SPARK regulates AGC kinases central to the Toxoplasma gondii asexual cycle.

Apicomplexan parasites balance proliferation, persistence, and spread in their metazoan hosts. AGC kinases, such as PKG, PKA, and the PDK1 ortholog SPARK, integrate environmental signals to toggle parasites between replicative and motile life stages. Recent studies have cataloged pathways downstream of apicomplexan PKG and PKA; however, less is known about the global integration of AGC kinase signaling cascades. Here, conditional genetics coupled to unbiased proteomics demonstrates that SPARK complexes with an elongin-like protein to regulate the stability of PKA and PKG in the model apicomplexan Toxoplasma gondii. Defects attributed to SPARK depletion develop after PKG and PKA are down-regulated. Parasites lacking SPARK differentiate into the chronic form of infection, which may arise from reduced activity of a coccidian-specific PKA ortholog. This work delineates the signaling topology of AGC kinases that together control transitions within the asexual cycle of this important family of parasites.

Functional Characterization of Six Eukaryotic Translation Initiation Factors of Toxoplasma gondii Using the CRISPR-Cas9 System.

Eukaryotic translation initiation factors (eIFs) are crucial for initiating protein translation and ensuring the correct assembly of mRNA-ribosomal subunit complexes. In this study, we investigated the effects of deleting six eIFs in the apicomplexan parasite Toxoplasma gondii using the CRISPR-Cas9 system. We determined the subcellular localization of these eIFs using C-terminal endogenous tagging and immunofluorescence analysis. Four eIFs (RH::315150-6HA, RH::286090-6HA, RH::249370-6HA, and RH::211410-6HA) were localized in the cytoplasm, while RH::224235-6HA was localized in the apicoplast. Additionally, RH::272640-6HA was found in both the basal complex and the cytoplasm of T. gondii. Functional characterization of the six RHΔeIFs strains was conducted using plaque assay, cell invasion assay, intracellular growth assay and egress assay in vitro, and virulence assay in mice. Disruption of five eIF genes (RHΔ315150, RHΔ272640, RHΔ249370, RHΔ211410, and RHΔ224235) did not affect the ability of the T. gondii RH strain to invade, replicate, form plaques and egress in vitro, or virulence in Kunming mice (p > 0.05). However, the RHΔ286090 strain showed slightly reduced invasion efficiency and virulence (p < 0.01) compared to the other five RHΔeIFs strains and the wild-type strain. The disruption of the TGGT1_286090 gene significantly impaired the ability of tachyzoites to differentiate into bradyzoites in both type I RH and type II Pru strains. These findings reveal that the eukaryotic translation initiation factor TGGT1_286090 is crucial for T. gondii bradyzoite differentiation and may serve as a potential target for drug development and an attenuated vaccine against T. gondii.

Toxoplasma gondii chitinase-like protein TgCLP1 regulates the parasite cyst burden.

Toxoplasma, an important intracellular parasite of humans and animals, causes life-threatening toxoplasmosis in immunocompromised individuals. Although Toxoplasma secretory proteins during acute infection (tachyzoite, which divides rapidly and causes inflammation) have been extensively characterized, those involved in chronic infection (bradyzoite, which divides slowly and is surrounded by a cyst wall) remain uncertain. Regulation of the cyst wall is essential to the parasite life cycle, and polysaccharides, such as chitin, in the cyst wall are necessary to sustain latent infection. Toxoplasma secretory proteins during the bradyzoite stage may have important roles in regulating the cyst wall via polysaccharides. Here, we focused on characterizing the hypothetical T. gondii chitinase, chitinase-like protein 1 (TgCLP1). We found that the chitinase-like domain containing TgCLP1 is partially present in the bradyzoite microneme and confirmed, albeit partially, its previous identification in the tachyzoite microneme. Furthermore, although parasites lacking TgCLP1 could convert from tachyzoites to bradyzoites and make an intact cyst wall, they failed to convert from bradyzoites to tachyzoites, indicating that TgCLP1 is necessary for bradyzoite reactivation. Taken together, our findings deepen our understanding of the molecular basis of recrudescence and could contribute to the development of novel strategies for the control of toxoplasmosis.

