Signal transduction induced in Trypanosoma cruzi metacyclic trypomastigotes during the invasion of mammalian cells

Metacyclogenesis as the Starting Point of Chagas Disease

Chagas disease is a neglected infectious disease caused by the protozoan Trypanosoma cruzi, primarily transmitted by triatomine vectors, and it threatens approximately seventy-five million people worldwide. This parasite undergoes a complex life cycle, transitioning between hosts and shifting from extracellular to intracellular stages. To ensure its survival in these diverse environments, T. cruzi undergoes extreme morphological and molecular changes. The metacyclic trypomastigote (MT) form, which arises from the metacyclogenesis (MTG) process in the triatomine hindgut, serves as a crucial link between the insect and human hosts and can be considered the starting point of Chagas disease. This review provides an overview of the current knowledge regarding the parasite's life cycle, molecular pathways, and mechanisms involved in metabolic and morphological adaptations during MTG, enabling the MT to evade the immune system and successfully infect human cells.

mTOR signaling inhibition decreases lysosome migration and impairs the success of Trypanosoma cruzi infection and replication in cardiomyocytes

Chagas disease is caused by the parasite Trypanosoma cruzi (T. cruzi) and, among all the chronic manifestations of the disease, Chronic Chagas Cardiomyopathy (CCC) is the most severe outcome. Despite high burden and public health importance in Latin America, there is a gap in understanding the molecular mechanisms that results in CCC development. Previous studies showed that T. cruzi uses the host machinery for infection and replication, including the repurposing of the responses to intracellular infection such as mitochondrial activity, vacuolar membrane, and lysosomal activation in benefit of parasite infection and replication. One common signaling upstream to many responses to parasite infection is mTOR pathway, previous associated to several downstream cellular mechanisms including autophagy, mitophagy and lysosomal activation. Here, using human iPSC derived cardiomyocytes (hiPSCCM), we show the mTOR pathway is activated in hiPSCCM after T. cruzi infection, and the inhibition of mTOR with rapamycin reduced number of T. cruzi 48 h post infection (hpi). Rapamycin treatment also reduced lysosome migration from nuclei region to cell periphery resulting in less T. cruzi inside the parasitophorous vacuole (PV) in the first hour of infection. In addition, the number of parasites leaving the PV to the cytoplasm to replicate in later times of infection was also lower after rapamycin treatment. Altogether, our data suggest that host's mTOR activation concomitant with parasite infection modulates lysosome migration and that T. cruzi uses this mechanism to achieve infection and replication. Modulating this mechanism with rapamycin impaired the success of T. cruzi life cycle independent of mitophagy.

Exosomes: from biology to immunotherapy in infectious diseases

Exosomes are extracellular vesicles derived from the endosomal compartment, which are released by all kinds of eukaryotic and prokaryotic organisms. These vesicles contain a variety of biomolecules that differ both in quantity and type depending on the origin and cellular state. Exosomes are internalized by recipient cells, delivering their content and thus contributing to cell-cell communication in health and disease. During infections exosomes may exert a dual role, on one hand, they can transmit pathogen-related molecules mediating further infection and damage, and on the other hand, they can protect the host by activating the immune response and reducing pathogen spread. Selective packaging of pathogenic components may mediate these effects. Recently, quantitative analysis of samples by omics technologies has allowed a deep characterization of the proteins, lipids, RNA, and metabolite cargoes of exosomes. Knowledge about the content of these vesicles may facilitate their therapeutic application. Furthermore, as exosomes have been detected in almost all biological fluids, pathogenic or host-derived components can be identified in liquid biopsies, making them suitable for diagnosis and prognosis. This review attempts to organize the recent findings on exosome composition and function during viral, bacterial, fungal, and protozoan infections, and their contribution to host defense or to pathogen spread. Moreover, we summarize the current perspectives and future directions regarding the potential application of exosomes for prophylactic and therapeutic purposes.

Pro-arrhythmogenic effects of Trypanosoma cruzi conditioned medium proteins in a model of bovine chromaffin cells

Asymptomatic sudden death is the principal cause of mortality in Chagas disease. There is little information about molecular mechanisms involved in the pathophysiology of malignant arrhythmias in Chagasic patients. Previous studies have involved Trypanosoma cruzi secretion proteins in the genesis of arrhythmias ex vivo, but the molecular mechanisms involved are still unresolved. Thus, the aim was to determine the effect of these secreted proteins on the cellular excitability throughout to test its effects on catecholamine secretion, sodium-, calcium-, and potassium-conductance and action potential (AP) firing. Conditioned medium was obtained from the co-culture of T. cruzi and Vero cells (African green monkey kidney cells) and ultra-filtered for concentrating immunogenic high molecular weight parasite proteins. Chromaffin cells were assessed with the parasite and Vero cells control medium. Parasite-secreted proteins induce catecholamine secretion in a dose-dependent manner. Additionally, T. cruzi conditioned medium induced depression of both calcium conductance and calcium and voltage-dependent potassium current. Interestingly, this fact was related to the abolishment of the hyperpolarization phase of the AP produced by the parasite medium. Taken together, these results suggest that T. cruzi proteins may be involved in the genesis of pro-arrhythmic conditions that could influence the appearance of malignant arrhythmias in Chagasic patients.

All Roads Lead to Cytosol: Trypanosoma cruzi Multi-Strategic Approach to Invasion

T. cruzi has a complex life cycle involving four developmental stages namely, epimastigotes, metacyclic trypomastigotes, amastigotes and bloodstream trypomastigotes. Although trypomastigotes are the infective forms, extracellular amastigotes have also shown the ability to invade host cells. Both stages can invade a broad spectrum of host tissues, in fact, almost any nucleated cell can be the target of infection. To add complexity, the parasite presents high genetic variability with differential characteristics such as infectivity. In this review, we address the several strategies T. cruzi has developed to subvert the host cell signaling machinery in order to gain access to the host cell cytoplasm. Special attention is made to the numerous parasite/host protein interactions and to the set of signaling cascades activated during the formation of a parasite-containing vesicle, the parasitophorous vacuole, from which the parasite escapes to the cytosol, where differentiation and replication take place.

Lipid metabolism in Trypanosoma cruzi: A review

The cellular membranes of Trypanosoma cruzi, like all eukaryotes, contain varying amounts of phospholipids, sphingolipids, neutral lipids and sterols. A multitude of pathways exist for the de novo synthesis of these lipid families but Trypanosoma cruzi has also become adapted to scavenge some of these lipids from the host. Completion of the TriTryp genomes has led to the identification of many putative genes involved in lipid synthesis, revealing some interesting differences to higher eukaryotes. Although many enzymes involved in lipid synthesis have yet to be characterised, completed experiments have shown the indispensability of some lipid metabolic pathways. Furthermore, the bioactive lipids of Trypanosoma cruzi and their effects on the host are becoming increasingly studied. Further studies on lipid metabolism in Trypanosoma cruzi will no doubt reveal some attractive targets for therapeutic intervention as well as reveal the interplay between parasite lipids, host response and pathogenesis.

Disruption of Intracellular Calcium Homeostasis as a Therapeutic Target Against Trypanosoma cruzi

There is no effective cure for Chagas disease, which is caused by infection with the arthropod-borne parasite, Trypanosoma cruzi. In the search for new drugs to treat Chagas disease, potential therapeutic targets have been identified by exploiting the differences between the mechanisms involved in intracellular Ca²⁺ homeostasis, both in humans and in trypanosomatids. In the trypanosomatid, intracellular Ca²⁺ regulation requires the concerted action of three intracellular organelles, the endoplasmic reticulum, the single unique mitochondrion, and the acidocalcisomes. The single unique mitochondrion and the acidocalcisomes also play central roles in parasite bioenergetics. At the parasite plasma membrane, a Ca²⁺-⁻ATPase (PMCA) with significant differences from its human counterpart is responsible for Ca²⁺ extrusion; a distinctive sphingosine-activated Ca²⁺ channel controls Ca²⁺ entrance to the parasite interior. Several potential anti-trypansosomatid drugs have been demonstrated to modulate one or more of these mechanisms for Ca²⁺ regulation. The antiarrhythmic agent amiodarone and its derivatives have been shown to exert trypanocidal effects through the disruption of parasite Ca²⁺ homeostasis. Similarly, the amiodarone-derivative dronedarone disrupts Ca²⁺ homeostasis in T. cruzi epimastigotes, collapsing the mitochondrial membrane potential (ΔΨ_m), and inducing a large increase in the intracellular Ca²⁺ concentration ([Ca²⁺]_i) from this organelle and from the acidocalcisomes in the parasite cytoplasm. The same general mechanism has been demonstrated for SQ109, a new anti-tuberculosis drug with potent trypanocidal effect. Miltefosine similarly induces a large increase in the [Ca²⁺]_i acting on the sphingosine-activated Ca²⁺ channel, the mitochondrion and acidocalcisomes. These examples, in conjunction with other evidence we review herein, strongly support targeting Ca²⁺ homeostasis as a strategy against Chagas disease.

