A Novel Trichomonas vaginalis Surface Protein Modulates Parasite Attachment via Protein:Host Cell Proteoglycan Interaction

Trichomonas vaginalis extracellular vesicles up-regulate and directly transfer adherence factors promoting host cell colonization

Trichomonas vaginalis, a common sexually transmitted parasite that colonizes the human urogenital tract, secretes extracellular vesicles (TvEVs) that are taken up by human cells and are speculated to be taken up by parasites as well. While the crosstalk between TvEVs and human cells has led to insight into host:parasite interactions, roles for TvEVs in infection have largely been one-sided, with little known about the effect of TvEV uptake by T. vaginalis. Approximately 11% of infections are found to be coinfections of multiple T. vaginalis strains. Clinical isolates often differ in their adherence to and cytolysis of host cells, underscoring the importance of understanding the effects of TvEV uptake within the parasite population. To address this question, our lab tested the ability of a less adherent strain of T. vaginalis, G3, to take up fluorescently labeled TvEVs derived from both itself (G3-EVs) and TvEVs from a more adherent strain of the parasite (B7RC2-EVs). Here, we showed that TvEVs generated from the more adherent strain are internalized more efficiently compared to the less adherent strain. Additionally, preincubation of G3 parasites with B7RC2-EVs increases parasite aggregation and adherence to host cells. Transcriptomics revealed that TvEVs up-regulate expression of predicted parasite membrane proteins and identified an adherence factor, heteropolysaccharide binding protein (HPB2). Finally, using comparative proteomics and superresolution microscopy, we demonstrated direct transfer of an adherence factor, cadherin-like protein, from TvEVs to the recipient parasite's surface. This work identifies TvEVs as a mediator of parasite:parasite communication that may impact pathogenesis during mixed infections.

Trichomonas vaginalis: Monolayer and Cluster Formation-Ultrastructural Aspects Using High-Resolution Scanning Electron Microscopy

Trichomonas vaginalis is an extracellular protozoan parasite that causes human trichomoniasis, a sexually transmitted infection (STI) that affects approximately 270 million people worldwide. The phenomenon of T. vaginalis adhesion to inert substrates has been described in several reports. Still, very few studies on cluster formation have been conducted, and more detailed analyses of the contact regions between the parasites' membranes in these aggregate formations have not been carried out. The present study aims to show that T. vaginalis forms a tight monolayer, similar to an epithelium, with parasites firmly adhered to the culture flask bottom by interdigitations and in the absence of host cells. In addition, we analyzed and compared the formation of the clusters, focusing on parasite aggregates that float in the culture flasks. We employed various imaging techniques, including high-resolution scanning electron microscopy, transmission electron microscopy, cytochemistry, TEM tomography, and dye injection. We analyzed whether the monolayer behaves as an epithelium, analyzing cell junctions, cell communication, and ultrastructural aspects, and concluded that monolayer formation differs from cluster formation in many aspects. The monolayers form strong adhesion, whereas the clusters have fragile attachments. We did not find fusion or the passage of molecules between neighbor-attached cells; there is no need for different strains to form filopodia, cytonemes, and extracellular vesicles during cluster and monolayer formation.

Trichomonas vaginalis adherence phenotypes and extracellular vesicles impact parasite survival in a novel in vivo model of pathogenesis

Trichomonas vaginalis is a human infective parasite responsible for trichomoniasis-the most common, non-viral, sexually transmitted infection worldwide. T. vaginalis resides exclusively in the urogenital tract of both men and women. In women, T. vaginalis has been found colonizing the cervix and vaginal tract while in men it has been identified in the upper and lower urogenital tract and in secreted fluids such as semen, urethral discharge, urine, and prostatic fluid. Despite the over 270 million cases of trichomoniasis annually worldwide, T. vaginalis continues to be a highly neglected organism and thus poorly studied. Here we have developed a male mouse model for studying T. vaginalis pathogenesis in vivo by delivering parasites into the murine urogenital tract (MUT) via transurethral catheterization. Parasite burden was assessed ex-vivo using a nanoluciferase-based gene expression assay which allowed quantification of parasites pre- and post-inoculation. Using this model and read-out approach, we show that T. vaginalis can be found within MUT tissue up to 72 hrs post-inoculation. Furthermore, we also demonstrate that parasites that exhibit increased parasite adherence in vitro also have higher parasite burden in mice in vivo. These data provide evidence that parasite adherence to host cells aids in parasite persistence in vivo and molecular determinants found to correlate with host cell adherence in vitro are applicable to infection in vivo. Finally, we show that co-inoculation of T. vaginalis extracellular vesicles (TvEVs) and parasites results in higher parasite burden in vivo. These findings confirm our previous in vitro-based predictions that TvEVs assist the parasite in colonizing the host. The establishment of this pathogenesis model for T. vaginalis sets the stage for identifying and examining parasite factors that contribute to and influence infection outcomes.