Copaifera spp. oleoresins and two isolated compounds (ent-kaurenoic and ent-polyalthic acid) inhibit Toxoplasma gondii growth in vitro.

Toxoplasmosis affects about one-third of the world's population. The disease treatment methods pose several side effects and do not efficiently eliminate the parasite, making the search for new therapeutic approaches necessary. We aimed to assess the anti-Toxoplasma gondii activity of four Copaifera oleoresins (ORs) and two isolated diterpene acids, named ent-kaurenoic and ent-polyalthic acid. We used HeLa cells as an experimental model of toxoplasmosis. Uninfected and infected HeLa cells were submitted to the treatments, and the parasite intracellular proliferation, cytokine levels and ROS production were measured. Also, tachyzoites were pre-treated and the parasite invasion was determined. Finally, an in silico analysis was performed to identify potential parasite targets. Our data show that the non-cytotoxic concentrations of ORs and diterpene acids controlled the invasion and proliferation of T. gondii in HeLa cells, thus highlighting the possible direct action on parasites. In addition, some compounds tested controlled parasite proliferation in an irreversible manner. An additional and non-exclusive mechanism of action involves the modulation of host cell components, by affecting the upregulation of the IL-6. Additionally, molecular docking suggested that ent-polyalthic acid has a high affinity for the active site of the TgCDPK1 protein. Copaifera ORs have great antiparasitic activity against T. gondii, and this effect can be partially explained by the presence of the isolated compounds ent-kaurenoic and ent-polyalthic acid.

The trophoblast surface becomes refractory to adhesion by congenitally transmitted Toxoplasma gondii and Listeria monocytogenes during cytotrophoblast to syncytiotrophoblast development.

The placenta is a critical barrier against viral, bacterial, and eukaryotic pathogens. For most teratogenic pathogens, the precise molecular mechanisms of placental resistance are still being unraveled. Given the importance of understanding these mechanisms and challenges in replicating trophoblast-pathogen interactions using in vitro models, we tested an existing stem-cell-derived model of trophoblast development for its relevance to infection with Toxoplasma gondii. We grew human trophoblast stem cells (TSCT) under conditions leading to either syncytiotrophoblast (TSSYN) or cytotrophoblast (TSCYT) and infected them with T. gondii. We evaluated T. gondii proliferation and invasion, cell ultrastructure, as well as for transcriptome changes after infection. TSSYNs cells showed similar ultrastructure compared to primary cells and villous explants when analyzed by transmission electron microscopy and scanning electron microscopy (SEM), a resistance to T. gondii adhesion could be visualized on the SEM level. Furthermore, TSSYNs were highly refractory to parasite adhesion and replication, while TSCYTs were not. RNA-seq data on mock-treated and infected cells identified differences between cell types as well as how they responded to T. gondii infection. We also evaluated if TSSC-derived SYNs and CYTs had distinct resistance profiles to another vertically transmitted facultative intracellular pathogen, Listeria monocytogenes. We demonstrate that TSSYNs are highly resistant to L. monocytogenes, while TSCYTs are not. Like T. gondii, TSSYN resistance to L. monocytogenes was at the level of bacterial adhesion. Altogether, our data indicate that stem-cell-derived trophoblasts recapitulate resistance profiles of primary cells to T. gondii and highlight the critical importance of the placental surface in cell-autonomous resistance to teratogens.IMPORTANCECongenital toxoplasmosis can cause a devastating consequence to the fetus. To reach the fetus's tissues, Toxoplasma gondii must cross the placenta barrier. However, how this parasite crosses the placenta and the precise molecular mechanisms of placental resistance to this parasite are still unknown. In this study, we aimed to characterize a new cellular model of human trophoblast stem cells to determine their resistance, susceptibility, and response to T. gondii. Syncytiotrophoblast derived from trophoblast stem cells recapitulate the resistance profile similarly to placenta cells. We also showed that these cells are highly resistant to Listeria monocytogenes, at the level of bacterial adhesion. Our results suggest that resisting pathogen adhesion/attachment may be a generalized mechanism of syncytiotrophoblast resistance, and trophoblast stem cells represent a promising model to investigate cell-intrinsic mechanisms of resistance to pathogen adhesion and replication.

