Molecular basis of host epithelial cell recognition by Trichomonas vaginalis

Sandwich enzyme-linked aptamer-based assay for the detection of Trichomonas vaginalis

Trichomoniasis is the most prevalent curable, non-viral sexually transmitted infection (STI), with an estimated 156 million new infections in 2020. It can potentially result in adverse birth outcomes as well as infertility in men, whilst it also increases the risk of acquiring HIV and contracting other vaginal infections. It is mostly prevalent among women in low-income countries and especially in Africa and the Americas. This STI is caused by Trichomonas vaginalis (TV) and a robust, cost-effective, sensitive, specific and rapid diagnostic test is urgently required. We report the screening of 6 full-length and 4 truncated aptamers previously selected in our group for use in a microplate-based sandwich assay. The combination of dual aptamers comprising a short 14-mer truncated capture aptamer (termed A1_14mer) and a full-length non-truncated reporter aptamer (A6) was elucidated to be the optimum pair for a sensitive sandwich enzyme-linked aptamer assay (ELAA) for the detection of TV achieving a detection limit of 3.02 × 104 TV cells/mL. The results obtained with the A1_14mer-A6 ELAA correlate excellently with wet-mount microscopy for the detection of TV in clinical specimens, cervicovaginal lavages and vaginal swabs, highlighting the potential clinical application of this assay for cost-effective population screening and subsequent prevention of the onset of complications associated with undiagnosed and untreated TV.

Trichomonas vaginalis adhesion protein 65 (TvAP65) modulates parasite pathogenicity by interacting with host cell proteins

Trichomonas vaginalis (T. vaginalis) is a widespread and important sexually transmitted pathogen. Adherence to the surface of the host cell is the precondition forthis parasite's parasitism and pathogenicity. Adhesion protein 65 (TvAP65) plays a key role in the process of adhesion. However, how TvAP65 mediates the adhesion and pathogenicity of T. vaginalis to host cellsis unclear. In this study, we knocked down the expression of TvAP65 in trophozoites by small RNA interference. The number of T. vaginalis trophozoites adhering to VK2/E6E7 cells was decreased significantly, and the inhibition of VK2/E6E7 cells proliferation and VK2/E6E7 cells apoptosis and death induced by T. vaginalis were reduced, after the expression of TvAP65 was knocked down. Animal challenge experiments showed that the pathogenicity of trophozoites was decreased by passive immunization with anti-rTvAP65 PcAbs or blocking the TvAP65 protein. Immunofluorescence analysis showed that TvAP65 could bind to VK2/E6E7 cells. In order to screen the molecules interacting with TvAP65 on the host cells, we successfully constructed the cDNA library of VK2/E6E7 cells, and thirteen protein molecules interacting with TvAP65 were screened by yeast two-hybrid system. The interaction between TvAP65 and BNIP3 was further confirmed by coimmunoprecipitation and colocalization. When both TvAP65 and BNIP3 were knocked down by small RNA interference, the number of T. vaginalis adhering to VK2/E6E7 cells and the inhibition of VK2/E6E7 cells proliferation were significantly lower than those of the group with knockdown of TvAP65 or BNIP3 alone. Therefore, the interaction of TvAP65 and BNIP3 in the pathogenesis of T. vaginalis infecting host cells is not unique and involves other molecules. Our study elucidated that the interaction between TvAP65 and BNIP3 mediated the adhesion and pathogenicity of T. vaginalis to host cells, provided a basis for searching for the drug targets of anti-T. vaginalis, and afforded new ideas for the prevention and treatment of trichomoniasis.

The interaction between adhesion protein 33 (TvAP33) and BNIP3 mediates the adhesion and pathogenicity of Trichomonas vaginalis to host cells

BACKGROUND

Trichomonas vaginalis is a widespread and important sexually transmitted pathogen. Adherence to the surface of the host cell is the precondition for the parasitism and pathogenicity of this parasite. Trichomonas vaginalis adhesion protein 33 (TvAP33) plays a key role in the process of adhesion, but how this protein mediates the adhesion and pathogenicity of T. vaginalis to host cells is unclear.

METHODS

The expression of TvAP33 in trophozoites was knocked down by small interfering RNA. VK2/E6E7 cells and mice infected with T. vaginalis were used to evaluate the pathogenicity of T. vaginalis. We constructed a complementary DNA library of VK2/E6E7 cells and screened the protein molecules interacting with TvAP33 by the yeast two-hybrid system. The interaction between TvAP33 and BNIP3 (Bcl-2 interacting protein 3) was analyzed by co-immunoprecipitation and colocalization.

RESULTS

Following knockdown of TvAP33 expression, the number of T. vaginalis trophozoites adhering to VK2/E6E7 cells decreased significantly, and the inhibition of VK2/E6E7 cell proliferation and VK2/E6E7 cell apoptosis and death induced by T. vaginalis were reduced. Animal challenge experiments showed that the pathogenicity of trophozoites decreased following passive immunization with TvAP33 antiserum or blocking of the TvAP33 protein. Immunofluorescence analysis revealed that TvAP33 could bind to VK2/E6E7 cells. Eighteen protein molecules interacting with TvAP33 were identified by the yeast two-hybrid system. The interaction between TvAP33 and BNIP3 was further confirmed by co-immunoprecipitation and colocalization. When the expression of both TvAP33 and BNIP3 in trophozoites was knocked down by small RNA interference, the number of T. vaginalis adhering to VK2/E6E7 cells and the inhibition of VK2/E6E7 cell proliferation were significantly lower compared to trophozoites with only knockdown of TvAP33 or only BNIP3. Therefore, the interaction of TvAP33 and BNIP3 in the pathogenesis of T. vaginalis infecting host cells is not unique and involves other molecules.

CONCLUSIONS

Our study showed that the interaction between TvAP33 and BNIP3 mediated the adhesion and pathogenicity of T. vaginalis to host cells, providing a basis for searching for drug targets for T. vaginalis as well as new ideas for the prevention and treatment of trichomoniasis.

Roles of Cysteine Proteases in Biology and Pathogenesis of Parasites

Cysteine proteases, also known as thiol proteases, are a class of nucleophilic proteolytic enzymes containing cysteine residues in the enzymatic domain. These proteases generally play a pivotal role in many biological reactions, such as catabolic functions and protein processing, in all living organisms. They specifically take part in many important biological processes, especially in the absorption of nutrients, invasion, virulence, and immune evasion of parasitic organisms from unicellular protozoa to multicellular helminths. They can also be used as parasite diagnostic antigens and targets for gene modification and chemotherapy, as well as vaccine candidates, due to their species and even life-cycle stage specificity. This article highlights current knowledge on parasitic cysteine protease types, biological functions, and their applications in immunodiagnosis and chemotherapy.

Distinct features of the host-parasite interactions between nonadherent and adherent Trichomonas vaginalis isolates

Cytoadherence of Trichomonas vaginalis to human vaginal epithelial cells (hVECs) was previously shown to involve surface lipoglycans and several reputed adhesins on the parasite. Herein, we report some new observations on the host-parasite interactions of adherent versus nonadherent T. vaginalis isolates to hVECs. The binding of the TH17 adherent isolate to hVECs exhibited an initial discrete phase followed by an aggregation phase inhibited by lactose. T. vaginalis infection immediately induced surface expression of galectin-1 and -3, with extracellular amounts in the spent medium initially decreasing and then increasing thereafter over the next 60 min. Extracellular galectin-1 and -3 were detected on the parasite surface but only the TH17 adherent isolate could uptake galectin-3 via the lysosomes. Only the adherent isolate could morphologically transform from the round-up flagellate with numerous transient protrusions into a flat amoeboid form on contact with the solid surface. Cytochalasin D challenge revealed that actin organization was essential to parasite morphogenesis and cytoadherence. Real-time microscopy showed that parasite exploring and anchoring on hVECs via the axostyle may be required for initial cytoadherence. Together, the parasite cytoskeleton behaviors may collaborate with cell surface adhesion molecules for cytoadherence. The nonadherent isolate migrated faster than the adherent isolate, with motility transiently increasing in the presence of hVECs. Meanwhile, differential histone acetylation was detected between the two isolates. Also, TH17 without Mycoplasma symbiosis suggests that symbiont might not determine TH17 innate cytoadherence. Our findings regarding distinctive host-parasite interactions of the isolates may provide novel insights into T. vaginalis infection.

