1,720,979 research outputs found
Nonlinear analytic and semi-analytic nodal methods for multigroup neutron diffusion calculations
No full textTwo advanced nodal methods for the solution of the multigroup neutron diffusion equations are developed, using the nonlinear coarse-mesh finite difference (CMFD) scheme. Based on the analytic and semi-analytic methods, the relationships between the flux and current on the nodal surface are derived, by which the two-node problem is formulated in an efficient way. The issue of the complex eigenmodes and the instability problem inherent in the analytic solution are considered in order to have an efficient and stable algorithm. The numerical results demonstrate the effectiveness of the two methods
Progestogens regulate endothelial actin cytoskeleton and cell movement via the actin-binding protein moesin
No full textThe endothelial effects of progestogens are poorly investigated. Actin remodeling and cell movement are fundamental for endothelial function and are controlled by the actin-binding protein moesin. In this work, we studied the effects of progesterone and medroxyprogesterone acetate (MPA) on actin remodeling, moesin activation and cell movement in human endothelial cells. Our findings show that progesterone and MPA trigger a rapid endothelial actin rearrangement, with the formation of cortical actin complexes, pseudopodia and membrane ruffles. Both progestogens trigger a rapid progesterone receptor (PR)-dependent moesin activation via a non-genomic signaling cascade involving G proteins, the small GTPase RhoA and the Rho-associated kinase (ROCK-2). In addition, MPA signaling also requires the recruitment of phosphatidylinositol-3 kinase (PI3K). Both progestogens enhance endothelial cell migration, which is prevented by moesin silencing or by blockade of PR, G proteins, PI3K, mitogen-activated protein kinases or ROCK-2. Progesterone and MPA potentiate 17beta-estradiol (E2) induced-moesin activation. However, they partially reduce cell migration induced by E2. In conclusion, progesterone and MPA regulate endothelial cell movement by rapidly signaling to the actin-binding protein moesin and to the actin cytoskeleton. These findings provide new information on the biological actions of progestins on human endothelial cells that are relevant for vascular function
Endothelial regulation of eNOS, PAI-1 and t-PA by testosterone and dihydrotestosterone in vitro and in vivo
No full textThe aim of this study is the identification of direct endothelial regulation by the androgens testosterone (T) and dihydrotestosterone (DHT). We tested the effects of T and DHT on nitric oxide (NO) synthesis and on tissue plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) expression in human endothelial cells and in ovariectomized (OVX) rats. The results showed that at physiological concentrations T and DHT increase endothelial synthesis of NO. This depends on a rapid recruitment of the extracellular-related kinase (ERK) 1/2 and of the phosphatidylinositol 3-OH kinase (PI3K)/Akt cascades, resulting in endothelial nitric oxide synthase (eNOS) Ser(1177)-phosphorylation. In addition, a later increase of eNOS expression is found. With supra-physiological amounts of T or DHT the induction of NO synthesis is lost. A concentration-related increase of t-PA expression starting from physiological concentrations of T or DHT is found, whereas PAI-1 is augmented only with higher doses. Although DHT exerts these actions through androgen receptors (AR), T acts in part through aromatase-dependent conversion to 17β-estradiol. Ovariectomy is associated with significant changes in eNOS, t-PA and PAI-1 expression in the aorta of Wistar rats and T and DHT result in modifications on eNOS, PAI-1 and t-PA that are in line with the in vitro experiments. In conclusion, T and DHT act on endothelial cells through AR or via conversion to estradiol. Physiological, but not higher amounts are associated with enhanced NO synthesis and an increased t-PA/PAI-1 ratio. These findings are useful to understand the impact of androgens in ageing individual
Progesterone receptor enhances breast cancer cell motility and invasion via extranuclear activation of focal adhesion kinase
No full textWhile progesterone plays multiple roles in the process of breast development and differentiation, its role in breast cancer is less understood. We have shown previously that progestins stimulate breast cancer cell migration and invasion because of the activation of rapid signaling cascades leading to modifications in the actin cytoskeleton and cell membrane that are required for cell movement. In this study, we have investigated the effects of progesterone on the formation of focal adhesion (FA) complexes, which provide anchoring sites for cell attachment to the extracellular matrix during cell movement and invasion. In T47-D breast cancer cells, progesterone rapidly enhances FA kinase (FAK) phosphorylation at Tyr(397) in a time- and concentration-dependent manner. As a result, exposure to progesterone leads to increased formation of FA complexes within specialized cell membrane protrusions. The cascade of events required for this phenomenon involves progesterone receptor interaction with the tyrosine kinase c-Src, which activates the phosphatidylinositol-3-kinase/Akt pathway and the small GTPase RhoA/Rho-associated kinase complex. In the presence of progesterone, T47-D breast cancer cells display enhanced horizontal migration and invasion of three-dimensional matrices, which is reversed by small interfering RNAs abrogating FAK. In conclusion, progesterone promotes breast cancer cell movement and invasion by facilitating the formation of FA complexes via the rapid regulation of FAK. These results provide novel mechanistic views on the effects of progesterone on breast cancer progression, and may in the future be helpful to develop new strategies for the treatment of endocrine-sensitive breast cancer
Rapid signaling of estrogen to WAVE1 and moesin controls neuronal spine formation via the actin cytoskeleton
No full textEstrogens are important regulators of neuronal cell morphology, and this is thought to be critical for gender-specific differences in brain function and dysfunction. Dendritic spine formation is dependent on actin remodeling by the WASP-family verprolin homologous (WAVE1) protein, which controls actin polymerization through the actin-related protein (Arp)-2/3 complex. Emerging evidence indicates that estrogens are effective regulators of the actin cytoskeleton in various cell types via rapid, extranuclear signaling mechanisms. We here show that 17beta-estradiol (E2) administration to rat cortical neurons leads to phosphorylation of WAVE1 on the serine residues 310, 397, and 441 and to WAVE1 redistribution toward the cell membrane at sites of dendritic spine formation. WAVE1 phosphorylation is found to be triggered by a Galpha(i)/Gbeta protein-dependent, rapid extranuclear signaling of estrogen receptor alpha to c-Src and to the small GTPase Rac1. Rac1 recruits the cyclin-dependent kinase (Cdk5) that directly phosphorylates WAVE1 on the three serine residues. After WAVE1 phosphorylation by E2, the Arp-2/3 complex concentrates at sites of spine formation, where it triggers the local reorganization of actin fibers. In parallel, E2 recruits a Galpha(13)-dependent pathway to RhoA and ROCK-2, leading to activation of actin remodeling via the actin-binding protein, moesin. Silencing of WAVE1 or of moesin abrogates the increase in dendritic spines induced by E2 in cortical neurons. In conclusion, our findings indicate that the control of actin polymerization and branching via moesin or WAVE1 is a key function of estrogen receptor alpha in neurons, which may be particularly relevant for the regulation of dendritic spines
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
17ß-estradiol attenuates atherosclerosis development: the possible role of hydrogen sulfide.
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