Essential oil of oregano (Origanum vulgare L.) reduces infection and proliferation of Toxoplasma gondii in BeWo cells with induction of autophagy and death of tachyzoites through a mechanism similar to necrosis.

Toxoplasmosis poses a global health threat, ranging from asymptomatic cases to severe, potentially fatal manifestations, especially in immunocompromised individuals and congenital transmission. Prior research suggests that oregano essential oil (OEO) exhibits diverse biological effects, including antiparasitic activity against Toxoplasma gondii. Given concerns about current treatments, exploring new compounds is important. This study was to assess the toxicity of OEO on BeWo cells and T. gondii tachyzoites, as well as to evaluate its effectiveness in in vitro infection models and determine its direct action on free tachyzoites. OEO toxicity on BeWo cells and T. gondii tachyzoites was assessed by MTT and trypan blue methods, determining cytotoxic concentration (CC50), inhibitory concentration (IC50), and selectivity index (SI). Infection and proliferation indices were analyzed. Direct assessments of the parasite included reactive oxygen species (ROS) levels, mitochondrial membrane potential, necrosis, and apoptosis, as well as electron microscopy. Oregano oil exhibited low cytotoxicity on BeWo cells (CC50: 114.8 µg/mL ± 0.01) and reduced parasite viability (IC50 12.5 ± 0.06 µg/mL), demonstrating 9.18 times greater selectivity for parasites than BeWo cells. OEO treatment significantly decreased intracellular proliferation in infected cells by 84% after 24 h with 50 µg/mL. Mechanistic investigations revealed increased ROS levels, mitochondrial depolarization, and lipid droplet formation, linked to autophagy induction and plasma membrane permeabilization. These alterations, observed through electron microscopy, suggested a necrotic process confirmed by propidium iodide labeling. OEO treatment demonstrated anti-T. gondii action through cellular and metabolic change while maintaining low toxicity to trophoblastic cells.

AP2XII-1 and AP2XI-2 Suppress Schizogony Gene Expression in Toxoplasma gondii.

Toxoplasma gondii is an intracellular parasite that is important in medicine and veterinary science and undergoes distinct developmental transitions in its intermediate and definitive hosts. The switch between stages of T. gondii is meticulously regulated by a variety of factors. Previous studies have explored the role of the microrchidia (MORC) protein complex as a transcriptional suppressor of sexual commitment. By utilizing immunoprecipitation and mass spectrometry, constituents of this protein complex have been identified, including MORC, Histone Deacetylase 3 (HDAC3), and several ApiAP2 transcription factors. Conditional knockout of MORC or inhibition of HDAC3 results in upregulation of a set of genes associated with schizogony and sexual stages in T. gondii tachyzoites. Here, our focus extends to two primary ApiAP2s (AP2XII-1 and AP2XI-2), demonstrating their significant impact on the fitness of asexual tachyzoites and their target genes. Notably, the targeted disruption of AP2XII-1 and AP2XI-2 resulted in a profound alteration in merozoite-specific genes targeted by the MORC-HDAC3 complex. Additionally, considerable overlap was observed in downstream gene profiles between AP2XII-1 and AP2XI-2, with AP2XII-1 specifically binding to a subset of ApiAP2 transcription factors, including AP2XI-2. These findings reveal an intricate cascade of ApiAP2 regulatory networks involved in T. gondii schizogony development, orchestrated by AP2XII-1 and AP2XI-2. This study provides valuable insights into the transcriptional regulation of T. gondii growth and development, shedding light on the intricate life cycle of this parasitic pathogen.

