Thursday, December 29, 2016

Phylogeography of Toxoplasma gondii points to a South American origin

 2016 Dec 24. pii: S1567-1348(16)30549-4. doi: 10.1016/j.meegid.2016.12.020. [Epub ahead of print]

Abstract

Toxoplasma gondii, a protozoan found ubiquitously in mammals and birds, is the etiologic agent of toxoplasmosis, a disease causing substantial public health burden worldwide, including about 200,000 new cases of congenital toxoplasmosis each year. Clinical severity has been shown to vary across geographical regions, with South America exhibiting the highest burden. Unfortunately, the drivers of these heterogeneities are still poorly understood, and the geographical origin and historical spread of the pathogen worldwide are currently uncertain. A worldwide sample of 168 T. gondii isolates gathered in 13 populations was sequenced for five fragments of genes (140 single nucleotide polymorphisms from 3153bp per isolate). Phylogeny based on Maximum likelihood methods with estimation of the time to the most recent common ancestor (TMRCA) and geostatistical analyses were performed for inferring the putative origin of T. gondii. We show that extant strains of the pathogen likely evolved from a South American ancestor, around 1.5 million years ago, and reconstruct the subsequent spread of the pathogen worldwide. This emergence is much more recent than the appearance of ancestral T. gondii, believed to have taken place about 11 My ago, and follows the arrival of felids in this part of the world. We posit that an ancestral lineage of T. gondii likely arrived in South America with felids and that the evolution of oral infectivity through carnivorism and the radiation of felids in this region enabled a new strain to outcompete the ancestral lineage and undergo a pandemic radiation.

KEYWORDS: 

Genetic diversity; Maximum likelihood phylogeny; Phylogeography; Time to the most recent common ancestor (TMRCA); Toxoplasma gondii
PMID:
 
28028000
 
DOI:
 
10.1016/j.meegid.2016.12.020

Wednesday, December 28, 2016

Towards a molecular architecture of the centrosome in Toxoplasma gondii

 2016 Dec 27. doi: 10.1002/cm.21353. [Epub ahead of print]

Abstract

Toxoplasma gondii is the causative agent of toxoplasmosis. The pathogenicity of this unicellular parasite is tightly linked to its ability to efficiently proliferate within its host. Tachyzoites, the fast dividing form of the parasite, divide by endodyogeny. This process involves a single round of DNA replication, closed nuclear mitosis, and assembly of two daughter cells within a mother. The successful completion of endodyogeny relies on the temporal and spatial coordination of a plethora of simultaneous events. It has been shown that the Toxoplasma centrosome serves as signaling hub which nucleates spindle microtubules during mitosis and organizes the scaffolding of daughter cells components during cytokinesis. In addition, the centrosome is essential for inheriting both the apicoplast (a chloroplast-like organelle) and the Golgi apparatus. A growing body of evidence supports the notion that the T. gondii centrosome diverges in protein composition, structure and organization from its counterparts in higher eukaryotes making it an attractive source of potentially druggable targets. Here, we summarize the current knowledge on T. gondii centrosomal proteins and extend the putative centrosomal protein repertoire by in silico identification of mammalian centrosomal protein orthologs. We propose a working model for the organization and architecture of the centrosome in Toxoplasma parasites. Experimental validation of our proposed model will uncover how each predicted protein translates into the biology of centrosome, cytokinesis, karyokinesis, and organelle inheritance in Toxoplasma parasites. This article is protected by copyright. All rights reserved.
PMID:
 
28026138
 
DOI:
 
10.1002/cm.21353

Tuesday, December 27, 2016

Pravastatin and simvastatin inhibit the adhesion, replication and proliferation of Toxoplasma gondii

