Toxoplasma-induced changes in host risk behaviour are independent of parasite-derived AaaH2 tyrosine hydroxylase

Functional Characterization of the Thrombospondin-Related Paralogous Proteins Rhoptry Discharge Factors 1 and 2 Unveils Phenotypic Plasticity in Toxoplasma gondii Rhoptry Exocytosis

To gain access to the intracellular cytoplasmic niche essential for their growth and replication, apicomplexan parasites such as Toxoplasma gondii rely on the timely secretion of two types of apical organelles named micronemes and rhoptries. Rhoptry proteins are key to host cell invasion and remodeling, however, the molecular mechanisms underlying the tight control of rhoptry discharge are poorly understood. Here, we report the identification and functional characterization of two novel T. gondii thrombospondin-related proteins implicated in rhoptry exocytosis. The two proteins, already annotated as MIC15 and MIC14, were renamed rhoptry discharge factor 1 (RDF1) and rhoptry discharge factor 2 (RDF2) and found to be exclusive of the Coccidia class of apicomplexan parasites. Furthermore, they were shown to have a paralogous relationship and share a C-terminal transmembrane domain followed by a short cytoplasmic tail. Immunofluorescence analysis of T. gondii tachyzoites revealed that RDF1 presents a diffuse punctate localization not reminiscent of any know subcellular compartment, whereas RDF2 was not detected. Using a conditional knockdown approach, we demonstrated that RDF1 loss caused a marked growth defect. The lack of the protein did not affect parasite gliding motility, host cell attachment, replication and egress, whereas invasion was dramatically reduced. Notably, while RDF1 depletion did not result in altered microneme exocytosis, rhoptry discharge was found to be heavily impaired. Interestingly, rhoptry secretion was reversed by spontaneous upregulation of the RDF2 gene in knockdown parasites grown under constant RDF1 repression. Collectively, our results identify RDF1 and RDF2 as additional key players in the pathway controlling rhoptry discharge. Furthermore, this study unveils a new example of compensatory mechanism contributing to phenotypic plasticity in T. gondii.

Toxoplasma Reduces Complications of Parkinson’s Disease: An Experimental Study in BALB/c Mice

Background

Parkinson's disease (PD) has been described in dopamine brain level reductions. Conversely, several studies have shown that Toxoplasma parasite can increase the level of dopamine in an infected host. This study was conducted to assess the serum, cerebral dopamine levels, and downregulation of Parkinson's disease manifestations in mice with chronic toxoplasmosis.

Methods

PD induction was done by oral inoculation of rotenone into BALB/c mice. To induce the chronic infection, cysts of T. gondii Prugniaud strain (genotype II) were injected intraperitoneally into the mice. The rotarod test was used for the evaluation of functional motor disorders in experimental mice. The serum and cerebral dopamine levels of the mice were also measured by using high-performance liquid chromatography (HPLC) on consecutive periods (10 days).

Results

Findings of the rotarod test showed the highest and lowest average of running duration belonged to the uninfected mice and PD mice, respectively. Remarkably, the running duration of infected mice with PD was higher than PD mice. As well, the level of serum and cerebral dopamine increased in mice with PD and toxoplasmosis in comparison with PD mice.

Conclusion

Increasing the serum and cerebral dopamine levels in mice infected with toxoplasmosis is related to the presence of the parasite. Moreover, the dopamine upregulation due to the infection is effective in the reduction of PD complications.

4-Arylthiosemicarbazide Derivatives as Toxoplasmic Aromatic Amino Acid Hydroxylase Inhibitors and Anti-inflammatory Agents