Mechanisms of adaptation and evolution in Toxoplasma gondii.

Toxoplasma has high host flexibility, infecting all nucleated cells of mammals and birds. This implies that during its infective process the parasite must constantly adapt to different environmental situations, which in turn leads to modifications in its metabolism, regulation of gene transcription, translation of mRNAs and stage specific factors. There are conserved pathways that support these adaptations, which we aim to elucidate in this review. We begin by exploring the widespread epigenetic mechanisms and transcription regulators, continue with the supportive role of Heat Shock Proteins (Hsp), the translation regulation, stress granules, and finish with the emergence of contingency genes in highly variable genomic domains, such as subtelomeres. Within epigenetics, the discovery of a new histone variant of the H2B family (H2B.Z), contributing to T. gondii virulence and differentiation, but also gene expression regulation and its association with the metabolic state of the parasite, is highlighted. Associated with the regulation of gene expression are transcription factors (TFs). An overview of the main findings on TF and development is presented. We also emphasize the role of Hsp90 and Tgj1 in T. gondii metabolic fitness and the regulation of protein translation. Translation regulation is also highlighted as a mechanism for adaptation to conditions encountered by the parasite as well as stress granules containing mRNA and proteins generated in the extracellular tachyzoite. Another important aspect in evolution and adaptability are the subtelomeres because of their high variability and gene duplication rate. Toxoplasma possess multigene families of membrane proteins and contingency genes that are associated with different metabolic stresses. Among them parasite differentiation and environmental stresses stand out, including those that lead tachyzoite to bradyzoite conversion. Finally, we are interested in positioning protozoa as valuable evolution models, focusing on research related to the Extended Evolutionary Synthesis, based on models recently generated, such as extracellular adaptation and ex vivo cyst recrudescence.

In vitro production of cat-restricted Toxoplasma pre-sexual stages.

Sexual reproduction of Toxoplasma gondii, confined to the felid gut, remains largely uncharted owing to ethical concerns regarding the use of cats as model organisms. Chromatin modifiers dictate the developmental fate of the parasite during its multistage life cycle, but their targeting to stage-specific cistromes is poorly described1,2. Here we found that the transcription factors AP2XII-1 and AP2XI-2 operate during the tachyzoite stage, a hallmark of acute toxoplasmosis, to silence genes necessary for merozoites, a developmental stage critical for subsequent sexual commitment and transmission to the next host, including humans. Their conditional and simultaneous depletion leads to a marked change in the transcriptional program, promoting a full transition from tachyzoites to merozoites. These in vitro-cultured pre-gametes have unique protein markers and undergo typical asexual endopolygenic division cycles. In tachyzoites, AP2XII-1 and AP2XI-2 bind DNA as heterodimers at merozoite promoters and recruit MORC and HDAC3 (ref. 1), thereby limiting chromatin accessibility and transcription. Consequently, the commitment to merogony stems from a profound epigenetic rewiring orchestrated by AP2XII-1 and AP2XI-2. Successful production of merozoites in vitro paves the way for future studies on Toxoplasma sexual development without the need for cat infections and holds promise for the development of therapies to prevent parasite transmission.

Manipulative neuroparasites: uncovering the intricacies of neurological host control.

