The use of the green fluorescent protein to monitor and improve transfection in Trypanosoma cruzi

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.

Indigenous people from Amazon show genetic signatures of pathogen-driven selection

Ecological conditions in the Amazon rainforests are historically favorable for the transmission of numerous tropical diseases, especially vector-borne diseases. The high diversity of pathogens likely contributes to the strong selective pressures for human survival and reproduction in this region. However, the genetic basis of human adaptation to this complex ecosystem remains unclear. This study investigates the possible footprints of genetic adaptation to the Amazon rainforest environment by analyzing the genomic data of 19 native populations. The results based on genomic and functional analysis showed an intense signal of natural selection in a set of genes related to Trypanosoma cruzi infection, which is the pathogen responsible for Chagas disease, a neglected tropical parasitic disease native to the Americas that is currently spreading worldwide.

Cardiomyocyte infection by Trypanosoma cruzi promotes innate immune response and glycolysis activation

Introduction

Chagas cardiomyopathy, a disease caused by Trypanosoma cruzi (T. cruzi) infection, is a major contributor to heart failure in Latin America. There are significant gaps in our understanding of the mechanism for infection of human cardiomyocytes, the pathways activated during the acute phase of the disease, and the molecular changes that lead to the progression of cardiomyopathy.

Methods

To investigate the effects of T. cruzi on human cardiomyocytes during infection, we infected induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) with the parasite and analyzed cellular, molecular, and metabolic responses at 3 hours, 24 hours, and 48 hours post infection (hpi) using transcriptomics (RNAseq), proteomics (LC-MS), and metabolomics (GC-MS and Seahorse) analyses.

Results

Analyses of multiomic data revealed that cardiomyocyte infection caused a rapid increase in genes and proteins related to activation innate and adaptive immune systems and pathways, including alpha and gamma interferons, HIF-1α signaling, and glycolysis. These responses resemble prototypic responses observed in pathogen-activated immune cells. Infection also caused an activation of glycolysis that was dependent on HIF-1α signaling. Using gene editing and pharmacological inhibitors, we found that T. cruzi uptake was mediated in part by the glucose-facilitated transporter GLUT4 and that the attenuation of glycolysis, HIF-1α activation, or GLUT4 expression decreased T. cruzi infection. In contrast, pre-activation of pro-inflammatory immune responses with LPS resulted in increased infection rates.

Conclusion

These findings suggest that T. cruzi exploits a HIF-1α-dependent, cardiomyocyte-intrinsic stress-response activation of glycolysis to promote intracellular infection and replication. These chronic immuno-metabolic responses by cardiomyocytes promote dysfunction, cell death, and the emergence of cardiomyopathy.

Different Transcriptomic Response to T. cruzi Infection in hiPSC-Derived Cardiomyocytes From Chagas Disease Patients With and Without Chronic Cardiomyopathy

Chagas disease is a tropical zoonosis caused by Trypanosoma cruzi. After infection, the host present an acute phase, usually asymptomatic, in which an extensive parasite proliferation and intense innate immune activity occurs, followed by a chronic phase, characterized by low parasitemia and development of specific immunity. Most individuals in the chronic phase remain without symptoms or organ damage, a state called indeterminate IND form. However, 20 to 40% of individuals develop cardiac or gastrointestinal complications at any time in life. Cardiomyocytes have an important role in the development of Chronic Chagas Cardiomyopathy (CCC) due to transcriptional and metabolic alterations that are crucial for the parasite survival and replication. However, it still not clear why some infected individuals progress to a cardiomyopathy phase, while others remain asymptomatic. In this work, we used hiPSCs-derived cardiomyocytes (hiPSC-CM) to investigate patterns of infection, proliferation and transcriptional response in IND and CCC patients. Our data show that T. cruzi infection and proliferation efficiency do not differ significantly in PBMCs and hiPSC-CM from both groups. However, RNA-seq analysis in hiPSC-CM infected for 24 hours showed a significantly different transcriptional response to the parasite in cells from IND or CCC patients. Cardiomyocytes from IND showed significant differences in the expression of genes related to antigen processing and presentation, as well as, immune co-stimulatory molecules. Furthermore, the downregulation of collagen production genes and extracellular matrix components was significantly different in these cells. Cardiomyocytes from CCC, in turn, showed increased expression of mTORC1 pathway and unfolded protein response genes, both associated to increased intracellular ROS production. These data point to a differential pattern of response, determined by baseline genetic differences between groups, which may have an impact on the development of a chronic outcome with or without the presentation of cardiac symptoms.

