Toxoplasma gondii acetyl-CoA synthetase is involved in fatty acid elongation (of long fatty acid chains) during tachyzoite life stages

A novel SUN1-ALLAN complex coordinates segregation of the bipartite MTOC across the nuclear envelope during rapid closed mitosis in Plasmodium

Mitosis in eukaryotes involves reorganization of the nuclear envelope (NE) and microtubule-organizing centres (MTOCs). During male gametogenesis in Plasmodium, the causative agent of malaria, mitosis is exceptionally rapid and highly divergent. Within 8 min, the haploid male gametocyte genome undergoes three replication cycles (1N to 8N), while maintaining an intact NE. Axonemes assemble in the cytoplasm and connect to a bipartite MTOC-containing nuclear pole (NP) and cytoplasmic basal body, producing eight flagellated gametes. The mechanisms coordinating NE remodelling, MTOC dynamics, and flagellum assembly remain poorly understood. We identify the SUN1-ALLAN complex as a novel mediator of NE remodelling and bipartite MTOC coordination during Plasmodium male gametogenesis. SUN1, a conserved NE protein, localizes to dynamic loops and focal points at the nucleoplasmic face of the spindle poles. ALLAN, a divergent allantoicase, has a location like that of SUN1, and these proteins form a unique complex, detected by live-cell imaging, ultrastructural expansion microscopy, and interactomics. Deletion of either SUN1 or ALLAN genes disrupts nuclear MTOC organization, leading to basal body mis-segregation, defective spindle assembly, and impaired spindle microtubule-kinetochore attachment, but axoneme formation remains intact. Ultrastructural analysis revealed nuclear and cytoplasmic MTOC miscoordination, producing aberrant flagellated gametes lacking nuclear material. These defects block development in the mosquito and parasite transmission, highlighting the essential functions of this complex.

Iron‑sulfur cluster biogenesis and function in Apicomplexa parasites

Iron‑sulfur cluster are ubiquitous and ancient protein cofactors that support a wide array of essential cellular functions. In eukaryotes, their assembly requires specific and dedicated machineries in each subcellular compartment. Apicomplexans are parasitic protists that are collectively responsible for a significant burden on the health of humans and other animals, and most of them harbor two organelles of endosymbiotic origin: a mitochondrion, and a plastid of high metabolic importance called the apicoplast. Consequently, apicomplexan parasites have distinct iron‑sulfur cluster assembly machineries located to their endosymbiotic organelles, as well as a cytosolic pathway. Recent findings have not only shown the importance of iron‑sulfur cluster assembly for the fitness of these parasites, but also highlighted parasite-specific features that may be promising for the development of targeted anti-parasitic strategies.

Glabridin exhibits potent inhibitory effects against Toxoplasma gondii in vitro and in vivo

BACKGROUND

Toxoplasma gondii is an obligate protozoan parasite capable of infecting a wide range of warm-blooded animals and humans. Current treatment options, primarily pyrimethamine and sulfadiazine, have limitations, such as high recurrence rates, long treatment durations, and limited effectiveness against T. gondii. There is an unmet need for novel, safe, low-toxicity, and highly effective treatments. This study aimed to evaluate the anti-T. gondii effects of glabridin, a natural compound derived from the roots of a widely used medicinal plant.

METHODS

The cytotoxicity of glabridin in Vero cells was assessed using a CCK-8 cell viability assay. Quantitative polymerase chain reaction (qPCR) targeting the Tg-529 gene was developed to quantify T. gondii and assess the inhibitory effects of glabridin on parasite proliferation. Ultrastructural changes in T. gondii after treatment were examined using electron microscopy. The levels of reactive oxygen species (ROS) and mitochondrial membrane potential (ΔΨm) were examined to assess the effects of glabridin on ROS levels and ΔΨm in T. gondii tachyzoites. Additionally, metabolomics and transcriptomics analyses were conducted to investigate the mechanisms underlying glabridin's anti-T. gondii effects.

RESULTS

Glabridin exhibited low toxicity to host cells and effectively inhibited T. gondii invasion and proliferation in vitro in a time-dependent manner. Glabridin-treated tachyzoites exhibited significant structural alterations, along with increased ROS production and a reduction in ΔΨm. Metabolomic analysis indicated that glabridin significantly affected amino acid metabolism pathways in T. gondii. In vivo, glabridin treatment significantly improved survival rates in T. gondii-infected BALB/c mice at a dosage of 100 mg/kg.

CONCLUSIONS

This study demonstrates that glabridin has potent anti-T. gondii effects in vitro and in vivo, likely through disruption of amino acid metabolism in the parasite. These findings highlight glabridin's potential as a promising therapeutic agent for toxoplasmosis.

In artemisinin-resistant falciparum malaria parasites, mitochondrial metabolic pathways are essential for survival but not those of apicoplast

Emergence and spread of parasite resistance to artemisinins, the first-line antimalarial therapy, threaten the malaria eradication policy. To identify therapeutic targets to eliminate artemisinin-resistant parasites, the functioning of the apicoplast and the mitochondrion was studied, focusing on the fatty acid synthesis type II (FASII) pathway in the apicoplast and the electron transfer chain in the mitochondrion. A significant enrichment of the FASII pathway among the up-regulated genes in artemisinin-resistant parasites under dihydroartemisinin treatment was found, in agreement with published transcriptomic data. However, using GC-MS analyzes of fatty acids, we demonstrated for the first time that the FASII pathway is non-functional, ruling out the use of FASII inhibitors to target artemisinin-resistant parasites. Conversely, by assessing the modulation of the oxygen consumption rate, we evidenced that mitochondrial respiration remains functional and flexible in artemisinin-resistant parasites and even at the quiescent stage. Two novel compounds targeting electron transport chain (ELQ300, ELQ400) efficiently killed quiescent artemisinin-resistant parasites. Therefore, mitochondrial respiration represents a key target for the elimination of artemisinin-resistant persistent Plasmodium falciparum parasites.