Approximately one-third of the human population is infected with the intracellular cosmopolitan protozoan Toxoplasma gondii (Tg), and a specific treatment for this parasite is still needed. Additionally, the increasing resistance of Tg to drugs has become a challenge for numerous research centers. The high selectivity of a compound toward the protozoan, along with low cytotoxicity toward the host cells, form the basis for further research, which aims at determining the molecular targets of the active compounds. Thiosemicarbazide derivatives are biologically active organic compounds. Previous studies on the initial preselection of 58 new 4-arylthiosemicarbazide derivatives in terms of their anti-Tg activity and selectivity made it possible to select two promising derivatives for further research. One of the important amino acids involved in the proliferation of Tg and the formation of parasitophorous vacuoles is tyrosine, which is converted by two unique aromatic amino acid hydroxylases to levodopa. Enzymatic studies with two derivatives (R: para-nitro and meta-iodo) and recombinant aromatic amino acid hydroxylase (AAHs) obtained in the E. coli expression system were performed, and the results indicated that toxoplasmic AAHs are a molecular target for 4-arylthiosemicarbazide derivatives. Moreover, the drug affinity responsive target stability assay also confirmed that the selected compounds bind to AAHs. Additionally, the anti-inflammatory activity of these derivatives was tested using THP1-Blue™ NF-κB reporter cells due to the similarity of the thiosemicarbazide scaffold to thiosemicarbazone, both of which are known NF-κB pathway inhibitors.

Epigenetic Manipulation of Psychiatric Behavioral Disorders Induced by Toxoplasma gondii

Toxoplasma gondii is known to have a complex life cycle and infect almost all kinds of warm-blooded animals around the world. The brain of the host could be persistently infected by cerebral cysts, and a variety of psychiatric disorders such as schizophrenia and suicide have been reported to be related with latent toxoplasmosis. The infected animals showed fear reduction and a tendency to be preyed upon. However, the mechanism of this “parasites manipulation” effects have not been elucidated. Here, we reviewed the recent infection prevalence of toxoplasmosis and the evidence of mental and behavioral disorders induced by T. gondii and discussed the related physiological basis including dopamine dysregulation and gamma-aminobutyric acid (GABA) pathway and the controversial opinion of the necessity for cerebral cysts existence. Based on the recent advances, we speculated that the neuroendocrine programs and neurotransmitter imbalance may play a key role in this process. Simultaneously, studies in the evaluation of the expression pattern of related genes, long noncoding RNAs (lncRNAs), and mRNAs of the host provides a new point for understanding the mechanism of neurotransmitter dysfunction induced by parasite manipulation. Therefore, we summarized the animal models, T. gondii strains, and behavioral tests used in the related epigenetic studies and the responsible epigenetic processes; pinpointed opportunities and challenges in future research including the causality evidence of human psychiatric disorders, the statistical analysis for rodent-infected host to be more vulnerable preyed upon; and identified responsible genes and drug targets through epigenetics.

Evaluation of the Tyrosine and Dopamine Serum Levels in Experimental Infected BALB/c Mice with Chronic Toxoplasmosis

Background

Toxoplasma parasite alters the transduction of neurotransmitter signals and leads to changes in the level of brain neurotransmitters including tyrosine and dopamine, so behavior changes can occur in infected hosts. Based on this concept, this study was conducted for evaluation of the tyrosine and dopamine serum levels in infected mice with chronic toxoplasmosis.

Materials and Methods

Toxoplasma gondii (Prugniaud strain II) was injected intraperitoneally into BALB/c mice to induce chronic toxoplasmosis. Modified agglutination test (MAT), polymerase chain reaction (PCR), and microscopic methods were conducted to confirm the induction of chronic toxoplasmosis. The infected mouse sera were separated at days 40, 50, 60, 70, and 80 for evaluation of tyrosine and dopamine serum levels using high-performance liquid chromatography (HPLC).

Results

Microscopic methods confirmed the formation of the Toxoplasma cysts in mouse tissues. Inducing chronic toxoplasmosis is also confirmed by MAT, PCR, and histological methods. HPLC results indicated a decrease in serum tyrosine level at day 40 in infected mice in comparison to control, and the levels were too low to be measured at other times. However, a significantly high serum dopamine level was observed that gradually increased after parasite inoculation.

Conclusions

No detection of tyrosine level in most of the sample groups is probably related to the very low concentration of tyrosine in sera. However, low concentration of tyrosine at day 40 and increase of dopamine in most of the sample groups suggest the production of dopamine from tyrosine due to the presence of Toxoplasma in infected mice.

Seasonal variations and public search interests in Toxoplasma: a 16-year retrospective analysis of big data on Google Trends

BACKGROUND

This study aims to understand whether there is a seasonal change in the internet search interest for Toxoplasma by using the data derived from Google Trends (GT).