Cyclophilin 19 secreted in the host cell cytosol by Trypanosoma cruzi promotes ROS production required for parasite growth

Infection by Trypanosoma cruzi, the protozoan parasite that causes Chagas disease, depends on reactive oxygen species (ROS), which has been described to induce parasite proliferation in mammalian host cells. It is unknown how the parasite manages to increase host ROS levels. Here, we found that intracellular T. cruzi forms release in the host cytosol its major cyclophilin of 19 kDa (TcCyp19). Parasites depleted of TcCyp19 by using CRISPR/Cas9 gene replacement proliferate inefficiently and fail to increase ROS, compared to wild type parasites or parasites with restored TcCyp19 gene expression. Expression of TcCyp19 in L6 rat myoblast increased ROS levels and restored the proliferation of TcCyp19 depleted parasites. These events could also be inhibited by cyclosporin A, (a cyclophilin inhibitor), and by polyethylene glycol-linked to antioxidant enzymes. TcCyp19 was found more concentrated in the membrane leading edges of the host cells in regions that also accumulate phosphorylated p47^phox , as observed to the endogenous cyclophilin A, suggesting some mechanisms involved with the translocation process of the regulatory subunit p47^phox in the activation of the NADPH oxidase enzymatic complex. We concluded that cyclophilin released in the host cell cytosol by T. cruzi mediates the increase of ROS, required to boost parasite proliferation in mammalian hosts.

EIF2α phosphorylation is regulated in intracellular amastigotes for the generation of infective Trypanosoma cruzi trypomastigote forms

Trypanosomatids regulate gene expression mainly at the post-transcriptional level through processing, exporting and stabilising mRNA and control of translation. In most eukaryotes, protein synthesis is regulated by phosphorylation of eukaryotic initiation factor 2 (eIF2) at serine 51. Phosphorylation halts overall translation by decreasing availability of initiator tRNA^met to form translating ribosomes. In trypanosomatids, the N-terminus of eIF2α is extended with threonine 169 the homologous phosphorylated residue. Here, we evaluated whether eIF2α phosphorylation varies during the Trypanosoma cruzi life cycle, the etiological agent of Chagas' disease. Total levels of eIF2α are diminished in infective and non-replicative trypomastigotes compared with proliferative forms from the intestine of the insect vector or amastigotes from mammalian cells, consistent with decreased protein synthesis reported in infective forms. eIF2α phosphorylation increases in proliferative intracellular forms prior to differentiation into trypomastigotes. Parasites overexpressing eIF2α^T169A or with an endogenous CRISPR/Cas9-generated eIF2α^T169A mutation were created and analysis revealed alterations to the proteome, largely unrelated to the presence of μORF in epimastigotes. eIF2α^T169A mutant parasites produced fewer trypomastigotes with lower infectivity than wild type, with increased levels of sialylated mucins and oligomannose glycoproteins, and decreased galactofuranose epitopes and the surface protease GP63 on the cell surface. We conclude that eIF2α expression and phosphorylation levels affect proteins relevant for intracellular progression of T. cruzi.

Induction of autophagy increases the proteolytic activity of reservosomes during Trypanosoma cruzi metacyclogenesis

Cruzipain, the major cysteine protease of the pathogenic protozoa Trypanosoma cruzi, is an important virulence factor that plays a key role in the parasite nutrition, differentiation and host cell infection. Cruzipain is synthesized as a zymogen, matured, and delivered to reservosomes. These organelles that store proteins and lipids ingested by endocytosis undergo a dramatic decrease in number during the metacyclogenesis of T. cruzi. Autophagy is a process that digests the own cell components to supply energy under starvation or different stress situations. This pathway is important during cell growth, differentiation and death. Previously, we showed that the autophagy pathway of T. cruzi is induced during metacyclogenesis. This work aimed to evaluate the participation of macroautophagy/autophagy in the distribution and function of reservosomes and cruzipain during this process. We found that parasite starvation promotes the cruzipain delivery to reservosomes. Enhanced autophagy increases acidity and hydrolytic activity in these compartments resulting in cruzipain enzymatic activation and self- processing. Inhibition of autophagy similarly impairs cruzipain traffic and activity than protease inhibitors, whereas mutant parasites that exhibit increased basal autophagy, also display increased cruzipain processing under control conditions. Further experiments showed that autophagy induced cruzipain activation and self-processing promote T. cruzi differentiation and host cell infection. These findings highlight the key role of T. cruzi autophagy in these processes and reveal a potential new target for Chagas disease therapy.Abbreviations: Baf: bafilomycin A₁; CTE: C-terminal extension; Cz: cruzipain; IIF: indirect immunofluorescence; K777: vinyl sulfone with specific Cz inhibitory activity; Prot Inh: broad-spectrum protease inhibitor; Spa1: spautin-1; Wort: wortmannin.

