Host cell actin remodeling in response to Trypanosoma cruzi: trypomastigote versus amastigote entry

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.

The Parasitic Intracellular Lifestyle of Trypanosomatids: Parasitophorous Vacuole Development and Survival

The trypanosomatid (protozoan) parasites Trypanosoma cruzi and Leishmania spp. are causative agents of Chagas disease and Leishmaniasis, respectively. They display high morphological plasticity, are capable of developing in both invertebrate and vertebrate hosts, and are the only trypanosomatids that can survive and multiply inside mammalian host cells. During internalization by host cells, these parasites are lodged in "parasitophorous vacuoles" (PVs) comprised of host cell endolysosomal system components. PVs effectively shelter parasites within the host cell. PV development and maturation (acidification, acquisition of membrane markers, and/or volumetric expansion) precede parasite escape from the vacuole and ultimately from the host cell, which are key determinants of infective burden and persistence. PV biogenesis varies, depending on trypanosomatid species, in terms of morphology (e.g., size), biochemical composition, and parasite-mediated processes that coopt host cell machinery. PVs play essential roles in the intracellular development (i.e., morphological differentiation and/or multiplication) of T. cruzi and Leishmania spp. They are of great research interest as potential gateways for drug delivery systems and other therapeutic strategies for suppression of parasite multiplication and control of the large spectrum of diseases caused by these trypanosomatids. This mini-review focuses on mechanisms of PV biogenesis, and processes whereby PVs of T. cruzi and Leishmania spp. promote parasite persistence within and dissemination among mammalian host cells.

Clathrin coated pit dependent pathway for Trypanosoma cruzi internalization into host cells

A number of intracellular pathogens are internalized by host cells via multiple endocytic pathways, including Trypanosoma cruzi, the etiological agent of Chagas disease. Clathrin-mediated endocytosis is the most characterized endocytic pathway in mammalian cells. Its machinery was described as being required in mammalian cells for the internalization of large particles, including pathogenic bacteria, fungi, and large virus. To investigate whether T. cruzi entry into host cells can also take advantage of the clathrin-coated vesicle-dependent process, we utilized well-known inhibitors of clathrin-coated vesicle formation (sucrose hypertonic medium, chlorpromazine hydrochloride and pitstop 2) and small interference RNA (siRNA). All treatments drastically reduced the internalization of infective trypomastigotes and amastigotes of T. cruzi by phagocytic (macrophages) and epithelial cells. Clathrin labeling, as observed by fluorescence and electron microscopy, was also observed around the parasites from the initial stages of infection until the complete formation of the parasitophorous vacuole. These unexpected observations suggest the participation of the clathrin pathway in the T. cruzi entry process.

Utilization of proliferable extracellular amastigotes for transient gene expression, drug sensitivity assay, and CRISPR/Cas9-mediated gene knockout in Trypanosoma cruzi

Trypanosoma cruzi has three distinct life cycle stages; epimastigote, trypomastigote, and amastigote. Amastigote is the replication stage in host mammalian cells, hence this stage of parasite has clinical significance in drug development research. Presence of extracellular amastigotes (EA) and their infection capability have been known for some decades. Here, we demonstrate that EA can be utilized as an axenic culture to aid in stage-specific study of T. cruzi. Amastigote-like property of axenic amastigote can be sustained in LIT medium at 37°C at least for 1 week, judging from their morphology, amastigote-specific UTR-regulated GFP expression, and stage-specific expression of selected endogenous genes. Inhibitory effect of benznidazole and nifurtimox on axenic amastigotes was comparable to that on intracellular amastigotes. Exogenous nucleic acids can be transfected into EA via conventional electroporation, and selective marker could be utilized for enrichment of transfectants. We also demonstrate that CRISPR/Cas9-mediated gene knockout can be performed in EA. Essentiality of the target gene can be evaluated by the growth capability of the knockout EA, either by continuation of axenic culturing or by host infection and following replication as intracellular amastigotes. By taking advantage of the accessibility and sturdiness of EA, we can potentially expand our experimental freedom in studying amastigote stage of T. cruzi.

