Characterization of a RAB5 homologue in Trypanosoma cruzi

Extracellular Vesicles: Potential Role in Remote Signaling and Inflammation in Trypanosoma cruzi-Triggered Disease

Extracellular vesicles (EVs) act as cell communicators and immune response modulators and may be employed as disease biomarkers and drug delivery systems. In infectious diseases, EVs can be released by the pathogen itself or by the host cells (infected or uninfected), potentially impacting the outcome of the immune response and pathological processes. Chagas disease (CD) is caused by infection by the protozoan Trypanosoma cruzi and is the main cause of heart failure in endemic areas. This illness attracted worldwide attention due to the presence of symptomatic seropositive subjects in North America, Asia, Oceania, and Europe. In the acute phase of infection, nonspecific signs, and symptoms contribute to miss diagnosis and early etiological treatment. In this phase, the immune response is crucial for parasite control; however, parasite persistence, dysregulated immune response, and intrinsic tissue factors may contribute to the pathogenesis of chronic CD. Most seropositive subjects remain in the indeterminate chronic form, and from 30 to 40% of the subjects develop cardiac, digestive, or cardio-digestive manifestations. Identification of EVs containing T. cruzi antigens suggests that these vesicles may target host cells and regulate cellular processes and the immune response by molecular mechanisms that remain to be determined. Parasite-released EVs modulate the host-parasite interplay, stimulate intracellular parasite differentiation and survival, and promote a regulatory cytokine profile in experimental models of CD. EVs derived from the parasite-cell interaction inhibit complement-mediated parasite lysis, allowing evasion. EVs released by T. cruzi-infected cells also regulate surrounding cells, maintaining a proinflammatory profile. After a brief review of the basic features of EVs, the present study focuses on potential participation of T. cruzi-secreted EVs in cell infection and persistence of low-grade parasite load in the chronic phase of infection. We also discuss the role of EVs in shaping the host immune response and in pathogenesis and progression of CD.

Basic Biology of Trypanosoma cruzi

The present review addresses basic aspects of the biology of the pathogenic protozoa Trypanosoma cruzi and some comparative information of Trypanosoma brucei. Like eukaryotic cells, their cellular organization is similar to that of mammalian hosts. However, these parasites present structural particularities. That is why the following topics are emphasized in this paper: developmental stages of the life cycle in the vertebrate and invertebrate hosts; the cytoskeleton of the protozoa, especially the sub-pellicular microtubules; the flagellum and its attachment to the protozoan body through specialized junctions; the kinetoplast-mitochondrion complex, including its structural organization and DNA replication; glycosome and its role in the metabolism of the cell; acidocalcisome, describing its morphology, biochemistry, and functional role; cytostome and the endocytic pathway; the organization of the endoplasmic reticulum and Golgi complex; the nucleus, describing its structural organization during interphase and division; and the process of interaction of the parasite with host cells. The unique characteristics of these structures also make them interesting chemotherapeutic targets. Therefore, further understanding of cell biology aspects contributes to the development of drugs for chemotherapy.

Tridimensional Electron Microscopy Analysis of the Early Endosomes and Endocytic Traffic in Trypanosoma cruzi Epimastigotes

Trypanosoma cruzi epimastigotes internalize macromolecules avidly by endocytosis. Previously, we identified a tubule-vesicular network likely to correspond to the early-endosomes. However, a detailed ultrastructural characterization of these endosomes was missing. Here, we combined endocytosis assays with ultrastructural data from high-resolution electron microscopy to produce a 3D analysis of epimastigote endosomes and their interactions with endocytic organelles. We showed that endocytic cargo was found in carrier vesicles budding from the cytopharynx. These vesicles appeared to fuse with a tubule-vesicular network of early endosomes identified by ultrastructural features including the presence of intermembrane invaginations and coated membrane sections. Within the posterior region of the cell, endosomes localized preferentially on the side nearest to the cytopharynx microtubules. At 4°C, cargo accumulated at a shortened cytopharynx, and subsequent temperature shift to 12°C led to slow cargo delivery to endosomes and, later, to reservosomes. Bridges between reservosomes and endosomes resemble heterotypic fusion. Reservosomes are excluded from the posterior end of the cell, with no preferential cargo delivery to reservosomes closer to the nucleus. Our 3D analysis indicates that epimastigotes accomplish high-speed endocytic traffic by cargo transfer to a bona fide early-endosome and then directly from endosomes to reservosomes, via multiple and simultaneous heterotypic fusion events.