Manipulative neuroparasites are a fascinating group of organisms that possess the ability to hijack the nervous systems of their hosts, manipulating their behavior in order to enhance their own survival and reproductive success. This review provides an overview of the different strategies employed by manipulative neuroparasites, ranging from viruses to parasitic worms and fungi. By examining specific examples, such as Toxoplasma gondii, Leucochloridium paradoxum, and Ophiocordyceps unilateralis, we highlight the complex mechanisms employed by these parasites to manipulate their hosts' behavior. We explore the mechanisms through which these parasites alter the neural processes and behavior of their hosts, including the modulation of neurotransmitters, hormonal pathways, and neural circuits. This review focuses less on the diseases that neuroparasites induce and more on the process of their neurological manipulation. We also investigate the fundamental mechanisms of host manipulation in the developing field of neuroparasitology, which blends neuroscience and parasitology. Finally, understanding the complex interaction between manipulative neuroparasites and their hosts may help us to better understand the fundamentals of behavior, neurology, and host-parasite relationships.

Toxoplasma TgAtg8-TgAtg3 Interaction Primarily Contributes to Apicoplast Inheritance and Parasite Growth in Tachyzoite.

The apicoplast, which harbors key pathways involved in biosynthesis of vital metabolites, is a unique and essential nonphotosynthetic plastid organelle in apicomplexan parasites. Intriguingly, autophagy-related protein 8 (Atg8), a highly conserved eukaryotic protein, can localize to the outermost membrane of the apicoplast and modulate its inheritance in both Toxoplasma and Plasmodium parasites. The Atg8-Atg3 interaction plays a key role in Atg8 lipidation and localization, and our previously work in Toxoplasma has suggested that the core Atg8-family interacting motif (AIM) in TgAtg3, 239FADI242, and the R27 residue of TgAtg8 contribute to TgAtg8-TgAtg3 interaction in vitro. However, little is known about the function of this interaction or its importance in tachyzoite growth in Toxoplasma gondii. Here, we generated two complemented cell lines, TgAtg3F239A/I242A and TgAtg8R27E, based on the TgAtg3 and TgAtg8 conditional knockdown cell lines, respectively. We found that both mutant complemented cell lines were severely affected in terms of tachyzoite growth and displayed delayed death upon conditional knockdown of endogenous TgAtg3 or TgAtg8. Intriguingly, both complemented lines appeared to be defective in TgAtg8 lipidation and apicoplast inheritance. Moreover, we showed that the interaction of TgAtg8 and TgAtg3 is critical for TgAtg8 apicoplast localization. In addition, we found that the TgAtg3F239A/I242A complemented line exhibits an integral mitochondrial network upon ablation of endogenous TgAtg3, which is distinct from TgAtg3-depleted parasites with a fragmented mitochondrial network. Taken together, this work solidifies the contribution of the TgAtg8-TgAtg3 interaction to apicoplast inheritance and the growth of T. gondii tachyzoites. IMPORTANCEToxoplasma gondiiis a widespread intracellular parasite infecting a variety of warm-blooded animals, including humans. Current frontline treatment of toxoplasmosis suffers many drawbacks, including toxicity, drug resistance, and failure to eradicate tissue cysts, underscoring the need to identify novel drug targets for suppression or treatment of toxoplasmosis. TgAtg8 is thought to serve multiple functions in lipidation and is considered essential to the growth and development of both tachyzoites and bradyzoites. Here, we show that Toxoplasma gondii has adapted a conserved Atg8-Atg3 interaction, required for canonical autophagy in other eukaryotes, to function specifically in apicoplast inheritance. Our finding not only highlights the importance of TgAtg8-TgAtg3 interaction in tachyzoite growth but also suggests that this interaction is a promising drug target for the therapy of toxoplasmosis.

Comparative Phosphoproteomic Analysis of Sporulated Oocysts and Tachyzoites of Toxoplasma gondii Reveals Stage-Specific Patterns.

