1,720,964 research outputs found
Evolution of the eukaryotic ARP2/3 activators of the WASP family: WASP, WAVE, WASH, and WHAMM, and the proposed new family members WAWH and WAML
Full text linkAbstract Background WASP family proteins stimulate the actin-nucleating activity of the ARP2/3 complex. They include members of the well-known WASP and WAVE/Scar proteins, and the recently identified WASH and WHAMM proteins. WASP family proteins contain family specific N-terminal domains followed by proline-rich regions and C-terminal VCA domains that harbour the ARP2/3-activating regions. Results To reveal the evolution of ARP2/3 activation by WASP family proteins we performed a "holistic" analysis by manually assembling and annotating all homologs in most of the eukaryotic genomes available. We have identified two new families: the WAML proteins (WASP and MIM like), which combine the membrane-deforming and actin bundling functions of the IMD domains with the ARP2/3-activating VCA regions, and the WAWH protein (WASP without WH1 domain) that have been identified in amoebae, Apusozoa, and the anole lizard. Surprisingly, with one exception we did not identify any alternative splice forms for WASP family proteins, which is in strong contrast to other actin-binding proteins like Ena/VASP, MIM, or NHS proteins that share domains with WASP proteins. Conclusions Our analysis showed that the last common ancestor of the eukaryotes must have contained a homolog of WASP, WAVE, and WASH. Specific families have subsequently been lost in many taxa like the WASPs in plants, algae, Stramenopiles, and Euglenozoa, and the WASH proteins in fungi. The WHAMM proteins are metazoa specific and have most probably been invented by the Eumetazoa. The diversity of WASP family proteins has strongly been increased by many species- and taxon-specific gene duplications and multimerisations. All data is freely accessible via http://www.cymobase.org.</p
Proteomic analysis of short-term preload-induced eccentric cardiac hypertrophy
Full text linkBackground: Hemodynamic load leads to cardiac hypertrophy and heart failure. While afterload (pressure overload) induces concentric hypertrophy, elevation of preload (volume overload) yields eccentric hypertrophy and is associated with a better outcome. Here we analysed the proteomic pattern of mice subjected to short-term preload. Methods and Results: Female FVB/N mice were subjected to aortocaval shunt-induced volume overload that leads to an eccentric hypertrophy (left ventricular weight/tibia length +31 %) with sustained systolic heart function at 1 week after operation. Two-dimensional gel electrophoresis (2-DE) followed by mass spectrometric analysis showed alteration in the expression of 25 protein spots representing 21 different proteins. 64 % of these protein spots were up-regulated and 36 % of the protein spots were consistently down-regulated. Interestingly, alpha-1-antitrypsin was down-regulated, indicating higher elastin degradation and possibly contributing to the early dilatation. In addition to contractile and mitochondrial proteins, polymerase I and transcript release factor protein (PTRF) was also up-regulated, possibly contributing to the preload-induced signal transduction. Conclusions: Our findings reveal the proteomic changes of early-stage eccentric myocardial remodeling after volume overload. Induced expression of some of the respiratory chain enzymes suggests a metabolic shift towards an oxidative phosphorylation that might contribute to the favorable remodeling seen in early VO. Down-regulation of alpha-1-antitrypsin might contribute to extracellular matrix remodeling and left ventricular dilatation. We also identified PTRF as a potential signaling regulator of volume overload-induced cardiac hypertrophy
Genetic deletion of calcium/calmodulin-dependent protein kinase type II delta does not mitigate adverse myocardial remodeling in volume-overloaded hearts