Autophagy plays a protective role against Trypanosoma cruzi infection in mice

Autophagy is a catabolic pathway required for cellular and organism homeostasis. Autophagy participates in the innate and adaptive immune responses at different levels. Xenophagy is a class of selective autophagy that involves the elimination of intracellular pathogens. Trypanosoma cruzi is the causative agent of Chagas, a disease that affects 8 million individuals worldwide. Previously, our group has demonstrated that autophagy participates in the invasion of T. cruzi in non-phagocytic cells. In this work we have studied the involvement of autophagy in the development of T. cruzi infection in mice. Beclin-1 is a protein essential for autophagy, required for autophagosome biogenesis and maturation. We have performed an acute model of infection on the autophagic deficient Beclin-1 heterozygous knock-out mice (Bcln^±) and compared to control Bcln^+/+ animals. In addition, we have analyzed the infection process in both peritoneal cells and RAW macrophages. Our results have shown that the infection was more aggressive in the autophagy-deficient mice, which displayed higher numbers of parasitemia, heart´s parasitic nests and mortality rates. We have also found that peritoneal cells derived from Bcln^± animals and RAW macrophages treated with autophagy inhibitors displayed higher levels of infection compared to controls. Interestingly, free cytosolic parasites recruited LC3 protein and other markers of xenophagy in control compared to autophagy-deficient cells. Taken together, these data suggest that autophagy plays a protective role against T. cruzi infection in mice, xenophagy being one of the processes activated as part of the repertoire of immune responses generated by the host.

The regulation of autophagy differentially affects Trypanosoma cruzi metacyclogenesis

Autophagy is a cellular process required for the removal of aged organelles and cytosolic components through lysosomal degradation. All types of eukaryotic cells from yeasts to mammalian cells have the machinery to activate autophagy as a result of many physiological and pathological situations. The most frequent stimulus of autophagy is starvation and the result, in this case, is the fast generation of utilizable food (e.g. amino acids and basic nutrients) to maintain the vital biological processes. In some organisms, starvation also triggers other associated processes such as differentiation. The protozoan parasite Trypanosoma cruzi undergoes a series of differentiation processes throughout its complex life cycle. Although not all autophagic genes have been identified in the T. cruzi genome, previous works have demonstrated the presence of essential autophagic-related proteins. Under starvation conditions, TcAtg8, which is the parasite homolog of Atg8/LC3 in other organisms, is located in autophagosome-like vesicles. In this work, we have characterized the autophagic pathway during T. cruzi differentiation from the epimastigote to metacyclic trypomastigote form, a process called metacyclogenesis. We demonstrated that autophagy is stimulated during metacyclogenesis and that the induction of autophagy promotes this process. Moreover, with exception of bafilomycin, other classical autophagy modulators have similar effects on T. cruzi autophagy. We also showed that spermidine and related polyamines can positively regulate parasite autophagy and differentiation. We concluded that both polyamine metabolism and autophagy are key processes during T. cruzi metacyclogenesis that could be exploited as drug targets to avoid the parasite cycle progression.

In spite of its old discovery, more than one hundred years ago, Trypanosoma cruzi, the causative agent of Chagas’ disease, is still prevalent in the world, infecting more than 6 million people mostly in Latin America, where this illness is endemic. Only two approved drugs, benznidazole and nifurtimox, are currently used for the treatment of Chagas’ disease. Although efficient for the acute phase, they are poorly effective in the chronic period of the disease and they cause many undesirable side effects. There is an urgent need for therapeutic alternatives. To this end, identifying and validating novel molecular targets is critically relevant. This study describes the effect of different inhibitors on the T. cruzi autophagic pathway, a process required for parasite differentiation. Herein, we demonstrate that the regulation of parasite autophagy exhibits similarities and differences with host cell autophagy. Our study provides new insights that could be used to avoid T. cruzi cycle progression in both insect and mammalian hosts.

The superfamily keeps growing: Identification in trypanosomatids of RibJ, the first riboflavin transporter family in protists

Background

Trypanosomatid parasites represent a major health issue affecting hundreds of million people worldwide, with clinical treatments that are partially effective and/or very toxic. They are responsible for serious human and plant diseases including Trypanosoma cruzi (Chagas disease), Trypanosoma brucei (Sleeping sickness), Leishmania spp. (Leishmaniasis), and Phytomonas spp. (phytoparasites). Both, animals and trypanosomatids lack the biosynthetic riboflavin (vitamin B2) pathway, the vital precursor of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) cofactors. While metazoans obtain riboflavin from the diet through RFVT/SLC52 transporters, the riboflavin transport mechanisms in trypanosomatids still remain unknown.

Methodology/Principal findings

Here, we show that riboflavin is imported with high affinity in Trypanosoma cruzi, Trypanosoma brucei, Leishmania (Leishmania) mexicana, Crithidia fasciculata and Phytomonas Jma using radiolabeled riboflavin transport assays. The vitamin is incorporated through a saturable carrier-mediated process. Effective competitive uptake occurs with riboflavin analogs roseoflavin, lumiflavin and lumichrome, and co-factor derivatives FMN and FAD. Moreover, important biological processes evaluated in T. cruzi (i.e. proliferation, metacyclogenesis and amastigote replication) are dependent on riboflavin availability. In addition, the riboflavin competitive analogs were found to interfere with parasite physiology on riboflavin-dependent processes. By means of bioinformatics analyses we identified a novel family of riboflavin transporters (RibJ) in trypanosomatids. Two RibJ members, TcRibJ and TbRibJ from T. cruzi and T. brucei respectively, were functionally characterized using homologous and/or heterologous expression systems.