The molecular characterization and immune protection of adhesion protein 65 (AP65) of Trichomonas vaginalis

BACKGROUND

Adherence to the surface of the host cell is the precondition for T. vaginalis parasitism and pathogenicity, causing urogenital infection. The AP65 of T. vaginalis (TvAP65) involves in the process of adhesion. So, the present study was aimed at investigating the molecular characterization and vaccine candidacy of TvAP65 for protecting the host from the onset of Trichomoniasis.

METHODS

The open reading frame (ORF) of TvAP65 was amplified and then inserted into pET-32a (+) to clone recombinant TvAP65 (rTvAP65). The immunoblotting determined the immunogenicity and molecular size of TvAP65, while immunofluorescence staining visualized and the precise localization of TvAP65 in T. vaginalis trophozoites. Animal challenge and enzyme-linked immunosorbent assay (ELISA) test were used to evaluate the immunoprotection and the types of the immune response of TvAP65.

RESULTS

By the sequence analysis, TvAP65 encoded a 63.13 kDa protein that consisted 567 amino acid residues with a high antigenic index. The western blotting revealed that rTvAP65 and native TvAP65 could interact with the antibodies in the rat serums post hoc rTvAP65 immunization and the serums from the mice that were experimentally infected with T. vaginalis, respectively. Immunofluorescence stained TvAP65 on the surface of T. vaginalis trophozoites. Moreover, following emulsification with Freund's adjuvant, rTvAP65 was subsequently administered to BALB/c mice three times at 0, 2, and 4 weeks and the results from this animal challenge experiments showed significant increases in immunoglobulins of IgG2a, IgG1, and IgG, and cytokine of IFN-γ, and IL-2, and 10. Lastly, rTvAP65 vaccinated animals had a prolonged survival time (26.80 ± 4.05) after challenged by T. vaginalis.

CONCLUSIONS

TvAP65 mediated the adhesion of T. vaginalis to the host epithelia for the pathogenesis of the parasite and can be considered as a candidate protein for designing a functional vaccine that induces cell-mediated and humoral immunity against the T. vaginalis infection.

The Molecular Characterization and Immunity Identification of Trichomonas vaginalis Adhesion Protein 33 (AP33)

Trichomoniasis is caused by Trichomonas vaginalis (T. vaginalis), which is a widespread and serious sexually transmitted pathogen in humans. The procedure of T. vaginalis adherence to the host cell is the precondition for T. vaginalis parasitism and pathogenicity. The AP33 adhesin of T. vaginalis (TvAP33) plays a key role in the process of adhesion. In this study, the specific primers for polymerase chain reaction (PCR) were designed based on the sequence of TvAP33 (GenBank Accession No. U87098.1) to amplify the open reading frame (ORF), and the ORF was inserted into pET-32a (+) to produce recombinant TvAP33 (rTvAP33). The sequence analysis indicated that the TvAP33 gene encoded a protein of 309 amino acids with 32.53 kDa, and the protein was predicted to have a high antigen index. Western blotting assay showed rTvAP33 was successfully recognized by the sera of mice experimentally infected with T. vaginalis, while native TvAP33 in the somatic extract of T. vaginalis trophozoite was as well detected by sera from rats immunized with the rTvAP33. Immunofluorescence analysis using an antibody against rTvAP33 demonstrated that the protein was expressed and located on the surface of T. vaginalis trophozoites. The recombinant protein was emulsified in Freund's adjuvant and used to immunize BALB/C mice three times at days 0, 14, and 28. The result of animal challenge experiments revealed the levels of IgG, IgG1, and IgG2a, and IL-4, IL-10, and IL17 among rTvAP33 vaccinated animals were integrally increased. Moreover, the rTvAP33 vaccinated animals were apparently prolonged survival time (26.45 ± 4.10) after challenge infection with this parasite. All these results indicated that TvAP33 could be used as vaccine candidate antigen to induce cell-mediated and humoral immunity.

Microbiota in vaginal health and pathogenesis of recurrent vulvovaginal infections: a critical review

Recurrent vulvovaginal infections (RVVI) has not only become an epidemiological and clinical problem but also include large social and psychological consequences. Understanding the mechanisms of both commensalism and pathogenesis are necessary for the development of efficient diagnosis and treatment strategies for these enigmatic vaginal infections. Through this review, an attempt has been made to analyze vaginal microbiota (VMB) from scratch and to provide an update on its current understanding in relation to health and common RVVI i.e. bacterial vaginosis, vulvovaginal candidiaisis and Trichomoniasis, making the present review first of its kind. For this, potentially relevant studies were retrieved from data sources and critical analysis of the literature was made. Though, culture-independent methods have greatly unfolded the mystery regarding vaginal bacterial microbiome, there are only a few studies regarding the composition and diversity of vaginal mycobiome and different Trichomonas vaginalis strains. This scenario suggests a need of further studies based on comparative genomics of RVVI pathogens to improve our perceptive of RVVI pathogenesis that is still not clear (Fig. 5). Besides this, the review details the rationale for Lactobacilli dominance and changes that occur in healthy VMB throughout a women's life. Moreover, the list of possible agents continues to expand and new species recognised in both health and VVI are updated in this review. The review concludes with the controversies challenging the widely accepted dogma i.e. "VMB dominated with Lactobacilli is healthier than a diverse VMB". These controversies, over the past decade, have complicated the definition of vaginal health and vaginal infections with no definite conclusion. Thus, further studies on newly recognised microbial agents may reveal answers to these controversies. Conversely, VMB of women could be an answer but it is not enough to just look at the microbiology. We have to look at the woman itself, as VMB which is fine for one woman may be troublesome for others. These differences in women's response to the same VMB may be determined by a permutation of behavioural, cultural, genetic and various other anonymous factors, exploration of which may lead to proper definition of vaginal health and disease.

Characterization of a novel endogenous cysteine proteinase inhibitor, trichocystatin-3 (TC-3), localized on the surface of Trichomonas vaginalis

Trichomonas vaginalis is a flagellated protist responsible for human trichomoniasis. T. vaginalis has three genes encoding for endogenous cysteine proteinase (CP) inhibitors, known as trichocystatin-1 through trichocystatin-3 (TC-1, TC-2, and TC-3). These inhibitors belong to the cystatin family. In this study, we characterized trichocystatin-3 (TC-3), an endogenous cysteine proteinase (CP) inhibitor of T. vaginalis. TC-3 possesses a signal peptide in the N-terminus and two putative glycosylation sites (typical of family 2, cystatins) but lacks the PW motif and cysteine residues (typical of family 1, stefins). Native TC-3 was recognized as an ∼18 kDa protein band in a T. vaginalis protein extract. By confocal microscopy, endogenous TC-3 was found in the Golgi complex, cytoplasm, large vesicles, and the plasma membrane. These localizations are consistent with an in silico prediction. In addition, the purified recombinant protein (TC-3r) functions as an inhibitor of cathepsin L CPs, such as human liver cathepsin L and trichomonad CPs, present in a proteinase-resistant extract (PRE). Via a pull-down assay using TC-3r as bait and PRE, we identified several trichomonad CPs targeted by TC-3, primarily TvCP3. These CP-TC-3 interactions occur in vesicles, in the cytoplasm, and on the parasite surface. In addition, TC-3r showed a protective effect on HeLa cell monolayers by inhibiting trichomonad surface CPs involved in cellular damage. Our results show that the endogenous inhibitor TC-3 plays a key role in the regulation of endogenous CP proteolytic activity.