METHODS

The present study searched for the relative search volume (RSV) for the search term 'Toxoplasma' in GT within six major English-speaking countries (Australia, New Zealand [Southern Hemisphere] and Canada, Ireland, the UK and the USA [Northern Hemisphere] from 1 January 2004 to 31 December 2019, utilizing the category of 'health'. Data regarding the RSV of Toxoplasma was obtained and further statistical analysis was performed in R software using the 'season' package.

RESULTS

There were significantly seasonal patterns for the RSV of the search term 'Toxoplasma' in five countries (all p<0.05), except for the UK. A peak in December-March and a trough in July-September (Canada, Ireland, the UK and the USA) were observed, while a peak in June/August and a trough in December/February (Australia, New Zealand) were also found. Moreover, the presence of seasonal patterns regarding RSV for 'Toxoplasma' between the Southern and Northern Hemispheres was also found (both p<0.05), with a reversed meteorological month.

CONCLUSIONS

Overall, our study revealed the seasonal variation for Toxoplasma in using internet search data from GT, providing additional evidence on seasonal patterns in Toxoplasma.

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 IC_50Tg. 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).

Serum Tyrosine Level in Acute Murine Toxoplasmosis

Background

Toxoplasmosis is a zoonotic disease caused by the obligate intracellular parasite, Toxoplasma gondii. This global infectious disease has been associated with behavioral changes in rodents and can result in humans' neuropsychiatric symptoms. Since the neurotransmitters alteration can cause a behavioral change, in this study, tyrosine level, as a precursor of dopamine, was evaluated in acute murine toxoplasmosis during 2015 and 2016 in Shiraz, Iran.

Methods

At the first, 10⁵ tachyzoites of T. gondii were subcutaneously inoculated to 50 BALB/c mice as experimental groups and 10 mice inoculated by PBS considered as the control group. After that, daily, one group of mice was bled, and sera were collected. Then, their serum tyrosine level was evaluated by HPLC method.

Results

After data analysis, the maximum mean serum tyrosine level was seen at 2^th day of post parasite inoculation (0.0194 mg/ ml), with a significant difference compared to the control group (0.0117 mg/ ml, P=0.025). Moreover, the least quantity of serum tyrosine (0.076 mg/ml) was seen on the 5^th day, after parasite inoculation, however, no significant difference was seen.

Conclusion

Serum tyrosine level increased in 2 d after inoculation of Toxoplasma, but the level regularly decreased in successive days. Tyrosine level increased by phenylalanine hydroxylase 2 days after inoculation, then tyrosine decreased by tyrosine hydroxylase in the next days. Toxoplasma tyrosine hydroxylase enzymes, at primary days of toxoplasmosis, effect on tyrosine production, and after that, the most effect on tyrosine consumption.

Behavioral Manipulation by Toxoplasma gondii: Does Brain Residence Matter?

The protozoan parasite Toxoplasma gondii infects a wide range of intermediate hosts. The parasite produces brain cysts during the latent phase of its infection, in parallel to causing a loss of innate aversion in the rat host towards cat odors. Host behavioral change presumably reflects a parasitic manipulation to increase predation by definitive felid hosts, although evidence for increased predation is not yet available. In this opinion piece, we propose a neuroendocrine loop to explain the role of gonadal steroids in the parasitized hosts in mediating the behavioral manipulation. We argue that the presence of tissue cysts within the host brain is merely incidental to the behavioral change, without a necessary or sufficient role.

When fiction becomes fact: exaggerating host manipulation by parasites

In an era where some find fake news around every corner, the use of sensationalism has inevitably found its way into the scientific literature. This is especially the case for host manipulation by parasites, a phenomenon in which a parasite causes remarkable change in the appearance or behaviour of its host. This concept, which has deservedly garnered popular interest throughout the world in recent years, is nearly 50 years old. In the past two decades, the use of scientific metaphors, including anthropomorphisms and science fiction, to describe host manipulation has become more and more prevalent. It is possible that the repeated use of such catchy, yet misleading words in both the popular media and the scientific literature could unintentionally hamper our understanding of the complexity and extent of host manipulation, ultimately shaping its narrative in part or in full. In this commentary, the impacts of exaggerating host manipulation are brought to light by examining trends in the use of embellishing words. By looking at key examples of exaggerated claims from widely reported host-parasite systems found in the recent scientific literature, it would appear that some of the fiction surrounding host manipulation has since become fact.