Mechanisms of Infectivity and Evasion Derived from Microvesicles Cargo Produced by Trypanosoma cruzi

Cell invasion by the intracellular protozoans requires interaction of proteins from both the host and the parasite. Many parasites establish chronic infections, showing they have the potential to escape the immune system; for example, Trypanosoma cruzi is an intracellular parasite that causes Chagas disease. Parasite internalization into host cell requires secreted and surface molecules, such as microvesicles. The release of microvesicles and other vesicles, such as exosomes, by different eukaryotic organisms was first observed in the late twentieth century. The characterization and function of these vesicles have recently been the focus of several investigations. In this review, we discuss the release of microvesicles by T. cruzi. The molecular content of these vesicles is composed of several molecules that take place during parasite-host cell interaction and contribute to the parasite-driven mechanism of evasion from the host immune system. These new findings appear to have a profound impact on the comprehension of T. cruzi biology and highlight novel potential strategies for developing more efficient therapeutic approaches.

The Dialogue of the Host-Parasite Relationship: Leishmania spp. and Trypanosoma cruzi Infection

The intracellular protozoa Leishmania spp. and Trypanosoma cruzi and the causative agents of Leishmaniasis and Chagas disease, respectively, belong to the Trypanosomatidae family. Together, these two neglected tropical diseases affect approximately 25 million people worldwide. Whether the host can control the infection or develops disease depends on the complex interaction between parasite and host. Parasite surface and secreted molecules are involved in triggering specific signaling pathways essential for parasite entry and intracellular survival. The recognition of the parasite antigens by host immune cells generates a specific immune response. Leishmania spp. and T. cruzi have a multifaceted repertoire of strategies to evade or subvert the immune system by interfering with a range of signal transduction pathways in host cells, which causes the inhibition of the protective response and contributes to their persistence in the host. The current therapeutic strategies in leishmaniasis and trypanosomiasis are very limited. Efficacy is variable, toxicity is high, and the emergence of resistance is increasingly common. In this review, we discuss the molecular basis of the host-parasite interaction of Leishmania and Trypanosoma cruzi infection and their mechanisms of subverting the immune response and how this knowledge can be used as a tool for the development of new drugs.

Evidence of reversible bradycardia and arrhythmias caused by immunogenic proteins secreted by T. cruzi in isolated rat hearts

Rationale

Chagas cardiomyopathy, caused by the protozoan Trypanosoma cruzi, is characterized by alterations in intracellular ion, heart failure and arrhythmias. Arrhythmias have been related to sudden death, even in asymptomatic patients, and their molecular mechanisms have not been fully elucidated.

Objective

The aim of this study is to demonstrate the effect of proteins secreted by T. cruzi on healthy, isolated beating rat heart model under a non-damage-inducing protocol.

Methods and Results

We established a non-damage-inducing recirculation-reoxygenation model where ultrafiltrate fractions of conditioned medium control or conditioned infected medium were perfused at a standard flow rate and under partial oxygenation. Western blotting with chagasic patient serum was performed to determine the antigenicity of the conditioned infected medium fractions. We observed bradycardia, ventricular fibrillation and complete atrioventricular block in hearts during perfusion with >50 kDa conditioned infected culture medium. The preincubation of conditioned infected medium with chagasic serum abolished the bradycardia and arrhythmias. The proteins present in the conditioned infected culture medium of >50 kDa fractions were recognized by the chagasic patient sera associated with arrhythmias.

Conclusions

These results suggest that proteins secreted by T. cruzi are involved in Chagas disease arrhythmias and may be a potential biomarker in chagasic patients.

Chagas disease, caused by the parasite Trypanosoma cruzi, is an endemic disease of Latin-American countries, affecting an estimated 8 million people in 21 countries. It is spread by the bite of triatomine reduvid bug. Due to immigration towards non-endemic regions, the disease can spread and affect people around the world via blood transfusions. Infection usually occurs in childhood, and some patients may develop acute myocarditis; however, most remain asymptomatic for many years before chronic cardiac and/or gastrointestinal manifestations appear. Chagas disease is characterized by an acute phase, which is generally asymptomatic, or oligosymptomatic, an indeterminate phase, which may persist for several years, and a chronic phase in which dilated cardiomyopathy and arrhythmias are primarily observed and sudden death may occur. Once heart failure develops, death usually occurs within several years. In this work, we demonstrate the pathophysiological role of proteins secreted by T. cruzi on cardiac arrhythmias. The antigenicity of these fractions was tested by an immunological test using chagasic patients’ sera associated with arrhythmias. We showed that perfusion of the proteins secreted by T. cruzi, in an isolated beating rat heart model, induced cardiac arrhythmias such as bradycardia and complete atrioventricular block.

Quantitative proteomic and phosphoproteomic analysis of Trypanosoma cruzi amastigogenesis

Chagas disease is a tropical neglected disease endemic in Latin America caused by the protozoan Trypanosoma cruzi. The parasite has four major life stages: epimastigote, metacyclic trypomastigote, bloodstream trypomastigote, and amastigote. The differentiation from infective trypomastigotes into replicative amastigotes, called amastigogenesis, takes place in vivo inside mammalian host cells after a period of incubation in an acidic phagolysosome. This differentiation process can be mimicked in vitro by incubating tissue-culture-derived trypomastigotes in acidic DMEM. Here we used this well-established differentiation protocol to perform a comprehensive quantitative proteomic and phosphoproteomic analysis of T. cruzi amastigogenesis. Samples from fully differentiated forms and two biologically relevant intermediate time points were Lys-C/trypsin digested, iTRAQ-labeled, and multiplexed. Subsequently, phosphopeptides were enriched using a TiO2 matrix. Non-phosphorylated peptides were fractionated via hydrophilic interaction liquid chromatography prior to LC-MS/MS analysis. LC-MS/MS and bioinformatics procedures were used for protein and phosphopeptide quantitation, identification, and phosphorylation site assignment. We were able to identify regulated proteins and pathways involved in coordinating amastigogenesis. We also observed that a significant proportion of the regulated proteins were membrane proteins. Modulated phosphorylation events coordinated by protein kinases and phosphatases that are part of the signaling cascade induced by incubation in acidic medium were also evinced. To our knowledge, this work is the most comprehensive quantitative proteomics study of T. cruzi amastigogenesis, and these data will serve as a trustworthy basis for future studies, and possibly for new potential drug targets.

Mammalian cellular culture models of Trypanosoma cruzi infection: a review of the published literature

Cellular culture infection with Trypanosoma cruzi is a tool used to dissect the biological mechanisms behind Chagas disease as well as to screen potential trypanocidal compounds. Data on these models are highly heterogeneous, which represents a challenge when attempting to compare different studies. The purpose of this review is to provide an overview of the cell culture infectivity assays performed to date. Scientific journal databases were searched for articles in which cultured cells were infected with any Trypanosoma cruzi strain or isolate regardless of the study’s goal. From these articles the cell type, parasite genotype, culture conditions and infectivity results were extracted. This review represents an initial step toward the unification of infectivity model data. Important differences were detected when comparing the pathophysiology of Chagas disease with the experimental conditions used in the analyzed studies. While Trypanosoma cruzi preferentially infects stromal cells in vivo, most of the assays employ epithelial cell lines. Furthermore, the most commonly used parasite strain (Tulahuen-TcVI) is associated with chagasic cardiomyopathy only in the Southern Cone of South America. Suggestions to overcome these discrepancies include the use of stromal cell lines and parasite genotypes associated with the known characteristics of the natural history of Chagas disease.