A secreted Heat shock protein 90 of Trichomonas vaginalis

Trichomonas vaginalis is a causative agent of Trichomoniasis, a leading non-viral sexually transmitted disease worldwide. In the current study, we show Heat shock protein 90 is essential for its growth. Upon genomic analysis of the parasite, it was found to possess seven ORFs which could potentially encode Hsp90 isoforms. We identified a cytosolic Hsp90 homolog, four homologs which can align to truncated cytosolic Hsp90 gene products along with two Grp94 homologs (ER isoform of Hsp90). However, both Grp94 orthologs lacked an ER retention motif. In cancer cells, it is very well established that Hsp90 is secreted and regulates key clients involved in metastases, migration, and invasion. Since Trichomonas Grp94 lacks ER retention motif, we examined the possibility of its secretion. By using cell biology and biochemical approaches we show that the Grp94 isoform of Hsp90 is secreted by the parasite by the classical ER-Golgi pathway. This is the first report of a genome encoded secreted Hsp90 in a clinically important parasitic protozoan.

Hsp90 is an essential chaperone in eukaryotes and it is often described as a master regulator of cellular homeostasis. In addition to its well-known functions inside the cell, extracellular Hsp90 has also been implicated in migration and invasion of tumor cells. We have, for the first time, identified the presence of an extracellular Hsp90 in a parasitic protozoan, Trichomonas vaginalis. The extracellular Hsp90 is a Grp94 homolog that lacks a canonical ER retention signal. Our analysis of Grp94 sequences from protozoa shows that it is uncommon for a Grp94 to lack ER retention signal. In the current study, we characterized the biochemical parameters and established the extracellular localization of this Hsp90 paralog. This secreted Hsp90 in Trichomonas can potentially modulate host-pathogen interaction.

Detecting the Diversity of Mycoplasma and Ureaplasma Endosymbionts Hosted by Trichomonas vaginalis Isolates

Objectives: The symbiosis of Trichomonas vaginalis and Mycoplasma hominis is the first described association between two obligate human parasites. Trichomonas is the niche and the vector for the transmission of M. hominis infection. This clinically significant symbiosis may affect T. vaginalis virulence and susceptibility to treatment. The aims of this study were to investigate the intracellularly present Mycoplasma and Ureaplasma species in T. vaginalis strains isolated from the vaginal discharge of infected women as well as to trace the diversity pattern among the species detected in the isolated strains. Methods: Hundred pure T. vaginalis cultures were isolated from ~7,500 patient specimens presented with clinical purulent vaginitis. PCR and sequencing for Mycoplasma/Ureaplasma spp. were performed in DNA extracted from the pure cultures. In addition, vaginal discharge samples were cultured for the presence of M. hominis and U. urealyticum. Phylogenetic analysis assisted the identification of interspecies relationships between the Mycoplasma and Ureaplasma isolates. Results: Fifty four percentage of T. vaginalis isolates were harboring Mycoplasma spp. Phylogenetic analysis revealed three distinct clusters, two with already characterized M. hominis and Ureaplasma spp. (37% of total Mycoplasma spp.), whereas one group formed a distinct cluster matched with the newly identified species Candidatus Mycoplasma girerdii (59.3%) and one or more unknown Mycoplasma spp. (3.7%). Conclusions:T. vaginalis strains associated with vaginal infection might host intracellular mycoplasmas or ureaplasmas. Intracellular Mollicutes that remain undetected in the extracellular environment when conventional diagnostic methods are implemented may comprise either novel species, such as Candidatus M. giredii, or unknown species with yet unexplored clinical significance.

Adenosine, but not guanosine, protects vaginal epithelial cells from Trichomonas vaginalis cytotoxicity

Trichomonas vaginalis causes the most common non-viral sexually transmitted disease worldwide. The cytoadherence and cytotoxicity upon the vaginal epithelial cells are crucial for the infection. Extracellular nucleotides are released during cell damage and, along with their nucleosides, can activate purinoceptors. The opposing effects of nucleotides versus nucleosides are regulated by ectonucleotidases. Herein we evaluated the hemolysis and cytolysis induced by T. vaginalis, as well as the extracellular nucleotide hydrolysis along with the effects mediated by nucleotides and nucleosides on cytotoxicity. In addition, the gene expression of purinoceptors in host cells was determined. The hemolysis and cytolysis exerted by all T. vaginalis isolates presented positive Pearson correlation. All T. vaginalis isolates were able to hydrolyze nucleotides, showing higher NTPDase than ecto-5'-nucleotidase activity. The most cytotoxic isolate, TV-LACM6, hydrolyzes ATP, GTP with more efficiency than AMP and GMP. The vaginal epithelial cell line (HMVII) expressed the genes for all subtypes of P1, P2X and P2Y receptors. Finally, when nucleotides and nucleosides were tested, the cytotoxic effect elicited by TV-LACM6 was increased with nucleotides. In contrast, the cytotoxicity was reversed by adenosine in presence of EHNA, but not by guanosine, contributing to the understanding of the purinergic signaling role on T. vaginalis cytotoxicity.

The Glycolytic Enzyme Triosephosphate Isomerase of Trichomonas vaginalis Is a Surface-Associated Protein Induced by Glucose That Functions as a Laminin- and Fibronectin-Binding Protein

Triosephosphate isomerase of Trichomonas vaginalis (TvTIM) is a 27-kDa cytoplasmic protein encoded by two genes, tvtim1 and tvtim2, that participates in glucose metabolism. TvTIM is also localized to the parasite surface. Thus, the goal of this study was to identify the novel functions of the surface-associated TvTIM in T. vaginalis and to assess the effect of glucose as an environmental factor that regulates its expression and localization. Reverse transcription-PCR (RT-PCR) showed that the tvtim genes were differentially expressed in response to glucose concentration. tvtim1 was overexpressed under glucose-restricted (GR) conditions, whereas tvtim2 was overexpressed under glucose-rich, or high-glucose (HG), conditions. Western blot and indirect immunofluorescence assays also showed that glucose positively affected the amount and surface localization of TvTIM in T. vaginalis Affinity ligand assays demonstrated that the recombinant TvTIM1 and TvTIM2 proteins bound to laminin (Lm) and fibronectin (Fn) but not to plasminogen. Moreover, higher levels of adherence to Lm and Fn were detected in parasites grown under HG conditions than in those grown under GR conditions. Furthermore, pretreatment of trichomonads with an anti-TvTIMr polyclonal antibody or pretreatment of Lm- or Fn-coated wells with both recombinant proteins (TvTIM1r and TvTIM2r) specifically reduced the binding of live parasites to Lm and Fn in a concentration-dependent manner. Moreover, T. vaginalis was exposed to different glucose concentrations during vaginal infection of women with trichomoniasis. Our data indicate that TvTIM is a surface-associated protein under HG conditions that mediates specific binding to Lm and Fn as a novel virulence factor of T. vaginalis.

Trichomoniasis - are we giving the deserved attention to the most common non-viral sexually transmitted disease worldwide?

ETIOLOGY

Trichomonas vaginalis is the etiologic agent of trichomoniasis, the most common non-viral sexually transmitted disease (STD) in the world. Transmission: Trichomoniasis is transmitted by sexual intercourse and transmission via fomites is rare. Epidemiology, incidence and prevalence: The WHO estimates an incidence of 276 million new cases each year and prevalence of 187 million of infected individuals. However, the infection is not notifiable. Pathology/Symptomatology: The T. vaginalis infection results in a variety of clinical manifestations - in most cases the patients are asymptomatic, but some may develop signs typically associated to the disease. Importantly, the main issue concerning trichomoniasis is its relationship with serious health consequences such as cancer, adverse pregnancy outcomes, infertility, and HIV acquisition. Molecular mechanisms of infection: To achieve success in parasitism trichomonads develop a complex process against the host cells that includes dependent- and independent-contact mechanisms. This multifactorial pathogenesis includes molecules such as soluble factors, secreted proteinases, adhesins, lipophosphoglycan that culminate in cytoadherence and cytotoxicity against the host cells. Treatment and curability: The treatment with metronidazole or tinidazole is recommended; however, cure failures remain problematic due to noncompliance, reinfection and/or lack of treatment of sexual partners, inaccurate diagnosis, or drug resistance. Therefore, new therapeutic alternatives are urgently needed. Protection: Strategies for protection including sexual behavior, condom usage, and therapy have not contributed to the decrease on disease prevalence, pointing to the need for innovative approaches. Vaccine development has been hampered by the lack of long-lasting humoral immunity associated to the absence of good animal models.