No full textCalcium/calmodulin-dependent protein kinase type II delta (CaMKIIδ), the predominant CaMKII isoform expressed in the heart, has been implicated in the progression of myocardial infarction- and pressure overload-induced pathological remodeling. However, the role of CaMKIIδ in volume overload (VO) has not been explored. We have previously reported an activation of CaMKII during transition to HF in long-term VO. Here, we address whether CaMKIIδ is critically involved in the mortality, myocardial remodeling, and heart failure (HF) progression in response to VO. CaMKIIδ knockout (δ-KO) and wild-type (WT) littermates were exposed to aortocaval shunt-induced VO, and the progression of adverse myocardial remodeling was assessed by serial echocardiography, histological and molecular analyses. The mortality rates during 10 weeks of VO were similar in δ-KO and WT mice. Both genotypes displayed comparable eccentric myocardial hypertrophy, altered left ventricle geometry, perturbed systolic and diastolic functions after shunt. Additionally, cardiomyocytes hypertrophy, augmented myocyte apoptosis, and up-regulation of hypertrophic genes were also not significantly different in δ-KO versus WT hearts after shunt. Therefore, CaMKIIδ signaling seems to be dispensable for the progression of VO-induced maladaptive cardiac remodeling. Accordingly, we hypothesize that CaMKIIδ-inhibition as a therapeutic approach might not be helpful in the context of VO-triggered HF
From Chromatin Readers to Heart Failure: BET Protein Family Members in Cardiac Remodeling
Full text linkHeart failure (HF) is the pathologic inability of the heart to supply the body with sufficient amounts of oxygen-rich blood. This increasingly common, life-threatening condition occurs in the final stage of various cardiac pathologies that reduce heart function. Common pharmacotherapies of HF aim to inhibit the renin-angiotensin system and adrenergic receptors that are activated in response to the reduced pumping function and have been available for over 20 years. However, the morbidity and mortality rates of affected patients remain high. To this day the development of new, more effective therapies poses a major challenge in medical research.
The new therapeutic strategy investigated in this work is based on increasing evidence that epigenetics play an important role in the pathogenesis of HF. The rationale behind targeting epigenetic processes to treat the development of HF is that they modulate multiple transcriptional networks simultaneously. For instance, the small molecule JQ1 was shown to displace the bromodomain and extraterminal domain (BET) reader proteins BRD2, BRD3, and BRD4 from chromatin, preventing re-expression of the fetal gene program, pathologic hypertrophy, and fibrosis after pressure overload (PO). To allow effective and safe application of BET inhibition as treatment for HF, it is necessary to assess if targeting BET proteins has added benefits in comparison to current pharmacotherapies such as improved survival and to elucidate functions of individual BET members specifically in cardiac cells. However, previous studies miss to report mortality rates for JQ1 treated animals and do not consider that JQ1 acts systemically and inhibits all four BET family members alike. Thus, the mechanisms underlying BET-mediated cardio protection remain elusive.
First, to characterize and validate cardiac BET expression at baseline and in response to PO I performed gene expression analysis and immunoblotting using hearts of adult wildtype mice. I identified Brd2 as the highest expressed BET family member in the heart with four times higher mRNA levels compared to Brd3/Brd4 and revealed TAC-induced expression of the long BRD4 isoform.
Second, to describe the effect of BET inhibition on life expectancy after PO induction I monitored the survival of JQ1-treated wildtype mice for up to 2 months after TAC and analyzed the hearts using echocardiography as well as histological and molecular methods. I found PO-dependent mortality unchanged with JQ1-mediated BET inhibition and observed pathologic changes such as expression of cardiac stress markers, cardiomegaly, cardiomyocyte hypertrophy, interstitial fibrosis, and systolic dysfunction, which were comparable to vehicle-treated animals after TAC. This contradicts previous reports on cardio-protective features of JQ1 in a mouse PO model (Anand et al. 2013). As experimental differences such as sex, age, mouse strain, TAC-performance, and JQ1-batch cannot be excluded as explanations for the discrepant results, future studies should take these possible confounding factors into account. Moreover, a reliable cardiac-specific biomarker of BET-inhibition should be explored to allow successful therapy monitoring.