Toxoplasma gondii is an obligate intracellular protozoan of severe threat to humans and livestock, whose life history harbors both gamic and apogamic stages. Chinese 1 (ToxoDB#9) was a preponderant genotype epidemic in food-derived animals and humans in China, with a different pathogenesis from the strains from the other nations of the world. Posttranslational modifications (PTMs) of proteins were critical mediators of the biology, developmental transforms, and pathogenesis of protozoan parasites. The phosphoprotein profiling and the difference between the developmental phases of T. gondii, contributing to development and infectivity, remain unknown. A quantitative phosphoproteomic approach using IBT integrated with TiO2 affinity chromatography was applied to identify and analyze the difference in the phosphoproteomes between the sporulated oocysts and the tachyzoites of the virulent ToxoDB#9 (PYS) strain of T. gondii. A total of 4058 differential phosphopeptides, consisting of 2597 upregulated and 1461 downregulated phosphopeptides, were characterized between sporulated the oocysts and tachyzoites. Twenty-one motifs extracted from the upregulated phosphopeptides contained 19 serine motifs and 2 threonine motifs (GxxTP and TP), whereas 16 motifs identified from downregulated phosphopeptides included 13 serine motifs and 3 threonine motifs (KxxT, RxxT, and TP). Beyond the traditional kinases, some infrequent classes of kinases, including Ab1, EGFR, INSR, Jak, Src and Syk, were found to be corresponding to motifs from the upregulated and downregulated phosphopeptides. Remarkable functional properties of the differentially expressed phosphoproteins were discovered by GO analysis, KEGG pathway analysis, and STRING analysis. S8GFS8 (DNMT1-RFD domain-containing protein) and S8F5G5 (Histone kinase SNF1) were the two most connected peptides in the kinase-associated network. Out of these, phosphorylated modifications in histone kinase SNF1 have functioned in mitosis and interphase of T. gondii, as well as in the regulation of gene expression relevant to differentiation. Our study discovered a remarkable difference in the abundance of phosphopeptides between the sporulated oocysts and tachyzoites of the virulent ToxoDB#9 (PYS) strain of T. gondii, which may provide a new resource for understanding stage-specific differences in PTMs and may enhance the illustration of the regulatory mechanisms contributing to the development and infectivity of T. gondii.

Bicyclic azetidines target acute and chronic stages of Toxoplasma gondii by inhibiting parasite phenylalanyl t-RNA synthetase.

Toxoplasma gondii commonly infects humans and while most infections are controlled by the immune response, currently approved drugs are not capable of clearing chronic infection in humans. Hence, approximately one third of the world's human population is at risk of reactivation, potentially leading to severe sequelae. To identify new candidates for treating chronic infection, we investigated a series of compounds derived from diversity-oriented synthesis. Bicyclic azetidines are potent low nanomolar inhibitors of phenylalanine tRNA synthetase (PheRS) in T. gondii, with excellent selectivity. Biochemical and genetic studies validate PheRS as the primary target of bicyclic azetidines in T. gondii, providing a structural basis for rational design of improved analogs. Favorable pharmacokinetic properties of a lead compound provide excellent protection from acute infection and partial protection from chronic infection in an immunocompromised mouse model of toxoplasmosis. Collectively, PheRS inhibitors of the bicyclic azetidine series offer promise for treatment of chronic toxoplasmosis.

Pantothenate biosynthesis is critical for chronic infection by the neurotropic parasite Toxoplasma gondii.

Coenzyme A (CoA) is an essential molecule acting in metabolism, post-translational modification, and regulation of gene expression. While all organisms synthesize CoA, many, including humans, are unable to produce its precursor, pantothenate. Intriguingly, like most plants, fungi and bacteria, parasites of the coccidian subgroup of Apicomplexa, including the human pathogen Toxoplasma gondii, possess all the enzymes required for de novo synthesis of pantothenate. Here, the importance of CoA and pantothenate biosynthesis for the acute and chronic stages of T. gondii infection is dissected through genetic, biochemical and metabolomic approaches, revealing that CoA synthesis is essential for T. gondii tachyzoites, due to the parasite's inability to salvage CoA or intermediates of the pathway. In contrast, pantothenate synthesis is only partially active in T. gondii tachyzoites, making the parasite reliant on its uptake. However, pantothenate synthesis is crucial for the establishment of chronic infection, offering a promising target for intervention against the persistent stage of T. gondii.