Transferrin: Endocytosis and Cell Signaling in Parasitic Protozoa

Iron is the fourth most abundant element on Earth and the most abundant metal in the human body. This element is crucial for life because almost all organisms need iron for several biological activities. This is the case with pathogenic organisms, which are at the vanguard in the battle with the human host for iron. The latest regulates Fe concentration through several iron-containing proteins, such as transferrin. The transferrin receptor transports iron to each cell that needs it and maintains it away from pathogens. Parasites have developed several strategies to obtain iron as the expression of specific transferrin receptors localized on plasma membrane, internalized through endocytosis. Signal transduction pathways related to the activation of the receptor have functional importance in proliferation. The study of transferrin receptors and other proteins with action in the signaling networks is important because these proteins could be used as therapeutic targets due to their specificity or to differences with the human counterpart. In this work, we describe proteins that participate in signal transduction processes, especially those that involve transferrin endocytosis, and we compare these processes with those found in T. brucei, T. cruzi, Leishmania spp., and E. histolytica parasites.

Expression and cellular trafficking of GP82 and GP90 glycoproteins during Trypanosoma cruzi metacyclogenesis

Background

The transformation of noninfective epimastigotes into infective metacyclic trypomastigotes (metacyclogenesis) is a fundamental step in the life cycle of Trypanosoma cruzi, comprising several morphological and biochemical changes. GP82 and GP90 are glycoproteins expressed at the surface of metacyclic trypomastigote, with opposite roles in mammalian cell invasion. GP82 is an adhesin that promotes cell invasion, while GP90 acts as a negative regulator of parasite internalization. Our understanding of the synthesis and intracellular trafficking of GP82 and GP90 during metacyclogenesis is still limited. Therefore, we decided to determine whether GP82 and GP90 are expressed only in fully differentiated metacyclic forms or they start to be expressed in intermediate forms undergoing differentiation.

Methods

Parasite populations enriched in intermediate forms undergoing differentiation were analyzed by quantitative real-time PCR, Western blot, flow cytometry and immunofluorescence to assess GP82 and GP90 expression.

Results

We found that GP82 and GP90 mRNAs and proteins are expressed in intermediate forms and reach higher levels in fully differentiated metacyclic forms. Surprisingly, GP82 and GP90 presented distinct cellular localizations in intermediate forms compared to metacyclic trypomastigotes. In intermediate forms, GP82 is localized in organelles at the posterior region and colocalizes with cruzipain, while GP90 is localized at the flagellar pocket region.

Conclusions

This study discloses new aspects of protein expression and trafficking during T. cruzi differentiation by showing that the machinery involved in GP82 and GP90 gene expression starts to operate early in the differentiation process and that different secretion pathways are responsible for delivering these glycoproteins toward the cell surface.

Electron microscopy and cytochemistry analysis of the endocytic pathway of pathogenic protozoa

Endocytosis is essential for eukaryotic cell survival and has been well characterized in mammal and yeast cells. Among protozoa it is also important for evading from host immune defenses and to support intense proliferation characteristic of some life cycle stages. Here we focused on the contribution of morphological and cytochemical studies to the understanding of endocytosis in Trichomonas, Giardia, Entamoeba, Plasmodium, and trypanosomatids, mainly Trypanosoma cruzi, and also Trypanosoma brucei and Leishmania.