Toxoplasma gondii infection damages the perineuronal nets in a murine model

BACKGROUND

Behavioral and neurochemical alterations associated with toxoplasmosis may be influenced by the persistence of tissue cysts and activation of an immune response in the brain of Toxoplasma gondii-infected hosts. The cerebral extracellular matrix is organised as perineuronal nets (PNNs) that are both released and ensheath by some neurons and glial cells. There is evidences to suggest that PNNs impairment is a pathophysiological mechanism associated with neuropsychiatric conditions. However, there is a lack of information regarding the impact of parasitic infections on the PNNs integrity and how this could affect the host’s behavior.

OBJECTIVES

In this context, we aimed to analyse the impact of T. gondii infection on cyst burden, PNNs integrity, and possible effects in the locomotor activity of chronically infected mice.

METHODS

We infected mice with T. gondii ME-49 strain. After thirty days, we assessed locomotor performance of animals using the open field test, followed by evaluation of cysts burden and PNNs integrity in four brain regions (primary and secondary motor cortices, prefrontal and somesthetic cortex) to assess the PNNs integrity using Wisteria floribunda agglutinin (WFA) labeling by immunohistochemical analyses.

FINDINGS AND MAIN CONCLUSIONS

Our findings revealed a random distribution of cysts in the brain, the disruption of PNNs surrounding neurons in four areas of the cerebral cortex and hyperlocomotor behavior in T. gondii-infected mice. These results can contribute to elucidate the link toxoplasmosis with the establishment of neuroinflammatory response in neuropsychiatric disorders and to raise a discussion about the mechanisms related to changes in brain connectivity, with possible behavioral repercussions during chronic T. gondii infection.

Majid R. A Review on the Prevalence of Toxoplasma gondii in Humans and Animals Reported in Malaysia from 2008-2018

Toxoplasmosis is a disease caused by the protozoan parasite Toxoplasma gondii (T. gondii). Human toxoplasmosis seroprevalence in Malaysia has increased since it was first reported in 1973 as shown in previous reviews of 1991 and 2007. However, over a decade since the last review, comprehensive data on toxoplasmosis in Malaysia is lacking. This work aimed at reviewing articles on toxoplasmosis research in Malaysia in order to identify the research gaps, create public awareness, and efforts made so far and proffer management options on the disease. The present review examines the available published research articles from 2008 to 2018 related to toxoplasmosis research conducted in Malaysia. The articles reviewed were retrieved from nine credible databases such as Web of Science, Google Scholar, ScienceDirect, PubMed, Scopus, Springer, Wiley online library, Ovid, and Cochrane using the keywords; Malaysia, toxoplasmosis, Toxoplasma gondii, toxoplasma encephalitis, seroprevalence, human immunodeficiency virus (HIV) patients, pregnant women, genotype strain, anti-toxoplasma antibodies, felines, and vaccine. The data highlighted seropositive cases from healthy community members in Pangkor Island (59.7%) and among migrant workers (57.4%) at alarming rates, as well as 42.5% in pregnant women. Data on animal seroprevalence were limited and there was no information on cats as the definitive host. Genetic characterization of Toxoplasma gondii from HIV patients; pregnant women, and domestic cats is lacking. This present review on toxoplasmosis is beneficial to researchers, health workers, animal health professionals, and policymakers. Therefore, attention is required to educate and enlighten health workers and the general public about the risk factors associated with T. gondii infection in Malaysia.

Latent Toxoplasmosis Effects on Rodents and Humans: How Much is Real and How Much is Media Hype?

Toxoplasma gondii is a ubiquitous, intracellular protozoan parasite with a broad range of intermediate hosts, including humans and rodents. In many hosts, T. gondii establishes a latent long-term infection by converting from its rapidly dividing or lytic form to its slowly replicating and encysting form. In humans and rodents, the major organ for encystment is the central nervous system (CNS), which has led many to investigate how this persistent CNS infection might influence rodent and human behavior and, more recently, neurodegenerative diseases.