Mitochondria shed their outer membrane in response to infection-induced stress.

The outer mitochondrial membrane (OMM) is essential for cellular homeostasis. Yet little is known of the mechanisms that remodel it during natural stresses. We found that large "SPOTs" (structures positive for OMM) emerge during Toxoplasma gondii infection in mammalian cells. SPOTs mediated the depletion of the OMM proteins mitofusin 1 and 2, which restrict parasite growth. The formation of SPOTs depended on the parasite effector TgMAF1 and the host mitochondrial import receptor TOM70, which is required for optimal parasite proliferation. TOM70 enabled TgMAF1 to interact with the host OMM translocase SAM50. The ablation of SAM50 or the overexpression of an OMM-targeted protein promoted OMM remodeling independently of infection. Thus, Toxoplasma hijacks the formation of SPOTs, a cellular response to OMM stress, to promote its growth.

Differential contribution of two organelles of endosymbiotic origin to iron-sulfur cluster synthesis and overall fitness in Toxoplasma.

Iron-sulfur (Fe-S) clusters are one of the most ancient and ubiquitous prosthetic groups, and they are required by a variety of proteins involved in important metabolic processes. Apicomplexan parasites have inherited different plastidic and mitochondrial Fe-S clusters biosynthesis pathways through endosymbiosis. We have investigated the relative contributions of these pathways to the fitness of Toxoplasma gondii, an apicomplexan parasite causing disease in humans, by generating specific mutants. Phenotypic analysis and quantitative proteomics allowed us to highlight notable differences in these mutants. Both Fe-S cluster synthesis pathways are necessary for optimal parasite growth in vitro, but their disruption leads to markedly different fates: impairment of the plastidic pathway leads to a loss of the organelle and to parasite death, while disruption of the mitochondrial pathway trigger differentiation into a stress resistance stage. This highlights that otherwise similar biochemical pathways hosted by different sub-cellular compartments can have very different contributions to the biology of the parasites, which is something to consider when exploring novel strategies for therapeutic intervention.

A plastid two-pore channel essential for inter-organelle communication and growth of Toxoplasma gondii.

Two-pore channels (TPCs) are a ubiquitous family of cation channels that localize to acidic organelles in animals and plants to regulate numerous Ca2+-dependent events. Little is known about TPCs in unicellular organisms despite their ancient origins. Here, we characterize a TPC from Toxoplasma gondii, the causative agent of toxoplasmosis. TgTPC is a member of a novel clad of TPCs in Apicomplexa, distinct from previously identified TPCs and only present in coccidians. We show that TgTPC localizes not to acidic organelles but to the apicoplast, a non-photosynthetic plastid found in most apicomplexan parasites. Conditional silencing of TgTPC resulted in progressive loss of apicoplast integrity, severely affecting growth and the lytic cycle. Isolation of TPC null mutants revealed a selective role for TPCs in replication independent of apicoplast loss that required conserved residues within the pore-lining region. Using a genetically-encoded Ca2+ indicator targeted to the apicoplast, we show that Ca2+ signals deriving from the ER but not from the extracellular space are selectively transmitted to the lumen. Deletion of the TgTPC gene caused reduced apicoplast Ca2+ uptake and membrane contact site formation between the apicoplast and the ER. Fundamental roles for TPCs in maintaining organelle integrity, inter-organelle communication and growth emerge.

In vitro activity of N-phenyl-1,10-phenanthroline-2-amines against tachyzoites and bradyzoites of Toxoplasma gondii.