 2016 Dec 21. pii: S0001-706X(16)30531-9. doi: 10.1016/j.actatropica.2016.12.006. [Epub ahead of print]

Abstract

The conventional treatment for toxoplasmosis with pyrimethamine and sulfadiazine shows toxic effects to the host, and it is therefore necessary to search for new drugs. Some studies suggest the use of statins, which inhibit cholesterol synthesis in humans and also the initial processes of isoprenoid biosynthesis in the parasite. Thus, the objective of this study was to evaluate the activity of the statins pravastatin and simvastatin in HeLa cells infected in vitro with the RH strain of T. gondii. HeLa cells (1×105) were infected with T. gondii tachyzoites (5×105) following two different treatment protocols. In the first protocol, T. gondii tachyzoites were pretreated with pravastatin (50 and 100μg/mL) and simvastatin (1.56 and 3.125μg/mL) for 30min prior to infection. In the second, HeLa cells were first infected (5×105) with tachyzoites and subsequently treated with pravastatin and simvastatin for 24h at the concentrations noted above. Initially, we evaluated the cytotoxicity of drugs by the MTT assay, number of tachyzoites adhered to cells, number of infected cells, and viability of tachyzoites by trypan blue exclusion. The supernatant of the cell cultures was collected post-treatment for determination of the pattern of Th1/Th2/Th17 cytokines by cytometric bead array. There was no cytotoxicity to HeLa cells with 50 and 100μg/mL pravastatin and 1.56 and 3.125μg/mL simvastatin. There was no change in the viability of tachyzoites that received pretreatment. Regarding the pre- and post-treatment of the cells with pravastatin and simvastatin alone, there was a reduction in adhesion, invasion and proliferation of cells to T. gondii. As for the production of cytokines, we found that IL-6 and IL-17 were significantly reduced in cells infected with T. gondii and treated with pravastatin and simvastatin, when compared to control. Based on these results, we can infer that pravastatin and simvastatin alone possess antiproliferative effects on tachyzoites forms of T. gondii, giving these drugs new therapeutic uses.

KEYWORDS: 

HeLa cell; Toxoplasma gondii; statins
PMID:
 
28012901
 
DOI:
 
10.1016/j.actatropica.2016.12.006
[PubMed - as supplied by publisher]

Toxoplasma gondii plaque assays revisited: Improvements for ultrastructural and quantitative evaluation of lytic parasite growth

 2016 Dec 20. pii: S0014-4894(16)30393-9. doi: 10.1016/j.exppara.2016.12.015. [Epub ahead of print]

Abstract

Lytic growth of intracellular Toxoplasma gondii tachyzoite stages over a period of days results in plaques within mononolayers of host cells. Plaque assays are in frequent use to isolate single clones and to investigate invasion, replication and egress over a longer time frame. To allow correlating plaque morphology and/or size with ultrastructural examination of individual parasites we introduce a simple protocol for correlative light and electron microscopy (CLEM) of entire plaques. We also illustrate the advantages of visualizing only the boundaries of plaques by staining for infected cells ('positive staining') rather than the traditional staining of the intact cell monolayer, thus outlining the area of lysed cells ('negative staining'). Tachyzoites expressing β-galactosidase of Escherichia coli are an easy to visualize histochemical marker for this purpose. Quantitative measurements of plaque area with our compiled user-friendly ImageJ macros are compared to commercial software for ease and shown to be more accurate for some applications. Finally, a chemically defined medium is shown to be superior to the fetal bovine serum-containing medium for plaque assays, resulting in larger plaques. The reported additions and changes of the plaque assay procedure offer improved ways to analyze subtle differences in invasion, pathogen growth and egress. Our chemically defined medium will improve standardization of e.g. drug screening assays.

KEYWORDS: 

Apicomplexa; Correlative light and electron microscopy; Histochemical staining; Plaque assay; Replication
PMID:
 
28011168
 
DOI:
 
10.1016/j.exppara.2016.12.015

Wednesday, December 21, 2016

Toxoplasma gondii autophagy-related protein ATG9 is crucial for the survival of parasites in their host


2016 Dec 19. doi: 10.1111/cmi.12712. [Epub ahead of print]


Autophagy is a conserved, life-promoting, catabolic process involved in the recycling of non-essential cellular components in response to stress. The parasite Toxoplasma gondii is an early-diverging eukaryote in which part of the autophagy machinery is not exclusively involved in a catabolic process, but instead has been repurposed for an original function in organelle inheritance during cell division. This function, depending essentially on protein TgATG8 and its membrane conjugation system, is crucial for parasite survival and prevented an in depth study of autophagy in the mutants generated so far in Toxoplasma. Thus, in order to decipher the primary function of canonical autophagy in the parasites, we generated a cell line deficient for TgATG9, a protein thought to be involved in the early steps of the autophagy process. While the protein proved to be dispensable for the development of these obligate intracellular parasites in vitro, the absence of TgATG9 led to a reduced ability to sustain prolonged extracellular stress. Importantly, depletion of the protein significantly reduced parasites survival in macrophages, and markedly attenuated their virulence in mice. Altogether, this shows TgATG9 is important for the fate of Toxoplasma in immune cells and contributes to the overall virulence of the parasite, possibly through an involvement in a canonical autophagy pathway.
PMID:
27992947
DOI:
10.1111/cmi.12712