Mechanisms of Tritrichomonas foetus Pathogenicity in Cats with Insights from Venereal Trichomonosis

Almost 20 years has passed since trichomonosis was first recognized as a potential cause of diarrhea in domestic cats. Despite progress in confirming disease causation, developing means for diagnosis, and identifying approaches to treatment of the infection, we still know very little about how this parasite causes diarrhea. With increasing recognition of resistance of trichomonosis to treatment with 5‐nitroimidazole drugs, new treatment strategies based on an understanding of disease pathogenesis are needed. In this review, lessons learned from the pathogenesis of venereal trichomonosis in people and cattle are applied to clinical observations of trichomonosis in cats in effort to generate insight into areas where further research may be beneficial.

Exploring the mechanism of how tvMyb2 recognizes and binds ap65-1 by molecular dynamics simulations and free energy calculations

Molecular dynamic simulations and MMPBSA calculations of tvMyb2-ap65-1 complex and its mutants, our work give important information to understand the interactions between tvMyb2-ap65-1.

RNA-Binding Proteins in Trichomonas vaginalis: Atypical Multifunctional Proteins

Iron homeostasis is highly regulated in vertebrates through a regulatory system mediated by RNA-protein interactions between the iron regulatory proteins (IRPs) that interact with an iron responsive element (IRE) located in certain mRNAs, dubbed the IRE-IRP regulatory system. Trichomonas vaginalis, the causal agent of trichomoniasis, presents high iron dependency to regulate its growth, metabolism, and virulence properties. Although T. vaginalis lacks IRPs or proteins with aconitase activity, possesses gene expression mechanisms of iron regulation at the transcriptional and posttranscriptional levels. However, only one gene with iron regulation at the transcriptional level has been described. Recently, our research group described an iron posttranscriptional regulatory mechanism in the T. vaginalis tvcp4 and tvcp12 cysteine proteinase mRNAs. The tvcp4 and tvcp12 mRNAs have a stem-loop structure in the 5'-coding region or in the 3'-UTR, respectively that interacts with T. vaginalis multifunctional proteins HSP70, α-Actinin, and Actin under iron starvation condition, causing translation inhibition or mRNA stabilization similar to the previously characterized IRE-IRP system in eukaryotes. Herein, we summarize recent progress and shed some light on atypical RNA-binding proteins that may participate in the iron posttranscriptional regulation in T. vaginalis.

The Pathogenesis of Human Cervical Epithelium Cells Induced by Interacting with Trichomonas vaginalis

BACKGROUND

Trichomonas vaginalis is a protozoan parasite that occurs in the urogenital-vaginal tract and is the primary causative agent of trichomoniasis, a common sexually transmitted disease in humans. The aggregation of this protozoan tends to destroy epithelial cells and induce pathogenesis.

PRINCIPAL FINDINGS

This study cultured T. vaginalis and human cervical epithelial cells (Z172) under the same conditions in the experiments. Following co-culturing for ten hours, the protozoans became attached to Z172, such that the cells presented a round shape and underwent shrinkage. Time-lapse recording and flow cytometry on interacted Z172 revealed that 70% had been disrupted, 18% presented a necrosis-like morphology and 8% showed signs of apoptosis. Gene expression profiling revealed in the seven inflammatory Z172 genes as well as in T. vaginalis genes that code for adhesion proteins 65 and 65-1.

SIGNIFICANCE

These results suggest that cytopathogenic effects progress while Z172 is in contact with T. vaginalis, and the resulting morphological changes can be categorized as disruption.

The biology of Trichomonas vaginalis in the light of urogenital tract infection

The human pathogen Trichomonas vaginalis is a parasitic protist. It is a representative of the eukaryotic supergroup Excavata that includes a few other protist parasites such as Leishmania, Trypanosoma and Giardia. T. vaginalis is the agent of trichomoniasis and in the US alone, one in 30 women tests positive for this parasite. The disease is easily treated with metronidazole in most cases, but resistant strains are on the rise. The biology of Trichomonas is remarkable: it includes for example the biggest protist genome currently sequenced, the expression of about 30,000 protein-encoding genes (and thousands of lncRNAs and pseudogenes), anaerobic hydrogenosomes, rapid morphogenesis during infection, the secretion of exosomes, the manipulation of the vaginal microbiota through phagocytosis and a rich strain-dependent diversity. Here we provide an overview of Trichomonas biology with a focus on its relevance for pathogenicity and summarise the most recent advances. With some respect this parasite offers the opportunity to serve as a model system to study certain aspects of cell and genome biology, but tackling the complex biology of T. vaginalis is also important to better understand the effects that accompany infection and direct symptoms.

Immunity in urogenital protozoa

Innate and adaptive immunity play a significant role in urogenital infections. Innate immunity is provided by the epithelial cells and mucus lining along with acidic pH, which forms a strong physical barrier against the pathogens in female reproductive tract. Cells of innate immune system, antimicrobial peptides, cytokines, chemokines and adaptive immunity in the reproductive tract are evolved during infection, and a pro-inflammatory response is generated to fight against the invading pathogen Trichomonas vaginalis, a primary urogenital protozoa, the etiological agent of human trichomoniasis, a curable sexually transmitted infection. The involvement of the urogenital tract by other protozoal infections such as P. falciparum, Trypanosoma, Leishmania, Toxoplasma, Entamoeba histolytica and Acanthamoeba infection is rarely reported. Trichomonas induce pro-inflammatory and immunosuppressive responses in infected subjects. Multifactorial pathogenic mechanisms including parasite adherence, cysteine proteases, lipophosphoglycan, free radical, cytokine generation and Toll-like receptors appear to interplay with the induction of local and systemic immune responses that ultimately determine the outcome of the infection. However, the involvement of urogenital pathogen-specific immune mechanisms and effect of normal local resident flora on the outcome (symptomatic vs. asymptomatic) of infection are poorly understood. Moreover, immune interactions in trichomoniasis subjects co-infected with bacterial and viral pathogens need to be elucidated.

Trichomonas vaginalis: Clinical relevance, pathogenicity and diagnosis

Trichomonas vaginalis is the etiological agent of trichomoniasis, the most prevalent non-viral sexually transmitted disease worldwide. Trichomoniasis is a widespread, global health concern and occurring at an increasing rate. Infections of the female genital tract can cause a range of symptoms, including vaginitis and cervicitis, while infections in males are generally asymptomatic. The relatively mild symptoms, and lack of evidence for any serious sequelae, have historically led to this disease being under diagnosed, and under researched. However, growing evidence that T. vaginalis infection is associated with other disease states with high morbidity in both men and women has increased the efforts to diagnose and treat patients harboring this parasite. The pathology of trichomoniasis results from damage to the host epithelia, caused by a variety of processes during infection and recent work has highlighted the complex interactions between the parasite and host, commensal microbiome and accompanying symbionts. The commercial release of a number of nucleic acid amplification tests (NAATs) has added to the available diagnostic options. Immunoassay based Point of Care testing is currently available, and a recent initial evaluation of a NAAT Point of Care system has given promising results, which would enable testing and treatment in a single visit.

Biological roles of cysteine proteinases in the pathogenesis of Trichomonas vaginalis

Human trichomonosis, infection with Trichomonas vaginalis, is the most common non-viral sexually transmitted disease in the world. The host-parasite interaction and pathophysiological processes of trichomonosis remain incompletely understood. This review focuses on the advancements reached in the area of the pathogenesis of T. vaginalis, especially in the role of the cysteine proteinases. It highlights various approaches made in this field and lists a group of trichomonad cysteine proteinases involved in diverse processes such as invasion of the mucous layer, cytoadherence, cytotoxicity, cytoskeleton disruption of red blood cells, hemolysis, and evasion of the host immune response. A better understanding of the biological roles of cysteine proteinases in the pathogenesis of this parasite could be used in the identification of new chemotherapeutic targets. An additional advantage could be the development of a vaccine in order to reduce transmission of T. vaginalis.