An endoplasmic reticulum localized acetyl-CoA transporter is required for efficient fatty acid synthesis in Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite that can infect humans and diverse animals. Fatty acids are critical for the growth and proliferation of T. gondii, which has at least two pathways to synthesize fatty acids, including the type II de novo synthesis pathway in the apicoplast and the elongation pathway in the endoplasmic reticulum (ER). Acetyl-CoA is the key substrate for both fatty acid synthesis pathways. In the apicoplast, acetyl-CoA is mainly provided by the pyruvate dehydrogenase complex. However, how the ER acquires acetyl-CoA is not fully understood. Here, we identified a putative acetyl-CoA transporter (TgAT1) that localized to the ER of T. gondii. Deletion of TgAT1 impaired parasite growth and invasion in vitro and attenuated tachyzoite virulence in vivo. Metabolic tracing using 13C-acetate found that loss of TgAT1 reduced the incorporation of 13C into certain fatty acids, suggesting reduced activities of elongation. Truncation of AT1 was previously reported to confer resistance to the antimalarial compound GNF179 in Plasmodium falciparum. Interestingly, GNF179 had much weaker inhibitory effect on Toxoplasma than on Plasmodium. In addition, deletion of AT1 did not affect the susceptibility of Toxoplasma to GNF179, suggesting that this compound might be taken up differently or has different inhibitory mechanisms in these parasites. Together, our data show that TgAT1 has important roles for parasite growth and fatty acid synthesis, but its disruption does not confer GNF179 resistance in T. gondii.

Cell cycle-regulated transcription factor AP2XII-9 is a key activator for asexual division and apicoplast inheritance in Toxoplasma gondii tachyzoite

Toxoplasma gondii is an intracellular parasitic protozoan that poses a significant risk to the fetus carried by a pregnant woman or to immunocompromised individuals. T. gondii tachyzoites duplicate rapidly in host cells during acute infection through endodyogeny. This highly regulated division process is accompanied by complex gene regulation networks. TgAP2XII-9 is a cell cycle-regulated transcription factor, but its specific role in the parasite cell cycle is not fully understood. In this study, we demonstrate that TgAP2XII-9 is identified as a nuclear transcription factor and is dominantly expressed during the S/M phase of the tachyzoite cell cycle. Cleavage Under Targets and Tagmentation (CUT&Tag) results indicate that TgAP2XII-9 targets key genes for the moving junction machinery (RON2, 4, and 8) and daughter cell inner membrane complex (IMC). TgAP2XII-9 deficiency resulted in a significant downregulation of rhoptry proteins and rhoptry neck proteins, leading to a severe defect in the invasion and egress efficiency of tachyzoites. Additionally, the loss of TgAP2XII-9 correlated with a substantial downregulation of multiple IMC and apicoplast proteins, leading to disorders of daughter bud formation and apicoplast inheritance and further contributing to the inability of cell division and intracellular proliferation. Our study reveals that TgAP2XII-9 acts as a critical S/M-phase regulator that orchestrates the endodyogeny and apicoplast division in T. gondii tachyzoites. This study contributes to a broader understanding of the complexity of the parasite's cell cycle and its key regulators.

IMPORTANCE

The intracellular apicoplast parasite Toxoplasma gondii poses a great threat to the public health. The acute infection of T. gondii tachyzoites relies on efficient invasion by forming a moving junction structure and also fast replication by highly regulated endodyogeny. This study shows that an ApiAP2 transcription factor, TgAP2XII-9, acts as an activator for the S/M-phase gene expression, including genes related to daughter buds and moving junction formation. Loss of TgAP2XII-9 results in significant growth defects and disorders in endodyogeny and apicoplast inheritance of the parasites. Our results provide valuable insights into the transcriptional regulation of the parasite cell cycle and invading machinery in T. gondii.

3-Benzylmenadiones and their Heteroaromatic Analogues Target the Apicoplast of Apicomplexa Parasites: Synthesis and Bioimaging Studies

The apicoplast is an essential organelle for the viability of apicomplexan parasites Plasmodium falciparum or Toxoplasma gondii, which has been proposed as a suitable drug target for the development of new antiplasmodial drug-candidates. Plasmodione, an antimalarial redox-active lead drug is active at low nM concentrations on several blood stages of Plasmodiumsuch as early rings and gametocytes. Nevertheless, its precise biological targets remain unknown. Here, we described the synthesis and the evaluation of new heteroaromatic analogues of plasmodione, active on asexual blood P. falciparum stages and T. gondii tachyzoites. Using a bioimaging-based analysis, we followed the morphological alterations of T. gondii tachyzoites and revealed a specific loss of the apicoplast upon drug treatment. Lipidomic and fluxomic analyses determined that drug treatment severely impacts apicoplast-hosted FASII activity in T. gondii tachyzoites, further supporting that the apicoplast is a primary target of plasmodione analogues. To follow the drug localization, "clickable" analogues of plasmodione were designed as tools for fluorescence imaging through a Cu(I)-catalyzed azide-alkyne cycloaddition reaction. Short-time incubation of two probes with P. falciparum trophozoites and T. gondii tachyzoites showed that the clicked products localize within, or in the vicinity of, the apicoplast of both Apicomplexa parasites. In P. falciparum, the fluorescence signal was also associated with the mitochondrion, suggesting that bioactivation and activity of plasmodione and related analogues are potentially associated with these two organelles in malaria parasites.