Toxoplasma-infected subjects report an Obsessive-Compulsive Disorder diagnosis more often

2016 Dec 16;40:82-87. doi: 10.1016/j.eurpsy.2016.09.001. [Epub ahead of print]

BACKGROUND:

Latent toxoplasmosis, the life-long presence of dormant stages of Toxoplasma in immunoprivileged organs and of anamnestic IgG antibodies in blood, affects about 30% of humans. Infected subjects have an increased incidence of various disorders, including schizophrenia. Several studies, as well as the character of toxoplasmosis-associated disturbance of neurotransmitters, suggest that toxoplasmosis could also play an etiological role in Obsessive-Compulsive Disorder (OCD).

METHODS:

The aim of the present cross-sectional study performed on a population of 7471 volunteers was to confirm the association between toxoplasmosis and OCD, and toxoplasmosis and psychological symptoms of OCD estimated by the standard Obsessive-Compulsive Inventory-Revised (OCI-R).

RESULTS:

Incidence of OCD was 2.18% (n=39) in men and 2.28% (n=83) in women. Subjects with toxoplasmosis had about a 2.5 times higher odds of OCD and about a 2.7 times higher odds of learning disabilities. The incidence of 18 other neuropsychiatric disorders did not differ between Toxoplasma-infected and Toxoplasma-free subjects. The infected subjects, even the OCD-free subjects, scored higher on the OCI-R.

LIMITATIONS:

Examined subjects provided the information about their toxoplasmosis and OCD statuses themselves, which could result in underrating the strength of observed associations.

CONCLUSIONS:

The results confirmed earlier reports of the association between toxoplasmosis and OCD. They also support recent claims that latent toxoplasmosis is in fact a serious disease with many impacts on quality of life of patients.

KEYWORDS:

Infection; Learning disabilities; Mental disorder; Parasites; Risk factors; Toxoplasmosis
PMID:
27992837
DOI:
10.1016/j.eurpsy.2016.09.001

Tuesday, December 20, 2016

Targeting of tail-anchored membrane proteins to subcellular organelles in Toxoplasma gondii

2016 Dec 19. doi: 10.1111/tra.12464. [Epub ahead of print]


Proper protein localization is essential for critical cellular processes, including vesicle-mediated transport and protein translocation. Tail-anchored (TA) proteins are integrated into organellar membranes via the C-terminus, orienting the N-terminus towards the cytosol. Localization of TA proteins occurs post-translationally and is governed by the C-terminus, which contains the integral transmembrane domain (TMD) and targeting sequence. Targeting of TA proteins is dependent on the hydrophobicity of the TMD as well as the length and composition of flanking amino acid sequences. We previously identified an unusual homologue of elongator protein, Elp3, in the apicomplexan parasite Toxoplasma gondii as a TA protein targeting the outer mitochondrial membrane. We sought to gain further insight into TA proteins and their targeting mechanisms using this early-branching eukaryote as a model. Our bioinformatics analysis uncovered 59 predicted TA proteins in Toxoplasma, nine of which were selected for follow-up analyses based on representative features. We identified novel TA proteins that traffic to specific organelles in Toxoplasma, including the parasite endoplasmic reticulum, mitochondrion, and Golgi apparatus. Domain swap experiments elucidated that targeting of TA proteins to these specific organelles was strongly influenced by the TMD sequence, including charge of the flanking C-terminal sequence.

KEYWORDS:

Golgi apparatus; endoplasmic reticulum; membrane protein; mitochondria; protein localization; protein trafficking
PMID:
27991712
DOI:
10.1111/tra.12464

Toxoplasma gondii: One Organism, Multiple Models

 2016 Dec 14. pii: S1471-4922(16)30205-7. doi: 10.1016/j.pt.2016.11.007. [Epub ahead of print]

Abstract

Toxoplasma gondii is an intensely studied protozoan parasite. It is also used as a model organism to research additional clinically relevant human and veterinary parasites due to ease of in vitro culture and genetic manipulation. Recently, it has been developed as a model of inflammatory bowel disease, due to their similar pathologies. However, researchers vary widely in how they use T. gondii, which makes study comparisons and interpretation difficult. The aim of this review is to provide researchers with a tool to: (i) determine the appropriateness of the different T. gondii models to their research, (ii) interpret results from the wide range of study conditions, and (iii) consider new advances in technology which could improve or refine their experimental setup.