Cysteine protease activity of feline Tritrichomonas foetus promotes adhesion-dependent cytotoxicity to intestinal epithelial cells

Trichomonads are obligate protozoan parasites most renowned as venereal pathogens of the reproductive tract of humans and cattle. Recently, a trichomonad highly similar to bovine venereal Tritrichomonas foetus but having a unique tropism for the intestinal tract was recognized as a significant cause of colitis in domestic cats. Despite a high prevalence, worldwide distribution, and lack of consistently effective drugs for treatment of the infection, the cellular mechanisms of T. foetus pathogenicity in the intestinal tract have not been examined. The aims of this study were to determine the pathogenic effect of feline T. foetus on porcine intestinal epithelial cells, the dependence of T. foetus pathogenicity on adhesion of T. foetus to the intestinal epithelium, and the identity of mediators responsible for these effects. Using an in vitro coculture approach to model feline T. foetus infection of the intestinal epithelium, these studies demonstrate that T. foetus promotes a direct contact-dependent activation of intestinal epithelial cell apoptosis signaling and progressive monolayer destruction. Moreover, these pathological effects were demonstrated to be largely dependent on T. foetus cell-associated cysteine protease activity. Finally, T. foetus cysteine proteases were identified as enabling cytopathic effects by promoting adhesion of T. foetus to the intestinal epithelium. The present studies are the first to examine the cellular mechanisms of pathogenicity of T. foetus toward the intestinal epithelium and support further investigation of the cysteine proteases as virulence factors in vivo and as potential therapeutic targets for ameliorating the pathological effects of intestinal trichomonosis.

α -Actinin TvACTN3 of Trichomonas vaginalis is an RNA-binding protein that could participate in its posttranscriptional iron regulatory mechanism

Trichomonas vaginalis is a sexually transmitted flagellated protist parasite responsible for trichomoniasis. This parasite is dependent on high levels of iron, favoring its growth and multiplication. Iron also differentially regulates some trichomonad virulence properties by unknown mechanisms. However, there is evidence to support the existence of gene regulatory mechanisms at the transcriptional and posttranscriptional levels that are mediated by iron concentration in T. vaginalis. Thus, the goal of this study was to identify an RNA-binding protein in T. vaginalis that interacts with the tvcp4 RNA stem-loop structure, which may participate in a posttranscriptional iron regulatory mechanism mediated by RNA-protein interactions. We performed RNA electrophoretic mobility shift assay (REMSA) and supershift, UV cross-linking, Northwestern blot, and western blot (WB) assays using cytoplasmic protein extracts from T. vaginalis with the tvcp4 RNA hairpin structure as a probe. We identified a 135-kDa protein isolated by the UV cross-linking assays as α-actinin 3 (TvACTN3) by MALDI-TOF-MS that was confirmed by LS-MS/MS and de novo sequencing. TvACTN3 is a cytoplasmic protein that specifically binds to hairpin RNA structures from trichomonads and humans when the parasites are grown under iron-depleted conditions. Thus, TvACTN3 could participate in the regulation of gene expression by iron in T. vaginalis through a parallel posttranscriptional mechanism similar to that of the IRE/IRP system.

Structural and thermodynamic folding characterization of triosephosphate isomerases from Trichomonas vaginalis reveals the role of destabilizing mutations following gene duplication

We report the structures and thermodynamic analysis of the unfolding of two triosephosphate isomerases (TvTIM1 and TvTIM2) from Trichomonas vaginalis. Both isoforms differ by the character of four amino acids: E/Q 18, I/V 24, I/V 45, and P/A 239. Despite the high sequence and structural similarities between both isoforms, they display substantial differences in their stabilities. TvTIM1 (E18, I24, I45, and P239) is more stable and less dissociable than TvTIM2 (Q18, V24, V45, and A239). We postulate that the identities of residues 24 and 45 are responsible for the differences in monomer stability and dimer dissociability, respectively. The structural difference between both amino acids is one methyl group. In TvTIMs, residue 24 is involved in packing α-helix 1 against α-helix 2 of each monomer and residue 45 is located at the center of the dimer interface forming a "ball and socket" interplay with a hydrophobic cavity. The mutation of valine at position 45 for an alanine in TvTIM2 produces a protein that migrates as a monomer by gel filtration. A comparison with known TIM structures indicates that this kind of interplay is a conserved feature that stabilizes dimeric TIM structures. In addition, TvTIMs are located in the cytoplasm and in the membrane. As TvTIM2 is an easily dissociable dimer, the dual localization of TvTIMs may be related to the acquisition of a moonlighting activity of monomeric TvTIM2. To our knowledge, this is the simplest example of how a single amino acid substitution can provide alternative function to a TIM barrel protein.

Sphingomyelinase activity of Trichomonas vaginalis extract and subfractions

Trichomoniasis is one of the most common acute sexually transmitted curable diseases, and it is disseminated worldwide generating more than 170 million cases annually. Trichomonas vaginalis is the parasite that causes trichomoniasis and has the ability to destroy cell monolayers of the vaginal mucosa in vitro. Sphingomyelinases (SMase) are enzymes that catalyze the hydrolysis of sphingomyelin into ceramide and phosphorylcholine. Ceramide appears to be a second messenger lipid in programmed apoptosis, cell differentiation, and cell proliferation. Sphingomyelinase is probably a major source of ceramide in cells. Signal transduction mediated by ceramide leads cells to produce cytokine induced apoptosis during several inflammatory responses. SMase are also relevant toxins in several microorganisms. The main objective of this research is to identify SMase activity of T. vaginalis in the total extract (TE), P30, and S30 subfractions from brooked trophozoites. It was found that these fractions of T. vaginalis have SMase activity, which comes principally from P30 subfraction and was mainly type C. Enzymatic activity of SMase increased linearly with time and is pH dependent with two peaks by pH 5.5 and pH 7.5. The addition of manganese to the reaction mixture increased the SMase activity by 1.97.

TvMP50 is an immunogenic metalloproteinase during male trichomoniasis

Trichomonas vaginalis, a human urogenital tract parasite, is capable of surviving in the male microenvironment, despite of the presence of Zn(2+). Concentrations > 1.6 mM of Zn(2+) have a trichomonacidal effect; however, in the presence of ≤1.6 mM Zn(2+), several trichomonad proteins are up- or down-regulated. Herein, we analyzed the proteome of a T. vaginalis male isolate (HGMN01) grown in the presence of Zn(2+) and found 32 protein spots that were immunorecognized by male trichomoniasis patient serum. Using mass spectrometry (MS), the proteins were identified and compared with 23 spots that were immunorecognized in the proteome of a female isolate using the same serum. Interestingly, we found a 50-kDa metallopeptidase (TvMP50). Unexpectedly, this proteinase was immunodetected by the serum of male trichomoniasis patients but not by the female patient serum or sera from healthy men and women. We analyzed the T. vaginalis genome and localized the mp50 gene in locus TVAG_403460. Using an RT-PCR assay, we amplified a 1320-bp mp50 mRNA transcript that was expressed in the presence of Zn(2+) in the HGMN01 and CNCD147 T. vaginalis isolates. According to a Western blot assay, native TvMP50 was differentially expressed in the presence of Zn(2+). The TvMP50 proteolytic activity increased in the presence of Zn(2+) in both isolates and was inhibited by EDTA but not by ptosyl-L-lysine chloromethyl ketone (TLCK), E64, leupeptin, or phenylmethane sulfonyl fluoride. Furthermore, the recombinant TvMP50 had proteolytic activity that was inhibited by EDTA. These data suggested that TvMP50 is immunogenic during male trichomoniasis, and Zn(2+) induces its expression.