Toxoplasma gondii is a ubiquitous, intracellular protozoan parasite with a broad range of intermediate hosts, including humans and rodents. In many hosts, T. gondii establishes a latent long-term infection by converting from its rapidly dividing or lytic form to its slowly replicating and encysting form. In humans and rodents, the major organ for encystment is the central nervous system (CNS), which has led many to investigate how this persistent CNS infection might influence rodent and human behavior and, more recently, neurodegenerative diseases. Given the interest in this topic, here we seek to take a global approach to the data for and against the effects of latent T. gondii on behavior and neurodegeneration and the proposed mechanisms that might underlie behavior modifications.

Toxoplasma Cathepsin Protease B and Aspartyl Protease 1 Are Dispensable for Endolysosomal Protein Digestion

Roughly one-third of the human population is chronically infected with the intracellular single-celled parasite Toxoplasma gondii, but little is known about how this organism persists inside people. Previous research suggested that a parasite proteolytic enzyme, termed cathepsin protease L, is important for Toxoplasma persistence; however, it remained possible that other associated proteolytic enzymes could also be involved in the long-term survival of the parasite during infection. Here, we show that two proteolytic enzymes associated with cathepsin protease L play dispensable roles and are dependent on cathepsin L to reach maturity, which differs from the corresponding enzymes in humans. These findings establish a divergent hierarchy of proteases and help focus attention principally on cathepsin protease L as a potential target for interrupting Toxoplasma chronic infection.

The lysosome-like vacuolar compartment (VAC) is a major site of proteolysis in the intracellular parasite Toxoplasma gondii. Previous studies have shown that genetic ablation of a VAC-residing cysteine protease, cathepsin protease L (CPL), resulted in the accumulation of undigested protein in the VAC and loss of parasite viability during the chronic stage of infection. However, since the maturation of another VAC localizing protease, cathepsin protease B (CPB), is dependent on CPL, it remained unknown whether these defects result directly from ablation of CPL or indirectly from a lack of CPB maturation. Likewise, although a previously described cathepsin D-like aspartyl protease 1 (ASP1) could also play a role in proteolysis, its definitive residence and function in the Toxoplasma endolysosomal system were not well defined. Here, we demonstrate that CPB is not necessary for protein turnover in the VAC and that CPB-deficient parasites have normal growth and viability in both the acute and chronic stages of infection. We also show that ASP1 depends on CPL for correct maturation, and it resides in the T. gondii VAC, where, similar to CPB, it plays a dispensable role in protein digestion. Taken together with previous work, our findings suggest that CPL is the dominant protease in a hierarchy of proteolytic enzymes within the VAC. This unusual lack of redundancy for CPL in T. gondii makes it a single exploitable target for disrupting chronic toxoplasmosis.

IMPORTANCE Roughly one-third of the human population is chronically infected with the intracellular single-celled parasite Toxoplasma gondii, but little is known about how this organism persists inside people. Previous research suggested that a parasite proteolytic enzyme, termed cathepsin protease L, is important for Toxoplasma persistence; however, it remained possible that other associated proteolytic enzymes could also be involved in the long-term survival of the parasite during infection. Here, we show that two proteolytic enzymes associated with cathepsin protease L play dispensable roles and are dependent on cathepsin L to reach maturity, which differs from the corresponding enzymes in humans. These findings establish a divergent hierarchy of proteases and help focus attention principally on cathepsin protease L as a potential target for interrupting Toxoplasma chronic infection.

Benzo[b]thiophene-thiazoles as potent anti-Toxoplasma gondii agents: Design, synthesis, tyrosinase/tyrosine hydroxylase inhibitors, molecular docking study, and antioxidant activity

Synthesis and investigation of anti-Toxoplasma gondii activity of novel thiazoles containing benzo [b]thiophene moiety are presented. Among the derivatives, compound 3k with adamantyl group shows exceptionally high potency against Me49 strain with IC₅₀ (8.74 μM) value which is significantly lower than the activity of trimethoprim (IC₅₀ 39.23 μM). In addition, compounds 3a, 3b and 3k showed significant activity against RH strain (IC₅₀ 51.88-83.49 μM). The results of the cytotoxicity evaluation showed that Toxoplasma gondii growth was inhibited at non-cytotoxic concentrations for the mammalian L929 fibroblast (CC₃₀ ∼ 880 μM). The most active compound 3k showed tyrosinase inhibition effect, with IC₅₀ value of 328.5 μM. The binding energies calculated for compounds 3a-3e, 3k are strongly correlated with the experimentally determined values of tyrosinase inhibition activity. Moreover, the binding energies corresponding to the same ligands and calculated for both tyrosinase and tyrosine hydroxylase are also correlated with each other, suggesting that tyrosinase inhibitors may also have an inhibitory effect on tyrosine hydroxylase. Compounds 3j and 3k have also very strong antioxidant activity (IC₅₀ 15.9 and 15.5 μM), respectively, which is ten times higher than well-known antioxidant BHT.