KEYWORDS: 

Toxoplasma; in vitro models; in vivo models; mouse models; parasites
PMID:
 
27988095
 
DOI:
 
10.1016/j.pt.2016.11.007

Saturday, December 17, 2016

An Apicomplexan Actin-Binding Protein Serves as a Connector and Lipid Sensor to Coordinate Motility and Invasion

 2016 Dec 14;20(6):731-743. doi: 10.1016/j.chom.2016.10.020.

Abstract

Apicomplexa exhibit a unique form of substrate-dependent gliding motility central for host cell invasion and parasite dissemination. Gliding is powered by rearward translocation of apically secreted transmembrane adhesins via their interaction with the parasite actomyosin system. We report a conserved armadillo and pleckstrin homology (PH) domain-containing protein, termed glideosome-associated connector (GAC), that mediates apicomplexan gliding motility, invasion, and egress by connecting the micronemal adhesins with the actomyosin system. TgGAC binds to and stabilizes filamentous actin and specifically associates with the transmembrane adhesin TgMIC2. GAC localizes to the apical pole in invasive stages of Toxoplasma gondii and Plasmodium berghei, and apical positioning of TgGAC depends on an apical lysine methyltransferase, TgAKMT. GAC PH domain also binds to phosphatidic acid, a lipid mediator associated with microneme exocytosis. Collectively, these findings indicate a central role for GAC in spatially and temporally coordinating gliding motility and invasion.

KEYWORDS: 

actin dynamic; apicomplexa; glideosome; gliding motility; invasion and egress; lysine methyltransferase; microneme; phosphatidic acid; plasmodium; toxoplasma
PMID:
 
27978434
 
DOI:
 
10.1016/j.chom.2016.10.020

Opposing transcriptional mechanisms regulate Toxoplasma development

Opposing transcriptional mechanisms regulate Toxoplasma development.


Dong-Pyo HongJoshua B RadkeMichael W White

doi: https://doi.org/10.1101/094847

Abstract

The Toxoplasma biology that underlies human chronic infection is developmental conversion of the acute tachyzoite stage into the latent bradyzoite stage. We investigated the role of two alkaline-stress induced ApiAP2 transcription factors, AP2IV-3 and AP2IX-9, in bradyzoite development. These factors were expressed in two overlapping waves during bradyzoite development with AP2IX-9 increasing expression earlier than AP2IV-3, which peaked as AP2IX-9 expression was declining. Disruption of the AP2IX-9 gene enhanced, while deletion of AP2IV-3 gene decreased tissue cyst formation demonstrating these factors have opposite functions in bradyzoite development. Conversely, conditional overexpression of FKBP-modified of AP2IX-9 or AP2IV-3 with the small molecule Shield 1 had a reciprocal effect on tissue cyst formation confirming the conclusions of the knockout experiments. The AP2IX-9 repressor and AP2IV-3 activator tissue cyst phenotypes were borne out in gene expression studies that determined many of the same bradyzoite genes were regulated in an opposite manner by these transcription factors. A common gene target was the canonical bradyzoite marker, BAG1, and mechanistic experiments determined that like AP2IX-9, AP2IV-3 regulates a BAG1 promoter-luciferase reporter and specific binds the BAG1 promoter in parasite chromatin. Altogether, these results suggest the AP2IX-9 transcriptional repressor and AP2IV-3 transcriptional activator likely compete to control bradyzoite gene expression, which may permit Toxoplasma to better adapt to different tissue environments and select a suitable host cell for long term survival of the dormant tissue cyst.

Friday, December 16, 2016

A Critical Role for Toxoplasma gondii Vacuolar Protein Sorting VPS9 in Secretory Organelle Biogenesis and Host Infection


2016 Dec 14;6:38842. doi: 10.1038/srep38842.


Accurate sorting of proteins to the three types of parasite-specific secretory organelles namely rhoptry, microneme and dense granule in Toxoplasma gondii is crucial for successful host cell invasion by this obligate intracellular parasite. Despite its tiny body architecture and limited trafficking machinery, T. gondii relies heavily on transport of vesicles containing proteins, lipids and important virulence-like factors that are delivered to these secretory organelles. However, our understanding on how trafficking of vesicles operates in the parasite is still limited. Here, we show that the T. gondii vacuolar protein sorting 9 (TgVps9), has guanine nucleotide exchange factor (GEF) activity towards Rab5a and is crucial for sorting of proteins destined to secretory organelles. Our results illuminate features of TgVps9 protein as a key trafficking facilitator that regulates protein maturation, secretory organelle formation and secretion, thereby ensuring a primary role in host infection by T. gondii.
PMID:
27966671
DOI:
10.1038/srep38842

Wednesday, December 14, 2016

Lifelong Persistence of Toxoplasma Cysts: A Questionable Dogma?