Analysis of the NTPDase and ecto-5'-nucleotidase profiles in serum-limited Trichomonas vaginalis

Trichomonas vaginalis is a parasite of the human urogenital tract that causes trichomonosis, the most prevalent non-viral sexually transmitted disease. Ectonucleoside triphosphate diphosphohydrolase (NTPDase) family members, which hydrolyse extracellular ATP and ADP and ecto-5'-nucleotidase, which hydrolyses AMP, have been characterised in T. vaginalis. For trichomonad culture, the growth medium is supplemented with 10% serum, which is an important source of nutrients, such as adenosine. Here, we investigated the ATP metabolism of T. vaginalis trophozoites from long-term cultures and clinical isolates under limited bovine serum conditions (1% serum). The specific enzymatic activities were expressed as nmol inorganic phosphate (Pi) released/min/mg protein, the gene expression patterns were determined by reverse transcriptase-polymerase chain reaction, the extracellular adenine nucleotide hydrolysis was analysed by high performance liquid chromatography and the cell cycle analysis was assessed by flow cytometry. Serum limitation led to the profound activation of NTPDase and ecto-5'-nucleotidase activities. Furthermore, the levels of NTPDase A and B transcripts increased and extracellular ATP metabolism was activated, which led to enhanced ATP hydrolysis and the formation of ADP and AMP. Moreover, the cell cycle was arrested at the G0/G1 stage, which suggested adenosine uptake. Our data suggest that under conditions of serum limitation, NTPDase and ecto-5'-nucleotidase play a role in providing the adenosine required for T. vaginalis growth and that this process contributes to the establishment of parasitism.

The TvLEGU-1, a legumain-like cysteine proteinase, plays a key role in Trichomonas vaginalis cytoadherence

The goal of this paper was to characterize a Trichomonas vaginalis cysteine proteinase (CP) legumain-1 (TvLEGU-1) and determine its potential role as a virulence factor during T. vaginalis infection. A 30-kDa band, which migrates in three protein spots (pI~6.3, ~6.5, and ~6.7) with a different type and level of phosphorylation, was identified as TvLEGU-1 by one- and two-dimensional Western blot (WB) assays, using a protease-rich trichomonad extract and polyclonal antibodies produced against the recombinant TvLEGU-1 (anti-TvLEGU-1r). Its identification was confirmed by mass spectrometry. Immunofluorescence, cell binding, and WB assays showed that TvLEGU-1 is upregulated by iron at the protein level, localized on the trichomonad surface and in lysosomes and Golgi complex, bound to the surface of HeLa cells, and was found in vaginal secretions. Additionally, the IgG and Fab fractions of the anti-TvLEGU-1r antibody inhibited trichomonal cytoadherence up to 45%. Moreover, the Aza-Peptidyl Michael Acceptor that inhibited legumain proteolytic activity in live parasites also reduced levels of trichomonal cytoadherence up to 80%. In conclusion, our data show that the proteolytic activity of TvLEGU-1 is necessary for trichomonal adherence. Thus, TvLEGU-1 is a novel virulence factor upregulated by iron. This is the first report that a legumain-like CP plays a role in a pathogen cytoadherence.

Comparative transcriptomic and proteomic analyses of Trichomonas vaginalis following adherence to fibronectin

The morphological transformation of Trichomonas vaginalis from an ellipsoid form in batch culture to an adherent amoeboid form results from the contact of parasites with vaginal epithelial cells and with immobilized fibronectin (FN), a basement membrane component. This suggests host signaling of the parasite. We applied integrated transcriptomic and proteomic approaches to investigate the molecular responses of T. vaginalis upon binding to FN. A transcriptome analysis was performed by using large-scale expressed-sequence-tag (EST) sequencing. A total of 20,704 ESTs generated from batch culture (trophozoite-EST) versus FN-amoeboid trichomonad (FN-EST) cDNA libraries were analyzed. The FN-EST library revealed decreased amounts of transcripts that were of lower abundance in the trophozoite-EST library. There was a shift by FN-bound organisms to the expression of transcripts encoding essential proteins, possibly indicating the expression of genes for adaptation to the morphological changes needed for the FN-adhesive processes. In addition, we identified 43 differentially expressed proteins in the proteomes of FN-bound and unbound trichomonads. Among these proteins, cysteine peptidase, glyceraldehyde-3-phosphate dehydrogenase (an FN-binding protein), and stress-related proteins were upregulated in the FN-adherent cells. Stress-related genes and proteins were highly expressed in both the transcriptome and proteome of FN-bound organisms, implying that these genes and proteins may play critical roles in the response to adherence. This is the first report of a comparative proteomic and transcriptomic analysis after the binding of T. vaginalis to FN. This approach may lead to the discovery of novel virulence genes and affirm the role of genes involved in disease pathogenesis. This knowledge will permit a greater understanding of the complex host-parasite interplay.

Phosphoproteome profiling of the sexually transmitted pathogen Trichomonas vaginalis

BACKGROUND/PURPOSE(S)

Trichomoniasis caused by Trichomonas vaginalis is the most common non-viral sexually transmitted infection. Morphological transformation from the trophozoite stage to the amoeboid or pseudocyst stage is crucial for T. vaginalis infection and survival. Protein phosphorylation is a key post-translational modification involved in the regulation of several biological processes in various prokaryotes and eukaryotes. More than 880 protein kinases have been identified in the T. vaginalis genome. However, little is known about the phosphorylation of specific proteins and the distribution of phosphorylated proteins in different stages of the morphological transformation of T. vaginalis.

METHODS

To obtain a more comprehensive understanding of the T. vaginalis phosphoproteome, we analyzed phosphorylated proteins in the three morphological stages using titanium dioxide combined with LC-MS/MS.

RESULTS

A total of 93 phosphopeptides originating from 82 unique proteins were identified. Among these proteins, 21 were detected in all stages, 29 were identified in two different stages, and 32 were stage specific.

CONCLUSION

Identification of stage-specific phosphorylated proteins indicates that phosphorylation of these proteins may play a key role in the morphological transformation of T. vaginalis.

A protein phosphatase 1 gamma (PP1γ) of the human protozoan parasite Trichomonas vaginalis is involved in proliferation and cell attachment to the host cell

In this work, evidence for a critical role of Trichomonas vaginalis protein phosphatase 1 gamma (TvPP1γ) in proliferation and attachment of the parasite to the mammalian cell is provided. Firstly, proliferation and attachment of T. vaginalis parasites to HeLa cells was blocked by calyculin A (CA), a potent PP1 inhibitor. Secondly, it was demonstrated that the enzyme activity of native and recombinant TvPP1γ proteins was inhibited by CA. Thirdly, reverse genetic studies confirmed that antisense oligonucleotides targeted to PP1γ but not PP1α or β inhibited proliferation and attachment of trichomonads CA-treated parasites underwent cytoskeletal modifications, including a lack of axostyle typical labelling, suggesting that cytoskeletal phosphorylation could be regulated by a CA-sensitive phosphatase where the role of PP1γ could not be ruled out. Analysis of subcellular distribution of TvPP1γ by cell fractionation and electron microscopy demonstrated the association between TvPP1γ and the cytoskeleton. The expression of adhesins, AP120 and AP65, at the cell surface was also inhibited by CA. The concomitant inhibition of expression of adhesins and changes in the cytoskeleton in CA-treated parasites suggest a specific role for PP1γ -dependent dephosphorylation in the early stages of the host-parasite interaction. Molecular modelling of TvPP1γ showed the conservation of residues critical for maintaining proper folding into the gross structure common to PP1 proteins. Taken together, these results suggest that TvPP1γ could be considered a potential novel drug target for treatment of trichomoniasis.

