Endothelial cell invasion by Toxoplasma gondii: differences between cell types and parasite strains

Modeling the human placental barrier to understand Toxoplasma gondii´s vertical transmission

Toxoplasma gondii is a ubiquitous apicomplexan parasite that can infect virtually any warm-blooded animal. Acquired infection during pregnancy and the placental breach, is at the core of the most devastating consequences of toxoplasmosis. T. gondii can severely impact the pregnancy’s outcome causing miscarriages, stillbirths, premature births, babies with hydrocephalus, microcephaly or intellectual disability, and other later onset neurological, ophthalmological or auditory diseases. To tackle T. gondii’s vertical transmission, it is important to understand the mechanisms underlying host-parasite interactions at the maternal-fetal interface. Nonetheless, the complexity of the human placenta and the ethical concerns associated with its study, have narrowed the modeling of parasite vertical transmission to animal models, encompassing several unavoidable experimental limitations. Some of these difficulties have been overcome by the development of different human cell lines and a variety of primary cultures obtained from human placentas. These cellular models, though extremely valuable, have limited ability to recreate what happens in vivo. During the last decades, the development of new biomaterials and the increase in stem cell knowledge have led to the generation of more physiologically relevant in vitro models. These cell cultures incorporate new dimensions and cellular diversity, emerging as promising tools for unraveling the poorly understood T. gondii´s infection mechanisms during pregnancy. Herein, we review the state of the art of 2D and 3D cultures to approach the biology of T. gondii pertaining to vertical transmission, highlighting the challenges and experimental opportunities of these up-and-coming experimental platforms.

Unifying Virulence Evaluation in Toxoplasma gondii: A Timely Task

Toxoplasma gondii, a major zoonotic pathogen, possess a significant genetic and phenotypic diversity that have been proposed to be responsible for the variation in clinical outcomes, mainly related to reproductive failure and ocular and neurological signs. Different T. gondii haplogroups showed strong phenotypic differences in laboratory mouse infections, which provide a suitable model for mimicking acute and chronic infections. In addition, it has been observed that degrees of virulence might be related to the physiological status of the host and its genetic background. Currently, mortality rate (lethality) in outbred laboratory mice is the most significant phenotypic marker, which has been well defined for the three archetypal clonal types (I, II and III) of T. gondii; nevertheless, such a trait seems to be insufficient to discriminate between different degrees of virulence of field isolates. Many other non-lethal parameters, observed both in in vivo and in vitro experimental models, have been suggested as highly informative, yielding promising discriminatory power. Although intra-genotype variations have been observed in phenotypic characteristics, there is no clear picture of the phenotypes circulating worldwide; therefore, a global overview of T. gondii strain mortality in mice is presented here. Molecular characterization has been normalized to some extent, but this is not the case for the phenotypic characterization and definition of virulence. The present paper proposes a baseline (minimum required information) for the phenotypic characterization of T. gondii virulence and intends to highlight the needs for consistent methods when a panel of T. gondii isolates is evaluated for virulence.

Evaluation of biological behavior of Toxoplasma gondii atypical isolates # 14 and # 163

Toxoplasma gondii is an obligate intracellular protozoan parasite capable of infecting warm-blooded animals, including humans. A highly diverse genetic population has been reported in Central and South America, predominating mainly atypical genotypes. Different genotypes showed different biological behavior in mice. The aim of this study was to evaluate the biological behavior of T. gondii isolates obtained from Macropus rufogriseus (TgMr) and Saimiri boliviensis (TgSb) identified as atypical genotypes # 14 and # 163, respectively. Strains RH, ME49 and VEG were used as reference for clonal types I, II and III, respectively. In vitro invasion and replication capacity assays were analyzed at 6 and 18 hpi, respectively. In vivo assay was performed in Swiss mice (n = 30) using 1 × 102 and 1 × 103 parasites/mouse as infective doses (ME49, VEG, TgMr, TgSb and negative control). Morbi-mortality and tissues PCR were assessed. Lymphoproliferation assays were performed and gamma interferon was measured by ELISA. The ME49 strain showed the highest invasion, followed by TgSb and VEG, while RH and TgMr presented the lowest invasions. The RH strain and the TgSb isolate showed more endodyogeny events (fastest doubling times) than VEG and ME49 strains and the TgMr isolate. Both atypical isolates showed high virulence (100% morbi-mortality, at 8-10 dpi) and parasite DNA was detected in all tissue samples. Splenocytes from mice inoculated with TgMr and TgSb registered the highest values of gamma interferon. An in vitro invasion-replication index was established which correlates inversely with virulence in mice. In conclusion, T. gondii atypical isolates # 14 and # 163 showed a different in vitro behavior than clonal strains, with low invasion-replication indexes but being highly virulent in mouse model.

Toxoplasma gondii: One Organism, Multiple Models

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

Toxoplasma gondii-skeletal muscle cells interaction increases lipid droplet biogenesis and positively modulates the production of IL-12, IFN-g and PGE2

Background

The interest in the mechanisms involved in Toxoplasma gondii lipid acquisition has steadily increased during the past few decades, but it remains not completely understood. Here, we investigated the biogenesis and the fate of lipid droplets (LD) of skeletal muscle cells (SkMC) during their interaction with T. gondii by confocal and electron microscopy. We also evaluated whether infected SkMC modulates the production of prostaglandin E₂ (PGE₂), cytokines interleukin-12 (IL-12) and interferon-gamma (INF-g), and also the cyclooxygenase-2 (COX-2) gene induction.

Methods

Primary culture of skeletal muscle cells were infected with tachyzoites of T. gondii and analysed by confocal microscopy for observation of LD. Ultrastructural cytochemistry was also used for lipid and sarcoplasmatic reticulum (SR) detection. Dosage of cytokines (IL-12 and INF-g) by ELISA technique and enzyme-linked immunoassay (EIA) for PGE₂ measurement were employed. The COX-2 gene expression analysis was performed by real time reverse transcriptase polymerase chain reaction (qRT-PCR).

Results

We demonstrated that T. gondii infection of SkMC leads to increase in LD number and area in a time course dependent manner. Moreover, the ultrastructural analysis demonstrated that SR and LD are in direct contact with parasitophorous vacuole membrane (PVM), within the vacuolar matrix, around it and interacting directly with the membrane of parasite, indicating that LD are recruited and deliver their content inside the parasitophorous vacuole (PV) in T. gondii-infected SkMC. We also observed a positive modulation of the production of IL-12 and IFN-g, increase of COX-2 mRNA levels in the first hour of T. gondii-SkMC interaction and an increase of prostaglandin E₂ (PGE₂) synthesis from 6 h up to 48 h of infection.

Conclusions

Taken together, the close association between SR and LD with PV could represent a source of lipids as well as other nutrients for the parasite survival, and together with the increased levels of IL-12, INF-g and inflammatory indicators PGE₂ and COX-2 might contribute to the establishment and maintenance of chronic phase of the T. gondii infection in muscle cell.