1,721,104 research outputs found
New insights into the role of cholesterol-related pathways in apicomplexan parasite infections
Get PDFCoccidia are a large family of obligate intracellular parasites that belong to the apicomplexan phylum and are responsible for diseases in human and animal populations. In this context, veterinary-relevant coccidian species are grouped into certain families, such as Sarcocistidae (i. e. Toxoplasma gondii, Neospora caninum and Besnoitia besnoiti) and Eimeriidae (i. e. Eimeria bovis and Eimeria arloingi) which largely differ in terms of life cycle and host specificity. It is well-known that coccidian parasites highly rely on host cell metabolism and their capacity to hijack their host cell to fulfill their metabolic requirements during intracellular development. In that context, complex molecules like cholesterol are scavenged from host cells to sustain proliferative requirements. Physiologically, cells obtain cholesterol either by de novo biosynthesis or by extracellular uptake. The latter is largely driven by LDL internalization in mammalian cells, which is accepted as pivotal route to be exploited by apicomplexan parasites. Nevertheless, since coccidian biology largely differs between species, the overall knowledge on cholesterol acquisition by coccidia has been oversimplified. As such, alternative cholesterol-related acquisition routes driven by NPC1L1, P-pg and SR-BI have scarcely been considered, so far. Related to these topics, the following results were achieved in the current work:
GC-MS-based profiling of cholesterol-related sterols in B. besnoiti-infected primary endothelial cells showed an enhancement of several cholesterol precursors. Together with the finding of statin-mediated inhibition of B. besnoiti replication, these data strongly suggest a key role of cholesterol de novo biosynthesis in infected host cells. Furthermore, beneficial effects of LDL-supplementation on parasite proliferation proved acLDL as pivotal extracellular cholesterol source for B. besnoiti replication, thereby indicating that this coccidian parasite exploits alternative routes to sustain its cholesterol requirements. Moreover, in the case of E. bovis first merogony, lipidomic profiling revealed an enhancement of phytosterols over time indicating that this coccidian parasite significantly relies on extracellular sources for cholesterol acquisition. Interestingly, analysis of downstream cholesterol metabolites additionally documented an accumulation of cholesteryl esters and oxysterols (especially 25 hydroxycholesterol) throughout first merogony. Considering that exogenous oxysterols treatments impeded E. bovis macromeront development, these molecules may also result from anti-parasitic responses of infected-host cells.
Regarding the participation of alternative cholesterol-related routes, the use of ezetimibe as NPC1L1 blocker revealed strong parasitostatic effects on T. gondii, N. caninum and B. besnoiti tachzoite proliferation. However, the absence of anti-coccidian effects driven by the in vivo active metabolite (glucoronated ezetimibe), in addition to the inconsistent gene expression of NPC1L1 in infected cells suggest that ezetimibe might affect parasite replication by an NPC1L1-independent mechanism. Additionally, chemical blockage of the ABC transporter P-gp by different generations of inhibitors (verapamil, valspodar, tariquidar) revealed differences in terms of anti-coccidian efficacies. Specifically, treatments with verapamil consistently reduced T. gondii, N. caninum and B. besnoiti replication and generated neutral lipid accumulation in host cells. Likewise, valspodar treatments induced singnificant anti-invasive and anti-proliferative effects in these three parasite species but failed to influence cellular neutral lipid abundance. In contrast, the most specific P-gp inhibitor tariquidar exclusively diminished B. besnoiti invasion and replication but failed to affect T. gondii or N. caninum, thereby suggesting parasite-specific reactions. Interestingly, blockage of the scavenger receptor SR-BI by BLT-1 treatments induced significant antireplicative effects not only in the fast-replicating coccidia T. gondii, N. caninum and B. besnoiti, but also in the pathogenic Eimeria species E. bovis and E. arloingi, thereby evidencing potentially conserved SR-BI-related mechanisms as key events for coccidian replication. However, BLT-1 treatments of free sporozoites and tachyzoites exclusively affected host cell invasion capacity in the latter group, being paralleled with a sustained Ca++ flux over time.
Finally, studies on N. caninum host cell egress by live cell imaging revealed an infectiondriven Ca++ redistribution leading to increased Ca++ signals within intracellular N. caninum meronts. Furthermore, analyses on ionophore-induced N. caninum egress proved egress performance to be mainly influenced by meront maturity and showed no differences in Ca++ redistribution between time points of infection (24 or 42 h p. i.)
