Amastigote Synapse: The Tricks of Trypanosoma cruzi Extracellular Amastigotes

Biogenesis of extracellular vesicles in protozoan parasites: The ESCRT complex in the trafficking fast lane?

Extracellular vesicles (EVs) provide a central mechanism of cell-cell communication. While EVs are found in most organisms, their pathogenesis-promoting roles in parasites are of particular interest given the potential for medical insight and consequential therapeutic intervention. Yet, a key feature of EVs in human parasitic protozoa remains elusive: their mechanisms of biogenesis. Here, we survey the current knowledge on the biogenesis pathways of EVs secreted by the four main clades of human parasitic protozoa: apicomplexans, trypanosomatids, flagellates, and amoebae. In particular, we shine a light on findings pertaining to the Endosomal Sorting Complex Required for Transport (ESCRT) machinery, as in mammals it plays important roles in EV biogenesis. This review highlights the diversity in EV biogenesis in protozoa, as well as the related involvement of the ESCRT system in these unique organisms.

A Review on the Immunological Response against Trypanosoma cruzi

Chagas disease is a chronic systemic infection transmitted by Trypanosoma cruzi. Its life cycle consists of different stages in vector insects and host mammals. Trypanosoma cruzi strains cause different clinical manifestations of Chagas disease alongside geographic differences in morbidity and mortality. Natural killer cells provide the cytokine interferon-gamma in the initial phases of T. cruzi infection. Phagocytes secrete cytokines that promote inflammation and activation of other cells involved in defence. Dendritic cells, monocytes and macrophages modulate the adaptive immune response, and B lymphocytes activate an effective humoral immune response to T. cruzi. This review focuses on the main immune mechanisms acting during T. cruzi infection, on the strategies activated by the pathogen against the host cells, on the processes involved in inflammasome and virulence factors and on the new strategies for preventing, controlling and treating this disease.

Extensible membrane nanotubules mediate attachment of Trypanosoma cruzi epimastigotes under flow

Trypanosoma cruzi is the etiological agent of Chagas disease, an important cause of infectious chronic myocardiopathy in Latin America. The life cycle of the parasite involves two main hosts: a triatomine (arthropod hematophagous vector) and a mammal. Epimastigotes are flagellated forms inside the triatomine gut; they mature in its intestine into metacyclic trypomastigotes, the infective form for humans. Parasites attach despite the shear stress generated by fluid flow in the intestines of the host, but little is known about the mechanisms that stabilize attachment in these conditions. Here, we describe the effect of varying levels of shear stress on attached T. cruzi epimastigotes using a parallel plate flow chamber. When flow is applied, parasites are partially dragged but maintain a connection to the surface via ~40 nm wide filaments (nanotubules) and the activity of flagella is reduced. When flow stops, parasites return near their original position and flagellar motion resumes. Nanotubule elongation increases with increasing shear stress and is consistent with a model of membrane tether extension under force. Fluorescent probes used to confirm membrane composition also show micron-wide anchoring pads at the distal end of the nanotubules. Multiple tethering accounts for more resistance to large shear stresses and for reduced flagellar movement when flow is stopped. The formation of membrane nanotubules is a possible mechanism to enhance adherence to host cells under shear stress, favoring the continuity of the parasite´s life cycle.

Successful invasion of Trypanosoma cruzi trypomastigotes is dependent of host cell actin cytoskeleton

Cellular invasion by Trypanosoma cruzi metacyclic trypomastigotes (MTs) or tissue culture trypomastigotes (TCTs) is a complex process involving host-parasite cellular and molecular interactions. Particularly, the involvement of host cell actin cytoskeleton during trypomastigote invasion is poorly investigated and still, the results controversial. In the present work we compare side by side both trypomastigote forms and employing state of art live cell imaging we show for the first time the dynamic mobilization of host cell actin cytoskeleton to MT and TCT invasion sites. Moreover, cytochalasin D, latrunculin B, and jasplakinolide-pretreated cells inhibited MT and TCT invasion. Furthermore, our results demonstrated that TCT invasion decreased in RhoA, Rac1, and Cdc-42 GTPase-depleted cells, whereas MT invasion decreased only in Cdc42-and RhoA-depleted cells. Interestingly, depletion of the three studied GTPases induced a scattered lysosomal distribution throughout the cytosol. These observations indicate that GTPase depletion is sufficient to impair parasite invasion despite the importance of lysosome spread in trypomastigote invasion. Together, our results demonstrate that the host cell actin cytoskeleton plays a direct role during TCT and MT invasion.