Conclusions/Significance

The RibJ family represents the first riboflavin transporters found in protists and the third eukaryotic family known to date. The essentiality of riboflavin for trypanosomatids, and the structural/biochemical differences that RFVT/SLC52 and RibJ present, make the riboflavin transporter -and its downstream metabolism- a potential trypanocidal drug target.

In this work, we show that riboflavin plays a key role in the trypanosomatid life cycles and describe a novel family of riboflavin transporters (RibJ) with uptake function. Despite the vital importance of riboflavin for all living cells, RibJ are the first transporters described in protists. We functionally characterized the T. cruzi and T. brucei RibJ members and the effect of riboflavin analogs on parasite physiology. The structural and biochemical differences presented between human transporters and RibJ members make riboflavin transport and downstream metabolism, attractive and potential trypanosomatid targets.

Trypanosoma cruzi Differentiates and Multiplies within Chimeric Parasitophorous Vacuoles in Macrophages Coinfected with Leishmania amazonensis

The trypanosomatids Leishmania amazonensis and Trypanosoma cruzi are excellent models for the study of the cell biology of intracellular protozoan infections. After their uptake by mammalian cells, the parasitic protozoan flagellates L. amazonensis and T. cruzi lodge within acidified parasitophorous vacuoles (PVs). However, whereas L. amazonensis develops in spacious, phagolysosome-like PVs that may enclose numerous parasites, T. cruzi is transiently hosted within smaller vacuoles from which it soon escapes to the host cell cytosol. To investigate if parasite-specific vacuoles are required for the survival and differentiation of T. cruzi, we constructed chimeric vacuoles by infection of L. amazonensis amastigote-infected macrophages with T. cruzi epimastigotes (EPIs) or metacyclic trypomastigotes (MTs). These chimeric vacuoles, easily observed by microscopy, allowed the entry and fate of T. cruzi in L. amazonensis PVs to be dynamically recorded by multidimensional imaging of coinfected cells. We found that although T. cruzi EPIs remained motile and conserved their morphology in chimeric vacuoles, T. cruzi MTs differentiated into amastigote-like forms capable of multiplying. These results demonstrate that the large adaptive vacuoles of L. amazonensis are permissive to T. cruzi survival and differentiation and that noninfective EPIs are spared from destruction within the chimeric PVs. We conclude that T. cruzi differentiation can take place in Leishmania-containing vacuoles, suggesting this occurs prior to their escape into the host cell cytosol.

Trypanosoma cruzi: single cell live imaging inside infected tissues

Although imaging the live Trypanosoma cruzi parasite is a routine technique in most laboratories, identification of the parasite in infected tissues and organs has been hindered by their intrinsic opaque nature. We describe a simple method for in vivo observation of live single-cell Trypanosoma cruzi parasites inside mammalian host tissues. BALB/c or C57BL/6 mice infected with DsRed-CL or GFP-G trypomastigotes had their organs removed and sectioned with surgical blades. Ex vivo organ sections were observed under confocal microscopy. For the first time, this procedure enabled imaging of individual amastigotes, intermediate forms and motile trypomastigotes within infected tissues of mammalian hosts.

Expanding the tool box for genetic manipulation of Trypanosoma cruzi

Trypanosoma cruzi is a protozoan parasite that causes Chagas disease, an illness that affects 6-7 million people and for which there is no effective drug therapy or vaccine. The publication of its complete genome sequence allowed a rapid advance in molecular studies including in silico screening of genes involved with pathogenicity as well as molecular targets for the development of new diagnostic methods, drug therapies and prophylactic vaccines. Alongside with in silico genomic analyses, methods to study gene function in this parasite such as gene deletion, overexpression, mutant complementation and reporter gene expression have been largely explored. More recently, the use of genome-wide strategies is producing a shift towards a global perspective on gene function studies, with the examination of the expression and biological roles of gene networks in different stages of the parasite life cycle and under different contexts of host parasite interactions. Here we describe the molecular tools and protocols currently available to perform genetic manipulation of the T. cruzi genome, with emphasis on recently described strategies of gene editing that will facilitate large-scale functional genomic analyses. These new methodologies are long overdue, since more efficient protocols for genetic manipulation in T. cruzi are urgently needed for a better understanding of the biology of this parasite and molecular processes involved with the complex and often harmful, interaction with its human host.