Guanabenz Reverses a Key Behavioral Change Caused by Latent Toxoplasmosis in Mice by Reducing Neuroinflammation

Toxoplasma gondii is an intracellular parasite that has infected one-third of humans. The infection is permanent because the replicative form (tachyzoite) converts into a latent tissue cyst form (bradyzoite) that evades host immunity and is impervious to current drugs. The continued presence of these parasitic cysts hinders treatment and leads to chronic infection that has been linked to behavioral changes in rodents and neurological disease in humans. How these behavioral changes occur, and whether they are due to parasite manipulation or the host response to infection, remains an outstanding question. We previously showed that guanabenz possesses antiparasitic activity; here, we show that guanabenz reproducibly lowers brain cyst burden up to 80% in chronically infected male and female BALB/cJ mice when given intraperitoneally but not when administered by gavage or in food. Regardless of the administration route, guanabenz reverses Toxoplasma-induced hyperactivity in latently infected mice. In contrast, guanabenz increases cyst burden when given to chronically infected C57BL/6J mice yet still reverses Toxoplasma-induced hyperactivity. Examination of the brains from chronically infected BALB/cJ and C57BL/6J mice shows that guanabenz decreases inflammation and perivascular cuffing in each strain. Our study establishes a robust model for cyst reduction in BALB/cJ mice and shows for the first time that it is possible to reverse a key behavioral change associated with latent toxoplasmosis. The rescue from parasite-induced hyperactivity correlates with a decrease in neuroinflammation rather than reduced cyst counts, suggesting that some behavioral changes arise from host responses to infection.IMPORTANCE Toxoplasma gondii is a common parasite of animals, including up to one-third of humans. The single-celled parasite persists within hosts for the duration of their life as tissue cysts, giving rise to chronic infection. Latent toxoplasmosis is correlated with neurological dysfunction in humans and results in dramatic behavioral changes in rodents. When infected, mice and rats adapt behaviors that make them more likely to be devoured by cats, the only host that supports the sexual stage of the parasite. In this study, we establish a new mouse model of tissue cyst depletion using a drug called guanabenz and show that it is possible to reverse a key behavior change back to normal in infected animals. We also show that the mechanism appears to have nothing to do with parasite cyst burden but rather the degree of neuroinflammation produced by chronic infection.

Efficient genome engineering of Toxoplasma gondii using the TALEN technique

Background

Aromatic amino acid hydroxylase 2 (AAH2) is a bradyzoite-specific upregulated protein that may alter host behaviour by altering the host dopaminergic pathway. To better understand the role of the parasite’s AAH2 in host-parasite interactions, we generated an AAH2 fluorescent marker strain of T. gondii using the TALEN technique.

Methods

We generated an AAH2 fluorescent marker strain of T. gondii, which was designated PRU/AAH2-eGFP, using the TALEN technique. This strain stably expressed pyrimethamine resistance for screening and expressed enhanced green fluorescent protein (eGFP)-tagged AAH2 in the bradyzoite stage. The bradyzoite conversion of PRU/AAH2-eGFP was observed both in vitro and in vivo. The fluorescence localization of AAH2 in mouse models of chronic infection was observed by a Bruker in vivo imaging system.

Results

Transgenic T. gondii was successfully generated by the TALEN system. The eGFP-tagged AAH2 could be detected by in vivo imaging.

Conclusions

This study verified the feasibility of using TALEN technology for T. gondii research and provided an in vivo imaging method for in vivo research of bradyzoite-stage proteins.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3378-y) contains supplementary material, which is available to authorized users.