Chagas Disease Diagnostic Applications: Present Knowledge and Future Steps

Chagas disease, caused by the protozoan Trypanosoma cruzi, is a lifelong and debilitating illness of major significance throughout Latin America and an emergent threat to global public health. Being a neglected disease, the vast majority of Chagasic patients have limited access to proper diagnosis and treatment, and there is only a marginal investment into R&D for drug and vaccine development. In this context, identification of novel biomarkers able to transcend the current limits of diagnostic methods surfaces as a main priority in Chagas disease applied research. The expectation is that these novel biomarkers will provide reliable, reproducible and accurate results irrespective of the genetic background, infecting parasite strain, stage of disease, and clinical-associated features of Chagasic populations. In addition, they should be able to address other still unmet diagnostic needs, including early detection of congenital T. cruzi transmission, rapid assessment of treatment efficiency or failure, indication/prediction of disease progression and direct parasite typification in clinical samples. The lack of access of poor and neglected populations to essential diagnostics also stresses the necessity of developing new methods operational in point-of-care settings. In summary, emergent diagnostic tests integrating these novel and tailored tools should provide a significant impact on the effectiveness of current intervention schemes and on the clinical management of Chagasic patients. In this chapter, we discuss the present knowledge and possible future steps in Chagas disease diagnostic applications, as well as the opportunity provided by recent advances in high-throughput methods for biomarker discovery.

Insight into the Exoproteome of the Tissue-Derived Trypomastigote form of Trypanosoma cruzi

The protozoan parasite Trypanosoma cruzi causes Chagas disease, one of the major neglected infectious diseases. It has the potential to infect any nucleated mammalian cell. The secreted/excreted protein repertoire released by T. cruzi trypomastigotes is crucial in host-pathogen interactions. In this study, mammalian tissue culture-derived trypomastigotes (Y strain) were used to characterize the exoproteome of the infective bloodstream life form. Proteins released into the serum-free culture medium after 3 h of incubation were harvested and digested with trypsin. NanoLC-MS/MS analysis resulted in the identification of 540 proteins, the largest set of released proteins identified to date in Trypanosoma spp. Bioinformatic analysis predicted most identified proteins as secreted, predominantly by non-classical pathways, and involved in host-cell infection. Some proteins possess predicted GPI-anchor signals, these being mostly trans-sialidases, mucin associated surface proteins and surface glycoproteins. Moreover, we enriched phosphopeptides and glycopeptides from tryptic digests. The majority of identified glycoproteins are trans-sialidases and surface glycoproteins involved in host-parasite interaction. Conversely, most identified phosphoproteins have no Gene Ontology classification. The existence of various proteins related to similar functions in the exoproteome likely reflects this parasite's enhanced mechanisms for adhesion, invasion, and internalization of different host-cell types, and escape from immune defenses.

AFAP-1L1-mediated actin filaments crosslinks hinder Trypanosoma cruzi cell invasion and intracellular multiplication

Host actin cytoskeleton polymerization has been shown to play an important role during Trypanosoma cruzi internalization into mammalian cell. The structure and dynamics of the actin cytoskeleton in cells are regulated by a vast number of actin-binding proteins. Here we aimed to verify the impact of AFAP-1L1, during invasion and multiplication of T. cruzi. Knocking-down AFAP-1L1 increased parasite cell invasion and intracellular multiplication. Thus, we have shown that the integrity of the machinery formed by AFAP-1L1 in actin cytoskeleton polymerization is important to hinder parasite infection.

Mechanisms of cellular invasion by intracellular parasites

Numerous disease-causing parasites must invade host cells in order to prosper. Collectively, such pathogens are responsible for a staggering amount of human sickness and death throughout the world. Leishmaniasis, Chagas disease, toxoplasmosis, and malaria are neglected diseases and therefore are linked to socio-economical and geographical factors, affecting well-over half the world's population. Such obligate intracellular parasites have co-evolved with humans to establish a complexity of specific molecular parasite-host cell interactions, forming the basis of the parasite's cellular tropism. They make use of such interactions to invade host cells as a means to migrate through various tissues, to evade the host immune system, and to undergo intracellular replication. These cellular migration and invasion events are absolutely essential for the completion of the lifecycles of these parasites and lead to their for disease pathogenesis. This review is an overview of the molecular mechanisms of protozoan parasite invasion of host cells and discussion of therapeutic strategies, which could be developed by targeting these invasion pathways. Specifically, we focus on four species of protozoan parasites Leishmania, Trypanosoma cruzi, Plasmodium, and Toxoplasma, which are responsible for significant morbidity and mortality.