Characterization of Trypanosoma cruzi Sirtuins as Possible Drug Targets for Chagas Disease

Acetylation of lysine is a major posttranslational modification of proteins and is catalyzed by lysine acetyltransferases, while lysine deacetylases remove acetyl groups. Among the deacetylases, the sirtuins are NAD(+)-dependent enzymes, which modulate gene silencing, DNA damage repair, and several metabolic processes. As sirtuin-specific inhibitors have been proposed as drugs for inhibiting the proliferation of tumor cells, in this study, we investigated the role of these inhibitors in the growth and differentiation of Trypanosoma cruzi, the agent of Chagas disease. We found that the use of salermide during parasite infection prevented growth and initial multiplication after mammalian cell invasion by T. cruzi at concentrations that did not affect host cell viability. In addition, in vivo infection was partially controlled upon administration of salermide. There are two sirtuins in T. cruzi, TcSir2rp1 and TcSir2rp3. By using specific antibodies and cell lines overexpressing the tagged versions of these enzymes, we found that TcSir2rp1 is localized in the cytosol and TcSir2rp3 in the mitochondrion. TcSir2rp1 overexpression acts to impair parasite growth and differentiation, whereas the wild-type version of TcSir2rp3 and not an enzyme mutated in the active site improves both. The effects observed with TcSir2rp3 were fully reverted by adding salermide, which inhibited TcSir2rp3 expressed in Escherichia coli with a 50% inhibitory concentration (IC50) ± standard error of 1 ± 0.5 μM. We concluded that sirtuin inhibitors targeting TcSir2rp3 could be used in Chagas disease chemotherapy.

Stress induces changes in the phosphorylation of Trypanosoma cruzi RNA polymerase II, affecting its association with chromatin and RNA processing

The phosphorylation of the carboxy-terminal heptapeptide repeats of the largest subunit of RNA polymerase II (Pol II) controls several transcription-related events in eukaryotes. Trypanosomatids lack these typical repeats and display an unusual transcription control. RNA Pol II associates with the transcription site of the spliced leader (SL) RNA, which is used in the trans-splicing of all mRNAs transcribed on long polycistronic units. We found that Trypanosoma cruzi RNA Pol II associated with chromatin is highly phosphorylated. When transcription is inhibited by actinomycin D, the enzyme runs off from SL genes, remaining hyperphosphorylated and associated with polycistronic transcription units. Upon heat shock, the enzyme is dephosphorylated and remains associated with the chromatin. Transcription is partially inhibited with the accumulation of housekeeping precursor mRNAs, except for heat shock genes. DNA damage caused dephosphorylation and transcription arrest, with RNA Pol II dissociating from chromatin although staying at the SL. In the presence of calyculin A, the hyperphosphorylated form detached from chromatin, including the SL loci. These results indicate that in trypanosomes, the unusual RNA Pol II is phosphorylated during the transcription of SL and polycistronic operons. Different types of stresses modify its phosphorylation state, affecting pre-RNA processing.

An image-based algorithm for precise and accurate high throughput assessment of drug activity against the human parasite Trypanosoma cruzi

We present a customized high content (image-based) and high throughput screening algorithm for the quantification of Trypanosoma cruzi infection in host cells. Based solely on DNA staining and single-channel images, the algorithm precisely segments and identifies the nuclei and cytoplasm of mammalian host cells as well as the intracellular parasites infecting the cells. The algorithm outputs statistical parameters including the total number of cells, number of infected cells and the total number of parasites per image, the average number of parasites per infected cell, and the infection ratio (defined as the number of infected cells divided by the total number of cells). Accurate and precise estimation of these parameters allow for both quantification of compound activity against parasites, as well as the compound cytotoxicity, thus eliminating the need for an additional toxicity-assay, hereby reducing screening costs significantly. We validate the performance of the algorithm using two known drugs against T.cruzi: Benznidazole and Nifurtimox. Also, we have checked the performance of the cell detection with manual inspection of the images. Finally, from the titration of the two compounds, we confirm that the algorithm provides the expected half maximal effective concentration (EC50) of the anti-T. cruzi activity.

Eukaryotic initiation factor 5A dephosphorylation is required for translational arrest in stationary phase cells

The protein known as eIF5A (eukaryotic initiation factor 5A) has an elusive role in translation. It has a unique and essential hypusine modification at a conserved lysine residue in most eukaryotes. In addition, this protein is modified by phosphorylation with unknown functions. In the present study we show that a phosphorylated state of eIF5A predominates in exponentially growing Trypanosoma cruzi cells, and extensive dephosphorylation occurs in cells in stationary phase. Phosphorylation occurs mainly at Ser(2), as shown in yeast eIF5A. In addition, a novel phosphorylation site was identified at Tyr(21). In exponential cells, T. cruzi eIF5A is partially associated with polysomes, compatible with a proposed function as an elongation factor, and becomes relatively enriched in polysomal fractions in stationary phase. Overexpression of the wild-type eIF5A, or eIF5A with Ser(2) replaced by an aspartate residue, but not by alanine, increases the rate of cell proliferation and protein synthesis. However, the presence of an aspartate residue instead of Ser(2) is toxic for cells reaching the stationary phase, which show a less-pronounced protein synthesis arrest and a decreased amount of eIF5A in dense fractions of sucrose gradients. We conclude that eIF5A phosphorylation and dephosphorylation cycles regulate translation according to the growth conditions.

