1,720,959 research outputs found
Metal Ion Regulation in the Central Nervous System and in Glutamatergic Synapses: Role of the Cellular Prion Protein
Full text linkDespite many efforts, the molecular mechanisms underlying the pathophysiology of neurodegenerative disorders have not been fully understood. Results published in literature highlight that different neurodegenerative diseases share common features: protein aggregation in neuronal tissue; oxidation of neuronal tissue mediated by redox-active metal ions interaction with a target protein; and functional demise. So, unveiling the physiological function of protein that aggregate in neurodegenerating tissues, as well as their interplay with metal ions, becomes a prominent issue, in order to understand the etiological trigger and to define a possible therapeutic strategy.
Metal ions are essential elements for cellular processes, but at the same they are potentially dangerous since they can give rise to Fenton reaction and oxidative/nitrosative stress. So, their homeostasis is strictly regulated in each district of the organism, but in particular in the brain. The brain, having the highest metabolic rate and depending predominantly on oxidative metabolism for its energy, has developed fine mechanisms to compartmentalize, distribute, uptake and excrete the different ionic species. Alterations in one of these mechanisms can lead to great neuronal damages, and maybe neurodegenerative disorders.
This work has been focused on the cellular prion protein (PrPC), whose conformational isoform, the scrapie prion protein (PrPSc) is the causative agent of prion disordes and whose function has not been clearly defined, yet. Metal ions are a common denominator to all the cellular pathways in which PrPC seems to be actively involved. In particular, metal ions homeostasis maintainance, neuroprotection in excitotoxic condition and ionotropic receptor modulation have been studied.
In the first part of the project, PrPC role in metal ion homeostais maintainance has been investigated. To this aim, copper, manganese, zinc and iron content, as well as metal binding proteins expression have been measured in a PrP knockout murine model, compared to wild-type. The results describe the global rearrangement occurring in the expression of metal binding proteins to maintain trace metals homeostasis, trying to compensate PrPC absence. At the same time, a pronounced decrease in Ceruloplasmin ferroxidase activity has been detected in PrP null mouse serum, pointing out a global impairment in copper metabolism in PrPC absence. In the second part of the project, the importance of the interaction between PrPC and copper ions in excitotoxic conditions and in synapses functionality has been studied. It has been published that PrP null mice show higher levels of neuronal cell death in stressful conditions and when subjected to toxic treatment with glutamate receptor agonists. Moreover, these mice show altered kinetics of N-methyl-D-aspartate (NMDA) receptor current. These alterations appears to be due to an inhibitory regulation that PrPC exerts on NMDA receptors via copper ions, lacking in PrP null hippocampi. First, the enhanced suceptibility to excitotoxicity of PrP knockout mice has been verified and characterised in organotypic hippocampal cultures upon treatment with NMDA. Higher neuronal cell death levels have been detected in all the investigated hippocampal regions. To identify which cellular regulatory mechanism is alterd in PrPC absence, the expression of the proteins mainly involved in excitotoxicity has been compared between PrP knockout and wild-type hippocampi. Among other minor differences, a different modulation of calcium transporters expression has been identified in PrP knockout hippocampi and brains. This global alteration appears to be necessary to maintain calcium homeostasis, since calcium content measurements did not reveal any strong difference between PrP null and wild-type samples.
NMDA receptors can be S-nitrosylated on extracellular cysteines and this reaction is always inhibitory. S-nytrosilation requires an electron acceptor to occur, for this reason copper ions are often involved in these kind of reactions. Moreover, copper ions are known to modulate NMDA receptor activity, but the precise mechanism has not been described, yet. Since PrPC is known to support the S-nitrosylation of other membrane proteins, the S-nitrosylation levels of NMDA receptor subunits GluN1 and GluN2A have been measured in PrP knockout hippocampi from adult mice and compared to wild-type ones. Results show that the S-nitrosylated fractions of both GluN1 and GluN2A are reduced in PrP absence. So, this reveals that PrPC modulates NMDA receptor activity providing the copper ions necessary to support their inhibitory S-nitrosylation reaction. Through this mechanism, PrPC contributes to inhibit NMDA receptor currents, as well as to protect neurons in excitotoxic conditions
Prion Protein and Aging
Full text linkThe cellular prion protein (PrPC) has been widely investigated ever since its conformational isoform, the prion (or PrPSc), was identified as the etiological agent of prion disorders. The high homology shared by the PrPC-encoding gene among mammals, its high turnover rate and expression in every tissue strongly suggest that PrPC may possess key physiological functions. Therefore, defining PrPC roles, properties and fate in the physiology of mammalian cells would be fundamental to understand its pathological involvement in prion diseases. Since the incidence of these neurodegenerative disorders is enhanced in aging, understanding PrPC functions in this life phase may be of crucial importance. Indeed, a large body of evidence suggests that PrPC plays a neuroprotective and antioxidant role. Moreover, it has been suggested that PrPC is involved in Alzheimer disease, another neurodegenerative pathology that develops predominantly in the aging population. In prion diseases, PrPC function is likely lost upon protein aggregation occurring in the course of the disease. Additionally, the aging process may alter PrPC biochemical properties, thus influencing its propensity to convert into PrPSc. Both phenomena may contribute to the disease development and progression. In Alzheimer disease, PrPC has a controversial role because its presence seems to mediate β-amyloid toxicity, while its down-regulation correlates with neuronal death. The role of PrPC in aging has been investigated from different perspectives, often leading to contrasting results. The putative protein functions in aging have been studied in relation to memory, behavior and myelin maintenance. In aging mice, PrPC changes in subcellular localization and post-translational modifications have been explored in an attempt to relate them to different protein roles and propensity to convert into PrPSc. Here we provide an overview of the most relevant studies attempting to delineate PrPC functions and fate in aging
Prion protein and copper cooperatively protect neurons by modulating NMDA receptor through S-nitrosylation
Full text linkAIMS:
Several neurodegenerative disorders show alterations in glutamatergic synapses and increased susceptibility to excitotoxicity. Mounting evidence suggests a central role for the cellular prion protein (PrP(C)) in neuroprotection. Therefore, the loss of PrP(C) function occurring in prion disorders may contribute to the disease progression and neurodegeneration. Indeed, PrP(C) modulates N-methyl-d-aspartate receptors (NMDAR), thus preventing cell death. In this study, we show that PrP(C) and copper cooperatively inhibit NMDAR through S-nitrosylation, a post-translational modification resulting from the chemical reaction of nitric oxide (NO) with cysteines.
