in free ubiquitin levels. Exogenous ubiquitin restored p53 degradation to extracts from injured neurons confirming that Mdm2 function was intact. Finally, antisense-mediated downregulation of ubiquitin in cultured hippocampal neurons resulted in p53 and Mdm2 accumulation as well as apoptotic death. These results point to a novel mechanism to stabilize p53 and promote neuronal cell death in the central nervous system.
No preview · Article · Aug 2001 · Molecular Brain Research
[Show abstract][Hide abstract] ABSTRACT: Increased levels of neuron-specific enolase (NSE), a key glycolytic enzyme, in either the cerebrospinal fluid or the serum is correlated with both the duration and the outcome of status epilepticus. To further understand the molecular basis of seizure-induced elevations in NSE protein, we investigated NSE mRNA expression in the adult rat brain following systemic administration of kainic acid. The findings demonstrated either no change or a decrease in NSE gene expression during, and following, status epilepticus, suggesting that posttranscriptional mechanisms are responsible for seizure-induced increases in NSE protein.
No preview · Article · Oct 1999 · Experimental Neurology
[Show abstract][Hide abstract] ABSTRACT: Astrocytes are potent regulators of brain capillary endothelial cell function. Recently, astrocytes were shown to regulate brain capillary endothelial expression of the fibrinolytic enzyme tissue plasminogen activator (tPA) and the anticoagulant thrombomodulin (TM). To study the mechanism of this process, we examined the hypothesis that astrocyte regulation of endothelial tPA and TM is mediated by transforming growth factor-beta (TGF-beta).
Brain capillary endothelial cells were grown in blood-brain barrier models. We examined astrocyte-endothelial cocultures, endothelial monocultures, and astrocyte-conditioned media (ACM) for the expression of TGF-beta. We also incubated endothelial cells with ACM to determine the role of TGF-beta. Following 24 hours of incubation, we assayed for tPA and TM mRNA, as well as tPA and TM activity.
Astrocyte-endothelial cocultures and ACM exhibited significantly higher levels of active TGF-beta than brain endothelial monocultures and endothelial cells grown in nonconditioned media, respectively. Brain endothelial cells incubated with ACM exhibited reduced tPA and TM mRNA and activity. Treatment with exogenous TGF-beta produced dose-dependent reductions in tPA and TM. The effects of ACM on both tPA and TM were blocked by TGF-beta neutralizing antibody.
These data indicate that TGF-beta mediates astrocyte regulation of brain capillary endothelial expression of tPA and TM.
[Show abstract][Hide abstract] ABSTRACT: Previous studies have implicated the tumor suppressor gene, p53, in neuronal apoptosis due to excitotoxin treatment. To test whether p53 protein functions as a transcription factor during excitotoxic cell death, we used electrophoretic mobility shift assays to measure p53 sequence-specific DNA-binding activity following kainic acid (KA)-induced seizures. A rapid and significant increase in p53 DNA-binding activity was observed in extracts from kainate-vulnerable brain regions at 2.5 h after seizure onset, an effect which lasted up to 16 h after seizure-onset. DNA binding activity returned to normal by 30 h after KA injection. Pre-treatment with the protein synthesis inhibitor cycloheximide, as well as pre-incubation with PAb421, a p53 monoclonal antibody, significantly attenuated p53 DNA-binding activity induced by KA treatment. These results indicate that p53 protein may function as a transcription factor, following KA treatment, to regulate the expression of p53-responsive genes involved in neuronal apoptosis.
No preview · Article · Feb 1999 · Molecular Brain Research
[Show abstract][Hide abstract] ABSTRACT: The anticoagulant transmembrane glycoprotein thrombomodulin (TM) is expressed at the luminal surface of vascular endothelial cells. Recently, we showed that TM antigen and TM mRNA are expressed in brain microvessels in several species and that brain capillaries have the capability to activate protein C. The activation of protein C in brain microcirculation was greatly impaired by major stroke risk factors in rats due to downregulation of TM. In this study, a partial sequence of TM was determined from TM mRNA from brain capillaries examined in brain capillaries of the rat, a species that provides a useful model to investigate stroke mechanisms in relation to brain hemostasis. The predicted deduced amino acid sequences for rat TM were compared with other TM sequences. Particularly high homology (77-100%) among functional domains of the protein, i.e., the epidermal growth factor repeats (EGFRs) 1-6 and the transmembrane region, was observed between mice and rats. Somewhat less degree of homology was observed for bovine and human EGFRs 1-6, while the homology of the transmembrane region was 92-96%. All cysteine residues were conserved among the TM sequences, and specific amino acids previously suggested to be essential for activation of protein C by thrombin TM were highly conserved. We conclude that the highly conserved mRNA and protein sequences may reflect a similar anticoagulant role of TM in brain endothelial and systemic vascular endothelial cells across different species.
No preview · Article · Jan 1999 · Thrombosis Research