Molecular and functional characterization of a Trypanosoma cruzi nuclear adenylate kinase isoform

Trypanosoma cruzi, the etiological agent of Chagas' disease, is an early divergent eukaryote in which control of gene expression relies mainly in post-transcriptional mechanisms. Transcription levels are globally up and down regulated during the transition between proliferating and non-proliferating life-cycle stages. In this work we characterized a nuclear adenylate kinase isoform (TcADKn) that is involved in ribosome biogenesis. Nuclear adenylate kinases have been recently described in a few organisms, being all related to RNA metabolism. Depending on active transcription and translation, TcADKn localizes in the nucleolus or the cytoplasm. A non-canonical nuclear localization signal was mapped towards the N-terminal of the protein, being the phosphate-binding loop essential for its localization. In addition, TcADKn nuclear exportation depends on the nuclear exportation adapter CRM1. TcADKn nuclear shuttling is governed by nutrient availability, oxidative stress and by the equivalent in T. cruzi of the mammalian TOR (Target of Rapamycin) pathway. One of the biological functions of TcADKn is ribosomal 18S RNA processing by direct interaction with ribosomal protein TcRps14. Finally, TcADKn expression is regulated by its 3′ UTR mRNA. Depending on extracellular conditions, cells modulate protein translation rates regulating ribosome biogenesis and nuclear adenylate kinases are probably key components in these processes.

Infection with Trypanosoma cruzi produces a condition known as Chagas disease which affects at least 17 million people. Adenylate kinases, so called myokinases, are involved in a wide variety of processes, mainly related to their role in nucleotide interconversion and energy management. Recently, nuclear isoforms have been described in several organisms. This “atypical” isoform in terms of primary structure was associated to ribosomes biogenesis in yeast and to Cajal body organization in humans. Moreover nuclear adenylate kinases are essential for maintaining cellular homeostasis. In this manuscript we characterized T. cruzi nuclear adenylate kinase (TcADKn). TcADKn localizes in the nucleolus or cell cytoplasm. Nuclear shuttling mechanisms were also studied for the first time, being dependent on nutrient availability, oxidative stress and by the equivalent of the mammalian TOR pathway in T. cruzi. Furthermore we characterized the signals involved in nuclear importation and exportation processes. In addition, TcADKn expression levels are regulated at an mRNA level, being its 3′UTR involved in this process. These findings are the first steps in the understanding of ribosome processing in trypanosomatids.

Nuclear structure of Trypanosoma cruzi

The presence of nucleus in living organisms characterizes the Eukaryote domain. The nucleus compartmentalizes the genetic material surrounded by a double membrane called nuclear envelope. The nucleus has been observed since the advent of the light microscope, and sub-compartments such as nucleoli, diverse nuclear bodies and condensed chromosomes have been later recognized, being part of highly organized and dynamic structure. The significance and function of such organization has increased with the understanding of transcription, replication, DNA repair, recombination processes. It is now recognized as consequence of adding complexity and regulation in more complex eukaryotic cells. Here we provide a description of the actual stage of knowledge of the nuclear structure of Trypanosoma cruzi. As an early divergent eukaryote, it presents unique and/or reduced events of DNA replication, transcription and repair as well as RNA processing and transport to the cytosol. Nevertheless, it shows peculiar structure changes accordingly to the cell cycle and stage of differentiation. T. cruzi proliferates only as epimastigote and amastigote stages, and when these forms differentiate in trypomastigote forms, their cell cycle is arrested. This arrested stage is capable of invading mammalian cells and of surviving harsh conditions, such as the gut of the insect vector and mammalian macrophages. Transcription and replication decrease during transformation in trypomastigotes implicating large alterations in the nuclear structure. Recent evidences also suggest that T. cruzi nucleus respond to oxidative and nutritional stresses. Due to the phylogenetic proximity with other well-known trypanosomes, such as Trypanosoma brucei and Leishmania major, they are expected to have similar nuclear organization, although differences are noticed due to distinct life cycles, cellular organizations and the specific adaptations for surviving in different host environments. Therefore, the general features of T. cruzi nuclear structure regarding unique characteristics of this protozoan parasite will be described.

Protein synthesis attenuation by phosphorylation of eIF2α is required for the differentiation of Trypanosoma cruzi into infective forms