Involvement of mast cells in inflammation induced by Trichomonas vaginalis via crosstalk with vaginal epithelial cells

Vaginal epithelial cells (VECs) are thought to function as immune-responsive cells in trichomoniasis, and mast cells have been detected in vaginal smears and the vaginal wall in trichomoniasis. It therefore seemed possible that the VEC-trichomonad reaction might affect the activity of mast cells present in the lamina propria of the vaginal mucosa. In this study, we tested whether culture supernatants of VEC incubated with Trichomonas vaginalis (TCM) could stimulate mast cells. When VECs (MS74) were incubated with live trichomonads, IL-8, IL-6 and MCP-1 expressions increased in the TCM, and mast cells (HMC-1) and human neutrophils migrated more actively towards the TCM. Also, when the TCM was added to mast cells, β-hexosaminidase and cytokines (IL-8 and TNF-α) expressions were increased. Moreover, the culture supernatant of mast cells incubated with TCM (M-TCM) had more increased chemotactic activity for neutrophils than that of TCM. We conclude that inflammatory mediators made by VECs in response to activation by T. vaginalis activate and attract mast cells and then stimulate them to induce neutrophil migration. Our results indicate, for the first time, that VECs play a role in the infiltration of mast cells and neutrophils early in T. vaginalis infection.

Pyruvate : ferredoxin oxidoreductase (PFO) is a surface-associated cell-binding protein in Trichomonas vaginalis and is involved in trichomonal adherence to host cells

The Trichomonas vaginalis 120 kDa protein adhesin (AP120) is induced under iron-rich conditions and has sequence homology with pyruvate : ferredoxin oxidoreductase A (PFO A), a hydrogenosomal enzyme that is absent in humans. This homology raises the possibility that, like AP120, PFO might be localized to the parasite surface and participate in cytoadherence. Here, the cellular localization and function of PFO that was expressed under various iron concentrations was investigated using a polyclonal antibody generated against the 50 kDa recombinant C-terminal region of PFO A (anti-PFO50). In Western blot assays, this antibody recognized a 120 kDa protein band in total protein extracts, and proteins with affinity to the surface of HeLa cells from parasites grown under iron-rich conditions. In addition to localization that is typical of hydrogenosomal proteins, PFOs that were expressed under iron-rich conditions were found to localize at the surface. This localization was demonstrated using immunofluorescence and co-localization assays, as well as immunogold transmission electron microscopy. In addition to describing its enzyme activity, we describe a novel function in trichomonal host interaction for the PFO localized on the parasite surface. The anti-PFO50 antibody reduced the levels of T. vaginalis adherence to HeLa cell monolayers in a concentration-dependent manner. Thus, T. vaginalis PFO is an example of a surface-associated cell-binding protein that lacks enzyme activity and that is involved in cytoadherence. Additionally, PFO behaves like AP120 in parasites grown under iron-rich conditions. Therefore, these data suggest that AP120 and PFO A are encoded by the same gene, namely pfo a.

A microscopic description and ultrastructural characterisation of Dientamoeba fragilis: an emerging cause of human enteric disease

Dientamoeba fragilis is a pathogenic trichomonad found in the gastrointestinal tract of humans and is implicated as a cause of diarrhoea. Despite its discovery over a century ago, there has been no recent thorough description of this parasite by microscopy. Scanning electron microscopy, transmission electron microscopy, confocal and light microscopy were therefore used to characterise D. fragilis populations growing in xenic culture. Two different populations - smooth and ruffled cells - were identifiable by scanning electron microscopy. No flagella, pelta structures, undulating membrane or pseudocyst-like forms were present. The organelles in D. fragilis were analysed by transmission electron microscopy; like Trichomonas and Histomonas, D. fragilis contains hydrogenosomes that presumably represent the site of anaerobic respiration. The nuclear morphology of D. fragilis trophozoites grown in vitro and trophozoites from clinical isolates were also compared by confocal microscopy and light microscopy. The majority of cells grown in culture were mononucleate while most cells in permanent stained faecal smears were binucleate. The two nuclei of D. fragilis are morphologically indistinguishable and contain equivalent amounts of DNA as determined by DAPI staining. The approximate cell and nuclear volume of four isolates of D. fragilis were measured and shown to be comparable to other trichomonads. In addition, the discovery of a virus-like particle is reported, to our knowledge for the first time in D. fragilis. This study therefore provides extensive and novel details of the ultrastructure of a neglected protozoan parasite that is an emerging cause of human disease.

Molecular basis of the recognition of the ap65-1 gene transcription promoter elements by a Myb protein from the protozoan parasite Trichomonas vaginalis

Iron-inducible transcription of the ap65-1 gene in Trichomonas vaginalis involves at least three Myb-like transcriptional factors (tvMyb1, tvMyb2 and tvMyb3) that differentially bind to two closely spaced promoter sites, MRE-1/MRE-2r and MRE-2f. Here, we defined a fragment of tvMyb2 comprising residues 40-156 (tvMyb2₄₀₋₁₅₆) as the minimum structural unit that retains near full binding affinity with the promoter DNAs. Like c-Myb in vertebrates, the DNA-free tvMyb2₄₀₋₁₅₆ has a flexible and open conformation. Upon binding to the promoter DNA elements, tvMyb2₄₀₋₁₅₆ undergoes significant conformational re-arrangement and structure stabilization. Crystal structures of tvMyb2₄₀₋₁₅₆ in complex with promoter element-containing DNA oligomers showed that 5'-a/gACGAT-3' is the specific base sequence recognized by tvMyb2₄₀₋₁₅₆, which does not fully conform to that of the Myb binding site sequence. Furthermore, Lys⁴⁹, which is upstream of the R2 motif (amino acids 52-102) also participates in specific DNA sequence recognition. Intriguingly, tvMyb2₄₀₋₁₅₆ binds to the promoter elements in an orientation opposite to that proposed in the HADDOCK model of the tvMyb1₃₅₋₁₄₁/MRE-1-MRE-2r complex. These results shed new light on understanding the molecular mechanism of Myb-DNA recognition and provide a framework to study the molecular basis of transcriptional regulation of myriad Mybs in T. vaginalis.

Immunohistochemical study of the vaginal inflammatory response in experimental trichomoniasis

In the present paper, the acute and subchronical inflammatory processes of the vaginal epithelial were studied in mice experimentally infected with two Trichomonas vaginalis strains of different pathogenicity, by means of histological and immunological methods. There was an increase in the stratified epithelium layers as well as edema produced by the increase of vascularization in the propia submucosa and infiltration of leukocytes. The proliferation of the vaginal epithelium favors the settlement and persistence of the parasitic infection. All of the findings corresponded with signs of a systemic disease being observed in the animals, including significant weight loss and also intestinal invasion. The entire inflammatory process has been corroborated by studies of adhesion molecules such as E-Selectin, VCAM-1 and PECAM-1. A correlation between the time of appearance and the perseverance of the inflammatory process with E-Selectin and VCAM-1 expression was observed, but not with PECAM-1. The strain with a higher pathogenicity was able to invade deep vaginal tissues and thus, parasites could not be detected by vaginal washings. This may be an important cause of diagnosis and treatment failure. Also, by the different localization of trichomonads, it appeared that the battle between host and parasite took place in different areas dependent upon the characteristics of the strain.

Glyceraldehyde-3-phosphate dehydrogenase is a surface-associated, fibronectin-binding protein of Trichomonas vaginalis

Trichomonas vaginalis colonizes the urogenital tract of humans and causes trichomonosis, the most prevalent nonviral sexually transmitted disease. We have shown an association of T. vaginalis with basement membrane extracellular matrix components, a property which we hypothesize is important for colonization and persistence. In this study, we identify a fibronectin (FN)-binding protein of T. vaginalis. A monoclonal antibody (MAb) from a library of hybridomas that inhibited the binding of T. vaginalis organisms to immobilized FN was identified. The MAb (called ws1) recognized a 39-kDa protein and was used to screen a cDNA expression library of T. vaginalis. A 1,086-bp reactive cDNA clone that encoded a protein of 362 amino acids with identity to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was obtained. The gapdh gene was cloned, and recombinant GAPDH (rGAPDH) was expressed in Escherichia coli cells. Natural GAPDH and rGAPDH bound to immobilized FN and to plasminogen and collagen but not to laminin. MAb ws1 inhibited binding to FN. GAPDH was detected on the surface of trichomonads and was upregulated in synthesis and surface expression by iron. Higher levels of binding to FN were seen for organisms grown in iron-replete medium than for organisms grown in iron-depleted medium. In addition, decreased synthesis of GAPDH by antisense transfection of T. vaginalis gave lower levels of organisms bound to FN and had no adverse effect on growth kinetics. Finally, GAPDH did not associate with immortalized vaginal epithelial cells (VECs), and neither GAPDH nor MAb ws1 inhibited the adherence of trichomonads to VECs. These results indicate that GAPDH is a surface-associated protein of T. vaginalis with alternative functions.