Characterization of a Trypanosoma cruzi antigen with homology to intracellular mammalian lectins

Two cDNAs, isolated from a Trypanosoma cruzi amastigote library immunoscreened with sera from patients with Chagas disease, encode proteins with sequence homology to eukaryotic components of the cellular sorting and recycling machinery. These proteins, denominated TcAGL, present an N-terminal lectin domain and a C-terminal region containing repetitive amino acids and a poly-glutamine tract. They are products of polymorphic alleles of a single copy gene constitutively expressed during the parasite life cycle. Polyclonal antibodies obtained from mice immunized with the recombinant antigen recognize proteins with apparent molecular weight ranging from 95 to 120 kDa in cell lysates from all three life stages and in various strains of the parasite. Sera from Chagas disease patients recognize the recombinant antigen in ELISA and immunoprecipitation assays but not in Western blot assays under denaturing conditions. Consistent with its proposed role in the glycoprotein secreting pathway, immunofluorescence analyses and expression of a green fluorescent protein-tagged TcAGL protein indicate a sub-cellular localization in the vicinity of the flagellar pocket membrane and the Golgi complex of the parasite.

TcRho1, the Trypanosoma cruzi Rho homologue, regulates cell-adhesion properties: Evidence for a conserved function

Rho proteins are members of the Ras superfamily of small GTPases. In higher eukaryotes these proteins play pivotal role in cell movement, phagocytosis, intracellular transport, cell-adhesion, and maintenance of cell morphology, mainly through the regulation of actin microfilaments. The GTPase TcRho1 is the only member of the Rho family described in human protozoan parasite Trypanosoma cruzi. We previously demonstrated that TcRho1 is actually required for differentiation of epimastigote to trypomastigote forms during the parasite cell cycle. In the present work, we describe cellular phenotypes induced by TcRho1 heterologous expression in NIH 3T3 fibroblasts. The NIH-3T3 lineages expressing the TcRho1-G15V and TcRho1-Q76L mutants displayed decreased levels of migration compared to the control lineage NIH-3T3 pcDNA3.1, a phenotype probably due to distinct cell-substrate adhesion properties expressed by the mutant cell lines. Accordingly, cell-substrate adhesion assays revealed that the mutant cell lines of NIH-3T3 expressing TcRho1-positive dominants constructions present enhanced substrate-adhesion phenotype. Furthermore, similar experiments with T. cruzi expressing TcRho1 mutants also revealed an enhancement of cell attachment. These results suggest that TcRho1 plays a conserved regulatory role in cell-substrate adhesion in both NIH-3T3 fibroblasts and T. cruzi epimastigotes. Taken together, our data corroborate the notion that TcRho1 may regulate the substrate-adhesion in T. cruzi, a critical step for successful progression of the parasite life cycle.

Characterization of RAB-like4, the first identified RAB-like protein from Trypanosoma cruzi with GTPase activity

RAB proteins, which belong to the RAS superfamily, regulate exocytic and endocytic pathways of eukaryotic cells, controlling vesicle docking and fusion. Few RAB proteins have been identified in parasites. Molecular markers for cellular compartments are important to studies concerning about the protein traffic in Trypanosoma cruzi, the causal agent of Chagas disease. In this work, we describe the characterization of TcRABL4, the first RAB-like gene identified in T. cruzi (GenBank Accession No.: ), present as a single-copy gene. TcRABL4 contains all five consensus RAB motifs but lacks cysteine residues at the C terminus, which are essential to isoprenylation, an absolute prerequisite for membrane association of these proteins. TcRABL4 is a functional GTPase that is able to bind and hydrolyze GTP, and its gene is transcribed as a single 1.2 kb mRNA in epimastigotes. TcRABL4 appears to be differentially regulated in the three cell forms of the parasite, and the protein is not associated to membranes, unlike other RAB proteins. It is possible that TcRABL4 may be a member of a novel family of small GTPases.