Chagas' disease is a potentially life-threatening illness caused by the unicellular protozoan parasite Trypanosoma cruzi. It is transmitted to humans by triatomine bugs where T. cruzi multiplies and differentiates in the digestive tract. The differentiation of proliferative and non-infective epimastigotes into infective metacyclic trypomastigotes (metacyclogenesis) can be correlated to nutrient exhaustion in the gut of the insect vector. In vitro, metacyclic-trypomastigotes can be obtained when epimastigotes are submitted to nutritional stress suggesting that metacyclogenesis is triggered by nutrient starvation. The molecular mechanism underlying such event is not understood. Here, we investigated the role of one of the key signaling responses elicited by nutritional stress in all other eukaryotes, the inhibition of translation initiation by the phosphorylation of the eukaryotic initiation factor 2α (eIF2α), during the in vitro differentiation of T. cruzi. Monospecific antibodies that recognize the phosphorylated Tc-eIF2α form were generated and used to demonstrate that parasites subjected to nutritional stress show increased levels of Tc-eIF2α phosphorylation. This was accompanied by a drastic inhibition of global translation initiation, as determined by polysomal profiles. A strain of T. cruzi overexpressing a mutant Tc-eIF2α, incapable of being phosphorylated, showed a block on translation initiation, indicating that such a nutritional stress in trypanosomatids induces the conserved translation inhibition response. In addition, Tc-eIF2α phosphorylation is critical for parasite differentiation since the overexpression of the mutant eIF2α in epimastigotes abolished metacyclogenesis. This work defines the role of eIF2α phosphorylation as a key step in T. cruzi differentiation.

Trypanosoma cruzi Coexpressing Ornithine Decarboxylase and Green Fluorescence Proteins as a Tool to Study the Role of Polyamines in Chagas Disease Pathology

Polyamines are essential for Trypanosoma cruzi, the causative agent of Chagas disease. As T. cruzi behaves as a natural auxotrophic organism, it relies on host polyamines biosynthesis. In this paper we obtained a double-transfected T. cruzi parasite that expresses the green fluorescent protein (GFP) and a heterologous ornithine decarboxylase (ODC), used itself as a novel selectable marker. These autotrophic and fluorescent parasites were characterized; the ODC presented an apparent Km for ornithine of 0.51 ± 0.16 mM and an estimated V_max value of 476.2 nmoles/h/mg of protein. These expressing ODC parasites showed higher metacyclogenesis capacity than the auxotrophic counterpart, supporting the idea that polyamines are engaged in this process. This double-transfected T. cruzi parasite results in a powerful tool—easy to follow by its fluorescence—to study the role of polyamines in Chagas disease pathology and in related processes such as parasite survival, invasion, proliferation, metacyclogenesis, and tissue spreading.

Genetic techniques in Trypanosoma cruzi

It is almost 20 years since genetic manipulation of Trypanosoma cruzi was first reported. In this time, there have been steady improvements in the available vector systems, and the applications of the technology have been extended into new areas. Episomal vectors have been modified to enhance the level of expression of transfected genes and to facilitate the sub-cellular location of their products. Integrative vectors have been adapted to allow the development of inducible expression systems and the construction of vectors which enable genome modification through telomere-associated chromosome fragmentation. The uses of reverse genetic approaches to dissect peroxide metabolism and the mechanisms of drug activity and resistance in T. cruzi are illustrated in this chapter as examples of how the technology has been used to investigate biological function. Although there remains scope to improve the flexibility of these systems, they have made valuable contributions towards exploiting the genome sequence data and providing a greater understanding of parasite biology and the mechanisms of infection.

Complement C2 receptor inhibitor trispanning confers an increased ability to resist complement-mediated lysis in Trypanosoma cruzi

The ability to resist complement differs between the Y and Colombiana Trypanosoma cruzi strains. We found that the Y strain of T. cruzi was more able to resist the classical and lectin pathways of complement activation than the Colombiana strain. The complement C2 receptor inhibitor trispanning gene (CRIT) is highly conserved in both strains. At the protein level, CRIT is expressed only in stationary-phase epimastigotes of the Y but not the Colombiana strain and is expressed in infectious metacyclic trypomastigotes of both strains. Y strain epimastigotes with an overexpressed CRIT gene (pTEX-CRIT) had higher survival in normal human serum (NHS). Overexpression of the Y strain CRIT gene in Colombiana epimastigote forms increased the parasite's resistance to lysis mediated by the classical and lectin pathways but not to lysis mediated by alternative pathways. CRIT involvement on the parasite surface was confirmed by showing that the lytic activity of NHS against epimastigotes could be restored by adding excess C2.

Cell culture and animal infection with distinct Trypanosoma cruzi strains expressing red and green fluorescent proteins

Different strains of Trypanosoma cruzi were transfected with an expression vector that allows the integration of green fluorescent protein (GFP) and red fluorescent protein (RFP) genes into the beta-tubulin locus by homologous recombination. The sites of integration of the GFP and RFP markers were determined by pulse-field gel electrophoresis and Southern blot analyses. Cloned cell lines selected from transfected epimastigote populations maintained high levels of fluorescent protein expression even after 6 months of in vitro culture of epimastigotes in the absence of drug selection. Fluorescent trypomastigotes and amastigotes were observed within Vero cells in culture as well as in hearts and diaphragms of infected mice. The infectivity of the GFP- and RFP-expressing parasites in tissue culture cells was comparable to wild type populations. Furthermore, GFP- and RFP-expressing parasites were able to produce similar levels of parasitemia in mice compared with wild type parasites. Cell cultures infected simultaneously with two cloned cell lines from the same parasite strain, each one expressing a distinct fluorescent marker, showed that at least two different parasites are able to infect the same cell. Double-infected cells were also detected when GFP- and RFP-expressing parasites were derived from strains belonging to two distinct T. cruzi lineages. These results show the usefulness of parasites expressing GFP and RFP for the study of various aspects of T. cruzi infection including the mechanisms of cell invasion, genetic exchange among parasites and the differential tissue distribution in animal models of Chagas disease.