Toxoplasma acyl-CoA synthetase TgACS3 is crucial to channel host fatty acids in lipid droplets and for parasite propagation

Apicomplexa comprise important pathogenic parasitic protists that heavily depend on lipid acquisition to survive within their human host cells. Lipid synthesis relies on the incorporation of an essential combination of fatty acids (FAs) either generated by a metabolically adaptable de novo synthesis in the parasite or by scavenging from the host cell. The incorporation of FAs into membrane lipids depends on their obligate metabolic activation by specific enzyme groups, acyl-CoA synthetases (ACSs). Each ACS has its own specificity, so it can fulfill specific metabolic functions. Whilst such functionalities have been well studied in other eukaryotic models, their roles and importance in Apicomplexa are currently very limited, especially for Toxoplasma gondii. Here, we report the identification of seven putative ACSs encoded by the genome of T. gondii (TgACS), which localize to different sub-cellular compartments of the parasite, suggesting exclusive functions. We show that the perinuclear/cytoplasmic TgACS3 regulates the replication and growth of Toxoplasma tachyzoites. Conditional disruption of TgACS3 shows that the enzyme is required for parasite propagation and survival, especially under high host nutrient content. Lipidomic analysis of parasites lacking TgACS3 reveals its role in the activation of host-derived FAs that are used for i) parasite membrane phospholipid and ii) storage triacylglycerol (TAG) syntheses, allowing proper membrane biogenesis of parasite progenies. Altogether, our results reveal the role of TgACS3 as the bulk FA activator for membrane biogenesis allowing intracellular division and survival in T. gondii tachyzoites, further pointing to the importance of ACS and FA metabolism for the parasite.

Metabolic reprogramming of hypoxic tumor-associated macrophages through CSF-1R targeting favors treatment efficiency in colorectal cancers

BACKGROUND

Tumor-associated macrophages participate in the complex network of support that favors tumor growth. Among the various strategies that have been developed to target these cells, the blockade of the colony-stimulating factor 1 receptor (CSF-1R) receptor is one of the most promising ones. Here, we characterize the resulting state of human macrophages exposed to a CSF-1R kinase inhibitor.

METHODS

Using RNA sequencing and metabolomics approach, we characterize the reprogramming of human monocyte-derived macrophages under CSF-1R targeting.

RESULTS

We find that CSF-1R receptor inhibition in human macrophages is able to impair cholesterol synthesis, fatty acid metabolism and hypoxia-driven expression of dihydropyrimidine dehydrogenase, an enzyme responsible for the 5-fluorouracil macrophage-mediated chemoresistance. We show that this inhibition of the CSF-1R receptor leads to a downregulation of the expression of sterol regulatory element-binding protein 2, a transcription factor that controls cholesterol and fatty acid synthesis. We also show that the inhibition of extracellular signal-regulated kinase 1/2 phosphorylation resulting from targeting the CSF-1R receptor destabilizes the expression of hypoxic induced factor 2 alpha in hypoxia resulting in the downregulation of dihydropyrimidine dehydrogenase expression restoring the sensitivity to 5-fluorouracil in colorectal cancer.

CONCLUSIONS

These results reveal the unexpected metabolic rewiring resulting from the CSF-1R receptor targeting of human macrophages and its potential to reverse macrophage-mediated chemoresistance in colorectal tumors.

Stearoyl-CoA desaturase regulates organelle biogenesis and hepatic merozoite formation in Plasmodium berghei

Plasmodium is an obligate intracellular parasite that requires intense lipid synthesis for membrane biogenesis and survival. One of the principal membrane components is oleic acid, which is needed to maintain the membrane's biophysical properties and fluidity. The malaria parasite can modify fatty acids, and stearoyl-CoA Δ9-desaturase (Scd) is an enzyme that catalyzes the synthesis of oleic acid by desaturation of stearic acid. Scd is dispensable in P. falciparum blood stages; however, its role in mosquito and liver stages remains unknown. We show that P. berghei Scd localizes to the ER in the blood and liver stages. Disruption of Scd in the rodent malaria parasite P. berghei did not affect parasite blood stage propagation, mosquito stage development, or early liver-stage development. However, when Scd KO sporozoites were inoculated intravenously or by mosquito bite into mice, they failed to initiate blood-stage infection. Immunofluorescence analysis revealed that organelle biogenesis was impaired and merozoite formation was abolished, which initiates blood-stage infections. Genetic complementation of the KO parasites restored merozoite formation to a level similar to that of WT parasites. Mice immunized with Scd KO sporozoites confer long-lasting sterile protection against infectious sporozoite challenge. Thus, the Scd KO parasite is an appealing candidate for inducing protective pre-erythrocytic immunity and hence its utility as a GAP.

The acyl-CoA synthetase TgACS1 allows neutral lipid metabolism and extracellular motility in Toxoplasma gondii through relocation via its peroxisomal targeting sequence (PTS) under low nutrient conditions