Toxoplasma gondiiis an apicomplexan parasite, the causative agent of toxoplasmosis, a common disease in the world. Toxoplasmosis could be severe, especially in immunocompromised patients. The current therapy is limited, where pyrimethamine and sulfadiazine are the best choices despite being associated with side effects and ineffective against the bradyzoites, the parasitic form present during the chronic phase of the infection. Thus, new therapies against both tachyzoites and bradyzoites from T. gondii are urgent. Herein, we present the anti-T. gondii effect of 1,10-phenanthroline and its N-phenyl-1,10-phenanthroline-2-amine derivatives. The chemical modification of 1,10-phenanthroline tonew derivatives improved the anti-T. gondiiactivity 3.4 fold. The most active derivative presented ED50in the nanomolar range, the smallest value found was for Ph8, 0.1 µM for 96 h of treatment. The host cell viability was maintained after the treatment with the compounds, which were found to be highly selective presenting large selectivity indexes. Treatment with derivatives for 96 h was able to eliminate the T. gondii infection irreversibly. The ultrastructural alterations caused after the treatment with the most effective derivative (Ph8) included signs of cell death, specifically revealed by the Tunel assay for detection of DNA fragmentation. The Phen derivatives were also able to control the growth of the in vitro-derived bradyzoite forms of T. gondii EGS strain, causing its lysis and death. These findings promote the 1,10-phenanthroline derivatives as potential lead compounds for the development of a treatment for acute and chronic phases of toxoplasmosis.

Cyclooxygenase (COX)-2 modulates Toxoplasma gondii infection, immune response and lipid droplets formation in human trophoblast cells and villous explants.

Congenital toxoplasmosis is represented by the transplacental passage of Toxoplasma gondii from the mother to the fetus. Our studies demonstrated that T. gondii developed mechanisms to evade of the host immune response, such as cyclooxygenase (COX)-2 and prostaglandin E2 (PGE2) induction, and these mediators can be produced/stored in lipid droplets (LDs). The aim of this study was to evaluate the role of COX-2 and LDs during T. gondii infection in human trophoblast cells and villous explants. Our data demonstrated that COX-2 inhibitors decreased T. gondii replication in trophoblast cells and villous. In BeWo cells, the COX-2 inhibitors induced an increase of pro-inflammatory cytokines (IL-6 and MIF), and a decrease in anti-inflammatory cytokines (IL-4 and IL-10). In HTR-8/SVneo cells, the COX-2 inhibitors induced an increase of IL-6 and nitrite and decreased IL-4 and TGF-ß1. In villous explants, the COX-2 inhibitors increased MIF and decreased TNF-α and IL-10. Furthermore, T. gondii induced an increase in LDs in BeWo and HTR-8/SVneo, but COX-2 inhibitors reduced LDs in both cells type. We highlighted that COX-2 is a key factor to T. gondii proliferation in human trophoblast cells, since its inhibition induced a pro-inflammatory response capable of controlling parasitism and leading to a decrease in the availability of LDs, which are essentials for parasite growth.

4-Arylthiosemicarbazide derivatives as a new class of tyrosinase inhibitors and anti-Toxoplasma gondii agents.

We report herein anti-proliferation effects of 4-arylthiosemicarbazides, with a cyclopentane substitution at N1 position, on highly virulent RH strain of Toxoplasma gondii. Among them, the highest in vitro anti-Toxoplasma activity was found with the meta-iodo derivative. Further experiments demonstrated inhibitory effects of thiosemicarbazides on tyrosinase (Tyr) activity, and good correlation was found between percentage of Tyr inhibition and IC50Tg. To confirm the concept that thiosemicarbazides are able to disrupt tyrosine metabolism in Toxoplasma tachyzoites, the most potent Tyr inhibitors were tested for their efficacy of T. gondii growth inhibition. All of them significantly reduced the number of tachyzoites in the parasitophorous vacuoles (PVs) compared to untreated cells, as well as inhibited tachyzoites growth by impeding cell division. Collectively, these results indicate that compounds with the thiosemicarbazide scaffold are able to disrupt tyrosine metabolism in Toxoplasma tachyzoites by deregulation of their crucial enzyme tyrosine hydroxylase (TyrH).