Third, using conditional alleles I generated mice expressing a truncated BRD2 protein lacking the first bromodomain, Brd2∆BDI, and mice with a cardiomyocyte-specific Brd4-knockout, Brd4 KO, to investigate whether these gene deletions alter the response to PO. Homozygous Brd2∆BDI mice were viable and their hearts and cardiac functions were not significantly different from Cre-positive control mice at baseline and after PO induction. In contrast, cardiomyocyte-specific homozygous deletion of Brd4 during early embryonic development was lethal suggesting that BRD4 is essential during cardiogenesis. For further examination Brd4 KO was induced at postnatal week five and resulted in animals that were viable for over 12 months. Adult Brd4 KO mice showed basal concentric hypertrophy, preserved ejection fraction, mild interstitial fibrosis, and cardiac stress marker expression. These features are characteristic for hypertrophic cardiomyopathy (HCM) and were further supported by transcriptome analysis that revealed differential expression of genes involved in extracellular matrix remodeling, energy metabolism, sarcomere composition, and cardiac muscle contraction. Moreover, Brd4 KO mice subjected to TAC showed significantly higher mortality within the first month after surgery, which might be attributed to diastolic dysfunction or arrythmias. Nevertheless, no significant wall thickening or left ventricular mass increase, despite the basal hypertrophy was observed in Brd4 KO mice after TAC. This lack of stress response was confirmed by mRNA sequencing as no relevant changes were detected in Brd4 KO animals after TAC compared to Sham. However, Brd4 KO mice that survived the acute phase of PO showed better heart function in comparison to TAC control.
My findings suggest that the function of BRD2 in cardiomyocytes is either independent from its first bromodomain, substituted by another protein upon disruption, or not essential and therefore needs further investigation. Furthermore, beside the established function of BRD4 as co-activator of cardiac stress response, my findings lead to the conclusion that BRD4 has a second function as co-repressor of e.g. pro-hypertrophic genes in the healthy heart. I further propose that the shift between both cardiac functions might be mediated by a stress-induced switch from the short to the long Brd4 isoform and a respective interaction with e.g. an inactive or active P-TEFb complex (Schröder et al. 2012).
My thesis provides the first functional insight into cardiomyocyte-specific loss of Brd4 in vivo, links it to the development of HCM, establishes basal BRD4-mediated negative regulation of transcription, and provides evidence for its depletion to blunt stress-response. These findings could contribute to the development of more selective therapeutic approaches for HF as compared to inhibition of all BET members and to our understanding of HCM development and manifestation.2021-02-0
Molecular and structural transition mechanisms in long‐term volume overload
No full textAimWe have previously reported that early phase (1week) of experimental volume overload (VO) has an adaptive phenotype while wall stress-matched pressure overload (PO) is maladaptive. Here we investigate the transition from adaptation to heart failure (HF) in long-term VO. Methods and resultsFVB/N wild-type mice were subjected to VO induced by aortocaval shunt, and were followed by serial echocardiography until in vivo left ventricular ejection fraction was below <50% (13535days). Heart failure was evident from increased lung and liver weight and increased mortality compared with sham. Maladaptive remodelling resulted in significantly reduced sarcomeric titin phosphorylation (causing increased sarcomeric stiffness), whereas interstitial fibrosis was not increased. This was paralleled by re-expression of the fetal gene program, activation of calcium/calmodulin-dependent protein kinase II (CaMKII), decreased protein kinase B (Akt) phosphorylation, high oxidative stress, and increased apoptosis. Consistently, development of HF and mortality were significantly aggravated in Akt-deficient mice. ConclusionTransition to HF in VO is associated with decreased Akt and increased CaMKII signalling pathways together with increased oxidative stress and apoptosis. Lack of interstitial fibrosis together with sarcomeric titin hypophosphorylation indicates an increased stiffness at the sarcomeric but not matrix level in VO-induced HF (in contrast to PO). Transition to HF may result from myocyte loss and myocyte dysfunction owing to increased stiffness
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
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