Cell surface proteome analysis of human-hosted Trypanosoma cruzi life stages

Chagas' disease is a neglected infectious illness, caused by the protozoan Trypanosoma cruzi. It remains a challenging health issue in Latin America, where it is endemic, and so far there is no immunoprophylatic vaccine or satisfactory chemotherapic treatment for its chronic stage. The present work addressed the analysis of the plasma membrane (PM) subproteome from T. cruzi human-hosted life stages, trypomastigote and axenic amastigote, by two complementary PM protein enrichment techniques followed by identification using an LC-MS/MS approach. The results revealed an extensive repertoire of proteins in the PM subproteomes, including enzymes that might be suitable candidates for drug intervention. The comparison of the cell surface proteome among the life forms revealed some potentially stage-specific enzymes, although the majority was shared by both stages. Bioinformatic analysis showed that the vast majority of the identified proteins are membrane-derived and/or possess predicted transmembrane domains. They are mainly involved in host cell infection, protein adhesion, cell signaling, and the modulation of mammalian host immune response. Several virulence factors and proteins potentially capable of acting at a number of metabolic pathways of the host and also to regulate cell differentiation of the parasite itself were also found.

The gp82 surface molecule of Trypanosoma cruzi metacyclic forms

Gp82 is a surface glycoprotein expressed in Trypanosoma cruzi metacyclic trypomastigotes, the parasite forms from the insect vector that initiate infection in the mammalian host. Studies with metacyclic forms generated in vitro, as counterparts of insect-borne parasites, have shown that gp82 plays an essential role in host cell invasion and in the establishment of infection by the oral route. Among the gp82 properties relevant for infection are the gastric mucin-binding capacity and the ability to induce the target cell signaling cascades that result in actin cytoskeleton disruption and lysosome exocytosis, events that facilitate parasite internalization. The gp82 sequences from genetically divergent T. cruzi strains are highly conserved, displaying >90 % identity. Both the host cell-binding sites, as well as the gastric mucin-binding sequence of gp82, are localized in the C-terminal domain of the molecule. In the gp82 structure model, the main cell-binding site consists of an α-helix, which connects the N-terminal β-propeller domain to the C-terminal β-sandwich domain, where the second cell binding site is nested. The two cell binding sites are fully exposed on gp82 surface. Downstream and close to the α-helix is the gp82 gastric mucin-binding site, which is partially exposed. All available data support the notion that gp82 is structurally suited for metacyclic trypomastigote invasion of host cells and for initiating infection by the oral route.

Trypanosoma cruzi: Entry into Mammalian Host Cells and Parasitophorous Vacuole Formation

Trypanosoma cruzi, the causative agent of Chagas disease, is transmitted to vertebrate hosts by blood-sucking insects. This protozoan is an obligate intracellular parasite. The infective forms of the parasite are the metacyclic trypomastigotes, amastigotes, and bloodstream trypomastigotes. The recognition between the parasite and mammalian host cell, involves numerous molecules present in both cell types, and similar to several intracellular pathogens, T. cruzi is internalized by host cells via multiple endocytic pathways. Morphological studies demonstrated that after the interaction of the infective forms of T. cruzi with phagocytic or non-phagocytic cell types, plasma membrane (PM) protrusions can form, showing similarity with those observed during canonical phagocytosis or macropinocytic events. Additionally, several molecules known to be molecular markers of membrane rafts, macropinocytosis, and phagocytosis have been demonstrated to be present at the invasion site. These events may or may not depend on the host cell lysosomes and cytoskeleton. In addition, after penetration, components of the host endosomal-lysosomal system, such as early endosomes, late endosomes, and lysosomes, participate in the formation of the nascent parasitophorous vacuole (PV). Dynamin, a molecule involved in vesicle formation, has been shown to be involved in the PV release from the host cell PM. This review focuses on the multiple pathways that T. cruzi can use to enter the host cells until complete PV formation. We will describe different endocytic processes, such as phagocytosis, macropinocytosis, and endocytosis using membrane microdomains and clathrin-dependent endocytosis and show results that are consistent with their use by this smart parasite. We will also discuss others mechanisms that have been described, such as active penetration and the process that takes advantage of cell membrane wound repair.

Inositol 1,4,5-trisphosphate receptor regulates replication, differentiation, infectivity and virulence of the parasitic protist Trypanosoma cruzi

In animals, inositol 1,4,5-trisphosphate receptors (IP3 Rs) are ion channels that play a pivotal role in many biological processes by mediating Ca(2+) release from the endoplasmic reticulum. Here, we report the identification and characterization of a novel IP3 R in the parasitic protist, Trypanosoma cruzi, the pathogen responsible for Chagas disease. DT40 cells lacking endogenous IP3 R genes expressing T. cruzi IP3 R (TcIP3 R) exhibited IP3 -mediated Ca(2+) release from the ER, and demonstrated receptor binding to IP3 . TcIP3 R was expressed throughout the parasite life cycle but the expression level was much lower in bloodstream trypomastigotes than in intracellular amastigotes or epimastigotes. Disruption of two of the three TcIP3 R gene loci led to the death of the parasite, suggesting that IP3 R is essential for T. cruzi. Parasites expressing reduced or increased levels of TcIP3 R displayed defects in growth, transformation and infectivity, indicating that TcIP3 R is an important regulator of the parasite's life cycle. Furthermore, mice infected with T. cruzi expressing reduced levels of TcIP3 R exhibited a reduction of disease symptoms, indicating that TcIP3 R is an important virulence factor. Combined with the fact that the primary structure of TcIP3 R has low similarity to that of mammalian IP3 Rs, TcIP3 R is a promising drug target for Chagas disease.

Induction of chagasic-like arrhythmias in the isolated beating hearts of healthy rats perfused with Trypanosoma cruzi-conditioned medium

Chagas' myocardiopathy, caused by the intracellular protozoan Trypanosoma cruzi, is characterized by microvascular alterations, heart failure and arrhythmias. Ischemia and arrythmogenesis have been attributed to proteins shed by the parasite, although this has not been fully demonstrated. The aim of the present investigation was to study the effect of substances shed by T. cruzi on ischemia/reperfusion-induced arrhythmias. We performed a triple ischemia-reperfusion (I/R) protocol whereby the isolated beating rat hearts were perfused with either Vero-control or Vero T. cruzi-infected conditioned medium during the different stages of ischemia and subsequently reperfused with Tyrode's solution. ECG and heart rate were recorded during the entire experiment. We observed that triple I/R-induced bradycardia was associated with the generation of auricular-ventricular blockade during ischemia and non-sustained nodal and ventricular tachycardia during reperfusion. Interestingly, perfusion with Vero-infected medium produced a delay in the reperfusion-induced recovery of heart rate, increased the frequency of tachycardic events and induced ventricular fibrillation. These results suggest that the presence of parasite-shed substances in conditioned media enhances the arrhythmogenic effects that occur during the I/R protocol.

Cell signaling during Trypanosoma cruzi invasion

Cell signaling is an essential requirement for mammalian cell invasion by Trypanosoma cruzi. Depending on the parasite strain and the parasite developmental form, distinct signaling pathways may be induced. In this short review, we focus on the data coming from studies with metacyclic trypomastigotes (MT) generated in vitro and tissue culture-derived trypomastigotes (TCT), used as counterparts of insect-borne and bloodstream parasites, respectively. During invasion of host cells by MT or TCT, intracellular Ca²⁺ mobilization and host cell lysosomal exocytosis are triggered. Invasion mediated by MT surface molecule gp82 requires the activation of mammalian target of rapamycin (mTOR), phosphatidylinositol 3-kinase (PI3K), and protein kinase C (PKC) in the host cell, associated with Ca²⁺-dependent disruption of the actin cytoskeleton. In MT, protein tyrosine kinase, PI3K, phospholipase C, and PKC appear to be activated. TCT invasion, on the other hand, does not rely on mTOR activation, rather on target cell PI3K, and may involve the host cell autophagy for parasite internalization. Enzymes, such as oligopeptidase B and the major T. cruzi cysteine proteinase cruzipain, have been shown to generate molecules that induce target cell Ca²⁺ signal. In addition, TCT may trigger host cell responses mediated by transforming growth factor β receptor or integrin family member. Further investigations are needed for a more complete and detailed picture of T. cruzi invasion.

