1,720,959 research outputs found
Exploring Orai2 function in alzheimer's disease models based on presenilin 2 and amyloid precursor protein mutants
Get PDFAlzheimer's disease (AD) is the most common form of dementia among elderly population. More than twenty years ago the so-called amyloid hypothesis was formulated based on the major histopathological hallmarks of AD, among which the amyloid plaques are the most known and studied. This hypothesis was prompted by the discovery of three genes that, whereas mutated, are associated with the familial forms of the disease (FAD). One of these genes encodes for the amyloid precursor protein (APP), a single-pass type I transmembrane protein that undergoes sequential cleavages operated by the secretase family of enzymes. The last and key secretase, called gamma-secretase, is composed of four proteins, among which we found either presenilin 1 (PS1) or presenilin 2 (PS2), encoded by other two genes (PSEN1/PSEN2) that are responsible for FAD pathogenesis. Autosomic dominant mutations in either APP, PSEN1 or PSEN2 cause accelerated Abeta deposition due to an increased Abeta42/Abeta40 ratio. While the vast majority of AD cases are sporadic, FAD patients bearing PS2 mutations show a clinical course much similar to that of sporadic patients.
By many groups it was found that PSs are capable of perturbing cellular Ca2+ homeostasis, and, particularly, our group demonstrated that PS2, either bearing FAD-linked mutations or wild-type (WT), lowers endoplasmic reticulum (ER) and Golgi apparatus Ca2+ content, interacts with SERCA pump, dampening its function, and tethers ER and mitochondria; all of these pleiotropic effects are independent of its gamma-secretase activity. Recently another group identified PS2 as a regulator of the ER Ca2+ content, together with Orai2, a plasma membrane channel implicated in the Store-Operated Ca2+ Entry (SOCE). This latter phenomenon is impaired in AD, and specifically it is down-tuned in mutant PS-bearing cells. Taken together this body of information offered an interesting background to study the interplay between ER Ca2+ levels, SOCE defects and APP processing/Abeta production. Taking advantage of the PS2-based AD mouse models available in our laboratory, namely the homozygous single transgenic (TG) line expressing the FAD-linked mutant PS2-N141I (line PS2.30H) and the homozygous double transgenic (2TG) line expressing PS2-N141I together with the Swedish double mutant APP-K670M/N671L (line B6.152H), we could investigate the expression pattern of Orai2 in the nervous tissue.
Western blot analyses on cortices and hippocampi revealed that Orai2 was overexpressed in cortices from TG and 2TG mice, when compared to C57BL/6 (WT) mice. This overexpression was mainly due to the neuronal contribution since it was even higher in cortical neuronal cultures and in situ Orai2 was found only in neurons, as assayed by immunohistochemical analysis of brain slices. Orai2 up-regulation, that is the condition found in TG and 2TG neurons, is capable of perturbing cellular Ca2+ homeostasis. Particularly, when overexpressed it caused a significant decrease in IP3-induced ER Ca2+ release in both H4-APPswe and HEK29T cells; these results are consistent with a decreased ER Ca2+ level, as measured with the ER-targeted probe G-CEPIA1er. In addition to this, Orai2 revealed to be a less efficient mediator of SOCE than Orai1, since it dampened SOCE when overexpressed alone and it produced a much smaller SOCE when overexpressed with STIM1 as compared with Orai1 plus STIM1 overexpression. Conversely to our expectations, Orai2 downregulation had a noticeable effect neither on IP3-induced ER Ca2+ release nor on total store Ca2+ content; it however improved Ca2+ entry upon store depletion. As far as subcellular localization goes, Orai2 overexpression did not increase the fraction of protein present in the ER and it appeared that most of the protein was found at the early endosomal level, as revealed by immunofluorescence staining of various subcellular compartments. This holds true moving to cortical neurons, where Orai2 was preferentially found in Rab5-EEA1 positive endosomes in primary cultures from WT mice, with a dramatic accumulation at this level in neurons from 2TG mice, possibly reflecting the increased early-endosome compartment that characterizes the AD phenotype. Orai2 localization is, however, dynamic, meaning that it moves in and out of endosomes when properly stimulating neurons with compounds able to induce neuronal activity or to stimulate SOCE. This behaviour is anyway different among the three genotypes, with TG neurons showing a greater tendency to retrieve Orai2 in endosomes upon cell stimulation, and 2TG neurons being unable to properly tune their endosome pool, possibly because of its higher accumulation level. Whether these changes involve also Orai1 has still to be evaluated and it will give us a better picture of this unknown phenomenon. Finally, evidence is provided that a down-tuning of SOCE is associated with increased levels of secreted Abeta42, as measured by ELISA performed on conditioned media from mutant APP-expressing cells such as CHO-7PA2 and H4-APPswe
When, where and how? Focus on neuronal calcium dysfunctions in Alzheimer's Disease.
Get PDFAlzheimer’s disease (AD), since its characterization as a precise form of dementia with its own pathological
hallmarks, has captured scientists’ attention because of its complexity. The last 30 years have been
filled with discoveries regarding the elusive aetiology of this disease and, thanks to advances in molecular
biology and live imaging techniques, we now know that an important role is played by calcium (Ca2+).
Ca2+, as ubiquitous second messenger, regulates a vast variety of cellular processes, from neuronal excitation
and communication, to muscle fibre contraction and hormone secretion, with its action spanning
a temporal scale that goes from microseconds to hours. It is therefore very challenging to conceive a
single hypothesis that can integrate the numerous findings on this issue with those coming from the
classical fields of AD research such as amyloid-beta (A) and tau pathology. In this contribution, we will
focus our attention on the Ca2+ hypothesis of AD, dissecting it, as much as possible, in its subcellular
localization, where the Ca2+ signal meets its specificity. We will also follow the temporal evolution of the
Ca2+ hypothesis, providing some of the most updated discoveries. Whenever possible, we will link the
findings regarding Ca2+ dysfunction to the other players involved in AD pathogenesis, hoping to provide
a crossover body of evidence, useful to amplify the knowledge that will lead towards the discovery of an
effective therapy
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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