RESULTS:
Comparing wild-type Prnp (Prnp(+/+)) and PrP(C) knockout (Prnp(0/0)) mouse hippocampi, we found that GluN1 and GluN2A S-nitrosylation decrease in Prnp(0/0). Using organotypic hippocampal cultures, we found that copper chelation decreases NMDAR S-nitrosylation in Prnp(+/+) but not in Prnp(0/0). This suggests that PrP(C) requires copper to support the chemical reaction between NO and thiols. We explored PrP(C)-Cu neuroprotective role by evaluating neuron susceptibility to excitotoxicity in Prnp(+/+) and Prnp(0/0) cultures. We found that (i) PrP(C)-Cu modulates GluN2A-containing NMDAR, those inhibited by S-nitrosylation; (ii) PrP(C) and copper are interdependent to protect neurons from insults; (iii) neuronal NO synthase inhibition affects susceptibility in wild-type but not in Prnp(0/0), while (iv) the addition of a NO donor enhances Prnp(0/0) neurons survival.
INNOVATION AND CONCLUSIONS:
Our results show that PrP(C) and copper support NMDAR S-nitrosylation and cooperatively exert neuroprotection. In addition to NMDAR, PrP(C) may also favor the S-nitrosylation of other proteins. Therefore, this mechanism may be investigated in the context of the different cellular processes in which PrP(C) is involved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Proteomics of rat hypothalamus, hippocampus and pre-frontal/frontal cortex after central administration of the neuropeptide PACAP
No full textPituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that exerts pleiotropic functions, acting as a hypophysiotropic factor, a neurotrophic and a neuroprotective agent. The molecular pathways activated by PACAP to exert its physiological roles in brain are incompletely understood. In this study, adrenocorticotropic hormone (ACTH), prolactin, luteinising hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), brain-derived neurotrophic factor and corticosterone blood levels were determined before and 20, 40, 60, and 120 min after PACAP intracerebroventricular administration. PACAP treatment increased ACTH, corticosterone, LH and FSH blood concentrations, while it decreased TSH levels. A proteomics investigation was carried out in hypothalamus, hippocampus and pre-frontal/frontal cortex (P/FC) using 2-dimensional gel electrophoresis at 120 min, the end-point suggested by studies on PACAP hypophysiotropic activities. Spots showing statistically significant alterations after PACAP treatment were identified by Matrix-assisted laser desorption/ionization-Time of flight mass spectrometry. Identified proteins were consistent with PACAP involvement in different molecular processes in brain. Altered expression levels were observed for proteins involved in cytoskeleton modulation and synaptic plasticity: actin in the hypothalamus; stathmin, dynamin, profilin and cofilin in hippocampus; synapsin in P/FC. Proteins involved in cellular differentiation were also modulated: glutathione-S-transferase α and peroxiredoxin in hippocampus; nucleoside diphosphate kinase in P/FC. Alterations were detected in proteins involved in neuroprotection, neurodegeneration and apoptosis: ubiquitin carboxyl-terminal hydrolase isozyme L1 and heat shock protein 90-β in hypothalamus; α-synuclein in hippocampus; glyceraldehyde-3-phosphate dehydrogenase and prohibitin in P/FC. This proteomics study identified new proteins involved in molecular mechanisms mediating PACAP functions in the central nervous system
Prions Strongly Reduce NMDA Receptor S-Nitrosylation Levels at Pre-symptomatic and Terminal Stages of Prion Diseases
No full textPrion diseases are fatal neurodegenerative disorders characterized by the cellular prion protein (PrPC) conversion into a misfolded and infectious isoform termed prion or PrPSc. The neuropathological mechanism underlying prion toxicity is still unclear, and the debate on prion protein gain- or loss-of-function is still open. PrPC participates to a plethora of physiological mechanisms. For instance, PrPC and copper cooperatively modulate N-methyl-D-aspartate receptor (NMDAR) activity by mediating S-nitrosylation, an inhibitory post-translational modification, hence protecting neurons from excitotoxicity. Here, NMDAR S-nitrosylation levels were biochemically investigated at pre- and post-symptomatic stages of mice intracerebrally inoculated with RML, 139A, and ME7 prion strains. Neuropathological aspects of prion disease were studied by histological analysis and proteinase K digestion. We report that hippocampal NMDAR S-nitrosylation is greatly reduced in all three prion strain infections in both pre-symptomatic and terminal stages of mouse disease. Indeed, we show that NMDAR S-nitrosylation dysregulation affecting prion-inoculated animals precedes the appearance of clinical signs of disease and visible neuropathological changes, such as PrPSc accumulation and deposition. The pre-symptomatic reduction of NMDAR S-nitrosylation in prion-infected mice may be a possible cause of neuronal death in prion pathology, and it might contribute to the pathology progression opening new therapeutic strategies against prion disorders
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