Congenital and oral transmission of American trypanosomiasis: an overview of physiopathogenic aspects

Chagas disease or American trypanosomiasis is a pathology affecting about 8-11 million people in Mexico, Central America, and South America, more than 300 000 persons in the United States as well as an indeterminate number of people in other non-endemic countries such as USA, Spain, Canada and Switzerland. The aetiological agent is Trypanosoma cruzi, a protozoan transmitted by multiple routes; among them, congenital route emerges as one of the most important mechanisms of spreading Chagas disease worldwide even in non-endemic countries and the oral route as the responsible of multiple outbreaks of acute Chagas disease in regions where the vectorial route has been interrupted. The aim of this review is to illustrate the recent research and advances in host-pathogen interaction making a model of how the virulence factors of the parasite would interact with the physiology and immune system components of the placental barrier and gastrointestinal tract in order to establish a response against T. cruzi infection. This review also presents the epidemiological, clinical and diagnostic features of congenital and oral Chagas disease in order to update the reader about the emerging scenarios of Chagas disease transmission.

Mammalian cell invasion by closely related Trypanosoma species T. dionisii and T. cruzi

Protozoan parasites of the genus Trypanosoma can infect virtually all mammalian species. Within this genus, Trypanosoma dionisii from bats and Trypanosoma cruzi that causes Chagas' disease, belonging to the subgenus Schizotrypanum, can invade mammalian cells. The mechanisms of cell invasion by T. dionisii are poorly understood. To address that question, metacyclic trypomastigotes (MT) and human epithelial HeLa cells were used. Similarly to genetically divergent T. cruzi strains G (TcI) and CL (TcVI), associated, respectively with marsupial and human infections, T. dionisii infectivity increased under nutritional stress, a condition that induces host cell lysosome exocytosis required for parasite internalization. For efficient internalization, T. dionisii depended on MT protein tyrosine kinase (PTK) and Ca(2+) mobilization from acidocalcisomes, whereas T. cruzi strains also relied on phosphatidylinositol 3-kinase (PI3K), protein kinase C (PKC) and Ca(2+) released from thapsigargin-sensitive compartments. T. dionisii-induced signaling in host cells implicated PKC and Ca(2+) mobilized from thapsigargin-sensitive stores, like T. cruzi, but without PI3K involvement. Unlike T. cruzi, T. dionisii metacyclic forms did not use l-proline as source of energy required for internalization. Molecules related to T. cruzi surface glycoproteins involved in MT-host cell interaction were undetectable in T. dionisii. The difference in the surface profile of the two species was also inferred from the susceptibility of T. dionisii metacyclic forms to complement-mediated lysis, as opposed to complete resistance of T. cruzi. In summary, the two Trypanosoma species display distinct surface profiles but invade host cells through a common mechanism involving lysosome mobilization to the site of parasite entry.

Molecular mechanisms of host cell invasion by Trypanosoma cruzi

The protozoan parasite Trypanosoma cruzi, the etiologic agent of Chagas disease, is an obligate intracellular protozoan pathogen. Overlapping mechanisms ensure successful infection, yet the relationship between these cellular events and clinical disease remains obscure. This review explores the process of cell invasion from the perspective of cell surface interactions, intracellular signaling, modulation of the host cytoskeleton and endosomal compartment, and the intracellular innate immune response to infection.

Molecular mechanisms of Trypanosoma cruzi infection by oral route

Frequent reports on outbreaks of acute Chagas' disease by ingestion of food contaminated with parasites from triatomine insects illustrate the importance of this mode of transmission. Studies on oral Trypanosoma cruzi infection in mice have indicated that metacyclic trypomastigotes invade the gastric mucosal epithelium. A key molecule in this process is gp82, a stage-specific surface glycoprotein that binds to both gastric mucin and to target epithelial cells. By triggering Ca2+ signalling, gp82 promotes parasite internalisation. Gp82 is relatively resistant to peptic digestion at acidic pH, thus preserving the properties critical for oral infection. The infection process is also influenced by gp90, a metacyclic stage-specific molecule that negatively regulates the invasion process. T. cruzi strains expressing high gp90 levels invade cells poorly in vitro. However, their infectivity by oral route varies considerably due to varying susceptibilities of different gp90 isoforms to peptic digestion. Parasites expressing pepsin-susceptible gp90 become highly invasive against target cells upon contact with gastric juice. Such is the case of a T. cruzi isolate from an acute case of orally acquired Chagas' disease; the gp90 from this strain is extensively degraded upon short period of parasite permanence in the gastric milieu. If such an exacerbation of infectivity occurs in humans, it may be responsible for the severity of Chagas' disease reported in outbreaks of oral infection.

Trypanosoma cruzi GP63 proteins undergo stage-specific differential posttranslational modification and are important for host cell infection

The protozoan Trypanosoma cruzi expresses multiple isoforms of the GP63 family of metalloproteases. Polyclonal antiserum against recombinant GP63 of T. cruzi (TcGP63) was used to study TcGP63 expression and localization in this organism. Western blot analysis revealed that TcGP63 is 61 kDa in epimastigotes, amastigotes, and tissue culture-derived trypomastigotes but 55 kDa in metacyclic trypomastigotes. Antiserum specific for Leishmania amazonensis GP63 specifically reacted with a 55-kDa TcGP63 form in metacyclic trypomastigotes, suggesting stage-specific expression of different isoforms. Surface biotinylation and endoglycosidase digestion experiments showed that TcGP63 is an ecto-glycoprotein in epimastigotes but is intracellular and lacking in N-linked glycans in metacyclic trypomastigotes. Immunofluorescence microscopy showed that TcGP63 is localized on the surfaces of epimastigotes but distributed intracellularly in metacyclic trypomastigotes. TcGP63 is soluble in cold Triton X-100, in contrast to Leishmania GP63, which is detergent resistant in this medium, suggesting that GP63 is not raft associated in T. cruzi. Western blot comparison of our antiserum to a previously described anti-peptide TcGP63 antiserum indicates that each antiserum recognizes distinct TcGP63 proteins. Preincubation of trypomastigotes with either TcGP63 antiserum or a purified TcGP63 C-terminal subfragment reduced infection of host myoblasts. These results show that TcGP63 is expressed at all life stages and that individual isoforms play a role in host cell infection.

Probing Trypanosoma cruzi biology with DNA microarrays

The application of genome-scale approaches to study Trypanosoma cruzi-host interactions at different stages of the infective process is becoming possible with sequencing and assembly of the T. cruzi genome nearing completion and sequence information available for both human and mouse genomes. Investigators have recently begun to exploit DNA microarray technology to analyze host transcriptional responses to T. cruzi infection and dissect developmental processes in the complex T. cruzi life-cycle. Collectively, information generated from these and future studies will provide valuable insights into the molecular requirements for establishment of T. cruzi infection in the host and highlight the molecular events coinciding with disease progression. While the field is in its infancy, the availability of genomic information and increased accessibility to relatively high-throughput technologies represents a significant advancement toward identification of novel drug targets and vaccine candidates for the treatment and prevention of Chagas' disease.