An Atypical F-Actin Capping Protein Modulates Cytoskeleton Behaviors Crucial for Trichomonas vaginalis Colonization

Cytoadherence and migration are crucial for pathogens to establish colonization in the host. In contrast to a nonadherent isolate of Trichomonas vaginalis, an adherent one expresses more actin-related machinery proteins with more active flagellate-amoeboid morphogenesis, amoeba migration, and cytoadherence, activities that were abrogated by an actin assembly blocker. By immunoprecipitation coupled with label-free quantitative proteomics, an F-actin capping protein (T. vaginalis F-actin capping protein subunit α [TvFACPα]) was identified from the actin-centric interactome. His-TvFACPα was detected at the barbed end of a growing F-actin filament, which inhibited elongation and possessed atypical activity in binding G-actin in in vitro assays. TvFACPα partially colocalized with F-actin at the parasite pseudopod protrusion and formed a protein complex with α-actin through its C-terminal domain. Meanwhile, TvFACPα overexpression suppressed F-actin polymerization, amoeboid morphogenesis, and cytoadherence in this parasite. Ser2 phosphorylation of TvFACPα enriched in the amoeboid stage of adhered trophozoites was reduced by a casein kinase II (CKII) inhibitor. Site-directed mutagenesis and CKII inhibitor treatment revealed that Ser2 phosphorylation acts as a switching signal to alter TvFACPα actin-binding activity and the consequent actin cytoskeleton behaviors. Through CKII signaling, TvFACPα also controls the conversion of adherent trophozoites from amoeboid migration to the flagellate form with axonemal motility. Together, CKII-dependent Ser2 phosphorylation regulates TvFACPα binding to actin to fine-tune cytoskeleton dynamics and drive crucial behaviors underlying host colonization by T. vaginalis. IMPORTANCE Trichomoniasis is one of the most prevalent nonviral sexually transmitted diseases. T. vaginalis cytoadherence to urogenital epithelium cells is the first step in the colonization of the host. However, studies on the mechanisms of cytoadherence have focused mainly on the role of adhesion molecules, and their effects are limited when analyzed by loss- or gain-of-function assays. This study proposes an extra pathway in which the actin cytoskeleton mediated by a capping protein α-subunit may play roles in parasite morphogenesis, cytoadherence, and motility, which are crucial for colonization. Once the origin of the cytoskeleton dynamics could be manipulated, the consequent activities would be controlled as well. This mechanism may provide new potential therapeutic targets to impair this parasite infection and relieve the increasing impact of drug resistance on clinical and public health.

The L-Rhamnose Biosynthetic Pathway in Trichomonas vaginalis: Identification and Characterization of UDP-D-Glucose 4,6-dehydratase

Trichomonas vaginalis is the causative agent of one of the most widespread sexually transmitted diseases in the world. The adhesion of the parasite to the vaginal epithelial cells is mediated by specific proteins and by a complex glycan structure, the lipoglycan (TvLG), which covers the pathogen surface. L-rhamnose is an important component of TvLG, comprising up to 40% of the monosaccharides. Thus, the inhibition of its production could lead to a severe alteration in the TvLG structure, making the L-rhamnose biosynthetic pathway an attractive pharmacologic target. We report the identification and characterization of the first committed and limiting step of the L-rhamnose biosynthetic pathway, UDP-D-glucose 4,6-dehydratase (UGD, EC 4.2.1.76). The enzyme shows a strong preference for UDP-D-glucose compared to dTDP-D-glucose; we propose that the mechanism underlying the higher affinity for the UDP-bound substrate is mediated by the differential recognition of ribose versus the deoxyribose of the nucleotide moiety. The identification of the enzymes responsible for the following steps of the L-rhamnose pathway (epimerization and reduction) was more elusive. However, sequence analyses suggest that in T. vaginalis L-rhamnose synthesis proceeds through a mechanism different from the typical eukaryotic pathways, displaying intermediate features between the eukaryotic and prokaryotic pathways and involving separate enzymes for the epimerase and reductase activities, as observed in bacteria. Altogether, these results form the basis for a better understanding of the formation of the complex glycan structures on TvLG and the possible use of L-rhamnose biosynthetic enzymes for the development of selective inhibitors.

The state of the art of extracellular vesicle research in protozoan infection

Protozoan diseases seriously affect the health of human beings, livestock and poultry and lead to high economic and medical costs. Extracellular vesicles (EVs) are membranous structures formed through biological processes that play important roles in immune regulation. Studies have shown that parasites transmit information to hosts through EVs to modulate host immune responses. The major roles played by EVs released from parasites involve facilitating parasitization of the host. In this review, we discuss relevant recently obtained data on EVs secreted by different kinds of protozoa, including their molecular mechanisms, and discuss the roles played by EVs in the occurrence and development of parasitic diseases.

