1,720,980 research outputs found
Inducible adeno-associated virus vectors promote functional angiogenesis in adult organisms via regulated vascular endothelial growth factor expression
No full textAIMS: Members of the vascular endothelial growth factor (VEGF) family are among the most promising cytokines to induce neovascularization of ischaemic tissues; however, their unregulated expression often results in major undesired effects. Here, we describe the properties of inducible vectors based on the adeno-associated virus (AAV), allowing precise control of VEGF expression, and exploit these vectors to define the kinetics of the angiogenic response elicited by the factor. METHODS AND RESULTS: Based on a tetracycline-inducible transactivator, we designed an AAV vector system allowing the pharmacological regulation of VEGF production in vivo and tested its efficacy in inducing functional neoangiogenesis in both normoperfused and ischaemic skeletal muscle in mice by a combination of histological, immunofluorescent, and molecular imaging techniques. We observed that a prolonged expression of VEGF was required to determine the formation of stable vessels, able to persist upon withdrawal of the angiogenic stimulus. However, the vessels formed in the presence of continuous VEGF expression consisted mainly of dilated and leaky capillaries. As determined after pinhole scintigraphy, this abnormal vasculature accounted for a significant drop in functional tissue perfusion. In contrast, transient VEGF expression, followed by a period of VEGF withdrawal, allowed maintenance of functional perfusion under resting conditions and during exercise. This VEGF-inducible system was highly effective in improving vascularization and function in a hind-limb ischaemia model. CONCLUSION: Together, these results clearly indicate that the fine tuning of VEGF expression is required to achieve the formation of a stable vasculature able to sustain functional neovascularization
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
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
A gene transfer approach, based on Adeno-Associated Viral (AAV) vectors, to study the process of vessel maturation and stabilization
Full text link2007/2008The main goal of angiogenic gene therapy is the formation of functional new blood vessels adequate to restore blood flow in ischemic tissues. Angiogenesis is a complex process, consisting in the sprouting of new capillaries from pre-existing vessels to form an immature vascular network, which subsequently undergoes functional maturation and remodelling. Many factors are involved in this process and, among them, the VEGF family members are universally recognized as the key players.
During my PhD I exploited gene transfer by vectors based on the Adeno-Associated Virus (AAV) to express several factors involved in the angiogenic process, in an attempt to define the molecular and cellular mechanisms of vessel maturation and stabilization. Most experiments were performed by vector injection in the mouse and rat skeletal muscle, followed by detailed histological, immunohistochemical and functional analysis.
First of all the angiogenic effect driven by two main VEGF isoforms, VEGF165 and VEGF121 was compared. AAV-VEGF165 and AAV-VEGF121 appeared equally able to induce endothelial cell proliferation, leading to the formation of new CD31 positive capillaries. However, only the longest VEGF165 isoform was capable to recruit -SMA positive cells around growing capillaries and therefore giving rise to small arteries. The acquisition of a smooth muscle cell layer can be considered as marker of vessel maturation. This was also confirmed by a permeability assay, which showed that VEGF121-induced vessels were more permeable compared to those induced by VEGF165.
Interestingly, the presence of -SMA positive vessels was paralleled by the recruitment of CD11b positive mononuclear cells from the bone marrow, cells which were not recruited by VEGF121. The presence of these infiltrating cells in close proximity to the newly formed arterioles suggested their possible role in smooth muscle cell recruitment and vessel maturation. Real-time PCR allowed observing that the infiltrating CD11b positive cells expressed a cocktail of cytokines implicated in vessel maturation, such as TGF- and PDGF-B. As a proof of concept of the paracrine activity of these cells in vessel maturation, we developed an AAV-PDGF-B vector, which, when co-injected with AAV-VEGF121, was arteriogenic even in absence of cellular infiltration. Thus, the expression of PDGF-B partially substitutes for the cells observed in the muscles injected by AAV-VEGF165 to form arterial vessels. To verify the functionality of the vessels induced by AAV-VEGF165 we delivered this vector to different animal models of tissue ischemia: a flap ischemia model and an in vivo chamber for tissue engineering based on an artero-venous loop. In both the models, VEGF165 expression induced the formation of -SMA positive vessels, which turned out to improve flap survival in the flap models, and to promote the formation of new vascularized tissue in the chamber.
Despite the presence of several arteries, other vessels formed by VEGF165 were abnormally enlarged and leaky, often forming vascular lacunae. This observation indicated that VEGF gene transfer might not be sufficient for the formation of a fully functional vascular network, and that other factors might be required in order to achieve functional competence of the neovessels. We observed that the combined expression of VEGF165 with Angiopoietin-1, which is known to stabilize endothelial and mural cell interactions, resulted in a significant reduction of vessel permeability and improved blood flow, as assessed by positron emission tomography (PET) and single photon emission tomography (SPECT).
These findings reveal that a fine control of the expression of angiogenic factors is needed to achieve the formation of stable and functional vessels. The presence of -SMA positive cells might be considered as a first step in vessel maturation but further stabilization factors have to take part to the process in order to tighten the cell-cell junctions. Moreover, we showed that a detailed histological and functional analysis ex vivo might not be sufficient to characterized the new vasculature, requiring imaging techniques such as PET or SPECT.XX Ciclo197
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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