Trypanosoma cruzi: parasite and host cell signaling during the invasion process

Mammalian cell invasion by Trypanosoma cruzi is a complex process in which various parasite and host cell components interact, triggering the activation of signaling cascades and Ca2+ mobilization in both cells. Using metacyclic trypomastigotes (MT) generated in vitro and tissue culture-derived trypomastigotes (TCT), as counterparts of insect-borne and bloodstream parasites, respectively, the mechanisms of host cell invasion by T. cruzi have been partially elucidated. Distinct sets of molecules are engaged by MT and TCT to enter target cells. MT make use of surface glycoproteins with dual Ca2+ signaling activity, in a manner dependent of T. cruzi isolate. In highly infective MT, the binding of gp82 to its receptor triggers a signaling cascade involving protein tyrosine kinase, phospholipase C and production of inositol 1,4,5-triphosphate, whereas in poorly invasive MT, the mucin-like gp35/50 induces the activation of a signaling route in which adenylate cyclase, generation of cAMP and Ca2+ mobilization from acidocalcisomes are implicated. The host cell signaling pathways activated by MT remain to be determined. Differently from MT, the TCT surface molecules that bind to host cells as a prelude to invasion, such as the glycoproteins of gp85 family, appear to be devoid of signaling properties, but they may induce TCT enzymes, such as oligopeptidase B and cruzipain, to generate Ca2+ signaling factors of parasite or host cell origin. Host cell responses mediated by TGF-beta receptor or integrin family member may also be triggered by TCT. A more complete and detailed picture of T. cruzi invasion needs further investigations.

Trypanosoma cruzi infection by oral route: how the interplay between parasite and host components modulates infectivity

Trypanosoma cruzi infection by oral route constitutes the most important mode of transmission in some geographical regions, as illustrated by reports on microepidemics and outbreaks of acute Chagas' disease acquired by ingestion of food contaminated with parasites from triatomine insects. In the mouse model, T. cruzi metacyclic trypomastigotes invade the gastric mucosal epithelium, a unique portal of entry for systemic infection. High efficiency of metacyclic forms in establishing infection by oral route is associated with expression of gp82, a stage-specific surface molecule that binds to gastric mucin and to epithelial cells. Gp82 promotes parasite entry by triggering the signaling cascades leading to intracellular Ca(2+) mobilization. T. cruzi strains deficient in gp82 can effectively invade cells in vitro, by engaging the Ca(2+) signal-inducing surface glycoprotein gp30. However, they are poorly infective in mice by oral route because gp30 has low affinity for gastric mucin. Metacyclic forms also express gp90, a stage-specific surface glycoprotein that binds to host cells and acts as a negative regulator of invasion. T. cruzi strains expressing gp90 at high levels, in addition to gp82 and gp30, are all poor cell invaders in vitro. Notwithstanding, their infectivity by oral route may vary because, unlike gp82 and gp30, which resist degradation by pepsin in the gastric milieu, the gp90 isoforms of different strains have varying susceptibility to peptic digestion. For instance, in a T. cruzi isolate, derived from an acute case of Chagas' disease acquired by oral route, gp90 is extensively degraded by gastric juice in the mouse stomach and this renders the parasite highly invasive towards target cells. If such an exacerbation of infectivity occurs in humans, it may be responsible for the severity of the disease reported in outbreaks of oral infection.

Structure and expression of three gp82 gene subfamilies of Trypanosoma cruzi

The glycoprotein gp82 is a GPI-anchored cell surface protein of Trypanosoma cruzi and is involved in cell invasion. Gp82 is encoded by multiple genes. To investigate the genetic basis of its biological function, we analyzed structure and expression of gp82 multigene family members in the Peruvian and Guatemalan strains. Three major groups of gp82 genes (A, B and C) were categorized by analyzing multiple DNA clones from the genomic PCR products. Within each group, 95-97% homology was observed, whereas between the groups, homology was 67-79%. The copy numbers of groups A, B and C as determined by real-time PCR were 18, 8 and 7 copies, respectively, in the Peru-2 strain. Significant elevation of the mRNA expression levels (5-10 times more) of all the subfamily genes was observed in the metacyclic stage compared with the epimastigote stage. When we focused on the binding motif sequence reported previously, we found substantial difference between that of A and C. However, the peptide inhibition invasion assay showed no functional difference. Taken together, we demonstrated that three subfamilies of gp82 were in the genome of T. cruzi and maintained their functional structure, and that the mRNA expressions of those genes were equally controlled in a stage-specific manner.

Expression and cellular localization of molecules of the gp82 family in Trypanosoma cruzi metacyclic trypomastigotes

A member of the Trypanosoma cruzi gp82 family, expressed on metacyclic trypomastigote surface and identified by monoclonal antibody (MAb) 3F6, plays a key role in host cell invasion. Apart from the gp82 defined by MAb 3F6, no information is available on members of this protein family. From cDNA clones encoding gp82 proteins sharing 59.1% sequence identity, we produced the recombinant proteins J18 and C03, the former containing and the latter lacking the epitope for MAb 3F6. Polyclonal antibodies to J18 and C03 proteins were generated and used, along with MAb 3F6, to analyze the expression and cellular localization of gp82 family members in metacyclic forms of CL and G strains, which belong to highly divergent genetic groups. By two-dimensional gel electrophoresis and immunoblotting, molecules of 82 to 86 kDa, focusing at pH 4.6 to 5.4, and molecules of 72 to 88 kDa, focusing at pH 4.9 to 5.7, were visualized in CL and G strains, respectively. Flow cytometry and microscopic analysis revealed in both strains similar expression of MAb 3F6-reactive gp82 in live and permeabilized parasites, indicating its surface localization. The reaction of live parasites of both strains with anti-J18 antibodies was weaker than with MAb 3F6 and was increased by permeabilization. Anti-C03 antibodies bound predominantly to flagellar components in permeabilized G strain parasites, but in the CL strain the flagellum was not the preferential target for these antibodies. Host cell invasion of metacyclic forms was inhibited by J18 protein, as well as by MAb 3F6 and anti-J18 antibodies, but not by C03 protein or anti-C03 antibodies.

Trypanosoma cruzi cell invasion and traffic: influence of Coxiella burnetii and pH in a comparative study between distinct infective forms

Previous studies have shown that Coxiella burnetii, an intracellular bacterium that resides within acidified vacuoles with secondary lysosomal characteristics, is an effective modulator of the intracellular traffic of trypomastigote forms of Trypanosoma cruzi. In addition, vacuolar and cellular pH are related to fusion events that result in doubly infected phagosomes. T. cruzi, the etiological agent of Chagas' disease, occurs as different strains grouped in two major phylogenetic lineages: T. cruzi I, associated with the sylvatic cycle, and T. cruzi II, linked to the human disease. In this work we compared extracellular amastigotes (EA), metacyclic trypomastigotes (MT) and tissue culture derived trypomastigotes (TCT) belonging to T. cruzi I or T. cruzi II for their ability to invade and escape from their parasitophorous vacuole (PV), in Vero cells or Vero cells harboring the bacterium, C. burnetti. Distinct invasion patterns were observed between different infective stages and between infective forms of different strains. Studies on the transference kinetics revealed that pH modulates the intracellular traffic of each infective stage, but this influence is not exclusive for each phylogenetic group. Endosomal to lysosomal sequential labeling with EEA-1 and LAMP-1 of the PV formed during the entry of each infective form revealed that the phagosome maturation processes are distinct but not strain-dependent. Due to their low hemolysin and trans-sialidase activities, MTs are retained for longer periods in LAMP-1 positive vacuoles. Our results thus suggest that despite the contrasting invasion capabilities, parasites of distinct phylogenetic group behave in similar fashion once inside the host cell.

Cell invasion by Trypanosoma cruzi amastigotes of distinct infectivities: studies on signaling pathways

Trypanosoma cruzi metacyclic trypomastigotes of the major phylogenetic lineages use specific signaling pathways to invade host cells. Using a panel of drugs, we studied if the differences in the ability of extracellular amastigotes (EA) from G (T. cruzi I) and CL (T. cruzi II) strains to invade host cells could be associated to activation of specific signaling routes. Sonicated extracts from G or CL strain EA induced transient raises in HeLa cell intracellular Ca(2+) levels in a dose-dependent manner. Treatment of EA with drugs that affect Ca(2+) release from inositol-1,4,5-triphosphate-sensitive stores did not significantly affect the infectivity of either strain, whereas EA of both strains treated with ionomycin plus NH(4)Cl or nigericin that release Ca(2+) from acidocalcisomes had their infectivity reduced. Treatment of parasites with adenylate cyclase activator forskolin increased the infectivity of both strains towards HeLa cells. These data, taken together, suggest that, for host cell invasion, G and CL strain EA engage signaling pathways that lead to an increase of cyclic adenosine monophosphate and Ca(2+) mobilization from acidocalcisomes. Moreover, treatment of EA with genistein reduced by approximately 45% the invasion of HeLa cells by G but not by CL strain, implicating a protein tyrosine kinase in the process. In line with this, HeLa cell extracts contained a protein tyrosine kinase activity that mediated the phosphorylation of 87- and 175-kDa polypeptides of EA from G but not from CL strain. Regarding the target cell response, the activation of host PI3 kinase appears to be required for invasion by either strain as treatment of HeLa cells with wortmannin reduced EA infectivity. These data overall reinforce the concept that cell invasion by T. cruzi EA markedly differs from the process involving metacyclic trypomastigotes.