 2016 Nov 16. pii: S1471-4922(16)30190-8. doi: 10.1016/j.pt.2016.10.007. [Epub ahead of print]

Abstract

It is believed that infection by Toxoplasma gondii triggers a lifelong protective immunity due to the persistence of parasitic cysts which induce immunoprotection against reinfection. A review of the scientific literature since the 1950s did not yield any definitive data regarding the duration of cysts in the host or the presence of lifelong protective immunity, which led us to question this dogma. We put forward the hypothesis that sustained immunity to T. gondii requires repeated antigenic stimulations. The decline of seroprevalence recently observed in many countries might contribute to explain the loss of immunity. We address the potential consequences of this phenomenon, should it persist and worsen.

KEYWORDS: 

lifelong immunity; premunition; toxoplasmosis
PMID:
 
27939103
 
DOI:
 
10.1016/j.pt.2016.10.007

Monday, December 12, 2016

Loss of a doublecortin (DCX) domain protein causes structural defects in a tubulin-based organelle of Toxoplasma gondii and impairs host-cell invasion


2016 Dec 8. pii: mbc.E16-08-0587. [Epub ahead of print]


The ∼6000 species in phylum Apicomplexa are single-celled obligate intracellular parasites. Their defining characteristic is the "apical complex", membranous and cytoskeletal elements at the apical end of the cell that participate in host-cell invasion. The apical complex of Toxoplasma gondii and some other apicomplexans includes a cone-shaped assembly, the "conoid", which (in T. gondii) comprises 14 spirally arranged fibers that are non-tubular polymers of tubulin. The tubulin dimers of the conoid fibers make canonical microtubules elsewhere in the same cell, suggesting that non-tubulin protein dictates their special arrangement in the conoid fibers. One candidate for this role is TgDCX, which has a doublecortin (DCX) domain and a TPPP/P25-alpha domain, both of which are known modulators of tubulin polymer structure. Loss of TgDCX radically disrupts the structure of the conoid, severely impairs host-cell invasion, and slows growth. Both the conoid structural defects and the impaired invasion of TgDCX null parasites are corrected by re-introduction of a TgDCX coding sequence. The non-tubular polymeric form of tubulin found in the conoid is not found in the host cell, suggesting that TgDCX may be an attractive target for new parasite-specific chemotherapeutic agents.
PMID:
27932494
DOI:
10.1091/mbc.E16-08-0587

Friday, December 09, 2016

Genetic Evidence for Cytochrome b Qi Site Inhibition by 4(1H)-quinolone-3-diarylethers and Antimycin in Toxoplasma gondii

2016 Dec 5. pii: AAC.01866-16. [Epub ahead of print]


Toxoplasma gondii is an apicomplexan parasite that causes fatal and debilitating brain and eye disease. Endochin-like-quinolones (ELQs) are preclinical compounds that are efficacious against apicomplexan-caused diseases including toxoplasmosis, malaria and babesiosis. Of the ELQs, ELQ-316 has demonstrated the greatest efficacy against acute and chronic experimental toxoplasmosis. Although genetic analyses in other organisms have highlighted the importance of the cytochrome bc1 complex Qi site for ELQ sensitivity, the mechanism of action of ELQs against T. gondii and the mechanism of ELQ-316 remains unknown. Here we describe the selection and genetic characterization of T. gondii clones resistant to ELQ-316. A T. gondii strain selected under ELQ-316 drug pressure was found to possess a Thr222-Pro amino acid substitution that confers 49-fold resistance to ELQ-316 and 19-fold resistance to antimycin, a well-characterized Qi site inhibitor. These findings provide further evidence for ELQ Qi site inhibition in T. gondii and greater insight into the interaction of Qi site inhibitors with the apicomplexan cytochrome bc1 complex.
PMID:
27919897
DOI:
10.1128/AAC.01866-16
[PubMed - as supplied by publisher]