Omics Analyses of Trichomonas vaginalis Actin and Tubulin and Their Participation in Intercellular Interactions and Cytokinesis

Actin and tubulin proteins from Trichomonas vaginalis are crucial for morphogenesis and mitosis. This parasite has 10 and 11 genes coding bonafide actin and tubulin proteins, respectively. Hence, the goal of this work was to analyze these actin and tubulin genes, their expression at the mRNA and protein levels, and their parasite localization in intercellular interaction and cytokinesis. Representative bonafide actin (tvact1) and tubulin (tvtubα1) genes were cloned into and expressed in Escherichia coli. The recombinant proteins TvACT1r and TvTUBα1r were affinity purified and used as antigens to produce polyclonal antibodies. These antibodies were used in 1DE and 2DE WB and indirect immunofluorescence assays (IFA). By IFA, actin was detected as a ring on the periphery of ameboid, ovoid, and cold-induced cyst-like parasites, on pseudopods of amoeboid parasites, and in cytoplasmic extensions (filopodia) in cell–cell interactions. Tubulin was detected in the axostyle, flagellum, undulating membrane, and paradesmose during mitosis. Paradesmose was observed by IFA mainly during cytokinesis. By scanning electron microscopy, a tubulin-containing nanotubular structure similar to the tunneling nanotubes (TNTs) was also detected in the last stage of cytokinesis. In conclusion, actin and tubulin are multigene families differentially expressed that play important roles in intercellular interactions and cytokinesis.

Proteomic Analysis of Trichomonas vaginalis Phagolysosome, Lysosomal Targeting, and Unconventional Secretion of Cysteine Peptidases

The lysosome represents a central degradative compartment of eukaryote cells, yet little is known about the biogenesis and function of this organelle in parasitic protists. Whereas the mannose 6-phosphate (M6P)-dependent system is dominant for lysosomal targeting in metazoans, oligosaccharide-independent sorting has been reported in other eukaryotes. In this study, we investigated the phagolysosomal proteome of the human parasite Trichomonas vaginalis, its protein targeting and the involvement of lysosomes in hydrolase secretion. The organelles were purified using Percoll and OptiPrep gradient centrifugation and a novel purification protocol based on the phagocytosis of lactoferrin-covered magnetic nanoparticles. The analysis resulted in a lysosomal proteome of 462 proteins, which were sorted into 21 classes. Hydrolases represented the largest functional class and included proteases, lipases, phosphatases, and glycosidases. Identification of a large set of proteins involved in vesicular trafficking (80) and turnover of actin cytoskeleton rearrangement (29) indicate a dynamic phagolysosomal compartment. Several cysteine proteases such as TvCP2 were previously shown to be secreted. Our experiments showed that secretion of TvCP2 was strongly inhibited by chloroquine, which increases intralysosomal pH, thus indicating that TvCP2 secretion occurs through lysosomes rather than the classical secretory pathway. Unexpectedly, we identified divergent homologues of the M6P receptor TvMPR in the phagolysosomal proteome, although T. vaginalis lacks enzymes for M6P formation. To test whether oligosaccharides are involved in lysosomal targeting, we selected the lysosome-resident cysteine protease CLCP, which possesses two glycosylation sites. Mutation of any of the sites redirected CLCP to the secretory pathway. Similarly, the introduction of glycosylation sites to secreted β-amylase redirected this protein to lysosomes. Thus, unlike other parasitic protists, T. vaginalis seems to utilize glycosylation as a recognition marker for lysosomal hydrolases. Our findings provide the first insight into the complexity of T. vaginalis phagolysosomes, their biogenesis, and role in the unconventional secretion of cysteine peptidases.

VPS32, a member of the ESCRT complex, modulates adherence to host cells in the parasite Trichomonas vaginalis by affecting biogenesis and cargo sorting of released extracellular vesicles

Trichomonas vaginalis is a common sexually transmitted extracellular parasite that adheres to epithelial cells in the human urogenital tract. Extracellular vesicles (EVs) have been described as important players in the pathogenesis of this parasite as they deliver proteins and RNA into host cells and modulate parasite adherence. EVs are heterogeneous membrane vesicles released from virtually all cell types that collectively represent a new dimension of intercellular communication. The Endosomal Sorting Complex Required for Transport (ESCRT) machinery contributes to several key mechanisms in which it reshapes membranes. Based on this, some components of the ESCRT have been implicated in EVs biogenesis in other cells. Here, we demonstrated that VPS32, a member of ESCRTIII complex, contribute to the biogenesis and cargo sorting of extracellular vesicles in the parasite T. vaginalis. Moreover, we observe that parasites overexpressing VPS32 have a striking increase in adherence to host cells compared to control parasites; demonstrating a key role for this protein in mediating host: parasite interactions. These results provide valuable information on the molecular mechanisms involved in extracellular vesicles biogenesis, cargo-sorting, and parasite pathogenesis.