Apicomplexa parasites cause major diseases such as toxoplasmosis and malaria that have major health and economic burdens. These unicellular pathogens are obligate intracellular parasites that heavily depend on lipid metabolism for the survival within their hosts. Their lipid synthesis relies on an essential combination of fatty acids (FAs) obtained from both de novo synthesis and scavenging from the host. The constant flux of scavenged FA needs to be channeled toward parasite lipid storage, and these FA storages are timely mobilized during parasite division. In eukaryotes, the utilization of FA relies on their obligate metabolic activation mediated by acyl-co-enzyme A (CoA) synthases (ACSs), which catalyze the thioesterification of FA to a CoA. Besides the essential functions of FA for parasite survival, the presence and roles of ACS are yet to be determined in Apicomplexa. Here, we identified TgACS1 as a Toxoplasma gondii cytosolic ACS that is involved in FA mobilization in the parasite specifically during low host nutrient conditions, especially in extracellular stages where it adopts a different localization. Heterologous complementation of yeast ACS mutants confirmed TgACS1 as being an Acyl-CoA synthetase of the bubble gum family that is most likely involved in β-oxidation processes. We further demonstrate that TgACS1 is critical for gliding motility of extracellular parasite facing low nutrient conditions, by relocating to peroxisomal-like area.IMPORTANCEToxoplasma gondii, causing human toxoplasmosis, is an Apicomplexa parasite and model within this phylum that hosts major infectious agents, such as Plasmodium spp., responsible for malaria. The diseases caused by apicomplexans are responsible for major social and economic burdens affecting hundreds of millions of people, like toxoplasmosis chronically present in about one-third of the world's population. Lack of efficient vaccines, rapid emergence of resistance to existing treatments, and toxic side effects of current treatments all argue for the urgent need to develop new therapeutic tools to combat these diseases. Understanding the key metabolic pathways sustaining host-intracellular parasite interactions is pivotal to develop new efficient ways to kill these parasites. Current consensus supports parasite lipid synthesis and trafficking as pertinent target for novel treatments. Many processes of this essential lipid metabolism in the parasite are not fully understood. The capacity for the parasites to sense and metabolically adapt to the host physiological conditions has only recently been unraveled. Our results clearly indicate the role of acyl-co-enzyme A (CoA) synthetases for the essential metabolic activation of fatty acid (FA) used to maintain parasite propagation and survival. The significance of our research is (i) the identification of seven of these enzymes that localize at different cellular areas in T. gondii parasites; (ii) using lipidomic approaches, we show that TgACS1 mobilizes FA under low host nutrient content; (iii) yeast complementation showed that acyl-CoA synthase 1 (ACS1) is an ACS that is likely involved in peroxisomal β-oxidation; (iv) the importance of the peroxisomal targeting sequence for correct localization of TgACS1 to a peroxisomal-like compartment in extracellular parasites; and lastly, (v) that TgACS1 has a crucial role in energy production and extracellular parasite motility.

Lipid metabolism: the potential targets for toxoplasmosis treatment

Toxoplasmosis is a zoonosis caused by Toxoplasma gondii (T. gondii). The current treatment for toxoplasmosis remains constrained due to the absence of pharmaceutical interventions. Thus, the pursuit of more efficient targets is of great importance. Lipid metabolism in T. gondii, including fatty acid metabolism, phospholipid metabolism, and neutral lipid metabolism, assumes a crucial function in T. gondii because those pathways are largely involved in the formation of the membranous structure and cellular processes such as division, invasion, egress, replication, and apoptosis. The inhibitors of T. gondii's lipid metabolism can directly lead to the disturbance of various lipid component levels and serious destruction of membrane structure, ultimately leading to the death of the parasites. In this review, the specific lipid metabolism pathways, correlative enzymes, and inhibitors of lipid metabolism of T. gondii are elaborated in detail to generate novel ideas for the development of anti-T. gondii drugs that target the parasites' lipid metabolism.

CRISPR Screens Identify Toxoplasma Genes That Determine Parasite Fitness in Interferon Gamma-Stimulated Human Cells

Toxoplasma virulence depends on its ability to evade or survive the toxoplasmacidal mechanisms induced by interferon gamma (IFNγ). While many Toxoplasma genes involved in the evasion of the murine IFNγ response have been identified, genes required to survive the human IFNγ response are largely unknown. In this study, we used a genome-wide loss-of-function screen to identify Toxoplasma genes important for parasite fitness in IFNγ-stimulated primary human fibroblasts. We generated gene knockouts for the top six hits from the screen and confirmed their importance for parasite growth in IFNγ-stimulated human fibroblasts. Of these six genes, three have homology to GRA32, localize to dense granules, and coimmunoprecipitate with each other and GRA32, suggesting they might form a complex. Deletion of individual members of this complex leads to early parasite egress in IFNγ-stimulated cells. Thus, prevention of early egress is an important Toxoplasma fitness determinant in IFNγ-stimulated human cells. IMPORTANCE Toxoplasma infection causes serious complications in immunocompromised individuals and in the developing fetus. During infection, certain immune cells release a protein called interferon gamma that activates cells to destroy the parasite or inhibit its growth. While most Toxoplasma parasites are cleared by this immune response, some can survive by blocking or evading the IFNγ-induced restrictive environment. Many Toxoplasma genes that determine parasite survival in IFNγ-activated murine cells are known but parasite genes conferring fitness in IFNγ-activated human cells are largely unknown. Using a Toxoplasma adapted genome-wide loss-of-function screen, we identified many Toxoplasma genes that determine parasite fitness in IFNγ-activated human cells. The gene products of four top hits play a role in preventing early parasite egress in IFNγ-stimulated human cells. Understanding how IFNγ-stimulated human cells inhibit Toxoplasma growth and how Toxoplasma counteracts this, could lead to the development of novel therapeutics.

A Plasmodium falciparum lysophospholipase regulates host fatty acid flux via parasite lipid storage to enable controlled asexual schizogony

Phospholipid metabolism is crucial for membrane biogenesis and homeostasis of Plasmodium falciparum. To generate such phospholipids, the parasite extensively scavenges, recycles, and reassembles host lipids. P. falciparum possesses an unusually large number of lysophospholipases, whose roles and importance remain to be elucidated. Here, we functionally characterize one P. falciparum lysophospholipase, PfLPL3, to reveal its key role in parasite propagation during asexual blood stages. PfLPL3 displays a dynamic localization throughout asexual stages, mainly localizing in the host-parasite interface. Inducible knockdown of PfLPL3 disrupts parasite development from trophozoites to schizont, inducing a drastic reduction in merozoite progenies. Detailed lipidomic analyses show that PfLPL3 generates fatty acids from scavenged host lipids to generate neutral lipids. These are then timely mobilized to allow schizogony and merozoite formation. We then identify inhibitors of PfLPL3 from Medicine for Malaria Venture (MMV) with potent antimalarial activity, which could also serve as pertinent chemical tools to study parasite lipid synthesis.