Histone H1 of Trypanosoma cruzi is concentrated in the nucleolus region and disperses upon phosphorylation during progression to mitosis

Phosphorylation of histone H1 is intimately related to the cell cycle progression in higher eukaryotes, reaching maximum levels during mitosis. We have previously shown that in the flagellated protozoan Trypanosoma cruzi, which does not condense chromatin during mitosis, histone H1 is phosphorylated at a single cyclin-dependent kinase site. By using an antibody that recognizes specifically the phosphorylated T. cruzi histone H1 site, we have now confirmed that T. cruzi histone H1 is also phosphorylated in a cell cycle-dependent manner. Differently from core histones, the bulk of nonphosphorylated histone H1 in G(1) and S phases of the cell cycle is concentrated in the central regions of the nucleus, which contains the nucleolus and less densely packed chromatin. When cells pass G(2), histone H1 becomes phosphorylated and starts to diffuse. At the onset of mitosis, histone H1 phosphorylation is maximal and found in the entire nuclear space. As permeabilized parasites preferentially lose phosphorylated histone H1, we conclude that this modification promotes its release from less condensed and nucleolar chromatin after G(2).

Expression of trypomastigote trans-sialidase in metacyclic forms of Trypanosoma cruzi increases parasite escape from its parasitophorous vacuole

Trypanosoma cruzi actively invades mammalian cells by forming parasitophorous vacuoles (PVs). After entry, the parasite has to escape from these vacuoles in order to replicate inside the host cell cytosol. Trans-sialidase (TS), a parasite enzyme that is used to obtain sialic acid from host glycoconjugates, has been implicated in cell invasion and PV exit, but how the enzyme acts in these processes is still unknown. Here we show that trypomastigotes derived from infected mammalian cells express and release 20 times more TS activity than axenic metacyclic trypomastigotes, which correspond to the infective forms derived from the insect vector. Both forms have the same capacity to invade mammalian cells, but cell derived trypomastigotes exit earlier from the vacuole. To test whether high TS expression is responsible for this increased exit from the PV, trypomastigote TS was expressed on the surface of metacyclic forms. Transfected and non-transfected metacyclics attached to and invaded HeLa or CHO cells equally. In contrast, metacyclics expressing TS on the surface escaped earlier from the vacuole than non-transfected metacyclics, or metacyclics expressing TS in their cytoplasm. Sialic acid may act as a barrier, which is removed by surface and/or secreted TS, because all types of parasites escaped earlier from the vacuoles of sialic acid-deficient Lec 2 cells than wild-type CHO cells. In addition, trypomastigotes and metacyclic forms expressing TS differentiated earlier into amastigotes. These results indicate that the increased expression of TS in cell-derived trypomastigotes is responsible for the earlier exit from the PV to the cytoplasm and their subsequent differentiation into amastigotes.

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.

Characterization of farnesylated protein tyrosine phosphatase TcPRL-1 from Trypanosoma cruzi

Protein tyrosine kinases and phosphatases play important roles in the regulation of cell growth, development, and differentiation. We report here the identification in Trypanosoma cruzi of a gene (TcPRL-1) encoding a protein tyrosine phosphatase. The predicted protein (TcPRL-1) shares ca. 35% identity with the mammalian protein tyrosine phosphatase known as phosphatase of regenerating liver 1 (PRL-1). Four copies of this protein tyrosine phosphatase are present in the T. cruzi genome, and Northern blot assays showed a transcript of approximately 750 bases. TcPRL-1 was detected by Western blot analysis only in amastigote extracts as a 21-kDa protein. TcPRL-1 was expressed in Escherichia coli, and its phosphatase activity was determined by using p-nitrophenylphosphate and a phosphorylated protein as substrates. In contrast to other PRLs, TcPRL-1 activity was not affected by pentamidine, and it was inhibited by very low concentrations of o-vanadate. TcPRL-1 has a C-terminal CAAX motif (CAVM) and is farnesylated in vitro by T. cruzi epimastigote extracts and in vivo according to the transfection results. After transfection of T. cruzi with a vector that expresses TcPRL-1 as a C-terminal fusion to green fluorescent protein, GFP-TcPRL-1 was detected in the endocytic pathway of epimastigotes, amastigotes, and trypomastigotes by colocalization with cruzipain and concanavalin A. Interestingly, a mutant form without the CAAX motif localized to the cytoplasm, in contrast to its mammalian counterparts that localize to the nucleus. The results of these studies on TcPRL-1 reveal that, even though the animal and parasite PRLs share similar kinetic properties, their susceptibilities to inhibitors, as well as their localization, are distinct, implying that they may be involved in different cellular processes.