Differentiating Trypanosoma cruzi in a Host Mammalian Cell Imaged in Aqueous Liquid by Atmospheric Scanning Electron Microscopy

Atmospheric Scanning Electron Microscopy (ASEM) is a powerful tool to observe a wet specimen at high resolution under atmospheric pressure. Here, we visualized a protozoan parasite Trypanosoma cruzi over the course of its infection cycle in the host mammalian cell. This is the first observation of intracellular parasite using a liquid-phase EM. Unlike regular SEM, aldehyde-fixed cell body of T. cruzi appears translucent, allowing the visualization of internal structures such as kinetoplast of trypomastigote and nucleus of amastigote. Plasma membrane of the host mammalian cell also appears translucent, which enabled direct observation of differentiating intracellular parasites and dynamic change of host cellular structures in their near-natural states. Various water-rich structures including micro- and macro- vesicles were visualized around T. cruzi. In addition, Correlative Light and Electron Microscopy exploiting open sample dish of ASEM allowed identification of parasite nucleus and transfected fluorescence-labeled parasites soon after internalization, while location of this morphological intermediate was otherwise obscure. Successful visualization of the differentiation of T. cruzi within the host cell demonstrated here opens up the possibility of using ASEM for observation of variety of intracellular parasites. IMPORTANCE Using Atmospheric Scanning Electron Microscopy (ASEM), we visualized interaction between infectious stage of Trypanosoma cruzi and completely intact host mammalian cell. Plasma membrane appears translucent under ASEM, which not only enables direct observation of T. cruzi within its host cell, but also reveals internal structures of the parasite itself. Sample deformation is minimal, since the specimen remains hydrated under atmospheric pressure at all times. This nature of ASEM, along with the open structure of ASEM sample dish, is suited for correlative light-electron microscopy, which can further be exploited in identification of fluorescent protein in the intracellular parasites.

Modulation of miR-145-5p and miR-146b-5p levels is linked to reduced parasite load in H9C2 Trypanosoma cruzi infected cardiomyoblasts

In the heart tissue of acutely Trypanosoma cruzi-infected mice miR-145-5p and miR-146b-5p are, respectively, downregulated and upregulated. Here, we used the H9C2 rat cardiomyoblast cell line infected with the Colombian T. cruzi strain to investigate the parasite-host cell interplay, focusing on the regulation of miR-145-5p and miR-146b-5p expression. Next, we explored the effects of interventions with the trypanosomicidal drug Benznidazole (Bz) alone or combined with Pentoxifylline (PTX), a methylxanthine derivative shown to modulate immunological and cardiac abnormalities in a model of chronic chagasic cardiomyopathy, on parasite load and expression of miR-145-5p and miR-146b-5p. The infection of H9C2 cells with trypomastigote forms allowed parasite cycle with intracellular forms multiplication and trypomastigote release. After 48 and 144 h of infection, upregulation of miR-145-5p (24 h: 2.38 ± 0.26; 48 h: 3.15 ± 0.9-fold change) and miR-146b-5b (24 h: 2.60 ± 0.46; 48 h: 2.97 ± 0.23-fold change) was detected. The peak of both miRNA levels paralleled with release of trypomastigote forms. Addition of 3 µM and 10 µM of Bz 48 h after infection reduced parasite load but did not interfere with miR-145-5p and miR-146b-5p levels. Addition of PTX did not interfere with Bz-induced parasite control efficacy. Conversely, combined Bz + PTX treatment decreased the levels of both microRNAs, resembling the expression levels detected in non-infected H9C2 cells. Moreover, the use of miR-145-5p and miR-146b-5p mimic/inhibitor systems before infection of H9C2 cells decreased parasite load, 72 h postinfection. When H9C2 cells were treated with miR-145-5p and miR-146b-5p mimic/inhibitor 48 h after infection, all the used systems, except the miR-146b-5p inhibitor, reduced parasite load. Altogether, our data indicate that these microRNAs putatively control signaling pathways crucial for parasite–host cell interaction. Thus, miR-145-5p and miR-146b-5p deserve to be further investigated as biomarkers of parasite control and tools to identify therapeutic adjuvants to etiological treatment in Chagas disease.