The Mitochondrial Pyruvate Carrier Coupling Glycolysis and the Tricarboxylic Acid Cycle Is Required for the Asexual Reproduction of Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite capable of infecting humans and animals. The organism has extraordinary metabolic resilience that allows it to establish parasitism in varied nutritional milieus of diverse host cells. Our earlier work has shown that, despite flexibility in the usage of glucose and glutamine as the major carbon precursors, the production of pyruvate by glycolytic enzymes is central to the parasite's growth. Pyruvate is metabolized in a number of subcellular compartments, including the mitochondrion, apicoplast, and cytosol. With the objective of examining the mechanism and importance of the mitochondrial pool of pyruvate imported from the cytosol, we identified the conserved mitochondrial pyruvate carrier (MPC) complex, consisting of two subunits, MPC1 and MPC2, in T. gondii. The two parasite proteins could complement a yeast mutant deficient in growth on leucine and valine. Genetic ablation of either one or both subunits reduced the parasite's growth, mimicking the deletion of branched-chain ketoacid dehydrogenase (BCKDH), which has been reported to convert pyruvate into acetyl-coenzyme A (CoA) in the mitochondrion. Metabolic labeling of the MPC mutants by isotopic glucose revealed impaired synthesis of acetyl-CoA, correlating with a global decrease in carbon flux through glycolysis and the tricarboxylic acid (TCA) cycle. Disruption of MPC proteins exerted only a modest effect on the parasite's virulence in mice, further highlighting its metabolic flexibility. In brief, our work reveals the modus operandi of pyruvate transport from the cytosol to the mitochondrion in the parasite, providing the missing link between glycolysis and the TCA cycle in T. gondii. IMPORTANCE T. gondii is a zoonotic parasite capable of infecting many warm-blooded organisms, including humans. Among others, a feature that allows it to parasitize multiple hosts is its exceptional metabolic plasticity. Although T. gondii can utilize different carbon sources, pyruvate homeostasis is critical for parasite growth. Pyruvate is produced primarily in the cytosol but metabolized in other organelles, such as the mitochondrion and apicoplast. The mechanism of import and physiological significance of pyruvate in these organelles remains unclear. Here, we identified the transporter of cytosol-derived pyruvate into the mitochondrion and studied its constituent subunits and their relevance. Our results show that cytosolic pyruvate is a major source of acetyl-CoA in the mitochondrion and that the mitochondrial pyruvate transporter is needed for optimal parasite growth. The mutants lacking the transporter are viable and virulent in a mouse model, underscoring the metabolic plasticity in the parasite's mitochondrion.

Development of a new quantification method of Sarcocystis cruzi through detection of the acetyl-CoA synthetase gene

Sarcocystis cruzi is a member of the genus Sarcocystis, infecting bovine animals such as cattle and bison as intermediate hosts, and canids such as dogs and raccoon dogs as definitive hosts. Acute sarcocystosis of S. cruzi causes occasional symptoms in cattle, including weight loss, reduced milk production, abortions, and death, and similar to other Sarcocystis species can potentially cause food poisoning in humans when raw or undercooked infected cattle meat is consumed. Despite these issues, genetic information on S. cruzi is scarce, and there is no specific quantitative method for the detection and quantification of the parasite in infected cattle. In this study, we aimed to develop a method based on high-throughput sequencing of S. cruzi genome and transcriptome that specifically and quantitatively detects the S. cruzi acetyl-CoA synthetase gene (ScACS). Cardiac muscles were collected from slaughterhouses in Saitama Prefecture to obtain sarcocysts from which DNA and RNA were extracted for the high-throughput sequencing. Using the sequences, we developed a specific quantitative PCR assay which could distinguish S. cruzi ACS from that of Toxoplasma gondii by taking advantage of the differences in their exon/intron organizations and validated the assay with the microscopic counting of the S. cruzi bradyzoites. Thus, this assay will be useful for future studies of S. cruzi pathogenesis in cattle and for the surveillance of infected animals, thereby easing public health concerns.

Glycosylation Analysis of Feline Small Intestine Following Toxoplasma gondii Infection

Simple Summary

Toxoplasma gondii has a serious impact on public health and the economic development of animal husbandry. Glycosylation, especially N-glycosylation, the pattern modification of proteins, is closely related to the biological functions of proteins, and our study used it to analyze glycosylation alterations in the small intestine of cats infected with T. gondii. The results of the present study showed that 56 glycosylated peptides were upregulated and 37 glycosylated peptides were downregulated. Additionally, we also identified eight N-glycosylated proteins of T. gondii including eight N-glycopeptides and eight N-glycosylation sites. Moreover, the protein eEF2 and its corresponding peptide sequence were identified, with GO terms (i.e., cellular process and metabolic process, cell and cell part, and catalytic activity) that were significantly enriched in the T. gondii MAPK pathway. In addition, the Clusters of Orthologous Groups of proteins (COG) function prediction results showed that posttranslational modification, protein turnover, and chaperones (11%) had the highest enrichment for T. gondii. The host proteins ICAM-1 and PPT1 and the endoplasmic reticulum stress pathway may play an important role in the glycosylation of T. gondii-infected hosts. Our study may provide a new target for T. gondii detection to prevent the spread of T. gondii oocysts in the future.