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
New aspects of coccidia-triggered modulation of the host cellular cell cycle
Get PDFApicomplexan parasites are a large group of protists with an obligate intracellular lifestyle, impacting human and veterinary health worldwide. The Sarcocystidae family contains notable species like Toxoplasma gondii, a critical zoonotic pathogen, and Neospora caninum, cause of abortion in cattle and of neurological disorders in canid hosts. Although both parasites differ in their host specificity and in distinct aspects of their life cycle, they also share common characteristics in their sophisticated ability to modulate host cell functions. Here, we focused on molecular and cellular mechanisms involved in parasite infection-driven host cell cycle dysregulation.
T. gondii is well recognized to significantly affect host cell cycle progression, regardless of MOI, infection times and, importantly, the cellular model used in experimentation. While many former studies used immortalized or tumour cells, potentially exhibiting dysregulated cell cycling, current analyses addressed T. gondii infections in primary cells by analyzing different cell types (fibroblasts, endothelial and epithelial cells) and donor species (human, bovine). Here, we revealed a T. gondii-driven cell type- and origin-independent S-phase arrest. Notably, cyclin B1, a critical regulator of mitosis entry, remained unchanged across all cell types, indicating that mitosis checkpoint modulation is not involved in host cellular S-phase stasis. Beyond interphase effects, T. gondii infection led to aberrant mitosis in all mitotic subphases, characterized by chromosome miscondensation and supernumerary centrosome formation. Moreover, all cell types showed an increased proportion of binucleated phenotypes, indicating impaired cytokinesis, which also occurred independently of cell origin or type.
Given that different T. gondii genotypes show varying pathogenicity in the field, host cell cycle regulation may also be influenced by haplotypes. To explore this, different strain infections (Me49, NED) were comparatively analysed in primary host cells. In line with RH, Me49 and NED strains also induced host S-phase arrest. Further analyses on key regulatory proteins of S-phase control and M-phase enter revealed a cyclin B1 downregulation only for NED infections. Additionally, the mitotic rate was reduced by NED infections, concomitant with altered chromosome arrangement and irregular chromosome bridges within the mitotic spindle. Moreover, T. gondii Me49 and NED strains also led to an enhanced proportion of binucleated host cells, indicative of cytokinesis failure. Thereby, this cellular phenotype was here described for the first time for all haplotype infections, demonstrating cytokinesis impairment as intrinsic, haplotype-independent mechanism of T. gondii.
Chromosome missegregation and cytokinesis impairment are key features of chromosome instability being associated with DNA damage in cells. As determined in the current work, RH, Me49 and NED strains indeed all induced DNA double-strand breaks with the RH strain driving - by far - the most pronounced effects. Moreover, referring to cytokinesis failure, a significant proportion of both RH- and NED-infected binucleated host cells showed DNA damage foci. Interestingly, NED-infected cells exhibited an increased proportion of micronuclei, thereby highlighting parasite strain-specific insults on host cellular genomic stability.
Under genotoxic stress, cells activate the DNA damage response to maintain genome integrity. Repair mechanisms for this type of damage include the homologous recombination (HR) and non-homologous end joining (NHEJ) pathways, which were here profiled for RH strain infections. As expected, the HR pathway was activated by an upregulation of ATM pathway-related proteins, which classically are induced by DNA double-strand breaks.
Finally, current cell cycle-related analyses were extended to N. caninum infections in the same host cell type to elucidate eventual species-specific strategies. N. caninum caused late S-phase arrest concomitant with cyclin A2 and cyclin B1 upregulation at 24 h p. i. (followed by cyclin A2 decrease at 32 h), confirming irregularities from S- to G2/M transition-phase. Interestingly, irregular nuclear morphologies were observed in N. caninum-infected cells, illustrated as invaginations and stretches of nuclear membrane disintegration and quantified as smaller nuclear areas, indicating that the host cellular nuclear structure was affected by N. caninum. Further analyses on the nuclear protein lamin B1 revealed an increased proportion of cells with inhomogeneous lamin B1 patterns, several nuclear folding and invaginations, phenomena reported for the first time for coccidian infections. Moreover, the perinuclear area was altered since actin filaments normally being anchored to the nuclear periphery and transversing the nucleus (actin cap) were absent in infected cells alongside with a decreased total cellular actin abundance, highlighting that N. caninum infection indeed interferes with the host actin cytoskeleton leading to nuclear membrane destabilization and abnormal shaping. Overall, these findings contrast with alterations induced by different T. gondii strains, emphasizing species-specific events in host cell modulation
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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