Toxoplasmosis: A pathway to neuropsychiatric disorders

Toxoplasma gondii is an obligate intracellular parasite that resides, in a latent form, in the human central nervous system. Infection with Toxoplasma drastically alters the behaviour of rodents and is associated with the incidence of specific neuropsychiatric conditions in humans. But the question remains: how does this pervasive human pathogen alter behaviour of the mammalian host? This fundamental question is receiving increasing attention as it has far reaching public health implications for a parasite that is very common in human populations. Our current understanding centres on neuronal changes that are elicited directly by this intracellular parasite versus indirect changes that occur due to activation of the immune system within the CNS, or a combination of both. In this review, we explore the interactions between Toxoplasma and its host, the proposed mechanisms and consequences on neuronal function and mental health, and discuss Toxoplasma infection as a public health issue.

Toxoplasma gondii: Biological Parameters of the Connection to Schizophrenia

It is increasingly evident that the brain is not truly an immune privileged site and that cells of the central nervous system are sensitive to the inflammation generated when the brain is fighting off infection. Among the many microorganisms that have access to the brain, the apicomplexan protozoan Toxoplasma gondii has been one of the most studied. This parasite has been associated with many neuropsychiatric disorders including schizophrenia. This article provides a comprehensive review of the status of Toxoplasma research in schizophrenia. Areas of interest include (1) the limitations and improvements of immune-based assays to detect these infections in humans, (2) recent discoveries concerning the schizophrenia-Toxoplasma association, (3) findings of Toxoplasma neuropathology in animal models related to schizophrenia pathogenesis, (4) interactions of Toxoplasma with the host genome, (5) gastrointestinal effects of Toxoplasma infections, and (6) therapeutic intervention of Toxoplasma infections.

Mind Control: How Parasites Manipulate Cognitive Functions in Their Insect Hosts

Neuro-parasitology is an emerging branch of science that deals with parasites that can control the nervous system of the host. It offers the possibility of discovering how one species (the parasite) modifies a particular neural network, and thus particular behaviors, of another species (the host). Such parasite-host interactions, developed over millions of years of evolution, provide unique tools by which one can determine how neuromodulation up-or-down regulates specific behaviors. In some of the most fascinating manipulations, the parasite taps into the host brain neuronal circuities to manipulate hosts cognitive functions. To name just a few examples, some worms induce crickets and other terrestrial insects to commit suicide in water, enabling the exit of the parasite into an aquatic environment favorable to its reproduction. In another example of behavioral manipulation, ants that consumed the secretions of a caterpillar containing dopamine are less likely to move away from the caterpillar and more likely to be aggressive. This benefits the caterpillar for without its ant bodyguards, it is more likely to be predated upon or attacked by parasitic insects that would lay eggs inside its body. Another example is the parasitic wasp, which induces a guarding behavior in its ladybug host in collaboration with a viral mutualist. To exert long-term behavioral manipulation of the host, parasite must secrete compounds that act through secondary messengers and/or directly on genes often modifying gene expression to produce long-lasting effects.

AAH2 gene is not required for dopamine-dependent neurochemical and behavioral abnormalities produced by Toxoplasma infection in mouse

Infection with the protozoan parasite, Toxoplasma gondii (T. gondii), has been associated with the increased risk for several psychiatric disorders. The exact mechanisms of a hypothesized contribution of T. gondii infection are poorly understood. The T. gondii genome contains two aromatic amino acid hydroxylase genes (AAH1 and AAH2) that encode proteins that can produce L-DOPA. One popular hypothesis posits that these encoded enzymes might influence dopamine (DA) production and hence DA synaptic transmission, leading to neurobehavioral abnormalities in the infected host. Prior studies have shown that deletion of these genes does not alter DA levels in the brain or exploratory activity in infected mice. However, possible effects of AAH gene deficiency on infection-induced brain and behavior alterations that are directly linked to DA synaptic transmission have not been evaluated. We found that chronic T. gondii infection of BALB/c mice leads to blunted response to amphetamine or cocaine and decreased expression of Dopamine Transporter (DAT) and Vesicular Monoamine Transporter 2 (VMAT2). Deletion of AAH2 had no effects on these changes in infected mice. Both wild type and Δaah2 strains produced comparable levels of neuroinflammation. Our findings demonstrate that AAH2 is not required for T. gondii infection-produced DA-dependent neurobehavioral abnormalities.