Abstract

Toxoplasma gondii (T. gondii) is responsible for severe human and livestock diseases, huge economic losses, and adversely affects the health of the public and the development of animal husbandry. Glycosylation is a common posttranslational modification of proteins in eukaryotes, and N-glycosylation is closely related to the biological functions of proteins. However, glycosylation alterations in the feline small intestine following T. gondii infection have not been reported. In this study, the experimental group was intragastrically challenged with 600 brain cysts of the Prugniuad (Pru) strain that were collected from infected mice. The cats’ intestinal epithelial tissues were harvested at 10 days post-infection and then sent for protein glycosylation analysis. High-performance liquid chromatography coupled to tandem mass spectrometry was used to analyze the glycosylation alterations in the small intestine of cats infected with T. gondii. The results of the present study showed that 56 glycosylated peptides were upregulated and 37 glycosylated peptides were downregulated in the feline small intestine infected by T. gondii. Additionally, we also identified eight N-glycosylated proteins of T. gondii including eight N-glycopeptides and eight N-glycosylation sites. The protein A0A086JND6_TOXGO (eEF2) and its corresponding peptide sequence were identified in T. gondii infection. Some special GO terms (i.e., cellular process and metabolic process, cell and cell part, and catalytic activity) were significantly enriched, and the Clusters of Orthologous Groups of proteins (COG) function prediction results showed that posttranslational modification, protein turnover, and chaperones (11%) had the highest enrichment for T. gondii. Interestingly, eEF2, a protein of T. gondii, is also involved in the significantly enriched T. gondii MAPK pathway. The host proteins ICAM-1 and PPT1 and the endoplasmic reticulum stress pathway may play an important role in the glycosylation of Toxoplasma-infected hosts. This is the first report showing that T. gondii oocysts can undergo N-glycosylation in the definitive host and that eEF2 is involved, which may provide a new target for T. gondii detection to prevent the spread of T. gondii oocysts in the future.

Toxoplasma metabolic flexibility in different growth conditions

Apicomplexan parasites have complex metabolic networks that coordinate acquisition of metabolites by de novo synthesis and by scavenging from the host. Toxoplasma gondii has a wide host range and may rely on the flexibility of this metabolic network. Currently, the literature categorizes genes as essential or dispensable according to their dispensability for parasite survival under nutrient-replete in vitro conditions. However, recent studies revealed correlations between medium composition and gene essentiality. Therefore, nutrient availability in the host environment likely determines the requirement of metabolic pathways, which may redefine priorities for drug target identification in a clinical setting. Here we review the recent work characterizing some of the major Toxoplasma metabolic pathways and their functional adaptation to host nutrient content.

Disrupting the plastidic iron-sulfur cluster biogenesis pathway in Toxoplasma gondii has pleiotropic effects irreversibly impacting parasite viability

Like many other apicomplexan parasites, Toxoplasma gondii contains a plastid harboring key metabolic pathways, including the sulfur utilization factor (SUF) pathway that is involved in the biosynthesis of iron-sulfur clusters. These cofactors are crucial for a variety of proteins involved in important metabolic reactions, potentially including plastidic pathways for the synthesis of isoprenoid and fatty acids. It was shown previously that impairing the NFS2 cysteine desulfurase, involved in the first step of the SUF pathway, leads to an irreversible killing of intracellular parasites. However, the metabolic impact of disrupting the pathway remained unexplored. Here, we generated another mutant of this pathway, deficient in the SUFC ATPase, and investigated in details the phenotypic consequences of TgNFS2 and TgSUFC depletion on the parasites. Our analysis confirms that Toxoplasma SUF mutants are severely and irreversibly impacted in division and membrane homeostasis, and suggests a defect in apicoplast-generated fatty acids. However, we show that increased scavenging from the host or supplementation with exogenous fatty acids do not fully restore parasite growth, suggesting that this is not the primary cause for the demise of the parasites and that other important cellular functions were affected. For instance, we also show that the SUF pathway is key for generating the isoprenoid-derived precursors necessary for the proper targeting of GPI-anchored proteins and for parasite motility. Thus, we conclude plastid-generated iron-sulfur clusters support the functions of proteins involved in several vital downstream cellular pathways, which implies the SUF machinery may be explored for new potential anti-Toxoplasma targets.

Preclinical characterization and target validation of the antimalarial pantothenamide MMV693183

Drug resistance and a dire lack of transmission-blocking antimalarials hamper malaria elimination. Here, we present the pantothenamide MMV693183 as a first-in-class acetyl-CoA synthetase (AcAS) inhibitor to enter preclinical development. Our studies demonstrate attractive drug-like properties and in vivo efficacy in a humanized mouse model of Plasmodium falciparum infection. The compound shows single digit nanomolar in vitro activity against P. falciparum and P. vivax clinical isolates, and potently blocks P. falciparum transmission to Anopheles mosquitoes. Genetic and biochemical studies identify AcAS as the target of the MMV693183-derived antimetabolite, CoA-MMV693183. Pharmacokinetic-pharmacodynamic modelling predict that a single 30 mg oral dose is sufficient to cure a malaria infection in humans. Toxicology studies in rats indicate a > 30-fold safety margin in relation to the predicted human efficacious exposure. In conclusion, MMV693183 represents a promising candidate for further (pre)clinical development with a novel mode of action for treatment of malaria and blocking transmission.

Here, de Vries et al. perform a pre-clinical characterization of the antimalarial compound MMV693183: the compound targets acetyl-CoA synthetase, has efficacy in humanized mice against Plasmodium falciparum infection, blocks transmission to mosquito vectors, is safe in rats, and pharmacokinetic-pharmacodynamic modeling informs about a potential oral human dosing regimen.

The flexibility of Apicomplexa parasites in lipid metabolism

Apicomplexa are obligate intracellular parasites responsible for major human infectious diseases such as toxoplasmosis and malaria, which pose social and economic burdens around the world. To survive and propagate, these parasites need to acquire a significant number of essential biomolecules from their hosts. Among these biomolecules, lipids are a key metabolite required for parasite membrane biogenesis, signaling events, and energy storage. Parasites can either scavenge lipids from their host or synthesize them de novo in a relict plastid, the apicoplast. During their complex life cycle (sexual/asexual/dormant), Apicomplexa infect a large variety of cells and their metabolic flexibility allows them to adapt to different host environments such as low/high fat content or low/high sugar levels. In this review, we discuss the role of lipids in Apicomplexa parasites and summarize recent findings on the metabolic mechanisms in host nutrient adaptation.