Molecular basis of mammalian cell invasion by Trypanosoma cruzi

Establishment of infection by Trypanosoma cruzi, the agent of Chagas' disease, depends on a series of events involving interactions of diverse parasite molecules with host components. Here we focus on the mechanisms of target cell invasion by metacyclic trypomastigotes (MT) and mammalian tissue culture trypomastigotes (TCT). During MT or TCT internalization, signal transduction pathways are activated both in the parasite and the target cell, leading to Ca2+ mobilization. For cell adhesion, MT engage surface glycoproteins, such as gp82 and gp35/50, which are Ca2+ signal-inducing molecules. In T. cruzi isolates that enter host cells in gp82-mediated manner, parasite protein tyrosine kinase as well as phospholipase C are activated, and Ca2+ is released from I P3-sensitive stores, whereas in T. cruzi isolates that attach to target cells mainly through gp35/50, the signaling pathway involving adenylate cyclase appears to be stimulated, with Ca2+ release from acidocalciosomes. In addition, T. cruzi isolate-dependent inhibitory signals, mediated by MT-specific gp90, may be triggered both in the host cell and the parasite. The repertoire of TCT molecules implicated in cell invasion includes surface glycoproteins of gp85 family, with members containing binding sites for laminin and cytokeratin 18, enzymes such as cruzipain, trans-sialidase, and an oligopeptidase B that generates a Ca2+-agonist from a precursor molecule.

Survival of Trypanosoma cruzi metacyclic trypomastigotes within Coxiella burnetii vacuoles: differentiation and replication within an acidic milieu

Coxiella burnetii, the etiological agent of Q fever, is an obligate intracellular bacterium that resides within acidified vacuoles with secondary lysosomal characteristics. Infective stages of Trypanosoma cruzi, the causative agent of Chagas' disease, actively invade a wide variety of cells, a process followed by lysosomal recruitment. Recently, we have investigated and characterized early events that occur in Vero cells persistently colonized with C. burnetii when doubly infected with T. cruzi trypomastigote forms. Kinetic studies of trypomastigote transfer indicated that parasitophorous vacuoles (PV) of metacyclic trypomastigotes are rapidly and efficiently fused to C. burnetii vacuoles. Based on these observations we have investigated the behavior of metacyclic trypomastigotes within C. burnetii vacuoles beyond 12 h of co-infection inside Vero cells. Using indirect immunofluorescence with MAb against different developmental stages, it was possible to follow the T. cruzi differentiation process within C. burnetii vacuoles after up to 96 h post-invasion. We observed that metacyclic trypomastigotes began to differentiate after 12 h of infection, and 24 h later amastigotes were the prevailing forms within C. burnetii vacuoles. T. cruzi amastigote replication within C. burnetii vacuoles was confirmed using video and time-lapse confocal microscopy and around 36 h of co-infection, cytokinesis took about 70 min to occur. After 72 h, we observed that amastigote forms seemed to escape from C. burnetii vacuoles. Labeling of amastigotes within C. burnetii vacuoles using a polyclonal antibody to C9 complement protein suggested that TcTOX (T. cruzi hemolysin) could play a role in parasite escape from C. burnetii. We concluded that T. cruzi has an outstanding adaptation capability and can survive within a hostile milieu such as C. burnetii vacuoles.

Trypanosoma cruzi surface molecule gp90 downregulates invasion of gastric mucosal epithelium in orally infected mice

Experiments were performed to elucidate why Trypanosoma cruzi isolates 573 and 587 differ widely in their efficiency to infect gastric mucosal epithelium when administered orally to mice. These isolates have the same surface profile and a similar capacity to enter host cells in vitro. Metacyclic forms of isolates 573 and 587 and the control CL isolate expressed similar levels of gp82, which is a cell invasion-promoting molecule. Expression of gp90, a molecule that downregulates cell invasion, was lower in the CL isolate. Consistent with this profile, approximately threefold fewer parasites of isolates 573 and 587 entered epithelial HeLa cells, as compared to the CL isolate. No difference in the rate of intracellular parasite replication was observed between isolates. When given orally to mice, metacyclic forms of isolate 573, like the CL isolate, produced high parasitemia (>10(6) parasites per ml at the peak), killing approximately 40% of animals, whereas infection with isolate 587 resulted in low parasitemia (<10(5) parasites per ml), with zero mortality. On the fourth day post-inoculation, tissue sections of the mouse stomach stained with hematoxylin and eosin showed a four to sixfold higher number of epithelial cells infected with isolate 573 or CL than with isolate 587. The rate of intracellular parasite development was similar in all isolates. Mimicking in vivo infection, parasites were treated with pepsin at acidic pH and then assayed for their ability to enter HeLa cells or explanted gastric epithelial cells. Pepsin extensively digested gp90 from isolate 573 and significantly increased invasion of both cells, but had minor effect on gp90 or infectivity of isolates 587 and CL. The profile of g82 digestion was similar in isolates 573 and 587, with partial degradation to a approximately 70 kDa fragment, which preserved the target cell binding domain as well as the region involved in gastric mucin adhesion. Gp82 from CL isolate was resistant to pepsin. Assays with parasites recovered from the mouse stomach 2 h after oral infection showed an extensive digestion of gp90 and increased infectivity of isolate 573, but not of isolate 587 or CL. Our data indicate that T. cruzi infection in vitro does not always correlate with in vivo infection because host factors may act on parasites, modulating their infectivity, as is the case of pepsin digestion of isolate 573 gp90.

Host cell signaling and Trypanosoma cruzi invasion: do all roads lead to lysosomes?

Trypanosoma cruzi, the protozoan parasite that causes Chagas' disease in humans, is capable of invading and replicating within a wide variety of nucleated mammalian cell types. Host cell invasion by infective T. cruzi trypomastigotes is governed by parasite-triggered activation of host cell signaling pathways. Recent studies highlighting a role for host cell phosphatidylinositol 3-kinases (PI3Ks) in the T. cruzi invasion process have revealed surprising new insights into the mechanism of host cell invasion by this pathogen. In this Perspective, we discuss these findings and propose alternative models of T. cruzi invasion that incorporate this new information.

Molecular basis of non-virulence of Trypanosoma cruzi clone CL-14

We investigated the properties of metacyclic trypomastigotes of non-virulent Trypanosoma cruzi clone CL-14, as compared to the parental isolate CL. In contrast to the CL isolate, which produces high parasitemias in mice, metacyclic forms of clone CL-14 failed to produce patent infection. In vitro, the number of clone CL-14 parasites that entered epithelial HeLa cells, after 1 h incubation, was approximately four-fold lower than that of the CL isolate and at 72 h post-infection intracellular replication was not apparent whereas cells infected with the CL isolate contained large number of parasites replicating as amastigotes. CL isolate metacyclic forms were long and slender, with the kinetoplast localised closer to the nucleus than to the posterior end, whereas clone CL-14 parasites were shorter, with the kinetoplast very close to the posterior end. Cysteine proteinase cruzipain and trans-sialidase activities were lower in CL isolate than in clone CL-14. The surface profile was similar, except that the expression of gp82, the stage-specific glycoprotein that promotes CL isolate mucosal infection in vivo and host cell invasion in vitro, was greatly reduced on the surface of clone CL-14 metacyclic forms. Genistein, a specific inhibitor of protein tyrosine kinase, which is activated in CL isolate by binding of gp82 to its host cell receptor, did not affect host cell entry of clone CL-14. In contrast with CL isolate, the infectivity of clone CL-14 was not affected by phospholipase C inhibitor U73122 but was diminished by a combination of ionomycin plus NH(4)Cl, which releases Ca(2+) from acidic vacuoles. Internalisation of clone CL-14, but not of CL isolate, was significantly increased by treating parasites with neuraminidase, which removes sialic acid from the mucin-like surface molecule gp35/50. Taken together, our data suggest an association between the non-virulence of clone CL-14 metacyclic forms and the reduced expression of gp82, which precludes the activation of signal transduction pathways leading to effective host cell invasion.