Trypanosoma cruzi infection in neotropical wild carnivores (Mammalia: Carnivora): at the top of the T. cruzi transmission chain

Little is known on the role played by Neotropical wild carnivores in the Trypanosoma cruzi transmission cycles. We investigated T. cruzi infection in wild carnivores from three sites in Brazil through parasitological and serological tests. The seven carnivore species examined were infected by T. cruzi, but high parasitemias detectable by hemoculture were found only in two Procyonidae species. Genotyping by Mini-exon gene, PCR-RFLP (1f8/Akw21I) and kDNA genomic targets revealed that the raccoon (Procyon cancrivorus) harbored TcI and the coatis (Nasua nasua) harbored TcI, TcII, TcIII-IV and Trypanosoma rangeli, in single and mixed infections, besides four T. cruzi isolates that displayed odd band patterns in the Mini-exon assay. These findings corroborate the coati can be a bioaccumulator of T. cruzi Discrete Typing Units (DTU) and may act as a transmission hub, a connection point joining sylvatic transmission cycles within terrestrial and arboreal mammals and vectors. Also, the odd band patterns observed in coatis' isolates reinforce that T. cruzi diversity might be much higher than currently acknowledged. Additionally, we assembled our data with T. cruzi infection on Neotropical carnivores' literature records to provide a comprehensive analysis of the infection patterns among distinct carnivore species, especially considering their ecological traits and phylogeny. Altogether, fifteen Neotropical carnivore species were found naturally infected by T. cruzi. Species diet was associated with T. cruzi infection rates, supporting the hypothesis that predator-prey links are important mechanisms for T. cruzi maintenance and dispersion in the wild. Distinct T. cruzi infection patterns across carnivore species and study sites were notable. Musteloidea species consistently exhibit high parasitemias in different studies which indicate their high infectivity potential. Mesocarnivores that feed on both invertebrates and mammals, including the coati, a host that can be bioaccumulator of T. cruzi DTU's, seem to take place at the top of the T. cruzi transmission chain.

Trypanosoma cruzi: role of δ-amastin on extracellular amastigote cell invasion and differentiation

Trypanosoma cruzi is a protozoan parasite that comprises different phylogenetic groups and is the causative agent of Chagas’ disease. Different T. cruzi strains present differences in infectivity in in vitro and in vivo experimental models, which are likely related to the expression of different virulence factors. Amastin is a surface glycoprotein abundantly expressed on the intracellular mammalian amastigote form of the parasite. In this study, we showed that a highly infective strain (G strain) of extracellular amastigote (EA) invasive forms expressed reduced RNA levels of amastin compared to a less infective strain (CL). The treatment of HeLa cells with recombinant δ-amastin reduced infectivity of EA forms. However, the ectopic expression of δ-amastin accelerated amastigote differentiation into trypomastigotes. Corroborating the virulence behavior in association with amastin expression, the EAs overexpressing amastin were precociously and robustly observed in the liver of susceptible mouse strains (A/JUnib), whereas parasitemia was never detected in in vivo assays. This is the first report on the regulatory role of amastin in the course of both in vitro and in vivo T. cruzi infection.

Endothelin and bradykinin: 'brothers-in-arms' in Chagas vasculopathies?

Reports of Chagas disease are increasing in non-endemic populations across the globe. Apart from vector eradication and prevention efforts by public health organizations, current pharmacological interventions are sparse and show important side effects. In this issue of the BJP, Andrade et al. elegantly demonstrate a new pharmacological paradigm whereby Trypanosoma cruzi host cell invasion requires significant cross-talk between receptors for kinins and endothelins. It is shown, for example, that acting via both ET(A) and ET(B) receptors, endothelin-1 (ET-1) cooperates with the (TLR2/CXCR2/B(2) kinin receptor) complex to activate inflammatory processes in response to invading trypomastigotes. This study by Andrade et al. prompts, however, several important questions, summarized in this Commentary, such as the putative role of chymase-dependent production of ET-1, the contentious protective role of ACE inhibitors in Chagasic patients, the unexplored role of de novo formed B(1) receptors for kinins triggered by cytokines and the putative role of compartmentalized calcium pools in host cell invasion by trypomastigotes.