Pantothenate and CoA biosynthesis in Apicomplexa and their promise as antiparasitic drug targets

The Apicomplexa phylum comprises thousands of distinct intracellular parasite species, including coccidians, haemosporidians, piroplasms, and cryptosporidia. These parasites are characterized by complex and divergent life cycles occupying a variety of host niches. Consequently, they exhibit distinct adaptations to the differences in nutritional availabilities, either relying on biosynthetic pathways or by salvaging metabolites from their host. Pantothenate (Pan, vitamin B5) is the precursor for the synthesis of an essential cofactor, coenzyme A (CoA), but among the apicomplexans, only the coccidian subgroup has the ability to synthesize Pan. While the pathway to synthesize CoA from Pan is largely conserved across all branches of life, there are differences in the redundancy of enzymes and possible alternative pathways to generate CoA from Pan. Impeding the scavenge of Pan and synthesis of Pan and CoA have been long recognized as potential targets for antimicrobial drug development, but in order to fully exploit these critical pathways, it is important to understand such differences. Recently, a potent class of pantothenamides (PanAms), Pan analogs, which target CoA-utilizing enzymes, has entered antimalarial preclinical development. The potential of PanAms to target multiple downstream pathways make them a promising compound class as broad antiparasitic drugs against other apicomplexans. In this review, we summarize the recent advances in understanding the Pan and CoA biosynthesis pathways, and the suitability of these pathways as drug targets in Apicomplexa, with a particular focus on the cyst-forming coccidian, Toxoplasma gondii, and the haemosporidian, Plasmodium falciparum.

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.

Promising Drug Targets and Compounds with Anti-Toxoplasma gondii Activity

Toxoplasmosis is a parasitic disease caused by the globally distributed protozoan parasite Toxoplasma gondii, which infects around one-third of the world population. This disease may result in serious complications for fetuses, newborns, and immunocompromised individuals. Current treatment options are old, limited, and possess toxic side effects. Long treatment durations are required since the current therapeutic system lacks efficiency against T. gondii tissue cysts, promoting the establishment of latent infection. This review highlights the most promising drug targets involved in anti-T. gondii drug discovery, including the mitochondrial electron transport chain, microneme secretion pathway, type II fatty acid synthesis, DNA synthesis and replication and, DNA expression as well as others. A description of some of the most promising compounds demonstrating antiparasitic activity, developed over the last decade through drug discovery and drug repurposing, is provided as a means of giving new perspectives for future research in this field.

Toxoplasma LIPIN is essential in channeling host lipid fluxes through membrane biogenesis and lipid storage

Apicomplexa are obligate intracellular parasites responsible for major human diseases. Their intracellular survival relies on intense lipid synthesis, which fuels membrane biogenesis. Parasite lipids are generated as an essential combination of fatty acids scavenged from the host and de novo synthesized within the parasite apicoplast. The molecular and metabolic mechanisms allowing regulation and channeling of these fatty acid fluxes for intracellular parasite survival are currently unknown. Here, we identify an essential phosphatidic acid phosphatase in Toxoplasma gondii, TgLIPIN, as the central metabolic nexus responsible for controlled lipid synthesis sustaining parasite development. Lipidomics reveal that TgLIPIN controls the synthesis of diacylglycerol and levels of phosphatidic acid that regulates the fine balance of lipids between storage and membrane biogenesis. Using fluxomic approaches, we uncover the first parasite host-scavenged lipidome and show that TgLIPIN prevents parasite death by 'lipotoxicity' through effective channeling of host-scavenged fatty acids to storage triacylglycerols and membrane phospholipids.

Gregarine single-cell transcriptomics reveals differential mitochondrial remodeling and adaptation in apicomplexans

BACKGROUND

Apicomplexa is a diverse phylum comprising unicellular endobiotic animal parasites and contains some of the most well-studied microbial eukaryotes including the devastating human pathogens Plasmodium falciparum and Cryptosporidium hominis. In contrast, data on the invertebrate-infecting gregarines remains sparse and their evolutionary relationship to other apicomplexans remains obscure. Most apicomplexans retain a highly modified plastid, while their mitochondria remain metabolically conserved. Cryptosporidium spp. inhabit an anaerobic host-gut environment and represent the known exception, having completely lost their plastid while retaining an extremely reduced mitochondrion that has lost its genome. Recent advances in single-cell sequencing have enabled the first broad genome-scale explorations of gregarines, providing evidence of differential plastid retention throughout the group. However, little is known about the retention and metabolic capacity of gregarine mitochondria.

RESULTS

Here, we sequenced transcriptomes from five species of gregarines isolated from cockroaches. We combined these data with those from other apicomplexans, performed detailed phylogenomic analyses, and characterized their mitochondrial metabolism. Our results support the placement of Cryptosporidium as the earliest diverging lineage of apicomplexans, which impacts our interpretation of evolutionary events within the phylum. By mapping in silico predictions of core mitochondrial pathways onto our phylogeny, we identified convergently reduced mitochondria. These data show that the electron transport chain has been independently lost three times across the phylum, twice within gregarines.

CONCLUSIONS

Apicomplexan lineages show variable functional restructuring of mitochondrial metabolism that appears to have been driven by adaptations to parasitism and anaerobiosis. Our findings indicate that apicomplexans are rife with convergent adaptations, with shared features including morphology, energy metabolism, and intracellularity.

Intracellular Parasites Toxoplasma gondii and Besnoitia besnoiti, Unveiled in Single Host Cells Using AP-SMALDI MS Imaging

The obligate intracellular apicomplexan parasites Toxoplasma gondii and Besnoitia besnoiti are important causes of disease in both humans and cattle. To date, effective specific treatments are lacking for both infections. To counteract severe symptoms leading to, e.g., disabilities and even abortion in the case of human toxoplasmosis and bovine besnoitiosis, novel targets are required for development of drugs and vaccines. A promising emerging technique for molecular characterization of organisms is high-resolution atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization (AP-SMALDI) mass spectrometry imaging (MSI) which enables semiquantitative visualization of metabolite distributions. MSI was here used to trace and characterize lipid metabolites in primary bovine umbilical vein endothelial cells (BUVECs) upon infection with tachyzoites, an early and pathogenic fast-replicating life stage of T. gondii and B. besnoiti. A cell bulk, derived from noninfected controls and parasite-infected cell pellets, was analyzed by AP-SMALDI MSI in technical and biological triplicates. Multivariate statistical analysis including hierarchical clustering and principle component analysis revealed infection-specific metabolites in both positive- and negative-ion mode, identified by combining database search and LC-MS² experiments. MSI analyses of host cell monolayers were conducted at 5 μm lateral resolution, allowing single apicomplexan-infected cells to be allocated. This is the first mass spectrometry imaging study on intracellular T. gondii and B. besnoiti infections and the first detailed metabolomic characterization of B. besnoiti tachyzoites. MSI was used here as an efficient tool to discriminate infected from noninfected cells at the single-cell level in vitro.