Evaluation of the Presence of a Thapsigargin-Sensitive Calcium Store in Trypanosomatids Using Trypanosoma evansi as a Model

Ca2+ plays an important role in the regulation of several important activities in different trypanosomatids. These parasites possess a Ca2+ transport system in the endoplasmic reticulum (ER) involved in Ca2+ homeostasis, which has been reported to be insensitive to thapsigargin, a classical inhibitor of the sarcoplasmic-ER Ca2+ adenosine triphosphatase (ATPase) (SERCA) in most eukaryotic cells. However, currently there is a controversy regarding the existence of a thapsigargin-sensitive ER Ca2+ store in these parasites. Therefore, we decided to explore the effect of this inhibitor using different methodological approaches. First, we selected Trypanosoma evansi as a parasite model to warrant the homogeneity of the population because this parasite has only a single life cycle, i.e., bloodstream-form trypomastigotes. Second, we compared the thapsigargin effect on Ca2+ homeostasis by spectrophotometrical Ca2+ measurements using 3 different approaches: whole-cell populations, cells that have been permeabilized by treatment with digitonin, and intact single cells. Our results demonstrate that a low concentration of thapsigargin induces Ca2+ release from intracellular Ca2+ stores in this parasite, which can be observed independently of the method used. Furthermore, the addition of thapsigargin before or after nigericin did not abolish its effect, showing that thapsigargin acts specifically on the ER. In conclusion, our results indicate the presence of a nonmitochondrial thapsigargin-sensitive Ca2+ store in T. evansi.

Infection by Trypanosoma cruzi metacyclic forms deficient in gp82 but expressing a related surface molecule, gp30

Trypanosoma cruzi metacyclic trypomastigotes invade and replicate in the gastric mucosal epithelium after oral infection. In this study we analyzed the process of infection by T. cruzi isolates deficient in the expression of gp82, the metacyclic stage-specific surface glycoprotein implicated in target cell entry in vitro and in promoting mucosal infection in mice after oral challenge. Mice infected by the oral route with metacyclic forms of gp82-deficient isolate 569 or 588 developed patent parasitemia but at greatly reduced levels compared to those infected with the gp82-expressing isolate CL. Metacyclic forms of both isolates expressed gp30, a surface glycoprotein detectable by monoclonal antibody (MAb) 3F6 directed to gp82. Otherwise, the gp82-deficient isolates displayed a surface profile similar to that of the CL isolate and also entered epithelial HeLa cells in a manner inhibitable by MAb 3F6 and dependent on the parasite signal transduction that involved the activation of protein tyrosine kinase and Ca(2+) mobilization from thapsigargin-sensitive stores. Like gp82, gp30 triggered the host cell Ca(2+) response required for parasite internalization. Purified gp30 and the recombinant gp82 inhibited HeLa cell invasion of metacyclic forms of isolates 569 and 588 by approximately 90 and approximately 70%, respectively. A cell invasion assay performed in the presence of gastric mucin, mimicking the in vivo infection, showed an inhibition of 70 to 75% in the internalization of gp82-deficient isolates but not of the CL isolate. The recombinant gp82 exhibited an adhesive capacity toward gastric mucin much higher than that of gp30. Taken together, our findings indicate that target cell entry of metacyclic trypomastigotes can be mediated either by gp82 or gp30 but that efficient mucosal infection depends on the expression of gp82.

Role of placental alkaline phosphatase in the internalization of trypomatigotes of Trypanosoma cruzi into HEp2 cells

BACKGROUND

In vitro, Trypanosoma cruzi invades a wide variety of mammalian cells by an unique process that is still poorly understood. Trypomastigotes adhere to specific receptors on the outer membrane of host cells before intracellular invasion, causing calcium ion mobilization and rearrangement of host cell microfilaments.

OBJECTIVE

To test if placental alkaline phosphatase (PLAP), a trophoblast plasma membrane protein anchored by a glycosylphosphatidylinositol molecule, is involved in the transplacental transmission of this parasite.

METHOD

We cultured HEp2 cells with the parasite and studied PLAP and actin microfilaments. The results were correlated with invasion rate.

RESULTS

Human HEp2 tumour cells express PLAP. HEp2 cells infected with trypomastigotes showed alteration in their alkaline phosphatase activity and a different pattern of actin organization, compared to control cells. Perturbation of PLAP from HEp2 cells before infection with T. cruzi trypomastigotes decreased the invasion rate.

CONCLUSION

Placental alkaline phosphatase could be involved in the internalization of T. cruzi into HEp2 cells, via activation of tyrosine kinase and rearrangement of actin microfilaments.

Trypanosoma cruzi infection induces microfilament depletion in human placenta syncytiotrophoblast

Congenital Chagas disease, endemic in Latin America, is associated with premature labour, miscarriage, and placentitis. Metacyclic trypomastigotes adhere to specific receptors on the outer membrane of host cells as a prelude to intracellular invasion, causing calcium ion mobilization, rearrangement of host cell microfilaments, recruitment of lysosomes and parasite internalization. The actin cytoskeleton plays an important role in many cellular processes including the parasite invasion into mammalian cells. In order to observe if placental cytoskeleton is altered in the process of parasite invasion into placental villi, actin microfilaments were studied. Using immunohistochemical techniques, it was observed that the presence of actin in the syncytiotrophoblast was intense throughout the brush border in control placentae belonging to non-chagasic women. But after culture with the trypomastigote, this labelling disappeared, indicating that the parasite induced disassembly of the cortical actin cytoskeleton when the placenta was infected. As a control, placentae from chagasic women were studied, and no actin was found. The same results were obtained by the electron microscope. We confirmed that cortical actin rearrangements may be an early step in the Trypanosoma cruzi invasion mechanism into placental cells, in order to allow lysosomes access to the plasma membrane, and formation of the parasitophorous vacuole. The recruitment of lysosomes occurs directly beneath the invasion site, and this process is required for parasite internalization.

Cell adhesion and Ca2+ signaling activity in stably transfected Trypanosoma cruzi epimastigotes expressing the metacyclic stage-specific surface molecule gp82

Metacyclic trypomastigotes of Trypanosoma cruzi express a developmentally regulated 82-kDa surface glycoprotein (gp82) that has been implicated in host cell invasion. gp82-mediated interaction of metacyclic forms with target cells induces in both cells activation of the signal transduction pathways, leading to intracellular Ca(2+) mobilization, which is required for parasite internalization. Noninfective epimastigotes do not express detectable levels of gp82 and are unable to induce a Ca(2+) response. We stably transfected epimastigotes with a T. cruzi expression vector carrying the metacyclic stage gp82 cDNA. These transfectants produced a functional gp82, which bound to and triggered a Ca(2+) response in HeLa cells, in the same manner as the metacyclic trypomastigote gp82. Such properties were not found in epimastigotes transfected with the plasmid vector alone. Epimastigotes expressing gp82 on the surface adhered to HeLa cells but were not internalized. Treatment of gp82-expressing epimastigotes with forskolin, an activator of adenylyl cyclase that increases the metacyclic trypomastigote entry into target cells, did not promote parasite internalization. P175, an intracellular tyrosine phosphorylated protein, which appears to play a role in gp82-dependent signaling cascade in metacyclic forms, was undetectable in epimastigotes, either transfected or not with pTEX-gp82. Overall, our results indicate that gp82 is required but not sufficient for target cell invasion.