Molecular and cellular mechanisms involved in the Trypanosoma cruzi/host cell interplay

The protozoan parasite Trypanosoma cruzi has a complex biological cycle that involves vertebrate and invertebrate hosts. In mammals, the infective trypomastigote form of this parasite can invade several cell types by exploiting phagocytic-like or nonphagocytic mechanisms depending on the class of cell involved. Morphological studies showed that when trypomastigotes contact macrophages, they induce the formation of plasma membrane protrusions that differ from the canonical phagocytosis that occurs in the case of noninfective epimastigotes. In contrast, when trypomastigotes infect epithelial or muscle cells, the cell surface is minimally modified, suggesting the induction of a different class of process. Lysosomal-dependent or -independent T. cruzi invasion of host cells are two different models that describe the molecular and cellular events activated during parasite entry into nonphagocytic cells. In this context, we have previously shown that induction of autophagy in host cells before infection favors T. cruzi invasion. Furthermore, we demonstrate that autophagosomes and the autophagosomal protein LC3 are recruited to the T. cruzi entry sites and that the newly formed T. cruzi parasitophorous vacuole has characteristics of an autophagolysosome. This review summarizes the current knowledge of the molecular and cellular mechanisms of T. cruzi invasion in nonphagocytic cells. Based on our findings, we propose a new model in which T. cruzi takes advantage of the upregulation of autophagy during starvation to increase its successful colonization of host cells.

Host cell invasion by Trypanosoma cruzi: a unique strategy that promotes persistence

The intracellular protozoan parasite Trypanosoma cruzi is the causative agent of Chagas' disease, a serious disorder that affects millions of people in Latin America. Despite the development of lifelong immunity following infections, the immune system fails to completely clear the parasites, which persist for decades within host tissues. Cardiomyopathy is one of the most serious clinical manifestations of the disease, and a major cause of sudden death in endemic areas. Despite decades of study, there is still debate about the apparent preferential tropism of the parasites for cardiac muscle, and its role in the pathology of the disease. In this review, we discuss these issues in light of recent observations, which indicate that T. cruzi invades host cells by subverting a highly conserved cellular pathway for the repair of plasma membrane lesions. Plasma membrane injury and repair is particularly prevalent in muscle cells, suggesting that the mechanism used by the parasites for cell invasion may be a primary determinant of tissue tropism, intracellular persistence, and Chagas' disease pathology.

Investigation of the potential involvement of eicosanoid metabolites in anti-diuretic hormone signaling in Rhodnius prolixus

The use of naturally occurring plant-derived compounds for controlling insect pests remains an attractive alternative to potentially dangerous synthetic chemical compounds. One prospective plant-based compound, isoforms of the so-called jack bean urease (JBU) from the jack bean, Canavalia ensiformis, as well a derived peptide, Jaburetox-2Ec, have insecticidal effects on an array of insect species. In the Chagas' disease vector, Rhodnius prolixus, some of the physiological effects attributed to these urease isoforms include inhibition of serotonin (5-HT)-stimulated fluid secretion by the Malpighian tubules (MTs). Here, we investigated whether the effects of these exogenous urease isoforms were targeting the neuroendocrine network involved in the anti-diuretic hormone (RhoprCAPA-2) signaling cascade. We show that pharmacological agents known to interfere with eicosanoid metabolite biosynthesis do not affect RhoprCAPA-2 inhibition of 5-HT-stimulated fluid secretion by MTs. In addition, we demonstrate that RhoprCAPA-2 inhibition of MTs is independent of extracellular or intracellular calcium. Using a heterologous system for analysis of receptor activation, we show that neither JBU nor Jaburetox-2Ec are agonists of the anti-diuretic hormone receptor, RhoprCAPAr1. Finally, activation of the receptor using sub-maximal doses of the natural ligand, RhoprCAPA-2, was not influenced by the presence of either JBU or Jaburetox-2Ec indicating that the urease isoforms do not compete with RhoprCAPA-2 for binding and activation of RhoprCAPAr1. Taken together, these results suggest that at least two distinct mechanisms leading to inhibition of fluid secretion by MTs exist in R. prolixus and, unlike the urease-related effects, the eicosanoid metabolite pathway is not involved in RhoprCAPA-2 mediated anti-diuresis.