Fatty Acid Biosynthesis in Chromerids

Fatty acids are essential components of biological membranes, important for the maintenance of cellular structures, especially in organisms with complex life cycles like protozoan parasites. Apicomplexans are obligate parasites responsible for various deadly diseases of humans and livestock. We analyzed the fatty acids produced by the closest phototrophic relatives of parasitic apicomplexans, the chromerids Chromera velia and Vitrella brassicaformis, and investigated the genes coding for enzymes involved in fatty acids biosynthesis in chromerids, in comparison to their parasitic relatives. Based on evidence from genomic and metabolomic data, we propose a model of fatty acid synthesis in chromerids: the plastid-localized FAS-II pathway is responsible for the de novo synthesis of fatty acids reaching the maximum length of 18 carbon units. Short saturated fatty acids (C14:0-C18:0) originate from the plastid are then elongated and desaturated in the cytosol and the endoplasmic reticulum. We identified giant FAS I-like multi-modular enzymes in both chromerids, which seem to be involved in polyketide synthesis and fatty acid elongation. This full-scale description of the biosynthesis of fatty acids and their derivatives provides important insights into the reductive evolutionary transition of a phototropic algal ancestor to obligate parasites.

Multi-omics analysis delineates the distinct functions of sub-cellular acetyl-CoA pools in Toxoplasma gondii

BACKGROUND

Acetyl-CoA is a key molecule in all organisms, implicated in several metabolic pathways as well as in transcriptional regulation and post-translational modification. The human pathogen Toxoplasma gondii possesses at least four enzymes which generate acetyl-CoA in the nucleo-cytosol (acetyl-CoA synthetase (ACS); ATP citrate lyase (ACL)), mitochondrion (branched-chain α-keto acid dehydrogenase-complex (BCKDH)) and apicoplast (pyruvate dehydrogenase complex (PDH)). Given the diverse functions of acetyl-CoA, we know very little about the role of sub-cellular acetyl-CoA pools in parasite physiology.

RESULTS

To assess the importance and functions of sub-cellular acetyl-CoA-pools, we measured the acetylome, transcriptome, proteome and metabolome of parasites lacking ACL/ACS or BCKDH. We demonstrate that ACL/ACS constitute a synthetic lethal pair. Loss of both enzymes causes a halt in fatty acid elongation, hypo-acetylation of nucleo-cytosolic and secretory proteins and broad changes in gene expression. In contrast, loss of BCKDH results in an altered TCA cycle, hypo-acetylation of mitochondrial proteins and few specific changes in gene expression. We provide evidence that changes in the acetylome, transcriptome and proteome of cells lacking BCKDH enable the metabolic adaptations and thus the survival of these parasites.

CONCLUSIONS

Using multi-omics and molecular tools, we obtain a global and integrative picture of the role of distinct acetyl-CoA pools in T. gondii physiology. Cytosolic acetyl-CoA is essential and is required for the synthesis of parasite-specific fatty acids. In contrast, loss of mitochondrial acetyl-CoA can be compensated for through metabolic adaptations implemented at the transcriptional, translational and post-translational level.

Functional characterization of acyl-CoA binding protein in Neospora caninum

Background

Lipid metabolism is pivotal for the growth of apicomplexan parasites. Lipid synthesis requires bulk carbon skeleton acyl-CoAs, the transport of which depends on the acyl-CoA binding protein (ACBP). In Neospora caninum, the causative agent of neosporosis, the FASII pathway is required for growth and pathogenicity. However, little is known about the fatty acid transport mechanism in N. caninum.

Methods

We have identified a cytosolic acyl-CoA binding protein, with highly conserved amino acid residues and a typical acyl-CoA binding domain in N. caninum. The recombinant NcACBP protein was expressed to verify the binding activities of NcACBP in vitro, and the heterologous expression of NcACBP in Δacbp yeast in vivo. Lipid extraction from ΔNcACBP or the wild-type of N. caninum was analyzed by GC-MS or TLC. Furthermore, transcriptome analysis was performed to compare the gene expression in different strains.

Results

The NcACBP recombinant protein was able to specifically bind acyl-CoA esters in vitro. A yeast complementation assay showed that heterologous expression of NcACBP rescued the phenotypic defects in Δacbp yeast, indicating of the binding activity of NcACBP in vivo. The disruption of NcACBP did not perturb the parasite’s growth but enhanced its pathogenicity in mice. The lipidomic analysis showed that disruption of NcACBP caused no obvious changes in the overall abundance and turnover of fatty acids while knockout resulted in the accumulation of triacylglycerol. Transcriptional analysis of ACBP-deficient parasites revealed differentially expressed genes involved in a wide range of biological processes such as lipid metabolism, posttranslational modification, and membrane biogenesis.

Conclusions

Our study demonstrated that genetic ablation of NcACBP did not impair the survival and growth phenotype of N. caninum but enhanced its pathogenicity in mice. This deletion did not affect the overall fatty acid composition but modified the abundance of TAG. The loss of NcACBP resulted in global changes in the expression of multiple genes. This study provides a foundation for elucidating the molecular mechanism of lipid metabolism in N. caninum.