Anti-Trichomonas activity of Sapindus saponins, a candidate for development as microbicidal contraceptive

OBJECTIVES

Trichomoniasis is the most common non-viral sexually transmitted disease and is caused by the protozoan Trichomonas vaginalis. In view of increased resistance of the parasite to classical drugs of the metronidazole family, the need for new unrelated agents is increasing. This study evaluates anti-Trichomonas activity of Sapindus saponins, a component of a herbal local contraceptive Consap recently marketed in India.

METHODS

The parasites were treated with saponins for MIC determination. Anti-Trichomonas activity of the saponins was evaluated using a cytoadherence assay, the substrate gel electrophoresis method and RT-PCR analysis. The effect of saponins on the mitochondrial potential of the host was determined by florescence-activated cell sorter. Actin cytoskeletal staining was used to determine the effect on parasite cytoskeleton.

RESULTS

Using in vitro susceptibility assay, the MIC of Sapindus saponins for T. vaginalis (0.005%) was found to be 10-fold lower than its effective spermicidal concentration (0.05%). Saponins concentration dependently inhibited the ability of parasites to adhere to HeLa cells and decreased proteolytic activity of the parasite's cysteine proteinases. This was associated with decreased expression of adhesin AP65 and membrane-expressed cysteine proteinase TvCP2 genes. Saponins produced no adverse effect on host cells in mitochondrial reduction potential measurement assay. Saponins also reversed the inhibitory mechanisms exerted by Trichomonas for evading host immunity. Early response of saponins to disrupt actin cytoskeleton in comparison with their effect on the nucleus suggests a membrane-mediated mode of action rather than via induction of apoptosis.

CONCLUSIONS

Findings demonstrate the potential of Sapindus saponins for development as a microbicidal contraceptive for human use. Further studies are required to evaluate its microbicidal activity against other sexually transmitted infections.

Differential soluble protein expression between Trichomonas vaginalis isolates exhibiting low and high virulence phenotypes

A comparative analysis of proteomic maps of long-term grown and fresh clinical Trichomonas vaginalis isolates exhibiting low and high virulence phenotypes, respectively, was performed using two-dimensional gel electrophoresis and mass spectrometry. Of 29 protein spots differentially expressed between the isolates, 19 were over-expressed in the isolate exhibiting high virulence phenotype: proteins associated with cytoskeletal dynamics, such as coronin and several isoforms of actin, as well as proteins involved in signal transduction, protein turnover, proteolysis, and energetic and polyamine metabolisms were identified. Some malate dehydrogenase, fructose-1,6-bisphosphate aldolase and ornithine cyclodeamidase isoforms were exclusively expressed by the highly virulent isolate. During interaction assays with VEC, parasites exhibiting high virulence phenotype rapidly adhered and switched to amoeboid forms. In contrast, low adhesion and no morphological transformation were observed in parasites displaying low virulence phenotype. Our findings demonstrate that expression of specific proteins by high and low virulence parasites could be associated with the ability of each isolate to undergo morphological transformation and interact with host cells. Such data represent an important step towards understanding of the complex interaction network of proteins that participate in the mechanism of pathogenesis of this protozoan.

Characterization of the Trichomonas vaginalis surface-associated AP65 and binding domain interacting with trichomonads and host cells

Background

AP65 is a prominent adhesin of Trichomonas vaginalis that mediates binding of parasites to host vaginal epithelial cells (VECs). AP65 with no secretion signal sequence, membrane targeting peptide, and anchoring motif was recently found to be secreted.

Results

We first wanted to demonstrate surface association of AP65 to the parasite followed by the identification of the binding epitope interacting with both organisms and VECs. AP65 was found to bind to trichomonads, but not to trypsin-treated parasites, in an auto-ligand assay, suggesting the existence of a surface protein associating with AP65. Since rabbit antiserum IgG antibodies reactive with epitopes localized to the N-terminal region of AP65 inhibit the attachment of live parasites to VECs, we hypothesized that the binding domain was localized to this region. We subcloned five overlapping fragments of AP65 called c1 through c5, and expression of recombinant clones was confirmed with antibodies to AP65. Each purified recombinant protein was then tested for binding activity using an established ligand assay, and fragment c1 with the first twenty-five amino acids in the N-terminal domain was required for binding to VECs and, surprisingly, also to parasites. Importantly, c1 competed with the binding of AP65 to both cells types.

Conclusion

T. vaginalis AP65 is a secreted, surface-associated protein and a model is proposed to explain how this secreted protein functions as an adhesin.

Immunogenic and plasminogen-binding surface-associated alpha-enolase of Trichomonas vaginalis

Trichomonas vaginalis is a protist that causes the most common human sexually transmitted infection. A T. vaginalis cDNA expression library was screened with pooled sera from patients with trichomoniasis. A highly reactive cDNA clone of 1,428 bp encoded a trichomonad protein of 472 amino acids with sequence identity to alpha-enolase (tv-eno1). The sequence alignment confirmed the highly conserved nature of the enzyme with 65% to 84% identity among organisms. The expression of tv-eno1 was up-regulated by contact of parasites with vaginal epithelial cells, and this is the first report demonstrating up-regulation by cytoadherence of a plasminogen-binding alpha-enolase in T. vaginalis. Immunofluorescence with monoclonal antibody of nonpermeabilized trichomonads showed tv-ENO1 on the surface. The recombinant tv-ENO1 was expressed in Escherichia coli as a glutathione S-transferase (GST)::tv-ENO1 fusion protein, which was cleaved using thrombin to obtain affinity-purified recombinant tv-ENO1 protein (tv-rENO1) detectable in immunoblots by sera of patients. Immobilized tv-rENO1 bound human plasminogen in a dose-dependent manner, and plasminogen binding by tv-rENO1 was confirmed in a ligand blot assay. The plasminogen-specific inhibitor epsilon-aminocaproic acid blocked the tv-rENO1-plasminogen association, indicating that lysines play a role in binding to tv-rENO1. Further, both parasites and tv-rENO1 activate plasminogen to plasmin that is mediated by tissue plasminogen activator. These data indicate that as with other bacterial pathogens, tv-ENO1 is an anchorless, surface-associated glycolytic enzyme of T. vaginalis.

Cysteine proteinase 30 (CP30) and antibody response to CP30 in serum and vaginal washes of symptomatic and asymptomatic Trichomonas vaginalis-infected women

Infection with Trichomonas vaginalis may be asymptomatic or with symptoms suggestive of vaginitis. Because cysteine proteinase 30 (CP30) of T. vaginalis is known to be a virulence marker that plays a role in cytoadherence, the aim of this study was to analyse the presence of CP30 and antibody to CP30 in clinical samples of symptomatic and asymptomatic infected women. CP30 was detected in all the serum and vaginal washes (VWs) of symptomatic women and in 65% of the serum and 80% of the VWs of asymptomatic women. This suggested that the majority of asymptomatic women also exhibit CP30 in the serum and VWs. Antibody to CP30 was detected in all the serum samples of symptomatic and asymptomatic women and in the VWs of only 54.5% of the symptomatic and 35% of the asymptomatic women. Antibody to CP30 was also detected in 3/20 of the serum samples and in none of the VWs from uninfected women. Significantly higher amounts of antibody (mean OD values) were observed in serum and VWs of symptomatic as compared to asymptomatic and healthy women (P<0.001). These results indicate that besides CP30, other factors may also be playing a role in leading to symptomatic infection, because CP30 was detected in clinical samples from all the symptomatic and the majority of the asymptomatic women. Although anti-CP30 antibodies do not appear to be protective, detection of antibody to CP30 antigen in serum samples may be used as a diagnostic tool.