Acidification modulates the traffic of Trypanosoma cruzi trypomastigotes in Vero cells harbouring Coxiella burnetii vacuoles

We studied the fate of different Trypanosoma cruzi trypomastigote forms after they invade Vero cells persistently colonised with Coxiella burnetii. When the invasion step was examined we found that persistent C. burnetii infection per se reduced only tissue-culture trypomastigote invasion, whereas raising vacuolar pH with Bafilomycin A1 and related drugs, increased invasion of both metacyclic and tissue-culture trypomastigotes when compared with control Vero cells. Kinetic studies of trypomastigote transfer indicated that metacyclic trypomastigotes parasitophorous vacuoles are more efficiently fused to C. burnetii vacuoles. The higher tissue-culture trypomastigote hemolysin and transialidase activities appear to facilitate their faster escape from the parasitophorous vacuole. Sialic acid deficient Lec-2 cells facilitate the escape of both forms. Endosomal-lysosomal sequential labelling with EEA1, LAMP-1, and Rab7 of the parasitophorous vacuoles formed during the entry of each infective form revealed that the phagosome maturation processes are also distinct. Measurements of C. burnetii vacuolar pH disclosed a marked preference for trypomastigote fusion with more acidic rickettsia vacuoles. Our results thus suggest that intravacuolar pH modulates the traffic of trypomastigote parasitophorous vacuoles in these doubly infected cells.

Cell signalling and Trypanosoma cruzi invasion

Mammalian cell invasion by the protozoan pathogen Trypanosoma cruzi is critical to its survival in the host. To promote its entry into a wide variety of non-professional phagocytic cells, infective trypomastigotes exploit an arsenal of heterogenous surface glycoproteins, secreted proteases and signalling agonists to actively manipulate multiple host cell signalling pathways. Signals initiated in the parasite upon contact with mammalian cells also function as critical regulators of the invasion process. Whereas the full spectrum of cellular responses modulated by T. cruzi is not yet known, mounting evidence suggests that these pathways impinge on a number of cellular processes, in particular the ubiquitous wound-repair mechanism exploited for lysosome-mediated parasite entry. Furthermore, differential engagement of host cell signalling pathways in a cell type-specific manner and modulation of host cell gene expression by T. cruzi are becoming recognized as essential determinants of infectivity and intracellular survival by this pathogen.

Activation of distinct signal transduction pathways in Trypanosoma cruzi isolates with differential capacity to invade host cells

Mammalian cell invasion by Trypanosoma cruzi requires the activation of signal transduction pathways that result in a Ca(2+) response both in the parasite and the host cell. By using drugs that interfere with the signalling processes, we investigated if the difference in the ability of T. cruzi isolates to invade host cells was associated with the activation of distinct signalling routes in the parasites. Experiments were performed with metacyclic trypomastigotes, the developmental forms that initiate infection in the mammalian host, using the highly invasive isolate CL and the poorly infective isolate G, which belong to distinct phylogenetic lineages. Treatment of parasites with adenylyl cyclase activator forskolin increased the infectivity of the G but not of the CL isolate towards HeLa cells. On the other hand, a specific protein tyrosine kinase inhibitor genistein reduced by approximately 75% the penetration of CL but not of G isolate into HeLa cells. In the CL but not in the G isolate, protein tyrosine kinase mediated the phosphorylation of a 175kDa protein in a manner inducible by a HeLa cell extract. Upon treatment with the phospholipase C inhibitor U73122, or with drugs such as caffeine, which affects Ca(2+) release from inositol-1,4,5-triphosphate-sensitive stores, or thapsigargin, an inhibitor of intracellular Ca(2+) transport ATPases, the infectivity of the CL but not of the G isolate diminished significantly (P<0.005). In both isolates, a combination of ionomycin plus NH(4)Cl or nigericin released Ca(2+) from acidic vacuoles containing a Ca(2+)/H(+) exchange system. This treatment reduced the infectivity of metacyclic forms of the G but not of the CL isolate. Taken together, these data suggest that, for host cell invasion, distinct signalling pathways are activated in metacyclic trypomastigotes of the two isolates, leading to Ca(2+) release from different intracellular compartments.

Role of placental alkaline phosphatase in the interaction between human placental trophoblast and Trypanosoma cruzi

Congenital Chagas disease, due to the intracellular parasite Trypanosoma cruzi, is associated with premature labor, miscarriage, and placentitis. Human enzyme placental alkaline phosphatase (PLAP) (EC 3.1.3.1.) is membrane-anchored through glycosylphosphatidylinositol (GPI). PLAP is present in plasma in late pregnancy, 36 to 40 weeks; there are lower levels in maternal Chagas disease. Infants born to such mothers may have congenital Chagas disease. Human placental villi (PV) were treated with phospholipase-C (PL-C) and then cultured with T. cruzi to determine the effect of the parasites on PLAP activity as an in vitro model. There is less PLAP activity after treatment by PL-C and during culture with T. cruzi. Pretreatment of PV with PL-C before culture with T. cruzi yielded essentially normal specific activity of PLAP and prevented or greatly reduced infective penetration of villi by parasites. The results are consistent with a pathogenetic role for placental alkaline phosphatase in congenital Chagas disease. Receptor activation of membrane attachment to PLAP may be a device used by T. cruzi to enable parasite invasion of human trophoblast.

Trypanosomal antioxidants and emerging aspects of redox regulation in the trypanosomatids

Leishmania and Trypanosoma are two genera of the protozoal Order Kinetoplastida that cause widespread diseases of humans and their livestock. The production of reactive oxygen and nitrogen intermediates by the host plays an important role in the control of infections by these organisms. Signal transduction and its redox regulation have not been studied in any depth in trypanosomatids, but homologs of the redox-sensitive signal transduction machinery of other eukaryotes have been recognized. These include homologs of activator protein-1, human apurinic endonuclease 1 (Ref-1) endonuclease, iron-responsive protein, protein kinases, and phosphatases. The detoxification of peroxide is catalyzed by a trypanothione-dependent system that has no counterpart in mammals, and thus ranks as one of the biochemical peculiarities of trypanosomatids. There is substantial evidence that trypanothione is essential for the survival of Trypanosoma brucei and for the virulence of Leishmania spp. Apart from trypanothione and its precursors, trypanosomatids also possess significant amounts of N(1)-methyl-4-mercaptohistidine or ovothiol A, but its function in the trypanosomatids is not presently understood. The biosynthesis of ovothiol A in Crithidia fasciculata proceeds by addition of sulfur from cysteine to histidine to form 4-mercaptohistidine. S-(4'-L-Histidyl)-L-cysteine sulfoxide is the transsulfuration intermediate. 4-Mercaptohistidine is subsequently methylated with S-adenosylmethionine as the likely methyl donor.

Trypanosoma cruzi: cruzipain and membrane-bound cysteine proteinase isoform(s) interacts with human alpha(2)-macroglobulin and pregnancy zone protein

Plasmatic levels of pregnancy zone protein (PZP) increase in children with acute Chagas disease. PZP, as well as alpha2-macroglobulin (alpha2-M), are able to interact with Trypanosoma cruzi proteinases. The interaction of alpha2-M and PZP with cruzipain, the major cysteine proteinase of T. cruzi, was investigated. Several molecular changes on both alpha-M inhibitors under reaction with cruzipain were found. PAGE analysis showed: (i) formation of complexes of intermediate mobility and tetramerization of native alpha2-M and PZP, respectively; (ii) limited proteolysis of bait region in alpha2-M and PZP, and (iii) covalent binding of cruzipain to PZP and alpha2-M. Conformational and structural changes experimented by alpha-Ms correlate with modifications of the enzyme electrophoretic mobility and activity. Cruzipain-alpha-M complexes were also detected by gelatin SDS-PAGE and immunoblotting using polyclonal anti-cruzipain antibodies. Concomitantly, alpha2-M and PZP impaired the activity of cruzipain towards Bz-Pro-Phe-Arg-pNA substrate. In addition, alpha-Ms were able to form covalent complexes with membrane isoforms of cysteine proteinases cross-reacting with cruzipain. The present study suggests that both human alpha-macroglobulin inhibitors could prevent or minimize harmful action of cruzipain on host's molecules and hypothetically regulate parasite functions controlled by cruzipain.