Molecular and Clinical Aspects of Chronic Manifestations in Chagas Disease: A State-of-the-Art Review

Chronic manifestations of Chagas disease present as disabling and life-threatening conditions affecting mainly the cardiovascular and gastrointestinal systems. Although meaningful research has outlined the different molecular mechanisms underlying Trypanosoma cruzi’s infection and the host-parasite interactions that follow, prompt diagnosis and treatment remain a challenge, particularly in developing countries and also in those where the disease is considered non-endemic. This review intends to present an up-to-date review of the parasite’s life cycle, genetic diversity, virulence factors, and infective mechanisms, as well as the epidemiology, clinical presentation, diagnosis, and treatment options of the main chronic complications of Chagas disease.

Mechanisms Associated with Trypanosoma cruzi Host Target Cell Adhesion, Recognition and Internalization

Chagas disease is caused by the kinetoplastid parasite Trypanosoma cruzi, which is mainly transmitted by hematophagous insect bites. The parasite's lifecycle has an obligate intracellular phase (amastigotes), while metacyclic and bloodstream-trypomastigotes are its infective forms. Mammalian host cell recognition of the parasite involves the interaction of numerous parasite and host cell plasma membrane molecules and domains (known as lipid rafts), thereby ensuring internalization by activating endocytosis mechanisms triggered by various signaling cascades in both host cells and the parasite. This increases cytoplasmatic Ca2+ and cAMP levels; cytoskeleton remodeling and endosome and lysosome intracellular system association are triggered, leading to parasitophorous vacuole formation. Its membrane becomes modified by containing the parasite's infectious form within it. Once it has become internalized, the parasite seeks parasitophorous vacuole lysis for continuing its intracellular lifecycle, fragmenting such a vacuole's membrane. This review covers the cellular and molecular mechanisms involved in T. cruzi adhesion to, recognition of and internalization in host target cells.

Trypanosoma cruzi extracellular amastigotes engage Rac1 and Cdc42 to invade RAW macrophages

Cell invasion by Trypanosoma cruzi extracellular amastigotes (EAs) relies significantly upon the host cell actin cytoskeleton. In past decades EAs have been established as a reliable model for phagocytosis inducer in non-phagocytic cells. Our current hypothesis is that EAs engage a phagocytosis-like mechanism in non-professional phagocytic cells; however, the molecular mechanisms in professional phagocytes still remain unexplored. In this work, we evaluated the involvement of Rac1 and Cdc42 in the actin-dependent internalization of EAs in RAW 246.7 macrophages. Kinetic assays showed similar internalization of EAs in unstimulated RAW and non-phagocytic HeLa cells but increased in LPS/IFN-γ stimulated RAW cells. However, depletion of Rac1, Cdc42 or RhoA inhibited EA internalization similarly in both unstimulated and stimulated RAW cells. Overexpression of active, but not the dominant-negative, construct of Rac1 increased EA internalization. Remarkably, for Cdc42, both the active and the inactive mutants decreased EA internalization when compared to wild type groups. Despite that both Rac1 and Cdc42 activation mutants were similarly recruited to and colocalized with actin at the EA-macrophage contact sites when compared to their native isoforms. Altogether, these results corroborate that EAs engage phagocytic processes to invade both professional and non-professional phagocytic cells providing evidences of converging actin mediated mechanisms induced by intracellular pathogens in both cell types.