Invasion and intracellular survival by protozoan parasites

Intracellular parasitism has arisen only a few times during the long ancestry of protozoan parasites including in diverse groups such as microsporidians, kinetoplastids, and apicomplexans. Strategies used to gain entry differ widely from injection (e.g. microsporidians), active penetration of the host cell (e.g. Toxoplasma), recruitment of lysosomes to a plasma membrane wound (e.g. Trypanosoma cruzi), to host cell-mediated phagocytosis (e.g. Leishmania). The resulting range of intracellular niches is equally diverse ranging from cytosolic (e.g. T. cruzi) to residing within a non-fusigenic vacuole (e.g. Toxoplasma, Encephalitozoon) or a modified phagolysosome (e.g. Leishmania). These lifestyle choices influence access to nutrients, interaction with host cell signaling pathways, and detection by pathogen recognition systems. As such, intracellular life requires a repertoire of adaptations to assure entry-exit from the cell, as well as to thwart innate immune mechanisms and prevent clearance. Elucidating these pathways at the cellular and molecular level may identify key steps that can be targeted to reduce parasite survival or augment immunologic responses and thereby prevent disease.

Involvement of host cell heparan sulfate proteoglycan in Trypanosoma cruzi amastigote attachment and invasion

Cell surface glycosaminoglycans (GAGs) play an important role in the attachment and invasion process of a variety of intracellular pathogens. We have previously demonstrated that heparan sulfate proteoglycans (HSPG) mediate the invasion of trypomastigote forms of Trypanosoma cruzi in cardiomyocytes. Herein, we analysed whether GAGs are also implicated in amastigote invasion. Competition assays with soluble GAGs revealed that treatment of T. cruzi amastigotes with heparin and heparan sulfate leads to a reduction in the infection ratio, achieving 82% and 65% inhibition of invasion, respectively. Other sulfated GAGs, such as chondroitin sulfate, dermatan sulfate and keratan sulfate, had no effect on the invasion process. In addition, a significant decrease in infection occurred after interaction of amastigotes with GAG-deficient Chinese Hamster Ovary (CHO) cells, decreasing from 20% and 28% in wild-type CHO cells to 5% and 9% in the mutant cells after 2 h and 4 h of infection, respectively. These findings suggest that amastigote invasion also involves host cell surface heparan sulfate proteoglycans. The knowledge of the mechanism triggered by heparan sulfate-binding T. cruzi proteins may provide new potential candidates for Chagas disease therapy.

Review on Trypanosoma cruzi: Host Cell Interaction

Trypanosoma cruzi, the causative agent of Chagas' disease, which affects a large number of individuals in Central and South America, is transmitted to vertebrate hosts by blood-sucking insects. This protozoan is an obligate intracellular parasite. The infective forms of the parasite are metacyclic and bloodstream trypomastigote and amastigote. Metacyclic trypomastigotes are released with the feces of the insect while amastigotes and bloodstream trypomastigotes are released from the infected host cells of the vertebrate host after a complex intracellular life cycle. The recognition between parasite and mammalian host cell involves numerous molecules present in both cell types. Here, we present a brief review of the interaction between Trypanosoma cruzi and its host cells, mainly emphasizing the mechanisms and molecules that participate in the T. cruzi invasion process of the mammalian cells.

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.

Isolation of an antileishmanial and antitrypanosomal flavanone from the leaves of Baccharis retusa DC. (Asteraceae)

In the course of selection of new bioactive compounds from Brazilian flora, the crude MeOH extract from the leaves of Baccharis retusa DC. (Asteraceae) showed potential against Leishmania sp. and Trypanosoma cruzi. Chromatographic fractionation of the dichloromethane phase from MeOH extract yielded great amounts of the bioactive derivative, which was characterized as 5,6,7-trihydroxy-4'-methoxyflavanone. The structure of this compound was established on the basis of spectroscopic data analysis, mainly nuclear magnetic resonance and mass spectrometry.