Signaling pathways involved in environmental sensing in Trypanosoma cruzi

Trypanosoma cruzi is a unicellular parasite and the etiologic agent of Chagas disease. The parasite has a digenetic life cycle alternating between mammalian and insect hosts, where it faces a variety of environmental conditions to which it must adapt in order to survive. The adaptation to these changes is mediated by signaling pathways that coordinate the cellular responses to the new environmental settings. Major environmental changes include temperature, nutrient availability, ionic composition, pH, osmolarity, oxidative stress, contact with host cells and tissues, host immune response, and intracellular life. Some of the signaling pathways and second messengers potentially involved in the response to these changes have been elucidated in recent years and will be the subject of this review.

Comparative Analysis of Virulence Mechanisms of Trypanosomatids Pathogenic to Humans

Trypanosoma brucei, Leishmania spp., and T. cruzi are flagellate protozoans of the family Trypanosomatidae and the causative agents of human African trypanosomiasis, leishmaniasis, and Chagas disease, respectively. These diseases affect humans worldwide and exert a significant impact on public health. Over the course of evolution, the parasites associated with these pathologies have developed mechanisms to circumvent the immune response system throughout the infection cycle. In cases of human infection, this function is undertaken by a group of proteins and processes that allow the parasites to propagate and survive during host invasion. In T. brucei, antigenic variation is promoted by variant surface glycoproteins and other proteins involved in evasion from the humoral immune response, which helps the parasite sustain itself in the extracellular milieu during infection. Conversely, Leishmania spp. and T. cruzi possess a more complex infection cycle, with specific intracellular stages. In addition to mechanisms for evading humoral immunity, the pathogens have also developed mechanisms for facilitating their adhesion and incorporation into host cells. In this review, the different immune evasion strategies at cellular and molecular levels developed by these human-pathogenic trypanosomatids have been discussed, with a focus on the key molecules responsible for mediating the invasion and evasion mechanisms and the effects of these molecules on virulence.

Mixed signals - how Trypanosoma cruzi exploits host-cell communication and signaling to establish infection

Chagas disease (American trypanosomiasis) is a 'neglected' pathology that affects millions of people worldwide, mainly in Latin America. Trypanosoma cruzi, the causative agent, is an obligate intracellular parasite with a complex and diverse biology that infects several mammalian species, including humans. Because of genetic variability among strains and the presence of four biochemically and morphologically distinct parasite forms, the outcome of T. cruzi infection varies considerably depending on host cell type and parasite strain. During the initial contact, cellular communication is established by host-recognition-mediated responses, followed by parasite adherence and penetration. For this purpose, T. cruzi expresses a variety of proteins that modify the host cell, enabling it to safely reach the cytoplasm. After entry into the host cell, T. cruzi forms a transitory structure termed 'parasitophorous vacuole' (PV), followed by its cytoplasmic replication and differentiation after PV rupture, and subsequent invasion of other cells. The success of infection, maintenance and survival inside host cells is facilitated by the ability of T. cruzi to subvert various host signaling mechanisms. We focus in this Review on the various mechanisms that induce host cytoskeletal rearrangements, activation of autophagy-related proteins and crosstalk among major immune response regulators, as well as recent studies on the JAK-STAT pathway.

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.

Trypanosoma cruzi Presenilin-Like Transmembrane Aspartyl Protease: Characterization and Cellular Localization

The increasing detection of infections of Trypanosoma cruzi, the etiological agent of Chagas disease, in non-endemic regions beyond Latin America has risen to be a major public health issue. With an impact in the millions of people, current treatments rely on antiquated drugs that produce severe side effects and are considered nearly ineffective for the chronic phase. The minimal progress in the development of new drugs highlights the need for advances in basic research on crucial biochemical pathways in T. cruzi to identify new targets. Here, we report on the T. cruzi presenilin-like transmembrane aspartyl enzyme, a protease of the aspartic class in a unique phylogenetic subgroup with T. vivax separate from protozoans. Computational analyses suggest it contains nine transmembrane domains and an active site with the characteristic PALP motif of the A22 family. Multiple linear B-cell epitopes were identified by SPOT-synthesis analysis with Chagasic patient sera. Two were chosen to generate rabbit antisera, whose signal was primarily localized to the flagellar pocket, intracellular vesicles, and endoplasmic reticulum in parasites by whole-cell immunofluorescence. The results suggest that the parasitic presenilin-like enzyme could have a role in the secretory pathway and serve as a target for the generation of new therapeutics specific to the T. cruzi.

Membrane-bound extracellular vesicles secreted by parasitic protozoa: cellular structures involved in the communication between cells

The focus of this review is a group of structures/organelles collectively known as extracellular vesicles (EVs) that are secreted by most, if not all, cells, varying from mammalian cells to protozoa and even bacteria. They vary in size: some are small (100-200 nm) and others are larger (> 200 nm). In protozoa, however, most of them are small or medium in size (200-400 nm). These include vesicles from different origins. We briefly review the biogenesis of this distinct group that includes (a) exosome, which originates from the multivesicular bodies, an important component of the endocytic pathway; (b) ectosome, formed from a budding process that takes place in the plasma membrane of the cells; (c) vesicles released from the cell surface following a process of patching and capping of ligand/receptor complexes; (d) other processes where tubules secreted by the parasite subsequently originate exosome-like structures. Here, special emphasis is given to EVs secreted by parasitic protozoa such as Leishmania, Trypanosoma, Plasmodium, Toxoplasma, Cryptosporidium, Trichomonas, and Giardia. Most of them have been characterized as exosomes that were isolated using several approaches and characterized by electron microscopy, proteomic analysis, and RNA sequencing. The results obtained show clearly that they present several proteins and different types of RNAs. From the functional point of view, it is now clear that the secreted exosomes can be incorporated by the parasite itself as well as by mammalian cells with which they interact. As a consequence, there is interference both with the parasite (induction of differentiation, changes in infectivity, etc.) and with the host cell. Therefore, the EVs constitute a new system of transference of signals among cells. On the other hand, there are suggestions that exosomes may constitute potential biotechnology tools and are important players of what has been designated as nanobiotechnology. They may constitute an important delivery system for gene therapy and molecular-displaying cell regulation capabilities when incorporated into other cells and even by interfering with the exosomal membrane during its biogenesis, targeting the vesicles via specific ligands to different cell types. These vesicles may reach the bloodstream, overflow through intercellular junctions, and even pass through the central nervous system blood barrier. There is evidence that it is possible to interfere with the composition of the exosomes by interfering with multivesicular body biogenesis.

Depletion of Host Cell Focal Adhesion Kinase Increases the Susceptibility to Invasion by Trypanosoma cruzi Metacyclic Forms

Focal adhesion kinase (FAK), a cytoplasmic protein tyrosine kinase (PTK), is implicated in diverse cellular processes, including the regulation of F-actin dynamics. Host cell F-actin rearrangement is critical for invasion of Trypanosoma cruzi, the protozoan parasite that causes Chagas disease. It is unknown whether FAK is involved in the internalization process of metacyclic trypomastigote (MT), the parasite form that is important for vectorial transmission. MT can enter the mammalian host through the ocular mucosa, lesion in the skin, or by the oral route. Oral infection by MT is currently a mode of transmission responsible for outbreaks of acute Chagas disease. Here we addressed the question by generating HeLa cell lines deficient in FAK. Host cell invasion assays showed that, as compared to control wild type (WT) cells, FAK-deficient cells were significantly more susceptible to parasite invasion. Lysosome spreading and a disarranged actin cytoskeleton, two features associated with susceptibility to MT invasion, were detected in FAK-deficient cells, as opposed to WT cells that exhibited a more organized F-actin arrangement, and lysosomes concentrated in the perinuclear area. As compared to WT cells, the capacity of FAK-deficient cells to bind a recombinant protein based on gp82, the MT surface molecule that mediates invasion, was higher. On the other hand, when treated with FAK-specific inhibitor PF573228, WT cells exhibited a dense meshwork of actin filaments, lysosome accumulation around the nucleus, and had increased resistance to MT invasion. In cells treated with PF573228, the phosphorylation levels of FAK were reduced and, as a consequence of FAK inactivation, diminished phosphorylation of extracellular signal-regulated protein kinases (ERK1/2) was observed. Fibronectin, known to impair MT invasion, induced the formation of thick bundles of F-actin and ERK1/2 dephosphorylation.